Removal of MTBE from Drinking Water Using Air Stripping: Case Studies

Transcription

1 Removal of MTBE from Drinking Water Using Air Stripping: Case Studies A Publication of: The California MTBE Research Partnership Association of California Water Agencies Oxygenated Fuels Association Western States Petroleum Association National Water Research Institute October 2006

2 Published by the National Water Research Institute NWRI Ellis Avenue P.O. Box Fountain Valley, California (741) Fax: (714)

3 Limitations This document was prepared by Malcolm Pirnie, Inc. and is intended for use by members of the California MTBE Research Partnership (Partnership) pursuant to the Partnership agreement. Malcolm Pirnie and the Partnership do not warrant, guarantee, or attest to the accuracy or completeness of the data, interpretations, practices, conclusions, suggestions, or recommendations contained herein. Use of this document, or reliance on any information contained herein, by any party or entity other than members of the Partnership, is at the sole risk of such parties or entities. i

4 Acknowledgements This report was prepared by Rula Deeb, Elisabeth Hawley, Andrew Stocking, Michael Kavanaugh, Amparo Flores, Stephanie Sue, Douglas Spiers, Michael Wooden, Gerald Crawford, and Guillermo Garcia of Malcolm Pirnie, Inc. The authors would like to acknowledge Rey Rodriguez (H 2 O R 2 Consulting Engineers, Inc.) and Jim Davidson (currently with Exponent, formerly of Alpine Environmental) for their assistance in collecting the data discussed in this report. The authors would like to thank the California MTBE Research Partnership and the National Water Research Institute (NWRI) for sponsoring this work. The authors especially wish to acknowledge Ronald Linsky ( ), former Executive Director of NWRI, for his excellent leadership of the Partnership and for his direction and support of this work. The authors are also grateful to the many members of the Partnership's Research Advisory Committee who provided valuable support and review, especially David Pierce (ChevronTexaco Energy Research and Technology Co.) and Bill Reetz (Kansas Department of Health and Environment). ii

5 Table of Contents Executive Summary Introduction Background Research Objectives Research Approach Report Overview Air Stripper Case Studies Packed Tower Air Stripper Lacrosse, Kansas Low Profile Air Stripper Somersworth, New Hampshire Packed Tower Air Stripper Culver City, California Low Profile Air Stripper Bridgeport, Connecticut Low Profile Air Stripper Chester, New Jersey Packed Tower Air Strippers Ridgewood, New Jersey Packed Tower Air Stripper Rockaway Township, New Jersey Low Profile Air Stripper Mammoth Lakes, California Low Profile Air Stripper Elmira, California Analysis Of System Cost And Performance Introduction Treatment Train Design Treatment System Performance Treatment System Costs Model Evaluation Overview of Modeling Software Programs Low Profile Air Stripper Somersworth, New Hampshire Low Profile Air Stripper Chester, New Jersey Packed Tower Air Stripper Lacrosse, Kansas Packed Tower Air Stripper Culver City, California Packed Tower Air Stripper Rockaway Township, New Jersey Summary of Modeling Results iii

6 5. Summary Of Findings Case Study Data Collection Case Study Data Analysis Model Validation Conclusions References...63 Appendices Appendix A...65 Appendix B...74 iv

7 1 Timeline for Remediation and Treatment at LaCrosse, Kansas Average Influent Water Quality Parameters at LaCrosse, Kansas Design/Operating Parameters for Packed Tower at LaCrosse, Kansas Capital and Annual O&M Costs (1997) at LaCrosse, Kansas Timeline for Remediation and Treatment at Somersworth, New Hampshire Average Influent Water Quality Parameters at Somersworth, New Hampshire Design/Operating Parameters for Low Profile Air Stripper at Somersworth, New Hampshire Capital and Annual O&M Costs (1996) at Somersworth, New Hampshire Average Influent Water Quality Parameters at Culver City, California NPDES Permit Limitations at Culver City, California Design/Operating Parameters for Packed Tower Air Stripper at Culver City, California Influent Contaminant Design Criteria at Culver City, California Influent Hydrocarbon Concentrations at Culver City, California Air Stripper Performance Data for MTBE at Culver City, California Capital and Annual O&M Costs (1999) at Culver City, California Average Influent Water Quality Parameters at Bridgeport, Connecticut Design/Operating Parameters for Low Profile Air Stripper at Bridgeport, Connecticut Air Stripper Performance Data for MTBE at Bridgeport, Connecticut Air Stripper Performance Data for BTEX Compounds at Bridgeport, Connecticut Capital and Annual O&M Costs (1995) at Bridgeport, Connecticut Average Influent Water Quality Parameters at Chester, New Jersey Design/Operating Parameters for Low Profile Air Stripper at Chester, New Jersey Capital and Annual O&M Costs (1998) at Chester, New Jersey...29 v Tables

8 24 Average Influent Water Quality Parameters at Ridgewood, New Jersey Design/Operating Parameters for Packed Tower Air Stripper at Ridgewood, New Jersey Capital and Annual O&M Costs (1991, 1997) at Ridgewood, New Jersey Design/Operating Parameters for Packed Air Stripping Tower at Rockaway Township, New Jersey VOC Criteria for 1995 Air Stripping Tower at Rockaway Township, New Jersey Average Influent Water Quality Parameters at Rockaway Township, New Jersey Capital and Annual O&M Costs (1995) at Rockaway Township, New Jersey Timeline of Events at Mammoth Lakes, California Influent Constituent Concentrations at Mammoth Lakes, California MTBE Air Stripping Performance Data at Mammoth Lakes, California MTBE Off-Gas Treatment Performance Data at Mammoth Lakes, California Timeline of Remediation at Elmira, California Average Influent Water Quality Parameters at Elmira, California a 37b Design/Operating Parameters for the Low Profile Air Stripper at Elmira, California...41 Design/Operating Parameters for the Off-Gas Treatment System (ADDOX TM ) at Elmira, California Capital and Annual O&M Costs (1997) at Elmira, California Comparison of the Design Parameters, Performance, and Costs Associated with each of the Packed Tower Air Stripper Systems Comparison of the Design Parameters, Performance, and Costs Associated with each of the Low Profile Air Stripper Systems Modeling Scenarios for Low Profile Air Stripper at Somersworth, New Hampshire Modeling Scenarios for Packed Tower Air Stripper at LaCrosse, Kansas Modeling Scenarios for Packed Tower Air Stripper at Rockaway Township, New Jersey...58 vi

9 A-1 Air Stripper Performance Data for MTBE at LaCrosse, Kansas...65 A-2 Air Stripper Performance Data for MTBE at Somersworth, New Hampshire...68 A-3 Air Stripper Performance Data for MTBE at Culver City, California A-4a Air Stripper Performance Data for MTBE at Bridgeport, Connecticut..70 A-4b Air Stripper Performance Data for BTEX at Bridgeport, Connecticut...70 A-5 Air Stripper Performance Data for MTBE at Rockaway Township, New Jersey...71 A-6 Off-Gas System Performance Data for MTBE at Elmira, California...73 B-1 Modeling Data Comparison for Low Profile Air Stripper at Somersworth, New Hampshire...74 B-2 Modeling Data Comparison for Packed Tower Air Stripper at LaCrosse, Kansas (Water Flow Rate = 480 gpm, Air to Water Ratio = 156)...76 B-3 Modeling Data Comparison for Packed Tower Air Stripper at LaCrosse, Kansas (Water Flow Rate = 350 gpm, Air to Water Ratio = 214)...77 B-4 Modeling Data Comparison for Packed Tower Air Stripper at Culver City, California...78 B-5 Modeling Data Comparison for Packed Tower Air Stripper at Rockaway Township, New Jersey...79 vii

10 Figures 1 MTBE concentrations at LaCrosse, Kansas Removal efficiency reliability at LaCrosse, Kansas MTBE concentrations at Somersworth, New Hampshire MTBE removal efficiency at Somersworth, New Hampshire Removal efficiency reliability at Somersworth, New Hampshire MTBE concentrations at Culver City, California MTBE removal efficiency at Culver City, California Air stripping performance at Culver City, California MTBE concentrations at Bridgeport, Connecticut a MTBE removal efficiency at Bridgeport, Connecticut b BTEX removal efficiency at Bridgeport, Connecticut Removal efficiency reliability at Bridgeport, Connecticut MTBE concentrations versus time at Rockaway, New Jersey MTBE removal efficiency versus time at Rockaway, New Jersey Removal efficiency reliability at Rockaway, New Jersey MTBE influent concentrations at Elmira, California Off-gas treatment influent concentrations of BTEX and TPH-G (1998 to 2000) at Elmira, California ADDOX TM performance summary test data at Elmira, California Cost summary of MTBE removal by air stripping Comparison of modeling results to actual performance viii

11 List of Acronyms, Symbols, and Abbreviations ASAP TM BTEX CaCO 3 cfm DCE DIPE ETBE GAC gpm Hp H 2 O2 kwh LUST MTBE µg/l mg/l NEEP NHDES NPDES O&M PCE ppbv ppmv scfm StEPP SVE TAME TBA TCE TPH-D TPH-G USEPA UST UV VOC Aeration System Analysis Program Benzene, toluene, ethylbenzene, and xylenes (o-, m-, p-xylene) Calcium carbonate Cubic feet per minute Dichloroethylene Di-isopropyl ether Ethyl tertiary butyl ether Granular activated carbon Gallons per minute Horsepower Hydrogen peroxide Kilowatt hour Leaking underground storage tank Methyl tertiary butyl ether Microgram per liter Milligram per liter North East Environmental Products New Hampshire Department of Environmental Services National Pollutant Discharge Elimination System Operation and maintenance Perchloroethylene Parts per billion by volume Parts per million by volume Standard cubic feet per minute Software to Estimate Physical Properties Soil vapor extraction Tertiary amyl methyl ether Tertiary butyl alcohol Trichloroethylene Total petroleum hydrocarbons quantified as diesel Total petroleum hydrocarbons quantified as gasoline U.S. Environmental Protection Agency Underground storage tank Ultraviolet Volatile organic compound ix

12 x

13 Executive Summary In response to an identified research need to assess the performance of air stripping to remove methyl tertiary butyl ether (MTBE) from contaminated groundwater, the California MTBE Research Partnership undertook this project to: Collect design, performance, and cost summary data from several packed tower and low profile air stripper treatment systems addressing MTBE contamination in groundwater supplies. Use the data from these case studies to develop a series of cost and reliability curves. Assess the accuracy of several available models used to predict the cost and performance of packed tower and low profile air strippers. Data from nine case study sites operating during the late 1990s were obtained and analyzed. Two models were chosen for evaluation: the Aeration System Analysis Program (ASAP TM ) Packed Tower Model and the North East Environmental Products (NEEP) ShallowTray Modeler software. Results indicate that a variety of different treatment train configurations can use air strippers to successfully remove a wide range of MTBE concentrations (i.e., from 10 to 2,400,000 micrograms per liter [µg/l]). Removal efficiencies ranged from 65 percent to greater than 99.9 percent. Capital costs (expressed in year 2000 dollars) ranged from $0.47/1,000 to $104/1,000 gallons system capacity. Operation and maintenance (O&M) costs were a function of flowrate and percent MTBE removal. Annual O&M costs ranged from $1/1,000 to $10/1,000 gallons to achieve greater than 90-percent removal and from $0.15/1,000 to $1/1,000 gallons to achieve greater than 65-percent removal. Commercially available models were found to predict actual removal efficiencies within 15 percent, demonstrating that modeling can be a valuable tool for assessing air stripper cost and performance during conceptual design or remedy selection 1

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15 1. Introduction 1.1 Background In 1995, the Lawrence Livermore National Laboratory reported that greater than 90 percent of the groundwater plumes (defined as the 10 micrograms per liter [µg/l] benzene isoconcentration level) emanating from underground storage tank (UST) gasoline releases in California were likely to stabilize (i.e., stop increasing in size) at distances less than 250 feet downgradient of leaking underground storage tank (LUST) releases (Rice et al., 1995). These plumes identified primarily by one or more benzene, toluene, ethylbenzene, and xylene (BTEX) components moved slowly and eventually stabilized due to natural biodegradation and retardation. Lawrence Livermore National Laboratory concluded that many BTEX plumes might not require active remediation due to these natural attenuating processes and that monitored natural attenuation could be a remedial strategy at many UST sites in California and other states. Shortly thereafter, methyl tertiary butyl ether (MTBE), an oxygenate added to gasoline to increase octane levels and to meet federal and state fuel specifications for oxygen content, was detected in drinking water wells in the City of Santa Monica, California (US Water News, 1996). This discovery caused regulatory agencies in California to immediately reassess cleanup strategies at gasoline UST sites. Groundwater samples collected at UST sites in California and elsewhere confirmed MTBE occurrence and, with it, new remediation challenges for UST owners. Some of the remediation challenges are apparent from MTBE s physical and chemical properties. MTBE is highly soluble in water, is only weakly sorbed to most soils, and exhibits a low tendency to volatilize from water. Consequently, MTBE partitions relatively easily into water from a gasoline/mtbe mixture, moves approximately at the rate of groundwater flow, and if no active remediation is undertaken can threaten downgradient water supply wells. Moreover, depending on the release scenario, MTBE may move farther than BTEX compounds, ultimately impacting a larger volume of groundwater compared to BTEX-only plumes. The ether structure of MTBE is not very susceptible to biodegradation. MTBE and other ether oxygenates were initially found to be resistant to biodegradation, thereby limiting the use of natural attenuation for contaminated groundwater cleanup at UST sites (Suflita and Mormile, 1993; Yeh and Novak, 1995). These characteristics of MTBE have increased the need for active remediation technologies at UST sites and the level of interest in the cost and performance of available ex situ groundwater treatment technologies. For example, the need for information on drinking water treatment technologies for MTBE was highlighted in a U.S. Environmental Protection Agency (USEPA) report titled Oxygenates in Water: Critical Information and Research Needs (U.S. Environmental Protection Agency, 1998). In February 2000, the California MTBE Research Partnership (Partnership) published a report summarizing the feasibility of using several technologies to remove MTBE from 3

16 drinking water (California MTBE Research Partnership, 2000). This report contained a theoretical analysis of treatment technologies with some reference to field applications. To further elucidate the ability of these technologies to remove MTBE from drinking water, the Partnership also funded efforts to gather information from field applications to verify the estimated cost and efficiency of these technologies to remove MTBE from contaminated water. For example, the Partnership published two reports focusing on MTBE removal using synthetic resins (California MTBE Research Partnership, 1999) and granular activated carbon (California MTBE Research Partnership, 2001). Recently, the Partnership published a comprehensive evaluation of MTBE remediation options (California MTBE Research Partnership, 2004). Additional data on MTBE treatment systems and costs is available through the USEPA s Technology Innovation Office (U.S. Environmental Protection Agency, 2005) and the Partnership. Air stripping is a well-established technology for removing volatile organic compounds (VOCs) from groundwater. Two configurations of air strippers include the low profile and packed tower systems. In a low profile aeration system, contaminated water is pumped to the top of the stripper, where it flows over an inlet weir onto a baffled aeration tray. Air is forced upward through perforations in the tray bottom, creating highly turbulent conditions to maximize the contact of water and air. In a packed tower air stripping system, contaminated water passes downward by gravity through a circular or rectangular column that is filled with either randomly packed or structured packing material. Air is introduced into the tower below the packed bed and flows upward through the column countercurrent to the flow of water. The successful and cost-effective application of air stripping to remove MTBE has not yet been demonstrated or widely accepted. The Partnership identified a research need to evaluate the effectiveness of air stripping for MTBE removal from groundwater, including actual cost and performance data from operating groundwater treatment systems. Air stripping system performance and cost data were collected between 1995 and 2001, at the same time as the collection of data for two other published Partnership reports (California MTBE Research Partnership, 1999, 2001). The analysis of these data is presented in this report. Between 2001 and 2005, numerous air strippers both packed tower and shallow tray configurations have been successfully used for both municipal drinking water treatment and remedial applications. The installation of these treatment systems has contributed to the recognition of air stripping as a cost-effective option for MTBE treatment. However, a summary of cost and performance data for MTBE removal via air stripping has still not been published, to our knowledge. Therefore, the summary presented in this report is unique. 1.2 Research Objectives The overall objective of the work summarized in this report is to evaluate the cost and performance of air strippers and associated off-gas treatment systems for removing MTBE from groundwater supplies. The primary objectives of the project include: 4

17 Collect performance data, water quality information, and cost summaries for several packed tower and low profile air strippers and their respective off-gas treatment processes for treating MTBE. Use the data from these case studies to develop a series of cost curves and reliability curves for packed tower and low profile air strippers as a function of removal efficiency, flow rate, and water quality. Identify the most sensitive parameters (e.g., water quality) that influence the cost and reliability of air stripping systems. Identify several available models used to estimate the cost and performance of packed tower air strippers and low profile air strippers. Use the performance data to assess the accuracy of the predictions generated by these models. Due to data limitations, the objectives were not fully met. For example, off-gas treatment system performance data were not available at every site. Data were not sufficient to conduct a quantitative sensitivity analysis of the most important parameters impacting air stripper performance. Thus, a qualitative review of air stripper operational and maintenance challenges was conducted. 1.3 Research Approach To evaluate the cost and performance of air stripping for MTBE, data from nine case studies were examined. At each site, air stripping was used to remove MTBE from contaminated groundwater. Five of the sites used low profile air strippers, and the other four sites used packed tower air strippers. The case studies included: 1. Packed tower air stripper LaCrosse, Kansas 2. Low profile air stripper Somersworth, New Hampshire 3. Packed tower air stripper Culver City, California 4. Low profile air stripper Bridgeport, Connecticut 5. Low profile air stripper Chester, New Jersey 6. Packed tower air stripper Ridgewood, New Jersey 7. Packed tower air stripper Rockaway Township, New Jersey 8. Low profile air stripper Mammoth Lakes, California 9. Low profile air stripper Elmira, California Data for this study were provided by environmental consultants, air stripper manufacturers, and regulators. At some of the sites, cost and performance data could not be shared with the Partnership due to ongoing litigation. The site background, description of the air stripping system, system performance, and technology cost were summarized for each site. System design parameters were tabulated 5

18 and performance data were plotted. Similarities and differences between the case studies were examined. For example, the treatment train design, performance, maintenance requirements, and costs were compared to identify common elements and potential additional considerations impacting system performance and cost. Cost data were expressed in year 2000 dollars and were normalized by flow rate to facilitate comparisons between different case study sites. Two commercially available and widely used models for air stripping performance were evaluated to assess the accuracy of their predictions. Case study parameters (e.g., flow rate, water temperature, reactor size, and influent contaminant concentrations) were entered into each model. Model predictions were compared with actual measurements of effluent water quality at case study sites. 1.4 Report Overview The research approach provided the framework for the organization of this report. Section 2 presents the data collected for each of the air stripping systems and associated offgas treatment, and includes a summary of site history, air stripper design, and operating data. Section 3 presents a summary of cost and performance trends for air stripping that were identified during the case study data analysis, including system operating parameters, percent MTBE removal, and unit costs (normalized by system flow rate). The most critical operating parameters for reducing costs and increasing system reliability were identified. Section 4 describes two models that are commonly used for predicting air stripper system cost and performance: the Aeration System Analysis Program (ASAP TM ) Packed Tower Model and the North East Environmental Products (NEEP) ShallowTray Modeler software. Key model input parameters and model-predicted system performance are summarized in this section. Modeling predictions are compared with actual system operating parameters to evaluate the accuracy of these models. Section 5 summarizes the main findings of this report and presents strategies for predicting whether or not air stripping will be a cost-effective and reliable treatment strategy for removing MTBE and other VOCs from groundwater at a given site. Section 6 contains a list of publications and other data referenced in this report. 6

19 2.1 PACKED TOWER AIR STRIPPER LACROSSE, KANSAS Site Background 2. Air Stripper Case Studies In 1992, three gasoline service stations in LaCrosse, Kansas, were identified as sources of soil and co-mingled groundwater contamination. The LUSTs at each of these three sites resulted in free-phase gasoline product and a petroleum hydrocarbon plume with MTBE concentrations exceeding 55,000 µg/l. The extent of groundwater contamination was characterized using numerous shallow monitoring wells. Sampling results indicated that the BTEX plume extended approximately 800 feet downgradient of the gasoline station tanks. A remediation system consisting of soil vapor extraction (SVE), groundwater pump-and-treat, and product recovery using skimmer pumps was installed in late 1995/early Due to the proximity of nearby receptors, the pump-and-treat and product recovery systems were kept in operation to provide hydraulic containment. The timeline of events related to remediation and treatment is presented in Table 1. Table 1. Timeline for Remediation and Treatment at LaCrosse, Kansas Milestone/Event Date Irrigation well sample February 17, 1997 Public water supply sample April 7, 1997 City notification April 23, 1997 Installation of temporary low profile stripper April 24, 1997 Additional (deeper) wells drilled April 24, 1997 ORC installation May 10, 1997 Permanent air stripper towers turned on September 16, 1997 Soil excavations August 17, 1998 SVE/sparge on November 13, 1998 Additional deep aquifer sparge on September 1, 1999 ORC : Oxygen release compound. In January 1997, a nearby resident complained of a chemical odor coming from an irrigation well located less than a mile downgradient of the gasoline service stations. Analytical studies confirmed that MTBE was present in the well at a concentration of 2,100 µg/l. Two adjacent municipal wells were subsequently sampled and were also found to be contaminated with MTBE concentrations of up to 1,050 µg/l. Because the two municipal wells were the only source of water for the community, an emergency response was formulated to notify local officials and evaluate treatment options. Additional monitoring wells were installed between the source area and municipal wells to confirm that contamination was coming from the three service stations. Nested wells were drilled to the base of the aquifer and screened at the same depth as the two public supply 7

20 wells (50 to 70 feet below ground surface [bgs]). Groundwater analytical data from the nested wells revealed high concentrations of MTBE (up to 1,290 µg/l) in the deeper wells, with lower to non-detectable concentrations in the shallow wells Description of Air Stripping System Since the two municipal wells were the only sources of potable water for a nearby community, a treatment system had to be quickly designed to ensure that the wells could continue to operate. Initially, a five-tray air stripper from the gasoline station pump-and-treat system installation was relocated to the water treatment facility as an emergency response measure to remove MTBE from the groundwater prior to water distribution. The tray stripper was designed to extract water from the clear well at one end and return the treated water at the opposite end. This pumping arrangement allowed a circulation of treated and raw water, which diluted MTBE concentrations in the water prior to its delivery into the distribution system. Flow rates into the tray stripper were limited to 250 gallons per minute (gpm). The tray stripper was used for 5 months until the packed tower air stripper system was installed. The permanent air stripping system was designed to treat up to 500 gpm. Influent water quality parameters are presented in Table 2. The influent to the permanent air stripping system is pre-chlorinated (0.5 to 1.0 milligrams per liter [mg/l] as residual) at each municipal well. Prior to entering the air stripping unit, the water is softened with lime, decreasing hardness from approximately 700 to 110 mg/l as calcium carbonate (CaCO 3 ), and routed into a settling basin for flocculation. It is then pumped into air stripper towers. Water exiting the packed towers is recycled back into the settling basin. Overflow water from the settling basin is directed through a sand and anthracite filter bed, then into a 200,000-gallon underground clear well and the distribution system. Table 2. Average Influent Water Quality Parameters at LaCrosse, Kansas Water Quality Parameter Concentration Alkalinity as CaCO 3 (mg/l) 131 Aluminum (mg/l) 432 Chloride (mg/l) 127 Corrosivity (mg/l) 0.17 Iron (mg/l) Magnesium (mg/l) 17 Nitrate (mg/l) 0.07 Sulfate (mg/l) 347 Total dissolved solids (mg/l) 858 Hardness (mg/l) 115 Turbidity (NTU) <0.5 ph 8.7 Temperature Not available NTU: Nepheleometric turbidity unit. 8

21 The permanent stripping system consists of two 33-foot tall, 6-foot diameter packed towers. The towers are partially enclosed within a steel pre-engineered building and contain 21 feet of 2-inch Jaeger Tripack TM packing material. The two units are operated in series to provide redundancy. The first packed tower air stripper is designed to decrease MTBE concentrations from up to 1,000 µg/l to less than 20 µg/l, while the second tower is used for water quality polishing to meet a treatment goal of less than 10 µg/l. The system flow rate ranges from 350 to 480 gpm (in summer months). The blowers can circulate 11,500 cubic feet per minute (cfm) of air through each tower. The air-to-water design ratio is 150 to 1. Other important design and operating parameters for the air stripping system are presented in Table 3. The air strippers are operated by city employees during normal pumping hours (8 am to 4 pm, 6 days per week). Sampling and routine maintenance duties are performed by facility employees with as-needed contractor support. Table 3. Design/Operating Parameters for Packed Tower at LaCrosse, Kansas Parameter Design Operating Tower specifications 6-feet diameter x 33-feet tall Fiberglass Packing material 2-inch Jaeger Tri-Pack filled to 21 feet Configuration Two towers in parallel Two towers in series Blower size (Hp) 2 x 15 Pump size (Hp) 3 x 15 Water flow rate (gpm) 500 Air flow rate (cfm) 10, in summer 350 in winter Air-water ratio 150:1 156:1 to 214:1 Maximum MTBE concentration 1, Average MTBE concentration 141 Maximum BTEX concentration Non-detect Non-detect MTBE treatment goal <10 <10 Removal efficiency (%) All off-gases released from the packed tower air strippers are directly discharged into the atmosphere without treatment Air Stripping System Performance Temporary Tray Strippers The five-tray air stripper reduced influent MTBE concentrations (200 to 600 µg/l) by an average of 40 percent. Effluent MTBE concentrations from the tray strippers ranged from 17 to 375 µg/l. The system operated as an emergency response measure until the packed tower air stripper was installed. 9

22 Permanent Packed Tower Air Strippers MTBE influent concentrations ranged from non-detect (less than 10 µg/l) to 973 µg/l. In most cases (greater than 90 percent of the time), effluent MTBE concentrations were less than 10 µg/l. The removal efficiency of the air strippers averaged 84 percent over the period of operation between 1997 and No significant operation and maintenance (O&M) problems have been reported to date, and there have been no problems with fouling or scaling. Manholes on the side of each tower provide visible evidence that the tower packing material has remained clean. System pressures in each tower have been stable since startup. The results of sampling events from the temporary tray air strippers (April 25, 1997, to September 10, 1997) and packed tower air strippers (September 16, 1997, to early 2000) are presented in Figure 1. The removal efficiency reliability for the two towers is presented in MTBE Concentration Figure 1. MTBE concentrations at LaCrosse, Kansas. Figure 2. Samples of the influent, first stripper effluent, second stripper effluent, and tap water are collected on a monthly basis. Detailed performance data is contained in Table A-1 of Appendix A. Total removal rates for MTBE average 95 percent after the second air stripper tower. As can be seen from available data (Figure 1), occasional spikes in MTBE concentrations are apparent in the influent water quality, which may be related to the use of a second public water supply well on Saturdays as the source of pumped groundwater. The second well has higher concentrations of MTBE (380 to 973 µg/l) compared to the first well (39.5 to 180 µg/l). Based on these findings, the city has decreased its usage of the second well by up to a factor of 4. The well is now only used for 5 to 10 hours per month. 10

23 Removal of Tikme Exceeding Removal Efficiency (%) Removal Efficiency (%) Figure 2. Removal efficiency reliability at LaCrosse, Kansas Technology Cost A breakdown of expenses for the permanent packed tower air strippers is presented in Table 4. Capital costs in 1997 were approximately $190,000. Annual O&M costs in the late 1990s were approximately $25,300. However, combined with the cost for remedial actions at the three gasoline station sites, the total cost of site remediation work exceeded 1 million dollars as of This includes the installation and 2-year operation of the pump-and-treat system, installation of two Oxygen Release Compound (ORC) barriers, source excavations, and in situ sparging systems in both the source and downgradient areas. 2.2 LOW PROFILE AIR STRIPPER SOMERSWORTH, NEW HAMPSHIRE Site Background During a routine tank inventory monitoring event in September 1996, a gasoline leak from a UST was detected at a retail gasoline dispensing facility in Somersworth, New Hampshire. It was estimated that 2,200 gallons of gasoline had leaked from the tanks, resulting in the presence of separate-phase hydrocarbons (SPH) in the subsurface and a dissolved-phase hydrocarbon plume. The site was added to the New Hampshire Department of Environmental Services (NHDES) list of spill response sites on October 4, In November 1996, three USTs were replaced. An SVE system, temporary groundwater extraction, and treatment system were installed. The SVE system was installed to address the area with free-phase hydrocarbon contamination. The temporary groundwater extraction 11

24 Table 4. Capital and Annual O&M Costs (1997) for LaCrosse, Kansas Capital Costs Towers (x 2) $119,916 Building $26,765 Concrete pad $11,142 Intake screens $3,300 Blowers and pumps $5,724 Freight $4,384 Control panel $2,031 Electrical, heating, and lighting $11,000 Stripper spare parts (including freight) $5,706 Total Capital Costs $189,968 Amortized annual costs at 7 percent for 30 years $15,309 Annual O&M Costs Labor (1 hour/week at $70/hour) $3,640 Electricity $13,200 Sampling (four/month at $39.25 each) $1,884 Monthly reports (12 at $50 each) $600 Quarterly reports (four at $1,500 each) $6,000 Total Annual O&M Costs $25,324 Total annual costs $40,633 Amortized Costs/1,000 Gallons $0.57 to 0.76* *Based on 350- to 480-gpm flow rate and 8-hours/day, 6-days/week operation. system pumped groundwater from six recovery wells into a 21,000-gallon fractionation tank through a trailer-mounted oil-water separator. The groundwater was then routed through a carbon treatment system consisting of four granular activated carbon (GAC) vessels operating in series. In December 1996, a low profile air stripper and an equalization tank were installed. The system was set up so that the oil-water separator drained into the 200- gallon equalization tank. Water was pumped out of the equalization tank and passed through the low profile air stripper. The chronology of groundwater treatment and soil remediation at the site is summarized in Table 5. Table 5. Timeline for Remediation and Treatment at Somersworth, New Hampshire Milestone/Event Date Gasoline leak detected September 26, 1996 Temporary treatment system start-up November 22, 1996 Permanent treatment system start-up December 10, 1996 Treated effluent ceases discharge to wastewater treatment plant and begins discharge to stormwater system August 4, 1999 Treatment system shut-down, due to low concentrations in the influent to the air stripper and low concentrations in the groundwater monitoring wells May

25 2.2.2 Description of Air Stripping System The air stripper in use at this site is a shallow tray low profile air stripper manufactured by NEEP. The operating water flow rate ranges from 3 to 10 gpm and the air-to-water ratio is 900 to 1. Influent water quality parameters are presented in Table 6, and design and operating parameters for the air stripper are presented in Table 7. Table 6. Average Influent Water Quality Parameters at Somersworth, New Hampshire Water Quality Parameter Value Iron (mg/l) 5.6 Effluent temperature ( F) 68 Table 7. Design/Operating Parameters for Low Profile Air Stripper at Somersworth, New Hampshire Parameter Design Operating Four trays Unit specifications ~5-feet wide, 6-feet long, and 6.5-feet high Configuration Single low profile air stripper Blower size (Hp) 7.5 Pump size (Hp) 1.5 Water flow rate (gpm) to 10, typically 10 Air flow rate (cfm) Air-water ratio 42:1 1,070:1 Maximum MTBE influent concentration 1,670,000 Average MTBE influent concentration 76,700 Removal efficiency (%) 98.3 The system is operated automatically on a continuous basis. Since treatment started, sampling has been performed once a month on the combined influent of six recovery wells. The effluent samples are collected from a sampling port at the base of the air stripper. Samples are analyzed for purgeable organics (USEPA Methods 8021B and 8260B) and total petroleum hydrocarbons (USEPA Method 418.1). Treatment system discharge was initially permitted under an NHDES Temporary Surface Water Discharge Permit and Temporary National Pollutant Discharge Elimination System (NPDES) Permit Exclusion. The treated groundwater was initially discharged to the municipal wastewater treatment facility. Since August 1999, all discharges have been made to the storm drainage system, which leads to Salmon Falls River. Air stripper off-gas is directly released into the atmosphere without treatment. 13

26 2.2.3 Air Stripping System Performance Influent concentrations of MTBE have ranged from approximately 200 to 1,000,000 µg/l, as shown in Figure 3. Removal efficiency typically ranged between 95 to 99 percent, with an average of 98 percent. The only exception occurred in March 1998, when the removal efficiency dropped to approximately 70 percent due primarily to silt build-up in the air stripper. Once the air stripper was cleaned, removal efficiencies improved to previous levels. Currently, the air stripper requires 16 hours of cleaning every quarter. Measured removal efficiency of the air stripper is graphically represented in Figures 4 and 5, based on data shown in Table A-2 of Appendix A. Figure 3. MTBE concentrations at Somersworth, New Hampshire. 12/12/1996 2/12/1997 4/12/1997 6/12/1997 8/12/ /12/ /12/1997 2/12/1998 4/12/1998 6/12/1998 8/12/ /12/ /12/1998 2/12/1999 4/12/1999 6/12/1999 8/12/ /12/ /12/1999 2/12/2000 MTBE Removal Efficiency (%) MTBE Concentration Figure 4. MTBE removal efficiency at Somersworth, New Hampshire. 14

27 Percentage of Time Exceeding Removal Efficiency (%) Removal Efficiency (%) Figure 5. Removal efficiency reliability at Somersworth, New Hampshire. The air stripping system has been operating reliably since December No major repairs or replacement parts have been needed since system operation began. During operation of the temporary treatment system (November 22, 1996, to December 9, 1996), a total of 92,400 gallons of groundwater were recovered, treated, and discharged. A status report shows that 2,566,300 gallons of water had been recovered, treated, and discharged from the start-up date of December 10, 1996, to February 28, Technology Cost The capital cost of air stripper installation totaled $43,000 (1996 dollars). As noted in Table 7, the system was originally designed to treat 160 gpm. If the operating maximum flowrate of 10 gpm had been anticipated, capital costs would have been even lower. Annual O&M costs have totaled $15,480 (actual costs during the late 1990s), as shown in Table 8. The total cost for site remediation and groundwater treatment at this site has exceeded 1 million dollars. Other approved capital costs in 1996 dollars for various aspects of the remediation project include recovery well installation and start-up ($81,281), temporary groundwater treatment system installation ($19,997), permanent treatment system installation ($76,091), and SVE system installation ($36,017). 2.3 PACKED TOWER AIR STRIPPER CULVER CITY, CALIFORNIA Site Background Groundwater treatment began in Culver City, California, in November 1999 to address petroleum hydrocarbons, BTEX, MTBE, and tertiary butyl alcohol (TBA) contamination. Groundwater is extracted from a total of eight wells screened in two drinking water aquifers. MTBE was first detected in the wells in late 1995, leading to the closure of the well field in 15

28 Table 8. Capital and Annual O&M Costs (1996) at Somersworth, New Hampshire Capital Costs Low profile air stripper $20,683 Electrical, heating, and lighting $16,779 Air stripper installation $5,460 Total capital costs $42,923 Amortized annual cost at 7 percent for 30 years $3,459 Annual O&M Costs Air stripper cleaning and maintenance (includes labor for 16 hours quarterly at $70/hour) $6,480 Electricity (based on $0.12/kWh) $7,000 Sampling (two/month) $2,000 Total Annual O&M Costs $15,480 Total annual costs $18,939 Amortized Costs/1,000 Gallons $ Based on treatment of 2,566,338 gallons between December 1997 and February At the time of data collection, legal investigations and site characterization activities were being undertaken by the City of Santa Monica, USEPA, and the Los Angeles Region of the California Regional Water Quality Control Board. An interim treatment system consisting of packed tower air stripper units was installed to remove contamination from a LUST at an operating gasoline service station. The extraction system was designed to provide hydraulic control over movement of the MTBE and BTEX plumes. The water is currently treated and discharged under an NPDES permit issued by the Los Angeles Region of the California Regional Water Quality Board. The treatment goal for MTBE under the NPDES permit is consistent with California s primary drinking water standard of 13 µg/l Description of Air Stripping System The groundwater treatment system consists of multiple unit processes to ensure that the effluent meets NPDES permit discharge requirements. Groundwater from the wells is pretreated with approximately 20 mg/l hydrogen peroxide (H 2 O 2 ) to oxidize ferrous iron to insoluble ferric iron. A series of three surge tanks is then used to precipitate the iron, followed by bag filters on the third surge tank to remove any remaining iron oxide particles. The effluent from the bag filters is treated with a sequestrant solution (20 mg/l of Betz Dearborn Scaletrol PDC9329) to reduce scaling in the stripper packing. After iron precipitation, the water is routed through three air strippers in series, each of which can be bypassed, if necessary, due to cleaning or repairs. 16

29 The packed tower air strippers, manufactured by Air Chem Systems, Inc., are operated in series. Each air stripper is 6 feet in diameter, 40 feet in height, and contains 25 feet of No. 2 NUPAC polypropylene packing material manufactured by Lantec Products, Inc. Typically, only two of the three stages are used in series during any given time. Treated water from the air stripper can undergo ultraviolet (UV) treatment in a 180 kilowatt (kw) medium pressure, horizontal PeroxPure reactor. H 2 O 2 can be added, if desired, to improve the removal efficiency of MTBE, TBA, or other organic compounds. Water is also passed through GAC prior to discharge into a stormwater drain. Off-gas from the air stripping system is treated using a regenerative thermal oxidizer (RTO) manufactured by Telkamp Systems, Inc., which has a capacity of 10,000 cfm. The inorganic parameters measured from samples collected at the air stripper inlet and outlet in February 2000 are presented in Table 9. The major flow and discharge limitations of the NPDES permit are summarized in Table 10. The system design and operating parameters for the air strippers are presented in Table 11, and the influent design parameters are presented in Table 12. Table 9. Average Influent Water Quality Parameters at Culver City, California Parameter Air Stripper Inlet Air Stripper Outlet Alkalinity (bicarbonate) (mg/l as CaCO 3 ) Alkalinity (carbonate) (mg/l as CaCO 3 ) Non-detect (<5) 24 Hardness (mg/l as CaCO 3 ) Iron (TTLC) (mg/l) Iron (filtered) (mg/l) Manganese (TTLC) (mg/l) ph Langlier Saturation Index TTLC: Total threshold limit concentration Air Stripping System Performance MTBE Removal Water samples are collected at the influent and effluent ports of the treatment system, as well as at the outlet of each air stripper. MTBE concentrations in the groundwater were reduced by the air stripping system from up to 17,000 µg/l to less than 2 µg/l (detection limit). The system has an overall removal efficiency of greater than 99.9 percent. The highest concentration of MTBE measured in samples collected for the outlet of the first air stripping column (S-01) was 8.4 µg/l (November 15, 1999). MTBE removal efficiency across the first air stripper tower ranges between 99.8 and 99.9 percent (most removal occurs in the first air stripper unit). 17

30 Parameter Table 10. NPDES Permit Limitations at Culver City, California Maximum Value Discharge rate (gpm) 400 TPH-G 100 Benzene 1 Toluene 150 Ethylbenzene 700 Ethylene dibromide 0.05 Total xylenes 1,750 MTBE 13 TBA 1,750 Sulfides (mg/l) 1.0 Biochemical oxygen demand at 20 C (mg/l) 30 Total suspended solids (mg/l) 50 Settleable solids (mg/l) 0.3 Turbidity (NTU) 150 Temperature ( F) 100 ph Range from 6.0 to 9.0 NTU: Nepheleometric turbidity unit. Parameter Design Operating Tower specifications (x 3) Packing Configuration Table 11. Design/Operating Parameters for Packed Tower Air Stripper at Culver City, California 6-feet diameter x 40-feet tall No. 2 NUPAC TM packing filled to 25 feet Three towers in series Water flow rate (gpm) Inlet water temperature ( F) Air flow rate (cfm) 10,000 7,000 Inlet air temperature ( F) 55 to 85 Air-water ratio 200:1 700:1 Maximum MTBE concentration Influent normal: 8,000 Influent maximum: 16,000 1st stage: 3,450 to17,000 2nd stage: 8.4 3rd stage: 1.4 MTBE treatment goal Maximum: 35 All stages: Non-detect (<2) Removal efficiency (%) > Table 12. Influent Contaminant Design Criteria at Culver City, California Constituent Normal Maximum MTBE 8,000 16,000 Benzene 1,000 5,000 Toluene 5,000 10,000 Ethylbenzene 1,000 4,000 Total xylenes 10,000 20,000 Other petroleum hydrocarbons 2,000 4,000 18

31 Influent MTBE concentrations have decreased steadily since the start-up of the system. In November 1999, the concentration was 17,000 µg/l. In December 1999 and in March 2000, MTBE influent concentrations dropped to 7,750 and 3,650 µg/l, respectively. Influent concentrations measured in April and May 2000 showed MTBE concentrations of 3,300 and 2,900 µg/l, respectively. Influent concentrations over time of MTBE and other gasoline constituents are presented in Table 13 and Figure 6. Performance data for the three air strippers are summarized in Table 14 and Figures 7 and 8. Detailed performance data is contained in Table A-3 of Appendix A. Table 13. Influent Hydrocarbon Concentrations at Culver City, California Constituent Nov Dec March April May TPH-G 14,000 14,000 10,000 10,000 10,000 Benzene Toluene 860 3,500 1,800 1,800 1,500 Ethylbenzene Xylenes 1,660 3,600 2,200 2,400 2,100 MTBE 17,000 7,750 2,800 3,300 2,900 TBA 3,500 1, Influent concentration based on two to three sets of analytical results provided by two different analytical laboratories. MTBE Concentration (mg/l) Data Point ID Figure 6. MTBE concentrations at Culver City, California. 19

32 Table 14. Air Stripper Performance Data for MTBE at Culver City, California Date Influent S-01 S-02 S-03 Effluent 11/10/99 17,000 NA NA NA ND (<1) 11/15/99 3, NA 12/20/99 6,300 NA NA NA ND (<1) 12/21/99 2,400 NA NA ND (<1) NA 01/13/00 4,500 NA NA NA ND (<1) 01/21/00 5, ND (<1) 1.1 NA 02/01/00 4, Offline 1.0 ND (<1) 02/12/00 3,000 ND (<1) Offline ND (<1) ND (<1) 02/16/00 3, Offline 1.5 ND (<1) 02/25/00 3,000 ND (<1) Offline ND (<1) ND (<1) 03/01/00 1 2,500 ND (<1) Offline ND (<1) ND (<1) 03/09/00 2,900 ND (<1) Offline ND (<1) ND (<1) 03/15/00 4,100 ND (<1) Offline ND (<1) ND (<1) 04/04/00 1 3,300 NA Offline ND (<1) ND (<5) 05/09/00 1 2,900 NA Offline ND (<1) ND (<5) 1 Influent concentrations based on two to three sets of analytical results provided by two different analytical laboratories. NA: Not available. ND: Non-detect. Removal Efficiency (%) Trial # Figure 7. MTBE removal efficiency at Culver City, California. 20

33 MTBE Concentration Figure 8. Air stripping performance at Culver City, California. Total Petroleum Hydrocarbon Quantified as Gasoline (TPH-G)/BTEX Removal The air stripping system removed total petroleum hydrocarbon quantified as gasoline (TPH-G)/ BTEX from groundwater to below laboratory detection limits (approximately 1 µg/l), with an overall removal efficiency equal to or greater than 99.9 percent. Moreover, all effluent samples from the first stripping column had non-detectable levels of TPH-G/BTEX, suggesting that TPH-G/BTEX removal essentially occurred in the first stripping column. TBA Removal Average monthly influent concentrations of TBA ranged from 260 to 3,500 µg/l between November 1999 to May During this period, TBA removal efficiency in the air stripping system increased from approximately 74 percent to greater than 90 percent. Most of the TBA removal occurred in the first air stripping column. The improvement in TBA removal efficiency over time is potentially due to the development of a microbial community on the surfaces of the air stripper packing that is capable of TBA degradation. The only apparent problem with air stripper operation was the build-up of scale in the pretreatment system. The system operates continuously. Between its start-up date of November 12, 1999, and March 15, 2000, this system treated 11,537,000 gallons of water. Based on this data, the flow rate of treated water is approximately 67 gpm. From March to May 2000, groundwater extraction rates were approximately 64 to 66 gpm. 21

34 2.3.4 Technology Cost The capital cost of the entire system (including pretreatment, the three air strippers, off-gas treatment, and GAC polishing) was approximately $1,714,000. Annual operating costs (including electricity, GAC, chemicals, labor, and supplies) are estimated to be $360,000. A breakdown of these costs is presented in Table 15. These costs are based on June 1998 estimates; actual costs may be higher or lower. Table 15. Capital and Annual O&M Costs (1999) at Culver City, California Capital Costs Pretreatment system, air strippers, off-gas treatment, and GAC polishing $1,714,000 Total capital costs $1,714,000 Amortized annual cost at 7 percent for 30 years $138,125 Annual O&M Costs Utility costs (electrical power and natural gas) $145,000 Granular activated carbon $20,000 Chemical costs (catalyst and scale control) $67,000 General O&M (labor and miscellaneous supplies) $127,000 Total Annual O&M Costs $359,000 Total annual costs $497,125 Amortized Costs/1000 Gallons 1 $ Based on a calculated treated groundwater flow rate of 94,000 gallons per day at continuous operation. 2.4 LOW PROFILE AIR STRIPPER BRIDGEPORT, CONNECTICUT Site Background In April 1995, groundwater treatment was installed to remediate a site impacted by a gasoline spill from a product terminal in Bridgeport, Connecticut. The system produced such consistently low MTBE concentrations that it ceased operation sometime in Description of Air Stripping System A heat exchanger was used to increase the temperature of the water from 55 F to approximately 65 F as a pretreatment step. After heating, the water enters the shallow tray low profile air stripping units, which are arranged in two parallel trains of two units. The air strippers are manufactured by Ejector Systems, Inc. (Model LP-5005). Water exiting the air strippers is further treated using GAC and sand dual media filtration. The water flow rate is approximately 11 gpm and the gas flow rate is approximately 500 standard cubic feet per minute (scfm), resulting in an air-to-water ratio of 340 to 1. The influent water quality parameters at the site are presented in Table 16. Design and operating parameters for the air stripping treatment system are summarized in Table

35 Table 16. Average Influent Water Quality Parameters at Bridgeport, Connecticut Water Quality Parameter Concentration Calcium (mg/l) 61 Iron (mg/l) 21 Manganese (mg/l) 5.2 Phosphate (mg/l) 0.2 Inlet ph 6.6 Temperature ( F) 55 to 65 Parameter Design Operating Unit specifications (x 4) Low profile air stripper Configuration Two parallel systems of two in series Water flow rate (gpm) Gas flow rate (cfm) 1, Air-water ratio 375:1 340:1 Maximum influent MTBE concentration Maximum influent BTEX concentration MTBE treatment goal 50 Removal efficiency (%) 99.9 AS: Air stripper. Table 17. Design/Operating Parameters for Low Profile Air Stripper at Bridgeport, Connecticut Primary AS: 2,400,000 Secondary AS: 14,000 Primary AS: 34,000 Secondary AS: 70 The off-gas released from the primary air stripper is treated with a catalytic oxidizer. Off-gases released from the secondary air stripper are directly exhausted to the atmosphere Air Stripping System Performance Initially, concentrations of MTBE entering the primary air stripper unit ranged from 280,000 to 2,400,000 µg/l. Concentrations entering the secondary air stripper unit ranged from 100 to 14,000 µg/l. Treated effluent MTBE concentrations ranged from 50 to 200 µg/l. Samples were collected on a monthly basis for a period of 1 year following the start-up of the treatment system, but regular sampling was discontinued soon after due to very low MTBE levels. By 1998, MTBE concentrations were low enough (i.e., 50 to 200 µg/l) for treatment system operation to cease. Influent and effluent data for MTBE and BTEX are presented in Tables 18 and 19, respectively. Influent and effluent MTBE data are represented in Figure 9. Removal efficiencies and performance data for the air stripper are illustrated in Figures 10a, 10b, and 11. All figures were generated using the detailed performance data shown in Tables A-4a and 4b of Appendix A. 23

36 Table 18. Air Stripper Performance Data for MTBE at Bridgeport, Connecticut Date Influent Primary Stripper Effluent Secondary Stripper Effluent April ,400,000 3,100 <50 May ,100,000 14,000 <50 June ,100,000 2,700 <50 July ,000 1,100 <50 August , <50 September , <50 October , <50 November , <50 December ,000 3, February ,000 1,400 <50 March ,000 6, Table 19. Air Stripper Performance Data for BTEX Compounds at Bridgeport, Connecticut Date Influent Primary Stripper Effluent Secondary Stripper Effluent April , <10 Mary ,600 <10 <10 June , July August , September ,000 <10 <10 October ,000 <10 <10 November ,900 <10 <10 December , <10 February ,500 <10 <10 March , <10 24

37 Removal Efficiency (%) MTBE Concentration (mg/l) Figure 9. MTBE concentrations at Bridgeport, Connecticut. Through S1 Through S2 Through S1 & S2 Figure 10a. MTBE removal efficiency at Bridgeport, Connecticut. 25

38 Removal Efficiency (%) Through S1 Through S2 Through S1 & S2 Figure 10b. BTEX removal efficiency at Bridgeport, Connecticut. Percentage of Time Exceeding Removal Efficiency (%) Removal Efficiency (%) Figure 11. Removal efficiency reliability at Bridgeport, Connecticut. 26

39 2.4.4 Technology Cost The capital cost of the system was approximately $530,000 (1995 dollars). Annual O&M costs were approximately $48,000 during the mid-1990s. A breakdown of these costs for removing MTBE from groundwater is presented in Table 20. Table 20. Capital and Annual O&M Costs (1995) at Bridgeport, Connecticut Capital Costs Towers (x 4) $132,500 Total Capital Costs $530,000 Amortized annual costs at 7 percent for 30 years $42,711 Annual O&M Costs Operating costs not related to MTBE treatment $84,000 Power requirement $6,000 Labor $5,760 Parts replacement $8,100 Air stripper cleaning $5,220 System oversight $6,000 Total Annual O&M Costs $48,000 Total annual costs $90,711 Amortized Costs/1,000 Gallons $ Based on an 11-gpm flow rate with continuous operation. 2.5 LOW PROFILE AIR STRIPPER CHESTER, NEW JERSEY Site Background In 1998, a low profile air stripper was installed at a site in Chester, New Jersey, to remove MTBE from a domestic well. The well water is pumped on an as-needed basis at 50 gpm. The treated water is stored prior to its use and then pumped at 15 gpm through the distribution system. The treatment system had been operating for over 18 months at the time of data collection for this report Description of Air Stripping System Prior to air stripping, extracted groundwater is passed through a two-step pretreatment system consisting of acid neutralization and water softening. Following pretreatment, the well water is routed to a four-tray shallow tray low profile air stripper manufactured by NEEP (Model #2341-P). The well water is then polished using GAC and chlorinated prior to use. 27

40 Influent water quality parameters of the extracted groundwater are shown in Table 21. Design and operating data for the air stripping system are presented in Table 22. Since the start-up of the system, no problems have been encountered and no parts have been replaced. System maintenance (i.e., cleaning and inspection) is performed on a semi-annual basis. The off-gas from the air stripper is directly exhausted to the atmosphere without prior treatment. Table 21. Average Influent Water Quality Parameters at Chester, New Jersey Water Quality Parameter Concentration Hardness (mg/l as CaCO 3 ) 257 ph 6.1 Temperature range ( F) 40 to 45 Table 22. Design/Operating Parameters for Low Profile Air Stripper at Chester, New Jersey Parameter Design Operating Unit specifications Four trays ~5-feet wide, 3.5-feet long, and 6.5-feet high Configuration Single low profile air stripper Water flow rate (gpm) 1 to Air flow rate (cfm) Air-water ratio 45:1 75:1 Maximum MTBE influent concentration Not available 220 MTBE effluent concentration 14 Other contaminants TCE Removal efficiency (%) Includes post-treatment GAC polishing step performance. TCE: Trichloroethylene Air Stripping System Performance Trichloroethylene (TCE) was detected in the well water at the beginning of system start-up. However, the treatment system has successfully reduced TCE to non-detectable levels. MTBE concentrations were reduced from up to 220 µg/l in the influent groundwater to concentrations as low as 14 µg/l after the GAC polish, giving an average MTBE removal efficiency of 94 percent for the entire system. Unfortunately, the effluent MTBE concentration out of the air stripper was not measured. Removal efficiency is less than or equal to 94 percent for the air stripper units. 28

41 2.5.4 Technology Cost The capital cost for installing the air stripper was $15,000 (1998 dollars), and an annual amount of $4,460 is needed for O&M. A detailed description of the costs related to the treatment system is presented in Table 23. Table 23. Capital and Annual O&M Costs (1998) at Chester, New Jersey Capital Costs Total Capital Costs $15,000 Amortized annual costs at 7 percent for 30 years $1,209 Annual O&M Costs Power requirements $3,267 Chemical addition (chlorine) $75 Labor (16 hours/year at $70/hour) $1,120 Total Annual O&M Costs $4,462 Total annual costs $5,671 Amortized Costs/1,000 Gallons $ Calculation based on 15-gpm flow rate and operation for periods of 12 hours/day, 7 days/week. 2.6 PACKED TOWER AIR STRIPPERS RIDGEWOOD, NEW JERSEY Site Background The treatment facility in Ridgewood, New Jersey, is an air stripping facility designed to remove VOCs from two municipal wells. The facility was originally designed to treat up to 635 gpm, although only 525 gpm is currently being pumped from the wells, which operate 75 percent of the time. The treatment facility was originally constructed in 1991 and consisted of a single air stripping tower designed to remove 99 percent of perchloroethylene (PCE) in the blended influent. Several influent water quality parameters for the blended groundwater supply are summarized in Table 24. Raw water from the two wells was pumped through the air stripper and into a clear well where chlorine was added for disinfection. From the clear well, the treated water was pumped into the municipal distribution system. In 1997, a second air Table 24. Average Influent Water Quality Parameters at Ridgewood, New Jersey Temperature ( F) 50 to 55 ph 7.7 Alkalinity (mg/l as CaCO 3 ) 160 to 170 Hardness (mg/l as CaCO 3 ) 200 to

42 stripping tower was added to the facility in response to the detection of MTBE in one of the wells. The facility was reconfigured such that the new air stripping tower (AST-2) was dedicated to treating water from the well containing MTBE, while the original air stripping tower (AST-1) was dedicated to the well without MTBE. The treated water from both air stripping towers was discharged into the clear well, after which the water was disinfected and distributed. The facility has continued to operate in this configuration Description of Air Stripping System As mentioned, AST-1 was originally designed to remove 99 percent of the PCE in the blended influent from the two wells. The design information for AST-1 is presented in Table 25. AST-2 was added in 1997 and designed to reduce MTBE concentrations in the influent from 689 to 15 µg/l (97.8 percent removal). This concentration was selected as a target concentration since it is close to MTBE s taste and odor threshold. The new air stripping tower has the Table 25. Design/Operating Parameters for Packed Tower Air Stripper at Ridgewood, New Jersey Parameter AST-1 AST-2 Design Operating Design Operating Manufacturer Hydro Group, Inc. 1 Hydro Group, Inc. 1 Model number PCS PCS Year installed Shell material Aluminum 2 Aluminum with interior coating Tower diameter (feet) Packed bed depth (feet) Packing media 2-inch Tri-Packs 3 2-inch Tri-Packs Other contaminants PCE PCE Maximum influent MTBE concentration Average influent MTBE concentration Effluent MTBE concentration 15 (goal); 70 (standard) Percent removal (%) Water flow rate (gpm) Liquid loading rate (gpm/sf) Air flow rate (cfm) 4,280 4,280 7,500 7,500 Air-water ratio 50:1 110:1 250:1 250:1 Number of air blowers 1 1 Blower motor size (Hp) Now Layne Christensen Company, Bridgewater, New Jersey. 2 Tower shell interior coated with epoxy in Jaeger Products, Inc., Houston, Texas. 30

43 same physical dimensions as AST-1, but was designed to handle a lower liquid loading rate at a higher air-to-water ratio than AST-1 (see Table 25). With the addition of AST-2, the operating parameters of AST-1 were modified because this air stripper was now treating only one well. Neither AST-1 nor AST-2 required off-gas treatment systems. A summary of the current operating configurations for both towers is provided in Table Air Stripping System Performance Following the installation of AST-2, MTBE was no longer detected in the raw well water. The treatment system continued operating to remove PCE. The only information available regarding MTBE removal rates at this facility is from system performance reports immediately prior to the installation of AST-2. For the first few months following the detection of MTBE, the original system was successful in reducing MTBE concentrations in the water to levels below New Jersey s maximum contaminant level (MCL) of 70 µg/l MTBE. At that time, the concentration of MTBE in the blended raw water from the two wells averaged approximately 90 µg/l. With AST-1 operating at a liquid loading rate of 20 gpm/square feet (sf) and an air-to-water ratio of 60 to 1, approximately 30 percent MTBE removal was achieved. Although no operating data is available to confirm satisfactory operation of the air stripping tower that was specifically designed to remove MTBE (AST-2), this case study illustrates that the original air stripper, which was not designed for MTBE removal, was able to achieve some reduction in MTBE Technology Cost The construction cost of the original air stripping system (AST-1) in 1991 was approximately $450,000 (which includes the air stripper, blower, piping, and controls, in addition to a concrete clear well, booster pumps, and a building to house the pumps, blowers, and controls). The cost associated with the addition of AST-2 in 1997 was approximately $200,000 (which includes the purchase of a new tower, blower, piping, and controls). This accounts for the construction costs associated with the extension of the existing building to house the new blower, in addition to the cost associated with an internal epoxy coating for the original air stripper (AST-1). Thus, the total capital cost of the facility is approximately $770,000. The O&M costs associated with the facility are approximately $72,000 per year. A breakdown of all the costs is presented in Table

44 Capital Costs Table 26. Capital and Annual O&M Costs (1991, 1997) at Ridgewood, New Jersey Installation of AST-1 (Includes tower, blower, piping, controls, concrete clear well, booster pumps and building to house tower, blower, and controls) Installation of AST-2 (Includes tower, blower, piping, controls, and building expansion) $450,000 $200,000 Total Capital Costs 1 $770,000 Amortized annual costs at 7 percent for 30 years $62,050 Annual O&M Costs Power requirements (unit cost of $0.12 kwh) $53,000 Sampling $5,000 Labor (5 hours/week at $40/hour) $11,000 Miscellaneous expenses $3,000 Total Annual O&M Costs $72,000 Total annual costs 1 $134,000 Amortized Costs/1,000 Gallons $ Cost is based on year 2000 values. 2 Based on a 525-gpm flow rate and 75 percent of the time operation. 2.7 PACKED TOWER AIR STRIPPER ROCKAWAY TOWNSHIP, NEW JERSEY Site Background A packed tower air stripper was installed in 1982 to treat volatile organic contaminants, including TCE, PCE, trans-1,2-dichloroethylene (DCE), di-isopropyl ether (DIPE), and MTBE, in the groundwater supply for Rockaway, New Jersey. The air stripper was originally a pretreatment step for GAC, but replaced GAC in 1983 as raw water DIPE and MTBE concentrations declined. The GAC system was maintained in operable condition to serve as a backup for the air stripper. This mode of operation continued until 1995, when the original air stripper was replaced with a new one. The new air stripping tower was not designed to remove DIPE and MTBE because their concentrations were declining over time. Within approximately 2 years of tower replacement, though, a second accidental UST release occurred, causing MTBE to appear once again in the supply wells. Since the MTBE levels resulting from the second release were relatively low (approximately 5 to 10 µg/l), the Township was able to modify the existing air stripping tower to provide adequate treatment. The modified system configuration is still maintained and has been effective in producing treated water with MTBE levels below 1 µg/l. 32

45 2.7.2 Description of Air Stripping System 1982 Treatment System The air stripping tower installed in 1982 was manufactured by Layne (currently known as Layne Christensen Company of Bridgewater, New Jersey). It was one of the first air stripping systems in the United States designed for VOC removal from municipal water supplies. To determine the design criteria for the air stripper, a series of pilot-scale tests was conducted at the Township s well site. Based on these tests, the air stripping tower was designed to achieve 99.9-percent removal of DIPE, which was determined to be primarily responsible for taste and odor problems. The design parameters of the 1982 air stripping tower are summarized in Table 27. The treated water was stored in a clear well followed by either polishing with GAC and chlorine disinfection or chlorine disinfection and direct routing into the distribution system. No off-gas treatment was required for this system. Table 27. Design/Operating Parameters for Packed Air Stripping Tower at Rockaway Township, New Jersey 1982 Tower 1995 Tower Parameter Design Operating Design Operating Manufacturer Layne Remedial Systems, Inc. Shell material Aluminum Fiberglass Reinforced Plastic Tower diameter (feet) 9 9 Packed bed depth (feet) Packing media 3-inch Tellerettes inch LanPacs 2 Other contaminants TCE, PCE, trans-1,2-dce, DIPE TCE, PCE, trans-1,2-dce Maximum MTBE influent concentration Effluent MTBE concentration 60 <1 5 to 10 <1 <1 Removal efficiency (%) Water flow rate (gpm) 1,400 1,500 Liquid loading rate (gpm/sf) Air flow rate (cfm) 37,500 20,000 Air-water ratio 100:1 100:1 Number of air blowers 2 1 Blower motor size (Hp) Ceilcote Co., Beria, Ohio. 2 Lantec Products, Inc., Agoura Hills, California. DCE: Dichloroethylene. DIPE: Di-isopropyl ether. 33

46 1995 Treatment System The replacement air stripping tower that was brought online in 1995 was manufactured by Remedial Systems, Inc., and was designed to meet VOC removal criteria (Table 28). The expected influent concentration for MTBE was relatively low. As a result, MTBE did not govern the air stripping tower design. By 1995, detections of MTBE and DIPE had ceased in the Township s water supply. From the criteria listed in Table 28, it is clear that the most stringent requirement was the 99.9-percent removal of TCE that was still present in the Township s groundwater supply. The design parameters for the second air stripping tower to meet these criteria are summarized in Table 27. The significant difference between the airto-water ratios for the original and replacement air stripping towers is primarily due to the fact that TCE has a much higher Henry s Law constant than MTBE and, therefore, is easier to remove from water. The design specifications for the replacement system were developed without the benefit of a pilot study. This was possible since the design of air stripping towers for removal of common VOCs, such as TCE, had become fairly routine by 1995 and sufficient operating data was available to use for this design. Compound Table 28. VOC Criteria for 1995 Air Stripping Tower at Rockaway Township, New Jersey In 1997, MTBE was again detected in the Township s water supply. The Township responded by replacing the existing 30 horsepower (Hp) blower motor with a new 35 Hp motor to increase air flow through the air stripping tower. This modification resulted in an air flow increase of approximately 200 cfm, which did not significantly affect the design air-to-water ratio Air Stripping System Performance 1982 Treatment System Design Influent Concentration Design Effluent Concentration Design Removal Efficiency (%) Chloroform cis-1,2-dichlorethylene ,1-dicholorethane ,1-dichlorethylene MTBE PCE ,1,1-trichlorethane TCE Carbon tetrachloride Although sampling data are not available for analysis in this report, the air stripping tower consistently achieved 95-percent removal of MTBE during the first 12 months of operation (February 1982 to February 1983). Influent MTBE concentrations during this period ranged from 50 to 60 µg/l and, thereafter, decreased to below 10 µg/l. Since the detection limit for 34

47 MTBE is 0.5 µg/l, analyzing the air stripping tower performance after February 1983 became difficult. The only measure of performance from 1983 to 1995 is that the air stripping tower operating alone was able to eliminate taste and odor problems in the Township s drinking water supply Treatment System A summary of representative influent water quality parameters is provided in Table 29. As shown in Figure 12 and Table A-5 of Appendix A, the concentration of MTBE in the combined raw influent ranged from non-detect (less than 0.5 µg/l) to 11.4 µg/l. During this same 30-month time period, the maximum MTBE concentration in the air stripping tower effluent was 2.0 µg/l. Furthermore, MTBE was non-detect in 47 of the 69 samples collected. Table 29. Average Influent Water Quality Parameters at Rockaway Township, New Jersey Water Quality Parameter Value Temperature ( F) 50 to 55 Total dissolved solids (mg/l) 374 Manganese (mg/l) 0.01 Iron (mg/l) 0.05 Hardness as CaCO 3 (mg/l) 217 ph 7.37 Corrosivity 0.28 MTBE Concentration (ppb) Sample Date Figure 12. MTBE concentrations versus time at Rockaway, New Jersey. 35

48 Although the low influent MTBE levels make it difficult to analyze the performance of this air stripping tower, it was possible to draw some conclusions from the data where MTBE was detected in the effluent. Figure 13 shows that while the air stripping tower performance varied widely over the period of operation, the average MTBE removal efficiency was approximately 65 percent. Figure 14, which depicts the performance reliability curve for this system, indicates that this tower removed 80 percent of MTBE approximately 45 percent of the time. However, the system was operating at low MTBE influent concentrations, which MTBE Removal Efficiency Sampling Date Figure 13. MTBE removal efficiency versus time at Rockaway, New Jersey Percentage of Time Exceeding Removal Efficiency Removal Efficiency Figure 14. Removal efficiency reliability at Rockaway, New Jersey. 36

49 may have resulted in reduced removal efficiency. Although percent MTBE removal was low, the data available for the 1995 air stripping tower indicate that this system is capable of achieving a moderate degree of MTBE removal, even though it was not specifically designed for this VOC Technology Cost 1982 Treatment System The total construction cost of the air stripping system in 1982 was approximately $375,000. Using historical Consumer Price Index values published by the U.S. Department of Labor, this equates to $645,750 in year 2000 dollars. While this cost may seem excessive in comparison to modern air stripping systems, the cost should be considered in the context of the time: a limited number of manufacturers were available in 1982 and experience with full-scale construction was limited. The estimated annual O&M costs associated with the air stripping tower were approximately $160,000 (in year 2000 dollars). These costs include power ($135,000), 1 sampling ($11,000), labor ($11,000), 2 and an allowance for other miscellaneous repairs and replacement parts ($3,000) Treatment System A breakdown of costs for the 1995 treatment system is shown in Table 30. The construction cost associated with the replacement air stripping tower in 1995 was approximately $300,000, which included the costs for a new tower, clear well, air blower, piping, and a small building to house the blowers and booster pumps. This cost also included the demolition of the existing tower and blower, as well as the relocation of existing booster pumps. To develop a representative cost estimate for the air stripping system that is currently in operation at Rockaway Township, the following assumptions were made: First, an allowance for the demolition of the existing equipment was deducted from the construction cost given above since this would not be typically required for the construction of a new air stripping tower. Second, the cost associated with the two booster pumps was added to the construction cost since these units would typically be installed as part of the air stripping system. Finally, the cost of upgrading the blower motor in 1997 was added to the total cost. The net result, scaled to reflect year 2000 dollars, led to an estimated construction cost of $370, Based on a unit cost of $0.12/kilowatt hour (kwh). 2 Based on 5 hours per week at $40/hour (including fringe benefits). 37

50 Table 30. Capital and Annual O&M Costs (1995, 2000) at Rockaway Township, New Jersey Capital Costs Installation of current air stripping operation in 1995 (Includes tower, blower, piping, controls, clear well, booster pumps, and building to house tower, blower, booster pumps, and controls) $300,000 Total Capital Costs 1 $370,000 Amortized annual costs at 7 percent for 30 years $29,800 Annual O&M Costs Power requirements (unit cost of $0.12/kWh) $95,000 Sampling $11,000 Labor (5 hours/week at $40/hour) $11,000 Miscellaneous expenses $3,000 Total Annual O&M Costs 1 $120,000 Total annual costs $150,000 Amortized Costs/1,000 Gallons 2 $ Cost is based on year 2000 values. 2 Based on a 1,300-gpm flow rate and continuous operation. The estimated annual O&M costs associated with the replacement air stripping tower are approximately $120,000 in year 2000 dollars. These costs include power ($95,000), 3 sampling ($11,000), labor ($11,000), 4 and an allowance for other miscellaneous repairs and replacement parts ($3,000). Note that the power costs for the replacement system are significantly lower due to the fact that the two original 100 Hp blower motors have been replaced with a single 35 Hp unit. 2.8 LOW PROFILE AIR STRIPPER MAMMOTH LAKES, CALIFORNIA Site Background In 1999, a fuel leak in a UST was detected in Mammoth Lakes, California. Concentrations of MTBE measured in six groundwater monitoring wells in the vicinity of the leak ranged from non-detect (less than 5 µg/l) to as high as 463,000 µg/l. An interim groundwater treatment system was installed and used from January 2000 until March During this interim period, treated water was stored onsite in a 21,000-gallon storage tank. The full-scale treatment system was officially started in March Treated groundwater is now discharged to Dry Creek in accordance with an NPDES permit. An SVE system has also been installed at the site. Organic vapors that are extracted from the subsurface are destroyed using a catalytic/thermal oxidation unit. A timeline of events at the site is presented in Table Based on a unit cost of $0.12/kwh. 4 Based on 5 hours per week at $40/hour (including fringe benefits). 38

51 Table 31. Timeline of Events at Mammoth Lakes, California Milestone/Event Vapor extraction system change-over from 250 to 350 cfm thermal oxidizer unit Date January 13, 2000 Treatment system start-up and testing February 29, 2000 Treatment system begins discharge to Dry Creek March 10, 2000 Vapor extraction system unit shut down and maintenance May 24, 2000 Vapor extraction system restarted June 16, Description of Air Stripping System Four extraction wells are used to contain the groundwater plume. The system flow rate varies from approximately 2 to 15.5 gpm and averages 6.5 gpm. The water is heated and passed through two biologically activated GAC vessels to reduce concentrations of total nitrogen, total phosphorus, and bacteria prior to treatment with a shallow tray low profile air stripper. A liquid-phase GAC treats air stripper effluent prior to collection in a 21,000 gallon tank and discharge to Dry Creek. Influent concentrations for a number of constituents in the groundwater are shown in Table 32. Since the system start-up through June 2000, a total of 1,016,000 gallons of water have been treated. Table 32. Influent Constituent Concentrations for at Mammoth Lakes, California Constituent Influent Concentrations TPH-G 2,000 to 940,000 MTBE 660 to 97,000 Benzene 62 to 1,500 Air stripper off-gas is treated using two vapor-phase GAC vessels prior to discharge to the atmosphere. The flow rate of air through this treatment system is approximately 2,400 cfm Air Stripping System Performance MTBE effluent concentrations through the air stripper and the entire system can be found in Table 33. Removal efficiencies are greater than 99.9 percent through the air stripper. Off-gas treatment concentrations can be found in Table 34. Off-gas treatment removal efficiencies range from 93 to 99.7 percent Technology Cost No cost data was readily available for this site. 39

52 Table 33. MTBE Air Stripping Performance Data at Mammoth Lakes, California Date Influent Air Stripper Effluent Discharge Effluent 02/29/00 4, <0.5 03/01/00 4, <0.5 03/10/00 5, <0.5 03/11/00 6,200 NA NA 03/13/ <0.5 <0.5 03/16/ <0.5 03/22/00 5,800 <0.5 NA 03/29/00 5,400 NA NA 04/05/00 12,000 NA NA 04/12/00 8,500 NA NA 04/19/00 12,492 <0.5 <0.5 04/26/00 38,000 NA NA 05/04/00 35,000 NA <0.5 05/10/00 35,000 NA NA 05/16/00 18,000 NA NA 05/24/00 8,600 1 <0.5 06/01/00 15,000 1 <0.5 06/14/00 9,900 2 <0.5 NA: Not analyzed. Table 34. MTBE Off-Gas Treatment Performance Data at Mammoth Lakes, California Date MTBE Influent Off-Gas (ppmv) MTBE Effluent Off-Gas after First GAC Vessel (ppmv) MTBE Effluent Off-Gas after Second GAC Vessel (ppmv) 03/13/ < /01/ /14/ < LOW PROFILE AIR STRIPPER ELMIRA, CALIFORNIA Site Background In 1997, the remediation of a petroleum pipeline leak in Elmira, California, began with the installation of two extraction and treatment systems. A timeline of the site remediation events is included in Table 35. One of the systems included a low profile air stripping unit and adsorption off-gas treatment system. The air stripping system performance data and background information at the site were limited. However, performance information was available for the off-gas treatment system. 40

53 Table 35. Timeline of Remediation at Elmira, California Milestone/Event Residents in Elmira, California, begin complaining about petroleum odors. Petroleum leak is discovered. Saturation of soil in the area of municipal sewer is detected. Installation of extraction and treatment system (air stripper, liquid-phase GAC vessels in series, and vapor-phase GAC). Date Prior to Installation of new off-gas treatment system (ADDOX TM ). February Description of Air Stripping System Groundwater is extracted at an average rate of 25 gpm and passed through a treatment train consisting of the following: an oil/water separator, bag filter, solar heating array, low profile air stripper, and two liquid-phase GAC vessels operating in series. Anti-scalant, biogrowth control, and anti-foaming chemicals are added prior to the air stripper. The solar heating step improves air stripper efficiency. Influent water quality parameters at this site are listed in Table 36. Design parameters for the air stripping system are included in Table 37a. Table 36. Average Influent Water Quality Parameters at Elmira, California Water Quality Parameter Value Alkalinity as CaCO 3 (mg/l) 250 to 350 ph (estimated average) 7.5 Total organic carbon (estimated average) (ppm) 3.6 Temperature (average) ( F) 62 Table 37a. Design/Operating Parameters for the Low Profile Air Stripper at Elmira, California Parameter Design Operating Low Profile stripper specifications 4-foot, 2-inch wide x 6-foot, 2-inch long x 6-foot, 8-inch tall Four trays Configuration One air stripper One air stripper Blower size 15 Hp, originally 10 Hp blower added at inlet for off-gas treatment Water flow rate (gpm) 30 to 60 gpm 115 gpm 25 (average) 30 (maximum) Air flow rate (cfm) 600 Air-water ratio Maximum MTBE concentration 210,000 NA Maximum BTEX concentration 9,800 NA MTBE treatment goal 13 (required) 1 (design) Removal efficiency (%) >99.9 NA NA: Not available. 300 (average) 525 (maximum) NA 41

54 The low profile air stripper is manufactured by NEEP. The system has operated continuously with the exception of brief shutdown periods for scheduled and unscheduled maintenance and carbon changeouts. The system had been operating for approximately 3 years at the time of data collection for this report. Approximately 23,300,000 gallons had been treated as of July Samples are collected monthly at the air stripper influent and GAC effluent and are analyzed for total petroleum hydrocarbon (gas and diesel range), BTEX, MTBE, DIPE, TBA, ethyl tertiary butyl ether (ETBE), and tertiary-amyl methyl ether (TAME). Vapor-phase GAC vessels were originally installed to treat the air stripper off-gas. These were in use for approximately 3 years. In February 2000, a new off-gas treatment system called ADDOX TM (Model ADDOX6), manufactured by NEEP, was installed to provide more cost-effective off-gas treatment. GAC vessels remained at the site on standby. The ADDOX TM system had been in operation for several months at the time of data collection for this report. This unit remains under a testing phase by NEEP to assess the degree of O&M required by the system. An ADDOX TM system consists of two or more reaction chambers filled with an inorganic, non-combustible media. At least one chamber adsorbs, while the other desorbs, destroys, and regenerates. VOC-laden air enters the adsorbing chamber and the contaminants are captured on the adsorbent beds; clean air is then allowed to exit the chamber. The contaminants are released from the bed when a stream of clean, preheated air is blown into the chamber during the regeneration phase. The VOCs are oxidized into carbon dioxide and water through an exothermic catalytic oxidation reaction. The heat from the reaction increases VOC desorption from the media. According to a NEEP ADDOX TM system vendor, the adsorption/desorption cycle is every 4 hours for the system operating at this site. The system is designed to treat a maximum air flow rate of 600 scfm and a maximum VOC adsorption and destruction rate of 4.4 pounds per hour. The system is 11.5 feet long, 7.5 feet wide, and 9 feet tall, and designed to treat an off-gas stream containing total VOC concentrations of 255 parts per million by volume (ppmv), of which 151 ppmv is MTBE. Design parameters for the off-gas treatment system are included in Table 37b. Parameter Design Operating Specifications 7-feet, 6-inches wide x 11-feet, 6-inches long x 9-feet tall Configuration Two inorganic media beds alternating between adsorption and desorption/regeneration phases Blower size (Hp) 2 Air flow rate (cfm) 600 for adsorption, 60 for desorption Maximum MTBE concentration (ppmv) Maximum BTEX concentration (ppmv) 6.6 NA MTBE treatment goal (ppmv) <3 NA Removal efficiency (%) >98 >99 NA: Not available. Table 37b. Design/Operating Parameters for the Off-Gas Treatment System (ADDOX TM ) at Elmira, California for adsorption, 60 for desorption

55 2.9.3 Air Stripping System Performance Influent MTBE concentrations range from 1,700 to 100,000 µg/l. The final effluent from the system has consistently met NPDES discharge requirements. From start-up in September 1997 through December 1999, MTBE concentrations have decreased from a range of 70,000 to 100,000 µg/l to a range of 20,000 to 26,000 µg/l. This influent data is presented in Figure 15, based on detailed performance data shown in Table A-6 of Appendix A. Unfortunately, the performance of the air stripper cannot be independently evaluated from the rest of the treatment train because air stripper effluent has not been regularly monitored. MTBE Concentration Figure 15. MTBE influent concentrations at Elmira, California. Note: Effluent MTBE data are not available. VOC concentrations entering the off-gas treatment system (vapor-phase GAC) from December 1998 through March 2000 are provided in Figure 16. In almost every sampling event, effluent concentrations were reduced to non-detect (less than 0.1 ppmv). Unfortunately, a limited number of samples from the original off-gas treatment system contained detectable levels of MTBE. As shown in Figure 17, the ADDOX TM off-gas treatment system is more reliable than the vapor-phase GAC. During the first 3 months of operation, the ADDOX6 system treated 600 cfm off-gas containing 65 to 393 ppmv MTBE. Destruction efficiency ranged from 88.3 percent to greater than 99.9 percent Technology Cost Annual operating costs for the air stripper include the costs of power, labor, sampling, parts, and chemicals associated with cleaning, maintenance, and repairs. Annual O&M costs range from $18,350 to $31,050 (late 1990s). Approximately 4 to 6 hours per week are required to 43

56 Total Hydrocarbons TPHg Benzene Toluene Ethylbenzene Xylenes Concentration (ppmv) Note: Effluent samples were taken on 12/01/98 and 1/12/99 show that constituent concentrations were <0.1 ppmv (ND), with the exception of the total hydrocarbons on 12/01/98, which had concentration of 2.16 ppmv. Figure 16. Off-gas treatment influent concentrations of BTEX and TPH-G (1998 to 2000) at Elmira, California. Note: MTBE influent concentrations are shown in Figure 17. VOC Concentration (ppmv) Sample Date Figure 17. ADDOX TM performance summary test data at Elmira, California. 44

57 maintain the entire treatment system. At the time of data collection, the air stripper had only required cleaning three times (approximately once per year). Minimal replacement parts have been needed. The capital cost for the air stripper unit and control system ranged from $25,000 to $30,000 (1997 dollars); the capital cost for air stripper appurtenances, including the filters, oil/water separator, and vapor-phase GAC vessels, was between $75,000 and $100,000. The capital cost of the ADDOX6 off-gas treatment system is approximately $70,000. The annual operating cost is projected based solely on the initial operating costs, since the unit has only been in operation since February NEEP s initial O&M cost estimate is based on assumptions about contaminant levels, the time for adsorption and desorption cycles, quarterly sampling, and an electrical usage rate of $4,205 per year ($11.52/day). Actual maintenance and cleaning costs for the system were unknown at the time of data collection for this report. No major repairs or problems have occurred since system start-up. Routine maintenance and troubleshooting can be monitored by the NEEP headquarters in New Hampshire through a modem interface that is installed in the control panel. Capital and annual operating costs for the ADDOX TM system are included in Table 38. Table 38. Capital and Annual O&M Costs (1997) at Elmira, California Capital Costs Air stripper $25,000 to $30,000 ADDOX TM $70,000 Controls and appurtenances $75,000 to $100,000 Total Capital Costs 1 $185,000 Amortized annual costs at 7 percent for 30 years $14,910 Annual O&M Costs Labor (4 to 6 hours/week at $110/hour) $23,400 to $33,800 Electricity $7,500 to $10,000 Electricity for ADDOX6 $4,205 Parts for cleaning, maintenance, and repairs $10,000 to $20,000 Sampling (once per month at $400) $4,800 Total Annual O&M Costs 1 $61,355 Total annual costs $76,263 Amortized Costs/1,000 Gallons 2 $ Total amounts are based on an average of the given amounts. 2 Based on continuous operation at 25 gpm. 45

58 3. Analysis of System Cost and Performance 3.1 INTRODUCTION As illustrated by these case studies, a variety of air stripper designs and treatment system configurations can successfully meet the challenges posed by a range of MTBE concentrations, influent water quality profiles, and effluent requirements. The nine case studies presented in Section 2 illustrate the variability in system flow rates, operating parameters, and air stripper configurations used for full-scale groundwater treatment. A comparison of the design parameters, performance data, and costs associated with each of the treatment system is presented in Tables 39 and 40. Although many differences in the treatment systems are apparent in these tables, several common elements are noticeable as well. These are detailed in the following sections discussing treatment train design, air stripper performance, and cost considerations. Location Table 39. Comparison of the Design Parameters, Performance, and Costs Associated with Each of the Packed Tower Air Stripping Systems LaCrosse, Kansas Culver City, California Ridgewood, New Jersey Rockaway Township, New Jersey Drinking water Yes No Yes Yes Off-gas treatment No Thermal oxidation No No Iron (mg/l) Not available 0.05 Alkalinity as CaCO 3 (mg/l) to 170 Not available Stripper configuration 6-feet diameter x 33-feet tall Fiberglass (x 2 series) 6-feet diameter x 39.5-feet tall (x 3 in series) 5.75-feet diameter x 23-feet tall Two aluminum towers (AST-1 and AST-2) 9-feet diameter x 25-feet tall Two strippers (AS-2 replaced AS-1 in 1995) Stripper operation start-up date September 1997 October (AST-1) 1997 (AST-2) February 1982 (AS-1) 1995 (AS-2) Stripper operation termination date Current Current Current 1995 (AS-1) Current (AS-2) Flow rate (gpm) 350 (winter) 480 (summer) (AST-1) 225 (AST-2) 1400 (AS-1) 1500 (AS-2) Operation mode 8hours/day; 6 day/week Continuous 75 percent Continuous Air-water ratio 156:1 to 214:1 670:1 110:1 (AST-1) 250:1 (AST-2) 100:1 Maximum MTBE concentration , (AST-1) 60 (AS-1) 10 (AS-2) (Continued on Next Page) 46

59 (Continued from Previous Page) Location Table 39. Comparison of the Design Parameters, Performance, and Costs Associated with Each of the Packed Tower Air Stripping Systems LaCrosse, Kansas Culver City, California Ridgewood, New Jersey Rockaway Township, New Jersey Average MTBE 153 4, (AST-1) 5 to 10 (AS-2) Effluent MTBE <10 <2 <70 (Goal) <1 (Goal) Other contaminants None BTEX, TPH-G,TBA PCE PCE; TCE; 1,1,1-TCA; chloroform; cis-1,2-dce; 1,1-DCE; 1,1-DCA; carbon tetrachloride Total capital costs $189,968 $1,714,000 $770,000 $300,000 Annual O&M costs $25,324 $359,000 $72,000 $120,000 Annual cost $40,633 $497,125 $134,052 $150,000 $/1,000 gallons $0.57 to $0.76 $14.00 $0.64 $0.22 Capital costs (year 2000 dollars) $203,816 $1,771,613 $826,131 $338,976 Amortized capital costs at 7 percent for 30 years (year 2000 dollars) Annual O&M costs (year 2000 dollars) Annual cost (year 2000 dollars) $/1,000 gallons (year 2000 dollars) $16,425 $142,768 $66,575 $27,317 $27,170 $371,067 $77,249 $120,000 $43,595 $513,835 $143,824 $147,317 $0.65 $4.89 $1.62 $0.19 DCA: Dichloroethane. DCE: Dichloroethylene. TCA: Trichloroethane. 47

60 Table 40. Comparison of the Design Parameters, Performance, and Costs Associated with Each of the Low Profile Air Stripping Systems Location Somersworth, New Hampshire Bridgeport, Connecticut Chester, New Jersey Mammoth Lakes, California Elmira, California Drinking water No No Yes No No Off-gas treatment No Catalytic oxidation No GAC ADDOX TM treatment Iron (mg/l) NA NA NA Alkalinity as CaCO 3 (mg/l) NA NA NA NA 250 to 350 Stripper configuration One 4 tray low profile air stripper Two sets of parallel low profile air strippers (primary and secondary) One 4 tray low profile air stripper One low profile air stripper One low profile air stripper Stripper operation start-up date Stripper operation termination date December 1996 April 1995 Fall 1998 February May Current Current Current Flow rate (gpm) 2 to 10 Typically to 15.5 Average Operation mode Continuous Continuous 12 hours/day, 7 days/week Continuous Continuous Air-water ratio 1,070:1 340:1 75:1 1,870:1 90:1 Maximum MTBE concentration Average MTBE 1,670,000 2,400, ,000 77, ,000 NA NA NA (210,000 design) NA (9,800 design) Effluent MTBE <5, <0.5 <1.0 (design) Other contaminants BTEX BTEX TCE BTEX, TPH-G BTEX, TBA, DIPE, ETBE, TAME, TPH-G, TPH-D Total capital costs $42,923 $530,000 $15,000 NA $185,000 Annual O&M costs $15,480 $48,000 $4,462 NA $61,355 Annual cost $18,939 $90,710 $5,670 NA $76,263 (Continued on Next Page) 48

61 (Continued from Previous Page) Table 40. Comparison of the Design Parameters, Performance, and Costs Associated with Each of the Low Profile Air Stripping Systems Location Somersworth, New Hampshire Bridgeport, Connecticut Chester, New Jersey Mammoth Lakes, California Elmira, California $/1,000 gallons $22.00 $15.69 $1.44 NA $3.53 Capital costs (year 2000 dollars) Amortized capital costs at 7 percent for 30 years (year 2000 dollars) Annual O&M costs (year 2000 dollars) Annual cost (year 2000 dollars) $/1,000 gallons (year 2000 dollars) $47,109 $598,858 $15,504 NA $198,486 $3,796 $48,260 $1,249 NA $15,995 $16,990 $52,681 $4,897 NA $67,338 $20,786 $100,941 $6,147 NA $83,333 $13.88 $17.46 $1.04 NA $6.34 NA: Not available. 3.2 TREATMENT TRAIN DESIGN Pretreatment In seven of the nine case studies summarized in this report, the extracted groundwater underwent some type of pretreatment prior to air stripping. The types of pretreatment used included ph adjustment, water softening, water heating, iron precipitation, oil/water separation, and biological GAC to reduce nutrient loading prior to the air stripper. The addition of chemicals to reduce scaling, biological growth, and foaming was also common. The two case studies examined in this report that did not employ pretreatment were both packed tower air stripper systems (located in Ridgewood, New Jersey, and Rockaway Township, New Jersey). Both of the systems were primarily designed to treat other VOCs (PCE and DIPE). MTBE concentrations in the first system were variable, but never required significant reduction (i.e., the required percent removal was less than 22 percent). In the second system, influent MTBE concentrations were low, ranging from non-detect (less than 0.5 µg/l) to 12 µg/l and, therefore, did not require significant reduction. Systems without pretreatment understandably may encounter more operational difficulties associated with scaling and biofouling, which will reduce the removal efficiency of the air stripper system. 49

62 3.2.2 Air Stripper System The configuration of the air stripper unit is one of the most obvious design choices. The case studies included in this review demonstrate that the appropriate configuration is determined primarily by the system flow rate. Systems with flow rates greater than 100 gpm were packed tower configuration; those less than 100 gpm were low profile air strippers. Other site constraints may influence the choice of air stripper design, particularly for systems with flow rates between 50 and 200 gpm. Packed tower units are more compact and require a reduced footprint area. However, the packed tower configuration is also more conspicuous than a low profile air stripper. The heights of packed tower systems analyzed in this report ranged from 25 to 35 feet. Air stripping units were used at two of the case study sites as interim treatment systems. Due to site-specific time constraints for implementing the interim remedy, pilot-testing was not conducted prior to system installation and full-scale use. At another site (Ridgewood, New Jersey), the air stripping unit was originally designed to address VOC contamination. Therefore, the design process was quite different at these sites. The use of air stripping as a temporary or interim remedy at these sites illustrates the convenience of this technology for quickly addressing MTBE contamination. Long-term or permanent air stripping system designs vary from site to site due to the desired amount of redundancy (i.e., factor of safety) and desired effluent quality. Since MTBE is not regulated under the Safe Drinking Water Act, air stripper systems in different states are required to meet different effluent concentrations for MTBE. Two of the case studies appear to have been over-designed; treatment train components were installed to ensure system reliability, but were not needed. At one of these two sites, the unused treatment train component was taken offline, but was later needed in response to a second UST release that increased influent MTBE concentrations. The balance between over-designing and underdesigning is site-specific. Long-term site plans, available funding, and state, local, and owner perceptions of acceptable system reliability and redundancy must be taken into account. The potential decline in MTBE influent concentrations over time should be considered during treatment system design. At five of the nine case studies discussed in this report, MTBE concentrations declined over time. Two of the systems no longer needed to operate after the first 3 to 6 years because MTBE concentrations were consistently low or non-detect. The ability to scale down the treatment system in response to declining influent concentrations would improve system cost-effectiveness Post-Treatment Post-treatment processes were common at sites examined in this report, regardless of whether treated water was used for drinking water or merely discharged into the environment. Posttreatment was not needed at only two systems prior to discharge or disinfection and use. 50

63 Liquid-phase GAC was employed at six treatment systems; sand and anthracite filtration was used at the seventh site. These filtration systems were designed to polish water quality and provide an extra degree of safety to ensure that treatment system effluent met discharge requirements. Post-treatment filtration was not designed to achieve VOC removal at any of the case study sites. One of the sites needed to employ additional post-treatment for VOC removal. At the packed tower air stripping system in Culver City, California, a UV/H 2 O 2 system was installed after the air stripping unit to disinfect and provide additional removal of oxygenates, including TBA. Although air stripping was found to remove up to 90 percent of TBA at one of the case study sites (Culver City, California), TBA is more difficult to remove from water than MTBE and may govern air stripping design or require the use of post-air stripper advanced oxidation to meet effluent TBA requirements. In summary, while post-treatment is commonly used to address other VOCs or provide a safety factor, it is not common to use several treatment technologies in series to remove MTBE Off-Gas Treatment Four of the nine sites included in the case study analysis treated off-gases from the air stripper units before emitting them to the atmosphere. Technologies used include thermal oxidation, catalytic oxidation, vapor-phase GAC, and an adsorption/thermal desorption and destruction system commercially available as the ADDOX TM system. While regulations vary nationwide, the need for an off-gas treatment system is typically governed by the expected mass released to the atmosphere per day. Emission requirements depend on state and local air quality regulations and on the proximity of potential receptors. Data from the four case studies was not sufficient to compare the design considerations of different types of off-gas treatment systems. 3.3 TREATMENT SYSTEM PERFORMANCE MTBE Removal The case studies demonstrate that air strippers can successfully treat groundwater with influent MTBE concentrations as high as 2,400,000 µg/l (Bridgeport, Connecticut) and as low as 10 µg/l (Rockaway Township, New Jersey). Depending on the design and operation of the air stripping system, average MTBE removal efficiencies ranged from 65 percent to greater than percent at the nine case studies included in this report. For the packed tower air stripping systems, average MTBE removal efficiencies were greater than 90 percent, with the exception of the site in Rockaway Township, New Jersey (where, on average, only 65 percent of MTBE was removed), and the site in Ridgewood, New Jersey (where approximately 30 percent was removed). However, the system at Rockaway Township, New Jersey, had low influent MTBE concentrations. Effluent MTBE 51

64 concentrations at this system were typically non-detect (less than 0.5 µg/l) and never exceeded 2 µg/l. The system at Ridgewood, New Jersey, was not designed for MTBE removal, but rather for PCE treatment. At the other packed tower treatment systems, effluent MTBE concentrations ranged from less than 2 µg/l to approximately 70 µg/l and were consistently below the state-specific standard for MTBE. For the low profile air stripping systems, average MTBE removal efficiencies were all greater than 90 percent. Average MTBE concentrations in treatment system effluent ranged from non-detect (less than 1 µg/l) to approximately 460 µg/l (site at Somersworth, New Hampshire). As with the packed tower air strippers, low profile air stripper performance was sufficient to meet the state MTBE standard. Although four of the case study air stripping systems implemented off-gas treatment, performance data were only available for two of the systems (Mammoth Lakes, California, and Elmira, California). At Mammoth Lakes, influent concentrations to the vapor-phase GAC system ranged from 15 to 590 parts per billion by volume (ppbv) MTBE. Capture and destruction values for MTBE ranged from 93.3 to 99.7 percent. At Elmira, California, influent concentrations to the ADDOX TM off-gas treatment system were higher, ranging from 65,000 to 393,000 ppbv MTBE. Capture and destruction efficiency for the ADDOX TM system ranged from 88.3 to 99.9 percent System Reliability Fouling and scaling were not an issue for most of the case study treatment systems, presumably because of the pretreatment systems described in Section Iron concentrations were fairly low in treatment system influent, ranging from 0.02 to 21 mg/l. Iron precipitation is lessened by a neutral or slightly acidic ph. Typically, the ph of influent water was neutral or slightly basic; ph ranged from 6.6 to 8.7. At one system (Somersworth, New Hampshire), a buildup of silt resulted in a temporary system shutdown. This was addressed by increasing the frequency of air stripper cleaning. A common theme among the case studies was fluctuations in influent MTBE concentrations that resulted in fluctuations in effluent concentrations. One response to increase system reliability is to address influent fluctuations. As discussed in Section 2.1.3, spikes in influent MTBE concentrations at the site in LaCrosse, Kansas, were dampened by limiting pumping from the most contaminated well. Another possibility is to install a blending tank prior to the air stripper influent. At other sites (e.g., Somersworth, New Hampshire), the efficiency of the air stripper system declined gradually over time as silt and other particles built up. After cleaning, air stripper efficiency improved greatly. Swings in operating efficiency can be addressed by better pretreatment systems or increasing the frequency of cleaning. Air stripper efficiency also decreases with temperature. Several air stripper systems reported this as a consideration (LaCrosse, Kansas, and Bridgeport, Connecticut). However, 52

65 temperature effects do not seem to be as important as the buildup of silt or changes in influent concentrations. For example, at the Connecticut site, the lowest removal efficiency was measured in August The impact of reduced temperatures during the winter months is not apparent in the case study performance data presented in this report. However, air stripping systems located in colder climates will have noticeably higher O&M costs during the winter months since these systems are typically equipped with heating elements. 3.4 TREATMENT SYSTEM COSTS Capital costs for the air stripping systems were reported to range from $15,000 ($ 1998) to $1.7 million (late 1990s). When expressed in year 2000 dollars to enable a direct comparison between system costs, capital costs ranged from $15,500 to $1.77 million. Normalized by the design capacity of the system, capital costs ranged from $0.47/1,000 to $104/1,000 gallons capacity. Taking the design log removal of MTBE into account, capital costs still ranged widely, from $0.47/1,000 to $85/1,000 gallons/log removal. Based on our review of the nine case studies presented in this report, O&M costs for air strippers were a function of both system flow rate and performance, as shown in Figure 18. The data illustrate efficiency of scale (i.e., lower unit O&M costs [$/1,000 gallons treated] as the size of the air stripping unit increased). The data also demonstrate that costs increase with percent removal of MTBE, as expected. Costs ranged from approximately $1 to $10/1,000 gallons for systems achieving greater than 90 percent removal. Costs were approximately $0.15 to $1/1,000 gallons for treatment systems achieving between 65- and 90-percent removal. Costs per kilogallon ($2000) Flowrate (gpm) Figure 18. Cost summary of MTBE removal by air stripping. Note: No cost data available for the site at Mammoth Lakes, California. 53

66 4. Model Evaluation 4.1 OVERVIEW OF MODELING SOFTWARE PROGRAMS The performance data from five of the nine air stripper case studies were used to evaluate the accuracy of two models that are commonly used to estimate the performance of low profile and packed tower air strippers. The models chosen for this exercise include NEEP ShallowTray Modeler software and the ASAP TM Packed Tower Model (Michigan Technological University, 2005) North East Environmental Products (NEEP) Shallow Tray Low Profile Air Stripper Model NEEP is a manufacturer of packed tower air strippers and low profile shallow tray air strippers (North East Environmental Products, 2005). As part of the quality testing, NEEP analyzed the performance of its commercially available ShallowTray low profile air stripper by analyzing over 10,000 samples to test the air stripper s performance at full-scale for removing VOCs (USEPA Method 624). Results were used to create performance curves illustrating removal efficiency at different VOC concentrations, temperatures, and flow rates. These performance curves are used in the proprietary ShallowTray Modeler software to simplify the process of predicting the performance of ShallowTray air stripping systems under different operating conditions. The ShallowTray model calculates removal versus flow rate for several contaminants, including BTEX, MTBE, and chlorinated VOCs. The model accounts for contaminant solubility, vapor pressure, water temperature, air temperature, and influent concentrations Aeration System Analysis Program (ASAP TM ) Packed Tower Model The ASAP TM model was developed at Michigan Technological University and is commercially available separately or in a package with other modeling software as a comprehensive modeling tool known as the Environmental Technologies Design Option Tool (ETDOT) (Michigan Technological University, 2005). ASAP TM uses mass transfer calculations to predict the performance of various air stripping designs, including packed towers, systems with bubble or diffused aeration, and systems with surface aeration. Since these calculations require chemical-specific properties (e.g., molecular weight, boiling point, Henry s law constant, liquid and gas diffusion coefficients, aqueous solubility), ASAP TM is linked to a program called Software to Estimate Physical Properties (StEPP), which contains the physical and chemical properties for over 600 compounds, many of which are designated USEPA priority pollutants. StEPP calculates the value of these properties at the specified temperature and pressure. The ASAP TM Packed Tower Aeration Model is designed to predict the performance of counter-current packed tower air strippers. This model calculates removal efficiency using 54

67 several simplifying assumptions, including steady-state, plug-flow reactor conditions for both air and water streams, clean influent air stream, and equilibrium of contaminant concentrations in air and water phases, as described by Henry s Law (ASAP, 2005). The model can be used to assess the preliminary design and feasibility of air stripping processes, plan pilot-scale studies, or interpret pilot-scale results. Model calculations can be performed in either the design or rating mode. In the design mode, the user specifies the required removal efficiency and the packed tower is then sized to meet the treatment objectives for all contaminants. Model output includes the packed tower design and effluent concentration for each contaminant of concern. In the rating mode, the performance of an operating packed tower can be compared with the expected performance to see if the air stripper is operating effectively. Actual operating parameters (e.g., temperature, contaminants, concentrations, packing material characteristics) are entered into the model by the user or chosen from the model s built-in database. The model-predicted removal efficiency is compared with observed removal efficiencies to see if the air stripper is meeting expectations. Additional information about the ASAP TM model can be found online (Michigan Technological University, 2005) or in Hokanson et al., LOW PROFILE AIR STRIPPER SOMERSWORTH, NEW HAMPSHIRE Modeled Scenarios The removal efficiency predicted by the NEEP ShallowTray Model was compared with the actual performance of the low profile air stripper operating in Somersworth, New Hampshire. Six different sets of parameters, or cases, were modeled, as shown in Table 41. Each case was tested at temperatures ranging between 66 to 70 F, centered around the average temperature of the effluent of 68 F. Cases One and Two had water flow rates of 3 and 10 gpm, respectively, to reflect the minimum and maximum water flow rates of the system. Case Three used an air-to-water ratio of approximately 800, which was typically maintained during system operation. For these three cases, the maximum air flow rate of 900 scfm was held constant to reflect the measured air-to-water ratio of 1,070. For Cases Four, Five, and Six, the water flow rate of 10 gpm was kept constant and the air flow rate was varied at 600, 675, and 750 scfm, respectively. Data for each case can be found in Table B-1 of Appendix B. Table 41. Modeling Scenarios for Low Profile Air Stripper at Somersworth, New Hampshire Parameter Actual Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 Water flow rate (gpm) 3 to 10, typically Air flow rate (scfm) Air-water ratio 1,070:1 2,244:1 673:1 801:1 450:1 505:1 560:1 Temperature ( F) to to to to to to 70 55

68 4.2.2 Discussion A comparison of the theoretical and actual effluent MTBE concentrations shows that the model predicted greater MTBE removal than what was actually observed. From August 1997 through April 1998, actual effluent concentrations were significantly higher than the estimated effluent concentrations, most likely due to the build-up of silt that occurred in the stripper. In Cases Four, Five, and Six, the effluent concentrations were greater than the first three cases, but the model still predicted lower effluent concentrations than produced by the actual system. 4.3 LOW PROFILE AIR STRIPPER CHESTER, NEW JERSEY Modeled Scenarios Data from the site at Chester, New Jersey, was verified using the NEEP ShallowTray Modeler software. Only one scenario was modeled for this site, which can be described as follows: NEEP Shallow Tray Low Profile Air Stripper: Model # Water flow rate 15 gpm. Air flow rate 150 scfm. Typical air-to-water ratio 75 to 1. Operational water temperature 40 to 45 F. Based on performance data, the influent MTBE concentration was fixed at 220 µg/l Discussion The model estimated an effluent MTBE concentration ranging from 74 to 86 µg/l for the varying temperatures, resulting in removal efficiencies ranging from 61 to 67 percent. The only effluent MTBE concentration provided for this site (less than 14 µg/l) was measured after the GAC polishing step, so no direct comparison to actual performance can be made. Therefore, the overall removal efficiency through the GAC polishing step is estimated to be greater than 81 percent, based on model data. 4.4 PACKED TOWER AIR STRIPPER LACROSSE, KANSAS Modeled Scenarios The removal efficiency predicted by the ASAP TM Packed Tower Model was compared with data from the packed tower air stripper operating in LaCrosse, Kansas. Two different cases were modeled to reflect differences between summer and winter flow rates. Typical operating 56

69 parameters and modeled cases are shown in Table 42. As indicated, flow rates of 480 and 350 gpm were used to represent summer and winter flow rates. Temperatures of 60 and 70 F were used for all of the tested parameters since the influent water temperature was unknown. An air flow rate of 10,000 cfm was used in the model, resulting in air-to-water ratios of 156 and 214. MTBE influent concentrations ranged from 46 to 954 µg/l for both modeled and actual scenarios. Effluent data was modeled for each of the two stages of the packed towers. Table 42. Modeling Scenarios for Packed Tower Air Stripper at LaCrosse, Kansas Parameter Actual Case 1 Case 2 Water flow rate (gpm) 480 (summer) 350 (winter) Air flow rate (scfm) 10,000 10,000 10,000 Air-water ratio 156:1 to 214:1 156:1 214:1 Temperature ( F) Not available 60 to to Discussion A comparison of the actual and theoretical concentrations modeled at each stage of the air stripper is presented in Tables B-2 and B-3 of Appendix B. The predicted effluent concentrations demonstrate better removal efficiencies than the actual effluent data. For 480 gpm, the model predicted a removal efficiency of 99 percent; for 350 gpm, the model predicted a removal efficiency of 99.5 percent. Actual data showed that the removal efficiency ranged from 41 to 100 percent. 4.5 PACKED TOWER AIR STRIPPER CULVER CITY, CALIFORNIA Modeled Scenarios ASAP TM model predictions were compared with actual removal efficiencies at a packed tower air stripper operating in Culver City, California. Packing properties (i.e., nominal size 2.5 inches, geometric surface area 55 square feet per cubic feet [ft 2 /ft 3 ], polypropylene material density 5.1 pounds per cubic feet [lbs/ft 3 ]) were inputted to the user-defined database because the actual packing material (No. 2 NUPAC TM ) was not available in the model. A temperature of 70 F was tested in the model to reflect the temperature range observed in the operational data for the system. Design parameters used in the model included the following: Water flow rate 200 gpm. Air flow rate 7,000 scfm. Typical air-to-water ratio 700 to 1. Operational temperature 70 F. 57

70 Actual MTBE concentrations entering the air stripper at Culver City, California, from November 1999 through March 2000 were used in the model Discussion Based on a comparison of the data, the model predicted lower effluent concentrations (0.04 to 0.06 µg/l) than the actual effluent data (1.1 to 8.4 µg/l). A comparison of the actual and theoretical concentrations modeled at each stage of the air stripper is presented in Table B-4 of Appendix B. 4.6 PACKED TOWER AIR STRIPPER ROCKAWAY TOWNSHIP, NEW JERSEY Modeled Scenario The predicted air stripper removal using the ASAP TM model was compared with actual removal from a packed tower air stripper operating in Rockaway Township, New Jersey. Temperatures of 50 and 55 F were used in the two modeling cases to reflect operational data for the system. A water flow rate of 1,500 gpm and an air-to-water ratio of 100 were used in the model. Actual influent MTBE concentrations observed in the performance data for the 1995 treatment system were also used in the model. Actual operating parameters and modeled input parameters for each case are shown in Table 43. Table 43. Modeling Scenarios for Packed Tower Air Stripper at Rockaway Township, New Jersey Parameter Actual Case 1 Case 2 Water flow rate (gpm) 1,500 1,500 1,500 Air flow rate (cfm) 20,000 20,000 20,000 Air-water ratio 100:1 100:1 100:1 Temperature ( F) 50 to Discussion A comparison of the actual and theoretical concentrations modeled at each stage of the air stripper is presented in Table B-5 of Appendix B. The comparison shows that the model predicted lower effluent concentrations than the actual effluent data. The model predicted removal efficiencies ranging between 93 and 96 percent through the air stripper; actual removal efficiencies ranged between 14 and 91 percent. 4.7 SUMMARY OF MODELING RESULTS The ASAP TM model predicted slightly better removal efficiency and slightly lower effluent MTBE concentrations than actual packed tower air stripping units at the four sites included 58

71 in the modeling analysis. There may be several reasons for this discrepancy. The ASAP TM model assumes that the hydraulic configuration of the packed tower reactor is plug flow for both air and water streams. This is the most efficient configuration. During actual system operation, some mixing, short-circuiting, or other non-ideal flow patterns may occur, reducing the effectiveness of contaminant-phase transfer from liquid to vapor. The percent removal predicted using the NEEP model was in general agreement with the observed concentration at the field site. A comparison of modeling results and actual system performance is shown in Figure 19. Predicted Removal Actual Removal Figure 19. Comparison of modeling results to actual performance. On average, observed removal efficiencies were approximately 15 percent lower (ranging 2 percent higher to 50 percent lower) than modeling predictions. The highest discrepancy between predicted and observed percent removal occurred for the site at Rockaway Township, New Jersey, where concentrations of MTBE were already fairly low in the influent (ranging from less than 0.5 to 6.9 µg/l MTBE over the period of operation used for the modeling exercise). Model predictions showed better agreement with actual system performance at systems with higher influent MTBE concentrations (e.g., Culver City, California, and Somersworth, New Hampshire). The ability of these models to accurately predict air stripper performance contributes to the growing acceptance of air stripping as a proven technology to remove MTBE from groundwater supplies. 59

72 5. Summary of Findings The California MTBE Research Partnership identified a research need to assess the efficacy of air stripping for removing MTBE from contaminated groundwater. MTBE contamination has been reported at UST sites across the country. Although air stripping is a well-established technology for VOCs, like PCE, the technology has not yet been demonstrated to be costeffective or reliable for MTBE treatment. As summarized in this report, the Partnership identified nine sites where air strippers are being used to address MTBE contamination in groundwater. The Partnership obtained cost and performance data for each of the sites and analyzed the data to assess the benefits, limitations, and costs of air stripping for MTBE. Two commercially available models for predicting air stripping performance were assessed by comparing model predictions with operating performance at several of the case study sites. Study findings, conclusions, and recommendations are summarized in this section. 5.1 CASE STUDY DATA COLLECTION Through research efforts, nine air stripper systems operating at full-scale to address MTBE contamination were identified. Information about site history, air stripper system design, configuration, influent MTBE concentrations, other influent water quality parameters, effluent MTBE goals, capital costs, and annual O&M costs were collected for each site. These data were provided to the Partnership by environmental consultants, air stripper manufacturers, and state regulators. Some of the data could not be shared with the Partnership due to ongoing litigation. Nevertheless, enough data was available to proceed with data analysis and model validation. 5.2 CASE STUDY DATA ANALYSIS The case study analysis indicated that a variety of different treatment train configurations can use air strippers to successfully remove a wide range of MTBE concentrations. Influent MTBE concentrations were as high as 2,400,000 µg/l and as low as 10 µg/l in the case studies included in this report. Average MTBE removal efficiencies ranged from 65 percent to greater than 99.9 percent, with the lower range occurring in systems that did not require significant MTBE reduction. Most of the air stripper system designs included some form of pretreatment to reduce the possibility of scaling, biological growth, and foaming. Heating elements were included prior to air stripping in colder climates. Fouling and scaling were not an issue for most of the case study treatment systems because of this pretreatment. A buildup of silt occurred in one system, resulting in a temporary system shutdown. This problem was addressed by cleaning the air stripper more frequently. Sites that did not employ pretreatment were designed to primarily remove other VOCs and did not require significant MTBE reduction. 60

73 Air stripper configuration was primarily determined by the economics of different flow rates. Systems with flow rates below approximately 100 gpm were low profile systems; those with flow rates greater than 100 gpm were packed tower configurations. Air strippers were used as interim treatment systems at some of the sites. Since air stripping is quick to implement, it is advantageous compared to other treatment methods (e.g., biological systems). Another advantage of air strippers is the applicability to other VOC contaminants. However, at sites with MTBE and TBA, the desired TBA removal may drive air stripping design considerations or necessitate post-treatment specific to TBA. Post-treatment was not needed for MTBE removal; however, GAC or other filtration systems were frequently used as a polishing step. Off-gases treatment technologies were needed at four of the nine case study sites. Technologies included thermal oxidation, catalytic oxidation, vapor-phase GAC, and an adsorption/thermal desorption system known as ADDOX TM. Data were not sufficient to compare the cost and performance of different types of off-gas treatment systems. Influent MTBE concentrations declined over time at five of the nine case study sites. Two of the air stripping systems were no longer needed after 3 and 6 years of operations since influent concentrations were below discharge standards or were non-detect. Fluctuations in influent MTBE concentrations and swings in operating efficiency were common at the air stripper case studies, but were successfully addressed by changing well usage patterns and increasing the frequency of cleaning. Air stripper efficiency also decreases with temperature. However, temperature effects were secondary to the effects of silt buildup or changes in influent concentrations. Systems in colder climates will understandably have higher O&M costs in winter due to heating costs. Capital costs for the air stripper systems ranged from $43,000 ($1997) to $1.7 million (late 1990s). Normalized by flow rate and expressed in year 2000 dollars, capital costs ranged from $0.47/1,000 to $103/1,000 gallons ($0.47/1,000 or $85/1,000 gallons/log removal). O&M costs were also a function of system flow rate and percent MTBE removal. Costs ranged from $1 to $10/1,000 gallons for systems achieving greater than 90-percent removal. Costs were approximately $0.15 to $1/1,000 gallons for systems achieving between 65- and 90-percent removal. 5.3 MODEL VALIDATION Two different air stripping models were validated using performance data from several low profile and packed tower air stripper case studies. The ASAP TM model created at Michigan Technological University was used to simulate the performance of three packed tower air strippers operating at LaCrosse, Kansas; Culver City, California; and Rockaway Township, New Jersey. In this modeling program, operating parameters, such as influent MTBE concentrations, air-to-water ratio, water flow rate, temperature, tower dimensions, and packing media, were specified. The model was used to predict effluent MTBE 61

74 concentrations. Predicted effluent concentrations were slightly lower than the observed concentrations at all four sites. Thus, the model-predicted removal efficiencies were slightly greater than observed efficiencies. For the low profile air strippers, a model created by NEEP was used to estimate effluent MTBE concentrations. A number of parameters were specified in the model, including airto-water ratio, temperature, and flow rates. As with the ASAP TM model, the NEEP model predicted slightly lower effluent MTBE concentrations than those observed at the low profile air stripper operating in Somersville, New Hampshire. Despite the optimistic bias of these two models in predicting more MTBE removal than was actually observed, the models agreed with observed removal efficiency within 15 percent. Model predictions showed even better agreement with actual system performance at systems with higher influent MTBE concentrations. The data illustrate that commercially available models are fairly accurate in predicting actual air stripper performance. 5.4 CONCLUSIONS Based on this review of air stripper systems that are operating to address MTBE contamination, air strippers can be used to successfully and reliably remove MTBE from drinking water supply systems or groundwater remediation systems. This study provides a brief overview of water quality parameters, air stripper design and performance data, and cost summaries for each case study. MTBE was successfully removed, with efficiencies greater than 90 percent, over a wide range of influent concentrations. Commercially available models have been demonstrated to predict actual MTBE removal efficiency to within 15 percent. Although model predictions of removal efficiency were biased slightly high, the models provide a valuable tool for assessing air stripper performance during remedy selection and conceptual treatment system design. Expressed in year 2000 dollars, capital costs ranged widely, from $0.47/1,000 to $103/1,000 gallons capacity. O&M costs associated with the case studies ranged from $0.15 to $11/1,000 gallons of water treated. 62

75 6. References California MTBE Research Partnership (1999). Evaluation of the Applicability of Synthetic Resin Sorbents for MTBE Removal from Water. National Water Research Institute, Fountain Valley, California. California MTBE Research Partnership (2000). Treatment Technologies for Removal of MTBE from Drinking Water: Air Stripping, Advanced Oxidation Processes, Granular Activated Carbon, Synthetic Resin Sorbents, Second Edition. National Water Research Institute, Fountain Valley, California. California MTBE Research Partnership (2001). Treating MTBE-Impacted Drinking Water Using Granular Activated Carbon. National Water Research Institute, Fountain Valley, California. California MTBE Research Partnership (2004). Evaluation of MTBE Remediation Options. National Water Research Institute, Fountain Valley, California. Hokanson, D.R., T.N. Rogers, D.W. Hand, F. Gobin, M.D. Miller, J.C. Crittenden, and J.E. Finn (1995). A Physical Property Resource Tool for Water Treatment Unit Operations. Proceedings of AWWA Annual Conference, Anaheim, California, pp Michigan Technological University (2005). Environmental Technologies Design Option Tool, ETDOT TM. Available online at North East Environmental Products (2005). North East Environmental Products, Inc Integrated Environmental Technologies. Available online at Suflita, J.M., and M.R. Mormile (1993). Anaerobic Biodegradation of Known and Potential Gasoline Oxygenates in the Terrestrial Subsurface. Environmental Science and Technology, 27(6): US Water News (1996). Santa Monica Water Supply Threatened by MTBE. US Water News Online. July. Available online at U.S. Environmental Protection Agency (1998). Oxygenates in Water: Critical Information and Research Needs. Office of Research and Development, Washington, D.C. EPA/600/R-98/048. U.S. Environmental Protection Agency (2005). Contaminant Focus: Methyl Tertiary Butyl Ether. Technology Innovation Program. Available online at Yeh, C.K., and J.T. Novak (1995). The Effect of Hydrogen Peroxide on the Degradation of Methyl and Ethyl Tert-Butyl Ether in Soils. Water Environment Research, 67(5):

76 64

77 Appendix A Date Table A-1. Air Stripper Performance Data for MTBE at La Cross, Kansas Influent Between Stripper 1st Tower Removal Efficiency (%) To Tower 2nd Tower Removal Efficiency (%) Tap 4/25/ /26/ /27/ /28/ /29/ /6/ /13/ /21/ /27/ /4/ /16/ /23/ /1/ /8/ /10/ /16/ /22/ /30/ /5/ /12/ /26/ /2/ /9/ /10/ < /16/ < /17/ < /18/ < <0.2 9/23/ < <0.2 9/24/ < <0.2 9/30/ < /8/ < <0.2 10/14/ < <0.2 <0.2 10/21/ < (Continued on Next Page) 65

78 (Continued from Previous Page) Date Table A-1. Air Stripper Performance Data for MTBE at La Cross, Kansas Influent Between Stripper 1st Tower Removal Efficiency (%) 66 To Tower 2nd Tower Removal Efficiency (%) Tap 10/29/ < /18/ < /9/ /29/ /13/ /26/ /11/ <0.2 2/24/ /3/ /3/ /10/ /10/ /18/ /18/ /24/ /24/ /25/ /25/ /1/ /1/ /9/ /15/ < <0.2 <0.2 4/21/ < <0.2 4/28/ < /6/ < /13/ < /20/ /27/ /2/ /9/ /16/ /24/ /1/ /7/ /14/ /21/ < /28/ (Continued on Next Page)

79 (Continued from Previous Page) Date Table A-1. Air Stripper Performance Data for MTBE at La Cross, Kansas Influent Between Stripper 1st Tower Removal Efficiency (%) To Tower 2nd Tower Removal Efficiency (%) Tap 8/4/ /11/ < /19/ /26/ < /1/ /9/ /16/ /30/ /6/ /14/ <0.2 10/20/ /28/ /3/ /12/ /18/ /24/ /2/ /8/ /16/ /21/ /28/ /6/ /12/ /3/ /3/ /6/1999 <0.2 <0.2 <0.2 <0.2 5/5/ /1/ /7/ /7/ /3/ /1/ /29/ /3/ /1/ /5/ /1/

80 Table A-2. Air Stripper Performance Data for MTBE at Somersworth, New Hampshire Date Flow (gallons) Influent Midfluent Effluent 11/22/96 4, ,000 8 <5.0 11/23/96 7,290 1,290,000 <2.0 <5.0 11/24/96 72, ,000 <2.0 <5.0 11/27/96 45,998 1,670,000 <2.0 <5.0 12/4/96 76, ,000 73,300 <5.0 12/10/96 1,376 NA NA <5.0 12/11/96 4,450 NA NA <5.0 12/12/96 12, ,000 33, /16/96 61, ,000 31, /23/96 85, , /30/96 129, ,000 1, /8/97 173, ,000 5, /4/97 1,240,000 <2.0 2/28/97 65, /10/97 32, /30/97 26, /3/97 16, /25/97 19, /31/97 39, /28/97 12, /15/97 25, /20/97 13, /18/97 7, /12/98 72, /19/98 80, /24/98 61,700 18,800 4/13/98 20,200 1,010 4/28/98 22, /26/98 26, /29/98 9, /29/98 16, /27/98 107, /30/98 12, /23/98 12, /21/98 10, /20/99 4, (Continued on Next Page) 68

81 (Continued from Previous Page) Table A-2. Air Stripper Performance Data for MTBE at Somersworth, New Hampshire Date Flow (gallons) Influent Midfluent Effluent 3/1/ /5/99 1, /4/99 1,040 <2.0 6/2/99 1, /7/99 1,100 <10.0 8/4/ <5.0 8/11/99 2,400 <5.0 8/18/99 2,900 <5.0 8/25/99 3, /31/99 8,800 <5.0 9/29/99 1,800 <5.0 10/27/ <5.0 11/30/ <5.0 12/28/ <5.0 1/27/ <5.0 2/28/ <5.0 3/30/ <5.0 NA = Not available. Trial # Table A-3. Air Stripper Performance Data for MTBE at Culver City, California Influent Effluent S 1 % Removal Effluent S 2 % Removal 1 3, ,400 < < , ,100 < < , ,500 < <

82 Table A-4a. Air Stripper Performance Data for MTBE at Bridgeport, Connecticut Date Influent Effluent S 1 Percent Removal S 1 Effluent S 2 Percent Removal S 2 Overall Percent Removal 4/1/95 2,400,000 3, /1/95 1,100,000 14, /1/95 1,100,000 2, /1/95 960,000 1, /1/95 630, /1/95 360, /1/95 490, /1/95 480, /1/95 480,000 3, /1/96 580,000 1, /1/96 200,000 6, Table A-4b. Air Stripper Performance Data for BTEX at Bridgeport, Connecticut Date Influent Effluent S 1 Percent Removal S 1 Effluent S 2 Percent Removal S 2 Overall Percent Removal 4/1/95 34, /1/95 14, /1/95 26, /1/95 22, /1/95 18, /1/95 10, /1/95 20, /1/95 15, /1/95 19, /1/96 16, /1/96 15,

83 Table A-5. Air Stripper Performance Data for MTBE at Rockaway Township, New Jersey Date Influent Effluent Efficiency (%) 9/3/ /10/ /17/ /24/ /1/ /8/ /15/ /24/ /29/ /5/ < /12/ < /26/ /3/ < /24/ < /31/ < /14/ < /21/ < /28/ /4/ /18/ /25/ < /4/ < /11/ < /18/ < /25/ /1/ /8/ /15/ /22/ < /29/ < /6/ < /13/ < /20/ < /3/ < /1/ < /19/ < (Continued on Next Page) 71

84 (Continued from Previous Page) Table A-5. Air Stripper Performance Data for MTBE at Rockaway Township, New Jersey Date Influent Effluent Efficiency (%) 9/2/ /14/ /21/ /28/ /4/ /18/ < /25/ < /30/98 <0.5 < /24/99 <0.5 < /6/99 <0.5 < /20/99 <0.5 < /3/99 <0.5 < /17/99 <0.5 < /1/ < /15/ < /29/ < /12/ < /26/99 <0.5 < /23/ < /6/ < /21/ < /4/ < /18/ < /1/99 <0.5 < /16/ < /30/ < /6/ < /13/ < /27/ < /3/ < /10/ < /7/00 <0.5 < /21/00 <0.5 <

85 Table A-6. Off-Gas System Performance Data for MTBE at Elmira, California Date Influent (ppmv) Effluent (ppmv) 2/17/ /17/ /17/ /15/ /15/ /14/ /14/ /14/ /14/ /14/ /14/ /20/ /22/ /24/ /29/ /3/ /5/ /7/ /12/ /26/

86 Appendix B Table B-1. Modeling Data Comparison for Low Profile Air Stripper at Somersworth, New Hampshire Date Influent Effluent Case 1 1 Case 2 1 Case 3 1 Case 4 1 Case 5 1 Case /22/ < /23/ < /24/ < /27/ < /04/ < /12/ /16/ /23/ /30/ /08/ /04/ < /28/ /10/ /30/ /03/ /25/ /31/ /28/ /15/ /20/ /18/ /12/ /19/ /24/ /13/ /28/ /26/ /29/ /29/ /27/ /30/ Data for all six cases ranges for 66 to 70 F. (Continued on Next Page) 74

87 Table B-1. Modeling Data Comparison for Low Profile Air Stripper at Somersworth, New Hampshire (Continued from Previous Page) Date Influent Effluent Case 1 1 Case 2 1 Case 3 1 Case 4 1 Case 5 1 Case /23/ /21/ /20/ /01/ /05/ /04/ < /02/ /07/ < /04/ < /11/ < /18/ < /25/ /31/ < /29/ < /27/ < /30/ < /28/ < /27/ < /28/ < /30/ < Data for all six cases ranges for 66 to 70 F. 75

88 Table B-2. Modeling Data Comparison for Packed Water Air Stripper at LaCrosse, Kansas (Water Flow Rate = 480 gpm, Air-to-Water Ratio = 156) Actual Influent Actual Effluent 1st Tower ASAP TM Influent at 60 F ASAP TM Effluent at 70 F Actual Effluent 2nd Tower ASAP TM Effluent at 60 F ASAP TM Effluent at 70 F ND ND ND ND ND ND ND NA ND = Non-detect. NA = Not available. 76

89 Table B-3. Modeling Data Comparison for Packed Water Air Stripper at LaCrosse, Kansas (Water Flow Rate = 350 gpm, Air-to-Water Ratio = 214) Actual Influent Actual Effluent 1st Tower ASAP TM Influent at 60 F ASAP TM Effluent at 70 F Actual Effluent 2nd Tower ASAP TM Effluent at 60 F ASAP TM Effluent at 70 F ND ND ND ND ND ND ND NA ND: Non-detect (<0.5 µg/l). NA = Not available. 77

90 Table B-4. Modeling Data Comparison for Low Profile Air Stripper at Culver City, California Date ND = Non-detect. NA = Not available. Influent Effluent from S-01 ASAP TM Effluent at 70 F 11/10/99 17,000 NA /15/99 3, /20/99 6,300 NA /21/99 2,400 NA /13/00 4,500 NA /21/00 5, /01/00 4, /12/00 3,000 ND /16/00 3, /25/00 3,000 ND /01/00 2,500 ND /09/00 2,900 ND /15/00 4,100 ND

91 Table B-5. Modeling Data Comparison for Low Profile Air Stripper at Rockaway Township, New Jersey Date Influent Effluent ASAP TM Effluent at 50 F ASAP TM Effluent at 55 F 10/15/ /24/ /29/ /05/ /12/ /26/ /10/ /07/ /14/ /28/ /04/ /11/ /18/ /25/ /01/ /08/ /15/ /14/ /21/ /28/ /04/ /06/ < /21/ < /04/ < /18/ < /16/ < /30/ < /06/ < /13/ < /27/ < /03/ < /10/ < /07/ < /21/ <

92 80