BULLETIN NO. 21A EVALUATION OF WASTEWATER TREATMENT OPTIONS USED IN RAPID INFILTRATION BASIN SYSTEMS (RIBS)

Transcription

1 State of Deaware DELAWARE GEOLOGICAL SURVEY David R. Wunsch, State Geoogist BULLETIN NO. 21A EVALUATION OF WASTEWATER TREATMENT OPTIONS USED IN RAPID INFILTRATION BASIN SYSTEMS (RIBS) By Müserref Türkmen 1, Edward F. Wather 2, A. Scott Andres 4, Anastasia A.E. Chirnside 3, Wiiam F. Ritter 4 Deaware Geoogica Survey University of Deaware Newark, Deaware Izmir Water and Sewerage Administration, Izmir, Turkey 2 South Water Management District, West Pam Beach, Forida 3 Deaware Geoogica Survey 4 Coege of Agricuture and Natura Resources, University of Deaware

2 TABLE OF CONTENTS Page ABSTRACT...1 INTRODUCTION...1 Wastewater and the Environment...1 Wastewater and RIBS...2 Environmenta Impact of RIBS...2 Purpose and Scope...3 Use of RIBS in Deaware...4 Treatment Practices Observed During This Study...4 Acknowedgments...5 METHODS...5 Site Visits, Samping, and Anaysis...5 Comparison of State Reguations on Land Appication of Wastewater...6 RESULTS AND DISCUSSION...7 State Reguatory Approaches and Technica Criteria...7 Effuent Characterization and Treatment Pant Performance-Deaware and New Jersey...11 Effuent Characterization and Treatment Pant Performance-A States...13 CONCLUSIONS AND RECOMMENDATIONS...15 REFERENCES CITED...16 APPENDICES...19

3 ILLUSTRATIONS Page Figure 1. Decision tree iustrating reguations, major permitting criteria, and monitoring requirements for RIBS... in Deaware...8 Figure 2. Decision tree iustrating reguations, major permitting criteria, and monitoring requirements for RIBS... in Forida...8 Figure 3. Decision tree iustrating reguations, major permitting criteria, and monitoring requirements for RIBS... in Maryand...9 Figure 4. Decision tree iustrating reguations, major permitting criteria, and monitoring requirements for RIBS... in New Jersey...9 Figure 5. Decision tree iustrating reguations, major permitting criteria, and monitoring requirements for RIBS... in North Caroina...10 Figure 6. Decision tree iustrating reguations, major permitting criteria, and monitoring requirements for RIBS... in Massachusetts...10 Figure 7. Concentrations of bioogica oxygen demand in the infuent and effuent sampes from different wastewater... treatment pants and percent remova rates...11 Figure 8. Concentrations of chemica oxygen demand in the infuent and effuent sampes from different wastewater... treatment pants and percent remova rates...11 Figure 9. Tota suspended soids concentrations in the infuent and effuentsampes and percent remova rates...12 Figure 10. Concentrations of tota nitrogen in the infuent and effuent sampes from different wastewater treatment... pants and percent remova rates...12 Figure 11. Tota phosphorus concentrations in the infuent and effuent sampesand percent remova rates...12 Figure 12. Indicator organism concentrations in the effuent sampes...13 Figure 13. Comparison of parameter exceedences based on treatment processes...13 Figure 14. Comparison of frequencies of nitrate exceedences...13 TABLES Tabe 1. Seected RIBS in United States...1 Tabe 2. Advanced treatment pants visited in Deaware and New Jersey...6 Tabe 3. Wastewater anaysis and anaytica methods...7 Tabe 4. Buffer distances for RIBS in Deaware and other states...11 APPENDICES Appendix 1. Anaytica resuts of infuent and effuent sampes from seected wastewater treatment pants in Deaware..19 Appendix 2. List of different treatment processes and their percent exceedences of effuent quaity imits...20

4 ACRONYMS USED IN THIS REPORT AS BC BCF BOD CE CH COD co/100 m DE DGS DNREC EA FG IT LBWD LSA MA MD µg/l mg/l N NC NH - 4 NJ NO - 3 O&M OD OP P RBC RIBS SBR SMWW SWA SC TKN TN TMDL TP TSS USEPA WBP WTP WWTP Activated Sudge Beaver Creek Breeder's Crown Farm Biochemica Oxygen Demand Coonia Estates Cape Henopen State Park Chemica oxygen demand Coonies per 100 miiiters Deaware Deaware Geoogica Survey Deaware Department of Natura Resources and Environmenta Contro Extended aeration Forest Grove Imhoff tank Land based wastewater disposa Landis Sewerage Authority Massachusetts Maryand Micrograms per iter Miigrams per iter Nitrogen North Caroina Ammonia New Jersey Nitrate Operation and maintenance Oxidation ditch Ortho-Phosphorus Phosphorus Rotating bioogica contactor Rapid infitration basin systems Sequencing batch reactor Standard Methods for Examination of Water and Wastewater Southwood Acres Stonewater Creek Tota Kjedah nitrogen Tota nitrogen Tota Maximum Daiy Load Tota phosphorus Tota suspended soids U.S. Environmenta Protection Agency West Bay Park Winsow Township Wastewater treatment pant

5 EVALUATION OF WASTEWATER TREATMENT OPTIONS USED IN RAPID INFILTRATION BASIN SYSTEMS (RIBS) ABSTRACT This technica report evauates severa aspects of potentia environmenta risks, use, and reguation of rapid infitration basin systems (RIBS) in Deaware. The report reviews and compares reguations regarding RIBS from Deaware, Forida, North Caroina, New Jersey, Maryand, and Massachusetts. Infuent and effuent sampes from ten advanced wastewater treatment systems that operate in conjunction with RIBS were coected and anayzed. Effuent data obtained from the Non- Hazardous Waste Sites database provided by the Deaware Department of Natura Resources and Environmenta Contro and other states were assessed. Performance evauations of the treatment processes that discharge to RIBS were ascertained from the exceedance of concentrations of reguated poutants in effuent sampes. Athough RIBS technoogy has the potentia to be a beneficia aternative to surface discharge and a means for groundwater recharge, this technoogy is appropriate ony if the adverse environmenta impacts are minimized. Overa operation and maintenance practices pay important roes in the performance of treatment pants. The most common and serious probems associated with treatment pants ocated in Deaware and neighboring states are high nutrient and pathogen concentrations in the effuent. In Deaware, the discharge of poory treated effuent to RIBS creates a risk of nutrient and pathogen contamination in the receiving water body, the shaow Coumbia aquifer. Years of appication of treated effuent with high nutrient, pathogen, and organic content to RIBS wi resut in significant risks for the environment and pubic heath. INTRODUCTION For hundreds of years, peope have disposed of their wastewater directy into surface waters. The and appication of wastewater is aso a ong standing practice for many communities (Wiiam and Beford, 1979; Bastian, 2005; Wiiams, 2006; Reed et a., 1984). However, as environmenta awareness has increased, oca governments are often required to both treat their wastewater, and find efficient and beneficia disposa options for their wastewater. By aw, wastewater coected from residences, industries, and institutions now either must be returned to receiving waters, appied to the and, or reused. The eve of treatment prior to discharge determines the impact of effuent on the receiving environment. Land-based wastewater disposa (LBWD) is the controed appication of treated effuent onto the soi, where it receives additiona treatment. LBWD methods have been used in the United States since the ate 19th century, especiay in the reativey arid, rapidy deveoping, west and southwest, where ow water suppies make water reuse and groundwater recharge essentia. The use of LBWD methods is now spreading into other ocations. One type of LBWD is RIBS, a and treatment system that resembes intermittent sand fitration. With RIBS, pretreated wastewater is appied to an infitration basin, from which it percoates through the soi and into the groundwater. The method is aso known as soi-aquifer treatment because physica, chemica, and bioogica mechanisms further treat the wastewater as it moves downward (Crites and Tchobanogous, 1998; Asano et a., 2006). When propery operated, RIBS may recharge the groundwater, provide further treatment to the treated effuent, and reduce the degradation of stream-water quaity. Some seected RIBS are shown in Tabe 1. Tabe 1. Seected RIBS in the United States. Wastewater and the Environment Municipa wastewater contains a variety of soid materias that differ in type, size, and density. Typica domestic wastewater contains mg/l tota soids, mg/l tota suspended soids (TSS), mg/l tota dissoved soids, and 5-20 mg/l setteabe soids (Crites and Tchobanogous, 1998). During treatment, coarse particuate are removed by setting. Usuay 60 percent of the suspended soids are setteabe; after setting they are removed (Tchobanogous and Stense, 2003). Some of the remaining suspended soids are removed by fitration or entrapment if the effuent is and appied. Aternating fooding-drying cyces during and appication aow these soids to desiccate or degrade. However, to prevent cogging and hydrauic faiure in a RIBS appication, dried soids need to be removed from the surface of the appication area or the area must be routiney scraped to prevent cogging and hydrauic faiure. Inadequate procedures for removing soids can increase the risk that the groundwater wi be contaminated by certain types of bacteria (Tchobanogous and Stense, 2003). Deaware Geoogica Survey BULLETIN 21A 1

6 In nature, poutants may be degraded bioogicay or chemicay. When biodegradabe carbonaceous organic materias are reeased into a body of water, microorganisms break them into smaer organic and inorganic moecues to meet their carbon and energy requirements. When this happens under aerobic conditions, the amount of oxygen the microorganisms consume is caed bioogica oxygen demand (BOD). When a ot of oxygen is needed for microorganisms to break down the poutants, a of the oxygen in the receiving environment may be depeted. A ack of oxygen kis off fish and other animas in the region resuting in an environmenta probem that is caed eutrophication. Therefore, BOD is the most widey used parameter to determine the eve of organic poution in wastewaters and surface waters. Simiary, chemica oxygen demand (COD) is used to determine the amount of oxygen required to oxidize poutants chemicay. A strong chemica oxidizing agent, commony potassium dichromate, is used to oxidize the organics in a COD test. BOD has traditionay been a more commony used measure of the strength of organic poution because treated effuents were disposed into an aquatic environment. However, for this project, we anayzed effuent sampes for both BOD and COD since, in the groundwater environment, some of the compex organic substances are hard to oxidize bioogicay but can be oxidized chemicay. Oxygen is aso required for biodegradation of noncarbonaceous matter, such as ammonia (NH 4 - ). In bioogica wastewater treatment, the oxidation of ammonium (NH 4 - ) to nitrate (NO 3 - ) consumes at east 40 percent of the tota oxygen; competition for oxygen between heterotrophic bacteria and nitrifying bacteria (Nitrosomonas, Nitrobacter) is normay the imiting factor for the conversion of organic matter and NH 4 -. In most cases, heterotrophic bacteria outcompete the sow-growing nitrifying bacteria, which die off due to ack of oxygen. In most cases, any bioogica treatment system without a separate nutrient remova unit is insufficient to meet the oxygen requirements of the system (Henze et a., 1997). However, better nutrient reduction aso eads to the remova of pharmaceuticas and persona care products (Cristen, 2006). For compete nitrogen (N) remova, denitrifying bacteria (Favobacteria, Bacius, Micrococcus) must reduce NO 3 - to N gas under anoxic conditions. When oxygen is competey depeted by heterotrophic and nitrifying bacteria, facutative bacteria may use NO 3 - as an oxygen source and produce N gas (Tchobanogous and Stense, 2003; Russe, 2006). Athough both N and phosphorus (P) are essentia nutrients for the growth of pants and other organisms, they can be harmfu when present in surface waters. Excess N and P is known to trigger aga booms and acceerate pant growth, utimatey bringing about the death of fish and other animas. Either N or P can be the imiting nutrient in a water body. Typica untreated domestic wastewater contains 4-15 mg/l tota phosphorus (TP) (Crites and Tchobanogous, 1998). P has a dramatic impact on surface waters even at very ow concentrations, especiay when it is the imiting nutrient in controing eutrophication. For this reason, it is essentia to contro P concentrations in treated effuent prior to its discharge. Deaware imits P discharge to bodies of surface water but currenty does not have any statewide P restrictions for groundwater. Wastewater treatment is compicated by the fact that P and N remova do not occur simutaneousy. To remove P, wastewater is sequenced into reactors where a group of bacteria use voatie fatty acids as carbon sources and then reease P into the system. If the conditions are changed from anaerobic to aerobic, the bacteria take up more P than they reease. The P-rich microorganisms become part of the wastewater sudge that is then removed (Crites and Tchobanogous, 1998; Tchobanogous and Stense, 2003). A major concern regarding treated wastewater is human disease caused by pathogenic organisms. Pathogens that are abundant and easy to test for are used to indicate the presence of human feca contamination. An idea indicator organism must be present whenever the target pathogenic organism is present (Tchobanogous and Stense, 2003). An exampe is coiform bacteria, which are found in the human intestina tract and indicate contamination by human feces. Another exampe is the pathogen, enterococci, which are found in the intestines of humans and animas, and are responsibe for serious infections (Fraser, 2008). Athough the enterococci generay occur in ower numbers than feca coiform, they exhibit better surviva in sediment and marine and estuarine waters, and so can be successfuy used in the risk assessment of these environments (Tchobanogous and Stense, 2003; Jin et a., 2004). Wastewater and RIBS Major wastewater constituents can be effectivey removed by the rapid infitration process. Organic poutants, soids and suspended soids are removed initiay by fitration and ater by microbia biodegradation. Adsorption of the remaining organic compounds takes pace in the soi; therefore to prevent cogging the basin with excessive organic materia and soids the oading rate is a very important parameter (Matsumoto and Caifornia Water Resources Center, 2004). Some of the benefits of RIBS incude: The eimination of the direct discharge of wastewater effuent to surface waters. The potentia treatment of wastewater effuent through fitration, adsorption and bioogica degradation. The repenishment of groundwater through the discharge of recaimed water to the RIBS. The abiity of the process to work in a seasons. Economic feasibiity, since the process does not require much and. Environmenta Impact of RIBS With the increase in environmenta consciousness, and appication sites may be monitored by government agencies, research institutes, and the pubic to prevent groundwater contamination. In addition, the ong-term impacts of RIBS on receiving environments in different regions of the United States have been studied by many researchers (Sumner and Bradner, 1996; Auenbach and Cesceri, 1980; Quanrud et a., 2003). 2 Deaware Geoogica Survey BULLETIN 21A

7 Nutrients (N, P), soids, pathogens, and organic compounds are the most common contaminants from RIBS that might reach surface or groundwater sources. N and P can be present in many forms in soi and wastewater depending on the redox potentia of the environment. Most of the N species found in water can have adverse effects on iving organisms (Stumm and Morgan, 1996). N in water is commony found as NO 3 -, the most oxidized form of N. High NO3 - concentrations in drinking water are strongy associated with bue baby syndrome, a potentiay fata condition that particuary affects infants (Knobeoch et a., 2000; Masters, 1998). The Safe Drinking Water Act imits NO 3 - -N concentration to 10 mg/l for pubic water suppies (USEPA, June 2003). However whie this federa reguation ensures the safety of pubic water sources, it does not appy to private wes. Thus, site specific, systematic, and detaied research on the potentia effects of RIBS on NO 3 - concentrations in the receiving environment is crucia. RIBS can provide effective natura N reduction in treated wastewater through a series of chemica and bioogica reactions. N remova depends on environmenta conditions such as oxygen avaiabiity and temperature. Higher N remova rates are achieved when NH 4 - in infuent wastewater is fuy oxidized to NO 3 -. Partice size, minera content, adsorption capacity and bioogica activity of the soi, treatment processes used to treat the wastewater, and operation strategies a pay important roes in N remova (Matsumoto and Caifornia Water Resources Center, 2004; Sumner and Bradner, 1996). Because these parameters differ between sites, so do the remova efficiencies. For instance, whie the tota nitrogen (TN) remova rate for RIBS in Coton, Caifornia, is reported to be 78 percent, it is around 50 percent for the Reedy Creek RIBS in Orange County, Forida. The importance of operation strategies in N remova was reported by Bouwer and Rice (1984), who measured amost no N remova during short and frequent fooding periods (2 days fooding, 5-10 days drying), but measured up to 30 percent N remova with onger fooding periods (10 days fooding, 2 weeks drying). Short and frequent fooding makes soi profies mosty aerobic, which imits NO 3 - to N conversion. No N is removed if the fooding periods are extremey ong since the ack of oxygen prevents NO 3 - formation. Because of these imitations, fooding schedues that optimize N remova shoud be deveoped for each individua RIB system. One we-studied and appication site in Cape Cod, Massachusetts, has been active for more than 60 years. At the site the disposa of secondariy treated wastewater into RIBS created a contaminated groundwater pume 6000 m ong, 30 m thick, and more than 1000 m wide (Repert et a., 2006). Dissoved N (mainy NO 3 - and NH4 - ), P, dissoved organic and inorganic carbon, choride, boron, organic N and NO 3 - are reported as the main poutants in the effuent discharged into the RIBS. Athough the and appication of wastewater ceased in 1995, the core of the pume remains anoxic, and its size and shape have not changed for at east 10 years (Repert et a., 2006; Savoie et a., 2006). This site shows that years of disposing treated effuent at high oading rates to a imited area may have irreversibe negative impacts on groundwater. Domestic and industria wastewater usuay contains a variety of organic compounds incuding pharmaceuticas, persona care products, and widey used househod and industria chemicas (Cordy et a., 2004; Conn et a., 2006; Aufdenkampe et a., 2006). Since these chemicas (i.e., emerging contaminants) can partiay be removed by existing wastewater treatment technoogies, they might reach the environment through surface water discharge or and appication of the effuent (Conn et a., 2006). Some of the emerging contaminants have been found to be toxic and are persistent in the environment. For exampe, the antiepieptic drugs, carbamazapine and primidone, were detected in the groundwater after eight years of groundwater recharge by treated effuent (Drewes et a., 2003). Barbiturates and sedative hypnotics used in veterinary medicine, mosty during mid-1960s, have been detected in groundwater sampes. Additiona biotic and abiotic tests did not show any degradation either under aerobic conditions or hydroysis, indicating that barbiturates may stay stabe in the aquatic environment for decades (Peschka et a., 2006). Purpose and Scope The popuation of southern Deaware (2000 Census data) is projected to increase by 20 percent by 2020 (Deaware Popuation Consortium, 2006). This increase in popuation is accompanied by a rise in proposed residentia subdivisions, incuding in southern New Caste, Kent, and Sussex Counties (Deaware Popuation Consortium, 2006). In Deaware, as in other states, many streams are subject to the EPA s Tota Maximum Daiy Load (TMDL) restrictions, which set a imit on the amount of a poutant that can be discharged into a water body without compromising water quaity. To meet water quaity standards, communities must construct and operate effective wastewater treatment faciities. The costs of constructing new or upgrading existing pubic wastewater treatment faciities can be daunting, especiay for states with imited budgets. An increasing number of communities are impementing communitywide and-based disposa systems for treated wastewater. Deaware is one of many states that has become more receptive to privatey funded and operated LBWD systems. With the need to meet TMDL restrictions and with budget concerns, many panned subdivisions have proposed RIBS for wastewater disposa. In January 2006, the Deaware Department of Natura Resources and Environmenta Contro (DNREC) initiated new guideines for designing and operating arge LBWD systems incuding RIBS. Athough RIBS have been used for wastewater disposa and groundwater recharge for the ast 25 years, primariy in arid regions, they have been used ess commony in Deaware. Therefore, the performance of RIBS and the potentia impacts of RIBS on the receiving environment are generay unknown for Deaware. Groundwater is the most important natura source of fresh water in Deaware, with thirteen major aquifers providing more than 100 miion gaons of water daiy (Wheeer, 2003). Amost a of the fresh water used south of the Chesapeake and Deaware Cana is obtained from groundwater (Taey, 1985). Deaware Geoogica Survey BULLETIN 21A 3

8 Groundwater is aso the source of about 70 percent of fresh water stream fow (Johnston, 1976). Contamination is a major concern. More than 90 percent of the water bodies in Deaware are pouted, primariy with pathogens and nutrients from nonpoint sources that are extremey difficut to contro (Denver et a., 2004; USEPA, 2002). Decades of inadequate agricutura and wastewater disposa practices have ed to serious eutrophication probems in surface water. Poor agricutura and wastewater disposa have aso ed to serious groundwater contamination by NO 3 - (Mier, 1972; Robertson, 1977; Taey, 1985; Ritter and Chirnside, 1982, 1984; Andres, 1991, Hamiton et a., 1993; Denver et a., 2004). The probems associated with groundwater contamination that are of primary concern vary by ocation. For exampe, three hydrauicay connected aquifers, the Mt. Laure, Rancocas, and Coumbia, are major water sources for domestic and pubic wes in southern New Caste County. Groundwater contamination caused by the and appication of wastewater in this region might adversey impact domestic or pubic wes in any or a of these aquifers. The connection between ground and surface water in the Inand Bays means that groundwater that becomes contaminated wi eventuay impact streams. This work was designed to study the effects of RIBS on groundwater contamination in Deaware. The objectives of this study were to: 1. Evauate the site seection criteria and performance of RIBS in the northeastern United States, incuding Deaware, and the wastewater treatment systems that may be used in conjunction with RIBS. 2. Review and compare existing DNREC permitted RIBS and associated wastewater treatment systems with their effuent data. 3. Review and compare operation and maintenance procedures used for other RIBS in the Mid-Atantic States and identify key eements of operation and maintenance protocos for RIBS in Deaware. 4. Evauate the performance of existing wastewater treatment systems in Deaware that may be used with RIBS. 5. Evauate existing and panned RIBS sites for future fied study. The competion of these objectives was essentia for addressing some of the questions regarding the siting, compiance, and pre-treatment requirements for RIBS. A primary goa of this project was to provide scientific information to the DNREC so that they coud improve existing guideines and reguations for on-site wastewater treatment and disposa systems. To do this we evauated the current practices for RIBS design, operation and maintenance, and environmenta compiance monitoring as it is done in Deaware and then compared that information with equivaent information from nearby states. Use of RIBS in Deaware As of 2011, RIBS in Deaware are covered under Reguations Governing the Design, Instaation and Operation of Onsite Systems (DNREC, 2004). However, very itte specific information regarding the design and operation of RIBS is present in the reguations. Instead, specifics are covered in Guideines for Preparing Preiminary Groundwater Impact Assessments for Large On-site Wastewater Treatment and Disposa Systems (State of Deaware, December 2005) and Large System Siting, Design and Operation Guideines (DNREC, 2006). These guideines are intended to minimize the impact of arge systems such as trenches, beds, drip ines, sand mounds, and RIBS on the receiving environment (DNREC, 2006). According to the guideines, if generated wastewater voume exceeds 20,000 gaons per day, it must be treated to meet secondary treatment standards, which require TN eves not to exceed 10 mg/l. Additionay, none of the disinfected wastewater being sent to any basin shoud exceed 200 co/100 m of feca coiform. Monthy average BOD and TSS concentrations in the effuent shoud not exceed 30 mg/l each. However, some sites receive permits that aow the DNREC and the operator some eeway in meeting guideines. For exampe, effuent from the Breeder s Crown wastewater treatment pant is aowed a imit of 25 mg/l of TN concentration because any site is subject ony to the reguations stated in its existing permit, (Hiary Moore, DNREC, persona correspondence), which for Breeder s Crown is the Reguations Governing the Design, Instaation and Operation of Onsite Systems (DNREC, 2004). The guideines do not recommend the addition of vegetation for RIBS; however, existing vegetation shoud be reguary maintained and grass cuttings removed from the basins. RIBS are required to be periodicay scarified to remove any accumuated soids and organic materias that may cog the basin and ower the infitration rate as part of routine maintenance. Detais for RIBS maintenance are given in the guideines (DNREC, 2006). Treatment Practices Observed During This Study Wastewater treatment pants using RIBS in Deaware empoy five different secondary treatment processes. The most common is the rotating bioogica reactor (RBC). First introduced in 1960 in West Germany and neary a decade ater in the United States, RBCs introduce a bioogica medium into wastewater in order to remove poutants prior to discharge. In an RBC, a series of cosey spaced circuar disks are 40 percent submerged in a tank containing wastewater. The pastic disks are typicay 3.6 m in diameter and have a fim of microorganisms growing on them. The disks are attached to a horizonta shaft that rotates sowy at about 1.0 to 1.6 revoutions per minute. As the RBC rotates, the microorganisms are periodicay exposed to the atmosphere, providing aeration and faciitating the bioogica degradation of the poutants by the microorganisms (Masters, 1998; Tchobanogous and Stense, 2003). The second type of treatment process is termed activated sudge (AS), a suspended-cuture system that has been in use since the eary 1900s. The name derives from the setted sudge containing microorganisms that is returned to the reactor to increase biomass avaiabiity and acceerate the treatment reactions. In a conventiona activated sudge 4 Deaware Geoogica Survey BULLETIN 21A

9 process, raw or setted sewage fows into a arge, concrete tank aong with a mixed popuation of microorganisms. The mixture (mixed iquor) then enters an aeration tank, where it is combined with a arge quantity of air, which acceerates the bioogica degradation of the wastes. After about 6 to 8 hours of aeration, the mixture fows into a arge setting tank where the biomass sowy settes out of suspension and the foccuant microorganisms are removed from the effuent stream. Most of the setted microorganisms, or activated sudge, are then recyced to the head of the aeration tank to be remixed with wastewater. Because new activated sudge is continuay being produced, some is removed or "wasted" from the process. The effuent from a propery designed and operated activated-sudge pant is of high quaity, usuay having BOD and TSS concentrations of equa to or ess than 10 mg/l (Crites and Tchobanogous, 1998). The remaining treatment processes are a variations on the conventiona AS process. The most common of these is the sequencing batch reactor (SBR). During the ate 1950s and eary 60s, improvements in equipment and technoogy ed to an increased interest in SBRs in the United States. Enhanced aeration devices and computer contro systems have made SBRs a more practica choice than conventiona activated-sudge systems. Whereas a conventiona system reies on mutipe tanks or basins, the SBR equipment is a variation of the activated sudge process, and is unique in its abiity to act as an equaization basin, aeration basin, and carifier within a singe reactor using a timed contro sequence (A-Rekabi et a., 2007; USEPA Office of Water, 2000). SBRs are a set of tanks that operate individuay on a fi-and-draw basis. Each tank has a cyce of five discrete time periods: Fi, React, Sette, Draw, and Ide. The tank is partiay fied with biomass that has accimated to the wastewater constituents during preceding cyces. Wastewater is aowed to enter the tank as Fi begins. Once the reactor is fu, it behaves ike a conventiona activated sudge system, with the React, Sette and Draw portions of the cyce, but without a continuous infuent or effuent fow. Aeration and mixing are discontinued after the bioogica reactions are compete, the biomass has setted, and the treated supernatant is removed. The period between Draw and Fi is termed Ide. Despite its name, this ide time can be used effectivey to sette sudge (Barbato, 2006). The extended aeration process (EA) is comparabe to the conventiona activated sudge process except that it operates in the endogenous respiration phase of the growth curve, which requires a ow organic oading and ong aeration time. Simiary, oxidation ditches (OD) typicay operate in an extended aeration mode with ong detention and soids retention times. OD originated in the Netherands in 1954 and there are currenty more than 9200 municipa oxidation ditch instaations in the United States (USEPA, 2000). The oxidation ditch is a ring- or ova-shaped channe equipped with mechanica aeration devices. Screened wastewater enters the ditch, is aerated, and circuates at about 0.8 to 1.2 ft/s (0.25 to 0.35 m/s) to maintain the soids in suspension. When designed and operated for N remova, this process achieves nitrification to ess than 1 mg/l NH 4 - -N The main advantage of the oxidation ditch is its ow operationa requirements, and operation and maintenance costs. However, compared to other modifications of the AS process, the concentrations of suspended soids in effuent associated with oxidation ditches are reativey high. Additionay, ODs require arge and areas that may be costy (USEPA, 2000; Crites and Tchobanogous, 1998). The fina type of treatment process is the Imhoff Tank (IT). Patented in 1906 and first used in Essen, Germany in 1908, the IT is one of the odest and simpest treatment processes. The IT was deveoped to address the deficiencies of septic tanks by preventing the remixing of removed soids whie promoting the decomposition of these soids within the same tank. In addition, the IT provides an effuent acceptabe for further treatment. An IT is a two-story tank in which sedimentation takes pace in the upper compartment and anaerobic digestion is accompished in the ower compartment. Imhoff tanks are sti used occasionay because they are simpe to operate, there is no mechanica equipment to maintain, and they do not require highy skied supervision (Crites and Tchobanogous, 1998; Seeger, 1999). Acknowedgments This project was funded by the DNREC through a grant from USEPA. DNREC staff members Hiary Moore and Kenneth Ganden deserve specia recognitions for their expertise and support. Former DGS member Hiary G. Trethewey is aso thanked for her contributions to the project. Eizabeth C. Woff and Jaime L. Tominson assisted with sampe coection. We thank anonymous members of the Groundwater Discharges and Water Suppy Sections of DNREC for reviewing this manuscript. METHODS The methods used in this study consist of two main parts. The first incudes the iterature search, site visits to the seected advanced wastewater treatment pants incuding RIBS, infuent and effuent samping, aboratory anayses, the coection of effuent quaity data from nearby states, data processing, and the interpretation of these data. The second was the assessment of current RIBS reguations and operation and maintenance strategies. Site Visits, Samping, and Anaysis Permitting agencies in Deaware, New Jersey, Massachusetts, and North Caroina provided data on the types of treatment systems currenty in use, reiabiity assessments of those systems, and quaity monitoring of effuent and/or wes. The DNREC Non-Hazardous Waste Sites database provided data on the permitted fow, pretreatment method, effuent quaity, and monitoring and inspection records on existing permitted RIBS in Deaware. We visited a nine of the operating RIBS in Deaware and three in New Jersey that were chosen based on their ocation, capacity, and treatment and discharge (e.g., RIBS discharge) methods. A ist of treatment pants that we visited is given in Tabe 2. We visited the 10 RIBS in summer 2007 to photograph the sites, interview the pant operators, and coect wastewater sampes. Listed beow are some of the questions that pant Deaware Geoogica Survey BULLETIN 21A 5

10 Tabe 2. Advanced treatment pants vivisted in Deaware and New Jersey. managers were asked: What type of treatment processes are used in this faciity? What is the average daiy fow rate of wastewater into the system? Is the pant operating at its design capacity? How ong has the pant been in operation? What is currenty being done with the treated effuent? What type of discharge method is used? How often are infuent and effuent sampes anayzed? What is done with wastewater sudge? Is it haued or is it and appied? How is the quaity of effuent in genera? Is the effuent disinfected prior to RIBS appication? If RIBS are used for effuent discharge, how many RIBS are there in the site? How ong have the RIBS been in operation? What are the fooding/drying and RIBS rotation schedues? What type of maintenance do RIBS require (i.e. scoring, excavating, mowing, vegetation remova)? How is the vegetation on RIBS being taken care of? How often? Have you ever had any operationa or maintenance probems? How did you sove them? Are there any monitoring or observation wes at the site? How many? For wastewater samping, dupicate 500 m sampes were paced into poyethyene bottes for both infuent and effuent. On-site conductivity and ph measurements were performed with a portabe AP50 ph/ion/conductivity instrument (Denver Instrument Company, Arvada, Coorado). Sampes were immediatey paced in ice and transported to the Water Quaity Laboratory at the University of Deaware. Sampes arrived at the aboratory within 2-3 hours of coection. A ist of anayses done at the Water Quaity Laboratory is given in Tabe 3. Remova rates of N, P, BOD, COD and soids were cacuated by using the anaytica resuts of infuent and effuent wastewater sampes for the different treatment pants in Deaware. TN concentrations were cacuated by adding the anaytica resuts of Kjedah-N, NO 3 - -N and nitrite-n. These resuts were used to evauate the performance of the wastewater treatment technoogies that are most commony used or proposed for use in Deaware. To assess the eve of compiance with generay accepted treatment standards (Tchobanogous and Stense, 2003), drinking water NO 3 - imits (USEPA, 2003), and Deaware Large System Reguations (DNREC, 2006) we determined exceedence frequencies for a tota of 49 treatment pants in Deaware, New Jersey, North Caroina, and Massachusetts. Effuent quaity data in DNREC s Non-Hazardous Waste Sites database (Hiary Moore, persona communication) combined with our anaytica resuts were used to evauate the exceedences. Each state s effuent data for different wastewater quaity parameters incuding BOD, TSS, TN, NO 3 - -N, and indicator organisms were used in the data anaysis. Comparison of State Reguations on Land Appication of Wastewater We aso evauated the siting criteria (depth to water tabe, presence or absence of restricting zones, proximity to wes and water bodies) and existing reguations or guideines used in permitting and monitoring RIBS in Deaware and other states. Our comparison of state programs that reguate RIBS focuses on states that have generay simiar cimatic and hydrogeoogic conditions. States with humid cimates and aquifers hosted by unconsoidated to weaky consoidated sedimentary deposits were chosen. Despite an extensive internet research, ony imited effuent data coud be obtained from New York, Maryand, and Pennsyvania. Subsequent correspondence and teephone conversations with officias from these states yieded itte additiona information concerning current reguations with regards to RIBS. It is possibe that there are other states for which we have not been abe to ocate the programs and reguations pertaining to RIBS. 6 Deaware Geoogica Survey BULLETIN 21A

11 Tabe 3. Wastewater anaysis and anaytica methods. RESULTS AND DISCUSSION State Reguatory Programs and Technica Criteria The reguatory approaches of states fit into a decision tree system. Sites are evauated by mutipe series of criteria, and the resut of each evauation step determines the next set of evauation criteria. The categories of requirements these states use for RIBS compiance are summarized as foows. Buffer zone distances Effuent imits (BOD/TSS/TN/coiform) Pretreatment requirements Depth to water tabe Monitoring we requirements Storage capacity Fow rate A states have certain criteria that must be met for RIBS to be aowed. These criteria incude minimum setback requirements from property boundaries and wes, minimum depth to groundwater, and bodies of surface water (Figs. 1-6). Amost a states have the prerogative to evauate each RIBS on a case by case basis. Fow rate is a major factor in determining the specific design and operation requirements for RIBS. For exampe, Deaware and New Jersey use an expected effuent fow rate of 20,000 gpd to determine if primary rather than secondary treatment is needed before the effuent is discharged to the infitration basins. It is foowing this step in the decision tree that states have the greatest differences in their reguatory requirements for the arger systems. These requirements fa into the categories of site exporation, effuent quaity imitations, and effuent and groundwater monitoring. USEPA guidance documents and severa texts state that an unsaturated zone between the base of the infitration basin and the water tabe is needed to aow for N remova from effuent (Crites and Tchobanogous, 1998; Crites, et a., 2006; USEPA, 1985; USEPA, 1999). These documents expain that biogeochemica mediated reactions in the N remova process incude mineraization or nitrification of organic N (to NH - 4 ), sorption of NH4 -, nitrification of NO3 -, and denitrification. Increasing the thickness of the vadose zone provides a margin of safety to guard against N contamination of groundwater shoud effuent quaity fai to meet reguations, guideines, or permit requirements. If the unsaturated zone is thin and the effuent contains substantia quantities of N, there is a significant risk that substantia amounts of N, in the forms of organic N, NH 4 -, or NO 3 - wi reach the water tabe. These chemica constituents wi trave down gradient with groundwater fow and wi eventuay discharge into a body of surface water or be pumped by a water suppy we. To reduce this risk, USEPA documents recommend that the thickness of the vadose zone under RIBS must take into account the expected effuent quaity (USEPA, 1985; USEPA, 1999), in addition to the expected water suppy and the environmenta uses of the shaow aquifer (USEPA, 2004). States have reacted differenty to USEPA guidance for determining the requirements for vadose zone thickness. Amongst the states with RIBS reguations that we surveyed, vadose zone thickness requirements range from as itte as 2 ft (Deaware) to as much as 10 ft (Maryand). In no state, do the reguations contain expanations for how the distance requirements were determined; however, we assume that the requirements refect a baance between the need for the wastewater treatment capacity to serve deveopment and environmenta protection, and the expected uses of the groundwater. As of 2011, Deaware s Large System Siting, Design and Operation Guideines requires ony two ft of separation distance between a RIBS site and the water tabe; that is, there are two ft between the base of the infitration bed and the mounded water tabe. Shoud the treated effuent not meet standards, further treatment by fitration and adsorption wi be negigibe in the sma 2-ft distance to groundwater. As a resut there is a significant risk of groundwater contamination in Deaware, especiay in Sussex and Kent Counties where the water tabe is shaow. The required separation distances between RIBS and environmentay sensitive receptors, such as wetands, surface waters, and potabe water suppy wes are isted in the Deaware guideines (Tabe 4). To minimize the risk of Deaware Geoogica Survey BULLETIN 21A 7

12 Figure 1. Decision tree iustrating reguations, major permitting criteria, and monitoring requirements for RIBS in Deaware (State of Deaware, 2005; DNREC, 2006). Figure 2. Decision tree iustrating reguations, major permitting criteria, and monitoring requirements for RIBS in Forida (Forida Department of Environmenta Protection, 2005). 8 Deaware Geoogica Survey BULLETIN 21A

13 Figure 3. Decision tree iustrating reguations, major permitting criteria, and monitoring requirements for RIBS in Maryand (State of Maryand, 2003). Distance of the bottom of RIBS to groundwater >10 ft Distance between proposed RIB site and: Property ine >50 ft Surface water, wes, channes >100 ft Loading rate: inches/week NO YES YES NO NO RIBS RIBS NO RIBS Fowrate >20,000 gpd NO YES Permeabiity test is required with singe-we shortterm pumping test (minimum 30 minutes) A minimum of 2 permeabiity tests are required in 3 wes, with the pumping we instaed within the proposed disposa area and 2 observation wes ocated at 90 degrees to the pumping we Effuent Limits for Option 2: Treated effuent discharge to groundwater BOD < 30 mg/l or 7000 bs BOD acre.year TSS <30 mg/l Tota Nitrogen <10 mg/l 2 mg/l in Pineand Tota Coiform <200 MPN/100 ml Chorination is not acceptabe means of disinfection Groundwater Monitoring Requirements Depending on the ocation and groundwater conditions, monitoring-we requirements vary case by case Figure 4. Decision tree iustrating reguations, major permitting criteria, and monitoring requirements for RIBS in New Jersey (State of New Jersey, 2002, 2005). Deaware Geoogica Survey BULLETIN 21A 9

14 Figure 5. Decision tree iustrating reguations, major permitting criteria, and monitoring requirements for RIBS in North Caroina (State of North Caroina, 2006). Figure 6. Decision tree iustrating reguations, major permitting criteria, and monitoring requirements for RIBS in Massachusetts (State of Massachusetts, 1984). 10 Deaware Geoogica Survey BULLETIN 21A

15 Tabe 4. Buffer distances for RIBS in Deaware and other states. Note that more stringent buffer distances may be required in some states according to fow rate. pants exceeded the concentration range given above. However, since the BOD concentrations in the wastewater of these pants were we beow the guideine imits, we concude that some of the organic matter was resistant to biodegradation and coud ony be degraded chemicay, which required more oxygen. Ony 1 out of 10 effuent sampes were measured at we above the TSS guideine of 30 mg/l for both Deaware and New Jersey (DNREC, 2006; State of New Jersey, 2002) (Fig. 9, Appendix 1). The highest TSS concentration of 112 mg/l was measured in the effuent of Forest Grove Wastewater Treatment Pant, which uses RBC as the main bioogica treatment process. During our visit to Forest Grove (FG) in Juy 2007, we observed soids foating at the surface of the secondary carification tank. The high con- contamination to sensitive receptors, many states require greater separation distances or use trave-time criteria based on site-specific hydrogeoogica conditions to determine an appropriate eve of protection for each site. Interestingy, Deaware requires the use of trave-time criteria in its source water protection program. North Caroina has a requirement that may be appropriate for Deaware. In some areas of the state, treatment pants must have additiona wastewater storage in case the pant mafunctions or has a treatment upset. This requirement provides an extra margin of safety in areas where groundwater contamination caused by the discharge of poory treated effuent poses a significant risk to sensitive receptors. Effuent Characterization and Treatment Pant Performance - Deaware and New Jersey Seven of the 10 treatment pants we visited were abe to remove at east 90 percent of the biodegradabe organic oad from the infuent wastewater using their existing advanced treatment processes (Fig. 7, Appendix 1). The anaytica resuts of the infuent/effuent sampes taken from LSA and WTP were aso incuded. Athough three of the effuent BOD concentrations were cose to the imit of 30 mg/l given in Large System Siting, Design and Operation Guideines, ony one of the treatment pants exceeded this requirement (DNREC, 2006). Treatment pants using the activated sudge process achieved the highest average BOD remova rates (98 percent), foowed in decreasing order by OD, SBR, IT, and RBC. Most of these treatment pants are residentia, sma community treatment pants that primariy receive domestic wastewater. The high BOD remova efficiencies are evidence that most of the poutants in this wastewater are easiy biodegradabe organic substances. Both New Jersey pants were abe to reduce the BOD eves beow the effuent BOD imit of 30 mg/l. The remova rates for COD in infuent and effuent wastewater sampes are sighty ower than those for BOD (Fig. 8, Appendix 1). Amost compete COD remova was measured in both of the treatment pants in New Jersey. Athough not stated in the guideines, mg/l COD effuent is usuay considered acceptabe for the and appication of wastewater (Tchobanogous and Stense, 2003). The effuent COD concentrations of 2 of the 10 treatment Figure 7. Concentrations of bioogica oxygen demand in the infuent and effuent sampes from different wastewater treatment pants and percent remova rates. Faciity abbreviations are isted in the front of this report. Figure 8. Concentrations of chemica oxygen demand in the infuent and effuent sampes from different wastewater treatment pants and percent remova rates. Faciity abbreviations are isted in the front of this report. Deaware Geoogica Survey BULLETIN 21A 11

16 Figure 9. Tota suspended soids concentrations in the infuent and effuent sampes from different wastewater treatment pants and percent remova rates. Faciity abbreviations are isted in the front of this report. centration of soids in the effuent is thought to be the resut of ongoing denitrification at the bottom of the carification tanks due to the anoxic conditions. As denitrification produces N gas, it rises to the surface and resuspends setted soids. High concentrations of soids were reported in the treatment pants that used the same tanks for bioogica treatment and nutrient remova with insufficient aeration. These resuts showed that the SBR process is the most efficient in TSS remova. Seasona temperature differences might aso pay an important roe in TSS concentration. Despite its state-of-theart design and operation and ow TSS concentrations, Landis Sewerage Authority (LSA) in Vineand, New Jersey, exhibits agae growth probems in its chorine contact/equaization tanks during the summer months (Dennis Pamer, LSA, persona communication). Since agae increase the concentration of soids, to prevent cogging of the RIBS from Apri through October, the effuent is used ony for spray irrigation. This type of agae probem was not observed in any of the treatment pants that we visited in Deaware. When the N remova efficiency of different treatment processes were compared, SBRs were found to be the most efficient (Fig. 10, Appendix 1). Ony 2 of the 8 treatment pants in Deaware met the effuent TN requirement, which is isted as 10 mg/l in the guideines (DNREC, 2006). However, among the sites we visited, ony four of the eight treatment pants (BC, SC, SWA and WBP) have a nutrient reduction process. According to our resuts, conventiona secondary wastewater treatment is inadequate for nutrient remova. The higher N concentrations in the effuent of the Coonia Estates Treatment Pant were due to incompete N remova, resuting in an increase in the NH 4 - concentration as a by-product. This suggests that the oxidation of NH 4 - to NO3 - is not compete due to the ack of dissoved oxygen caused by insufficient aeration in the system. High dissoved oxygen concentrations during aeration aso ead to a reduction in excess sudge production (Kuikowska et a., 2007). The Figure 10. Concentrations of tota nitrogen in the infuent and effuent sampes from different wastewater treatment pants and percent remova rates. Faciity abbreviations are isted at the front of this report. Figure 11. Tota phosphorus concentrations in the infuent and effuent sampes from different wastewater treatment pants and percent remova rates. Faciity abbreviations are isted in the front of this report. better performance of SBR processes in overa nutrient remova is primariy due to the intermittent oxygen suppy, which provides aerobic and anoxic conditions for compete N remova. Since the nutrients are concentrated in the sudge, the timey remova of excess sudge from the system prevents N and P from soubiizing back into the water (Tchobanogous and Stense, 2003). The remova rates of TP were significanty ower than those of any of the other parameters. As mentioned previousy, P remova is directy reated to the N remova efficiency of a treatment process. Despite being ower, the P remova performances of the treatment pants exhibited trends simiar to the N remova trends (Fig. 11, Appendix 1). Interestingy, in FG and Breeder s Crown Farm (BCF) the P concentrations were higher in the effuent sampes than in the infuent sampes. Since P removing bacteria reease extraceuar P into the system and 12 Deaware Geoogica Survey BULLETIN 21A

17 Figure 12. Indicator organism concentrations in the effuent sampes. Faciity abbreviations are isted at the front of this report. Dashed ine is the guideine imit 200 coonies/100ml. MPN is Most Probabe Number then uptake more than they reeased, higher P concentrations in the effuent indicate incompete P remova. Overa, the poor nutrient remova performance of the treatment pants was strongy correated with the RBC units that are used as the main bioogica treatment process. The highest P remova (100 percent) was observed at Stonewater Creek Treatment Pant, which utiizes a SBR system. The Deaware guideines state that a wastewater shoud undergo disinfection, preferaby by utravioet, prior to being sent to the infitration basins (DNREC, 2006). Disinfection must bring the feca coiform concentration beow 200 coonies/100 ml. In the wastewater treatment pants we samped, we found indicator organism concentrations above the imits in a majority of the effuent sampes (Fig. 12, Appendix 1). We anticipated this resut since the Cape Henopen State Park Wastewater Treatment Pant is the ony site that disinfects the treated effuent prior to RIBS discharge. Up to 100 percent virus or bacteria remova might be achieved via fitration, especiay in areas where the water tabe is deep. However, groundwater is more susceptibe to microbioogica contamination when the water eve is cose to the and surface as is the case in southern Deaware (Martin and Andres, 2008). Therefore, the proper pre-treatment and disinfection of wastewater prior to RIBS discharge is particuary important for Deaware. Effuent Characterization and Treatment Pant Performance - A States The treatment types, effuent quaity parameters, and percent exceedences from the wastewater treatment pants of four states are shown in Appendix 2, and the resuts are iustrated in Figures 13 and 14. An anaysis of the N data is compicated by differences in the anaytica schedues, samping frequencies, and effuent quaity requirements. For exampe, some of the treatment pants in Deaware are sti subject to a 25 mg/l TN effuent imit; as a resut, NO 3 - was not measured as frequenty as TN. Conversey, TN was not measured for EA pants in North Caroina. We have aggregated the data using the foowing assumption: TN is set equa to NO 3 - for North Figure 13. Comparison of parameter exceedences based on treatment processes. Figure 14. Comparison of frequencies of nitrate exceedences. Caroina pants that use EA and OD treatment processes and for SBR pants in other states that report ony NO 3 - concentrations. The effect of this assumption is that a pant exceeding a 10 mg/l NO 3 - -N imit wi aso exceed a 10 mg/l TN imit. There is the possibiity of a fase negative if an EA or OD pant that is experiencing treatment upset discharges poory treated effuent with high TN but itte NO 3 -. The EA process is used in 24 of 49 evauated treatment pants; most are ocated in North Caroina. Compared with the other treatment methods, EA has the highest representation in the anayzed data (Fig. 13). Athough most of the EA data sets did not incude TN vaues, more than three-fourths of those that did exceeded the 10 mg/l NO 3 - -N imit in mutipe months per year (Fig. 14). This is expected because a conventiona EA process increases the oxidation of NH 4 - to NO 3 - in the infuent but does not incude a denitrification Deaware Geoogica Survey BULLETIN 21A 13

18 step prior to discharge. Given that EA pants consistenty fai to meet NO - 3 standards, they pose a significant risk of causing high NO - 3 concentrations in groundwater, especiay in areas with a shaow (<10 ft) depth to groundwater. Less than 5 percent of the treatment pants using the EA process exceeded the TSS, coiform, and BOD imits, indicating the effectiveness of sufficient aeration for the remova of organics and suspended soids. Eeven treatment pants using SBR were evauated. These faciities behave simiary to EA faciities (Fig. 13), athough the percent imit exceedences for TSS, BOD and tota coiform were higher for SBR pants than EA pants. Compared to RBC, EA, and OD, the intermittent oxygen suppy in the SBR process eads to a ower but sti significant occurrence of imit exceedence for NO - 3. SBR pants do not exceed a TN imit of 30 mg/l. Athough the SBR process appears to be more efficient than other processes in NO - 3 and TN remova, the data indicate that SBR pants do not consistenty meet the NO - 3 standard (Fig. 14). This is a concern for Deaware, where NO - 3 contamination of groundwater poses risks to sensitive receptors. Less than 10 percent of the tota number of treatment pants studied exceeded the imits for TSS, BOD and tota coiform imits. Neary three-fourths of the pants exceeded the effuent NO - 3 imits in at east one month per year, and a significant proportion of the EA and SBR pants exceeded the NO - 3 imit in more than six months per year (Fig. 14). As expected, TN (10 mg/l imit) was the second most exceeded effuent quaity parameter. When the TN imit is increased to 30 mg/l, the overa exceedence percentage decreased sighty more than two times. The ong-term effects of NO - 3 and TN exceedence on groundwater quaity and the sensitive receptors down fow of the RIBS that receive poory treated effuent need to be investigated further. Five treatment pants used oxidation ditches (OD), three in North Caroina and two in New Jersey. Despite not having TSS and BOD records for the Winsow and Hammonton (New Jersey) WWTPs, an anaysis of the existing data showed that the exceedences of the percent TSS and BOD imits in OD pants are ower than those of RBC and SBR pants. Simiar to EA sites, the majority of OD sites do not have records for TN and so the TN exceedence percentages for both EA and OD sites may not represent the actua resuts. The tota coiform exceedence of OD sites is the second owest among a the treatment processes. As mentioned earier, since microorganisms tend to attach to the sma soid partices in the wastewater, the efficient remova of soids resuts in better remova of pathogens. The rotating bioogica contactor (RBC) process is used in 4 of the 49 treatment pants evauated, a of them ocated in Deaware. Treatment pants with the RBC process have very high exceedence imits for NO - 3, BOD, and TN (Fig. 13). These resuts agree with our aboratory anayses of effuent sampes taken from treatment pants with RBCs. As mentioned before, during our site visits, we observed that RBC sites had ower treatment performances when compared to other treatment processes. Since DNREC s Non-Hazardous Waste Sites database does not have tota coiform records for the treatment pants evauated in this project, none of the RBC sites have effuent coiform records. However, effuent sampe resuts from this study showed that a four RBC sites in Deaware have effuents with pathogen concentrations above the guideine imits of 200 coonies/ 100 ml. Shoud the RIBS have hydrauic probems and proonged periods in which effuent ponded in the RIBS, this woud be an immediate heath risk. The three treatment pants that use the activated sudge (AS) process were aso evauated. However, one treatment pant in Deaware does not have any records of anayses of NO 3 -, tota coiform, or tota N and so the ony information on effuent quaity for this pant is from the sampes that were taken during our site visit. This dataset shows that faciities with AS have the highest TSS percent imit exceedences. One of the most common reasons for high TSS probems in bioogica treatment units, especiay in carifiers, is caed sudge rising (Tchobanogous and Stense, 2003). Anoxic conditions in the setted sudge ayer trigger denitrification, which can ead to the sudge ayer becoming buoyant and foating to the surface aong with N gas. Increasing the frequency of sudge coection tends to reduce the sudge detention time in the carifiers, and can hep to reduce TSS probems. Another probabe reason for ow effuent quaity in AS pants is foaming, which is caused by certain types of fiamentous bacteria, particuary Microthrix parvicea and Nocardia (Tchobanogous and Stense, 2003). Since these organisms are hydrophobic, they attach to and therefore stabiize air bubbes, which cause foam formation. Spraying chorine on the foaming surface, reducing the oi and grease content in the wastewater, and adding cationic poymers are some of the common soutions used to prevent foaming. The ony treatment pant with an IT process that was evauated is ocated in Cape Henopen State Park in Deaware. This treatment pant was buit in 1941, upgraded in the eary 1980s, and has had operationa RIBS since The performance of this IT pant was evauated based on the aboratory test resuts of infuent/effuent sampes taken from the treatment pant and the effuent quaity records obtained from DNREC. TN was the ony parameter that was exceeded. Unike other treatment faciities that we visited in Deaware, this site disinfects the treated effuent prior to RIBS discharge. Disinfection with chorine gas owers the tota coiform concentration to beow guideine imits of 200 coonies/100 ml. CONCLUSIONS AND RECOMMENDATIONS Athough RIBS technoogy has the potentia to be a beneficia aternative to surface discharge and a means for groundwater recharge, RIBS is appropriate ony if the adverse environmenta impacts are minimized. Because of the costs associated with remediating or mitigating the probems that resut from poor management of WWTFs, reguations, poicies, and guideines shoud be stringent enough to protect pubic and environmenta heath from the possibe impacts of RIBS. Estabishing good poicies not ony improves the decision making process during permit appication and review, but aso minimizes the short and ong term impacts of RIBS on the receiving environment. 14 Deaware Geoogica Survey BULLETIN 21A

19 The most common and serious probems associated with treatment pants ocated in Deaware and neighboring states are high nutrient and pathogen concentrations in the effuent. Years of appication of treated effuent with high nutrient, pathogen, and organic content to RIBS wi resut in significant risks for the environment and pubic heath. Athough a simpe disinfection unit can remove pathogens from effuent, reducing high nutrient concentrations beow reguatory imits may require modifying treatment processes or upgrading treatment pants, steps that are much more significant and costy. Considering the high costs associated with fixing treatment pants, additiona permitting safeguards are needed to imit the risks of serious widespread groundwater contamination that resut from poory performing WWTPs. In Deaware, the discharge of poory treated effuent to RIBS creates a risk of nutrient and pathogen contamination in the receiving water body, the shaow Coumbia aquifer. The risk of serious groundwater contamination is most significant where the water tabe is shaow, as it is over much of Sussex and Kent Counties. In these ocations, effuent discharged into RIBS undergoes much ess additiona treatment before reaching the water tabe. The risk of serious groundwater contamination in areas with a deep water tabe is unknown. Because the Coumbia aquifer serves as a major source of potabe water and stream fow in this region, site seection for RIBS must take into account the potentia for damage to this resource. In cases where the depth to groundwater and the distance from sensitive receptors are adequate, RIBS design, construction, and operation must minimize the risk of groundwater contamination. The 3-ft thickness required in Forida refects that state s significant investment in water recamation to serve irrigation users and to contro sat water intrusion from sea eve canas (USEPA, 2004). The 3-ft thickness rue used in New Jersey in part refects the use of RIBS to augment and manage the quaity of basefow in streams draining the Pineands, where a majority of the RIBS are ocated. Furthermore, severa of the arger RIBS in New Jersey have repaced the direct surface water discharge that had impaired water quaity and habitats. The 10-ft depth to ground-water rue in Maryand refects the need to maintain water quaity in the shaow aquifer, which is a significant source of potabe water as we as the primary source of streamfow. These concerns are simiar to those in Deaware. The contro of N in wastewater effuent is of specia concern in Deaware. NO 3 - contamination of shaow groundwater has been a significant probem over arge areas of Deaware and Demarva for decades (Denver et a., 2004; Mier, 1972; Robertson, 1977; Ritter and Chirnside, 1982; Bachman, 1984; Andres, 1992). These studies have documented that oxic conditions in the shaow aquifer favor the persistence and transport of NO 3 - over great distances (kiometers) and time scaes (decades). Many additiona studies, incuding Andres, 1992; Hamiton et a., 1993; Peerito et a., 2006; and Bachman and Ferrari, 1995, have documented that NO 3 - has ed to the contamination of domestic and pubic water suppy wes and significanty contributes to the eutrophication of many surface water bodies. Neary four decades of research have shown that the infitration of water containing high concentrations of TN and/or NO 3 - into the ground creates conditions in which groundwater contamination by NO 3 - is certain, and contamination by other compounds is a significant risk. We strongy recommend that additiona treatment, engineering, operationa, and siting contros be used with RIBS to imit the discharge of NO 3 - and other contaminants into the water tabe. For exampe, a greater separation distance between the base of the infitration basins and the mounded water tabe, simiar to Maryand s 10-ft requirement, is a simpe way to imit the discharge of NO 3 - and TN to groundwater. As seen in other states, combinations of redundant engineering contros on the quaity of effuent discharged to the ground, and advanced effuent and groundwater monitoring can reduce the risks of contamination and thus substitute for a portion of the separation distance. We aso recommend that the fixed buffer distances between RIBS and streams and wes be more rigorousy defined to account for disposa rate, engineering contros, and the site specific characteristics of the aquifer. This ast concept is simiar to that used in the Source Water Protection Program. P impacts on groundwater due to RIBS have not been specificay studied in Deaware. Because proposed TMDLs in Deaware have P requirements, and P in groundwater wi eventuay reach streams, this issue warrants further attention. At this time, no reguations have been specificay deveoped for RIBS, and as a resut there have been a variety of approaches to RIBS design and site characterization taken by permit appicants. Reguations deveoped from a technicay-based assessment of RIBS in the region and a consideration of Deaware-specific hydrogeoogica and water resources issues is needed to provide the state with cear and consistent expectations for RIBS siting, design, and performance. In turn, reguations woud hep the designers, operators, and owners of RIBS to provide wastewater disposa systems that are environmentay sound and that protect pubic heath. Our evauation of the wastewater treatment sites we visited and the treated effuent data showed that overa operation and maintenance practices pay important roes in the performance of treatment pants. The most efficienty working WWTPs are usuay the ones with good management. Conversey, the pants with fewer or part-time personne, apparent safety hazards, and visibe probems with the treatment units (i.e. soids foating in the tanks, foaming) have ower treatment efficiencies and a greater number of probems with functioning of the RIBS. Deaware Geoogica Survey BULLETIN 21A 15

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