166 Engineered Approaches for 111 Silll Bioremedialion ofchlorinaled Soll'eIll COlllamillmiOIl MW-S. (2JW.{HB) IW-I. '<---'N'7"U-'-lr-'-;em-D,~;;;J

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1 165 ACCELERATED IN SITU BIOREMEDIATION OF CHLORINATED ETRE ES IN GROUNDWATER WITH HIGH SULFATE CONCENTRATIONS Cltristian D. Johnson. Rodney S. Skeen, and Mark G. Butcher (Battelle PNWD. Richland, Washington) Daniel P. Leigh and Lisa A. Bienkowski (IT Group, Pleasanton, California) Steve Granade (U.S. Navy. Naval Construction Battalion Center, Port Hueneme, California) Bryan Harre (U.S. Navy, Port Hueneme, California) Todd Margrave (U.S. Navy, San Diego. California) ABSTRACT: A pilot-scale test of accelerated in situ bioremediation of chlorinated ethenes is underway at a former underground storage tank site at the Naval Air Station Point Mugu in southern California. wo phases of nutrient addition are being used in trus field test. In the first phase lactate i being added to the contaminated aquifer in regular, bigb concentration pulses to stimulate sulfate reduction and remove sujfate in the groundwater. This is necessary since sulfate was shown to inhibit dechlorination at the site. During the first phase. only small amounts of reductive decwmination are expected. In the second phase, a more aggressive nutrient injection scenario is used to disperse lactate throughout the test region and initiate rapid reductive dechlorination. To date, the first injection phase bas been operating continuollsly for 42 days with the addition of a total of 6300 lb (2860 kg) of lactic acid. Vigorous sulfate reduction is occurring at distances of up to 68 ft (21 m) from the point of nutrient injection. INTRODUCTION The installation Restoration Program (IRP) Site 24 at Naval Air Station (NAS) Point Mugu in southern California has two fonner underground storage tank (UST) sites with contaminated groundwater. Historical records for these two UST sites (Site 23 and Site 55) show that the tanks were used for oil/water separation and for storage of waste solvents, respectively. Chlorinated ethelles and total petroleum hydrocarbons have been detected at both locations. Figure I shows a plan view of IRP Site 24. In 1997 a remediation alternative analysis was conducted to determine viable remediation technologies for both Site 23 and Site 55 [OHM, 1998]. The result of this evaluation was that UST Site 55 was found to be amenable to natural attenuation because the high organic carbon content from the petroleum hydrocarbon co-contamination would support degradation of all the chloroetl1t:nes in a reasonable time frame. However, UST Site 23 had a larger mass of chlorinated ethenes and much less organic carbon. Hence a pilot test of accelerated in situ bioremediation was implemented for UST Site 23 to demonstrate the effectiveness of the technology and to provide operating and cost information for evaluating a full-scale system.

2 166 Engineered Approaches for 111 Silll Bioremedialion ofchlorinaled Soll'eIll COlllamillmiOIl Building 356 IW-I MW-S. (2JW.{HB) '<---'N'7"U-'-lr-'-;em-D,~;;;J Fe~-d Piping MW1J-Q7B Building 354 FIGURE 1. Plan view ofjrp Sitc 24 with enlargement of the portion ofu T Site 23 where the ill situ biorcmediatiod pilot test is being conducted. Contour lines on the view ofirp Site 24 indicate the approximate extent of chlorinated ethcne plumes in the groundwater. Site 23 Characterization. lrp Site 24 is located approximately I mile (1.6) inland from the Pacific Ocean. The depth to groundwater is abollt 5 feet (1.5 m). A 5 ft (1.5 m) thick clay Layer extends from about 5 ft (1.5 m) below ground surface (bgs) to about loft (3.0 01) bgs. The layer from about loft (3.0 m) bgs to 30 ft (6.1 m) bgs consists of primarily sand with some silty sand and silt material and has been designated Zone B. The wells used in this pilot test are screened in this layer from 20 to 30 ft bgs. The regional groundwater gradient is approximately m/m to the south. The contaminants of concern at Site 23 are trichloroethene crce), dichloroethene (OCE; mostly cis-i,2-0ce). and vinyl chloride (VC). Sampling in August of 1997 showed that concentrations in Zone B were approximately 1700 ~g/l, 750 ~g/l, and 1 ~g/l for TeE, cis-i.2-dce, and Vc. respectively_ Because the site is so near the ocean. seawater intrusion has resulted in chloride and sulfate concentrations in Zone B of approximately mgll and 700 mgll. respectively. Pilot Test Design. The pilot test design was completed using the site model previously described [Johnson ct ai., and is reported in Appendix N of

3 167 OHM [1998]. Reactive How and transport was simulated using the site model with the RT3D code [Clement, 1997]. Figure I shows an enlargement of the northern portion of Site 23 with a plan view of the pilot test system. Figure 2 shows the concept for an in situ bioremediation system (as applied at UST Site 23), where groundwater is circulated in a closed loop from an extraction well to an injection well and through the contaminated aquifer. For this pilot test. groundwater is continuously recirculated at 10 gpm (0.63 Lis) between the extraction well (EW-I) and the injection well (IW-I). Lactate is periodically added to the recirculating groundwater prior to re-injection iilto the aquifer. Three monitoring wells (MW-I to 3) are placed in a line between EW-I and IW-l. Two additional offset monitoring wells (MW-4 and MW-5) are placed to collect data on lateral flow and transport. InjI~lion Wen Monito,ing Will EXlrIctlon Wen FIGURE 2. Conceptual design of an in situ bioremediation system. The purpose of the pilot test system is threefold. First. it is desired to demonstrate the ability to accelerate reductive dechlorination of the chlotoethenes to ethylene and other non-hazardous end products through the addition of lactate to the aquifer. The second purpose of the field test is collect sufficient field-data to design and cost a full-scale in situ biologjcal treatment system for Site 23. Tbis objective requires developing estimates of microbial transformation rates along with the stoichiometry of nutrient consumption and contaminant transformation. The third purpose is to develop a nutrient injection strategy that allows addition of an adequate amount of electron donor (i.e., lactate) withollt hiofouiing the injectjon well. To meet this objective the pilot test must demonstrate that the selected nutrient injection strategy delivers the required nutrients without an increase in the injection well pressure required for a specific flow rate. The design of the accelerated in situ bioremediation pilot test encompasses two nutrient injection phases. The objective of the first phase is to reduce the snl fate concentration in the groundwater to the point where sulfate is no longer a

4 168 Engilll~ered Approaches/or In Situ Biol'emediation a/chlorinated Solve'I! Contamination major sink f(:lr added electron donor. This phase is necessary since laboratory experiments at Oregon State University have indicated that reductive dechlorination at this site will not occur under sulfate reducing conditions [Semprini. personal communication]. During tbe first phase of operation. approximately 17 gajions per day of 88% lactic acid is injected at regular intervals. The objective of the second nutrient injection phase of the pilot test is to provide the necessary conditions for rapid reductive dechlor.ination. This second phase will be conducted after removing the bulk of the sulfate from the test area of the aquifer. A high concentration pulse of lactic acid will be injected along with a non-reactive tracer and pushed out into the now field. Once the material has reached MW-3 the recirculation wih be discontinued and gronndwater concentrations of the cblorocthenes, ethene. lactate, propionate, and acetate will be monitored with time. RESULTS AND DISCUSSION In the first nutrient ;njection phase, samples were collected for sulfate, lactate, acetate. propionate. and chlorinated ethenes. During this phase, lactic acid was injected into the aquijer in high concentration pulses at regular intervals to stimulate biological activity and sulfate reduction. Figure 3 shows the results to date for sulfate in MW-1. MW-2, MW-J. and EW-1. Figure 4 shows the corresponding results for the volatile organic acids (VOA). Volatile organic acids are calculated as the sum of acetate and propionate concentrations. Acetate comprises percent of tbe total VOA concentration, depending on how long the bacteria have been stimulated. After only 20 days of nutrient injections. sulfate levels in MW-I and MW-4 were reduced to less than 100 mg/l while the level of organic acids at both MW-I and MW-4 are consistently near 1150 mg/i,. By day 42, the sulfate levels in MW-2 have been reduced from approximately 700 mg/l to less than 20 mg/l. At the same time, VOA concentrations have risen to approximately 890 mgfl. Based OJ] reactive flow-and-transport modeling with RT3D. it was anticipated that the zone of reduced sulfate concentration would move to MW-3 by day 42, which has in fact occurred. On day 42 sulfate levels in MW-3 are approximately 300 mg/l and the VOA level is approximately 225 mg/l. Taken togt:ther. these data indicate that sulfate reduction and lactate fenncntation is occurring in the region between the injection well and MW-3. One of the objectives of this test is to demonstrate a nutrient injection strategy that allows addition of adequate levels of electron donor without biofouling the injection well. Biofouling has been a problem at other accelerated in situ bioremediation test sites [Hooker et ai., 1998]. To date, the system has been in operation for 35 days and over 5000 Ib (2300 kg) of lactic acid have been added to the aquifer at the test site. The injection flow rate has remained constant throughout the test and pressure increases in the injection well have been less than 3 psi (0.2 bar). This result indicates that significant biofouling of the well bore has not occurred.

5 ::J' OJ ~MW-1 Qj'... ns...-mw.2\ ~ 400 ::J!!!.... MW-3 -+-EW o L-~-~==:::;~~~~ o Elapsed Time from Start of Nutrient Injection (days) FIGURE 3. Conccntrations of sulfate during the first nutrient injection phase. Where error bars are not shown, they are within the size of tbc symbol. I I 1400 ::J' 1200 OJ Qj'... l'g c:: 'Q. ~!!: Qj' :I Cl) u ~ 200 ~MW MW-2... MW EW-1 ot--j...~ =4IC--...~~~=------~ o Elapsed Time from Start of Nutrient Injection (days) FIGuRE 4. Total volatile organic acid concentrations during the first nutrient injcction phase. here error bars are not shown, they are within the size of the symbol.

6 170 Engineered Appmachesjorln Si/ll B/Oremedialioll ojchlol'imlled Soh'enl ConfuminutiOI1 Simulations modeling Site 23 using RT3D indicate that during the first nutrient injection phase the concentrauons of chloroethenes should remain relatively unchanged. TCE concentrations through day 28 (after the start or nutrient injections) have been in the range of 970 to 1130 flg/l. Total DCE concentrations have been 145 to 180 J..Ig/L during the same period. It is possible that reductlve dechlorination has been stimulated, but effects are minor. The bulk of the reductive dechlorination activity will occur in the second nutrient injection phase. SUMMARY The pilot test of accelerated in situ bioremediation at NAS Point Mugu is currently underway. Injection of lactate into the aquifer has stimulated vigorous sulfate reduction activity to a distance of at least 50 feet from the injection well as indicated by a decrease in sulfate concentration and increases in <lcetate and propionate concentrations. An increase.in concentration of DeE at MW-3 is consistent with RT3D modeling predictions. No significant biofouling of the injection well has occurred during the first phase of nutrient injection. The pilot tcst will continue with pul$cd nutrient injections until the bulk of the sulfate has been removed from the test area of the aquifer. The second nutrient injection phase with a high concentration of lactate will then sustain rapid reductive dechlorination activity at this test site. Results of this pilot test will be used to show the effectiveness of the technology, to design and cost a full-scale system, and to provide an effective nutrient il~ectioll strategy. REFERENCES CJement, T. P "RTJD - A Modular Computer Code for Simulating Reactive Multi-Species Transport in 3-Dimensional Groundwater Aquifers." Pacific Northwest National Laboratory, Richland, Wasllington. PNNL-J J720. ( Hooker, B.S., R.S. Skeen, M.J. Truex, C.O. Johnson, B.M. Peyton. and D.B. Anderson "In.":J'iru Biorcmediation of Carbon Tetrachloride: Field Test Results." Bioremedia/ion Journal. 1(3): Johnson, C.D., R.S. Skeen, D.P. Leigh. T. P. Clement, and Y. Sun. 11)98. "Modeling Natural Attenuation of Chlorinated Ethenes Using the RT3D Code." In: Proceedings of the Himel' Environmenl Fet/era/ion 71"" Annual Conference and Exposition. WEflEC '98. Volume 3. Water Environment Federation. Alexandria, Virginia. pp OHM Remediation Services Corp. J998. Technical Memorandum frp SUe 24. Naval Air Station Point Mugu, Point Mugu, California. Document Number SW4628.