DATA EVALUATION OF IN SITU CHEMICAL TREATMENT FOR GROUNDWATER REMEDIATION AT LEAKING UNDERGROUND STORAGE TANK SITES IN LOS ANGELES AREA, CALIFORNIA

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1 DATA EVALUATION OF IN SITU CHEMICAL TREATMENT FOR GROUNDWATER REMEDIATION AT LEAKING UNDERGROUND STORAGE TANK SITES IN LOS ANGELES AREA, CALIFORNIA (November 24, 2008) Weixing Tong 1 and Yue Rong 2 Abstract This study evaluates groundwater monitoring data from 36 leaking underground fuel tank (LUFT) sites in Los Angeles Area, which have used in-situ chemical treatment as a remediation measure to clean up the petroleum hydrocarbon contamination. Three general chemical groups have been evaluated: (1) hydrogen peroxide (H 2 O 2 ) and Fenton s Reagent, (2) ozone (O 3 ), and (3) oxygen releasing compound (ORC). The analysis compares the maximum contaminant concentrations pre and post chemical injection and calculates the contaminant concentration change percentage. The preliminary analysis of the data indicated that effectiveness of the treatment is mostly related to the initial compound specific contaminant concentrations, sufficient period of time to work after injection, and the injection chemical specific to particular targeted contaminant compounds. The data suggest that all 3-group injection chemicals seem to work more effectively when initial benzene concentration is less than 5,000 µg/l and MTBE concentration is less than 10,000 µg/l. The study also indicates that hydrogen peroxide and Fenton s Reagent is the most effective chemical injection among these three chemical groups. Introduction In recent years, in-situ chemical treatment remediation technology has been increasingly applied for the cleanup of groundwater contamination at LUFT sites in Los Angeles area, California. In-situ chemical treatment includes injection of selected chemical or mixing of several chemicals to the contamination plume through the delegated delivery points. The purposes of the in-situ chemical injection methods are usually two folds: to stimulate chemical reaction (e.g., oxidation) to destroy contaminants, and to generate oxygen (O 2 ) to encourage or enhance bio-degradation. The in-situ cleanup method has been seen to be used in the following cleanup situations: 1) to remediate contaminants plumes, 2) to address localized hot-spot high concentrations, 3) to limit groundwater contaminant plume from migrating off site, and 4) to proceed final polishing after other remediation technologies. The California Water Code (CWC), section 13260, requires that any person discharging waste, or proposing to discharge waste other than into a community waste water collection system, which could affect the quality of the waters of the State, shall file a Report of Waste Discharge with the Regional Board, and section of the CWC 1 California Regional Water Quality Control Board Los Angeles Region, 320 W. 4 th Street, Suite 200, Los Angeles, CA 90013; (213) ; Fax: (213) ; wtong@waterboards.ca.gov 2 California Regional Water Quality Control Board Los Angeles Region, 320 W. 4 th Street, Suite 200, Los Angeles, CA 90013; (213) ; Fax: (213) ; yrong@waterboards.ca.gov

2 provides that a Regional Board may prescribe general waste discharge requirements (WDRs) for dischargers produced by similar operation, involving similar types of wastes, and requiring similar treatment standards (CWC amended 2008). The Los Angeles Regional Water Quality Control Board has adopted a general WDRs permit that applies to injections of compounds that either chemically oxidize/reduce the contaminants, or enhance bio-degradation. This study focuses on gasoline groundwater contamination cleanup cases in Los Angeles area, where WDRs permits were issued at 74 leaking underground storage tank sites for groundwater cleanup. Among these 74 sites, 20 sites applied hydrogen peroxide (H 2 O 2 ) and/or the Fenton s Reagent, 33 sites applied ozone (O 3 ) injection, and 17 sites applied ORC and RegenOx, and 4 sites applied others (FeO 4 S, Na 2 SO 4, Na 2 S 2 O 8, BioCritters and BioBooster) (Figure 1). Over 80% of these sites applied in-situ chemical treatment to clean up benzene and/or methyl tertiary butyl ether (MTBE) contamination. Only 36 sites have sufficient monitoring data of concentration changes to evaluate the effectiveness of the applied chemicals for groundwater cleanup. (Total Permits Issued = 74) $ %& (' ) +*, - /. % % 0 "! # Figure 1. General WDR permit types issued by Los Angeles Regional Water Quality Control Board for the LUFT sites using in situ chemical injection technology for groundwater remediation. In-situ Chemical Oxidation for Groundwater Contamination Remediation In situ chemical oxidation (ISCO) technology has been widely used to remediate groundwater contamination (chlorinated volatile organic compounds, petroleum hydrocarbons) for long time (Gates and Siegrist 1995, ESTCP 1999, Seol, et al, 2003). This approach delivers the selected chemical into the contaminated groundwater and either directly react with the contaminant (oxidation) or enhance the micro-biologic degradation of contaminants (Siegrist 1998; U.S. EPA 1998). The selected chemicals 2

3 are often delivered through either injection probes or dedicated injection wells under pressure (through pumping). The delivery points are selected based on plume distribution and sometime are in grid with a spacing distance between 5 feet to 20 feet (depending on permeability of the water-bearing zone material). Ozone is an oxygen molecule containing three oxygen atoms. Ozone gas is a very strong oxidizing agent that is very unstable and extremely reactive (U.S. EPA 1985). It cannot be shipped or stored; therefore, it must be generated on-site prior to or during application (Riser-Roberts, 1998). Ozone can be used to degrade recalcitrant compounds directly by creating an oxygenated compound without chemical degradation. Ozone increases the dissolved oxygen level in water for enhancing biological activity (Texas Research Institute, Inc., 1982). Ozone treatment may be very effective for enhancing biological activity, if the organic contaminants are relatively biodegradable. However, if much of the material is relatively biorefractory, the amount of ozone required would greatly increase the cost of the treatment. Hydrogen peroxide is a weaker oxidizing agent than ozone, but it is considerably more stable in water. It decomposes to form water and oxygen, and can supply improved oxygen levels. Hydrogen peroxide is a strong oxidant and is nonselective. It will act with any oxidizable material presented in soil and groundwater. Advantages of hydrogen peroxide include: 1) greater oxygen concentration can be delivered to the subsurface (100 mg/l H 2 O 2 provides 50 mg/l oxygen); 2) less equipment is required to oxygenate the subsurface; 3) hydrogen peroxide can be added in-line along with the nutrient solution (aeration wells are not necessary); and 4) hydrogen peroxide keeps the well free of heavy biogrowth. Fenton s Reagent is a solution of hydrogen peroxide and an iron catalyst that is used to oxidize contaminants. Fenton s Reagent uses trace amount of FeSO 4 and HCL (aka. muriatic acid or swimming pool acid) as catalysts that are injected into subsurface with the H 2 O 2. The petroleum hydrocarbons are oxidized and carbon dioxide and water are by-products of the reaction. The purpose of the catalysts is to strengthen the reaction of the H 2 O 2 with the petroleum hydrocarbons to break the hydrocarbon bonds to enhance remediation. The basis for the reaction is related to Fenton s Reaction wherein H 2 O 2 reacts with a trace amount of FeSO 4 to produce a hydroxyl radical (OH ). The OH radical is an extremely powerful oxidizer that rapidly reacts with the petroleum hydrocarbons yielding carbon dioxide and water. ORC is a patented formulation of magnesium peroxide that time-releases oxygen when hydrated. ORC is manufactured as a powder that when mixed with water forms a slurry for injection via direct-push equipment; or the slurry may be used to backfill augered bore holes. RegonOx TM is a solid alkaline oxidant built around a sodium percarbonate complex, which is activated using a proprietary, multi-part catalytic formula. The product is delivered to the treatment site in two parts. The two parts are combined and then added to subsurface using direct-push and/or soil mixing equipment. Field Data Evaluation This study uses the maximum concentration of targeted contaminant for evaluation and compares data between pre-treatment concentration (C 0 ) and most recent concentration (C r ). The following formula is used to calculate the concentration change percentage: 3

4 C = ( C C ) 0 C 0 r 100% (1) where C > 0, indicating contaminant concentration decreased after chemical injection; and C < 0, indicating contaminant concentration increased after chemical injection. The data used in the evaluation are all reported from quarterly groundwater monitoring reports or remediation progress reports. One groundwater monitoring well containing the maximum concentration of contaminant of study was selected per site for analysis. Four contaminants were analyzed in this study, including total petroleum hydrocarbon as gasoline (TPH g ), benzene, methyl tertiary butyl ether (MTBE), and tertiary butyl alcohol (TBA). The injection time was calculated from time of the first injection event to time of the most recent monitoring event. The effectiveness of ISCO is influenced by many factors. This preliminary study only focused on the contaminant concentration change. The study did not consider the water fluctuation at the site, lithology and soil type, injection volume and pressure, injection point spacing, injection frequency, plume size and concentration distribution, and natural attenuation parameters at the site. Nevertheless, one time concentration change over the time at a site can provide us an overall picture and trend of how these in-situ injection methods work. This trend analysis may be useful to advise intelligently future use of these in-situ methods. Contaminant Concentration Change versus Time Monitoring data from each site which has applied permitted chemical were used to calculate the concentration change after the injection. Figures 2 5 present the results for the concentration changes with respect to the application time for TPHg, benzene, MTBE, and TBA, respectively. The data points vary among the figures because each site has unique contaminant characterization, e.g., one site may only need to remediate benzene contamination (the other contaminants are either very low in concentration or non-detect). Figure 2 illustrates the maximum TPH g concentration change after injection of chemicals. The data indicate that hydrogen peroxide and Fenton s Reagent group has most positive results (most sites have >50% reduction), especially after significant amount of time (>10 months), whereas, oxygen release compound group has the least effective group (more than half of the sites showed concentration increase). This may attribute to the OH radical which has more power to attack the carbon-hydrogen (C-H) bonds in the petroleum hydrocarbons (TPHg) than oxygen does alone. Figure 3 illustrates the benzene concentration change after injection of chemicals. The data indicate that all three chemical injection groups have positive results for most of the sites. ORC group has higher percentage in term of total sites showing >50% reduction. Hydrogen peroxide and Fenton s Reagent group shows less effect. Figure 4 illustrates the MTBE concentration change after injection of chemicals. The data 4

5 eee e WWWW ^W ^W ^W ^W [[[[ indicate that all three chemical groups have positive results for most of the sites. Figure 5 illustrates the TBA concentration change after injection of chemicals. The data indicate that all three chemical groups have positive results for most of the sites. Nearly half of the sites do not have to remediate TBA. 2%4 45 cd [ab W`Z W`Z W`Z W`Z \\\ \ ]^ ]^ ]^ ]^ XXXX YZ YZ VVVV WWWW & %4 4 5 fhgjilkmonsipmhkfhqjnfsrsthguiwv xyzh{} ~mgl jfhgjn} 7k+qjkmguƒS S S :4 ;3<=?>A@ BDCFE G&>%= <%HDI?JLKM MNJ<%H ION<%B PRQS<%PT=&BDP&OG U Fenton's Reagent & Hydrogen Peroxide Oxygen release compounds Ozone Figure 2. The maximum total petroleum hydrocarbon as gasoline concentration change after injection of permitted chemicals. 5

6 µ µ µ µ ª ª ª ª ««««eee e WWWW ^W ^W ^W ^W [[[[ ĵ Š ³ «±² ª ª Š Š Š Nĵ Š ĵ ˆ7 Œ Œ h & š j j œ Ÿž N D 7 œ j S S 7š Ž Fenton's Reagent & Hydrogen Peroxide Oxygen release compounds Ozone Figure 3. The maximum benzene concentration change after injection of permitted chemicals cd [ab W`Z W`Z W`Z W`Z \ \\ \ ]^ ]^ ]^ ]^ XXXX YZ YZ VVVV WWWW & %4 2% : 4 ;3<=?>A@ BDCFE G> =3< HDI?JLKM MNJ<%H ION<%B PRQS<7PT=NBDP&OG U Fenton's Reagent & hydrogen peroxide Oxygen release compounds Ozone Figure 4 illustrates the MTBE concentration change after injection of permitted chemicals. 6

7 eee e WWWW ^W ^W ^W ^W [[[[ ÛÛÛ Û ÍÍÍÍ ÔÍ ÔÍ ÔÍ ÔÍ ÑÑÑÑ cd [ab W`Z W`Z W`Z W`Z \ \\ \ ]^ ]^ ]^ ]^ XXXX YZ YZ VVVV WWWW two sites are out of range (-436% in 31 months and -141% in 1 months) using ozone % :4 ; <j=n>a@ BCFEG> =3< HDI?J K&M M?J < HDI&O&< BDPRQ<7PT=NBDP&OG U Fenton's Reagent & Hydrogen Peroxide Oxygen release compounds Ozone Figure 5 illustrates the TBA concentration change after injection of permitted chemicals. j¹d¹ º ÙÚ Ñ Ø ÕÕÕÕ ÍÖ Ð ÍÖ Ð ÍÖ Ð ÍÖ Ð Ò ÒÒ Ò ÓÔ ÓÔ ÓÔ ÓÔ ÎÎÎÎ ÏÐ ÏÐ ÌÌÌÌ ÍÍÍÍ»¹ º ¹ º»¹ º j¹d¹ º 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000 ¼ ½¾ À%¾ÁÂDà Á&Ä7½¾TÅÀÆD½D ÀFÄj¾&ÇDÀ DÁÄ%½¾ÉÈhÄj¾TÊDÊDÅ Ë Fenton's Reagent & Hydrogen Peroxide Oxygen release compounds Ozone Figure 6. The maximum benzene concentration change after injection of permitted 7

8 ÿ ÿ ÿ ÿ óóóó úó úó úó úó chemical versus its initial concentration. àþþ7ß ýþ ûûûû óü ö óü ö óü ö óü ö ø øø ø ùú ùú ùú ùú ô ôôô òòò õö õö ò óóóó á Þ7ß Þ7ß Ü á Þ7ß ÜNàÞÞ7ß ÜNàjá Þ7ß Ü Ý ÞÞ7ß ,000 10, ,000 1,000,000 âã ä åæ7ä ç7èé ç êã%ä ëdæì ã èdæaêhä í æåç êã%äïîhêhä ð ðëdñ Fenton's Reagent & Hydrogen Peroxide Oxygen release compounds Ozone Figure 7. The maximum MTBE concentration change after injection of permitted chemical versus its initial concentration. Contaminant Concentration Change versus Initial Concentration This study also compared the targeted contaminant concentration verse their initial concentrations. The purpose of these analyses is to find the correlation between contaminant concentration change and their initial concentrations. This analysis does not consider the time factor. The data shown in Figure 6 indicate that for all the sites with benzene concentration greater than 5,000 ppb (there is a data gap between 5,000 ppb to 8,000 ppb range), the reduction percentage is less than 25%, which suggests that chemical oxidation may not be an effective approach if the initial benzene concentration is too high. On the other hand, sites with benzene concentration less than 5,000 ppb seem to work well (many sites has more than 50% reduction in concentration). Similarly, the data shown in Figure 7 indicate that for all the sites with MTBE concentration less than 10,000 ppb, the in-situ injection seems to work well in concentration reduction. Chromium VI Generation Associated with Ozone Injection Some case study indicates that ozone injection may convert chromium III (Cr III) to chromium VI (Cr VI) which is more soluble contaminant impacting water quality. This study also evaluated both total chromium and chromium VI data from eight sites which have been applied with ozone injection technology (most of these sites do not have baseline chromium data). One groundwater monitoring well containing the maximum chromium concentration was selected per site for the study. The data are presented in Table 1 and Figure 8. It appears that all the sites have not shown any significant increase of Cr IV concentration. Only two sites, one well at each site, had Cr VI detection greater than 5 µg/l (6.0 µg/l and 7.6 µg/l). 8

9 a W ^`_ Sh ijkl klmsn fe d c Y ^ Y ]^ a b \ ]^ Z[ Y Z V WX!#" $ % %'&)(!*% $ % %'&)(!,+ $".-/&0(!21 $ 3/&0(!,3 $ 4/&0(!,- $".+/&0( 8)9 :<;=?>6@A9 :.BDCFEHG<I:.9 JLKDJMN:.G<;OI:.PQ;RKS:*9 KTPQJRKS:.BS=U!,5 $64,&0(!,7 $ %/&0( Figure 8. Histogram shows the chromium analytic data from eight ozone injection sites. The values represent the maximum concentrations (in µg/l) at the site. Table 1. Chromium monitoring data from eight LUFT sites that are treated by ozone injection (concentration in µg/l) Well NO. Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7 Site 8 Total Cr Total Total Total Total Total Total Total Cr VI Cr Cr VI Cr Cr VI Cr Cr VI Cr Cr VI Cr Cr VI Cr Cr VI Cr Cr VI No No No No No No No No No Discussion and Conclusions The results of this study indicate that although in general all the three chemical groups 9

10 are effective in reducing contaminant concentration, some sites showed little or negative impact (concentration increase), suggesting that some chemicals may not be working at a particular environmental setting. Many factors can contribute to a concentration increase in a monitoring well, including 1) continuous source (from soil residual or leak near the source area); 2) high concentration plume flow from upgradient; 3) arising water level mobilizing adsorbed contaminants in the soil matrix; and 4) impermeable formation material that limits the injected chemical to be delivered to the targeted area. More importantly, we should understand that in theory, oxygen release process is to encourage bio-degradation, and therefore may take longer to see the positive results. In order to effectively apply ISCO approach for groundwater cleanup, some sites may need bench scale test and/or pilot test before the full scale of implementation. The initial contaminant concentration is an important factor for effectiveness of ISCO. The in-situ injection chemicals seem to work more effectively when initial benzene concentration is less than 5,000 µg/l and MTBE concentration is less than 10,000 µg/l. This may provide useful guidance in practice of ISCO application for the regulatory and industrial communities. This finding suggests that before selecting the injected chemical, it is very important to consider the site conditions and the limitation of the selected chemical. For example, according to the manufacturer of ORC, this product is generally recommended for application on sites with low dissolved phase contaminant concentration and yet two ORC injection sites in this study had initial benzene concentrations of 11,300 µg/l and MTBE concentration of 33,000 µg/l, respectively. Both sites showed the low effectiveness in the injection method. Ozone injection does not seem to generate chromium VI in most of the sites studied in Los Angeles area. The reason remains to be further investigated. The possible contributing factors include the initial groundwater chemistry, ph, temperature, injected ozone dosage, etc., which are beyond the scope of this study. The results and conclusions presented in this paper are preliminary, and need further investigation, particularly need more site-specific data to study the reasons why certain injection chemicals work better than others for particular contaminants. Nevertheless, the analysis results presented in this paper may provide us an overall idea and trend of these in-situ chemical injection methods performance, which may be useful to advise intelligently future use of these in-situ injection methods. Acknowledgements The authors wish to thank Ms. Kathleen Nugal, Ms. Alejandra Lopez, and Ms. Micaela Soto for assistance in gathering site information and monitoring data. References California State Water Resources Control Board amendment. Porter-Cologne Water Quality Control Act (California Water Code, Division 7. Water Quality) Environmental Security Technology Certification Program (ESTCP) Technology Status Review: In Situ Oxidation. Accessed June 23,

11 Gates, D.D., and R.L. Siegrist In situ chemical oxidation of trichloroethylene using hydrogen peroxide. Journal of Environmental Engineering 121, no. 9: Lowe, K.S., F.G. Gardner, and R.L. Siegrist Field evaluation of in situ chemical oxidation through well-to-well recirculation of NaMnO 4. Ground Water Monitoring & Remediation 22, no. 1: Riser-Roberts, E Remediation of petroleum contaminated soils: biological, physical, and chemical processes. Lewis Publishers Seol, Y., H. Zhang, and F.W. Schwartz A review of in situ chemical oxidation and heterogeneity. Environmental and Engineering Geoscience 9, no. 1: Siegrist, R.L In situ chemical oxidation: Technology features and application. Innovations in In-Situ Ground Water Remediation. Ground Water Remediation Technology Analysis Center, U.S. EPA Technology Innovation Office. December 1998, Atlanta, Georgia. Texas Research Institute, Inc., Enhancing the Microbial Degradation of Underground Gasoline by In creasing Available Oxygen. Report to American Petroleum Institute, Washington, D.C. U.S. EPA Handbook for Remedial Action at Waste Disposal Sites. Revised. EPA/625/6-85/006 U.S. EPA Field application of in situ remediation technologies: Chemical oxidation. U.S. EPA 542-R Office of Solid Waste and Emergency Response. Washington, D.C. 11