Occurrence and Attenuation of Lesser Chlorinated Compounds Associated with Legacy DNAPL Impacts – Case Study

James Peale (jpeale@maulfoster.com) and Michael Murray

(Maul Foster & Alongi, Inc., Portland, Oregon, USA) Jim Mueller and Josephine Molin (PeroxyChem, IL, USA)

Abstract: Groundwater at an active manufacturing facility on an 80-acre site in Portland, Oregon was impacted by TCE and its degradation products. Operations at the facility began in 1980, and included the use of primarily TCE, and other chlorinated solvents, from approximately 1980 to 1989. TCE and/or TCE-containing wastewater were released to the subsurface in the early 1980s, roughly between 1980 and 1984. Based upon bench and field pilot studies, ISCR-enhanced bioremediation was selected for primary source area treatment, implemented in early 2009, with demonstrated success in 2013. The site is also characterized by extensive impacts related to the historical (i.e., 1950s) disposal of manufactured gas plant (MGP) waste from an oil gasification facility. Impacts include significant amounts of MGP DNAPL, primarily composed of naphthalene, diesel range organics, and polycyclic aromatic hydrocarbons (PAHs). Samples of the MGP DNAPL collected near the former TCE source area and the ISCR injection zones exhibited elevated concentrations of not only TCE, but also 1,1,2-trichloroethane (112TCA), 1,1,2-trichloro-1,2,2-trifluoroethane (Freon 113), dichloromethane (DCM), and 1,2,3-trichloropropane (123TCP) as constituents of interest (COIs). The presence of these COIs was not expected, raising questions about the former use and potential release history. More importantly, the presence of high concentrations of these relatively soluble (aqueous solubility @ 25C of approximately 4,400 mg/L [112TCA]; 170 mg/L (Freon 113]; 13,000 mg/L [DCM]; and 1,900 mg/L [123TCP]) COIs adsorbed in NAPL represents a potential long-term source of aqueous phase and vapor phase impacts.

The objective of this work was to integrate COI data for DNAPL and groundwater into various transport models in order to help elucidate the site-specific environmental fate and effect of these compounds and to gain further insight into overall remedial performance. In so doing, myriad challenges and limitations are recognized, such as: i) uncertainties in COI source(s) including type, amount and location, ii) compound specific variances in groundwater transport, iii) differential degradation kinetics, and iv) convoluted and potentially overlapping degradation pathways. Analysis and Results. The existing data set from the site is extensive, and includes COI analysis of groundwater, MGP DNAPL, and soil vapor. The physio/chemical properties of the COIs are generally understood (Montgomery, 2007), allowing for comparison of groundwater and soil vapor data. Data from co-located MGP DNAPL and groundwater samples allowed for use of the effective solubility model (ESM) summarized in Pankow (1996) and described by others (Feenstra, 1992; Rivett, 2005) to describe and predict desorption of these compounds from the non-aqueous to the aqueous phase.

Portions of the study area are within the ISCR injection zones where active dechlorination of TCE is occurring. Groundwater samples taken from upgradient, within, and downgradient of the ISCR injection zone allowed for evaluation of this technology (intended for TCE and its degradation products) for the chlorinated alkanes, and prediction of downgradient fate and transport. Dechlorination or other reaction byproducts of 112TCA, Freon, TCP, and DCM were

also detected in samples collected in the study area, and the presentation will identify and rank potential reaction pathways indicated by the data and site conditions. Site Description: The site is an operating facility in Portland, Oregon, adjacent to the Willamette River. Industrial operations at the facility began in 1980, after the site had been developed by filling during the 1970s. Industrial operations at the facility included the use of TCE from approximately 1980 to 1989. TCE and/or TCE-containing wastewater were released to the subsurface, roughly between 1980 and 1984, but the exact date and volumes are unknown. The releases likely occurred immediately upgradient of the primary manufacturing building, which covers most of the groundwater plume between the source area and the riverbank (Figure 1). Groundwater flows from the upland under the river, with a small portion of the impacted plume intersecting transition zone water and surface water in the river. Figure 1 Site map and approximate extent of TCE in Groundwater

During the initial technology screening, a variety of remedial technologies were evaluated and eventually discarded due to incompatibility with facility operations, or the presence of legacy MGP-related impacts. The technology screening identified in situ chemical reduction (ISCR) as the most viable DNAPL source removal technology. Subsequent comparative bench testing (as described in Peale et al. 2008) identified the combination of EHC® and KB-1® as the best approach for treatment; these results were supported by subsequent field pilot testing (Peale et al., 2009), which in turn supported full scale implementation.

Implementation: Implementation consisted of an approximately 150 foot long PRB containing EHC and KB-1, installed at depths ranging from approximately 40 to 112 feet bgs using direct-push technology. Supplemental injections were completed upgradient of the PRB to treat additional source areas. EHC was injected first, followed later (usually 7 to 14 days) by KB-1 injections. The EHC was injected at four-foot vertical intervals, with two-foot offsets between injection rows to enhance the vertical coverage.

Injections commenced in January 2009 and were completed in June 2009 (Cascade Drilling of Portland, Oregon). Approximately 200 injection points were completed. A subsequent, smaller injection program upgradient of the first was implemented in 2012 upon discovery of a pool of MGP DNAPL containing elevated concentrations of TCE and the other source compound identified above. Performance data were collected from 24 deep and four shallow wells in the source area, and distant downgradient wells.

Data collection included an extensive suite of parameters to identify degradation rates and pathways. Target analytes included TCE and its degradation products, including ethene, ethane, and chloride. Secondary analytes that confirmed distribution and/or migration of the injected materials included iron, total organic carbon, ketones, and Gene-Trac© analysis for KB-1 bacteria by SiREM.

Investigation completed to support the EIB implementation identified upgradient areas of TCE contamination, with elevated concentrations in samples of MGP DNAPL in the shallow fill zone. DNAPL and groundwater data from the entire monitoring well and reconnaissance database (collected over 11 years) were used to evaluate the distribution of TCE and its degradation products (prior to, and during remediation), as summarized below: DNAPL Samples

Compound Analyses Detections Detection Frequency Max (ppb)

GeoMean (ppb)

TCE 138 111 80% 97,200,000 476,473 cDCE 138 131 95% 16,900,000 618,073 tDCE 138 66 48% 29,400 6,829 11DCE 138 59 43% 29,500 9,702 VC 138 70 51% 847,000 38,158 Groundwater Samples

Compound Analyses Detections Detection Frequency Max (ppb)

GeoMean (ppb)

TCE 2325 1454 63% 602,000 50.39 cDCE 2325 1870 80% 574,000 307.45 tDCE 2325 1212 52% 3,320 23.89 11DCE 2325 1059 46% 1,470 18.12 VC 2325 1792 77% 263,000 64.81

Samples of MGP DNAPL also contained elevated concentrations of 112TCA, Freon, TCP, and DCM; average and maximum concentrations are summarized in subsequent sections.

For the purpose of this paper, the chlorinated compounds in the table are referred to as source compounds, as they are all present in the MGP DNAPL samples at significantly elevated concentrations which would be characteristic of a source zone. The MGP DNAPL is primarily composed of naphthalene, diesel-range hydrocarbons, and BTEX compounds. Use of the Effective Solubility Model Data from co-located MGP DNAPL and groundwater samples allowed for use of the effective solubility model (ESM) summarized in Pankow (1996) and described by others (Feenstra, 1992; Rivett, 2005) to describe and predict desorption of these compounds from the non-aqueous to the aqueous phase. The ESM can be used to predict changes in aqueous phase concentrations of NAPL constituents based on changes in the mole fraction (Xi) of each compound (i). As both NAPL and aqueous phase data were collected, this evaluation compared the measured aqueous phase concentrations with ESM-predicted aqueous phase concentrations. Csat,i = XiCsat

Where Csat,i is the effective or aqueous solubility of the component (i) from the mixture; Xi is the mole fraction of component i measured in NAPL, and Csat is the pure compound solubility in water.

Pankow (1996) summarized earlier work that demonstrated that this equation produced effective solubility values that generally bracketed the range of observed values, but were sensitive to the assumed molecular weight of the unknown component of the mixture. Pankow also cited previous work that concluded that the ESM equation works well for predicting aqueous solubilities of binary mixtures. That ESM approach was previously used (Peale, 2011) to predict changes in the aqueous phase concentrations of TCE (relative to naphthalene) resulting from increased concentration gradients due to enhanced degradation rates of dissolved constituents in response to remediation activities. The effective solubilities (predicted aqueous values) for CVOCs potentially changing in response to ISCR were similarly calculated in a binary mode compared to relatively unchanged naphthalene concentrations. These calculations were repeated for Freon, TCP and 112TCA. Calculations were also performed for benzene as a compound not subject to ISCR-enhanced bioremediation for comparison. Effective solubility values were calculated for the major components of the DNAPL using the equation above.

Ratio of ESM Predicted Concentrations to Actual Groundwater Data TCE 112TCA TCP Freon Benzene Minimum 2.1 9.9 50.9 1.4 3.0 Maximum 72.0 53.3 19.7 1.4 25.4 Average 15.4 26.6 35.4 -- 9.7 n (paired data) 18 8 2 1 18 Paired data not available for Freon; average concentrations were used.

The data suggest significant overprediction of groundwater concentrations using the ESM for the chlorinated compounds (except Freon), and less overprediction of groundwater concentrations for benzene. Reaction byproducts of 112TCA, Freon, TCP, and DCM The conventional abiotic and biotic dechlorination pathways for TCE resulting from enhanced ISCR remediation have been documented at this site (Peale et al. 2009). Dechlorination pathways for two other source compounds – 112TCA and DCM – have been documented at other sites, but data demonstrating degradation of Freon 113 and TCP are relatively sparse. As summarize below, however, the data from this site are in general agreement with the proposed degradation pathways for 112TCA, DCM, Freon 113, and TCP.

112TCA This source COI was detected in about 10% of the DNAPL samples although no records or other data are available documenting the use of this compound during site operations. Reductive dechlorination of 112TCA results in step-wise formation of dichloroethane (DCA) isomers, chloroethane (CA), and ultimately ethane; as shown in Figure 2, conversion to 1,1-DCE may also occur via the elimination of chloride in response to abiotic degradation.

By looking for the presence of DCA, CA and ethane, evidence supporting the degradation of 112TCA pathway was evaluated using data from the source monitoring well (WS43-36) and downgradient monitoring wells, as summarized below:

DNAPL Samples

Compound Analyses Detections Detection Frequency Max (ppb) GeoMean (ppb)

112TCA 138 14 10% 9,250 5,210 11DCA 138 0 -- -- -- 12DCA 138 0 -- -- -- CA 138 0 -- -- --

Groundwater Samples

Compound Analyses Detections Detection Frequency Max (ppb) GeoMean (ppb)

112TCA 2325 190 8% 127 5.13 11DCA 2325 101 4% 6.02 0.51 12DCA 2325 105 5% 3.5 1.20 CA 2325 215 9% 82.9 4.92

Figure 2: Transformation pathways of chlorinated ethenes and ethanes in anaerobic conditions. Tobiszewski et al (2012)

112TCA was detected in 10% of the NAPL samples, with no detection of its degradation products. The parent compound was detected at approximately the same frequency, albeit at much lower concentrations, in groundwater downgradient from the source well. Of note, 11DCA (which is not shown as a pathway in Figure 1) was detected at generally the same frequency and concentrations as 12DCA. The data show accumulation of CA (byproduct of both 11DCA and 12DCA dechlorination) in downgradient groundwater samples.

DCM This compound and Freon 113 were the primary ingredients of a product called Freon-TMC, which was used to dry (dewater) silicon wafers during operations. Stepwise reductive dechlorination of dichloromethane can generate chloromethane and methane. This pathway was evaluated using data from the source monitoring well (WS43-36) and downgradient monitoring wells, as summarized in the following table:

DNAPL Samples

Compound Analyses Detections Detection Frequency Max (ppb)

GeoMean (ppb)

DCM 138 8 6% 55,400 28,503

CM 138 1 1% 2,510 Groundwater Samples

Compound Analyses Detections Detection Frequency Max (ppb)

GeoMean (ppb)

DCM 2325 1 0% 286 CM 2325 67 3% 144 2.55

As noted in the table, downgradient concentrations of DCM were not detected in groundwater, although CM and methane concentrations were. This may be the result of enhanced dechlorination of DCM in the aqueous phase, but may also reflect the very high solubility of DCM relative to the other source compounds. There are also recognized differences in transport of these compounds in aquifer systems, with significant difference in retardation factor potentially influencing and complicating data interpretation Methane is also generated at this site by the methanogenic reducing conditions enhanced by EHC injection, so methane concentrations and mass balances were not attempted. DCM and CM were not detected in soil vapor samples.

Freon 113 Dechlorination or other degradation reactions have been described in studies (Balsiger, 2005), but confirmation at hazardous waste sites is not well documented. Balsiger (2005) describes the formation of degradation products TFE and CTFE, by the pathways shown below (Figure 3).

None of these “intermediate” compounds were regularly reported during the course of performance monitoring. However, tentatively identified compound (TIC) searches were performed on groundwater samples and confirmed their presence. These data indicate that the di-chloroelimination (d) and hydrogenolysis (h) pathways are facilitated at the site, likely as a result of the EHC and/or KB-1 injections. This pathway was further evaluated using data from the source monitoring well (WS43-36) and downgradient monitoring wells, as summarized in the following table:

Figure 3: Transformation pathways of Freon113 from Balsiger et al. (2005)

DNAPL Samples Compound Analyses Detections Detection Frequency Max (ppb) GeoMean (ppb) Freon 113 29 21 72% 207,625 124,476 DCDFM 138 -- -- -- -- CTFE -- -- -- -- -- TFC -- -- -- -- --

Groundwater Samples Compound Analyses Detections Detection Frequency Max (ppb) GeoMean (ppb) Freon 113 277 10 4% 177 20.18 DCDFM 2325 88 4% 216 7.78 CTFE 15 (TIC) 5 33% 18.3 3.20 TFE 15 (TIC) 5 33% 12.8 2.80

Along with the parent compound Freon 113, dichlorodifluoromethane and trichlorofluoromethane were also detected in soil vapor samples and groundwater. These two latter compounds are often interpreted to be manufacturing impurities, as opposed to degradation products, but they were not detected in DNAPL analyzed. Hence, there may be multiple NAPL sources or they may indeed be degradation products of the ISCR treatment.

123TCP No records are available documenting the use of this compound during facility operations. Tratnyek et al. (2010) have developed extensive research into the degradation of 1,2,3-TCP. A variety or products and pathways have been identified as shown in the following figure:

Figure 4: Transformation pathways of 123TCP from Tratnyek et al. (2010)

The figure shows that degradation products such as 1,2-dichloropropane (12DCP) are predicted as a result of reduction reactions. Consistent with mechanics of the ISCR implemented at the site, 12DCP was detected in groundwater downgradient of the source area. However, other products

were also identified in groundwater – 2,2-dichloropropane (2,2DCP) and 1,1-dichloropropene (1,1DCPe) – downgradient of the source area. It is likely that these compounds are manufacturing contaminants, as opposed to reaction products. Alternatively, these could be byproducts of coupling reactions.

DNAPL Samples Compound Analyses Detections Detection Frequency Max (ppb) GeoMean (ppb) 123TCP 138 6 4% 6,210 3,784 12DCP 138 -- -- -- -- 22DCP 138 -- -- -- -- 11DCPe 138 -- -- -- -- Groundwater Samples Compound Analyses Detections Detection Frequency Max (ppb) GeoMean (ppb) 123TCP 2325 26 1% 20.4 0.88 12DCP 2325 8 0% 0.97 0.52 22DCP 2325 5 0% 0.39 0.34 11DCPe 2325 7 0% 94.5 0.93

123TCP and the associated compounds were not detected in soil vapor samples. Summary The data collected during monitoring of legacy DNAPL during ISCR-enhanced EIB of TCE and its degradation products demonstrated that:

1) TCE released to the subsurface not only sorbed into legacy DNAPL at high concentrations but was also distributed significantly downgradient. This distribution is not unexpected, based on historical information regarding use and releases.

2) High concentrations of TCA, Freon 113, DCM, and 123TCP where unexpectedly identified in the legacy MGP DNAPL, but – for various reasons - these source compounds did not result in significant distribution downgradient in groundwater.

3) The ESM model overpredicted groundwater concentrations for some of the compounds. 4) Degradation pathways for Freon and 123TCP suggested by others were confirmed. 5) Combined with observation (2), the data support the effectiveness of ISCR enhanced

bioremediation of these chlorinated solvents. Conclusion Discovery of unexpected chlorinated compounds upgradient of the presumed release area prompted further evaluation of an extensive data set collected prior to and during monitoring of groundwater undergoing successful ISCR-enhanced bioremediation. Anticipated degradation pathways commonly observed at other sites (e.g., for TCE and112TCA) were evaluated based upon anticipated degradation product concentrations. Degradation pathways for other compounds (e.g., Freon and 123TCP) which are less commonly observed were also confirmed. The ESM model was used to compare observed and actual groundwater concentrations downgradient of the non-aqueous phase source material. ESM calculations generally overpredicted groundwater concentrations, which along with the presence of degradation products suggests the effectiveness of ISCR-enhanced bioremediation for unanticipated chlorinated compounds at this site. Literature Cited

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Montgomery. J.H. 2007. Groundwater Chemicals Desk Reference. CRC Press. Boca Raton, Florida.

Pankow, James F. and Cherry, J. (1996) Dense Chlorinated Solvents and Other DNAPLs in Groundwater. Waterloo Press, Portland OR

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Tratnyek, Paul, and Sarathy, V; Salter, A.; Nurmi, T.; O’Brien Johnson, G.; DeVoe, T.; and Lee, P. (2010) Prospects for Remediation of 1,2,3-Trichloropropane by Natural and Engineered Abiotic Degradation Reactions. SERDP Project ER-1457.

U.S. EPA. 2014. Technical Fact Sheet – 1,2,3-Trichloropropane (TCP). Office of Solid Waste and Emergency Response (5106P). EPA 505-F-14-007. January.