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Thirty two soil samples were collected during monitoring well installation and sampled for VOCs
<br />with TICs, Semi-VOCs with TICs, TPHd, TPH1o, TPHueh, TPHjp4, TPHjp5, TPH as referenced
<br />by kerosene (TPHk), and industrial solvents (Tables 0U8-1 and 0U8-PTIC, soil samples 23-4
<br />through 23-6, 34-7 through 15). Results were typically ND, but TPHk was detected in two samples
<br />collected at depths of 10 feet (3,900 mg/kg) and 15 feet (1,400 mg/kg). The laboratory noted the
<br />kerosene was "weathered." These concentrations exceed the Industrial Threshold and Protection
<br />of Groundwater SSLs. Industrial solvent methanol was detected at a depth of 10 feet (3.7 mg/kg)
<br />and industrial solvent o-xylenes was detected at depths of 10 feet (2.2 mg/kg) and 15 feet (0.79
<br />mg/kg). The methanol concentration is below the Industrial Threshold and Protection of
<br />Groundwater SSL, but the o-xylenes concentration exceeds the Protection of Groundwater SSL
<br />of 0.19 mg/kg. Four VOC TICs were also detected at concentrations ranging from 0.26 mg/kg
<br />(Cyclohexane, 1-Ethyl-Methyl-, Cis-) to 5.8 mg/kg (Cyclohexane, 1,1,2,3-Tetramethyl-), and
<br />fourteen Semi-VOC TICs were detected at concentrations ranging from 3.3 mg/kg (Cyclopentane,
<br />1-Methyl-2-(-Propeny1)-) to 1,200 mg/kg (total unknown hydrocarbons). Unknown VOC TICs were
<br />also detected at concentrations of 1.87 and 1.98 mg/kg and unknown Semi-VOC TICs were
<br />detected at concentrations of 32.9 and 49.5 mg/kg.
<br />Six Hydropunch samples were also collected during monitoring well installation. Samples were
<br />analyzed for VOCs with TICs, Semi-VOCs with TICs, TPHd, TPH1o, TPHueh, TPHjp4, TPHjp5,
<br />and TPHk (Table 0U8-1, Hydropunch samples 34-7-HP through 34-12-HP). All results were ND,
<br />except for hydrocarbons with chains greater than about 010, which were detected as TPHueh in
<br />each sample at concentrations ranging from 120 to 620 ug/L. These concentrations exceed EPA
<br />Tap Water and Tier 1 Groundwater ESLs.
<br />These wells were sampled and analyzed for petroleum-related compounds during four events
<br />over an 8-year period: 1997, 2001, 2003, and 2005 (Tables 0U8-P and 0U8-PTIC, groundwater
<br />samples MW-16 through MW-21). Hydrocarbons with chains greater than approximately 010
<br />were noted as TPHueh at concentrations ranging from 250 to 2,900 ug/L in 1997; as TPHueh at
<br />concentrations ranging from 160 to 580 ug/L in 2001; and as TPHueh at concentrations ranging
<br />from 74 to 700 ug/L in 2001. No hydrocarbons were detected in 2005; however, laboratory
<br />reporting limits were generally 500 ug/L, which was higher than previous average detections.
<br />Moreover, the maximum concentration of 2,900 ug/L noted in 1997 was associated with MW-18,
<br />which was not sampled in subsequent years because it could not be located. When MW-18 and
<br />2005 data are removed to correct for these inconsistencies, average TPH concentrations
<br />decrease from 284 ug/L in 1997 to 227 ug/L in 2001 and then 203 ug/L in 2003. Regression
<br />analysis indicates a linear trend (R2 = 0.93), which, if projected beyond the monitoring period,
<br />indicates concentrations would have reached 100 ug/L sometime around 2013 and will reach 0
<br />ug/L around 2021 (Chart 0U8-P). This average declining concentration is consistent with
<br />expected natural attenuation; however, the last ND of less than 500 ug/L may still represent
<br />concentrations exceeding the TPHd Tier 1 and EPA Tap Water ESLs of 100 ug/L, and while the
<br />1:12 indicates that time alone can explain about 93% of the variance in average concentrations, the
<br />regression is based on limited. These wells were also sampled for TPHjp4, TPHjp5, and TPHk in
<br />1997. Results are all ND. It does not appear these wells were sampled for TPHjp4, TPHjp5, or
<br />TPHk in subsequent events.
<br />Petroleum/Solvents: Recommendations
<br />Based on the hydrocarbons detected in groundwater exceeding EPA Tap Water and Tier 1
<br />Groundwater ESLs, Kleinfelder recommends field exploration to confirm that petroleum-related
<br />groundwater contamination is naturally attenuating as expected. Kleinfelder also recommends
<br />investigation to ensure contamination does not pose health risks via soil vapor.
<br />20173951.001A/SAC17R68420 Page 15 of 26 November 2, 2017
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