ARCHIVED REPORTS_DRYWELL CLOSURE AND INVESTIGATION

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1 NOA Drywell Closure and Investigation Page 21 of 26 ' May 30, 2014 (COPC) below the ESLs can be assumed not to pose a significant threat to human health and the environment. For COPCs above groundwater ESLs, further evaluation is warranted. The following COPCs were detected in some of the analyzed groundwater samples below their respective groundwater ESL: Arsenic, Barium, Chromium, Selenium, Acetone, and 2-Butanone. These COPCs do not pose a significant threat to human health and the environment. The following COPCs were detected in some of the analyzed groundwater samples at levels above their respective Groundwater ESL: Mercury, TPH as Diesel and Total Recoverable Petroleum Hydrocarbons. Further evaluation of these COPCs is warranted. The groundwater ESL for Mercury, based on Aquatic Habitat Goals, is 0.025 pg/L. Mercury was 1 detected in DW-2 at a level of 0.057 Ng/L, more than twice the ESL level. However, the ESL is based on Aquatic Habitat Goals. This is not applicable to the subject property since there are no nearby aquatic habitat receptors downgradient (south) of the subject property. The health- based EPA Primary Maximum Contaminant Level (MCL) for drinking water is more applicable. The MCL for Mercury is 2 Ng/L. The detected levels of Mercury are below the MCL. Mercury is therefore not considered a COPC. The groundwater ESL and the US EPA Health Advisory for TPH as Diesel in groundwater is 100 pg/L. Groundwater collected from DW-1 (Sample Wl-V, see Plate 6) contains TPH as Diesel at levels of 2700 pg/L and groundwater collected from DW-2 (Sample W2-V, see Plate 7) contains TPH as Diesel at levels of 280 pg/L; these are above the recommended and regulatory limit of 100 Ng/L. TPH as Diesel is a COPC. TPH as Diesel is a mixture of petroleum hydrocarbons and is therefore not a direct indicator of human and environmental risks. The various chemical compounds in the mixture have diverse health effects. Impacts of TPH-Diesel should be evaluated in conjunction with indicator chemicals, including BTEX, MTBE, and Polycyclic Aromatic Compounds. None of these indicator chemicals were detected in groundwater. A risk assessment would be required to determine human health and environmental risk of the TPH as Diesel in on-site groundwater. Total Recoverable Petroleum Hydrocarbons (TRPH) is a measure of Total Petroleum Hydrocarbons in a sample based on extracting the contaminant from said sample. It is a widely used gross parameter for quantifying environmental contamination. However, it does not differentiate specific petroleum hydrocarbons. Sample W1-IV from DW-1 (see Plate 6) contains TRPH at levels of 2000 pg/L. There is not a groundwater ESL for TRPH. However, since TRPH is a measure of total petroleum hydrocarbons, groundwater ESLs for TPH as Gasoline, Diesel and Motor Oil of 100 pg/L is used. The 2000 pg/L concentration in sample Wl-IV is significantly elevated above the 100 Ng/L groundwater ESL for total petroleum hydrocarbons. Based on the elevated level of TPH as Diesel in groundwater, and absence of TPH as Gasoline and Motor Oil, the level of TRPH is likely a representation of TPH as Diesel concentration. TRPH is a COPC, specifically TPH as Diesel. The sample collected from DW-2 analyzed for TRPH did not detect TRPH above laboratory reporting limits. Petroleum hydrocarbons were detected at much higher levels in DW-1 than in DW-2, although these wells are only separated by one (1) foot. Groundwater analyzed for TPH as Diesel and ' TRPH was collected at 75 feet bgs from DW-1 and at 58.5 feet bgs from DW-2. As discussed in ' 902 Industrial Way• Lodi, CA 95240 • 209.367.3701 • Fax 209.333.8303 02014 Neil 0.Anderson Fi Associates, Inc.