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Air Sparging Pilot Test Related Activities Report and Remedial Action Work Plan
<br />Former Countryside Market, Stockton, California April 30, 2015
<br />In August 2001, two soil borings (CM-1 and CM-2) were completed on-Site at locations shown
<br />on Figure 2. Boring CM-1, located between the dispenser island and the former USTs, was
<br />advanced to 90 feet bgs. Boring CM-2, located approximately 25 feet south of CM-1, was
<br />completed to a depth of 50 feet bgs. During the completion of boring CM-1 groundwater was
<br />encountered at a depth of approximately 90 feet bgs. TPHg was detected above the RL in all
<br />eight soil samples collected from boring CM-1, including a maximum detection reported
<br />concentration of 15,000 mg/kg in the sample collected from 50 feet bgs. Boring CM-2 yielded
<br />TPHg above the laboratory RL in one of four analyzed soil samples at a concentration of 590
<br />mg/kg in the sample collected from 50 feet bgs (UEC, 2001).
<br />In addition, during the August 2001 environmental investigation one grab groundwater sample
<br />was collected from boring CM-1 and analyzed for TPHg, BTEX compounds, methyl tertiary butyl
<br />alcohol (MtBE), tertiary butyl alcohol (TBA), diisopropyl ether (DIPE), ethyl tertiary butyl ether
<br />(EtBE), tertiary amyl methyl ether (TAME), EDB, and 1,2-dichloroethene (1,2-DCA) [7-
<br />Oxygenates]. TPHg, BTEX compounds, and TBA were detected above the corresponding RLs
<br />at concentrations of 62,000 micrograms per liter (pg/L), 5,500 pg/L, 10,000 pg/L, 2,900 pg/L,
<br />8,300 pg/L, and 230 pg/L, respectively (UEC, 2001). No other analytes were detected above
<br />the corresponding RLs
<br />A site investigation was completed during the fourth quarter 2011 and first quarter 2012 that
<br />included the installation of five monitoring wells MW-1 through MW-5, sensitive receptor survey,
<br />and domestic well sampling. Petroleum hydrocarbon compounds were detected in monitoring
<br />and domestic wells during investigation activities. Results are presented in SGI's Site
<br />Investigation Report and Site Investigation Work Plan (SGI, 2012).
<br />An additional site investigation was performed between October 29 and November 1, 2012, which
<br />included the installation of two monitoring wells, MW-6 and MW-7 (Figure 2), and the completion of
<br />two soil borings. Two soil samples were collected from each soil boring and monitoring well and
<br />grab groundwater samples were collected from the soil borings. Results are presented in SGI's
<br />Site Investigation / Fourth Quarter 2012 Groundwater Monitoring and Sampling Report dated
<br />February 8, 2013 (SGI, 2013a). Historical detections of 1,2-DCA in the domestic well located at
<br />10967 Copperopolis Road resulted in the installation of a granular activated carbon (GAG)
<br />wellhead treatment system. Installation activities are presented in SGI's memorandum entitled,
<br />10967 Copperopolis Rd., Stockton, California — Wellhead Treatment (SGI, 2013b).
<br />On March 31, 2014, SGI completed a vertical groundwater investigation near the former USTs.
<br />Results are presented in SGI's Further Site Investigation / First Quarter 2014 Groundwater
<br />Monitoring and Sampling Report (SGI, 2014a) and indicate concentrations of petroleum
<br />hydrocarbons decrease with depth directly adjacent to the former USTs and do not exceed
<br />groundwater ESLs at depths at or below 139 feet bgs.
<br />In April 2015, SGI completed an off-site investigation to delineate the lateral and vertical extent of
<br />petroleum hydrocarbon constituents downgradient on the domestic supply well located at
<br />2-2 The Source Group, Inc.
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