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Mr. Barton • •
<br /> January 9, 2015
<br /> Page 2 of 5
<br /> milligrams per kilogram (mg/kg). The excavated soil was subsequently returned to the
<br /> excavation, and no investigation was performed (UEC, 2001).
<br /> In October 1995, approximately 40 cubic yards of hydrocarbon-affected soil was excavated.
<br /> The excavation reportedly reached depths between 11 and 13 feet bgs. A soil sample collected
<br /> from the bottom of the excavation contained TPHg, benzene, toluene, ethyl benzene, and total
<br /> xylenes at concentrations of 14,000 mg/kg, <0.005 mg/kg (non-detect), 37 mg/kg, 78 mg/kg,
<br /> and 340 mg/kg, respectively. The excavation was backfilled with clean soil and pea gravel
<br /> (UEC, 1995).
<br /> In August 2001, two soil borings (CM-1 and CM-2) were completed on-Site at locations shown
<br /> on Figure 2. CM-1 and CM-2 were advanced to 90 and 50 feet bgs, respectively. TPHg was
<br /> detected in all eight soil samples collected from CM-1 up to a maximum concentration of 15,000
<br /> mg/kg in the sample collected from 50 feet bgs. TPHg was detected in CM-2 in one of four
<br /> analyzed soil samples at 590 mg/kg in the sample collected at 50 feet bgs (UEC, 2001).
<br /> Groundwater was encountered in CM-1 at a depth of approximately 90 feet bgs. A grab
<br /> groundwater sample was collected from CM-1 and analyzed for TPHg, BTEX, MtBE, tertiary
<br /> butyl alcohol (TBA), diisopropyl ether (DIPE), ethyl tertiary butyl ether (EtBE), and tertiary amyl
<br /> methyl ether (TAME) and lead scavengers EDB and 1,2-dichloroethene (1,2-DCA). TPHg,
<br /> BTEX, and TBA were detected above the laboratory reporting limits at concentrations of 62,000
<br /> micrograms per liter (Ng/L), 5,500 pg/L, 10,000 pg/L, 2,900 pg/L, 8,300 pg/L, and 230 pg/L,
<br /> respectively. No other analytes were detected above the laboratory reporting limits (UEC,
<br /> 2001).
<br /> In 2011, SGI was contracted by DGS under the EAR Program to further investigate and
<br /> subsequently remediate the Site.
<br /> Initial site investigation activities conducted by SGI were completed during the fourth quarter
<br /> 2011 and first quarter 2012 that included the installation of five monitoring wells (MW-1 through
<br /> MW-5), sensitive receptor survey, and domestic well sampling. Petroleum hydrocarbons were
<br /> detected in soil and groundwater samples collected from downgradient monitoring wells MW-1
<br /> and MW-2 and on-Site monitoring well MW-5. TPHg in soil and groundwater was detected at a
<br /> maximum concentration of 2,700 mg/kg and 2,300 pg/L in MW-2, respectively. A Sensitive
<br /> Receptor Survey (SRS) identified six domestic wells bordering the Site. Subsequent sampling
<br /> yielded a detection of 1,2-DCA at a concentration of 10 pg/L in the down-gradient domestic well
<br /> located at 10967 Copperopolis Road (SGI, 2012a).
<br /> To help define the lateral extent of impacted groundwater an investigation was performed between
<br /> October 29 and November 1, 2012, which included the installation of two monitoring wells (MW-6
<br /> and MW-7) and the completion of two soil borings (SB-1 and SB-2) down gradient of the former
<br /> UST area. Petroleum hydrocarbons were detected in groundwater samples collected from MW-6
<br /> and SB-1, but were generally below the laboratory detection limits in MW-7 and SB-2 (SGI, 2012b).
<br /> Concentrations of 1,2-DCA in domestic well 10967 led to the installation of a granular activated
<br /> The Source Group,Inc.
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