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amec�9 <br /> former chemical storage shed, but detection limits were elevated (500 pg/L) due to <br /> high concentrations of chloroform in the sample (37,600 pg/L). <br /> • Phase 3 (1988): Seven monitoring wells were installed (M-6C, M-8C, M-10A, M- <br /> 1 OB, M-11 A, M-11 B, and M-1 2A). M-1 2A was onsite, near the northwestern corner <br /> of the Decaffeination Building; the other six wells were installed at locations offsite. <br /> Monitoring well M-12Awas sampled in June 1988. TCE, cDCE, and 1,1,1-TCA <br /> were detected at concentrations of 230 pg/L, 33 pg/L, and 84 pg/L, respectively in <br /> groundwater samples taken from M-1 2A. <br /> • Phase 4 (1989): Six offsite monitoring wells (M-6C2, M-81D, M-11C1, M-1 3A, M- <br /> 14A, M-1 4B), two onsite monitoring wells (M-15A, M-1 5B) and three onsite pilot test <br /> wells (EU-1, ED-1, and EI-1) were installed. <br /> • Phase 5 (1989): A well cycling study was conducted to assess the effects of onsite <br /> and offsite groundwater pumping on water levels monitoring wells onsite and close <br /> to the Site. This study showed that the pumping N-1 had the greatest influence on <br /> water levels in well M-6C2, where over one foot of drawdown was observed in <br /> response to pumping at N-1. Twelve offsite monitoring wells were installed in 1989. <br /> An offsite soil vapor survey was conducted at neighboring businesses (Regal <br /> Almond, Ripon Manufacturing and Guntert Steel). The survey involved collecting <br /> soil vapor samples at 35 locations for analysis of TCE, PCE, TCA, benzene, <br /> toluene, ethyl benzene and xylenes. The highest vapor concentration was for TCE <br /> (23 pg/L at a location on the Regal Almond property, west of the Site across <br /> Industrial Avenue). <br /> • Phase 6 (1990): Groundwater monitoring and groundwater flow modeling was <br /> conducted. <br /> • A third soil vapor survey was conducted in 1991, in which 20 soil vapor samples <br /> were collected from a depth of approximately 5 feet bgs at 20 locations on the <br /> former Regal Almond property (now Silverado Building Materials at 460 South <br /> Stockton Avenue). Concentrations of TCE in soil gas samples ranged from 2 - 8 <br /> pg/L at locations near the northwest corner of the property, in the parking lot, near <br /> the railroad spur, and also near the sewer lateral that extended from Regal Almond <br /> to the industrial sewer on Industrial Avenue. One soil gas sample from a location on <br /> the west side of the Regal Almond property was reported to contain cDCE at <br /> 5 pg/L. Former diesel and oil underground storage tank (UST) locations and an <br /> industrial well were also identified on the Regal Almond property. <br /> The Remedial Investigation Report (RI Report) was completed for the Site in 1994 (RUST, <br /> 1994b). Major findings and conclusions from the RI Report were: <br /> • Three major aquifer zones were identified (the Upper Aquifer Zone from the surface <br /> to approximately 120 feet bgs; the Clay Zone from 120 — 200 feet bgs, and the <br /> Lower Aquifer Zone, below 200 feet bgs). <br /> • Flow prior to 1975 was to the southwest, but shifted to the north due to heavy <br /> pumping in the vicinity of the City of Stockton, approximately 20 miles north of <br /> AMEC Geomatrix, Inc. <br /> hDoc_Safe\9000s\9837.005\4000 REGULATORY\SCM_01.30.09\1_text\SCM Report Final.doc 11 <br />