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San Joaquin County - Public Works 1810 E. Hazelton Avenue, Stockton, CA Site Background through February 2017 Page 2 of 5 On May 20, 2005, Ramage Environmental published Well Installation and Groundwater Monitoring Report, which documented the installation of one additional groundwater monitoring well (MW-7) and two remedial feasibility test wells (SVE-1A/B/C and AS-1/SVE-2B). Ramage Environmental continued to conduct quarterly groundwater sampling and publishing groundwater monitoring reports through the second quarter of 2010. All measurements and data dated prior to June 2010 were provided by Ramage Environmental. Condor Earth Technologies, Inc. (Condor) is not responsible for the accuracy and completeness of information collected and developed by others. On April 29, 2011, Condor collected field inspection samples, groundwater parameters, and groundwater samples from MW-1 through MW-7 for the second quarter 2011 semi-annual groundwater monitoring event. Between May 14, 2010, and April 29, 2011, the groundwater surface in the seven monitoring wells rose an average of 2.15 feet, the groundwater gradient decreased from 0.0024 feet per foot (ft/ft) to 0.0018 ft/ft, and the direction of groundwater flow remained toward the northeast. The groundwater flow direction and gradient appear to be consistent with recent historical trends. Between May 14, 2010, and April 29, 2011, the concentrations of gasoline compounds in groundwater were generally similar in MW-1 and generally decreased in MW-2 and MW-4. The concentration of methyl tertiary-butyl ether (MTBE) in the down-gradient well MW-4 decreased from 29.8 micrograms per liter (4/1) to 29 lag/l. The concentration of MTBE in MW-4 has decreased in each of the last seven sampling events. Gasoline hydrocarbons were concentrated near MW-1 and decreased in concentration with distance from the source area. The lateral extents of TPH-G and benzene appeared to be defined by the four perimeter wells MW-3, MW-4, MW-5 and MW-7 and the lateral extent of MTBE in groundwater appeared to be mostly defined, except in the down-gradient direction. Condor recommended that the remedial feasibility testing and vertical investigation tasks be completed. Condor also recommended that groundwater monitoring continue under the following revised semi- annual schedule: MW-1, MW-2, and MW-4 (semi-annually), MW-6 (annually), and MW-3, MW-5, and MW-7 (every two years). On June 9 and 10, 2011, Condor conducted an air sparge and soil vapor extraction pilot test with the approval and oversight of the San Joaquin County Environmental Health Department (SJCEHD). The two-day test included soil vapor extraction tests at the wells SVE-1A, SVE-1B, and SVE-2B, a longer term test at MW-1, and an air sparge and soil vapor extraction test at MW-1. The results of the SVE pilot test indicated that vapor extraction flow rates of 63 to 81 scfm can be achieved and maintained with equipment similar to that used in the test. Condor estimated the radius of influence for SVE wells was approximately 50 feet. The hydrocarbon extraction rate was highest at MW-1 (10 pounds per hour), and SVE-1B had the highest extraction rate (2.5 pounds per hour) among the SVE wells. Condor estimates the radius of influence for air sparge well AS-1 is approximately 30 feet. The air sparge pilot test did not indicate that air sparging would increase the SVE hydrocarbon extraction rate, but it did indicate that air sparging would be effective for decreasing groundwater hydrocarbon concentrations in the vicinity of the air sparge well. The results of the pilot test were included in the Air Sparge/ Soil Vapor Extraction Pilot Test Report June 2011, dated January 20, 2012. Between April 29, 2011, and November 3, 2011, the groundwater surface in the seven monitoring wells raised an average of 0.82 feet, the groundwater gradient remained unchanged at 0.0018 ft/ft, and the