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ATC Associates Inc. 11.17 Lone Palm Avenue,Suite 201 Modesto,California 95351 209-579-2221 fax:209-579-2225 ASS O C I ATE S INC . Due to the adoption of Resolution No. 2009-0042 by the State Water Resources Control Board (SWRCB), groundwater monitoring and sampling activities were reduced to a modified semiannual/biennial schedule. In a letter dated June 22, 2009, the San Joaquin County EHD requested to collect groundwater samples from wells MW-1, MW-4, MW-5, and MW-8 semi- annually and from all wells at the site biennially. Based on the request,the wells will be sampled using the schedule below. Odd Digit Years Even Digit Years First Quarter Third Ouarter First Quarter Third Quarter MW-1,MW-4, MW-1,MW-4, MW-1, MW-4, All wells MW-5, and MW-8 MW-5, and MW-8 MW-5, and MW-8 Additionally, the EHD granted ATC's request to discontinue analyzing groundwater samples collected from the site for di-isopropyl ether (DIPE), ethyl tertiary-butyl ether (ETBE), 1,2- dichloroethane (1,2-DCA), and 1,2-dibromoethane(EDB). Confirmation groundwater samples were collected from the site to evaluate the lateral and vertical extent of impacted groundwater beneath the site. A soil boring (SB-6) was advanced to first encountered groundwater to evaluate the lateral extent of impacted groundwater northwest of the source area. Two discrete grab groundwater samples (HP-1 and HP-2) were collected using a hydropunch sampling tool in the vicinity of CPT-2. HP-1 was advanced to an approximate depth of 45 feet bgs and HP-2 was advanced to an approximate depth of 70 feet bgs. MTBE was the only analyte of interest detected in the groundwater sample collected from SB-6. None of the analytes of interest were detected in the groundwater samples collected from HP-1 and HP-2. A soil gas study was conducted in September 2010 to evaluate the potential for soil vapor intrusion into the existing commercial structure located on-site. Based on the results of the soil gas study activities, there does not appear to be a risk to human health. SCOPE OF WORK Indoor Air Study ATC proposes to conduct indoor air sampling to evaluate air quality within the structure at the site. The sampling activities will be conducted on a normal business day to collect a representative indoor air samples that are consistent with routine activities associated with the commercial usage of the property. The indoor air sample will be collected using a one liter summa canister equipped with a certified flow control mechanism as provided by the analytical laboratory. The summa canister will collect the indoor air sample over a period of eight to ten hours and will be placed within the breathing zone for most adults, estimated to be approximately three to five feet above the interior floor. ATC will inventory and remove all indoor chemicals at least 48 hours prior to sampling, S:\Environmental\25847\37 Tracy\Reports\Workplans IA Wkpin.doc 3 ATC Associates Inc.