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Ar <br /> HORIZON ENVIRONMENTAL INC. <br /> Specialists in Site Assessment.Remedial Testing,Design and Operation <br /> rr� <br /> December 29,2009 � �° <br /> � t <br /> Mr. Michael J. Infurna <br /> San Joaquin County Environmental Health Department <br /> 600 East Main Street <br /> Stockton, California 95202-3029 <br /> Subject: Technical Justification for No Soil Gas )Investigation <br /> Beacon Station No. 3641; LOP Case#: 1125 <br /> 1210 East Hammer Lane, Stockton, California <br /> Mr. Infurna: <br /> At the request of Ultramar, Inc. (Ultramar), Horizon Environmental Inc. (Horizon) has <br /> prepared this technical justification to address the risk of vapor intrusion at the subject site <br /> located in San Joaquin County as shown on Figure 1. In a letter dated 16 November 2009 <br /> (enclosed), the San Joaquin County Environmental Health Department (EHD) advised <br /> Ultramar that the vapor intrusion risk could be addressed by comparison of site conditions to <br /> environmental screening levels (ESLs), and evaluation of site physical characteristics, <br /> exposure pathways and land usage. <br /> Site Description and Background <br /> The site is an operating service station located on the southwest corner of the intersection of <br /> East Hammer Lane and Kathleen Drive in a commercial area and on the north side of a <br /> larger retail center. Structures and installations at the site include a station building, <br /> gasoline dispenser islands under a canopy, and former and existing gasoline underground <br /> storage tanks (USTs) as shown on Figure 2. With the exception of relatively small areas of <br /> planters, the site surface is paved with concrete or asphalt. Site usage is expected to remain <br /> unchanged for the foreseeable future. Surrounding land usage is commercial to the west, <br /> south and east,and residential across Hammer Lane to the north. <br /> Four gasoline USTs and associated dispenser and product lines were excavated and removed <br /> from a common basin at the site in June 1996. The UST basin was over-excavated to 18 feet <br /> below surface grade (bsg) and clean fill was replaced in the basin to approximately 15 feet <br /> bsg. Soil samples collected from borings during subsequent site investigations indicate that <br /> the lateral extent of impacted soil was limited to the UST basin and southwest dispenser <br /> area. Soils encountered in well borings to the depth explored consist predominantly of <br /> sandy silts and clayey silts with subordinate silty sands and sand. Soil analytical data are <br /> summarized in Table 1. <br /> Groundwater was found to be impacted as a result of groundwater sampling from the initial <br /> monitoring well MW-1. Quarterly groundwater monitoring has been performed at the site <br /> 4970 Windplay Drive,#C5 • EI Dorado Hills,CA 95762 • (916)939-2170 • FAX(916)939-2172 <br /> P.O.Box 5283 • Bakersfield,CA 93388 • (661)589-8389 • FAX(661)589-1456 <br />