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4 Brusca File No. 137 - Page 2 May 2, 2018 Murphy Parkway Property Soil Gas Monitoring 3 , �{l131111►117 The approximate 48 -acre subject parcel is located about 500 feet easterly of Murphy Parkway and about 1,500 feet southerly of East Louise Avenue in a commercial and industrial area of Lathrop, San Joaquin County, California (See Plate 1, Vicinity Map). The subject property is currently vacant/undeveloped land. Development of the property is planned, including the construction of a large light-industrial/warehouse building and associated pavements. The general layout of the planned development is shown on Plate 2, Site Map. The lead agency overseeing environmental conditions at the site is the San Joaquin County Environmental Health Department (SJCEHD). CalRecycle and the Central Valley Regional Water Quality Control Board (CVRWQCB) also have been involved with review of site conditions. Discussions with these agencies have indicated that initiation of a soil gas monitoring program is required in conjunction with clearance/approval of the property for development due to the presence of uncharacterized wastes that reportedly exist offsite to the west of the subject property (property formerly occupied by a cogeneration facility). As requested by the SJCEHD our firm prepared a Soil Gas Monitoring Workplan dated August 10, 2017.1 Upon review, The SJCEHD requested minor modifications to the Workplan, and we prepared an Addendum to the Workplan dated November 7, 2017. Z The required soil gas monitoring program consists of monthly monitoring for a period of one year, and quarterly monitoring for a period of four years thereafter. The SJCEHD indicated approval of the monitoring program via email on November 8, 2017. The soil gas monitoring wells (identified as SGMW1 and SGMW2) were installed on January 16, 2018; the locations of the wells are shown on Plates 2 and 3.3 SOIL GAS MONITORING/SAMPLING Soil gas monitoring/sampling was performed at the site on April 17, 2018. At that time, the soil gas monitoring wells were inspected to confirm they were sound and without damage. Prior to sample collection, each well was screened with a portable gas indicator (GEM 2000) connected to the sampling ports on the wells. Screening measurements (including methane percentage, carbon dioxide percentage, oxygen percentage, and hydrogen sulfide concentration) were recorded and are presented on the attached Table I. As shown on Table 1, methane was not detected in either of the soil gas monitoring wells via field screening. Following screening, laboratory -provided sampling containers (one -liter Summa canisters) were attached to -the sampling ports on the wells for the collection of soil gas samples, and soil gas samples were collected from each well. 1 Brusca Associates, Inc.; "Soil Gas Monitoring Workplan, Murphy Parkway Property, APN 198-012-009, 17100 Murphy Parkway, Lathrop, California"; August 10, 2017. 2 Brusca Associates, Inc.; "Addendum to Soil Gas Monitoring Workplan, Murphy Parkway Property, APN 198-012- 009, 17100 Murphy Parkway, Lathrop, California"; November 7, 2017. 3 Brusca Associates, Inc.; "Soil Gas Monitoring Wells Installation, Murphy Parkway Property, APN 198-012-009, 17100 Murphy Parkway, Lathrop, California"; February 12, 2018.