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ENGEO <br />Expect Excellence <br />GEOTECHNICAL <br />ENVIRONMENTAL <br />WATER RESOURCES <br />CONSTRUCTION SERVICES <br /> <br />Project No. <br />12066.002.000 <br />November 30, 2018 <br />Ms. Linda Turkette <br />San Joaquin County Environmental Health Department <br />1868 E HazeIton Ave <br />Stockton, CA 95205 <br />Subject: Mountain House Neighborhood A, Units 3 and 4 <br />Central Parkway <br />Mountain House, California <br />SOIL GAS CHARACTERIZATION REPORT <br />Reference: ENGEO, Soil Gas Characterization Work Plan, Mountain House Neighborhood A, <br />Units 3 and 4, Central Parkway, Mountain House, California; November 14, 2018. <br />We are pleased to submit the findings from our soil gas sampling conducted at the subject <br />property (Property) located in Mountain House, California. The purpose of sampling was to <br />evaluate potential soil gas concentrations associated with the existing onsite petroleum pipeline. <br />Sampling was conducted in accordance with the approved Work Plan with the following revisions: <br />Samples were recovered from "nested" borings, instead of collocated borings. <br />Samples were not recovered from location SG-10, due to constraints with a PG&E <br />high-pressure gas transmission pipeline. <br />SITE DESCRIPTION <br />The Property is located east of South Central Parkway, in Mountain House, San Joaquin County, <br />California (Figure 1). The Property consists of undeveloped residential lots, appurtenant streets, <br />and a proposed community park. Previous environmental investigations have identified <br />subsurface impacts resulting from a petroleum release associated with the Chevron (Crimson) <br />pipeline. The sample area consisted of five sample locations, located along the northeastern side <br />of the petroleum pipeline (Figure 2). <br />SITE CHARACTERIZATION <br />Soil Gas Sampling <br />Field sampling activities were performed on November 20, 2018, which consisted of 10 soil gas <br />samples at five locations along the petroleum pipeline. <br />Ten soil gas samples were collected from temporary nested well points. Samples were collected <br />from a depth of approximately 5 and 10 feet below the ground surface (bgs). The soil gas samples <br />were collected from the temporary probes advanced with a Geoprobee direct push rig and <br />constructed in general accordance with the Department of Toxic Substances Control (DTSC) <br />Final Advisory Active Soil Gas Investigations (April 2012) and under permit from the San Joaquin <br />County Environmental Health Department. Figure 3 provides the typical nested soil gas well <br />detail. <br />2010 Crow Canyon Place, Suite 250 • San Ramon, CA 94583 • (925) 395-2507 • Fax (888) 279-2698 <br />www.engeo.com