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ENGEO <br />Expect Excellence <br />GEOTECHNICAL <br />ENVIRONMENTAL <br />WATER RESOURCES <br />CONSTRUCTION SERVICES <br />Project No. <br />12066.002.000 <br />November 30, 2018 <br />Revised January 22, 2019 <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 />References: 1. ENGEO, Soil Gas Characterization Work Plan, Mountain House Neighborhood A, <br />Units 3 and 4, Central Parkway, Mountain House, California; November 14, 2018. <br />2. ENGEO, Soil Gas Characterization Work Plan Addendum, Mountain House <br />Neighborhood A, Units 3 and 4, Central Parkway, Mountain House, California; <br />January 8, 2019. <br />Dear Ms. Turkette: <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 activities were conducted in accordance with the approved Work Plan with the following <br />revisions: <br />Samples recovered from locations SG-5 through SG-9 were "nested" borings, instead of <br />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. Soil gas sampling locations are shown on Figure 2. <br />The specific base elevation of the petroleum pipeline is unknown; however, based on previous <br />experience, we estimate pipeline trench is approximately 6 to 8 feet below the ground surface. In <br />the western portion of the study area (samples SG-5, SG-11, SG-12), the base of the pipeline is <br />expected to be at an elevation of 154 to 156 feet above mean sea level. For reference, the graded <br />residential pads to the north (approximately 150 feet northeast) are situated at an elevation of <br />148 feet msl (6 to 8 feet below the pipeline). <br />2010 Crow Canyon Place, Suite 250 • San Ramon, CA 94583 • (925) 395-2507 • Fax (888) 279-2698 <br />www.engeo.corn