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r <br /> s <br /> r a3255 Mission Blvd Suite B Fremont CA 94539 {4151651-19%A /!eo' GeoS stems <br /> ' May 10, 1987 <br /> AGS Job 86103-2 <br /> 0510QKIR <br /> Mr. Quentin D. Kirsch <br /> 190 East Amber Way <br /> Hanford, CA 93238 <br /> ` Subject: Report of subsurface environmental investigation: soil <br /> borings and well installation at Cardlock Station #27, <br /> 3300 Waterloo road, Stockton, California. <br /> Y Dear Mr. Kirsch: <br /> =4 We have enclosed a copy of our report of an environmental <br /> investigation conducted at the above-referenced site. Six soil <br /> s borings were drilled and four monitoring wells installed during <br /> this investigation. <br /> J <br /> Samples of ground water taken from the four monitoring wells were <br /> analyzed and found to contain hydrocarbons at levels below action <br /> levels established by the California Department of Health <br /> Services for drinking water except in MW-4, which was found to <br /> contain benzene at a concentration of 1. 2 parts per billion <br /> (ppb) . The established drinking water standard for benzene is <br /> 0.7 ppb. Soil samples collected from soil borings were found to <br /> contain low levels of hydrocarbons immediately below the tank <br /> backfill material. <br /> A ground water gradient was calculated which indicates ground <br /> water flow at the time of measurement was to the south. This <br /> direction of flow is not consistent with the easterly direction <br /> previously inferred based on information supplied by the San <br /> Joaquin Local Health District. With your prior approval, a <br /> fourth well was installed directly down-gradient from the tank <br /> cavity. <br /> state and local regulatory agencies may require mitigation of <br /> hydrocarbon contamination at the base of the tank cavity in <br /> conjunction with, or prior to, the proposed in situ lining of the <br /> faulty diesel product storage tank. Periodic monitoring of <br /> ground water would be necessary in order to evaluate the need for <br /> mitigation of the low levels detected. <br /> BQ010990 <br />