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4 <br /> ry <br /> M & ASSOCIATES <br /> S <br /> RNVIRONMEWAL t BIVOINURINO SERVICES <br /> Iinl RICHMOND AVE. April 21 , 19807 <br /> BUILDING 1, SUITE 1008 <br /> HOUSTON, TEXAS 770!12-2617 <br /> Mr. Jim Thompson - <br /> Kayo Oil Company <br /> 900 South Cherokee Lane <br /> Lodi , California 95240 <br /> Reference: Recommended Actions for <br /> Groundwater Assessment at the <br /> Cherokee Lodi Service Station <br /> Dear Mr. Thompson: <br /> This letter is to summarize what GMS & Associates has done <br /> to date and what we propose to do to complete a ground water <br /> assessment report for the above referenced facility. <br /> Our review of past geotechnical boring logs, monitor well <br /> construction records, water level data and water quality data <br /> revealed inconsistencies that could not be explained. We then ran <br /> cased hole electric logs on all wells to obtain a non-subjective, <br /> reproducible subsurface stratigraphic record for each well . The <br /> electric logging was very successful . <br /> The electric logs showed the entire site is underlain by a <br /> shallow, usually dry silty sand which in turn is underlain by a <br /> tight , clayey silt which acts as a barrier to downward migration <br /> of water in the upper zone. Under this barrier zone is a <br /> relatively clean sand that is water bearing. This lower zone is <br /> probably under unconfined or water table conditions but that can <br /> not be determined with certainty at the present time due to the <br /> way many of the wells were constructed. <br /> Comparison of the monitor well construction records and the <br /> electric logs confirmed our early suspicions. Several of the <br /> monitor wells have been drilled, screened and gravel packed <br /> across the barrier zone. These monitor wells are acting as <br /> vertical drains and are injecting by gravity flow water that may <br /> have been impacted by accidental hydrocarbon releases and that <br /> would normally perch above the tight clayey silt. Many of the <br /> monitor wells also had fill in the bottom of the screens, in <br /> places as much as 10 feet. This is due to the well screen and <br /> gravel pack not being sized properly to match the geologic <br /> formation being screened. Also many of the monitor wells were not <br /> drilled deep enough or were drilled just into the top of the <br /> lower water bearing zone but were plugged with fill . These two <br /> types of monitor wells can not provide reliable water level data <br /> nor can the monitor wells that are screened across the barrier <br /> zone. <br /> ( 713 )498 - 3302 <br />