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•rte <br /> Fit <br /> LATHROP PROPERTY <br /> WKA No. 1164.02 <br /> January 30, 1992 <br /> Page 10 <br /> placed one monitoring well{W3}at the location on the property at which we encountered the <br /> highest concentration of soils contamination by petroleum hydrocarbons;this location is in the <br /> central area of the backfilled excavation.,Two additional wells were constructed northerly <br /> from W3 under the presumption, based on regional ground water flow, that at least one or <br /> the wells would be dov:ngradient from the suspect farmer LIST(s) location. <br /> f Well Construction <br /> z Each of the three wells was constructed of four-inch-diameter Schedule 40 PVC casing to a <br /> total d6pth of 21 Jeet, having a 0.20-inch slot size, screened interval from 21 to 11 feet.. <br /> i a Subsurface soil samples were collected at maximum five foot intervals during drilling and from <br /> the bottom of the boreholes. Given the lack of visual and olfactory field evidence of <br /> petroleum hydrocarbon soils contamination ,it the well locations, one sample from each <br /> �h borehole with the highest potential to be contam;hated was submitted to the analytical <br /> laboratory, as approved by San Joaquin County personnel. The soil samples obtained during <br /> well construction dobtained non-detectable concentrations_ of BTXBcE:and TPi•1 as gasoline or <br /> diesel.(Table 2 and Appendix C): <br /> a One five-gallon bucket of bentonite pellets was distributed around blank caang during the <br /> construction of each well, resulting in a bentonite seal from 8 to 6 feet bgs. The sand filter <br /> pack axtended around blank casing three feet above the top end of the slotted casing interval. <br /> Each well required from 3-112 to 4-112 100-lbs. bags of No. 3 Monterey Sand for its filter <br /> pack, which extended from 21 to 8 feet bgs. The wells were grouted from the depth of the <br /> bentonite seal, which was presaturated with potable water prior to grouting, to within one- <br /> foot of the well cover. )ncrete was poured from the upper level of grout to slightly above <br /> existing site grade at each well location. W 1 and W2 were set with Christy-box well covers; <br /> concrete was finished such that-ainwater will drain away from the well locations. An above- <br /> ground monument, also set in connrets, was used to finish W3. Each wei! was fitted with <br /> locking well caps. Plates 3 through 6 are monitoring well logs. <br /> Each of the three wells was developed on the day following installation (September 4, 1391 <br /> by the drillers, Spectrum Exploration, Inc. <br /> A reference mark was inscribed on the northerly side of the tap edge of the PVC well casings. <br /> The reference marks were surveyed by John M.Lopes, Registered Civil Engineer No'..16705, <br /> WALLACE•KUHL - - <br /> 4 Fr ASSOCIATES INC, <br /> r <br />