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` DEC 2 0 2000 <br /> Wright a.,r <br /> Environmental <br /> Services, Inc. <br /> December 19, 2000 <br /> Project No;-4184.I ; `Cbogtruction ♦ Engineering ♦ Remediation <br /> U � . , L - 7 . <br /> M&M Builders Supply <br /> P. O. Box 1107 <br /> Tracy, CA 95378-1107 <br /> Attn.: Mr. Shawn Kelly <br /> Re: Clarification for Exploratory Drilling <br /> Additional Site Assessment Investigation, <br /> and Groundwater Monitoring Well Installation <br /> M&M Builders, 8111 West 11th Street, Tracy, CA; <br /> PHS-EHD Site Code 1530 <br /> Dear Mr. Kelly, <br /> Wright Environmental Services, Inc. has prepared this letter to clarify points in the <br /> proposal dated October 16, 2000 for additional assessment at the above referenced site. <br /> This letter was requested by the San Joaquin County Public Health Service, Environmental <br /> Health Division(PHS-EHD) in their letter dated December 6, 2000. <br /> Estimated Depths of Borehole Exploratory Drilling <br /> The estimated depth of exploratory boring drilling is about 26 feet± for the vertical and <br /> lateral definition of groundwater. This estimated depth is selected because; <br /> • Soil samples collected at the 25- to 26-foot± depth under the former tank pits showed <br /> that contaminants were not detected with the exception of 1.4 milligrams per kilogram <br /> of Total Petroleum Hydrocarbons as Diesel TPHD. Volatile fuel components, <br /> including Methyl-Tert-Butyl Ether(MTBE) were not detected in these deeper samples. <br /> In our opinion, this defines the vertical groundwater contaminant extent. The lateral <br /> groundwater needs additional assessment. The additional borings will be advanced to <br /> 26-feet±to locate this working aquitard strata. <br /> • The soil stratigraphy at the 25-to 26-foot± depth was logged as Sandy Silt and Sandy <br /> Clay (the interpreted sandy aquifer strata occur from about 10- to 24-feet±). These <br /> strata are assumed to form the "working aquitard" wherein the boreholes were <br /> advanced to this depth encountering less conductive strata than those above it. Note <br /> that the term"aquitard" is defined as a leaky confining bed(AGI, 1987). Our previous <br /> experience has shown that it is prudent to advance boreholes to the minimum depth <br /> based on field observations to prevent possible additional leakage through over- <br /> advancement. Based upon the aforementioned chemical data, this choice for the <br /> aquitard for monitoring well construction and screening seems prudent. <br /> • Previous borings B-3, B-4 and B-5 were advanced to about 20-feet, where flowing <br /> conditions halted drilling. The additional boreholes will be advanced to the 26-foot <br /> depth to search for the presence of the aquitard(that is,to 26 feet±). If field conditions <br /> indicate continued advancement of a borehole during the next phase of work, the <br /> logging geologist will make a field decision to continue based upon the field <br /> observations. <br /> 67 E. 10th Street • Tracy,CA 95376 <br /> 209.833.0758 • Fax 209.832.5152 <br /> wright@inreach.com Lic.#651501 A-B HazMat Page 1 Uwebsit http://home.inreach.comlwright <br />