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T <br /> ,BC&D Properties <br /> Report, MW Installation and Monitoring <br /> Project No. 8.1.2 I <br /> December 17, 1992 <br /> ` Page 6 <br /> I <br /> u decrease has taken place over the past five years, from September 1987 to <br /> November 1992. <br /> I 4.2 Recommendations <br /> In light of the low levels of contamination and the natural attenuation of <br /> hydrocarbons occurring in the shallow aquifer being monitored at this site, GTI <br /> recommends that the frequency of groundwater monitoring by reduced to one <br /> annual event to take place during the spring (anticipated high water time of <br /> year). This monitoring event would include testing the four wells for TPH- # <br /> Gasoline and BTEX and measure the groundwater level in each well for <br /> groundwater gradient calculations. F <br /> A • k <br /> } <br /> The goal of reducing the frequency of groundwater monitoring is to reduce the <br /> ;costs of the corrective action program as we allow natural biodegradation to <br /> remove the hydrocarbons from the site. <br /> 5.0 QUALITY ASSURANCE PROGRAM <br /> The following measures were taken to ensure that a high quality study was <br /> conducted and that cross contamination did not occur. <br /> i <br /> 5.1 Equipment <br /> i <br /> I Wells were drilled with a 10.25 (OD) hollow stem continuous flight augers, <br /> owned and operated by Osterberg and Stewart, Inc. (contractor's license #446670) <br /> of Modesto. Soil samples were collected using a 2.0 (ID) modified California split ` <br /> spoon sampler lined with brass sample tubes. f <br /> 5.2 Boring Log <br /> A detailed log was made of each well boring. The information noted includes: <br /> sample depths, blow counts, horizons of detectable contamination (detected by <br /> field methods), soil classification utilizing the Unified Soil Classification System <br /> and sediment description (color, texture, composition, hardness, moisture <br /> content, and post-depositional changes that have occurred in the sediments). f <br /> II4 <br /> ,r I <br /> �' II <br /> I <br />