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3anuary 29 1999 <br /> Esti 205513 Q53 Tosco 75 srrvtce Station 58$6 5wckwn Caiitornia <br /> adjacent t to catch barns, drilling four soil borings, and constri-icting dual completion groundwater <br /> Q l�iW4SlD through 11,iVi{75fD) at discreet depths in tboring samples also <br /> 1The datade <br />• <br /> monitoring wells and analyses <br /> associated well development and <br /> indicated the ffollOw ng of soil an groundwater <br /> obtained during the investigation method detection <br /> Residual hydrocarbons were not <br /> detected <br /> ad actin or above <br /> hree on-site catch basins located ear the m) <br /> lttntts to soil samples collected fromarts per mi (ppm) <br /> g q ppm total extractable <br /> pump Islands (see Plate 2) exceptfor mass gasoline (TPPHum c0fleentra g)tions. of 3 p <br /> total purgeable petroleum hydrocarbonsm MTBE <br /> petroleum hydrocarbons as diesel (TEPHd), and 12 pQ <br /> Residual hydrocarbons in soil appear to have been delineated beneath the site tic <br /> 1997, static <br /> Groundwater was encountered at approximately 9 to 14 ft bps During May approximately b to <br /> groundwater elevations in the groundwater monitoring wells ranged from <br /> alculated <br /> draulic <br /> 95ftbgere <br /> s and the groundwater gradient was towards the southwest <br /> l u he same in the shallow yand deep <br /> gradient of a 0Q2 draulncco ter elevations w <br /> mmunication between the two depths <br /> wells, indicating by and lone <br /> The lateral and vertical extent of TPPHg and th the SiteolConcentrat ons of MTB were <br /> (BTEX) appear to have been delineated beneath <br /> the south and southwest based on the initial <br /> delineated in each direction except towards <br /> sampling of wells MW4SJD through MW75JD <br /> of the investigation, ERI submitted a Worst plana included <br /> additional and <br /> Based on the results Previous investigations, 2) performing <br /> reviewing available MTBE data from p 3 drilling three soil <br /> groundwater <br /> monitoring and sampling events and interpreting the <br /> ons(i€necessary),al)ate thegextent a <br /> dissolved MTBE in groundwater and select additional werotainin locations <br /> permit(s) and access agreement(s), <br /> borings adjacent to former catch Cbectnng sodsample appropriate <br /> groundwater monitoring well(s), <br /> drilling off-site soil boring(s), cot satiii groundwater samples, and analyzing selected soil <br /> the new well(s), g g <br /> developing and purging a report <br /> and groundwater samples, and 5) preparing erform a detailed <br /> plan requested Tosca complete the fallowing 1) p <br /> The County response to the work p q <br /> site assessment to evaluate the lateral and vertical extent of MTogEdwa groundwater samples fand e seven <br /> these <br /> Regional Nater Quality Control Board Central <br /> compounds have migrated off-site, and to addition, analyze and well <br /> oxygenated compounds identified m the California Rem perform a conduit study <br /> Valley Region (Regional Board) document dated July 18, 1.99 7, 2) <br /> facilities that may provide potential theprevicinity ntity of the s tete and 4) and <br /> survey to identify undergroundbeneath and in approximate time <br /> constituent migration, 3) characterize hydrogeology <br /> identify the source(s) <br /> of MTBE detected in groundwater beneath the site and the <br /> frame of MTBE/additives release and history durn datedThe <br /> request of Tosco, ERI submitted the Work Pian enn t on(and hiv <br /> addendum addressed the directivee Ligation ougust 8, 9 soil and <br /> At the req <br /> for a full dimensional d <br /> 2 <br />