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IFirrmtn& Helm 5 M Irma -8ec and Quarter 1998 Groundw iter Monitoring Auguq 11 1998 ' Page 7 4 SUMMARY/CONCLUSIONS I he gasolnie oa-ygenatc M [BE %gas cictec,ted in samples coilec,ted from monitor wells MW-2 and MW-3 at conLentrations of 3 000 lig/l and 1 800 ugd respectively MTBE was detected at a much loticr umcentration of 2 3 µg/l ui the ,Ample, cnllc.eted from MW-4 No oxygentates were detected in the sample collected from MW-1 TPH-G (0 5 Ing/1) buizcne (38 pg/[), etliylbc.nzene (30 jig/]), and X)lencs (42 lig/I) %sere detected III the. Sample L0llected from MW-4 No TPI f-G or 13 I EX constrtucnts were, reported to be present 1n any of the other wells I he detection limit-, for I PI I-G and 13 FEX were raised for the ,amplcs collected from MW-2 and MW-3 due to elevated M I BE C.oneentrations in those, samples Laboratory anaINIt"il resultS of the gIOLindwatei samples eoileeted during the See�ond quarter 1998 monitoring ' event were; generally Lunslstent with historical quarterly groundwater analytical data The MTRF e.oneentration In the. ,ame. ple nllccted from MW-2 dLLreased significantly, rLversing a trend of increasing coi7ecntrations associated Frith previous quarterly monitoring reS111ts ' Lvaluation of intruISIL bioremediation parameter, is best done using a data set that includes as much as one year of monitoring Additional monitoring of the intrinsic bioremediation parameters should COnElnuc. to evaluate the Ipotential for intrinsic bioremediation at the site Groundwater elevatioii measurements collected at the site on June 26, 1998, indicated that the average depth to ' groundwater was approximately 5 feet bgs which is consistent with groundwater elevation measurements collected on March 27, 1998 (rroundwater elevation contours for June 26, 1998, indicate that the groundwater graditnt at the Site is generally consistent with that measured on September 18, 1997, December 31, 1997, and March 27, ]99K In a te.icphone corivcI-sation on March 23, 1998 Mr Ronald Rowc, of the San Joaquin County Public Health Services/1 iivironmental Ilealth I)c,partment (PIIS/I 111)) sndlcated that based on his review of the proJect to date, he was requesting quarterly groundwater monitoring continue at thi, site and a work plan be prepared to conduct quarterly surface water sampling and additional investigation of the gasoline oxygenate/additive plume east of site monitor well MW-2 A work plan, as described above, was prepared by Condor on May 27, 1998 In correspondence dated July 1, 1998, Mr Rowe conditionally approved the work plan and requested an addendum On July 9, 1998, Condor submitted an Addendum to the Work Plan The scope of services outlined in the addendum included • Locating the, drinking water source for I ILrman & Helen's Marina + Sampling the, drinking water source for laboratory analysis of gasoline additives/oxygenates by EPA Method 8260 • Completing a survey ofthe area to identify users and receptors of ground or surface water within a 1,000 feet radius of the site • Installation of nine soil borings to further evaluate the eastern extent of the contaminant plume On July 27, 1998, Mr Rowe provided authorization of the work plan addendum and requested that the pre- treatment and post-treatment water supply associated with the drinking water system at the site be sampled and analysed by EPA methods approved for surface drinking water, including analysis for MTBE, DIPS, ETBE, TAME, Ethanol, and tertiary-butanol I LJ CONDOR