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Ifcrmdn & IleIen s Matini— Ihird Quarter 2000 (rioundwatei Moruto ring OLlObtr 17 2000 5 St,MMARY/( ON( LL', ONS On SLptember r -'000 ( L)Hdor L()nduLtLd quar-tL11N groundwater and ,urfaL.L water monitor inu at Merman Sc llLlLn S 'Marina I01-atcd at VLnILL fsland I-crry In StoLkton C alltorma I aboratory anaMILal rLSults of the groundwatLt SanrplLS collLLtLd during the third quartLr 2000 inonaormg LVLnt are generally consistent with ' historlLal quartLrly groundwater analytical data (iroundwatei elevation nicasuiLmLnts L01ILLted at thL site on ",LptLmber 7 2000 indiLatLd that thL average depth ' to gmUridwatLr was approximately 6 4 tCCt I)Llow the rriollrtui well and water ,urtacc measuring points (rroundwatLr LILvatfon uintnurs for ScptcmbLr 7 2000 Indicate that the gratindwater gradient at the site is generally conSistcnt with thL historical groundwatei gradient ' Historical laboratory anaMILal rLSults indicate that generally love concentrations of MTI3I' have bLLn prLsert in at least one of the ,urlat c water samples collected during the Surface water sampling events During the first ' quartLr 1999 munitoling Lvent however MTB[ was detected in samples DDN and DDS (980 and 3,500 gg/L, respectivLly) at SignifiLantly higher concentrations than In previous and subsequent monitoring events (with the exception of the first quarter 2000, monitoring event) 1'he historical high concentration of MTBE (4,700 µg/L) I detected in sample DDS was reported in the first quarter, 2000, monitoring event Additionally, the only surface water sample detections of TAME were reported in samples DDN and DDS during the first quarter, 1999, monitoring event During the current monitoring event, MTBb was detected at low concentrations in surface ' water samples DDI ' (1 7 pg/1 ) and IDCW (10 µg/L) The concentration of MTBE in surface water sample IDCW represents an histol ical high for that sample location '. As previously dlsLUSsed in Section 2 Condor has iLcommended additional site Lharacteriration and monitoring rather than an ak tIVL engineered 17CMLdial solution for the site basLd on thL results of UIL Soil and groundwater investigation conducted between 5eptembLr l I and September 13 2000 The results of the soil and gioundwater ' investigation indicated that the MTBh plume generally extended in relatively low concentrations in shallow groundwater beyond the drainage ditch and into the agricultural field to the cast of the site Iso-concentration contours for MTBE: in shallow groundwater are shown m .Figure 6, Appendix A Relatively high MTBE: ' concentrations were present in shallow groundwater to the west of the drainage ditch, southeast of site monitor well MW-2 The concLntration of N4TBL present at the location of DP-5 was approximately three orders of magnitude greater than the concertiation of MTBE at the location of DP-9 This relatively iapid attenuation of MTBk, concentrations Suggested that the MTBE. plume was being tiiincated by the hydraulic influence exerted by ' the island draina(cle channel punrprn�u that oLcui s at the south portion of the site The next quarter ly rr oi_rndwater monitoring event is scheduled to be conducted in December 2000 Please call us at (209) 234-0518 with any questions ' Respectfully submitted CONDOR EARI-1-1 I t_CIINOL S INC �S� ED �EoC—Ak c� IDonald F Ki esse No. 6430 Todd C, Iiafner California Registeied Senior Geologist Geologist 46430 q OF rtL�FOQ� \1 PdiAptojt;as�1412 N& 1 lelen s\Qu iiteily Monitoring Repart512000 0ctoberl3rdQuurt00 doc CONDOR