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s I CLEARWATER G is O U. P, ' I C - I• E,,0- lr]-enfn� �c'Ii[Ce5 ;! The groundwater flow direction observed this quarter.has returned to the northeasterly direction typically observed beneath the site(Figure 3).The groundwater levels are lower than those observed last quarter by approximately three feet. which is typical of this time of year at the site. The extent of dissolved-phase gasoline contamination remains well delineated by the existing monitoring well network (Figure 4). It is noteworthy that contaminant concentrations this quarter are once again significantly lower than pre- remediation levels, and considerably less than those observed iri the previous quarter. This reduction in contaminant concentrations is likely the direct result of active remediation afthe site from October 1998 to September 1999. Sample results indicate that the domestic well continues.tobe free of detectable gasoline hydrocarbon concentrations. The domestic well will continued to monitored on.a quarterly schedule. w Groundwater monitoring data and analytical results are presented in Table 1, and laboratory analytical reports are attached in Appendix C. ii 2.3 Groundwater Monitoring Recommendations'" Results of recent groundwater monitoring indicate that the•S•VE/AS system had a dramatic effect on dissolved-phase contaminant concentrations beneath the site. . Dissolved-phase contaminant concentrations for the plume are down approximately two orders of magnitude since the fourtWquarter 1998. Following shut-down of the"SVE/AS system, groundwater beneath the site will continued to be monitoredfor several quarters to evaluate post-remediation dissolved- phase contaminant trends. The wells will continue to-be monitored in accordance with the schedule previously recommended. Well I.D. Quarterly i'L Annually 1 (1st 2nd 3rd 4th Quarters) 1i Isi uarter) MW-1 DTW,TPHg.BTEX,MTBE MW-2 DTW,TPHg.BTEX.MTBE u I MW-3 DTW TPHe,BTEX,MTBE MW- DTW TPHe,BTEX.MTBE ff MW-5 DTW TPHg.BTEX.MTBE I MW-6 DTW TPHg.BTEX.NITBE MW-7 DTW TPHg,BTEX.MTBE G Domestic Well TPHjZ,BTEX.MTBE 1 Notes: t DTW=depth to water TPHg,BTEX=by EPA Method 8015/8020(modified) ek { MTBE=by EPA Method 8260 } a . k D-107 4Q99 GW&WP Confirmation Borings ! 3 .. November 15, 1999 9