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yeologiral Tecknics!nc Page 6 ' Groundwater Monitoring Report Project No 662 2 December 2,2005 ' activity The DO values are low for all of the sampled wells indicating that the wells are within the halo of reaction depleted water caused by biodegradation 3.0 CONCLUSIONS AND RECOMMENDATIONS ' Conclusions 1 The historical shallow groundwater trend is easterly ' 2 The deeper aquifer direction was to the southwest but additional monitoring is needed to determine trends It is noted that the three wells used for monitoring this level (MW-5, MW-6 &EW-1) are in a fairly linear geometry that should be viewed with caution ' 3 Shallow extraction well EW-2 is located in the former UST excavation and contained moderate MTBE (1330 ug/1) for the event This is only the third discrete sampling data from this well so a trend analysis cannot be made However, data from previous borings ' CPT-3 and CPT-4 indicate that higher concentrations of MTBE (10,000+ µg/1) were present in groundwater beneath the former UST excavation area in December 2003 The ' lower levels noted for the past three events may be a result of the dual phase extraction pilot test performed in December 2004 The pilot test resulted in over 32,000 gallons of extracted groundwater being removed from the subject area 4 Based on previous discrete groundwater sampling, the shallow MTBE groundwater plume does not extend to the down gradient location of MW-5 The CPT-7 boring was advanced adjacent to the MW-5 location and its groundwater sample at 29 feet bgs was ' free of contamination 5 The deeper aquifer MTBE plume is present in well MW-104 and attenuates to the location of MW-5 and MW-6 A sand layer is present at a depth of 38 — 48 feet across ' the site and it appears to act as a preferential pathway for contaminant migration 6 There are low levels of TPH-G, 303 - 330 µgll, present in shallow groundwater beneath the former UST excavation area It is noted that the laboratory reported that the sample ' chromatograms do not match a gasoline standard and result from a single peak within the gasoline range The CPT investigation completed in December 2003 revealed high levels of TPH-G beneath the former UST excavation (CPT-4 22,000 µg/1 TPH-G) As with the MTBE, the decrease in TPH-G concentrations may be a result of the dual phase extraction pilot test that resulted in over 32,000 gallons of extracted groundwater being removed from the subject area ' Recommendations 1 Continue quarterly groundwater monitoring 2 Perform the further soil and groundwater investigation proposed in the Additional Site Characterization Work Plan dated November 30, 2005 3 Perform interim remedial action by installing a high vacuum dual phase extraction unit to ' address the on site contamination Dual phased extraction should be performed on well EW-2 with a separate dedicated groundwater pump on EW--1 The treatment system should include carbon filtration of extracted groundwater to be discharged to City of