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CTO togicaI Technics Inc Page 5 3`d Quarter 2005 Groundwater Monitoring Report Project No 507 2 October 31,2005 ' 2.0 FINDINGS AND DISCUSSION The results of the groundwater sample analyses indicate the following • Wells MW-1, MW-2 and MW-3 remain free of detectable contamination • MW-4, MW-5 and MW-9 have significant BTEX and TPH-G contamination ' • MW-6 contains low levels of BTEX, TPH-G & MTBE concentrations • MW-8 has minor TPH-G & BTEX contamination ' • Water table well MW-7 did not contain BTEX or TPH-G concentrations above the laboratory reporting limits but it did contain 12 [tgll MTBE The well has intermittently contained MTBE since its installation in May 2001 The source of this contamination may be surface infiltration from unpaved areas and from the open storm water drainage ditch traversing the front of the parcel • Water table well MW-10 did not contain contaminant concentrations above the laboratory reporting limits since February 2002 • Deep well MW-109 did not contain contaminants above the laboratory reporting lirruts ' for the ninth consecutive event The reduction in contaminant concentrations from the first sampling event on June 1, 2001 is noted and sufficient monitoring has been performed to conclude that it was probably a drilling artifact or the bottom of the groundwater plume • Figure 4 illustrates the relationship between groundwater elevation and TPH-G concentrations in well MW-9 (located in the core of the plume) An inverse trend was consistent for the first four monitoring events, and then it was parallel between March 2001 and December 2002, but since has had a variable relationship Trend lines added to the data in Figure 4 show that as the groundwater elevation has lowered since 1999, the ' concentration of TPH-G has increased This probably indicates that concentration is directly related to groundwater level at the site • Figure 5 illustrates the relationship between groundwater elevation and TPH-G concentrations in well MW-5 (located up/cross gradient of the core of the plume) Trend lines added to the data in Figure 5 show that as the groundwater elevation has lowered ' since 1999 that the concentration of TPH-G has also decreased • Figure 6 indicates an inconsistent relationship between groundwater elevation and contaminant concentrations in well MW-6 ' • The groundwater gradient is relatively flat and the direction of groundwater flow has varied during the course of the investigation • Oxidation-Reduction Potential (ORP) and Dissolved Oxygen (DO) were measured (Table t4) and the results suggest that nine wells are either in the core of the containination plume or are immediately down gradient from the plume and within the halo of reaction depleted water caused by biodegradation of the contaminants e Figure 7 is a contour map indicating the TPH-G concentrations on August 19, 2005 The groundwater plume is localized in the vicinity of the former UST The bulls-eye pattern to the TPH-G contour map in Figure 7 shows that the center of the plume has not moved