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1 <br /> CIC64ka!7CCluilcs/XC Page 5 <br /> 12"4 Quarter 2005 Groundwater Monitonng Report <br /> Project No 507 2 <br /> 10 June 30,2005 <br /> 1 contained MTBE since its installation in May 2001 The source of this contamination <br /> may be surface infiltration from unpaved areas and from the open storm water drainage <br />' ditch traversing the front of the parcel <br /> • Water table well MW-10 did not contain contaminant concentrations above the laboratory <br /> reporting limits since February 2002 <br /> • Deep well MW-109 did not contain contaminants above the laboratory reporting limits <br /> for the seventh consecutive event The reduction in contaminant concentrations from the <br /> first sampling event on June 1, 2001 is noted and sufficient monitoring has been <br /> performed to conclude that it was probably a drilling artifact or the bottom of the <br /> groundwater plume <br />' • Figure 4 illustrates the relationship between groundwater elevation and TPH-G <br /> concentrations in well MW-9 (located in the core of the plume) An inverse trend was <br /> consistent for the first four monitoring events, and then it was parallel between March <br />' 2001 and December 2002, but since has had a variable relationship Trend lines added to <br /> the data in Figure 4 show that as the groundwater elevation has lowered since 1999, the <br /> concentration of TPH-G has increased This probably indicates that concentration is <br /> directly related to groundwater level at the site <br /> • Figure 5 illustrates the relationship between groundwater elevation and TPH-G <br /> concentrations in well MW-5 (located up/cross gradient of the core of the plume) Trend <br /> lines added to the data in Figure 5 show that as the groundwater elevation has lowered <br /> since 1999 that the concentration of TPH-G has also decreased <br />' • Figure 6 indicates an inconsistent relationship between groundwater elevation and <br /> contaminant concentrations in well MW-6 <br /> • The groundwater gradient is relatively flat and the direction of groundwater flow has <br />' varied during the course of the investigation <br /> • Oxidation-Reduction Potential (ORP) and Dissolved Oxygen (DO) were measured (Table <br /> 4) and the results suggest that eight wells are either in the core of the contamination <br /> plume or are immediately down gradient from the plume and within the halo of reaction <br /> depleted water caused by biodegradation of the contaminants <br /> • Figure 7 is a contour map indicating the TPH-G concentrations on May 27, 2005 The <br />' groundwater plume is localized in the vicinity of the former UST The bulls-eye pattern <br /> to the TPH-G contour map in Figure 7 shows that the center of the plume has not moved <br />' from its source and suggests that contaminant migration may be occurring primarily by <br /> diffusion with a slight influence by advection <br /> 1 <br /> 1 <br />