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Geological Tecluucs lac Page 6 Groundwater Momtonng Report Project No 723 2 October 29,2004 ' 3 Benzene • The shallow wells contained benzene concentrations ranging t0 3 - 369 ug/1 o The highest level of benzene was detected in well MW-5 that is located cross gradient of the former dispenser island o Well MW-9 is clean and defines the up gradient extent of the plume. ' o Down gradient well MW-8 contained 8 6 ug/1 benzene • The intermediate wells contained benzene concentrations ranging c0 3 — 13,100 ug/1 o The highest level of benzene was detected in well MW-3 that is located in the core of the gasoline plume o Well MW-109 is clean and defines the up gradient extent of the plume o Down gradient well MW-108 contained 9 8 ug/1 benzene • The deep wells contained benzene concentrations ranging<0 3 — 16 8 ug/1 o The highest level of benzene was detected in well MW-208 that is located down gradient of the former dispenser island o Well MW-209 is clean and defines the up gradient extent of the plume ' The distribution of groundwater contaminants is summarized as follows (Note The Isoconcentration contours are generated utilizing the SURFER® computer modeling program We recognize that computer generated contour maps do not provide the most accurate representation of what is taking place in the field However, even hand- contoured map at best provide a shadow of reality Both need to be looked at as interpretation, not reality) 1 TPH-G • Figure 4 illustrates the distribution of TPH-G in the shallow wells A localized high is centered in well MW-5 that attenuates to non-detectable levels in wells MW-7 & ' MW-9 The plume also attenuates to the east in the location of MW-8 • Figure 5 illustrates the distribution of TPH-G in the intermediate wells A localized ' high is centered in well MW-3 that attenuates to non-detectable levels in wells MW- 107 &MW-109 The plume also attenuates to the east in the location of MW-108 • Figure 6 illustrates the distribution of TPH-G in the deep wells A localized high is centered in well MW-208 and the concentrations attenuate to non-detectable levels in the southwest and northwest locations of MW-209&MW-207,respectively 2 MTBE • The MTBE concentrations were not confirmed utilizing EPA Method 8260 and therefore contour diagrams were not produced When Method 8260 is utilized the wells are non-detect for MTBE 9 MTBE appears not to be an issue at this site