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1 Geologwxf Technics Inc Page 5 Groundwater Monitoruig Report Project No 770 2 October 15,2002 ' 2.0 FINDINGS AND DISCUSSION ' The results of the groundwater sample analysis indicate the following • Diesel range petroleum hydrocarbons were detected in six of the site's eleven ' monitoring wells / • Well MW-5 contained 1130 µg/l diesel and this is a significant drop from the March 2002 high of 16,800 �Lg/l TPH-D � 1; • Minor BTEX constituents are present at levels ranging from 0 3 — 1 6 gg/1 in wells MW-S • Motor oil range petroleum hydrocarbons were not present in any of the groundwater ' samples at concentrations above the laboratory reporting limits • TPH-G was not present in any of the groundwater samples at concentrations above the ' laboratory reporting limits Four of the wells contained TPH-G for the September 2001 event only MW-1, MW-4, MW-6 and MW-105 / • Deep well MW-105 contained 93 4 µg/l TPH-D The well did not contain contaminant ' concentrations above the laboratory reporting limits for the previous two events • The lateral extent of the diesel groundwater plume is currently undefined due to the continuing fluctuations in groundwater direction • The vertical extent of the plume isontermi'�ttentl�,.defined by MW-105 • Oxidation-Reduction Potential (ORP) measurements show that seven monitoring wells ' are within the reaction depleted water caused by biodegradation of the contamination- plume These weus exhibit negative ORP values and all of the well ORP data are included in Tableof Appendix A The other wells have relatively low positive values ' suggesting that the water around these wells are on the outer fringe of the impacted halo An examination of the contaminant distribution and groundwater flow direction data doesn't reveal any obvious trends A consistent factor previously noted in the investigation was the increase in diesel concentrations in well MW-5, see Figure 4- MW-5 TPH-D vs Groundwater Elevation The concentrations had previously demonstrated an increasing ' trend, but a significant decrease was noted for this event The plot in Figure 4 suggests a predominant direct relationship between groundwater elevation and contaminant concentrations ' Well MW-4 lies adjacent to the former UST field ~ Figure 5- MW-4 TPH-D vs Groundwater Elevation suggests an inverse relationship between groundwater elevation and ' contaminant concentrations in well MW-4 It is noted that the groundwater elevation exceeded the screened interval of well MW-4 and dilution may be taking place ' Conversely, the water table lies within the screened interval of well MW-5 and this may represent a more accurate reflection of residual contamination leaching into groundwater