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Geofagi"t1¢cluairslru Page 6 Groundwater Monitonng Report Project No 770 2 March 31,2004 ' • Gasoline range petroleum hydrocarbons (TPH-G) were not detected in any of the wells for this event Several wells have had at least one event in which TPH-G was detected ' • Minor BTEX constituents are present at levels ranging from 0 3 — 1 5 µg/1 in wells MW- 4, MW-5, MW-6 and MW-7 ' O Motor oil range petroleum hydrocarbons were not present In any of the groundwater r samples at concentrations above the laboratory reporting limits 0 Deep wells MW-104 and MW-106 did not contain contaminant concentrations above ' the laboratory reporting limits • Deep well MW-105 contained 57 9 ug/l TPH-D This well mtennittently contains diesel contamination ' • The lateral extent of the diesel groundwater plume is currently undefined to the south • The vertical extent of the plume is intermittently defined by MW-l 04, 105, & 106 • Oxidation-Reduction Potential (ORP) measurements show that several monitoring wells are within the reaction depleted water caused by biodegradation of the contamination plume Wells MW-1, MW-4, MW-5, MW-7 and MW-105 exhibited negative ORP values and all of the wells' ORP data are included in Table 5 of Appendix A The other wells have varying positive values suggesting that the water around these wells is outside of or on the outer fringe of the halo of impacted groundwater 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 6- MW-5 TPH-D vs Groundwater Elevation The concentrations had previously demonstrated an increasing trend until June 2002 when wide fluctuations began The well has displayed decreasing ' concentrations for the past two events The plot in Figure 6 suggests that a previously direct relationship between groundwater elevation and contaminant concentrations has reversed since June 2002 ' Well MW-4 hes adjacent to the former - � UST field Figure 7 MW-4 TPH-D vs ' Groundwater Elevation suggests that a previously reverse relationship between groundwater elevation and contaminant concentrations has changed to a parallel relationship since September 2002 Well MW-5 continues to contain the highest concentrations of detected contaminants (see Figure 10) It has not been down gradient of the former UST location for the monitoring ' events completed by GTI to date The reason for this anomaly is not known, but could be related to geologic units that slope to the west Figure 9 illustrates the TPH-D concentrations in the deep wells A localized node is present in the location of MW-105 ' In Figure 10— MW-5 & MW-105 TPH-D versus Groundwater Elevation, well MW-5 contaminant concentrations have generally correlated with changes in the water table Well