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C'OlogicalTechnwsInc Page 5 Groundwater Monitonng Report Project No 770 2 January 17,2003 ' • Dee wells MW-104 105 & 106 did not contain contaminant concentrations above the Deep � ' laboratory reporting limits Deep well MW-105 has intermittently contained TPH-D The lateral extent of the diesel groundwater plume is currently undefined due to the continuing fluctuations in groundwater direction ;G • The vertical extent of the plume is defined by MW-104, 105, & 106 00'ffu- { ' 0 Oxidation-Reduction Potential (ORP) measurements show that seven monitoring wells l are within the reaction depleted water caused by biodegradation of the contamination plume These wells exhibit negative ORP values and all of the well ORP data are included in Table 5 of 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 halo5e^5 An examination of the contammant 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 wide fluctuations are noted for the past four events VThe 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 Well MW-5 continues to contain the highest concentrations of detected contaminants (see ' Figure 6) It has not been down gradient of the former UST location for the nine 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 Since none of the deep wells contained TPH-D, a contour diagram was not produced In Figure 7 — MW-5 & MW-105 TPH-D versus Groundwater Elevation, well MW-5 contaminant concentrations have generally correlated with changes in the water table Well MW-105, screened below the water table, exhibits a typically inverse relationship between ' contaminant concentrations and groundwater elevation GTI makes the following recommendations 0 Continue quarterly groundwater monitoring for determining direction and contaminant trends 0 Perform monthly groundwater level measurements for one year