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' QologwaI7echa=t u Page 6 Groundwater Monitoring Report Project No 770 2 February 7,2005 ' plume All the monitoring wells exhibited low to moderately positive ORP values except MW-4 and MW-105 The ORP data are included in Table 5 of Appendix A • The lateral extent of the diesel groundwater plume is not fully defined by the outer ring of wells (MW-3, 6 & 8), but the concentration of diesel is very low in these wells • The vertical extent of the plume is intermittently defined by MW-104, 105, & 106 The t groundwater around MW-105 is contaminated, however concentrations are so low that further investigation may not be needed at this time MW-5 An examination of the contaminant distribution and groundwater flow direction data reveals groundwater elevation is slowly declining since 2000 and that diesel concentrations are overall fairly stable, except for the August 2004 monitoring event A consistent factor previously noted in the investigation was the fluctuation in diesel concentrations in well MW-5 (see Figure 6- MW-5 TPH-D vs Groundwater Elevation) The concentrations had ' previously demonstrated a slight increasing trend until June 2002 when concentrations began to fluctuate for about a year Subsequently, the concentrations have been very consistent, except for August 2004 The cause for the very high spike in August is unclear, possibly due to low water level in the well and associated poor recharge to the well during purging and sampling Purging and sampling logs suggest that sample quality may be compromised due to low water level in the well The plot in Figure 6 suggests that a previously direct relationship between groundwater elevation and contaminant concentrations has reversed since June 2002 1 Well MW-5 continues to contain the highest concentrations of detected contaminants (see Figure 8) it is not down gradient of the former UST location and the reason for this anomaly is not known, but could be related to geologic units that slope to the west ' MW-4 Well MW-4 lies adjacent to the former UST field Figure 7-MW-4 TPH-D vs Groundwater ' Elevation suggests that a predominantly inverse relationship exists between groundwater elevation and contaminant concentrations In this figure the sudden increase in diesel ' concentrations for August 2004 coincides with the same phenomenon observed in MW-5 The cause is unknown at this time, but the concentration of diesel has decreased since that event ' MW-105 TPH-D was detected in MW-105 at 94 ug/l Detection of TPH-D in the last two quarters ' indicates that the contamination is moving vertically downward in an oblique angle to the northwest from the source ' In Figure 9— MW-5 & MW-105 TPH-D versus Groundwater Elevation, well MW-5 contaminant concentrations have previously exhibited a weak correlation with changes in the water table Since September 2001 the relationship has been reverse Well MW-105,