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1 Ge0togccal ncluucs tftc Page 5 ' Groundwater Monitormg Report Project No 770 2 July 7,2605 other events all displayed an easterly trend to groundwater direction It is noted that the gradients for these two events were higher than normal suggesting that off site production ' is influencing the aquifer A receptor well survey was completed for the site in January 2001 and two agricultural wells were identified approximately 1600 feet west of the site (see Map 1, Table 1 — Appendix D) If these wells were operated during the months in question, it is possible that the Marci site was within the cone of depression created by the well pumping The shallow aquifer did not reverse during this period and this may be due to the domestic wells to the southeast of the site that may be screened shallower than the agricultural wells and exert a primary influence on the water table that is easterly • Diesel range petroleum hydrocarbons were detected in four of the site's eleven monitoring wells sampled this quarter • Well MW-5 contained 35,000 µg/1 diesel Well MW-5 remains the most severely impacted well - $fn z arw 6v 04 al- 1 I,tel L i1 0"111+ • Well MW-4 also experienced a marked increase in diesel concentrations since the June 2004 event (from 496 to 2300 µg/1 TPH-D) Trace amount of benzene was also present in MW-4 (2 4 gg/1) for this monitoring event 0 Well MW-7 contained TPH-G (I 10 µg/1), TPH-D (1500 ug/1) and ethylbenzene (0 71 µg/l) • Deep wells MW-104, MW-105 and MW-106 did not contain contaminant concentrations above the laboratory reporting Iimits • Oxidation-Reduction Potential (ORP) measurements show moderately positive and negative ORP values in the monitoring wells The ORP data are included in Table 5 of Appendix A • The vertical extent of the plume is intermittently defined by MW-104, 105, & 106 The groundwater near these wells appears not to be contaminated 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 (see Figure 6- MW-5 TPH-D vs Groundwater Elevation) A consistent factor previously noted in the investigation was the fluctuation in diesel concentrations in well MW-5 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 I