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c,¢ofnguaI T"&VIcs lnc Page 5 Groundwater Monitoring Report Project No 770 2 November 9, 2005 reversal of groundwater direction by 180° in the deeper aquifer for the April and May ' 2003 sounding events is anomalous to the historical data 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 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 s Well MW-5 contained 7600 µg/l diesel- a significant decrease from the 35,000 ug/l ' recorded in June 2005 The well also contained 210 ug/1 TPH-G, 19 ug/1 ethylbenzene & 13 ug/l xylenes Well MW-5 remains the most severely impacted well v Well MW-1 contained 120 µg/1 diesel This well intermittently contains diesel. ' • Well MW-4 contained 2100 µg/1 diesel A trace amount of benzene was also present in MW-4 (1 8 gg/l) for this monitoring event a Well MW-6 contained trace benzene (0 91 ug/l) for the event This well intermittently contains low to trace levels of BTEX ® Well MW-7 contained 1800 ug/l TPH-D and 1 3 ug/1 benzene a Deep wells MW-104, MW-105 and MW-106 did not contain contaminant concentrations above the laboratory reporting limits ® Oxidation-Reduction Potential (ORP) measurements show moderately positive and ' negative ORP values in the monitoring wells Wells' MW-4, MW-5 and MW-105 negative values indicate that the wells are within the halo of reaction depleted water caused by biodegradation 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 grbundwater elevation is slowly declining since 2000 and that diesel concentrations are ' overall fairly stable, except for the August 2004 and June 2005 monitoring events (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, with the exceptions noted above The cause for the two recent high spikes is unclear, possibly due to low water level in the well and associated poor recharge to the well during purging and sampling This may account for the August 19 2004 spike in diesel concentration, but not the June 13, 2005 spike Purging and sampling logs suggest that J 1