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' GeologualTeckiucrl Page 5 Groundwater Momtoring Report Project No 770 2 August 27,2004 ' 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 well receptor 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 e Diesel range petroleum hydrocarbons were detected in three of the site's eleven monitoring wells ' • Well MW-5 contained 7310 Rgll diesel and remains the most severely impacted well • 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 ' 0 Minor BTEX constituents are present at levels ranging in small amount 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 samples at concentrations above the laboratory reporting limits • Deep wells MW-104, MW-105 and MW-106 did not contain contaminant concentrations above the laboratory reporting limits Well MW-105 intermittently contains diesel contamination o The groundwater samples were analyzed for 1,2-dichloroethane and 1,2-dibromoethane in accordance with SJCBHD's April 27, 2004 directive No well contained these contaminant concentrations above the laboratory reporting limit - 0 5 ug/l It is noted that the reporting limit for well MW-5 was elevated (50 ug/1) due to matrix interference (see ' page 8 of the Castle Analytical Laboratory report) • 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-104, 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 All the monitoring wells exhibited low to moderately positive ORP values except MW-105 The ORP data are included in Table 5 of Appendix A ' 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 plot in Figure 6 suggests that a previously direct relationship between groundwater elevation and contaminant concentrations ' has reversed since June 2002