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gW10gkal Tech=$w Page 5 Groundwater Momtonng Report Project No 770 2 November 8,2004 ' was not processing Geo Well files on that date and the depth to groundwater data will be transmitted when the system is responding 2.0 FINDINGS AND DISCUSSION ' The results of thegroundwater monitoring event indicate the following • The reversal of groundwater direction by 180°in the deeper aquifer for the April and May 2003 sounding events is anomalous to the historical data The deeper aquifer has been monitored by three wells (MW-104, MW-105 and MW-106) since June 2002 and the ' 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 seven of the site's eleven monitoring wells 0 Well MW-5 contained 99,000 µg/1 diesel and this represents a lump in one order of magnitude from the last event Well MW-5 remains the most severely impacted well o Well MW-4 also experienced a marked increase in diesel concentrations since the June 2004 event(from 496 to 5100 ug/1 TPH-D) ' • Gasoline range petroleum hydrocarbons (TPH-G) were detected in MW-5 (240-µg/1) in this monitoring event Several wells have had at least one event in which TPH-G was ' detected • Trace BTEX constituents are present in wells MW-4 and MW-7 for this monitoring event • Deep wells MW-104 and MW-106 did not contain contaminant concentrations above the ' laboratory reporting limits TPH-diesel was detected (170 µg/1) in MW-105 • The groundwater samples were analyzed for 1,2-dichloroethane and 1,2-dibromoethane in _ accordance with SJC/EHD's _April _27, 2004. _ directive No well_ contained these ' contaminant concentrations above the laboratory reporting limit - 0 5 ug/l • The lateral extent of the diesel groundwater plume is currently undefined to the south and west • 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