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Musco Family Olive Company _ 10 - 12 December 2006 , Well MW-2 Well MW-2 is a deep well and groundwater collected from well MW-2 has a distinct chemical signature when compared to other wells at the Musca site. Table 7 above summarizes the last four sampling events and concentrations detected in well MW-2. Groundwater observed in well MW-2 appears to be of marine origin as: evidenced by the elevated concentrations of TDS, chloride, and sodium. The chemical analytical data from well MW-2 will not be evaluated. Newly Installed Wells At the request of the Regional Water Board, Musco has installed one deep and three shallow wells to monitor groundwater quality beneath the Title 27 surface impoundments. The one deep well was installed near the northwest corner of Pond A to a depth of approximately 110 feet bgs. The well was constructed with 20 (90 to 110 feet) feet of machine slotted well screen. The two shallow wells were installed northeast and southeast of Pond B to become the down-gradient compliance wells; the third shallow well was installed southwest of Pond A to become the rip-gradient compliance well. All three shallow wells were installed to an approximate depth of 70 feet bgs and constructed with 20 (50 to 70 feet) feet of machine slotted well screen. A report of well installation and initial compliance sampling is pending. REVIEW OF GROUNDWATER DATA It is important to note the Musca site is situated in a complicated geologic environment where high strength wastewater and/or Pond solids have been land applied since early 1980. Since no onsite groundwater,data exists prior to the installation of the 13 groundwater monitoring wells in 2002, predischarge groundwater quality at the Musco property was not established. According to WDR No_ R5-2002-0148, Finding No. 48, the Discharger has not proposed a method or rationale for calculating background concentrations. Board staff had previously proposed the use of wells MW-1 and MW-8 to calculate background groundwater concentrations. However, the Discharger disagreed with the use of these wells, and Board staff agreed that further refinement of the site specific groundwater quality was necessary. As interim background groundwater quality data, Board staff determined that Musco's production well should be used for groundwater quality limits. The Discharger was to propose final background groundwater concentrations within two years of the revised WDRs No. R5-2002-0148. Current average analytical data for existing groundwater monitoring wells and interim background groundwater concentrations are shown in Table 9. The data for the monitoring wells is derived from the last four available sampling events of each well. TABLE 9 Average Groundwater Concentrations Well ID TDS' CI Na HCO3 (mg/L) (mg/L) (mg/L) (mg/L) Production Well* 2047 601 591 NA