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Musco Family Olive Company - 20 - 12 December 2006 purging of well water allowing impacted formation water beneath Field 95 to enter the well casing for sampling. c. Staff does not consider well MW-15 to be representative of shallow up-gradient groundwater. Based on a review of the historical groundwater flow data, it appears_ groundwater flows across the drainage swale and Reservoir through MW-15 to the north. Groundwater in the vicinity of well MW-15 does not flow toward the drainage swale. When water level elevations from well MW-15 are compared to Reservoir water levels, it is obvious Reservoir water is higher than groundwater. The average water level in well MW-15 between November 2002 and June 2006 was 338.45 feet msl_ Reservoir high and low water levels recorded between approximately the same period ranged between 341.00 and 350.50 feet msl. d. Shallow groundwater in the uplands and mid-gradient drainage swale is impacted with high TDS water indicative of spray irrigation impacts and wastewater impounded in the Reservoir and 1-million gallon pond. Elevated TDS, chloride, sodium, and bicarbonate have been detected above the interim standards since monitoring wells were installed. The monitoring well network for the shallow zone in the down-gradient area is inadequate and staff reject the interpretation that dilution of dissolved solids is occurring due to influx of higher elevation groundwater. e. Staff rejects the interpretation of onsite TDS concentrations in shallow groundwater as lower than TDS values reported offsite. Down-gradient TDS concentrations detected in well MW-17 averaged over the last four sampling events are approximately 1,975 mg/L. Well MW-17 appears to be at the concentration front of COCs and additional monitoring is required to determine trends in this well. TDS concentrations in well MW-17 appear to be slightly lower than offsite concentrations discussed in the Report. However, TDS in well MW-10 contained an average concentration of 2,375 mg/L. Well MW-10 is located at the eastern property boundary in the lowlands area of the Musco facility. Well MW-10 has not been sampled since August 2004. Offsite concentrations of CDCs have not been defined for the shallow or deep groundwater zones. f. The Report indicates that poorer quality deep groundwater is migrating onsite impacting onsite wells MW-7 (2,100 mg/L) and MW-12 (2,325 mg/L). The highest TDS values reported from offsite wells was 2,800 mg/L in 2004, and 2,111 mg/L in 1990. Both samples are located down-gradient of the Musco facility. According to Figure 4 of the Report, TDS values become lower as sampling moved to the east-southeast. In addition, lower TDS values (1,360 and 1860 mg/L) are reported north-northwest of the facility. Table 6 provides additional offsite water quality data. The average TDS, chloride, and sodium values for the wells sampled within two-miles of the Musco site were 11915, 321, and 431 mg/L. Elevated TDS and sulfate concentrations .in wells MW-7 and MW-12 could be a result of the surface impoundments leaking or impounded wastewater that is following a preferential pathway to the deep zone and affecting groundwater down-gradient of the facility. The deep zone on and offsite requires further evaluation.