SITE INFORMATION AND CORRESPONDENCE

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STAFF REPORT • • 11 MUSCO FAMILY OLIVE COMPANY AND THE STUDLEY COMPANY CONSIDERATION OF WDRS AND A C&A ORDER 6 September 2002 Regional Board Agenda Staff's review of the hydrogeology reports revealed that the site conditions are not adequately characterized and understood to establish a final background groundwater quality value. Additional subsurface investigation and groundwater monitoring is required to better understand the site conditions. After reviewing the alternatives for determining a background groundwater quality value, staff determined use of the on-site production well was the best interim measure of groundwater quality that is in use at the site. This well is screened from 50 to 607 feet below ground surface, so the analytical data is a composite of the concentrations in the shallow and deeper aquifers. In addition, five sampling events were conducted at this well, leading to better statistical confidence. Staff used the same method to calculate the background values as described in Alternative No. 3. The average of the five monitoring events was calculated, and two standard deviations were added, in a method consistent with CCR Title 27 Section 20415. Staff recognize this method of calculating the background groundwater quality is not the optimum method but based on the information and data available, believe it is appropriate for an interim concentration limit. The background groundwater quality, and resulting effluent limits, are: TDS 2,047 mg/L, chloride 601 mg/L, and sodium 597 mg/L. Additional Hydrogeologic Investigations The Discharger proposed additional investigations to better characterize the site and regional hydrogeology. The investigations are described in the 7 August 2002 Revised Background Water Quality Preliminary Evaluation Report, prepared by Kleinfelder. While the proposed studies may provide information on the regional groundwater quality, staff believe that additional studies should be focused on the Discharger's facility. Investigations of groundwater conditions in the region may not be applicable to the site-specific groundwater conditions. Items that should be addressed in future studies include: • A better understanding of the occurrence of groundwater at the site. Kleinfelder's model for the hydrogeology of the site contains too many uncertainties. The presence of perched zones in the land application areas is unsupported by Kleinfelder's boring logs presented in the 30 April 2002, "Groundwater Monitoring Well Installation, Sampling, and Analysis"report. The boring logs do not show saturated zones underlain by unsaturated zones. An alternative interpretation is the wells are screened in two zones, an unconfined(water table) and a confined zone. Further study is required to define the subsurface conditions. • The report recommends the use of Well MW-2 as a background well. Staff believe the excessively high concentrations observed in the well are likely due to an unknown source or other unknown factor. Additional investigation of the groundwater conditions at Well MW-2 is warranted. • The report describes similar concentrations in samples from Wells W-2 and MW-1 and suggests the data as a proof of no groundwater impact. Review of the Stiff diagrams for the wells on Plate 5 reveals an almost identical shape. However, staff believe the similarity may be a result of both wells defining the background groundwater conditions. Kleinfelder's statement that Well W-2 is the furthest downgradient well doesn't take into consideration the