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ORDER NO.R5-2002-0148 INFORMATION SHEET 8 MUSCO FAMILY OLIVE COMPANY AND THE STUDLEY COMPANY WASTEWATER TREATMENT AND LAND DISPOSAL FACILITY SAN JOAQUIN COUNTY DETERMINATION OF BACKGROUND WATER QUALITY The second major technical issue involves the determination of background water quality. This determination is necessary to analyze whether the Discharger's request to discharge effluent with a TDS concentration exceeding 4,500 mg/1 is acceptable. Once background water quality is known, then the Regional Board can set effluent limitations that will result in a discharge that meets the conditions of State Board Resolution No. 68-16 (the Antidegradation Policy). To determine the appropriate concentration limits for the wastewater discharge, staff reviewed the Regional Board's June 1989 "Designated Level Methodology for Waste Classification." Because the discharge is planned to continue indefinitely, use of an attenuation factor is not appropriate because all the attenuation processes will become saturated over time. Therefore the wastewater limits are set by the background groundwater quality. Although the Discharger presented an evaluation of the available data in the RWD, it did not provide an analysis of the data for proposed limits. As a result of the lack of proposed limits by the Discharger, staff interpreted the April 2002 groundwater sample event (the only available data at the time) and proposed background concentrations and the resulting effluent limits in the Tentative WDRs. The Discharger has taken issue with staff's evaluation, and has provided the results of a second round of on-site groundwater sampling. With additional data available, staff has revised the data interpretation, as discussed below. Background Water Quality Background water quality data is limited and due to the limited availability of the data, conclusions based on the data are tentative. The Discharger installed groundwater monitoring wells in 1985 for WDR Order No. 96-075 (the Title 27 WDRs). The wells have been reported as dry in most monitoring events. In April 2002 when the Discharger was required to install groundwater monitoring wells per the Time Schedule Order, Well W-2 was inspected and reported to contain groundwater. That well was added to the recently installed groundwater monitoring network. In April 2002, the Discharger installed 13 groundwater monitoring wells; however, Well MW-9 went dry during well development and has not recovered. The wells were to be installed in the first saturated interval; however, staff are concerned that some saturated intervals may have been drilled through without detecting groundwater. Because of the anticipated depth of some of the wells, the Discharger's consultant selected air rotary as the drilling technique. Because air rotary drilling might prevent installation of groundwater monitoring wells in the first saturated interval, staff required the Discharger to submit additional information describing how the wells would be constructed. The Discharger submitted a workplan addendum and the wells were installed. However, based on the results of the investigation, staff remains concerned that the first saturated interval may have been missed while drilling the deep wells. The first sample event for all the wells was performed in April 2002; a second sample event was performed in June 2002. The data collected in the two sample events is found in Finding No. 44 of the WDRs. Because of the limitations of the data and poorly understood hydrogeology of the site, several