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STAFF REPORT • • 6 MUSCO FAMILY OLIVE COMPANY AND THE STUDLEY COMPANY CONSIDERATION OF WDRS AND A C&A ORDER 6 September 2002 Regional Board Agenda months (December-February) when stormwater bypass is proposed and when the water balance indicates that wastewater will not be applied to land. Because of the uncertainties of tailwater generation and the importance to preparation of any future water balances, it is reasonable to require monitoring of the amount of tailwater generated. The Discharger has verbally described a plan (but has yet submitted a written description)to collect tailwater from the application areas in collection ditches and return the water to the storage pond in a sump/pump/piping arrangement. Monitoring of the tailwater will allow a better evaluation of the flow rate for future preparation of water balances. The monitoring might consist of totalizing meters or pump run time meters. If pump run time meters are used, annual calibration of the meters should be required because the Discharger has reported inaccurate metered flow rates in the wastewater discharge self-monitoring data. The Discharger also needs to either directly measure, or accurately estimate, the amount of stormwater which runs off the land application area and is collected in the storage pond. Finally, because the water balance contains optimistic assumptions, it is reasonable to include a requirement to cease the discharge to the either the 1-Mgal settling pond or the 84-Mgal storage pond if the freeboard in either is less than two feet at any time. This will minimize the possibility of spilling wastewater into the natural surface water drainage. The Discharger is also required to inform Regional Board staff of the freeboard violation immediately. BACKGROUND WATER QUALITY AND EFFLUENT LIMITATIONS 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 groundwater quality is known, then staff 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 Apri12002 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.