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WASTE DISCHARGE REQUIREMENTS ORDER R5-2013-0028 -21- DELICATO VINEYARDS, INC. DELICATO FAMILY VINEYARDS SAN JOAQUIN COUNTY implemented to date. If the required improvements do not result in significantly improved groundwater quality within five years of adoption of this Order, the Provisions require that the Discharger implement additional treatment or control as necessary to bring the discharge into compliance with the Basin Plan water quality objective. This Order also requires that the Discharger evaluate existing and potential future local agricultural uses of groundwater to support determination of a site-specific water quality objective that is protective of all beneficial uses. b. Nitrate. For nutrients such as nitrate, the potential for degradation depends on effluent quality; crop uptake, and the ability of the vadose zone below the LAAs to be conducive to nitrification and denitrification to convert the effluent nitrogen to nitrate and the nitrate to nitrogen gas before it reaches the water table. Most of the nitrogen in the process wastewater is present as TKN, which can readily mineralize and convert to nitrate (with some loss via ammonia volatilization) in the LAAs. Background groundwater quality is poor with respect to nitrogen and exceeds the primary MCL of 10 mg/L in background monitoring wells MW4, MW-5, and MW-1, which are upgradient of the current discharge locations. The poor quality background groundwater is likely due to the predominantly agricultural land use in the area. In contrast, nitrate concentrations in groundwater downgradient of the current unlined ponds and LAAs are below the primary MCL in MW-2 and MW-3. The expanded LAA system will maximize nitrogen uptake by crops and minimize the potential for nitrate to migrate to groundwater. Therefore, this Order requires that nutrients associated with the wastewater and other sources be applied to the LAAs at rates consistent with crop demand, and the Groundwater Limitations require that the discharge not cause any statistically significant increase in groundwater nitrate concentrations. c. Sulfate. The average sulfate concentration in the process wastewater averages 154 mg/L. Background groundwater sulfate concentrations are spatially variable with intrawell means that range from 8 mg/L to 97 mg/L. Sulfate concentrations in downgradient monitoring well MW-3 show clear evidence of degradation due to the concentrations exceeding the Secondary MCL of 250 mg/L since December 2009. Following completion of the improvements required by this Order, sulfate concentrations in the downgradient monitoring wells are expected to improve but it is not possible to predict the level of improvement that can achieved or when it might occur. Therefore, this Order sets a groundwater limitation for sulfate at the Secondary MCL. The intent of this limit is not to allow additional degradation beyond that which has already occurred, but as a safeguard to accommodate short-term increases due to the inherent uncertainty associated with future transport of waste constituents already present in the vadose zone beneath the existing LAAs.