SITE INFORMATION AND CORRESPONDENCE

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CLEANUP AND ABATEMERRRDER N0. 40 2 ROBERT MONDAVI CORPORATION ROBERT MONDAVI WINERY SAN JOAQUIN COUNTY DRAFT 8. All process area stormwater and facility wastewater flows by gravity to a distribution box where it can be directed to two of the four facultative ponds. 9. The facultative ponds are adjacent to the Mokelumne River and provide aerobic and anaerobic treatment of the waste prior to its discharge to approximately 70 acres of vineyards, where it is further treated passively by the land and/or taken up by the crop. 10. Wastewater is currently applied in an alternating fashion to a network of 2-foot wide by 1.5-foot deep furrows that are plowed between the rows of vines. 11. During the irrigation season, the volume of wastewater applied to the vineyard is typically augmented with well water or water from the Mokelumne River in order to meet the irrigation demands of the crop. The supplemental water is applied through a drip system. SOIL AND GROUNDWATER CONDITIONS 12. Site topography is flat and level, and site soils are predominantly sandy loams. Soil permeabilities range from moderate to rapid, with rates of water intake ranging from 1.5 inches to 3.0 inches per hour. 13. Seven groundwater monitoring wells (MW-1 through MW-7) were constructed on the site in December 2001. The total depth of the wells range from 35 to 75 below ground surface (bgs), with screened intervals of 15 to 20 feet in length. 14. The first encountered groundwater below the site has ranged from approximately 11 feet bgs in the southern portion of the facility near the Mokelumne River to approximately 65 feet bgs in the northern portion. Groundwater flow direction has been to the north or northwest, with an average gradient ranging from 0.0053 to 0.01 fllft. MW-1, MW-2, and MW-3 are in the southern portion of the facility, which is the hydraulically upgradient direction, while the remaining monitoring wells are hydraulically downgradient of some or all of the process wastewater storage, treatment, and disposal areas. 15. The groundwater monitoring data indicate that concentrations of dissolved solids often associated with winery wastewater, as well as nitrogen-related constituents, are elevated in some or all of the downgradient monitoring wells as compared to concentrations in the upgradient three monitoring wells. The average total dissolved solids concentrations in the downgradient wells range from two to ten times higher than in the upgradient wells. The data also indicate that nitrate as nitrogen concentrations in three of the downgradient wells range from ten to thirty times higher than in the upgradient wells, and in one well is three times higher than the California maximum contaminant level (MCL). The California MCL (i.e., drinking water standard) is equivalent to 10 mg/l of nitrate as nitrogen, while the average concentration of nitrate as nitrogen in one downgradient well is approximately 30 mg/1. 16. On 8 October 2003, Regional Board staff issued a letter to the Discharger, summarizing the conditions described in Finding No. 15, and requesting the preparation and submittal of a Groundwater Degradation Evaluation Report to ascertain whether or not the discharge from this facility is degrading groundwater.