SITE INFORMATION AND CORRESPONDENCE

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Bert E. Van Voris - 16 - 17 September 2004 Supervising Engineer the potential to create saturated soil conditions. These conditions may cause salt and other waste constituents to infiltrate deep into the soil profile and threaten to degrade shallow groundwater underlying the mid-gradient drainage swale area. While the background soil sampling location is outside of the area currently receiving sprinkler applications of wastewater, soil data collected prior to 2000 and in June 2004 by Regional Board staff(Inspection Report pending) strongly suggest that soil in the background location has been impacted by past discharges of olive leaves and possibly pond dredgings. Therefore, it is inappropriate to rely on data from this location as representing soils unaffected by Musco's discharge of wastewater and solids. The RWD appears to provide conflicting information regarding soil management. In one place, it attributes past and current difficulties in growing crops to irrigation management, yet elsewhere it recommends sulfuric acid additions to improve soil quality, seed germination, and crop growth. If it were only a matter of irrigation management, Musco has had ample opportunity to improve practices to ensure healthy crop cover was the norm and not the exception following acid treatment. The RWD does not evaluate the potential impact to groundwater quality due to the application of sulfuric acid to restore the soil properties damaged by Musco's sustained discharge. The benefit of restoring site soils comes at a cost of leaching excessive sodium and other constituents deeper into the soil profile and potentially to groundwater. Acid treatment will cause sodium and other salt constituents to leach deeper in the soil profile and potentially into shallow groundwater. The RWD does not evaluate the potential water quality impacts from acid treatment and instead relies on the clayey soils of the site to restrict deep percolation. Yet, the salinity of shallow groundwater is increasing and the RWD has not explained why, except that it may be attributable to the influx of high salinity groundwater from offsite (more below). The RWD should identify the TDS concentration of wastewater following acid treatment. It should also explain how it would be possible to sustain crop growth, let alone germinate planted seeds, when applying wastewater containing elevated sodium. It is apparent that additional steps must be implemented during this interim period to reduce discharge salinity, especially sodium content. Groundwater—Onsite The RWD summarizes information resulting from past efforts to characterize groundwater underlying the site, which lies on an alluvial fan formed from Diablo Range sediments. Site elevations vary from about 540 feet in the southwest to 240 feet on the northeast edge, where the Coastal Range and the San Joaquin Valley meet. There are at least three `encountered depths of groundwater' (1) a shallow 5-to 20 ft bgs, 5-to 20-ft thick zone with seasonally occurring groundwater (MW-1, MW-2, MW-3, and MW 13, MW-5, MW-6, MW-10, MW-11, and W-2); (2) an intermediate 20-to 60-ft bgs, 10-to 40-ft thick zone; and (3) a deeper 90 to 200 ft bgs, 50-to 110-ft thick zone (MW-4, MW-7, MW-8, MW-9, and MW-12). Shallow groundwater follows topography and preferentially flows toward low areas of the site—the drainage swale that diagonally bisects the Musco site into northwest and southeast halves. Groundwater