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D R A F T January 4, 2012 fields. In addition, Central Valley Water Board staff observed rapid percolation of untreated industrial wastewater during an inspection in November 2005. At that time, the pond was relatively dry and the industrial flow"was observed to be percolating into the pond bottom within a short distance from the outfall."34 An additional concern is that the thickness of the soil between the pond bottoms and groundwater may be inadequate to allow soil treatment of the percolating wastewater to occur. The bottom elevation of Pond 1 is 5.5 feet and of Pond 4 is 2.5 feet above mean sea level. The groundwater elevation recorded in a nearby monitoring well has historically varied from a high of 3.2 feet above mean sea level to a low of 11 feet below mean sea level. Historically- recorded high groundwater levels indicate that the separation between the bottom of Pond 1 and groundwater has been as little as 2.3 feet, and Pond 4 has been inundated by nearly a foot. A review of quarterly nitrate concentration and groundwater table elevation maps, matched by date, in the City's 2003 Groundwater Monitoring Status Report indicates that onsite nitrate concentrations remain highest in the pond area, an area near the center of the mound.35 The four closest groundwater monitoring wells to the storage ponds are WSM2, WSM3, WSM4, and WSM8. Because of the persistent groundwater mound underlying the Facility in the storage pond area, these wells are assumed to be hydraulically downgradient of the ponds for most, if not all, of the year. Between August 2001 and November 2005, all four wells exhibited average nitrate concentrations over 11 milligrams per liter (mg/L) as N.36 The applicable groundwater objective for nitrate is the maximum contaminant level of 10 mg/L as N. Three of the wells had peak concentrations, during this period, of over 36 mg/L, more than three times the maximum contaminant level for nitrate as N.37 This result would not be expected if the nitrate source were off-site. Groundwater in the area to the north of the Facility appears to flow in an easterly or northeasterly direction, making it unlikely that higher nitrate concentrations to the north of the Facility are responsible for the high onsite nitrate concentrations in the pond area. Peak EC concentrations are also present within the area of the mound. The highest average value was found in WSM-2, located near the onsite ponds.38 The value was 1,750 34 Letter from Pat Leary, Senior Engineer, Central Valley Water Board,to Richard Prima, Director, Public Works Department, City of Lodi,with enclosed Inspection Report(May 3, 2006)at p. 5 of Inspection Report,AR,vol. 3, item 63. 35 Fn.29, ante, appendices A&C. 36 Final Report,fn.31, ante, Figure 5-10. ' Ibid. 39 Id. at pp. 5-14. 14.