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CIL NITRATE LOADING STUDY RESULTS A. GROUNDWATER INFORMATION 1. ESTIMATED GROUNDWATER GRADIENT The static water level measured in nearby wells for other projects indicate the water table to be from 48 to 60 feet below grade. The Lines of Equal Depth Map and the Lines of Equal Elevation Map published by the San Joaquin County Flood Control District do not illustrate the groundwater depth and elevation for the most recent year published (2002). However, the 1992 Lines of Equal Elevation map illustrates the groundwater flow to be in a northeasterly direction. This direction is confirmed by the environmental cleanup of the contaminant plume originating from the Tracy Defense Depot. 2. ANALYSIS OF UNDERLYING GROUNDWATER As referenced above, it is known that there is a serious nitrate problem in the Valpico area. The Environmental Health Department has requested that surrounding domestic wells not be tested for this investigation. The Department has stipulated the domestic well that will serve both residential structures on the subject parcel must have a grout seal to 200 feet. This seal will create a greater likelihood that water from aquifers below the Corcoran clay layer will theoretically have lower k nitrate concentrations than aquifers above the Corcoran clay layer. After the domestic well is installed for the Rinauro's, it should be tested for nitrate concentration. The Maximum Contaminant Level (MCL) for nitrate (as NO3) is 45 ppm. If the nitrate concentration is above this number, bottled water should be consumed for drinking and cooking purposes. B. SURFACE WATER INFORMATION Surface water consists of all other water sources originating on the surface of the project, other than septic system effluent. These sources include rainfall, surface runoff, domestic irrigation and stormwater retention. Stormwater retention areas have been denoted on the attached schematic. h f rainfall the The San Joaquin County of Public Works - Isoh etal Ma indicate 13xnc es o to be q tY Y p Mean Annual Precipitation in the area of the project. After the new house is built and the modular home moved on-site, a percentage of the land surface will be impermeably covered with structures, concrete, etc. This will have an attenuating effect on the downward migration of nitrate molecules currently "in-transit" and on nitrate yet to be formed. These impermeable surfaces will be traded for potential point sources of nitrate: the on-site septic system, lawns, and landscaping. Domestic irrigation recharge can account for 250 to 1,500 gallons of water/day/residence during the spring and summer months(approx. 6 mos. out of the yr). Excessive lawn and landscape watering can lead to nitrogen leaching, and runoff to open areas. However,the groundwater pumped by the on-site domestic well and used for domestic irrigation can reduce the mass balance of nitrate since all plants readily use nitrate as a food source. This is provided of course,that fertilizer is carefully applied to lawns, gardens and landscaping, if at all. For example: if the well water for the new well has a"guess-estimated" nitrate concentration of 30 ppm NO3, this equals 30 ppm x Page -4- Chesney Consuking