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Twor2 water samples were taken per the request of the County Environmental Health Department. The first sample came from the on-site domestic well and was tested for nitrate and the agrichemicals DBCP and EDB. Test results indicate a nitrate concentration of 22 ppm which is approaching one-half the Maximum Contaminant Level (MCL) of 45 ppm. The agrichemicals DBCP and EDB were non-detect(ND). The second water sample was retrieved from water table encountered in the deep soil boring. This test result had a slightly lower nitrate concentration than the domestic well at 20 ppm nitrate. [5] CONCLUSIONS The nitrate concentrations in the on-site domestic well and the top water table reveals there has been nitrate impact to a medium extent. However, given the upgradient land use of agricultural production which is occurring above a shallow groundwater,these nitrate concentrations are to be expected. The significance of the two nitrate analyses being comparatively equal (20 ppm vs. 22 ppm) indicates that 1.) the nitrogen inputs occurring upgradient are in equilibrium with the movement of the top aquifer water table and underlying water aquifers and 2.)the indigenous clay soil may be having an attenuating influence on the downward migration of nitrate molecules, primarily through denitrification. The septic system for the subject property has been in operation for over 25 years,with no recorded failures according to the land owner. Wastewater flows for this facility would be significantly different in comparison with a residential structure. This certainly would have an effect on operational longevity. In reference to the repairs made to existing septic systems within the study area,it is noted that additional leachline was needed,which is indicative of leachfield failure through biomat formation. The percolation rate obtained for the subject property suggests there is sufficient percolative capacity of the soil to manage intermittent effluent flows. The perc rate for the unsaturated vadose zone test demonstrates that the percolation slows considerably as the soil becomes more saturated. If it should be proposed that the subject property undergo a change in land use, it will be a requirement of the Environmental Health Department to conduct a Nitrate Loading Study and a projection of wastewater flows. In addition,we are recommending that if the existing facility should be expanded,there should be a percolation test done in the proposed location of a new or additional leachfield. The leachfield(s) must consist of the proper square footage. Since the property is commercial, a 100% standby replacement area must be incorporated into the design of any future septic system. All related septic system structures and any domestic well must comply with the published "distance" requirements from property borders, roads, irrigation fields, etc. 3 —J—) Va(�ey Ag Research