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Analysis of water drawn from the domestic well which serves the homesite, reveals a nitrate concentration of 14 ppm NO3. The Maximum Contaminant Level(MCL)for NO3 in drinking water is 45 ppm. Therefore,the underlying aquifers have been minimally impacted from various nitrate sources. The pesticides DBCP and EDB were not detected(ND). Considering the intense,although relatively recent, agricultural production in this part of the County, a higher nitrate impact concentration would have been expected from the well analysis. Fourteen ppm of nitrate illustrates there are significant clay layers that probably attenuate the downward migration of nitrate. [5] CONCLUSIONS The percolation rate for the homesite Parcel suggests there would be effluent percolation at the shallower depths of approximately 46 inches below grade, but due to the higher clay content soil, percolative capacity decreases with soil saturation. This was evidenced during the percolation test. As referenced earlier,there are no plans to build on Parcel 1,or the Designated Remainder and it will remain in agricultural production. We are recommending that if there should ever be plans to build on the Designated Remainder,there must be a 25-foot deep percolation test done in the proposed location of the seepage pits. The leachfield(s) should consist of 10,000-12,000 square feet. This leachfield area will be largely dependent upon the number of bedrooms a proposed house will have. Additionally,if there will be several people inhabiting the residence, particularly children, a septic system should be oversized to accommodate additional wastewater flows. A 50% standby replacement area must also be incorporated into the design of any 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. The referenced leachfield area will help ensure stability and guard against leachfield failure. A failure would primarily result from the advanced formation of a"biomat" or"clogging mat" on the wetted soil/effluent interface. This mat is composed mostly of aerobic and anaerobic bacteria and bacterial products consisting of a slime of polyuronides and polysaccharides. If the soil/effluent interface is well aerated,a variety of soil microfauna such as nematodes and protozoa may digest the clogging mat bacteria. Since the subsurface soils consist of a heavier clay material, anaerobic conditions will probably prevail which may hasten leachfield failure. In this scenario,the seepage pits then manage most of the effluent, although seepage pits can also develop biomat formation. 3 ij Va(.ley Ag Research