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rFA ter Well Drillers Report (Well Log) for the on-site well, drilled August 2, 2002 can be foundpendix 5. The Well Log illustrates the underlying lithology to be "soil" (top soil) clay fromrface to 3 feet. However, our perc test borings revealed the top soil to be much "shallower;" ximately one foot deep. The remaining strata on the well log consists of intervening layers of red clay and gravel down to the well depth of 400 feet. Due to this intervening gravel strata, it is a possibility that perched water table conditions exist above the static water table depth of 172 feet. The water table was encountered at 150 feet. There does not appear to be any evidence of the Corcoran clay layer on this Well Log since the property is close to the Diablo Mountain Range. In reference to the chemical analysis of the soil samples, the important soil parameters for nitrate loading assessment are the organic matter content,pH, cation exchange capacity(CEC), clay content percentage, soluble salts, and the nitrate-nitrogen content. Considering the property soils have not been under agricultural production for many years, if ever, the organic matter content in these soils is low, contributing to a low estimated nitrogen release (ENR). The significance of cation exchange becomes important when the chemistry of septic effluent is analyzed. Nitrogen in septic tank effluent consists of approximately 75%N as the ammonium (NH4') ion form and 25%N in the organic form. If the ammonium ion is bound and eventually utilized, nitrification cannot occur. Consequently,the CEC has significant influence on ammonium molecules. The CEC measures the ability of the soil to theoretically trap and hold ammonium molecules. The soil samples indicate a medium CEC, which suggests there is some potential for the retention of ammonium molecules for microbial uptake and suppression of nitrification. Nitrification is an aerobic reaction accomplished predominately by autotrophic bacteria which convert ammonium (NH4') to nitrite (NO2) and subsequently to nitrate (NO). As referenced above, both the shallow and deeper surface and subsurface soils possess sufficient clay content to bind the ammonium ions, and to create microsites within the clay lattices that are anaerobic, thus promoting denitrification. It is noted on the Soil Analysis Report that the two soil samples have identical nitrate-nitrogen contents. These concentrations are very low, again indicating the soils have probably never been in agricultural production. The USDA aerial photo taken in the early 1970s indicates the property was not in ag production. This Iow soil nitrate-nitrogen concentration will contribute a very low concentration of nitrate in percolating vadose zone water. C. PERCOLATION TEST RESULTS Three shallow and two intermediate depth percolation tests were conducted in the center of the three Parcels, in what can be considered the"back"or east side of each Parcel. These locations are opposite Koster Road and closer to the concrete-lined Delta-Mendota Canal. Tests were done in these areas since the domestic well drilled on Parcel 2 is in the "front"of the Parcel, adjacent to Koster Road, and it is assumed that the wells for the other two Parcels will also be installed near Koster Road. Test locations are denoted on the Site Plan Map in Appendix 1. The intermediate depth perc tests done on Parcels 1 and 2 illustrate the perc potential for sump installation. Test results indicate sumps would be inadequate for acceptable septic effluent management from the proposed houses. 5 Chesney Consulting