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rrAs illustrated in the,photographic Plates, rust mottling was observed within the underlying sandy silt strata in the exploratory boring. Rust mottling occurs when anaerobic bacteria decompose organic matter and use iron (Fe") in their metabolic processes. This oxidation of iron creates rust. When these two conditions are present - organic matter and an anaerobic environment, denitrification (the conversion of nitrate to gaseous products and the primary means by which nitrate concentrations are reduced) is promoted. Although mottling may be attributed to geologic processes, it is most probably due to seasonal soil saturation whereby percolating soil water encounters-slower permeability strata and accumulates. This accumulation phenomenon is observed when water percolating through a fine-grained soil encounters a coarser-grained soil, as observed in photographic Plate D. The drilling procedures also included the Standard Penetration Test (SPT). The Log of Boring for the deep perc test boring illustrate the number of blows needed to advance the split spoon sampler, one foot per ASTM D-1586. SPT results for this boring are illustrated below in Table 1. The correlations between the soil conditions and the SPT are dependent upon the soil type encountered and are different for fine-grained vs. coarse-grained soils. Test results reveal the underlying soils to be relatively dense. This density may have some influence on saturated vs. unsaturated flow conditions, particularly in ' the thick sand stratum (8.0 ft to 20 ft) that was observed. It is known that a thick sand stratum also F. exists at the opposite end of Clements. Although this sand stratum is dense, significant permeability exists, which contributes to saturated flow. However, this stratum is thick enough that saturated flow conditions may not develop due to the distance percolating water or effluent must travel. The six soil samples retrieved from the 25 ft boring were analytically tested. These samples were submitted to A& L Western Agricultural Laboratories in Modesto under the attached Chain of Custody. The SOIL ANALYSIS REPORT (Appendix 4) illustrates the important parameters associated with nitrate loading potential. As expected, the test results indicate relatively low Cation Exchange Capacity. he or anic matter is of medium concentration�rFt. e�nce�oik _ which is favorable for denitrification. The nitrate-nitrogen content atatl- �4 m, with an estimated nitrogen release ENR of 941bs/Acre. An important soil parameter in nitrate loading assessment, is the cation exchange capacity(CEC). Clay soils have a higher CEC than other soil types. Cations (positively charged ions) such as NH4k1 K�, Ca" and Mg" are removed from solution by the clay soil fraction because the clay particles possess a negative charge. In cation exchange, a positively charged ion within the clay complex is replaced and released by another type of ion. Ionic exchange,.through its effects on nutrient availability and acidity, has an effect on biological and chemical transformations. 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 in the ammonium ion (NH4') form and 25%N in the organic form. If the ammonium ion is bound and eventually utilized, nitrification cannot occur. Nitrification is an aerobic reaction accomplished predominately by autotrophic bacteria which convert ammonium (NH4') to nitrite (NO2) and subsequently to nitrate (NO3). Page -4- Chesney Consulting