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7 7Rustmottling can be indicative of seasonal soil saturation and 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 mode 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 on top of this strata. Soil chemistry was done on three samples retrieved from 40 inches, 6 ft and 12 ft to analyze several constituents. The important parameters for nitrate loading assessment are the organic matter, pH, cation exchange capacity (CEC), clay content percentage, soluble salts, along with nitrate-nitrogen content. As the noted on the SOIL ANALYSIS REPORT under SAMPLE NUMBER LL40", the nitrate-nitrogen(NO3-N) concentration.is . _mat typical leachline depth. Nitrate-nitrogen Concentra ions at t e ft and 12 ft de the are 3 pm each. The soluble salts are low at 0.5, 0.2 and 0.1 mmhos/cm, respectively. Organic matter and the Estimated Nitrogen Release (ENR) will be discussed in Section III E. Since septic effluent is composed predominately of ammonium (NH4) ions, which is the precursor to nitrate, the pH, along with the CEC, have significant influence on ammonium molecules. The pH of the soil is neutral-to- alkaline which may slightly inhibit ammonium formation and stability, and may create a small propensity for ammonia (NH3) formation. The CEC measures the ability of the soil to theoretically trap and hold ammonium molecules. The deeper soils have a CEC of 12.6 and 3.3, respectively, which suggests there is some potential for the retention of ammonium molecules for microbial uptake and_ suppssozaitr�i„�� (nitratee formation atthe 6-ft de _ , but virtual none a the_ 12 ft de th. Fine-grained soils, or soils with sufficient organic matter have a higher CEC than other soil types. Cations (positively charged ions) such as NH4', K+, Ca" and Mg" may be removed from solution by the clay soil fraction. 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 a tremendous 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). There is a clay layer referred to as the Corcoran Clay found throughout most of California's Central Valley. According to the Well Logs'this clay layer is found at variable depths under the subject site_between_a_prox�atel� 40 feet and approximately 100 feet. It has been demonstrated from this Study that deeper wells which cony�tinu'through t slayer have lower nitrate concentrations. Aquifers below this clay layer may be partially recharged in other areas, such as the Coastal Range to the west and Sierra Nevada Range to the east where nitrate influences are less pronounced. 3 Nafky Ag research