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r7encounterteduat ont encounters a stratum of finer soil porosity such as clay or silt, which has a conductivity,percolation may be impeded. Strata of a clay/silt material were not If he deeper depths. ng effluent encounters a stratum of coarser porosity, such as a sandier material, this coarse stratum may temporarily impede the downward flow. This is contrary to conventional thinking where the thought would be that higher porosity would promote faster permeability. This impedance occurs because the macropores of a sandier material provide less attraction for the water molecules than do the smaller pores found in a finer material like clay and silt. When the wetting front encounters a coarser stratum, as was observed at the 10ft-15ft depth, the matric potential is lower in the soil material overlying this sandier stratum. Water always moves from a higher to lower potential (lower potential holds the water tighter), and the effluent will not readily move into this IOft-15 ft coarser stratum. Percolating effluent will accumulate above this stratum and nearly saturate the pores at the encountered sandier material. Eventually, gravitational forces overtake matric potential forces and the effluent will flow into the coarser stratum. Interestingly, the soil nitrate-nitrogen concentration decreased significantly from the 5 ft to 10 ft depth to the 10 ft to 15 ft depth. Saturated soil, which may occur above the coarser strata at the 10 ft to 15ft depth,theoretically creates anaerobic conditions. These environmental conditions promote denitrification which may explain this decrease in nitrate-nitrogen concentration. This is discussed in the Nitrate Loading/Soil Suitability Studies Phase III Report. Permeability can sometimes be difficult to correlate with soil texture, as illustrated when data from Table 1 is compared to data in Table 2. For example, soil samples from the 5 ft to 10 ft depth and the 20 ft to 25 ft depths have similar sand content percentages. Sand content can typically, but not always, be an indicator of a higher degree of permeability. But the 20 ft to 25 ft deep perc test rate was 2.5x faster than the 11.5 ft test, even with similar sand content percentages. In addition to the soil characteristics and subsequent percolation, nitrate loading will be a significant factor for this project. Consequently, analytical soil characteristics that influence nitrate-nitrogen loading have been referenced in Table 1. These factors include texture analysis, soil nitrogen content, organic matter content,pH and Cation Exchange Capacity(CEC). Table 2 below illustrates the percolation test results that have been correlated with application rates (also called acceptance rates). These application rates were adapted from Table 3, Page 24 of the SWRCB Water Quality Control Policy for Siting, Design, Operation, and Maintenance of Onsite Wastewater Treatment Systems. Page 3 of 7 Chesney Consulting