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IV. CONCLUSIONS AND RECOMMENDATIONS SSS§ 5.4,6.8. The surface and shallow subsurface soils underlying the subject property where the new filter bed is proposed to be installed, indicates very rapid permeability that is considered too rapid for EHD standards. Consequently, twelve (12) inches of peat material shall be placed equal depth on the floor of the excavated filter bed at the soil-effluent interface before the addition of one ft depth of drain rock. An additional six inches of drain rock to cover the four-inch dia. laterals is to be added, covered with geotechnical fabric and six inches of native soil cover. The volume of peat required= 1.0 ft x 1,200 sq ft= 1,200 cu ft or 44 cu yds. In addition to slowing the permeability rate, the peat will also supply additional functions. First, is to trap ammonium molecules within the septic effluent for microbial synthesis before these molecules can nitrify. Secondly, to create a large differential in the carbon:nitrogen ratio thus impeding nitrification. And thirdly, promoting anaerobic, water logged soils, which also impedes nitrification and promotes denitrification. This will reduce nitrate-nitrogen loading to an indeterminable extent, but has the potential to be a very significant decrease in loading. The nitrate loading calculations are conservative by using extremely conservative criteria. Any potential review of this project in the future will incorporate updated criteria and possibly environmental testing of the installed system for this project. Sources that may have, or may be, contributing nitrate to the underlying groundwater in this locale include indigenous soil concentrations from lightning/rainfall, past and present upgradient agricultural fertilizer inputs, septic systems, lawn/landscape fertilization and naturally occurring geological deposits. However,the proximity of large bodies of fresh water are contributing to a dilution effect. This phenomenon has been observed many times throughout San Joaquin County. Additional factors decreasing the groundwater nitrate concentration include denitrification, groundwater movement (both vertical and horizontal), and well pumping and hydraulics. If each of these sources and attenuating factors could be quantified on a mass balance basis, it may be that nitrate input is now roughly equivalent to output, or attenuation. Given that agricultural irrigation recharge was a large contributor to groundwater nitrate concentrations, and since the surrounding land has been farmed for several decades, it could be assumed that the nitrate concentrations in the underlying groundwater should be much higher than those observed, if the attenuating factors were not significant. There appears to be a small soil denitrification potential as referenced. Jenssen and Siegrist(1990) found the factors that favor denitrification are fine-grained soils such as silts layered with soils consisting of alternating fine-grained and coarser grained soils with distinct boundaries between the texturally different strata. This was observed in the perc test boring whereby percolating water encountering coarser soil strata accumulates on top of this stratum until sufficient soil moisture increases for the soil vadose water to travel into this higher porosity stratum. These strata differentiation may also explain the low soil nitrate-nitrogen concentrations. NLS§ 4. S§ 6.7.,)All decentralized wastewater management systems (septic systems)will �verriiially f ' . i the design components for this project are of maximum size for the proposed project, and the indigenous sandy soil structure, the lifespan can be considered significant. 10