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r l F CONCLUSIONS AND RECOMMENDATIONS SSS§ 6.7, 6.8 The percolation test results.for this project reveal dramatically varying subsurface soil= conditions. In accordance with EHD rules and regulations, the septic system disposal area for each i individual Parcel must be installed within 100 feet of the percolation test location. The perc test locations were decided upon to be 150 feet south of the proposed Sorrenti Lane, which is within an area most likely for residential development. As noted from the percolation test results, all the proposed Parcels possess favorable test results at f depths.representative of sumps and se?a -c p'ts. It has been the policy of EHD to require the installation of seepage pits to a dept of 25 f t in areas of the county designated for seepage pits, even though test results demonstrate - at s ps may be suitable. This policy is applicable for this project.TA new law that is to be implemented may restrict the installation of seepage pits (Assembly - Bill 885): Before this law is implemented, EHD may require the installation of seepage pits on the - subject Parcels because: 1.) They are the typical and principle effluent management structure installed" ' in.this area, 2.) There is a distance of approximately 55 feet between the bottom of a seepage pit at 25 feet b.g.s. and the current groundwater depth of 80 feet and will probably never rise closer than 10 feet to the bottom of a seepage pit (groundwater.35 fl deep), 3.) Seepage pits allow head pressure buildup to force effluent into the underlying anaerobic clay soils, and 4.) If effluent levels within the seepage E pit rise 10 to 18 feet above the bottom of the pit, the effluent could then be managed by the more permeable silty sand'strata encountered at the medium test depths. The soil analytical test results show low concentrations of subsurface soil nitrate-nitrogen, even though the subject.property has been under agricultural production for at least the last three decades. There is some nitrgen applied to the rice crops, although decomposing organic matter from residual crop decomposition would certainly supply subsurface nitrate-nitrogen higher_ than those concentrations observed, indicating substantial denitrification potential. Soil particle size analysis for the two subsurface soil profiles under Parcels 2 and 5 illustrate varying percentages of sand, silt and clay at the sampled depths. Clay content percentages are somewhat 'consistent between Parcels-3 through 6. Jenssen and Siegrist (1990) found the factors that favor denitrification are fine-grained soils such as clays and silts layered with soils consisting of alternating fine-grained and coarser grained soils with distinct boundaries between the texturally different strata. This was observed under all six proposed Parcels. Stratification may also contribute to the aforementioned increase in soil moisture content. Percolating water encountering coarser soil strata will accumulate on top of this coarser stratum until s_ufficient.soil moisture builds up for the water to travel into this stratum. The nitrate.loading calculations demonstrate the impact from the on-site systems f Pbelow e Maximum Contaminant Level.(MCL) standard for drinking water. Taking the existing nitrate concentration determined in the Sorrenti's on-site well (11.8 ppm nitrate)in .combination with the estimated theoretical recharge from the possible six homes,the resultant concentration will theoretically remain under the MCL. Page -8- Chesney Consulting