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IV. CONCLUSIONS AND RECOMMENDATIONS It is our opinion the subject site is suitable for its intended use with regard to septic effluent management and that potential environmental impact from nitrogen has been mitigated to an acceptable extent. The percolation rates obtained indicate a surprisingly permeable soil. If deemed by the Environmental Health Department, the permeability of the subsurface soils can be decreased by _ using the siltier, on-site surface material to impede percolation at the bottom of the leachline trenches. However, our calculations are based on the permeability of the soil eventually reaching an long term application rate (LTAR)of approximately 0.5 to 1.0 gals/ftZ/day due to biomat formation. Therefore, addition of a less permeable material may not be necessary. Without sophisticated groundwater monitoring over a long period of time, it is unknown as to the exact groundwater depth at different times of the year, as well as the groundwater directional flow. However, sufficient data has been collected and analyzed to determine that the groundwater table is currently an acceptable distance below grade for there to be adequate biological treatment, according to published scientific literature. Groundwater analyses of two wells in the area indicate a small-to-nonexistent impact to the underlying drinking water aquifers. The leachfields are designed to be perpendicular to the anticipated groundwater directional flow. Mounding effects under the leachfields should be of no concern since the saturated zone is at a sufficient depth. We do not recommend monitoring of the groundwater by the use of monitoring wells. We do recommend however,that as the Church continues to grow, an analyses of the vadose zone water under leachfield be completed. This should be done prior to the start of Phase H and certainly before the start of Phase III. Vadose zone water can be sampled by augering below the leachfield to obtain effluent samples. From these test results, a determination can be made regarding future design changes or further treatment of effluent. Accurate "as-builts" regarding the septic system should be supplied to the Environmental Health Department. The nitrate loading calculations demonstrate that under the leachfield,the groundwater will be theoretically impacted to 3 ppm over the current Maximum Contaminant Level (MCL) drinking water standards. But on an areal basis, the nitrogen contribution over the entire 15 acre site should be under the MCL and not impact the drinking water aquifers, nor the adjacent surface _ waters (the lagoon and Mokelumne River). As referenced,the influence from the river is substantial, based upon scientific studies. Predictability of relevant aspects of the underlying groundwater can only be made with long-term monitoring and sophisticated testing. To reduce septic tank loading, graywater originating from the baptistery may be used for landscape irrigation. However, graywater from the dishwasher must enter the septic system. t , (V 0J C6-ealr 54-j er�Jfr pr Nus t�c�c� 8 valfey Ag Pssearch