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1 . FHowever, given that the vast majority of upgradient land use in proximity to the property is in agricultural production, a higher percentage of nitrate may be originating from this source in comparison to upgradient septic systems. The percolation test results show the typical leachline depth soils at approximately 42 inches in depth are a tight, compacted soil with small porosity. Therefore, seepage pits are warranted in this area and F must be used for this project. The perc test results obtained from the deep perc tests indicate the need for seepage pits. Due to biomat formation, the Long Term Acceptance Rate (LTAR) for the seepage pits should stabilize at approximately 0.5 gallons/ft'/day according to the scientific literature. Therefore, the LTAR for each 36" pit should be: 243 ft'/3 ft dia. x 25 ft deep 121 gallons/day x three pits = 363 gallons/day of effluent absorbed per house. Calculated flows = 68 gals/person x 4 persons/house = 272 gals effluent generated/house. t Although the shallow percolation tests for each proposed parcel indicated medium, or non-existent percolation rates, leachline trenches can be constructed to take advantage of beneficial properties of F. the clay surface soils. It is recommended that leachlines trench sidewalls be opened with teeth on the isides of the backhoe bucket. The teeth on the cutting edge of the bucket can be used to scarify and F open the bottom of the trenches to the maximum extent possible. This will allow some effluent infiltration and percolation within the leachline trenches and promote denitrification within the anaerobic micro sites of the clay soil. If the proposed project is approved, it will be the requirement of EHD to stipulate the depth of the P P wells and the grout seal for each of the three new domestic wells. Before the wells are completed, water should be drawn from the aquifers where the wells are perforated and the water tested for nitrate and DBCP concentrations. If nitrate exceeds one-half the MCL and/or if DBCP is present, the E well should be drilled deeper and the grout seal also extended to a deeper depth. It is important to note that all septic systems have a lifespan. This lifespan is dependant on several factors and is therefore difficult to determine. Septic system failure would primarily result frorn the advanced formation of the biomat on the wetted soil/effluent interface. This mat is composed mostly ` of aerobic and anaerobic bacteria and bacterial products consisting of a slime of polyuronides and polysaccharides. If the soil/effluent interface is well aerated, a variety of soil microfauna such as ' nematodes and protozoa may digest the biomat bacteria. To lessen biomat formation, two septic tanks should be installed in series and filters should be installed in the second chamber of the second septic tank for each new house. In addition, no garbage disposals should be installed in the houses. The total length of leachline and the number of seepage pits will be dependant upon the number of bedrooms each new home will have. Additionally, the system should be oversized if a high number of people, especially children, will inhabit the new homes. A minimum 50% replacement area must be incorporated into the design. The septic systems for each new parcel must abide with Section 10 of the F4 San Joaquin County Sewage Standards. FNitrate loading can also occur from lawns/landscaping/gardens, which is estimated to be 20% and could be significantly higher. If the project is approved, buyers of the new homes should use"slow- release"nitrogen fertilizers to reduce nitrate loading from lawns and landscaping. F' it Fchesney Consulting