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r��Fi�lterbe�dconstruction details consist of two perforated leachlines on top of 1 ft of drain rock, underlain with 1 ft native soil (aerobic zone), underlain by 1 ft of imported sandy loam soil material (denitrification zone). Imported soil will originate from existing stockpile located at the contractor's yard for this project, Applegate Septic and Sewer. Excavated native will be used as the backfill "cap"to be brought to surrounding grade, which will readily allow oxygen intrusion. CONCLUSIONS AND RECOMMENDATIONS The shallow subsurface soils underlying the subject property where the new filter bed disposal area is to be installed, reveals a fine sand soil structure with exceedingly rapid permeability. Due to percolation testing that demonstrated rates less than 1 min/in, the filter bed disposal structure was designed to mitigate this excessive permeability by the importation of a sandy loam soil material, as referenced. The minimum soil depth from the floor of the filter bed to groundwater is promulgated on Pg S of the SJC Onsite Wastewater Treatment System Standards which states this minimum depth may be "mitigated by the system design or enhancement." This minimum soil depth requirement was initially promulgated by the Regional Water Quality Control Board. The import sandy loam soil to mitigate rapid permeability will also act as a denitrification stratum. As the effluent percolates through the drain rock and through the native high porosity sand, a percentage of the ammonium fraction will nitrify in these aerobic strata. Upon entering the imported sandy loam material, smaller porosity leads to a higher probability of anaerobic conditions within the clay microsites as the effluent percolates through this stratum. This stratum not only promotes denitrification but also the destruction of bacteria and viruses within the clay microsites. Sufficient area exists for the 100% replacement area, as detailed on the plans. All food waste should be handled as solid waste and disposed of in the garbage. All onsite wastewater treatment systems will eventually fail. A reasonably long lifespan of the disposal area can be expected based on the native soil characteristics, the perc rates obtained, and the incorporated design factors. Consideration should be given to pumping the septic tank every three years to mitigate nitrogen loading by extraction of septage. Page -3- Chesney Consulting