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i 2ut�ur7eLseptic Although the.deep-perc testing was conducted at what may considered"sump depth," system structures must-consist of:leachlines and seepage.pits. .Additionally,.even though three of the four Parcels had passing shallow perc tests,,,EHD recognizes this locale:to have poor soil permeability, and therefore they require seepage pits. Pits-will allow for hydraulic head to increase within the pit, in addition to increased holding capacity. Hydraulic head increases as the f' effluent level rises within the pits, thus forcing the effluent through the micropores of the underlying C clay soil. (§ 6.7) Pere test results reveal permeability at typical leachline depth; however, this permeability may be attributed to-root channels,:earthworm biopores, etc. As discussed below, the subject property soil is susceptible.to biomat formation. Therefore, consideration may be given to installing chambers instead of conventional."rock and pipe"leachlines. This will allow for greater oxygen diffusion into the soil-effluent-interface, thus theoretically assisting with biomat decomposition. If chambers are installed, the soil-effluent interface must be sufficiently scarified to allow effluent infiltration, and.nothing can be placed over the chambers (e.g., parking) which would cause the chambers to sink into the soil: (§ 6.7) Regarding the`shallow and deep perc test failures on Parcel B:.Precederit has been established by EHD (See PA-06-00673) whereby in the event of inconsistent/slow perc rates, or where both shallow and"deep perc test failures have occurred on any given Parcel of land, future installation of aseptic system may entail doubling the.number of the seepage pits calculated for the proposed development. Jt is my opinion based upon civil engineering judgment that doubling the seepage pits of the original calculated number shall be sufficient to theoretically create a reasonable lifespan for a proposed septic system on this Parcel. Septic system lifespan issues are discussed below. The Tentative Map in Appendix 3 illustrates the perc test locations. Mr. Nahas is aware that if a future leachfield area is proposed.to beinstalled'outside of the 100 ft radii from the perc test locations, EHD can require additional tests, or an engineered septic system. EHD requires that there be sufficient distance.for"treatment" of septic effluent before it encounters the groundwater table. This distance is normally regarded to be five-feet for leachlines and ten-feet for sumps and seepage pits. Therefore, sufficient distance exists between the bottom of a seepage pit at 25 ft and the current groundwater depth of approximately 107-ft (82 ft separation distance). The encountered underlying-soils possess increasing moisture content with increasing depth due to heavy rains this past winter. High moisture content soils are beneficial for the suppression of nitrification, and the promotion of denitrification of nitrate molecules that may have formed through nitrification in the upper soil environments, particularly if chambers are installed. k. The domestic and irrigation wells reveal a medium concentration of nitrate at 19 ppm which indicates some impact, most likely from:agricultural inputs. It may be that higher nitrate concentrations could have been obtained if the attenuating factors of soil inoisture content and intervening strata of clay were not present. The agrichemical DBCP was found to be Below Detectable Limits. (§ 6:$) The number of leachlines and septic tank size is unknown for any future residential structures since there is no proposal'to develop any of the proposed Parcels at the time of this Study. Page -7- Chesney Consulting