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r7aDetentionme Calculation: i Detention Time=2,000 gal tank capacity x 0.70(30%volume lost to sludge/scum accumulation) 1.5 (Peaking Factor)x 245 gals/day(ADF) Detention Time=3.8 days. The minimum acceptable detention time is 1.0 day. B. FILTER BED SIZING CALCULATIONS The proposed effluent disposal area is heavily constrained by driveways, to the north, south and west. The disposal area is 19 ft wide. Incorporating five ft setbacks from the driveways results in a 9 ft wide filter bed disposal area. The length of this area is also constrained. Therefore,the disposal area can now be considered engineer designed. My design criteria is based on the SJC Onsite Wastewater Treatment Systems Standards, Section 9.7.3: "Dispersal field application rates for engineer designed systems may also be determined using Table 3 in Water Quality Control Policy for Siting, Design, Operation, and Maintenance of Onsite Wastewater Treatment Systems. The established perc rate for this project was determined to be 18 minutes per inch(mpi). This translates to an application rate of 0.686 gallons per square foot/day(gals/sf/d), found in Table 3. The filter bed area is 9 ft wide N-S and 50 ft long E-W=450 sf. The effluent acceptance rate= 450 sf x 0.686 gals/sf/d=309 gpd. The ADF was calculated to be 245 gpd. Therefore, the filter bed is adequate size by more than 26%. C. 100% REPLACEMENT/RESERVE AREA The 100%replacement area is designated directly west of the primary disposal area, as illustrated on the design plans. The replacement area is also to be a rectangular filter bed construction, with equal square footage as the primary filter bed area. D.. OPERATIONAL PARAMETERS AND COMPONENTS SSS§ 3.7. The design of the filter bed disposal system is based upon the factors for efficient operation, disposal field longevity, and environmental protection. An overview of the system operation to serve the proposed facility is as follows: Influent from the Restrooms will gravity flow into a P&L Concrete, Inc. standard precast, 2,000 gallon septic tank. A Polylok, Inc. PL-68 effluent filter is to be installed at the outlet of this tank. Clarified effluent will gravity to a three-hole Distribution box (D-box), where the effluent will be equally distributed between two, 47 ft long leachlines, spaced 3 ft apart and with capped ends. A minimum of 12" of washed drain rock is to be placed under the perforated pipe and extending 2" above the perforated pipe. Geotechnical fabric is to be placed over the drain rock and backfilled to final grade with the native, excavated soil. Pae -8- Chesney Consulting