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Intermittent sand bed and sand filter septic system designs, specifications, model regulations. This article uses the New York State wastewater treatment standard for individual household septic systems to provide an example of state regulated design and installation of intermittent sand filter septic systems.
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Regulations for the Design of Alternative Septic Systems: Intermittent Sand Filter Septic Systems Design Criteria
For details about sand bed septic system design, installation, inspection, maintenance, or repair, see SAND BED SEPTIC SYSTEMS.
Original source: Title: Appendix 75-A.9 - Alternative Septic Systems [Regulation and System Design Criteria for Raised Septic Systems, Septic Mound Systems, Intermittent Sand Filter Bed Systems, Evaporation-Transpiration Septic Systems, Evaporation-Transpiration Absorption Septic Systems, and Other Alternative Septic Systems] Effective Date: 12/01/1990
(1) Sand Bed Septic Systems - General
In a sand filter septic system, the septic tank or aerobic unit effluent is intermittently spread across the surface of a bed of sand through a network of distribution lines. Collector pipes beneath the filter collect treated effluent after it has passed through the sand.
(2) Site Requirements for Sand Filter Bed Septic Systems
(i) All horizontal separation distances shown in Table 2 must be met and the minimum required vertical separation to groundwater must be met from the bottom of the collector pipes.
(ii) An environmental assessment determines that the development of the site with a sand filter is consistent with the overall development of the area and will cause no adverse environmental impacts.
(3) Design Criteria for Sand Filter Bed Septic Systems
(i) Septic tanks installed before a sand filter shall have dual compartments or two tanks in series. The use of a gas baffle on the outlet is strongly recommended.
(ii) The direct discharge of sand filter effluent to the ground surface or to a body of water shall not be approved by the Department of Health or a local health department acting as its agent.
(iii) Distributor lines shall be placed at three foot center lines as level as possible.
(iv) Collector pipes shall be centered between distribution lines at a slope of 1/16 to 1/8 inch per foot.
(v) Effluent shall be distributed to the sand filter by means of pressure distribution or siphon dosing. Pressure distribution lines shall be a minimum of 1.5 inches and a maximum of three inches in diameter. If siphon dosing is allowed, the distributor pipe(s) shall have a diameter of three to four inches.
(vi) The distribution system shall be designed to dose the filter at least three times daily based upon the design flow rates with each dose.
(vii) The sand media shall have an effective grain size of 0.25 to 1.0 mm. If nitrification is not required by the local health department, the effective grain size shall be in the range of 0.5 to 1.00 mm. All sand shall pass a 1/4 inch sieve.
(viii) The uniformity coefficient of the sand shall not exceed 4.0.
(ix) The maximum allowed daily sand loading rate shall be 1.15 gal/day/sq. ft.
(x) Effluent from the collector pipes shall be discharged to an absorption bed located below the original ground level or a mound that is built up above the original ground surface. The size of the bed/mound shall be based upon the estimated quantity of effluent reaching the collector pipe and an application rate of 1.2 gal/day/sq. ft. regardless of the underlying soil percolation. The fill material for the bed/mound shall consist of medium sand with a percolation rate, tested at the borrow pit, not faster than five minutes per inch. All minimum vertical and horizontal separation distances shall be maintained as described in Section 75-A.4.
(4) Construction of Sand Bed Septic Systems
(i) After excavation, the collector pipe shall be placed in 3/4 inches to 1 1/2 inches size aggregate.
(ii) There shall be a minimum of four inches of this aggregate beneath the entire system above the collectors.
(iii) A three inch layer of crushed stone or clean gravel with a size of 1/8 inches to 1/4 inches is carefully placed on top of the aggregate.
(iv) A minimum of 24 inches of the approved sand is placed above the crushed stone or gravel.
(v) The distributor pipes are placed in a layer of aggregate that provides a minimum of four inches across the entire surface of the filter and at least two inches above and below the distributor pipes.
(vi) A permeable geotextile, two inches of hay or straw, or untreated building paper is placed over the entire bed area to prevent the infiltration of fines into the filter.
(vii) The entire surface of the filter shall be covered with six to 12 inches of topsoil, mounded to enhance the runoff of rainwater from the system and seeded to grass.
(viii) The bed/mound following the filter shall be covered with 12 inches of topsoil and seeded to grass.
More Reading About Intermittent Sand Filter Bed Septic Systems
Sand Septic Filters in DESIGN ALTERNATIVES for Septic Systems, a discussion of various septic effluent filter media.
Using a Sand Bed Effluent Disposal System as a Component of Alternative Septic Systems for Difficult Sites. This document includes the NYS Appendix 75-A section on sand filter beds as well as sand filter bed design comments and advice from other experts
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