New York State Septic System Design Regulations 75-A.9 Alternative Septic Systems - Intermittent Sand Filter Septic Systems Design
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This document uses the New York State wastewater treatment standard for individual household septic systems(Appendix 75-A) to provide an example of state regulated design and installation of alternative septic system designs, including raised septic systems, septic mound systems, intermittent sand filter septic systems,
and evaportion-transpiration septic systems.
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Section 75-A.9 Alternative Septic Systems - (d) Intermittent Sand Filter Septic Systems Design Criteria
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
More expert information on this topic
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