New York Codes, Rules and Regulations › Title 10 - DEPARTMENT OF HEALTH › Chapter - APPENDICES › Appendix 75-A › Section 75-A.9 - Alternative subsurface treatment systems

Current through Register Vol. 46, No. 28, July 10, 2024
(a) General.
				Alternative subsurface treatment systems described in this section can be
				installed when site conditions exist that do not allow the use of conventional
				subsurface treatment systems.
(b)
				Raised System.
(1) A raised system is an
				absorption trench system constructed in fill material with acceptable
				permeability placed above the natural soil on a building lot.
(2) Site Requirements. A raised system may be
				used where all the following conditions are found:
(i) There is at least one foot of original
				soil with a faster than 60 minutes percolation rate, above any impermeable soil
				layer or bedrock, but not more than two feet.
(ii) The maximum high groundwater level must
				be at least one foot below the original ground surface.
(iii) Slopes shall not exceed 15%.
(iv) All minimum vertical and horizontal
				separation distances can be maintained as described in Table 2.
(3) Design Criteria.
(i) Percolation tests shall be conducted in
				the fill material at the borrow pit and after placement and setting at the
				construction site. The slower percolation rate of these tests shall be used for
				design purposes.
(ii) The total
				area beneath the absorption trenches, extending 2.5 feet in all directions from
				the outer edge of all trenches, is defined as the basal area. The minimum size
				of the basal area of the raised system shall be calculated based upon 0.2
				gpd/sq. ft. A conventional absorption trench system as described in subdivision
				75-A.8(b) is to be designed using the percolation rate of the fill material.
				The use of slowly permeable soils for the fill material will result in a trench
				system that will have a basal area larger than the minimum area calculated
				using 0.2 gpd/sq. ft.
(iii) The
				minimum size of the basal area of a raised system designed to receive effluent
				from an ETU located in an area described in subclauses 75- A.6(b)(6)(ii)(d)(1)
				or (2), shall be calculated based upon 0.3 gpd/sq. ft. A conventional
				absorption trench system as described in subdivision 75-A.8(b) is to be
				designed to distribute effluent evenly over the fill material basal
				area.
(iv) Sufficient fill material
				with a percolation rate of between 5 - 30 min/in is required to maintain at
				least two feet separation between the proposed bottom of the trenches and any
				boundary condition such as groundwater, bedrock, clay or other relatively
				impermeable soil or formation.
(v)
				The edge of the fill material shall be tapered at a slope of no greater than
				one vertical to three horizontal with a minimum 20 foot taper.
(vi) Horizontal separation distances shall be
				measured from the outside edge of the taper.
(vii) The system shall incorporate siphon
				dosing, pump dosing or pressure distribution. Gravity distribution may be
				allowed where both the following conditions are met:
(a) the local health department has a program
				incorporating site evaluation, system design approval, and construction
				inspection/certification; and
(b) a
				minimum of two feet of fill material with a percolation rate of 5 - 30 min/in
				shall be placed between the bottom of the trenches and the existing
				ground.
(viii) Curtain
				drains may be used to intercept and carry underground water away where high
				groundwater levels exist. Curtain drains shall be upslope from the system and
				at least 20 feet from the toe of slope of the fill material.
(4) Construction.
(i) Heavy construction equipment shall not be
				allowed within the area of the system. The underlying soil shall be undisturbed
				although the surface may be plowed with at least a double bottomed blade/furrow
				plow and the furrow turned upslope.
(ii) A system shall not be built in
				unstabilized fill material. The fill material shall be allowed to settle
				naturally for a period of at least six months to include one freeze-thaw cycle,
				or may be stabilized by mechanical compaction in shallow lifts if a fill
				material consisting of only a granular sand or sandy loam is used.
(iii) The absorption trenches shall be
				constructed in the fill material.
(iv) The entire surface of the system
				including the tapers shall be covered with a minimum of six inches of topsoil,
				mounded to enhance the runoff of rainwater from the system and seeded to
				grass.
(v) On sloping sites a
				diversion ditch or curtain drain small be installed uphill to prevent surface
				water runoff from reaching the raised system area.