| (a) General Requirement. The type and size of an OSSF shall
be determined on the basis of the soil and site information developed according
to §285.30 of this title (relating to Site Evaluation).
(b) Suitability. A standard subsurface absorption system may
be used if all the soil and site criteria are determined to be suitable under §285.91(5)
of this title (relating to Tables). If one or more of the soil and site criteria
categories are determined to be unsuitable, a standard subsurface absorption
system cannot be used except as noted in §285.91(5) of this title. If
it is determined that a standard subsurface absorption system cannot be used,
either a proprietary or a non-standard system may be used, provided all soil
and site criteria for that system can be met as required in §285.91(13)
of this title.
(c) Surface drainage criteria.
(1) Topography. Uniform slopes under 30% are suitable for standard
subsurface absorption systems. If the slope is less than 2%, steps shall be
taken to ensure there is adequate surface drainage over any subsurface disposal
field. The excavation for a standard subsurface absorption system shall be
parallel to the contour of the ground.
(2) Flood hazard. Any potential OSSF site within a 100-year
floodplain is subject to special planning requirements. The OSSF shall be
located so that a flood will not damage the OSSF during a flood event, resulting
in contamination of the environment. Planning materials shall indicate how
tank flotation is eliminated. Additionally, if the site is within the regulated
floodway, a professional engineer shall demonstrate that:
(A) the system shall not increase the height of the flood;
(B) all components, with the exception of risers, chlorinators,
cleanouts, sprinklers, and inspection ports, shall be completely buried without
adding fill; and
(C) non-buried components (e.g. alarms, junction boxes, and
compressors) shall be elevated above the 100-year flood elevation.
(d) Separation requirements. OSSFs shall be separated from
features, in the area where the OSSF is to be installed, that could be contaminated
by the OSSF or could prevent the proper operation of the system. The separation
requirements are in §285.91(10) of this title.
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