Current through September 24, 2024
(1)
Suitability of Site - Prior to the design of subsurface sewage disposal
systems, the suitability of the site must be demonstrated through acceptable
soil absorption rates, acceptable soil conditions, freedom from groundwater
interference or slowly permeable strata below the level of the disposal field
and other topographic characteristics. For lots that are not part of a
subdivision as defined herein, the Commissioner may determine site suitability,
acceptable soil absorption rates, acceptable soil conditions, freedom from
groundwater interference or impervious strata below the level of the disposal
field and other topographic characteristics. For lots that are not part of a
subdivision as defined herein, where the services of a soil consultant are
utilized, then the requirements established in subparagraph (3)(a) of Rule
0400-48-01-.03 may apply as deemed necessary by the Department either on an
area basis or site specific basis.
(2) Water Table- The water table shall be at
least four (4) feet below the bottom of the disposal field, except that a
lesser depth may be permitted where soil conditions provide adequate protection
for groundwater.
(a) Borings for determination
of perched groundwater and the water table may be required by the Commissioner.
In such cases, borings shall be made to a minimum depth of six (6) feet or as
site conditions so warrant. Sufficient time shall be provided for stabilization
of groundwater before water table elevations are recorded. In sandy soil this
may require as little as thirty (30) minutes, while clay soil may require
several hours or overnight. Borings shall be located by number on the plat.
Borings shall be conducted during the wettest part of the year and at a time
approved by the Commissioner.
(3) Rock - At sites where surface rock or
subsurface rock formations exist to such degree as to affect operational
effectiveness of subsurface sewage disposal systems, a sufficient number of
borings to a minimum depth of six (6) feet may be required by the Commissioner
to determine whether subsurface sewage disposal systems can be expected to give
satisfactory service. Such borings shall be located by number on the plat and
the results recorded.
(a) Rock formations
shall be at a depth greater than four (4) feet below the bottom of the disposal
field trenches, provided a lesser depth may be permitted where soil conditions
so warrant.
(b) Rock may be removed
in the septic tank excavation if a smooth, firm, level bedding is
provided.
(4) Other Site
Considerations:
(a) Areas consisting of fill
shall be excluded from the area considered for installation of the disposal
fields unless soil conditions provide for adequate filtration and will prevent
outcropping of sewage effluent.
(b)
Gullies, ravines, dry stream beds, natural drainage ways, sinkholes, wells,
springs, cisterns, streams and caves shall be excluded from consideration as
usable areas for subsurface sewage disposal systems.
(c) Sinks shall be considered unsuitable for
subsurface sewage disposal unless the following requirements are met:
1. Depth to rock formations must be a minimum
of four (4) feet from the surface of the ground and trench depth shall not
exceed thirty (30) inches.
2.
Slopes must be thirty (30) percent or less.
3. The area must not be subject to
flooding.
4. All other site
suitability criteria must be met.
(d) Maximum slope permitted for the area to
be used for the disposal field shall be determined by the consideration of
lateral flow of effluent to the surface of the slope. Slopes of more than
thirty (30) percent shall be considered unsuitable unless soil conditions will
prevent lateral movement of sewage effluent to the ground surface. Slopes
exceeding fifty (50) percent shall be considered unsuitable.
(e) Lot Grading - The area to be used for the
disposal field shall not be disturbed when grading the lot. However, where this
is unavoidable, a re-evaluation shall be made after grading has been completed.
After the suitability of any area to be used for subsurface sewage disposal has
been evaluated and approved for construction, no change shall be made to this
area unless the Commissioner is notified and a re-evaluation of the area's
suitability is made prior to the initiation of construction.
(f) When soils evaluations indicate the soil
absorption rate to be less than ten (10) minutes per inch, a conventional
subsurface sewage disposal system shall not be used.
(5) Soil Improvements
(a) Site Requirements
1. Sites where soil improvement is necessary
to change soil absorption rates to the acceptable range shall be considered
unsuitable for subsurface sewage disposal until the improvement is adequately
noted on the recorded final plat and in addition, noted on the permit at the
time of issuance.
2. Sites where
soil protection practices are necessary to maintain soil absorption rates
within the acceptable range shall be considered unsuitable for subsurface
sewage disposal until the protection practice is adequately noted on the
recorded final plat and in addition, noted on the permit at the time of
issuance.
(b) Design
1. The improvement and/or protection
practices shall be of such location, configuration and construction to
adequately collect, remove and discharge by gravity all interfering surface and
subsurface water and not to collect sewage or any effluent from a subsurface
sewage disposal system.
2. The
minimum trench width of the soil improvement and/or protection practice shall
be twelve (12) inches.
(c) Material Specifications
1. The gravel in the improvement and/or
protection practices must be of sufficient amount, size and quality to allow
storage and free movement of the collected water.
2. If an impermeable barrier is necessary for
proper performance of the improvement and/or protection practice, the barrier
must be of sufficient strength and durability to withstand the conditions under
which it must perform.
3. The
collection pipe must have a minimum diameter of four (4) inches, or equivalent,
and must be designed to collect groundwater. It must be constructed to
withstand the conditions and weights under which it must perform.
4. The outlet pipe must be at least ten (10)
feet in length and have a minimum diameter of three (3) inches, unless
otherwise specified on an engineered drainage plan, and be a minimum of
Schedule 40 PVC. The outlet pipe must be of sufficient length to extend into
the corrugated pipe in order to allow for a suitable connection. The outlet
pipe must be fixed to the corrugated pipe as to not allow for easy removal. The
outlet pipe must extend to the surface and the end must be modified to not
allow entry of animals, but will allow sediment to exit.
Authority:
T.C.A. §§
68-221-401 et seq. and 4-5-201 et
seq.
