Section 0400-48-01-.04 - ADDITIONAL SITE REQUIREMENTS AND LIMITATIONS FOR SUBDIVISION APPROVAL AND INDIVIDUAL LOTS AND ISSUANCE OF CONSTRUCTION PERMITS(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.Tenn. Comp. R. & Regs. 0400-48-01-.04
Original rule filed June 20, 2013; effective September 18, 2013. Rule renumbered from1200-01-06.Authority: T.C.A. §§ 68-221-401 et seq. and 4-5-201 et seq.