Rules & Regulations of the State of Tennessee
Title 0400 - Environment and Conservation
Subtitle 0400-48 - Water Resources (Groundwater Protection)
Chapter 0400-48-01 - Regulations To Govern Subsurface Sewage Disposal Systems (Transferred from 1200-01-06)
Section 0400-48-01-.15 - ALTERNATIVE METHODS OF SUBSURFACE SEWAGE DISPOSAL

Universal Citation: TN Comp Rules and Regs 0400-48-01-.15

Current through September 24, 2024

(1) Regarding alternative methods of subsurface sewage disposal, if a conflict occurs between this rule and other rules of these regulations, the items of this rule shall apply. However, the Commissioner may allow repairs if the site does not meet soil suitability and reserve area requirements. The wastewater flow for residences or other similar establishments served by alternative methods of subsurface sewage disposal shall be based upon one hundred fifty (150) gallons per bedroom per day.

(2) Large Alternative Subsurface Methods of Sewage Disposal - Any alternative subsurface sewage disposal system that has a wastewater flow greater than seven hundred fifty (750) gallons per day shall be considered a large alternative subsurface sewage disposal system.

(a) A site specific design for each large alternative subsurface sewage disposal system shall be submitted to the department for review.

(b) The design shall be stamped with the seal of a licensed engineer.

(c) Prior to design approval, a licensed engineer must agree, in writing, to monitor the installation and construction of the system and upon completion, provide a final set of as built plans encompassing all components of the system and certification that the installation is in accordance with the design specifications.

(d) It shall be the responsibility of the department to review the aforementioned design and notify the engineer, in writing, of approval of the plans, denial of the plans or needed modifications to the plans.

(3) A Low Pressure Pipe (LPP) system is a subsurface sewage disposal system, which has three (3) basic design principles different from conventional subsurface sewage disposal systems. They are:

(1) uniform distribution of effluent,

(2) dosing and resting cycles, and

(3) shallow placement of trenches. When lots that are less than twenty thousand (20,000) square feet are proposed, the department shall determine the necessity, location and design of buffer zones. LPP systems shall not be used to dispose of wastewater wherein the average concentration of grease exceeds one hundred fifty (150) milligrams per liter (mg/L) because of the clogging potential of the distribution network.

LPP systems designed to accommodate wastewater flows in excess of seven hundred fifty (750) gallons per day must be designed by a licensed engineer. The design shall be reviewed by the department applying the requirements of paragraph (2) of this rule.

(a) Site and Soil Requirements

1. Prior to the design of the LPP system, the suitability of the site must be demonstrated through acceptable soil absorption rates, acceptable soil conditions and other topographic characteristics. The acceptable soil absorption rate range shall be from ten (10) minutes per inch through seventy-five (75) minutes per inch as determined by an extra-high intensity soil map prepared by an approved soil consultant. If the soil absorption rate is determined to be greater than seventy-five (75) minutes per inch based upon the extra-high intensity soil map, then percolation tests may be conducted. However, soils with absorption rates in excess of seventy-five (75) minutes per inch due to wetness that cannot be corrected by drainage shall not be eligible for percolation tests. Percolation rates from seventy-six (76) minutes per inch through one hundred twenty (120) minutes per inch are acceptable if no water problems exist.

2. A minimum soil depth of thirty (30) inches over any underlying restrictive horizon is required. However, a modified LPP system may utilize a maximum of six (6) inches of compatible fill, as determined by an approved soil consultant, to obtain the required thirty (30) inches of depth.

3. Slopes of more than thirty (30) percent shall be considered unsuitable.

4. An area of suitable soil must be available to install the initial system and maintain a suitable area of adequate size for one hundred (100) percent duplication.

5. The size of the LPP system shall be determined by the following:

(i) An extra-high intensity soil map, provided by a soil consultant approved by the department, shall establish the soil absorption rate.

(ii) If the extra-high intensity soil map determines that a percolation test is necessary to establish a rate, the percolation holes shall be located in a grid pattern with maximum perpendicular distances between holes of twenty-five (25) feet and the gridded portion shall encompass the entire area to be utilized for the system and duplicate area. Greater distances may be allowed as determined by the Commissioner. The percolation test procedure in Rule 0400-48-01-.05 shall apply.

(iii) The daily wastewater flow divided by the loading rate (Table II) shall determine the area (ft2) required for the initial system.

(iv) Hydraulic overloading of the disposal field may occur when excessive amounts of effluent are distributed over a continuous common slope. Therefore, buffer zones are required if there is more than six (6) feet of elevation difference between the upper and lower laterals or if the distance between the upper and lower laterals exceeds fifty (50) feet. The buffer zone size and the use of soil improvement or soil protection practices are site specific and shall be determined by the Commissioner based on the recommendation of an approved soil consultant. The buffer zone shall not be included as part of the reserve area.

Table II. Maximum Loading Rate

Established Rate (mpi)	Loading Rate (gpd/ft 2 )
10	0.400
20	0.400
30	0.350
40	0.300
45	0.275
50	0.250
60	0.200
75	0.150
90	0.100
120	0.050

(b) Layout of the LPP System

1. The required linear footage is determined by dividing the amount of required square footage of suitable soil area by five (5).

2. The location of the septic tank, dosing chamber and the disposal field shall be in accordance with Rule 0400-48-01-.11.

3. The lateral lines shall be placed on contour and lengths shall not exceed those specified as follows:

*5/32 in. Orifice*	Maximum Lateral Length (ft)
	Pipe Size (in)
Hole Spacing (ft)	1	1.25	1.5	2
3	50	75	100	140
4	55	80	110	150
5	60	90	120	N/A
6	65	100	125	N/A
7	70	110	135	N/A
8	75	120	145	N/A

*3/16 in. Orifice*	Maximum Lateral Length (ft)
	Pipe Size (in)
Hole Spacing (ft)	1	1.25	1.5	2
3	30	55	75	115
4	35	60	85	130
5	40	65	100	145
6	45	75	110	150
7	50	80	115	N/A
8	55	85	125	N/A

*7/32 in. Orifice*	Maximum Lateral Length (ft)
	Pipe Size (in)
Hole Spacing (ft)	1	1.25	1.5	2
3	30	50	65	90
4	35	55	70	105
5	40	60	80	115
6	45	65	85	130
7	50	70	95	140
8	55	80	105	150

*1/4 in. Orifice*	Maximum Lateral Length (ft)
	Pipe Size (in)
Hole Spacing (ft)	1	1.25	1.5	2
3	30	40	60	80
4	35	45	65	90
5	35	55	70	100
6	40	60	75	110
7	40	65	80	120
8	45	70	85	130

4. The trench bottom of each lateral shall be at the same elevation throughout that lateral.

5. The distance between laterals (center to center) shall not be less than five (5) feet.

6. Trench width shall be a minimum of twelve (12) inches.

7. Trench depth shall range between eighteen (18) and twenty-two (22) inches.

8. A minimum of twelve (12) inches of soil material shall be present between the bottom of the trenches and the restrictive layer.

9. Individual lateral lines shall be a maximum of one hundred (100) feet in length, unless supported by an engineered design.

1. The dosing rate per linear foot of disposal trench shall be uniform over the entire system. This may be accomplished by varying the hole spacing, hole sizing or placement of valves in the manifold or laterals to compensate for changes in ground elevation. Table III shall be used to calculate dosing rates.

Table III.

Pressure Head vs. gpm Flow Per Hole

Pressure Head		Hole Diameter (in)
ft	psi	5/32	3/16	7/32
1	0.43	0.29	0.42	0.56
2	0.87	0.41	0.59	0.80
3	1.30	0.50	0.72	0.98
4	1.73	0.58	0.83	1.13
5	2.16	0.64	0.94	1.26

2. The first and last holes in a lateral shall be thirty (30) inches from the ends of the lateral. Hole spacing shall not exceed seven and one-half (71/2) feet.

3. Hole sizes shall be within the range of five thirty-seconds (5/32) inches through seven thirty-seconds (7/32) inches.

4. Calculation of gallons per minute (gpm) flow and total dynamic head.

(i) The gallons per minute flow amount that the pump must provide shall be determined by adding the gallons per minute flows per hole over the system dosed by that pump.

(ii) The total dynamic head (TDH) shall be determined by adding the following:

(I) Elevation head is the difference in elevation between the bottom of the pump and the highest ground elevation at the disposal field. The minimum assigned elevation head shall be five (5) feet.

(II) Friction head shall be determined from Appendix III plus fittings loss.

(III) A pressure head average of three (3) feet shall be used for TDH calculations. The range shall be one (1) through five (5) feet.

5. When pumping uphill, a check valve must be utilized if the volume of the supply line, manifold and the volume of the laterals that drain back into the pump tank exceeds one-fourth (1/4) daily flow.

6. The minimum dosing volume shall be determined by adding the volume of the supply line, manifold and five (5) times the volume of the laterals. If a check valve is utilized, the minimum dosing volume shall be determined by adding the volume of the manifold and five (5) times the volume of the laterals.

7. The dosing volume shall be between one-fourth (1/4) and one-half (1/2) daily flow, except in those situations where the minimum dose exceeds one-half (1/2) daily flow, then the calculated minimum dose shall be the dosing volume.

(d) Equipment and Material Specifications

1. Septic Tank and Dosing Chamber

(i) The septic tanks shall conform to all design, construction and installation criteria set forth in Rules 0400-48-01-.08 and 0400-48-01-.09.

(ii) The dosing chamber shall conform to all design construction and installation criteria set forth in Rule 0400-48-01-.12.

2. Pipe and Fittings

(i) All pipe materials shall be PVC and have a minimum equivalent strength of Schedule 40.

(ii) All fittings shall be pressure fittings.

(iii) All connections shall be adequately cleaned with cleaning solvent and glued with PVC solvent cement.

(iv) The gate or globe valve(s) and check valve shall be either bronze or PVC.

(v) The lateral pipe diameter shall be a minimum of one (1) inch.

(vi) The distal end of each lateral shall be equipped with a capped turn-up that provides above-ground access.

3. Pump, Float Controls and Alarm System

(i) The pump shall be an effluent pump of sufficient quality and size to meet or exceed the flow requirement and the total dynamic head requirement of the system.

(ii) The pump float controls must be adjustable and must be sealed against entry of effluent or gases.

(iii) Alarm System

(I) A high water alarm shall be required and consist of an audible and visible alarm located in a visible place and clearly marked "wastewater system alarm".

(II) The alarm and alarm switches shall be placed on a separate electrical circuit from the pump power line.

(III) The alarm float control shall be placed so as to be activated when the pump chamber water level rises above the "pump on" float control.

4. Disposal Field Media

The disposal field media size shall be within the range of one-half (1/2) to one (1) inch. It must be washed and free of fines.

(e) Installation Procedures

1. Site Preparation and Imported Fill

(i) The soil area reserved for the initial and duplicate systems must not be cut, filled, compacted or disturbed in any manner prior to or after system installation.

(ii) No site preparation shall occur if the soil is wet. The designated person responsible for monitoring system installation shall determine when the soil is adequately dry.

(iii) If imported fill is used during installation it must be of compatible material, which shall be determined by the soil consultant approved by the department. The area to be filled must be disked prior to adding fill. The fill material must be applied with a minimum amount of wheeled traffic and must be incorporated to ensure even mixing.

2. Supply Line and Manifold

(i) The manifold and laterals shall be designed and installed to drain after each use.

(ii) The supply line shall be designed and installed to drain after each use unless system design requires a check valve.

(iii) A tee to tee connection between the manifold and laterals shall be used except in situations where the topographic, soil and other site conditions allow the manifold and laterals to be at right angles. If the manifold and laterals are at right angles then crosses or tee to tee connections may be utilized.

3. Distribution Laterals

(i) The distribution laterals shall be constructed with a minimum disposal field media depth of nine (9) inches, with three (3) inches above the lateral pipe invert.

(ii) The disposal field media must be covered with untreated building paper, straw or other acceptable material that will allow movement of water and restrict soil movement.

4. Pump and Controls

(i) The pump must be placed so that the intake is a minimum of eight (8) inches above the bottom of the pump chamber.

(ii) As a means to remove the pump from the pump chamber, a material of sufficient strength and durability must be secured to the pump and access riser.

(iii) The pump control must be positioned so the "pump off" switch is slightly above the top of the pump and the "pump on" switch is at the desired dosing depth.

(iv) The pump outlet pipe must be connected to the supply manifold with a threaded union or similar device.

(v) A PVC or bronze, gate or globe valve shall be placed in the supply line to adjust the specific pressure head.

(vi) If the effluent is pumped downhill, a five thirty-seconds (5/32) inch siphon breaker hole must be drilled in the bottom of the supply line above the water level inside the pump tank.

(vii) All electrical installations shall be installed to meet the current wiring methods of the current edition of the "National Electric Code" (NEC) adopted by the State Fire Marshall's office.

5. The completed landscape must be shaped to prevent water from ponding or flowing over the system.

(4) A Mound System is a soil absorption system that is located above the natural soil surface and constructed with suitable fill material. The system differs from the conventional subsurface sewage disposal system in three (3) ways:

(1) uniform distribution of effluent,

(2) dosing and resting cycles and (3) above ground construction. When lots that are less than twenty thousand (20,000) square feet are proposed, the department shall determine the necessity, location and design of buffer zones. Mound systems shall not be used to dispose of wastewater wherein the average concentration of grease exceeds one hundred fifty (150) milligrams per liter (mg/L) because of the clogging potential of the distribution network.

Mound systems designed to accommodate wastewater flows in excess of seven hundred fifty (750) gallons per day must be designed by a licensed engineer in accordance with T.C.A. § 62-2-101 et seq. The design shall be reviewed by the department applying the requirements of paragraph (2) of this rule.

(a) Site and Soil Requirements

1. Prior to the design of the mound system, the suitability of the site must be demonstrated through acceptable soil absorption rates, acceptable soil conditions and other topographic characteristics.

2. The size of the mound system shall be determined by the following:

(i) An extra-high intensity soil map, provided by a soil consultant approved by the department, shall establish the soil absorption rate.

(ii) If the extra-high intensity soil map, determines that a percolation test is necessary to establish a rate, the percolation holes shall be located in a grid pattern with the maximum perpendicular distances between the holes being twenty-five (25) feet and the gridded portion shall encompass the entire area to be utilized for the system and duplicate area. Greater distances may be allowed as determined by the Commissioner. The percolation test procedure in Rule 0400-48-01-.05 shall apply.

(iii) The daily wastewater flow divided by the infiltrative capacity of medium sand (1.2 gal/ft2/day) shall determine the area (ft2) required for the distribution bed.

3. The requirements relating to rock, groundwater and other site conditions established in paragraphs (2), (3) and (4) of Rule0400-48-01-.04 shall apply. A minimum soil depth of twenty-four (24) inches over any underlying restrictive horizon is required. However, a modified mound system may utilize up to four (4) inches of additional sand backfill reducing the minimum depth of soil to any underlying restrictive horizon to twenty (20) inches.

4. The acceptable soil absorption rate range for the mound system shall be from ten (10) minutes per inch through seventy-five (75) minutes per inch as determined by an extra-high intensity soil map conducted by an approved soil consultant. If the soil absorption rate is determined to be greater than seventy-five (75) minutes per inch based upon a soils map prepared by an approved soil consultant, percolation tests may be conducted. However, soils with absorption rates in excess of seventy-five (75) minutes per inch due to wetness that cannot be corrected by drainage shall not be eligible for percolation tests. Percolation rates from seventy-six (76) minutes per inch through one hundred twenty (120) minutes per inch are acceptable if no water problems exist.

5. An area of suitable soil must be available to install the initial system and maintain a suitable area of adequate size for one hundred (100) percent duplication.

6. If tree stumps or boulders are present within the areas designated for the initial and duplicate systems, adequate area must be available to compensate for the area occupied by the boulders and tree stumps.

7. The basal area available for a mound must be equal to or greater than the basal area required for a given soil absorption rate.

(i) On sloping sites, the basal area available is that area directly below and downslope of the distribution bed. On level sites, the basal area available is that area below and on both sides of the distribution bed. That area below the end slopes shall not be included as available basal area.

(ii) The basal area required is determined by dividing the daily flow by infiltrative capacity of the soil. The infiltrative capacity for a given soil absorption rate can be found below:

Absorption Rate (mpi)	Infiltrative Capacity (gal/ft2/day)
10-29	1.20
30-60	0.74
61 - 120	0.24

8. Slopes steeper than twelve (12) percent shall not be utilized. Sites with soil absorption rates of sixty-one (61) through one hundred twenty (120) minutes per inch shall not exceed a slope of six (6) percent.

9. When cluster mounds are used, buffer zones are required at a frequency and size as determined by an extra-high intensity soil map and site evaluation.

(b) Layout of the Mound System

1. The mound shall be located so as to insure that the distribution bed is situated parallel to slope contour.

2. The location of the septic tank, dosing tank and disposal mound shall be in accordance with Rule 0400-48-01-.11.

3. The distribution bed shall be constructed level and its thickness shall be constant. A layer of uncompacted straw six (6) inches thick, untreated building paper or acceptable synthetic fabric shall be placed between the distribution bed and the clay cap.

4. Configuration

(i) The end slope gradient of the mound shall not be steeper than three (3) horizontal to one (1) vertical. The distance from the gravel bed to the toe of the end slope is calculated by multiplying the average mound height by the horizontal slope figure.

(ii) The upslope and downslope gradient of the mound shall not be steeper than three (3) horizontal to one (1) vertical. The distance from the gravel bed to the toe of either the upslope or the downslope side is calculated by multiplying the mound height at the appropriate edge of the gravel bed by the horizontal slope figure and then by the slope correction factor found in

Table IV.

Downslope and Upslope Width Corrections for Mounds on Sloping Sites

Slope Percent	Downslope Correction Factor	Upslope Correction Factor
0	1.00	1.00
2	1.06	0.94
4	1.14	0.89
6	1.22	0.86
8	1.32	0.80
10	1.44	0.77
12	1.57	0.73

(iii) The distribution bed thickness shall be a minimum of nine (9) inches with a minimum of six (6) inches of aggregate below the distribution network.

(iv) The bed width shall not exceed ten (10) feet.

(v) The sand fill thickness beneath the gravel bed shall be a minimum of one (1) foot.

(vi) The cap above the distribution bed shall consist of one (1) foot of clayey subsoil at its center tapering to one-half (1/2) foot at its edges.

(vii) The entire finished mound shall be covered with one-half (1/2) foot of soil material suitable for plant growth.

1. The dosing rate per linear foot of lateral shall be uniform throughout the entire distribution network.

2. Hole spacing and location shall be such so as to provide uniform distribution of effluent over the entire distribution bed. If the last hole is equal to or greater than one-half (1/2) of the hole spacing distance from the distal end of the lateral, a hole shall be placed in the end cap or adjacent to it.

3. Hole sizing, spacing, lateral length and diameter shall be derived from Table V. The hole diameter shall range from five thirty-seconds (5/32) through one- fourth (1/4) inch.

4. The system must be designed and placed so that the laterals and manifold drain after each dosing.

5. Calculation of gallons per minute (gpm) flow and total dynamic head (TDH).

(i) The gallons per minute flow, which the pump must provide, shall be determined by adding the combined gallons per minute flows of each hole.

(ii) The total dynamic head (TDH) shall be determined by adding the following:

(I) Elevation head is the difference in elevation between the bottom of the pump and the laterals in the distribution bed. The minimum assigned elevation head shall be five (5) feet.

(II) Friction head shall be determined from Appendix III plus fittings loss.

Table V.

Allowable Lateral Lengths (ft) for Three (3) Pipe Diameters, Three (3) Perforation Sizes and Two (2) Perforation Spacings

Perforation		Pipe Diameter (in)
Spacing	Diameter	1	1 1/4	1 1/2
30 in	5/32 in	42 ft	68 ft	85 ft
30 in	3/16 in	34 ft	52 ft	70 ft
30 in	7/32 in	30 ft	45 ft	57 ft
30 in 36 in	1/4 in 5/32 in	25 ft 45 ft	38 ft 70 ft	50 ft 90 ft
36 in	3/16 in	36 ft	60 ft	75 ft
36 in	7/32 in	33 ft	51 ft	63 ft
36 in	1/4 in	27 ft	42 ft	54 ft

(III) A pressure head average of three (3) feet shall be used for TDH calculations. The range shall be one (1) through five (5) feet.

6. The minimum dosing volume shall be determined by adding the volume of the supply line, manifold and five (5) times the volume of the laterals.

8. When pumping uphill, a check valve must be utilized if the volume of the supply line, manifold and the volume of the laterals that drain back into the pump tank exceeds one-fourth (1/4) of the daily flow. If a check valve is utilized, the minimum dosing volume shall be determined by adding the volume of the manifold and five (5) times the volume of the laterals.

(d) Equipment and Material Specifications

1. Septic Tank and Dosing Tank

(i) The septic tank shall conform to all design, construction and installation criteria set forth in Rules 0400-48-01-.08 and 0400-48-01-.09.

(ii) The dosing chamber shall conform to all design, construction and installation criteria set forth in Rule 0400-48-01-.12.

2. Pipe and Fittings

(i) All pipe materials shall be PVC and have a minimum equivalent strength of Schedule 40.

(ii) All fittings shall be pressure fittings.

(iii) All connections shall be adequately cleaned with cleaning solvent and glued with PVC solvent cement.

(iv) The gate or globe valve(s) and check valve shall be either bronze or PVC.

(v) The lateral pipe diameter shall be a minimum of one (1) inch.

(vi) The distal end of at least one (1) lateral shall be equipped with a capped turn-up.

3. Pump, Float Controls and Alarm System

(i) The pump shall be an effluent pump of sufficient quality and size to meet or exceed the gallons flow requirement and the total dynamic head requirement of the system.

(ii) The pump float controls must be adjustable and must be sealed against entry of effluent or gases.

(iii) Alarm System

(I) A high water alarm shall be required and consist of an audible and visible alarm located in a visible place and clearly marked "wastewater system alarm."

(II) The alarm and alarm switches shall be placed on a separate electrical circuit from the pump power line.

(III) The alarm float control shall be placed so as to be activated when the pump chamber water level rises above the "pump on" float control.

4. Disposal Field Media

The media size shall be within the range of one-half (1/2) to one (1) inch. It must be washed and free of fines.

5. Sand

(i) The particle sizes shall be predominantly (fifty (50) percent or greater) medium sand (0.50 to 0.25 mm) with no more than twenty (20) percent fine sand (0.25 to 0.10 mm) and be free from silt and clay.

(ii) The sand shall be composed of stable materials and not subject to chemical deterioration.

6. Clay Cap Above the Distribution Bed - The cap shall be clayey subsoil.

7. Final Cover - The final cover shall consist of non-clayey, friable, fertile soil capable of supporting plant growth.

(e) Installation Procedures

1. Site Preparation and Imported Fill

(i) The soil area reserved for the initial and duplicate systems must not be cut, filled, compacted or disturbed in any manner prior to or after system installation.

(ii) No site preparation shall occur if the soil is wet. The designated person responsible for monitoring system installation shall determine when the soil is adequately dry.

(iii) All trees within the area designated for the mound shall be cut to ground level and all excess vegetation shall be removed.

(iv) The area designated for the mound shall be plowed to a minimum depth of eight (8) inches prior to addition of the sand fill. This area shall be plowed on contour.

(v) After any area is plowed there shall be no large equipment or wheeled traffic on or over said area. If a small tracked vehicle is used for construction there shall be a minimum of six (6) inches of sand between the track and plowed layer.

2. Supply Line and Manifold

(i) The manifold and laterals shall be designed and installed to drain after each use.

(ii) The supply line shall be designed and installed to drain after each use unless the system design requires a check valve.

(iii) The supply line shall be installed so as to prevent freezing and shall not enter from the downslope side.

3. Pump and Controls

(i) The pump must be placed so that the intake is a minimum of eight (8) inches above the bottom of the pump chamber.

(ii) As a means to remove the pump from the pump chamber, a material of sufficient strength and durability must be secured to the pump and access riser.

(iii) The pump control must be positioned so the "pump off" switch is slightly above the top of the pump and the "pump on" switch is at the desired dosing depth.

(iv) The pump outlet pipe must be connected to the supply manifold with a threaded union or similar device.

(v) Immediately after the union, a gate or globe valve shall be placed in the supply line. The valve may be either PVC or bronze and shall be used to adjust the pressure on the system to the desired head.

(vi) If the effluent is pumped downhill, a five thirty-seconds (5/32) inch siphon breaker hole must be drilled in the bottom of supply line above the water level in the pump tank.

(vii) All electrical installations shall be installed to meet the current wiring methods of the current edition of the "National Electric Code" (NEC) adopted by the State Fire Marshall's office.

4. The completed system must be shaped to prevent water from ponding or flowing over the system.

(5) A Waste Stabilization Lagoon may provide satisfactory sewage treatment for residences where soil conditions are not suited for absorption systems and flows are seven hundred fifty (750) gallons per day or less. Waste stabilization lagoons require a minimum tract of five (5) acres.

(a) Site and Soil Requirements

1. Prior to the design of the waste stabilization lagoon, the suitability of the site must be demonstrated through acceptable soil absorption rates, acceptable soil conditions and other topographic characteristics.

2. The soil characteristics shall be determined by the following:

(i) An extra-high intensity soil map shall establish the soil rate. The absorption rate may be estimated by an approved soil consultant but may require approval by the department.

(ii) A pit profile description to a depth of six (6) feet below ground surface shall be generated for each lagoon cell (primary and duplicate). Each description shall identify: soil structure, soil color, including mottles, texture including coarse fragments, plasticity and consistency for each distinct horizon in the soil profile.

(iii) The depth of the seasonal high water table shall be noted if it is located within six (6) feet of the soil surface.

3. The soil absorption rate must be a minimum of one hundred twenty (120) minutes per inch as estimated by an approved soil consultant.

4. An area of suitable soil must be available to install the initial system and maintain a suitable area of adequate size for one hundred (100) percent duplication.

5. The lagoon shall be located in soils where the vertical separation from the bottom of the lagoon and bedrock and rock formations, or more permeable material, are a minimum of one (1) foot.

6. Predominant redoximorphic features shall not be located within six (6) inches of the ground surface. The lagoon shall not be located in areas subject to flooding as determined by the department. The soil profile shall not be hydric in classification.

7. Slopes greater than eight (8) percent shall be considered unsuitable.

8. Selection of the site shall include a clear sweep of the surrounding area by prevailing winds. Heavy timber must be removed for a distance of one hundred (100) feet from the water's edge to enhance wind action and prevent shading.

9. Areas consisting of fill shall be excluded from the area considered for installation of the waste stabilization lagoon and disposal field.

10. Lot Grading - The area to be used for the waste stabilization lagoon and disposal field shall not be disturbed when grading the lot. However, where this is unavoidable, a re-evaluation shall be made by an approved soil consultant after grading has been completed. After the suitability of any area to be used for a waste stabilization lagoon 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.

(b) Location - A minimum acreage tract of five (5) acres is required and larger areas may be necessary.

1. Minimum Separation Distances

(i) The lagoon shall be located a minimum of two hundred (200) feet from property lines, as measured from the water's edge.

(ii) The lagoon shall be located a minimum of two hundred (200) feet from the nearest residence, commercial or industrial establishments, any habitable building or public use area. With the owner's permission the lagoon may be within a lesser distance of his home.

(iii) The lagoon shall not be located closer than fifty (50) feet away from any spring or well. Greater horizontal separation distances may be required depending on engineering and hydrogeological data and type of water supply.

(iv) The lagoon shall not be closer than fifty (50) feet away from a stream, lake or impoundment.

(v) The lagoon shall not be located closer than fifty (50) feet from gullies, ravines, dry stream beds, natural drainage ways, sinks, caves and cut banks.

1. The capacity of a two (2) cell lagoon shall be equivalent to a sixty (60) day minimum retention time based upon an average daily sewage flow of one hundred fifty (150) gallons per bedroom for residences. The minimum water surface area of both cells shall be one thousand two hundred fifty (1,250) square feet.

2. A properly sized and constructed two (2) compartment septic tank shall precede the lagoon.

3. The shape of the lagoon shall be such that there are no narrow or elongated portions. Round, square or rectangular cells are considered most desirable. Rectangular cells shall have a length not exceeding three (3) times the width. No islands, peninsulas or coves shall be permitted. Embankments must be rounded at corners to minimize accumulations of floating materials.

4. The embankment top width shall be a minimum of two (2) feet.

5. The embankment slopes shall not be steeper than two (2) horizontal to one (1) vertical on the inner and outer sides.

6. Inner embankment slopes shall not be flatter than three (3) horizontal to one (1) vertical. Outer embankment slopes shall be sufficient to prevent the entrance of surface water into the lagoon.

7. Freeboard (the distance from the top of the water to the top of the embankment) shall be at least two (2) feet after settling. Additional freeboard may be provided.

8. Embankments shall be seeded with a locally hardy grass from the outside toe to the water line, to minimize erosion and facilitate weed control. Alfalfa or similar long-rooted crops that may interfere with the water holding capacity of the embankment shall not be used. Riprap may be necessary under unusual conditions to provide protection of embankments from erosion.

9. On sloping areas, a diversion ditch or soil improvement practices shall be located immediately upslope from the embankment. The ditch or soil improvement practice shall be installed to intercept and remove all surface and subsurface water and shall be protected from erosion.

10. The gravity flow lagoon influent line shall be Schedule 40 PVC or equivalent and have a minimum diameter of three (3) inches with a minimum grade of one-fourth (1/4) inch per foot. When gravity flow is utilized, the outlet invert of the septic tank shall be a minimum of one (1) foot above the high water level in the lagoon. The water level of each cell shall be at an elevation lower than the original ground surface.

11. The influent line shall be center discharging at a point two (2) feet beneath the water level. A watertight cleanout shall be provided in the influent line near the lagoon embankment and shall extend upwards to finished grade.

12. The effluent line from each cell shall be designed to maintain the water level of that cell at a depth of four (4) feet and be located so as to minimize short-circuiting from the influent line.

13. The effluent from the second cell shall be disposed of by a subsurface sewage disposal system.

14. The subsurface sewage disposal system shall be constructed according to paragraph (4) of Rule 0400-48-01-.07 and shall require a minimum of one hundred fifty (150) square feet of soil absorption trench bottom area.

15. The finished grade above the subsurface sewage disposal system shall be lower in elevation than the invert of the effluent discharge line from the last cell.

(d) Dosing of the System (applicable only when pumping is necessary)

1. If pumping to the lagoon is necessary, the total dynamic head (TDH) shall be determined by the summation of the elevation head, friction head and three (3) feet of pressure head.

2. The gallons per minute (gpm) flow amount, which the pump must provide shall be a minimum of ten (10) gpm.

3. The dosing volume shall be less than one-half (1/2) daily flow.

4. A check valve must be utilized when pumping uphill.

(e) Equipment and Material Specifications

1. Septic tank and dosing tank.

(i) The septic tank shall conform to all design, construction and installation criteria set forth in Rules 0400-48-01-.08 and 0400-48-01-.09.

(ii) The dosing chamber shall conform to all design, construction and installation criteria set forth in Rule 0400-48-01-.12.

2. Pipe Materials

(i) All pipe materials shall be PVC and have a minimum equivalent strength of Schedule 40 PVC.

(ii) If pumping is necessary, all fittings shall be pressure fittings.

(iii) All connections shall be adequately cleaned with cleaning solvent and glued with PVC solvent cement.

(f) Construction

1. The area designated for the lagoon liquid storage area and embankments shall be stripped of vegetation. The organic material removed during excavation of the lagoon shall not be used in embankment construction.

2. The area designated for the lagoon liquid storage area and embankments shall be stripped of soils that will not form an effective seal.

3. The liquid storage area of the lagoon must be sealed to prevent excessive exfiltration.

4. Embankments shall be constructed of impervious materials and compacted sufficiently to form a stable structure.

5. The influent line shall be installed at sufficient depth to protect the line from freezing and be properly bedded to prevent structural damage to the pipe from wheeled vehicles that cross the area. Slope of the line shall be such that excessive flow velocities do not cause scouring at the discharge point, but shall be adequate to prevent deposition within the line.

6. Effluent from the last cell shall be withdrawn from six (6) inches below the water surface. This shall be accomplished by placing a tee, with the run in a vertical position, on the inlet end of the effluent pipe.

7. The lagoon area shall be enclosed with a minimum four (4) feet high woven or chain-link or other restricting fence to preclude livestock and discourage trespassing. The fence shall be so located to permit mowing of the embankment top and slopes. A gate of sufficient width to accommodate mowing equipment shall be provided.

8. Appropriate warning signs shall be provided to designate the nature of the facility and discourage trespassing.

(g) Operation and Maintenance

1. It shall be necessary to fill the lagoon with water prior to using it for waste disposal.

2. Vegetation growing along the water's edge and in the water shall be mowed or otherwise removed at least annually.

3. It shall be necessary to maintain a consistent water depth of four (4) feet at all times of the year.

(6) A Subsurface Drip Disposal (SDD) System is a subsurface sewage disposal system, which utilizes pressurized drip irrigation line for the uniform application of treated wastewater throughout the disposal field. SDD systems shall be designed and installed to utilize the upper profiles of a suitable soils area through the uniform distribution of effluent, dosing and resting cycles, and shallow installation of the disposal line. SDD systems are to be proceeded by a treatment device capable of achieving secondary effluent treatment standards unless otherwise determined by this department.

SDD systems designed to accommodate wastewater flows in excess of seven hundred fifty (750) gallons per day must be designed by a licensed engineer. The design shall be reviewed by the department applying the requirements of paragraph (6) of this rule.

(a) Site and Soil Requirements

1. Prior to the design of the SDD system, the suitability of the site must be demonstrated through acceptable soil properties, soil conditions and topographical characteristics. Acceptable soil textural and structural properties are shown in Table VII.

2. The design and installation of the SDD system shall be based on the most restrictive naturally occurring soil horizon or layer to a depth of twenty (20) inches or twelve (12) inches below the installation depth of the drip line, whichever is greater.

3. An area of suitable soil must be available to install the primary system and maintain a suitable area of adequate size for a one hundred (100) percent duplicate area.

4. An extra-high intensity soil map, provided by a soil consultant listed by the department, shall establish the soil properties.

(i) An extra-high intensity soil map for use to design a SDD system shall provide site-specific profile descriptions establishing the texture and structure (shape and grade) for each suitable soil unit mapped.

(ii) Profile descriptions require the excavation of soil pits in order to allow for site-specific pedon descriptions. The soil column shall be described to a depth of thirty-six (36) inches or to rock or fragipan whichever is shallower. There shall be a minimum of two (2) pits per acre with at least one pit in any suitable soil unit intended for use, unless a different frequency is specified by the Commissioner.

(iii) Slope classes (Table VI) for extra-high intensity soil maps used for SDD systems shall be delineated as follows:

Table VI.

Slope Classes

0 - 9 %

10 - 20 %

20 - 30 %

30 - 40 %

40 - 50 %

>50 %

(iv) Percolation tests shall not be allowed to establish soil properties for the design of SDD systems.

5. The size of the SDD system shall be determined by the following:

(i) The daily wastewater flow divided by the loading rate (Table VII) shall determine the area (ft2) required for the initial system.

Table VII.

Hydraulic Loading Rates (gpd/ft2) - For Subsurface Drip Disposal (SDD) Systems

	STRUCTURE		HYDRAULIC LOADING RATE (gpd / ft 2) BOD<=30 mg/L
TEXTURE	SHAPE	GRADE	HYDRAULIC LOADING RATE (gpd / ft 2) BOD<=30 mg/L
Coarse Sand, Loamy Coarse Sand	NA	NA	NA*
Sand	NA	NA	NA
Loamy Sand, Fine Sand, Loamy Fine Sand, Very Fine Sand, Loamy Very Fine Sand	Single Grain	Moderate, Strong	0.50
	Single Grain	Massive, Weak	0.40
Coarse Sandy Loam, Sandy Loam	Massive	Structureless	0.30
	Platy	Weak	0.20
	Platy	Moderate, Strong	Not Used
	Blocky, Granular	Weak	0.40
	Blocky, Granular	Moderate, Strong	0.50
Loam	Massive	Structureless	0.20
	Platy	Weak, Moderate, Strong	Not Used
	Blocky, Granular	Weak	0.30
	Blocky, Granular	Moderate, Strong	0.40
Silt Loam	Massive	Structureless	0.20
	Platy	Weak, Moderate, Strong	Not Used
	Blocky, Granular	Weak	0.20
	Blocky, Granular	Moderate, Strong	0.30
Sandy Clay Loam, Clay Loam, Silty Clay Loam	Massive	Structureless	NA
	Platy	Weak, Moderate, Strong	Not Used
	Blocky, Granular	Weak	0.20
	Blocky, Granular	Moderate, Strong	0.20
Sandy Clay, Clay, Silty Clay	Massive	Structureless	Not Used
	Platy	Weak, Moderate, Strong	Not Used
	Blocky, Granular	Weak	0.075
	Blocky, Granular	Moderate, Strong	0.10

* Requires a special site investigation

Table VII compiled from: EPA, Netafilm, GeoFlow, AL, NC, MS, GA, TX, AR and TN

(ii) When slopes exceed nine (9) percent, slope correction factors (Table VIII) shall be used to adjust area requirements.

Table VIII.

Slope Correction Factors

Slope Class	Depth to R Lay<=23 in	estrictive er >=24 in
10%-20%	15%	0%
20% - 30%	35%	15%

(iii) Slopes of more than fifty (50) percent shall be considered unsuitable.

(iv) For sites with slopes between thirty (30) to fifty (50) percent a special investigation shall be conducted to evaluate those soils to determine: depth to rock, kind of rock and particle size class designation to a depth of six (6) feet or to hard rock, whichever is shallower.

(v) SDD systems designed for sites with slopes greater than thirty (30) percent must be designed by a licensed engineer. The department shall review the design.

(b) Design and Layout of the SDD System

1. The required minimum linear tubing footage is determined by dividing the amount of required square footage of suitable soil area by two (2). However when slope correction factors are required, the minimum linear tubing footage is calculated on the required square footage (without the addition of the slope correction factors) divided by two (2). The approximate tubing spacing is then determined by dividing the required square footage (including the slope correction factor) by the minimum linear tubing footage. Complete coverage of the required square footage (including any slope correction factor) is required. Designers are permitted to specify a closer tubing spacing and additional tubing, as soil and site conditions may accommodate to insure complete coverage of the disposal area.

2. The location of the septic tank, effluent treatment unit, dosing chamber, and the disposal field shall be in accordance with Rule0400-48-01-.11.

3. The drip disposal lines shall be placed on contour. The maximum length of a single line or maximum drip zone size shall be in compliance with the manufacturer's recommendations and is subject to approval by the department.

4. Drip disposal lines and drip emitters shall be spaced on twenty-four (24) inch centers unless an alternative spacing is required by the use of slope correction factors. Tubing spacing other than twenty-four (24) inch centers may be considered on a case-by-case basis through the GWP Central Office.

5. All components of an SDD system shall be designed and manufactured to resist the corrosive effects of wastewater and household chemicals, and meet applicable ASTM standards.

6. All SDD systems shall include an automatic filtration system capable of removing suspended solids to a level recommended by the drip disposal line manufacturer or to a maximum particle size of no more than 120 microns, whichever is smaller. The filtration system shall be sized to provide the specified filtration level at or above peak flow conditions.

7. All SDD systems shall be designed to automatically flush each disposal field or zone at a minimum fluid velocity of two (2) feet per second. Flushing velocity is measured at the distal end of the drip disposal line. Flushing frequency shall be at least the minimum frequency recommended by the drip disposal line manufacturer or at a minimum once every thirty (30) days.

8. The filter flush, and network forward flushing volumes are to be hydraulically acceptable to and not adversely affect the pretreatment unit design for systems that flush to the pre-treatment tank. Systems designed to continuously forward flush to the dosing tank shall incorporate a system to automatically flush the filter to the pre-treatment tank.

9. Air / vacuum release valves shall be placed at the highest point of each zone. All valves shall be installed under a protective cover allowing grade level access.

10. Non-pressure-compensating turbulent flow drip emitters shall not be used in any SDD or packaged SDD system.

11. Valves or appropriate fittings to allow for easy measurement of system pressures shall be provided on the pump output, and on each supply and return manifold of each zone.

12. SDD systems shall be timed dosed at regular intervals. Demand dosing shall not be used. Minimum dose calculations shall include at least three (3) times the volume of the tubing plus the volume of the supply and return manifolds. All SDD systems shall incorporate a flow meter to accurately determine the volume of flow to the disposal field. The approved system shall also provide the means to calculate pump cycles, alarm events, pump run time, and automated flushing events.

13. Systems designed to continuously forward flush shall incorporate a flow meter on the supply and return in order to accurately determine the volume of flow dosed in the disposal field.

14. SDD systems shall have a dosing tank capacity that will allow float placement to provide for a minimum working volume of fifty (50) percent of the peak design flow. This volume should be calculated from the timer enable to the high water alarm floats. The dosing chamber shall also provide a reserve capacity of at least fifty (50) percent of the peak daily flow above the high water alarm. The alarm and alarm switches shall be placed on a separate electrical circuit from the pump power line.

15. SDD systems shall be designed to prevent the redistribution of effluent by gravity in the disposal area.

1. All supply and return manifolds, lines and pressure pipe network elements shall be constructed using Schedule 40 PVC or equivalent.

2. Any turn in the drip disposal line greater than ninety (90) degrees shall be made using flexible sections of PVC or functional equivalent. The drip line shall be secured to the flexible PVC using fittings manufactured for that purpose.

3. All electrical installations shall be installed to meet the current wiring methods of the current edition of the "National Electric Code" (NEC) adopted by the Department of Commerce and Insurance.

4. Drip disposal line shall be installed at a depth of eight (8) to twelve (12) inches below the natural soil surface. A buffer of twelve (12) inches of undisturbed soil below the drip disposal line to rock or restrictive horizon shall be maintained throughout the disposal field.

5. Drip disposal line shall be installed with the contour of the ground and in such a manner to prevent damage to the tubing and comply with the manufacturer's recommendations.

(d) General Requirements

1. SDD systems may only be used if the effluent introduced to the SDD system has been treated to secondary effluent treatment standards.

2. Permits for SDD systems will only be considered for systems that are designed by a licensed engineer or have been previously approved as a packaged SDD system by this department.

3. This Department will maintain a list of approved SDD systems either packaged with an ATS or independently.

4. No manufacturer marketing an SDD system independently or packaged with an ATS in Tennessee shall deny the sale of replacement parts or deny technical guidance to any maintenance provider listed in accordance with Rule 0400-48-01-.23.

5. The property owner at the time of initial installation of a SDD system and any subsequent owner, for the life of the system, shall have in effect a contract for operation and maintenance of the SDD with an approved maintenance provider under Rule 0400-48-01-.23. These contracts will be reviewed by this department on an annual basis. This requirement can be included with the ATS contract specified in Rule 0400-48-01-.10.

6. SDD systems will not be considered for the purposes of subdivision plat approval or permit issuance unless the SDD system is to be utilized as the primary system.

7. SDD systems will be considered for residential applications up to and including fifteen hundred (1500) gallons per day. However, commercial applications may be considered by the department on an individual basis.

8. Upon installation of a packaged SDD system, a representative of the company holding the packaged approval shall inspect the system to certify that the system was installed to the approved specifications and provide GWP with a detailed layout of the system components. For systems designed by a licensed engineer, the engineer must submit construction as-built drawings showing the location of all components of the system.

Authority: T.C.A. §§ 68-221-401 et seq. and 4-5-201 et seq.

Disclaimer: These regulations may not be the most recent version. Tennessee may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.

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