Tenn. Comp. R. & Regs. 0400-40-05-.15 - MUNICIPAL SEPARATE STORM SEWER SYSTEMS
Permits issued to entities that operate a municipal separate storm sewer system (MS4) shall include the following effluent limitations to manage post-construction stormwater at all new development and redevelopment projects that disturb one or more acres of land, or less than one acre if part of a larger common plan of development, and discharge into the permittee's MS4:
Water Quality Treatment Volume and the Corresponding SCM Treatment Type for the 1-year, 24-hour design storm |
||
SCM Treatment Type |
WQTV |
Notes |
infiltration, evaporation, transpiration, and/or reuse |
runoff generated from the first 1 inch of the design storm |
Examples include, but are not limited to, bioretention, stormwater wetlands, and infiltration systems. |
biologically active filtration, with an underdrain |
runoff generated from the first 1.25 inches of the design storm |
To achieve biologically active filtration, SCMs must provide a minimum of 12 inches of internal water storage. |
sand or gravel filtration, settling ponds, extended detention ponds, and wet ponds |
runoff generated from the first 2.5 inches of the design storm or the first 75% of the design storm, whichever is less |
Examples include, but are not limited to, sand filters, permeable pavers, and underground gravel detention systems. Ponds must provide forebays comprising a minimum of 10% of the total design volume. Existing regional detention ponds are not subject to the forebay requirement. |
hydrodynamic separation, baffle box settling, other flow-through manufactured treatment devices (MTDs), and treatment trains using MTDs |
maximum runoff generated from the entire design storm |
Flow-through MTDs must provide an overall treatment efficiency of at least 80% TSS reduction. Refer to subparagraph (2)(d) of this rule. |
Alternative permanent stormwater standards that provide equal or equivalent reduction of pollutants to the above may be submitted to the Division for approval. |
Treatment trains using MTDs must provide an overall treatment efficiency of at least 80% TSS reduction utilizing the following formula:
The calculation:
R = A + B - (A x B)/100
Where:
R = total TSS percent removal from application of both SCMs,
A = the TSS percent removal rate applicable to the first SCM, and
B = the TSS percent removal rate applicable to the second SCM.
TSS removal rates for MTDs must be evaluated using industry-wide standards.
TSS removal rates for other SCMs must be from published reference literature.
Treatment trains using infiltration, evaporation, transpiration, reuse, or biologically active filtration followed by sand or gravel filtration, settling ponds, extended detention ponds, or wet ponds may subtract the treated WQTV of the upstream SCMs from the WQTV of the downstream SCMs.
Permittees shall develop and implement a set of requirements to establish, protect, and maintain permanent water quality riparian buffers to provide additional water quality treatment in riparian areas of new development and redevelopment projects that contain streams, including wetlands, ponds, and lakes. Riparian buffers must meet the following minimum standards:
Average buffer width (feet) |
Minimum buffer width (feet) |
Notes |
|
Waters with available parameters for siltation or habitat alteration or unassessed waters |
30 |
15 |
The criteria for the width of the buffer zone can be established on an average width basis at a project, as long as the minimum width of the buffer zone is more than the required minimum width at any measured location. If the new development or redevelopment site encompasses both sides of a stream, buffer averaging can be applied to both sides, but must be applied independently. |
Exceptional Tennessee Waters or waters with unavailable parameters for siltation or habitat alteration |
60 |
30 |
The predominant vegetation within the minimum buffer area should be trees. The remaining riparian buffers may be composed of herbaceous cover or infiltration-based SCMs.
The permittee shall develop and implement project plan review, approval, and enforcement procedures applicable, at a minimum, to all new development and redevelopment projects, which shall include:
Notes
Authority: T.C.A. §§ 4-5-201, et seq., and 69-3-101, et seq.
State regulations are updated quarterly; we currently have two versions available. Below is a comparison between our most recent version and the prior quarterly release. More comparison features will be added as we have more versions to compare.
Permits issued to entities that operate a municipal separate storm sewer system (MS4) shall include the following effluent limitations to manage post-construction stormwater at all new development and redevelopment projects that disturb one or more acres of land, or less than one acre if part of a larger common plan of development, and discharge into the permittee's MS4:
Water Quality Treatment Volume and the Corresponding SCM Treatment Type for the 1-year, 24-hour design storm | ||
SCM Treatment Type | WQTV | Notes |
infiltration, evaporation, transpiration, and/or reuse | runoff generated from the first 1 inch of the design storm | Examples include, but are not limited to, bioretention, stormwater wetlands, and infiltration systems. |
biologically active filtration, with an underdrain | runoff generated from the first 1.25 inches of the design storm | To achieve biologically active filtration, SCMs must provide a minimum of 12 inches of internal water storage. |
sand or gravel filtration, settling ponds, extended detention ponds, and wet ponds | runoff generated from the first 2.5 inches of the design storm or the first 75% of the design storm, whichever is less | Examples include, but are not limited to, sand filters, permeable pavers, and underground gravel detention systems. Ponds must provide forebays comprising a minimum of 10% of the total design volume. Existing regional detention ponds are not subject to the forebay requirement. |
hydrodynamic separation, baffle box settling, other flow-through manufactured treatment devices (MTDs), and treatment trains using MTDs | maximum runoff generated from the entire design storm | Flow-through MTDs must provide an overall treatment efficiency of at least 80% TSS reduction. Refer to subparagraph (2)(d) of this rule. |
Alternative permanent stormwater standards that provide equal or equivalent reduction of pollutants to the above may be submitted to the Division for approval. |
Treatment trains using MTDs must provide an overall treatment efficiency of at least 80% TSS reduction utilizing the following formula:
The calculation:
R = A + B - (A x B)/100
Where:
R = total TSS percent removal from application of both SCMs,
A = the TSS percent removal rate applicable to the first SCM, and
B = the TSS percent removal rate applicable to the second SCM.
TSS removal rates for MTDs must be evaluated using industry-wide standards.
TSS removal rates for other SCMs must be from published reference literature.
Treatment trains using infiltration, evaporation, transpiration, reuse, or biologically active filtration followed by sand or gravel filtration, settling ponds, extended detention ponds, or wet ponds may subtract the treated WQTV of the upstream SCMs from the WQTV of the downstream SCMs.
Permittees shall develop and implement a set of requirements to establish, protect, and maintain permanent water quality riparian buffers to provide additional water quality treatment in riparian areas of new development and redevelopment projects that contain streams, including wetlands, ponds, and lakes. Riparian buffers must meet the following minimum standards:
Average buffer width (feet) | Minimum buffer width (feet) | Notes | |
Waters with available parameters for siltation or habitat alteration or unassessed waters | 30 | 15 | The criteria for the width of the buffer zone can be established on an average width basis at a project, as long as the minimum width of the buffer zone is more than the required minimum width at any measured location. If the new development or redevelopment site encompasses both sides of a stream, buffer averaging can be applied to both sides, but must be applied independently. |
Exceptional Tennessee Waters or waters with unavailable parameters for siltation or habitat alteration | 60 | 30 |
The predominant vegetation within the minimum buffer area should be trees. The remaining riparian buffers may be composed of herbaceous cover or infiltration-based SCMs.
The permittee shall develop and implement project plan review, approval, and enforcement procedures applicable, at a minimum, to all new development and redevelopment projects, which shall include:
Notes
Authority: T.C.A. §§ 4-5-201, et seq., and 69-3-101, et seq.