4.4.8 Stormwater Management
(See last page for summary of changes)
· This section contains a general discussion only with no subsections. Topics may include:
Existing drainage basins
How existing soils, vegetation, topography, climate, etc. may affect erosion/sedimentation
Potential sources of water pollution from motor vehicles, etc.
Polluted Water bodies - Section 303(d)
Point Source Discharges
Total Maximum Daily Load (TMDL) Watershed (SEQR)
Effects (impacts) assessment
Effects on water quality
Toler Analysis
First Flush Analysis
Permanent stormwater quality practices
Stormwater quantity practices
Erosion prevention and sediment control
Pollutant Loadings and Impacts from Highway Stormwater Runoff
State Pollutant Discharge Elimination System (SPDES)
National Pollutant Discharge Elimination System (NPDES)
Mitigation (avoiding, minimizing, rectifying, reducing or eliminating, compensating)
Stormwater Pollution Prevention Plan (SWPPP) in final design
Erosion/sediment control specifications and notes in final design
Stormwater management specifications and notes in final design
Activities to be done in final design (i.e., SWPPP design, SPDES/NPDES approval)
· Regulatory Framework and Guidance:
ECL Article 17, Title 7 - Point Source Discharges
NYSDOT’s Stormwater Management Program (SWMP) for policies regarding stormwater
NYSDOT HDM Chapter 8: Design Requirements and Guidance for SPDES General Permit GP-02-01
NYSDEC Stormwater Management Design Manual, Chapter 5
NYSDOT Standard Specifications, Section 209 Soil Erosion and Sediment Control
· Interagency Coordination
Document any consultation or coordination with outside agencies (meetings, site visits, major submissions and correspondence, permit needs, consultation, etc.).
NYSDEC - Stormwater Notice of Intent
NYSDEC - SPDES Permit review and approval
NYSDEC - Protection of Waters (ECL Article 15)
EPA - Notice of Intent (Federal)
EPA - NPDES Permit review and approval
· Cross-reference:
2.3.3.4 Drainage Systems (existing)
3.3.3.4 Drainage Systems (proposed)
4.4.2 Regulated Waterbodies and Watercourses
4.6 Construction Effects
4.7 Indirect (Secondary) Effects
4.8 Cumulative Effects
· Permits should be obtained prior to advertisement; permits shall have been obtained prior to award.
· If consulting with the NYC Dept. of Environmental Protection, SWPPP plans must be submitted at least 30 days prior to PS&E.
· A Notice of Intent, signed by the Regional Director or a designee, to use GP-02-01, may be required to be submitted to NYSDEC.
· FHWA guidance from Technical Advisory T6640.8A
The draft EIS should also identify any locations where roadway runoff or other non-point source pollution may have an adverse impact on sensitive water resources such as water supply reservoirs, ground water recharge areas, and high quality streams. The 1981 FHWA research report entitled "Constituents of Highway Runoff," the 1985 report entitled "Management Practices for Mitigation of Highway Stormwater Runoff Pollution," and the 1987 report entitled "Effects of Highway Runoff on Receiving Waters" contain procedures for estimating pollutant loading from highway runoff and would be helpful in determining the level of potential impacts and appropriate mitigation measures. The draft EIS should identify the potential impacts of each alternative and proposed mitigation measures.
· To access NYSDEC’s Stormwater Interactive Map use this link: http://www.dec.ny.gov/pubs/42937.html
[Use for projects that DO NOT require a SPDES permit]
This project will disturb less than one acre and will not require a SPDES permit. While this project is not required to assess the requirements for stormwater management practices, they will be considered where reasonable and feasible.
[Use for projects that DO NOT require a SPDES Permit with Erosion and Sediment Control Measures]
· See the design guidance in HDM Chapter 8. A SPDES permit is required for projects or non-maintenance activities which disturb more than one acre. Soil disturbance includes grading existing vegetated areas, as well as the removal of existing pavement that exposes soil or disturbs the bottom 6” of subbase material. Permanent stormwater quality practices may be required.
Erosion and sedimentation control plans will be developed and incorporated into the project. Erosion and sedimentation control measures may include: straw mulch, erosion control fabric, temporary seeding, silt fence, check dams, inlet protection, and temporary sedimentation/detention ponds.
[Use for projects that DO require a SPDES permit]
A SPDES General Permit GP-02-01 will be required because the project has more than one acre of soil disturbance. A Stormwater Pollution Prevention Plan (SWPPP) with the appropriate sediment and erosion control measures will be developed. Based on the SWPPP, permanent stormwater management practices may be required depending on the total amount of disturbance and changes in total impervious area.
[Use for projects that DO require a SPDES permit]
This project will disturb more than one acre and will require a SPDES permit. This project is required to assess the requirements for stormwater management practices. The results of the SPDES assessment indicate that stormwater quantity controls are not required since the project outlets into a fourth order stream OR stormwater quantity controls are required since the project outlets into a insert order number order stream.
[Use if the project corridor does NOT involve a TMDL watershed or 303(d) water body]
· NYSDEC’s 303(d)/TMDL List is available on the DEC web site: http://www.dec.ny.gov/chemical/31290.html
The project corridor is not adjacent to or discharging runoff to a TMDL Watershed or a listed 303(d) water body.
[Use if the project involves a TMDL watershed or 303(d) water body]
· NYSDEC’s 303(d)/TMDL List is available on the DEC web site: http://www.dec.ny.gov/chemical/31290.html
The project corridor is located within a TMDL Watershed (Unnamed Lake Watershed). This project will be evaluated for water quality treatment practices to reduce pollutant and phosphorous loadings.
[Use for projects with a stream within the project’s area of potential effect, that DO NOT need a DEC Article 15 Protection of Waters permit]
Based on the classification of the insert name of waterbody located within the project area, a NYSDEC Protection of Waters permit is not required for this project. Although a permit is not required, this project should not diminish the water quality standards of the – waterbody. During construction, precautions should be taken to prevent contamination of the waterbody by silt, sediment, fuels, solvents, lubricants, or any other pollutants. Promptly after construction, care will be taken to stabilize all disturbed areas. Vegetated pipe outlet locations will be utilized, as well as plantings in old roadbed locations to allow water to percolate prior to entering the waterbody.
[Use for projects that add through lanes in urban areas and DO NOT need a SPDES permit]
Projects that disturb soils and increase the extent of impervious surfaces have the potential to affect the quality and quantity of stormwater run-off that may discharge into subsurface or surface waters. Although the project will increase impervious surfaces, and will disturb more than one acre of soil cumulatively, the run-off will not drain directly into any waters of the United States. Under these circumstances, the project is not subject to the General State Pollution Discharge Elimination System (SPDES) permit for construction activities (GP-02-01) issued to NYSDOT and implemented in accordance with a Memorandum of Understanding (MOU) between NYSDOT and the NYS Department of Environmental Conversation (NYSDEC). Under the MOU, the “project site” refers to the area within the contract limit lines and the “disturbance of one or more acres of total land area” is defined as “any activity that disturbs or exposes soil” by clearing, grubbing, excavating or grading operations during the life of the project. Construction activities involving previously paved travel lanes and shoulders are excluded from the SPDES general permit.
Currently, for most of the project length, extending from --- to ---, there is no effective control of stormwater run-off. Precipitation within the existing project area highway boundary either recharges to soils directly, or through occasional leaching basins. One part of the project, between -- and -- has a semi-closed drainage system comprised of a few leaching basins connected together and discharging into ---. The part of the project, between --- and ---, has a closed drainage system and discharges into --.
Due to the presence of a topographic high in the vertical alignment of ---, at approximately ---, the project right-of-way lies within two watersheds. The –- watershed, which extends from the high point to --- contains --- (stream, recharge basin, etc.). The –- watershed, which extends --- contains –- (stream, recharge basin, etc.). The proposed widening of --- involves the provision of a comprehensive closed drainage system that will discharge into the existing --- at --- and into ---, within the limits of the project. The drainage design for the -- portion of the project includes a new (recharge basin, leaching basin, etc.) located at ---. Another possible scenario that will be evaluated during the final design phases involves an extension of the proposed drainage system to discharge into an existing --- located at ---.
The provision of the closed drainage system will alleviate existing flooding problems and will prove beneficial by reducing roadway maintenance costs associated with the lack of adequate drainage. For more information about existing drainage and stormwater run-off, refer to Section 2.3.3.4 Drainage Systems. For more information about proposed drainage and stormwater run-off, refer to Section 3.3.3.4 Drainage Systems.
The project will employ effective erosion and sediment control practices during construction, as set forth in NYSDOT’s statewide stormwater and erosion and sedimentation control specifications, standard construction details, and design and construction guidance procedures. Erosion and sediment controls will be employed as part of an environmental initiative to restore wetlands described in Section 4.4.1. During the advance detail design phase, a Stormwater Pollution Prevention Plan (SWPPP) will be developed that incorporates the above specifications and standards.
[Use for projects in urban areas, requiring a SPDES permit, no Toler analysis, and a first flush analysis]
Route -- is located within the urbanized area of the City of -- and all Municipal Separate Stormwater Sewer Systems (MS4s) serving Route --- are automatically designated by the NYSDEC as “regulated” MS4s. This designation requires the City of --- to develop a Phase II stormwater program, including a Stormwater Pollution Prevention Plan (SWPPP). The SWPPP must be implemented and enforced in order to protect water quality and to satisfy the appropriate water quality requirements of the Environmental Conservation Law (ECL) and the Clean Water Act.
Since the limits of grading associated with the proposed construction of this project are expected to exceed 0.4 hectare (1 acre), a State Pollutant Discharge Elimination System (SPDES) General Permit for Construction Activities (GP-02-01), issued by the NYS Department of Environmental Conservation (NYSDEC), will be required.
The majority of increases in impervious area are directly related to adding traffic lanes AND/OR pedestrian and bicycle accommodations within the project limits. The effects of the increased area on water quality and quantity will be analyzed.
--- drainage areas within the project limits were identified using USGS contour maps and digital mapping. Pre- and post-development peak runoff discharges were calculated using the Rational Method for the two-year 24 hour storm. Discharges for each drainage area are summarized below in Table --.
Table --: Peak Flow Analysis
Drainage Area # | Pre-Constn. Peak Flow | Post-Constn. Peak Flow | Change in Peak Flow
1 x.xxx x.xxx x.xxx x.x%
NYSDEC typically requires peak flow attenuation when peak flows for the two-year storm are increased by 10% if post-development flows are greater than 0.140 m³/s (cubic meter per second). The results of the peak flow analysis indicate that -- % would be the largest increase, and therefore peak flow attenuation will not be required. It should be noted that the largest increase occurs in Area --, which is where the curbing was removed from the roadway to allow the runoff to sheet drain down to --. This is a documented Best Management Process that also provides a water quality benefit. The smaller peak flow increases will be tempered by reducing the culvert outlet lengths and establishing stone lined ditches along with stone check dams to slow the outfall.
Potential impact on surface water quality associated with the project would be the result of stormwater runoff and associated pollutants. Pollutants associated with the project could include deicing salts, particulates, nutrients, heavy metals, and hydrocarbons, including polynuclear aromatic hydrocarbons (PAH’s). Pollutant sources may include road surface material, vehicle exhaust and degradation, lubrication system losses, roadway maintenance activities, and by-products of combustion. Of these pollutants, deicing salts are considered a primary pollutant due to the potential quality of salts applied to the roadway during snow removal operations, and because they are potentially the most difficult to mitigate. Based on the very large watershed of ---- and no increase in lane-miles from pavement widening, an analysis quantifying the effects of deicing salts was not performed for the project.
There is the potential for an effect from the non-primary pollutants. An analysis of the first flush contaminants was performed for the project area to determine this effect. First flush pollutants refer to the high percentage of stormwater pollutants that are present in the runoff generated in the early part of storms due to the accumulation of pollutants that are present in the pavement surface. “First flush” is defined as the first 13 mm (½ inch) of runoff off land that has been made more impervious than pre-construction conditions. The pre-construction and post-construction impervious areas are then compared for each of the drainage areas to determine the amount of runoff requiring first flush attenuation. Refer to Table --.
Table --: First-Flush Volumes
Drainage Area # | First-Flush Volumes (m³)
1 XX
Based on the proposed design, there will be a minimal increase in the impervious area within the watersheds. The largest increase is from --- which is --- m long and will sheet drain through the vegetated areas between --- and ---. The attenuation of first flush volumes would be accomplished by following the hierarchy of methods for managing storm water quality, which can be found in Chapter 5 of the NYSDEC Stormwater Management Design Manual. For this project, water would be treated by maintaining sheet flow over vegetated areas, and utilizing open channels and grass channels where space permits.
Soil erosion plans and details will also be developed during the advance detail design phases of the project in accordance with Section 209 Soil Erosion and Sediment Control of the NYSDOT Standard Specifications in order to satisfy the SWPPP. These plans and details will include both temporary and permanent measures to prevent soil erosion and provide fences, seeding, mulching, and stabilized construction access points. These measures will serve to minimize the potential for pollutants from the proposed project to reach ---.
6/18/10 Summary of Changes
Minor revision; “Use for projects that DO require a SPDES permit” clarified.
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