APPENDIX B - HIGHWAY DRAINAGE
Appendix B
NYSDOT DESIGN REQUIREMENTS AND GUIDANCE
FOR
STATE POLLUTANT DISCHARGE ELIMINATION SYSTEM (SPDES)
GENERAL PERMIT FOR CONSTRUCTION ACTIVITY
May 16, 2014
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APPENDIX B - HIGHWAY DRAINAGE
TABLE OF CONTENTS
1.0BACKGROUND ……………………………………………………………………………..… x
1.1Permit Applicability ………………………………………………………….……… x
2.0 TECHNICAL INFORMATION ………………………………………………..…………….… x
2.1 DEFINITIONS…………………………………………………….……… x
2.1.1Disturbance …………………………………………………………...……… x
2.1.2Area of Disturbance ………………………………………………………… x
2.1.3Maximum Extent Practicable …………………………….………. x
2.1.4Routine Maintenance Activities ……... x
2.1.5Impervious Areas …………………………………………………...………. x
2.1.6New Development …………………………………………….…………….. x
2.1.7Redevelopment ……………………………………..……………………….. x
2.1.8Redevelopment Projects ………………………………….……………….. x
2.1.9Areas Beyond the Right-of-Way Limits …………………………………. x
2.2EROSION AND SEDIMENT CONTROL …………………………………………… x
2.2.1Technical Standards ……………………………………….……………….. x
2.2.2Erosion Hazard …………………………………………………………….… x
2.2.3Design of Temporary Sediment Basins ……………………………...…. x
2.3STORMWATER MANAGEMENT ………………………………………………..…. x
2.3.1Principles of Green Infrastructure …
2.3.2Stormwater Management Site Planning and Site Selection – 5 Step Process ……………………………………………………………
2.3.2.1Step 1: Site Planning to Minimize Disturbed Areas and Impervious Areas …………………………………….
2.3.2.2Step 2: Calculation of Water Quality Volume for the Site …………………………………………………………….
2.3.2.2.1Calculation of the Water Quality Volume in Phosphorus Restricted Watersheds ……………..
2.3.2.3Step 3: Runoff Reduction by Applying Green Infrastructure Techniques and Standard Stormwater Management Practices with Runoff Reduction (RRv) Capacity ………………………………………………………
2.3.2.4Step 4: Apply Standard or Alternative Stormwater Management Practices to Address Remaining Water Quality Volume ………………………………………………………………….
2.3.2.4.1Apply Standard Stormwater Management Practices to Address Remaining Water Quality Volume …………………………………………..
2.3.2.4.2Apply Alternative Stormwater Management Practices to Address Remaining Water Quality Volume (from Areas of Redevelopment) ………..
2.3.2.4.3Apply a Combination of Standard and Alternative Stormwater Management Practices with Impervious Cover Reduction to Address Remaining Water Quality Volume (from Areas of Redevelopment) ……………………………………..
2.3.2.5Step 5: Apply Volume and Peak Rate Control Practices ……………………………………………………..
2.3.2.5.1Stream Channel Protection Volume (Cpv) ……..
2.3.2.5.2Overbank Flood Control (Qp) ………………….
2.3.2.5.3Extreme Flood Control (Qf) ………………………
2.3.2.5.4Downstream Analysis ……………………………..
2.3.2.6Technical Deviations and Stormwater Crediting
2.3.2.7Projects That Do Not Require Stormwater Management Practices
2.4STORMWATER POLLUTION PREVENTION PLAN (SWPPP) ………………… x
2.5NOTICE OF INTENT …………………………………………………………………. x
2.6NOTICE OF TERMINATION ……………………………………………………..….. x
2.7REFERENCES ………………………………………………………………………... x
List of Exhibits
Exhibit 1 - Examples of Routine Maintenance Activities (relative to the SPDES General Permit for Construction Activity) ……………………………………………………... x
Exhibit 2A - Example Impervious and Disturbed Areas for a Highway Widening Segment .… x
Exhibit 2B - Example Impervious and Disturbed Areas for a Bridge Replacement Segment .. x
Exhibit 3 -Percentage of Water Quality Volume Provided by a Standard Stormwater Management Practice with RRv Capacity ……………………………………….…. x
Exhibit 4 - Downstream Analysis …………………………………………………………………. x
ATTACHMENT A - NYSDECSTORMWATER MANAGEMENT DESIGN MANUAL CHAPTER 6: DETAIL DESCRIPTORS TRANSLATED INTO NYSDOT ITEM NUMBERS
5/16/14
8B-1
APPENDIX B - HIGHWAY DRAINAGE
1.0BACKGROUND
Land development projects, including transportation improvement projects, and associated increases in impervious cover can alter the hydrologic response of local watersheds and increase stormwater runoff rates and volumes, contribute to flooding, stream channel erosion, sediment transport, and deposition. This runoff contributes to increased quantities of water-borne pollutants, but can be controlled and minimized through the effective use of best management practices to mitigate the adverse impacts of stormwater runoff.
The New York State Department of Environmental Conservation(NYSDEC) issues the State Pollutant Discharge Elimination System(SPDES) General Permit for Stormwater Discharges from Construction Activity, which establishes the criteria by which construction projects are regulated and are allowed to discharge stormwater. .
1.1Permit Applicability
Under the current SPDES General Permit for Construction Activity, the Department is required to obtain coverage under the general permit for any project that exceeds 1 acre of soil disturbance (or 5000 square feet in the New York City East of Hudson (EOH) Watershed). The designer should consult the SPDES General Permit for Construction Activityfor a list of activities which are ineligiblefor permit coverage. Among these activities are the following that may apply to Department projects:
- Construction activities for public roadway and linear utility projects that disturb 2 acres or more of land with no existing impervious cover and where the Soil Slope Phase is identified as an E or F (i.e., 25% or greater slopes, as identified in the County Soil Survey) within a watershed that is tributary to waters of the state classified as AA or AA-s (i.e., 2 acres of disturbance of steep slopes in AA and AA-s watersheds). Existing roadway embankments (including cut and fill slopes) that were built at a 25% or greater slope do not count as steep slopes in this case.
- Construction projects for which there is evidence of an adequate assessment of impacts to properties listed or eligible for listing on the State or National Register of Historic Places is either lacking or absent. This permit ineligibility does not apply to projects for which Adverse Effect determinations have been made and the procedures in the Project Development Manual have been followed.
2.0 TECHNICAL INFORMATION
2.1 DEFINITIONS
2.1.1Disturbance
Under the SPDES General Permit for Construction Activity, the Department is required to assess the requirements for stormwater management practices (SMPs) forany project that exceeds1 acre of soil disturbance(or 5000 square feet in the New York City East of Hudson (EOH) Watershed). Soil disturbance is defined as “any activity that results in the disruption or exposure ofsoil”. This soil disturbance definition also includesplacing fill and the removal of existing paved areas (such as travel lanes, shoulders, driveways, or parking areas) that exposessoil or disturbs the bottom 6” of subbase material, unless the work in these areas is considered a routine maintenance activity. The 6”) threshold applies in areas where the subbase meets the material requirements of Section 304 of the Standard Specifications. If the existing subbase material does not meet this requirement, the area should be considered disturbed area. Temporary disturbances (i.e., disturbances where the ground surface is returned to the pre-existing condition, including vegetation type, soil infiltration capacity, grade and elevation) should also be included in the disturbance calculation. Routine maintenance activities,such as pavement milling and filling, placing shoulder backupmaterial, and ditch cleaning, are not included in the disturbance calculations (see Section 2.1.4.
When determining if the project requires coverage under the SPDES General Permitfor Construction Activity, the designer should consider potential design changes during final design and construction such as flattened slopes and contractors operations. It may be beneficial to obtain general permit coverageif the project exceeds 0.9 acre) of disturbance during final design. This allows construction staff the opportunity to have minor, temporary impacts that increase the total disturbance limit over 1 acre (because coverage under the SPDES General Permit for Construction Activityhas already been obtained and a SWPPP has already been prepared) without changing the scope of the project (i.e., requiring the construction of stormwater management practices when none were previously required). In these cases, projects do not need to address the permanent stormwater management components of a Stormwater Pollution Prevention Plan (SWPPP).
2.1.2Area of Disturbance
When calculating the area of disturbance,worksites may be considered non-contiguous if they have logical termini, independent utility, and do not restrict consideration of future transportation projects. For most projects, this results in a separation of approximately 0.25 miles. Projects such as bridge painting, landscaping, sign and light foundation construction, and sign replacement, are typically exempt from SPDES stormwater permit requirements due to the limited soil disturbances and the non-contiguous nature of these projects. Each worksite is considered independent and separate when calculating the soil disturbance.
For example:
- If no sites are over the 1 acre (or 5000 square feet in the New York City East of Hudson (EOH) Watershed)threshold, then coverage under the SPDES General Permit for Construction Activityis not required (temporary and permanent erosion and sediment control is still required).
- Ifonly one site is over the 1 acre (or 5000 square feet in the New York City East of Hudson (EOH) Watershed)threshold and it does not qualify as a maintenance activity (See Section 2.1.4, only that site would require compliance with the permit (all other sites would not qualify for permit coverage).
Areas disturbed by the contractor outside of the Right-of-Way(ROW) limits are beyond the Department’s control and are not covered under the permit for the project. When working off the ROW, the contractor is responsible to determine applicability and obtain permit coverage, as needed, with SPDES and other regulations. (Note that disturbed areas used for contractor operations, including storage or staging areas within the Right-of-Way(ROW) limits can be included in the Department’s coverage under the SPDES General Permit for Construction Activity, but the SWPPP must be revised to include these areas.)
2.1.3Maximum Extent Practicable
The Department's policy is to comply with the requirements of the SPDES General Permitfor Construction Activity. The linear nature of highway projects, limited available ROW widths, constraints in urban areas, and the significant number and size of watersheds that may be involved, will provide challengesto meet the permit requirements. During the preliminary design stage, designers should review the project for possible locations for constructionof stormwater management practices to the maximum extent practicable. The following items may be considered impractical due to their extraordinary costs, maintenance difficulty, or substantial social, economic or environmental consequences.
- Pumping stormwater to permanent stormwater management practices.
- Acquisition of sensitive ROW areas including but not limited to taking of residences, relocating businesses, placing stormwater management practices in residential backyards, adverse effects to historic properties, etc.
- Largevault structures for stormwater detention (not including Stormwater Treatment Systems).
- ROW takings initiatedsolely for stormwater management practices, which would change the scope of the project, and subsequently effect the environmental determination and design schedule.
- Stormwater management practices thatexceed 5% of the total project costfor ROW and construction. This limit would not apply in TMDL watersheds, to projects with direct discharges to 303(d) list waterbodies, orprojects where post construction practices to address water quantity requirementsare requiredStormwater management practices that create significant social, economic, or environmental impacts.
- Locations of stormwater management practices that require lane closures of adjacent traffic on high volume (AADT >30,000, high speed (>50mph) highwaysfor routine maintenance of the practice.
- Stormwater management practices that require use of Jurisdictional Wetlands.
- Create a significant encroachment in flood plains or otherwise violate 23CFR 650 or 6NYCRR 502, Floodplain Management. Designers are encouraged to consult with their Regional Hydraulic Engineer and/or MO Hydraulic Engineering Unit for questions aboutfloodplain impacts.
In the event that designers can not meet the requirements of the permit, a meeting should be arranged with the regional DEC office to coordinate acceptable deviations to the technical standards. Any deviations to the technical standards are to be documented in the SWPPP and will require a 60 business day review period for the Notice of Intent (NOI).
2.1.4Routine Maintenance Activities
In the SPDES General Permit for Construction Activity, “Routine Maintenance Activity” is defined as "activities that maintain the original line and grade, hydraulic capacity, or original purpose of a facility." This includes traditional maintenance activities, such as ditch cleaning and shoulder reshaping, but also activities that meet the definition of routine maintenance that may be part of a larger construction project. Refer to Exhibit 1 for a list of routine maintenance activities. There is no limit on the amount of disturbed area for maintenance activities (i.e., maintenance activities are not included in the disturbance calculations for a project, regardless of the amount of soil disturbance associated with those activities).
In addition, designers should be aware that activities done by maintenance contracts can not categorically be considered "Routine Maintenance Activities". Projects should be reviewed for SPDES stormwater permit requirements independent of NYSDOT project type classification.
Exhibit 1 Examples of Routine Maintenance Activities (relative to the SPDES General Permit for Construction Activity)
1 / Cleaning and shaping of existing ditches and culverts that maintain the approximate original line and grade, and hydraulic capacity of the ditch.2 / Streambank restoration projects that do not include the placement of spoil material.
3 / Cleaning and shaping of existing ditches that does not maintain the approximate original line and grade, hydraulic capacity and purpose of the ditch if the changes to the line and grade, hydraulic capacity or purpose of the ditch are installed to improve water quality and quantity controls (e.g., installing grass lined ditch).
4 / Placing of aggregate shoulder backing that makes the transition between the shoulder and the ditch or embankment.
5 / Full depth milling and filling of existing asphalt pavements, replacement of concrete pavement slabs, and similar work that does not expose soil or disturb the bottom 6” of subbase material.
6 / Long-term use of equipment storage areas at or near NYSDOT maintenance facilities.
7 / Removal of sediment at the edge of the highway to restore a previously existing sheet-flow drainage connection from the highway surface to the highway ditch or embankment.
8 / Existing use of Canal Corp owned upland disposal sites for the canal.
9 / Replacement of curbs, gutters, sidewalks, and guiderail posts.
2.1.5Impervious Areas
Impervious areas should include concrete or asphalt pavement surfaces, compacted gravel surfaces that are more than 6”in depth, stone fillingand rooftops. Soils that are in Hydrologic Soil group D that are compacted as a result of construction activities that have not been restored using Soil Restoration techniques in the New York State Stormwater Management Design Manual, (hence referred to as the Stormwater Management Design Manual) should also be considered impervious.
2.1.6New Development
The term “New Development” as it relates to the SPDES General Permit for Construction Activity refers toimpervious surfacesconstructed within the disturbed area, such as widened shoulders, travel lanes or sidewalks that did not exist prior to the pre-construction condition. Temporary pavement placed for maintenance of traffic or pedestrian use, which is to be removed at completion of the contract, is not to be included in the new impervious area. Areas of new development may also be referred to as “New Construction” in the Notice of Intent.
2.1.7Redevelopment
Redevelopment is reconstruction of any existing impervious surfaces that involves disturbance of the bottom 6”layer of subbase material. These areas include impervious surfaces that are relocated or realigned in close proximity to the existing impervious surface, or replaced in the existing location. Redevelopment is distinguished from new development in that new development refers to construction on land where there had not been previous construction.
For areas undergoing redevelopment, pre-development means the condition just prior to construction. This is based on the assumption that the impervious surfaces have existed for a long period of time.
Although redevelopment activities are generally expected to comply with technical standards contained in the Stormwater Management Design Manual, the project’s SWPPP will be considered to be in conformance with the technical standardsif the redevelopment application criteria are met and the design utilizes alternative sizing and selection of stormwater management practices described herein.
The required redevelopment application criteria are:
(1) An existing impervious area is disturbed and then reconstructed as either a pervious or impervious surface, and
(2) There is inadequate space for controlling stormwater runoff from the reconstructed area, or
(3) The physical constraints (e.g., soils, water table, and hydraulic head)of the site do not allow meeting the required elements of the green infrastructure or standard stormwater management practices.
Note that criterion #1 and either #2 or #3 must be met.
The SWPPP for a project that includes redevelopment, with or without increased impervious area, must clearly identify and document the design difficulties and must clearly state that the redevelopment conditions meet the redevelopment application criteria in order to utilize the following alternative sizing and selection of stormwater management practices:
The alternative sizing and selection of stormwater management practicescriteria are:
1)ForWater Quantity, the following optionsmust be employed:
a)If redevelopment results in no increase in impervious area or changes to hydrology that increases the discharge rate from the site, the ten-year and hundred-year criteria do not apply. This is true because the calculated discharge of pre-development versus post-development flows results in zero net increase. This consideration does not mean that existing quantity controls may be neglected in planned designs. Existing quantity controls must be maintained for post-development flow discharge control.
b)Channel protectionfor a redevelopment project is not required if there is no increase in impervious area or changes to hydrology that increase the discharge rate. This criterion is not based on a pre- versus post-development comparison. However, for a redevelopment project this requirement is relaxed. If the hydrology and hydraulic study shows that the post-construction 1-year 24-hour discharge rate and velocity are less than or equal to the pre-construction discharge rate, providing 24-hour detention of the 1-year storm to meet the channel protection criteria is not required.
c)If the redevelopment results in an increase in the total impervious area and subsequently increased discharge rate, apply quantity controls for the increased discharge. If the redevelopment results in modified hydrology or flow due to discharge to other sub-watersheds, slope change, direct channelization, curb-line modification, etc., apply quantity controls for the increased discharge.
2)For Water Quality, the following options must be employed:
a)The plan proposes a reduction of existing impervious cover by a minimum of 25% of the total disturbed, impervious area. A reduction in site imperviousness will reduce the volume of stormwater runoff, thereby achieving, at least in part, stormwater criteria for both water quality and quantity. The final grading of the site should be planned to minimize runoff contribution from new pervious area onto the impervious cover. Effective implementation of this option requires restoration of soil properties in the newly created pervious areas. Soil restoration is achieved by practices such as soil amendment, deep-ripping, and de-compaction (See the Stormwater Management Design Manual, Section 5.1.6 Soil Restoration).