CWP12_401BMPs.pdf

Clean Water Policy 12

Colorado Best Management Practices

WATER QUALITY CONTROL

DIVISION

IMPLEMENTATION POLICY

COLORADO DEPARTMENT OF PUBLIC HEALTH

AND ENVIRONMENT

Implementation Policy Number: CW 12

Statutory or Regulatory Citations:

Regulation No. 82: 401 Certification Regulation

(5 CCR 1002-82)

Regulation No. 61: Colorado Discharge Permit System Regulations (5 CCR 1002-61)

Key Words: 401 water quality certification, best management practices (BMPs), control measures, discharge permits

COLORADO Water Quality Selection of Best Management

Practices

Approved by:

Nicole Rowan, Clean Water Program Manager

Drafted by: Elisabeth Miller, Scott Garncarz, Sarah Wheeler, Maura McGovern, Aimee Konowal, Nathan Moore

Effective Date: May 1, 2019

Scheduled Review Date: May 1, 2021

Background The Water Quality Control Commission (Commission) Regulation No. 82 was first adopted on November 6, 1985 to implement Colorado Revised Statue (C.R.S.) 25-8-302(1)(f), which became law on June 4, 1985. C.R.S. 25-8-302(1)(f) requires the Water Quality Control Division (Division) to review and certify, conditionally certify, or deny requests for certifications under the provisions of Section 401 of the federal Clean Water Act and this statue. Regulation No. 82 was adopted by the Commission to provide direction, as determined by the Colorado legislature, to define what conditions can be required by the Division in connection with the certification of federal licenses and permits under Section 401 of the federal Clean Water Act. This regulation is consistent with the Colorado Water Quality Control Act. Regulation No. 82 applies to individual permits issued by the U.S. Army Corps of Engineers under Section 404 of the federal Clean Water Act, Federal Energy Regulatory Commission (FERC) licenses for hydropower projects, and other federal permits which involve discharge into state waters. Regulation No. 82 describes the information required to process a Section 401 water quality certification (401 certification) by the Division. This includes the procedures, determinations, requirements, implementation and enforcement of the 401 certifications.

In 2018, Regulation No. 82 was updated by the Commission through a rulemaking hearing process. At this time, the Commission decided to remove Appendix I, The Selection of Best Management Practices for Clean Water Act Section 401 Certifications, from the regulation and to place the information in a Division policy instead. This will allow the Division to update the policy on a more frequent basis. Best Management Practices (BMPs) considered common industry practices that are in accordance with good engineering, hydrologic and pollution control, can change more frequently than the planned review for the regulation.

In accordance with Sections 82.4(A)(3), 82.4(C)(5), and 82.6(B) of the regulation, any 401 certification application must include the appropriate BMPs to protect water quality. A project applicant is responsible for choosing the appropriate BMPs to protect water quality during the construction and operation of a project, specifically, erosion and sediment control measures per Section 82.6(B).

Purpose This policy will provide guidance and references to applicants on the proper selection, installation and maintenance of BMPs that will mitigate, minimize or avoid unnecessary discharges to state waters. This BMP policy allows applicants to have a single document to reference in helping select the appropriate BMPs for the construction and operation of a project. This policy relating to BMPs for the construction and operation of a project is not intended to apply to or regulate impacts associated with water diversions, conveyance and storage facilities impacts (Regulation 82.12, Statement of Basis and Purpose). Best Management Practices can be relevant to other Commission regulations. For example, Regulation No. 61, Colorado Discharge Permit System Regulations.

Authority This policy, as directed in Section 82.1 of Regulation No. 82, allows the Division to maintain a policy document to assist in the development of BMPs as required by Sections 82.4(A)(3), 82.4(C)(5) and 82.6(B).

Table of Contents

1. Policy Introduction 4

2. Overview of Colorado’s Best Management Practices 4

2.1 Selection of Best Management Practices 5

2.2 Explanation of terms used in Best Management Practice Matrix 6

2.3 How to Apply BMP Matrix 7

2.4 Additional Information Regarding BMP selection 9

2.5 Best Management Practice Matrix 11

2.6 References and Other Sources of Information 28

Appendix 1 Water Control Plan A-1

A. Stormwater Protection A-1

B. Diversion of Surface Water A-1

C. Subsurface Dewatering A-3

1. Policy Introduction Best Management Practices are defined in Regulation 82.2(4) as “structural and non-structural methods, measures or practices implemented to prevent, reduce, or mitigate adverse water quality impacts resulting from construction and operation of a Project.” This policy is being developed based on recommendations from the Commission’s Regulation No. 82 rulemaking hearing that was held in November 2018.

This policy will provide direction to applicants for selecting the appropriate BMPs to protect water quality. This includes federal permits and licenses which require 401 water quality certifications from the state and applicants for a state discharge permit.

Regulation No. 82 sets forth the process to apply for a 401 certification in Colorado and identifies the procedures along with the criteria that will be used by the Division in acting on 401 certification requests. The information provided concerning BMPs in the 401 certification application will assist the Division in determining whether a project is issued a Regular Certification (82.5(A)(2)), or if a project will require additional conditions to protect water quality (82.5(A)(3)).

In conjunction with Commission Regulation No. 61, this policy will also assist in guiding potential discharge permit applicants in determining the best BMPs for the projects in which a state discharge permit is required. However, this policy does not supersede the requirements of discharge permits or division guidance for compliance with those permits. Additional restrictions or requirements may apply to the selection, design, and implementation of control measures for compliance with discharge permits, including but not limited to the Colorado discharge permit for stormwater discharges associated with construction activities.

2. Overview of Colorado’s Best Management Practices The selection of appropriate BMPs for a project must consider multiple factors. This can include the physical characteristics of sites, the objectives of treatment, safety, aesthetics, maintenance and cost (UDFCD, 2019). When selecting a BMP, the applicant also must take into account the installation, operation, and maintenance of the BMPs used for protecting water quality.

The BMPs described in this policy are mostly construction-related and are generally or potentially applicable under all the hydrologic conditions found in Colorado. A major component of a 401 certification is the identification of the proper BMPs. Selecting the proper BMPs involves two main components:

1. Proper design and construction of the water quality protective feature(s) for the project; and

2. Appropriate operation and maintenance of the protective feature(s) to ensure long-term compliance of the project.

In the context of 401 certifications, the project applicants are responsible for providing operation and maintenance plans that include BMP procedures and maintenance for all components of the project that affect water quality during the construction-related activities of the project.

During the construction and operation of a project, the properly selected BMP will protect the water quality of the receiving waters. In general, to be successful in protecting water quality the BMP must involve:

• Proper design to accommodate Colorado conditions;

• Proper construction of the BMP designed for the project to ensure the protection of water quality;

• Appropriate operation and maintenance of these features to guarantee the BMPs are successful in protecting water quality.

This policy will provide four tools to assist in the proper selection of BMPs for an applicant applying for a 401 certification. The three tools are:

• BMPs 401 Certification matrix;

• BMPs descriptions; and

• References and other sources of information

• Water Control Plan

The descriptions will provide further explanation of each of the BMPs listed in the matrix. The list of references and other sources of information provide more detailed information about individual BMPs.

2.1 Selection of Best Management Practices

This Division policy provides applicants for 401 certifications and discharge permits a tool to assist in the selection of BMPs for individual projects. The BMP matrix includes the best available information regarding practices known to be appropriate for construction related projects in Colorado. It is anticipated that the matrix may be revised and supplemented in the reviews of this policy and as common industry practices progress. The format of the matrix reflects that there can be a variety of BMPs for a project that may be appropriate, and that each project’s circumstances can be unique.

The matrix provides the applicant a way to determine either the most likely effective BMP for a particular pollutant scenario or it will assist the applicant in determining which BMPs would not be appropriate for the project. The development of a Water Control Plan which specifies how surface and subsurface water will be managed during construction around waterways will also help in the selection of appropriate BMPs for a project (Appendix 1). The list of BMPs are not meant to be exhaustive; rather, it is intended that applicants may select BMPs other than those included in the matrix.

The applicant for a project should consider the following criteria when selecting a BMP:

• Effectiveness at mitigation, minimization or prevention of pollution;

• Appropriateness for the type of project, site conditions and pollution source;

• Cost-effectiveness;

• Future maintenance;

• Opportunities for multi-use benefits.

2.2 Explanation of terms used in Best Management Practice

Matrix

Best Management Practices (BMPs)– structural and non-structural methods, measures or practices implemented to prevent, reduce or mitigate adverse water quality impacts resulting from construction and operation of a project.

Project Types– general categories and types of construction or development projects in Colorado that are likely to require 401 certification (e.g., bridges, crossing structures, channel work, utility construction, site development, roads and highways, instream mining, dams and reservoirs, specialty activities such as golf courses and driveways).

Sediment Problems– construction or development sites where sediment and erosion controls are necessary to prevent sediment pollution (e.g., sediment deposits and loading, steep slopes, stream bank instability, runoff or velocity controls, wind erosion, stormwater erosion).

Aquatic or Riparian Problems– construction or development sites where control practices are needed to protect aquatic or riparian environments or conditions (e.g., bank habitat, associated vegetative cover, preservation of habitat, life cycle impacts to plants and animals, water quality limitations that affect fish and wildlife).

Reference Types– categories that refer to structural or source controls, permanent best management practices, and specialty practices used by the Forest Service or Bureau of Land Management. Reference types are applicable to construction or development sites.

Structural BMPs- facilities constructed to passively treat runoff before it enters the receiving waters. Such BMPs (sometimes called “dirt moving” practices) used on a construction or development site can be either temporary or permanent, depending on the duration of their application, and are designed to reduce sediment pollution and other pollutants in runoff.

Additionally, they can provide for the protection of aquatic or riparian areas. A limited number of special use practices requiring additional demonstration under the semi-arid or mountainous conditions in Colorado are also listed in the matrix and can be used on a case-by-case basis. Special use practices have been developed for golf course projects, driveways and high-altitude construction. Some construction BMPs result in permanent sediment and erosion control structures, which are designed to work beyond the construction period.

Nonstructural BMPs- include pollution prevention practices and source control activities, and administrative controls designed to minimize or eliminate a problem before it occurs. Source control

BMPs are sometimes referred to as “good housekeeping” measures because a clean site will produce less pollutants than will a dirty one. Site planning and design of BMPs may, in and of itself, be considered a nonstructural BMP.

Dewatering-the practice of removing or draining groundwater or surface water from a riverbed, construction site, caisson, or mine shaft by pumping. This can include any movement of groundwater or surface water through or around a construction site and can also include channel diversions, or gravity feed systems.

2.3 How to Apply BMP Matrix

The purpose of the BMP Matrix is to cross-reference individual BMPs with the most common project types, as well as with the most common types of problems potentially resulting from projects.

Therefore, the horizontal axis of the matrix (across the top) lists “project types”, “potential sediment problems”, “potential aquatic or riparian problems” and “reference types”. The BMPs are listed on the vertical axis (down the left-hand side of the page). These BMPs are grouped into “design considerations”, “sediment controls”, “erosion controls”, “drainageway protection”, and “non-structural construction site practices”.

A 401 certification application should contain a list of appropriate BMPs proposed for a specific project, along with the required site plan, description, and location of those BMPs. The number and type of applicable practices depends on project design and generally must be determined on a case-by-case basis. The state has not defined a minimum number of practices that are appropriate for various projects. The matrix can assist an applicant in determining if a proposed practice is applicable to the desired pollution prevention or environmental protection outcome.

Example of How to Use the Matrix

1. Identify a general project or reference type from horizontal portion of matrix (example, “Bridges & Crossing Structures”).

2. Identify the major issue(s) such as sediment or other aquatic and/or water quality that may be a concern or likely pollutant (example, “Sediment Deposition/Loading”).

3. List only those practices in common for that project type and problem type (example, under “Design Considerations” there are six BMPs – site constraints, construction timing, identify applicable source controls, design of landscaping and vegetative practices, stormwater quality control planning and minimize directly connected impervious areas – that match for the combination of “Bridges & Crossing Structures” with “Sediment Deposition/Loading”). Proceed through the entire matrix in this manner.

4. Determine which of the BMPs identified under step 3 are necessary to the project (example, the consultant engineer believes only landscape and vegetative practices, stormwater quality control planning, site constraints (slope stability), and construction timing are necessary BMPs for this project).

5. Incorporate into project design – The 401 certification application would list under design considerations that the following BMPs are incorporated into the project design – Necessary landscaping and vegetative practices (list), a stormwater control plan that affects runoff features (list), slope stability features needed to reduce erosion potential (list), and a construction timing schedule (list).

Prior to using the matrix, an applicant needs to identify the potential problem areas that are specific to the project. In using the BMP matrix, an applicant should select a topic area or areas (project type, sediment problem, aquatic or riparian problem or reference type). Generally, only one topic area and one or more category areas need selection by the applicant. Based on this selection, a preliminary list of BMPs can be extracted from the matrix.

The applicant can then use the project design specifications to refine the BMP list for inclusion in a permit application. BMP design specifications are not included (see reference section for selected sources containing design specifications appropriate for Colorado geomorphic and climate conditions). As part of the 401 certification, the Division will determine the appropriateness of selected practices. The Division can require additional water quality protective conditions to be included with 401 certification.

An example that illustrates a site plan for a 401 certification project is shown in Figure 1. This example shows typical BMPs that may be incorporated for a drop structure construction project.

2.4 Additional Information Regarding BMP selection

Essential Design Considerations for All Projects

1. The BMPs listed in the matrix are based to a large extent on those described in the Urban

Drainage and Flood Control District’s Drainage Criteria Manual, Volume 3. This BMP manual contains most of the control methods used in Colorado for stormwater management and construction activities. BMPs applicable to 401 certification that are directed toward preserving or improving water quality fall into two general categories:

(1) Sediment and erosion control practices (and practices relating to other potential construction-related pollution sources) that reduce or prevent discharge of pollutants or maintain water quality in runoff and receiving waters during development and construction activities (Water Control Plan); and

(2) Stormwater practices that reduce loads after the construction phase. These BMPs are permanent structural facilities built at the time of development to supplement stormwater drainage and flood-control practices.

Both the construction and post-construction phases need to be considered in project design.

Sediment is one of the most prevalent pollutants associated with development and construction activities. Similar BMPs are applicable to both stormwater runoff and construction site runoff. The objective of erosion control is to limit the amount and rate of erosion occurring on disturbed areas. The objective of sediment control is to capture the soil that has been eroded before it leaves the construction site.

Despite the use of both erosion control and sediment control measures, it is recognized that some amount of sediment will remain in runoff leaving the construction site and entering the waterway as it relates to the 401 certification or construction around a waterway.

2. Temporal and Spatial Issues

Seasonal flow regimes (high flow versus low flow) can affect the types of BMPs that should be considered, as well as affect the timing of certain construction activities. Generally, construction activities will need to occur during low flow periods to protect water quality and minimize construction impacts. Direct activity within state waters should be minimized. For example, protection of sensitive aquatic species to minimize impacts during spawning periods may require careful selection and implementation of BMPs.

A project proponent needs to be aware of what types of aquatic animals, wildlife or endangered or threatened plants and animals could be affected by construction activities.

Consequently, a project proponent must consider timing and flow characteristics as part of the planning and design phase of a project. Consideration of temporal and spatial effects is important to ensure that designated uses, such as fisheries and recreational uses, are protected.

3. Colorado Limitations

Colorado is a diverse state that has construction activities occurring over a wide range of elevations altitude. A number of BMPs have been modified to work under the various Colorado conditions. Some particularly important considerations that can limit the application of certain BMPs in Colorado are listed below (this is not a complete list of limitations).

Seasonal planting limitations – Reestablishment of vegetation in areas disturbed by construction is dependent on appropriate soil texture, nutrient, and solar radiation conditions for plant growth that will limit seeding dates. Soil surface roughening, mulching, and geo-fabric application are particularly useful where temporary revegetation cannot be immediately established due to seasonal planting limitations.

High altitude construction – Short growing season, steep and rocky slopes, thin soil, high winds, fragile environments and vegetative-type limitations are prevalent.

Construction timing - Stabilization measures to be used should be appropriate for the time of year, site conditions and estimated duration of use. Phased grading and the protection of existing vegetation should also be considered in the construction schedule and erosion and sediment control plan.

Velocity controls – Steep terrain can significantly increase runoff velocities and requires consideration of stream-stability control practices, which may be different than those used in other states (e.g., silt fence will not serve as a velocity control practice under Colorado conditions).

Spring runoff – A project on a stream or river that is subject to high-flow conditions during spring snowmelt (generally March through June) must consider both the timing and depth of flows to be expected at the project site.

Storm event - runoff that occurs during the spring or summer seasons may result from short duration, high intensity thunderstorms that will affect the volume and discharge rates evident at a site. While the BMPs recommended for Colorado are sized to control water quality for the majority of storm-event volumes, special consideration in design may be required for projects located on streams subject to heavy spring runoff or built where stable flow-passage zones or spillways may be required for flooding conditions, fish movement or recreation.

Mine drainage – Colorado has an extensive mineralized belt running through the central mountains. Projects located near tailing or waste-rock piles, draining audits, previously dredged alluvium, or in the vicinity may require additional BMPs.

2.5 Best Management Practice Matrix

The following BMPs were determined to be appropriate for 401 certifications. Other BMPs can be substituted if they accomplish the same results and are in accordance with good engineering, hydrologic and pollution control practices.

Colorado Best Management Practices Appropriate for 401 Certification Matrix Construction, Temporary Or Permanent Practices

Planning Considerations

1. Design Considerations: The selection of BMPs for a development site should be made collaboratively as a result of coordination between the developer, local jurisdiction and any required regulatory agency. It is recommended that discussions regarding proposed BMPs occur early in each project.

a. Pre-Construction Planning

An erosion and sediment control plan is comprised of three major elements. The erosion control measures that will be used to limit erosion of soil from disturbed areas at a construction site; the sediment control measures that will be used to limit transport of sediment to off-site properties and downstream receiving waters; and the drainageway protection and runoff management measures that will be used to protect streams and other drainageways located on the construction site from erosion and sediment damages. A water control plan to manage subsurface, surface and storm flows during construction.

i. Site Constraints Some of the site constraints that should be considered during the planning phase include slope stability, drainage aspect and constructability, along with the general stream hydrology, stream morphology, natural flow volumes, water quality and aquatic ecology.

ii. Construction Timing Seasonality should be considered, particularly when construction must take place within streams and other waterways.

iii. Natural Resources Inventory & Evaluation

Provides basis for subsequent planning and design to avoid impacts to natural resources. It can include aquatic life, terrestrial life, riparian corridors, wetlands, open space, native species, endangered species, hydrology and drainage, soils, use-protection, classifications and standards, irrigation, stormwater, groundwater, water rights, water sources, geology, geomorphology, topography, etc.

Or Permanent Practices

Planning Considerations

iv. Pre-Design Planning Site Manager Input

Identification and evaluation of on-site information provides design criteria to solve existing or possible environmental problems. Involvement of the proposed site managers in the early design phases can lead to a more functional system design. The proposed site manager should be requested to review the water resources and natural resource inventories and provide recommendations to be incorporated into the design phases.

v. Identify Applicable Source Controls

Early in the design stage it should be recognized that the single most effective BMP for pollutants related to pesticide and fertilizer usage is the broad category of source controls.

Strictly limiting their use and using appropriate types for site conditions on a “management unit” basis under an Integrated Pest Management (IPM) strategy helps to reduce the potential for water quality problems.

vi. Drainage Designs Use “natural” drainage practices including preservation of natural drainage, wetlands, ponds, etc. Maintain wide undisturbed riparian (stream) corridors. Avoid flow concentration on-site and to adjacent hydrologically connected areas. Grading should maximize infiltration in the large available pervious areas, thereby promoting removal of runoff from surfaces and minimizing drainage problems on adjacent hydraulically connected areas.

vii. Conservation Easements Preserve wildlife habitat and wetlands and allow other development projects to continue in environmentally sensitive areas. Involve deeds to a charitable trust or environmental organization to maintain natural land or water areas, but does not surrender property title. Rather, it gives rights to an organization to maintain the land in an undeveloped, natural state. Benefits include public recognition, and in some cases, tax and liability reduction.

Planning Considerations

viii. Incorporate Wildlife Habitat Features

Use the resource inventories to identify important species, which may need protection or will be a part of the finished project. (Also identify pest species such as geese and ground squirrels.) Accommodating these species in the design phases can help reduce conflict with the environmental community and enable better management of the species during operation of the project.

ix. Advanced Irrigation Design

Computer-controlled irrigation systems can be used to reduce surface water runoff and groundwater recharge, thereby reducing the movement of fertilizer and pesticides. Water application rates correspond to consumptive use requirements.

Return flow reuse, stormwater reuse and use of treated wastewater effluent for irrigation should be used when environmentally, legally (water rights) and agronomically feasible.

b. Design Of Landscaping & Vegetative Practices

Seasonality and the local vegetative communities should be considered, particularly when construction must take place within streams and other waterways.

c. Minimize Disturbance Of Vegetation and/or Natural Wetlands

Pre-planning and phasing can minimize the impacts to selected vegetative types such as riparian vegetation and avoid disturbing natural wetlands. Current regulations intended to protect natural wetlands recognize a separate classification of wetlands constructed for a water quality treatment.

d. Local and State Stormwater Control Requirements

The implementation of this BMP is in the form of adoption or promulgation of ordinances, resolutions or executive orders granting authority to local government staff to review stormwater quality control plans and to either approve or present recommendations to elected officials for their approval;

requires a commitment of staff and fiscal resources of the local government to follow through with review, approval and enforcement of site-specific plans; regulations must be adopted specifying the content of stormwater quality control plans.

Planning Considerations

e. Minimizing Directly Connected Impervious Areas

Design site drainage flow paths to maximize flow over vegetated area; minimize ground slopes to limit erosion and slow down flow; select vegetation for survival values and water quality benefit.

f. Winter Maintenance Requirements - Road/Driveway

Winter maintenance requirements should be incorporated into plans (e.g., driveway orientation, sanding and snow removal).

2. Erosion Control Practices: The objective of erosion control is to limit the amount and rate of erosion occurring on disturbed areas. Despite the use of both erosion control and sediment control measures, it is recognized that some amount of sediment will remain in runoff leaving the construction site.

a. Surface Roughening Surface roughening provides temporary stabilization of disturbed areas from wind and water erosion; surface roughening should be performed after final grading to create depressions two to four-inches deep and four to six inches apart that are parallel to surface contours. It is particularly useful where revegetation cannot be immediately established due to seasonal planting limitations. Surface roughening only provides temporary protection and must be used in combination with other BMPs, such as mulching and temporary cover and perimeter sediment BMPs.

b. Mulching Mulching of all disturbed areas should occur within 14 days after final grade is reached on all portions of site not permanently stabilized or for which erosion control blankets are applied.

c. Revegetation Revegetation of a viable vegetative cover should occur within one year on all disturbed areas and stockpiles not permanently stabilized; Temporary vegetation is required on all disturbed areas having a period of exposure to final stabilization of one to two years; permanent vegetation is required on all disturbed areas having an exposure period longer than two years;

perennial vegetation should be considered for all revegetation efforts.

Planning Considerations

i. Temporary Seeding All disturbed areas must be mulched, or seeded and mulched, within 14 days after final grade is reached on any portion of the site not otherwise permanently stabilized. Areas that will remain in an interim condition for more than one year should be seeded. Under certain conditions, soil amendments and treatments may be necessary to provide an adequate growth medium to sustain vegetation.

ii. Permanent Seeding A vegetative cover should be established within one year on all disturbed areas and soil stockpiles not otherwise permanently stabilized. Vegetation is not considered established until a ground cover is achieved; which is sufficiently mature to control soil erosion and can survive severe weather conditions.

iii. Wetland Planting, Root Stock & Transplant

Disturbed wetland vegetation should be reused whenever possible. Wetland species should be compatible with the ecoregion where the activity occurs.

iv. Trees And Shrubs Trees and shrubs should be compatible with the ecoregion where the activity occurs. Generally a water source will be required to establish tree and shrubs.

v. High Altitude Seeding & Planting

Vegetation may not mature until the third growing season, requiring additional time in the implementation of best management practices. In addition to a short construction and growing season, high-altitude erosion control projects must contend with realities such as: less availability of nutrients;

plant roots can take up food only when the soil is free of frost;

less soil microbial activity; cold temperatures reduce activity of microorganisms that convert organic debris and inorganic matter to soil; less photosynthesis. Not all species are adapted to high elevation planting. The thinner atmosphere at high-elevation sites filters out less ultraviolet radiation from the sun.

These rays can damage leaf surfaces, disrupting photosynthesis and even killing plants.

vi. Special Seed Mixtures The seed mix for erosion control and stabilization during construction should be compatible with the final seeding needs.

Planning Considerations

d. Topsoil Preservation & Reuse

As a minimum, topsoil preservation and reuse involves the removal, stockpiling, and re-spreading of the surface six to eight inches of natural soil

e. Erosion Control Blankets Erosion control blankets are used in place of mulch on areas of high velocity runoff and/or steep grades, to aid in controlling erosion on critical areas by protected young vegetation.

Different slope grades will require implementing different erosion control blackets.

f. Interim Ground Stabilization

To provide vegetative cover on disturbed areas not paved or built upon for a period of two years or longer, or for an indeterminate length of time, a perennial grass should be planted.

g. Roads & Soil Stockpiles Roads and soil stockpiles should be covered as early as possible with the appropriate aggregate base; all road portions that are not paved or stabilized driving surfaces should be seeded and mulched within 14 days after final grading; stockpiles in place over 60 days should have temporary vegetation; stockpiles with 100 feet of drainageways need additional sediment control structures. Stockpile protection may rely on perimeter control or additional BMPs.

h. Dust Control In wind prone areas, roughened surfaces should include ridges oriented perpendicular to prevailing erosive winds in approximately a 1:4 ridge height to ridge width ratio. Cover or wet down areas or materials subject to wind erosion or blowing dust.

i. Check Dams Check dams are temporary structures designed to divert or slow water movement, drop out sediments. They can be used to protect existing habitat. Check dams can be removed from the site at the completion of construction or if permanent they require seeding and mulching consistent with revegetation BMPs.

Planning Considerations

3. Sediment Control Practices: The objective of sediment control is to capture the soil that has been eroded before it leaves the construction site. Sediment control will be site specific and can include vehicle tracking controls, sediment barriers, filters, dikes, traps or sediment basins, or a combination of any or all of these measures. Sediment controls must be constructed before land disturbance takes place. Earthen structures such as dams, dikes, and diversions will be mulched, as a minimum, within 14 days of installation.

Earthen structures that are expected to remain in place for more than one year must be seeded and mulched.

a. Vehicle Tracking Vehicle tracking controls should be implemented to minimize vehicle tracking of mud and dirt onto paved surfaces. Where tracking occurs, cleaning of paved surfaces prior to runoff events and at the end of each day; for sites greater than one acres, a rock pad or other alternative structural BMPs should be built at points of ingress and egress.

b. Slope-Length & Runoff Considerations

Cut-and-fill slopes must be designed and constructed to minimize erosion. This requires consideration of the length and steepness of the slope, the soil type, up-slope drainage area, groundwater conditions and other applicable factors. Slopes that are found to be eroding excessively will require additional slope stabilization until the problem is corrected.

c. Slope Diversion Dikes Slope diversion dikes located above disturbed areas may discharge to a permanent or temporary channel; diversion dikes located mid-slope on a disturbed area must discharge to temporary slope drains or other appropriate structure; diversion dikes located at the base of a disturbed area must discharge to a sediment trap or basin. A temporary diversion dike is a horizontal ridge of soil placed perpendicular to the slope and angled slightly to provide drainage along the contour.

Temporary diversion dikes can be constructed by excavation of a V-shaped trench or ditch and placement of the fill on the down-slope side of the cut.

Planning Considerations

d. Vegetation Buffers Buffer strips of natural vegetation can be left at the time of site grading, or can be created by using sod. A dense ground cover is necessary or runoff can channelize within the area. A width of 20 feet or more is recommended. This BMP cannot be used as a standalone sediment control measure for disturbed areas associated with construction.

i. Irrigated Grass Buffer Strips

Design is based on maintaining sheet-flow conditions across a uniformly graded, irrigated, dense grass cover strip. This BMP cannot be used as a standalone sediment control measure for disturbed areas associated with construction.

ii. Grass-Lined Swales Design is based on minimizing directly connected impervious areas to decrease runoff peaks, volumes and pollutant loads for slopes. This BMP cannot be used as a standalone sediment control measure for disturbed areas associated with construction.

iii. Road & Roadside Swales (Non-Erodible)

Roads and roadside swales should be provided for when road areas are not paved within 30-days of final grading; terracing and slope drains can be used in steep slope areas.

e. Sediment Entrapment Facilities

Sediment entrapment facilities for slope protection include straw bale barriers, silt fences, filter strips, sediment traps and sediment basins; at least one entrapment facility should capture run-off leaving a disturbed area.

i. Terracing Sediment can be controlled on slopes that are particularly steep by the use of terracing. During grading, relatively flat sections, or terraces, are created and separated at intervals by steep slope segments.

ii. Slope Drains There are certain instances when runoff must be directed down a slope within the disturbed area. A temporary slope drain can be used to protect these hill-slope areas from scour and additional erosion. A number of alternative designs and materials can be used for a slope drain. The slope drain should be implemented in a way to prevent erosion at the outfall.

Planning Considerations

iii. Straw Bale Barriers/Erosion Bales

Straw bales can be placed at the base of a hill-slope to act as a sediment barrier. This BMP also has proven to be one of the least effective practices. Straw bale installation is not recommended for use within a swale or channel. Straw bales are temporary in nature and may only perform for a period of weeks or months. This BMP is not recommended by the EPA.

iv. Silt Fence A silt fence is made of a woven synthetic material and acts to filter runoff. Silt fence can be placed as a temporary barrier at the base of a disturbed area but is not recommended for use in a channel or swale.

v. Filter Strips Vegetated filter strips act to cause deposition of sediment within the area of vegetation. This BMP cannot be used as a stand-alone perimeter sediment control measure.

vi. Sediment Traps A sediment trap is a temporary structure that is designed to fill with sediment. A sediment trap can be constructed by either excavating below grade or building an embankment across a swale. Excavated traps are less prone to failure than embankments. No pipe is used at the outlet, as in a sediment basin, and an open-channel spillway must be included in the design. A minimum of 900 cubic feet of storage volume must be provided for each tributary acre.

vii. Sediment Basins Areas draining more than five acres must be routed through a sediment basin. If the site is to include a stormwater quality or flood detention basin, the permanent detention facility may be used as the temporary sediment basin, provided the outlets are modified upon completion for this purpose. Such permanent detention facilities shall be restored to design grades, volumes, and configurations after site development is completed and the project is finalized.

viii. Brush Barrier A brush barrier is a temporary structure that is designed to strain sediment under low flow conditions or to protect existing habitat. This BMP cannot be used as a stand-alone perimeter sediment control measure.

Planning Considerations

f. Retention Ponds (12-Hr Wet Ponds)

Requires a base flow to maintain and to flush a permanent pool;

designed to empty capture volume over a 12-hour period;

design embankment-spillway-outlet system to prevent catastrophic failure

g. Long-term Retention Ponds (>12-Hr Wet Ponds)

Requires a large basin to capture volume for design periods over 12-hour period; special design considerations required to kept embankment-spillway-outlet system from catastrophic failure.

This should be viewed as a temporary BMP and not for permanent use.

h. Extended Detention Basins (Dry Basins)

Rely on an outlet designed to extend the emptying time of the basin’s capture volume; design embankment-spillway-outlet system to prevent catastrophic failure; design to empty capture volume over a 40-hour period.

i. Sand Filter Extended Detention Basin

A runoff storage zone is underlain by a vegetated sand bed with an underlying sand bed as an under-drain system. Runoff ponds in the surcharge zone and gradually infiltrates into sand bed filling the void spaces. Pollutant removal is provided through settling and filtering, and is suitable where there is no base flow or the sediment load is relatively low.

j. Porous Pavement Detention

A modular porous pavement that is flat and provides a 2-inch deep surcharge zone above its surface to temporarily store capture volume draining from adjacent tributary area, including its own surface. Runoff infiltrates into void spaces of gravel base course through sand filter and slowly exists through an underdrain.

k. Modular Block Porous Pavement

Design for even flow distribution over the entire porous surface;

assume permeable pavement areas are 30 percent impervious with subsoil infiltration and 60 percent impervious with no subsoil infiltration.

Planning Considerations

l. Porous Landscape Detention

A low-lying vegetated area underlain by a sand bed with an underdrain pipe. A shallow surcharge zone exists above the porous landscape detention for temporary storage of capture volume. Runoff ponds in the vegetated zone and gradually infiltrates into the underlying sand bed filling the void spaces.

The underdrain slowly dewaters the sand bed and provides a water quality benefit.

m. Infiltration Trenches Or Basins

This practice shows promise but needs further demonstration to determine pollutant removal effectiveness, develop design criteria that insures proper design, construction and maintenance.

n. Constructed Wetlands Basins

A constructed wetlands basin is a shallow retention pond which requires a perennial base flow to permit the growth of rushes, willows, cattails and reeds to slow down runoff and allow time for sedimentation, filtering and biological uptake. It is a sedimentation basin and a form of a treatment plant. These basins are built to enhance stormwater quality and do not replace natural wetlands.

o. Sediment Vaults, Water Quality Vaults & Inlets

Sediment or water quality vaults and specialized inlet vaults show promise but need further independent demonstration to determine pollutant removal effectiveness in semiarid climates or in mountainous areas and to develop cost-effective design criteria that insures proper design, construction and maintenance. Site-specific application of sediment vaults should be demonstrated where space limitations control types of applicable structural practices.

p. Steep Slope Stability Practices

The steep slope segments are prone to erosion, however, and must be stabilized in some manner. Retaining walls, gabions, cribbing, deadman anchors, rock-filled slope mattresses and other types of soil retention systems are available for use.

Planning Considerations

4. Drainageway Protection Practices: At times construction activities must occur adjacent to or within a drainage way. Whenever this occurs, bottom sediments will be disturbed and transported downstream. The goal of these BMPs is to minimize the movement of sediments resulting from construction activities that take place within any drainageway.

Temporary or permanent facilities can be installed to divert flowing water around such sediment-generating construction activities within drainageways.

a. Temporary Waterway Crossings & Diversions

Waterway crossing practices should limit construction vehicles in waterways to the maximum extent practicable. Temporary crossing or diversions are needed for actively-flowing water courses with regular crossing of construction vehicles.

Waterway crossings or diversions should be constructed to minimize sediment contributions from the built features such as hard armoring or compaction of side slopes and areas around culverts.

b. Permanent Waterway Crossings

Required stream crossings should minimize impact to riparian corridors, (i.e., wide, free-spanning bridges).

c. Stream Channel Lining Practices

Stability practices or temporary channels must be designed to be stable for the design flow with the channel shear stress less than the critical tractive shear stress for the channel lining material.

d. Outlet Protection Temporary slope drains, culverts, sediment traps and sediment basins must be protected from erosion and scour, check dams can be used in swales and ditches to protect these from down-cutting.

e. Inlet Protection All stormwater sewer inlets made operable during construction must have protection installed to minimize sediment-laden water entering the inlet or bypassing the inlet without treatment. Inlet protection is not a replacement for an adequately selected and implemented sediment entrapment

BMP.

Planning Considerations

f. Wetland Bottom Channel A wetland can be constructed or set into a drainageway to form a wetland bottom channel; requires a base flow to maintain wetland vegetation; pollutant removal efficiencies of constructed wetland bottoms vary significantly; removal efficiency design factors include influent concentrations, hydrology, soils, climate, vegetative type, growth zonation, maintenance and harvesting.

g. Edge Treatment Ponds & Waterways

Edge protection practices can be part of the project and help to limit erosion problems. Buffer strip edges provide water quality protection and stormwater management benefits. Landscaping practices can be used to establish edges to enhance and protect water quality.

h. Site-Specific Off-Site Velocity Control Practices (e.g. Golf Course, Instream Gravel Mining, Placer Mining)

Structural BMPs, which control runoff velocities, may be required in drainages at the boundaries of the golf course or other disturbances. Examples include drop structures and other energy dissipaters. These BMPs help to control erosion and water quality problems associated with sediment loading.

i. Stream Buffer Setbacks Construction stormwater permits require a 50 foot buffer along receiving waters or any waters in the project area, unless infeasible. It is recognized that certain activities require work instream and buffers may not be practicable. Regulation No. 82 requires Division approval prior to instream work begins.

5. Non-Sediment Construction Site Practices: Those BMPs that do not involve sediment or erosion control are intended to prevent or reduce the contamination of runoff waters.

They are broadly applicable to a variety of different sources or activities. By reducing pollutant generation or source control, adverse water quality impacts are reduced.

a. Material Storage, Handling & Petroleum Products

Spill containment and control at material storage site or staging area should include lined areas, diked areas, berming or gates to prevent extensive soil contamination. Berms may be made of concrete, earthen material, metal, synthetic liners, or any material that will safely contain a spill. Spill material is any material not allowed into surface waters or storm sewer systems according to local, state or federal regulation. Spill control devices include valves, slide gates, or any other device that can contain spill material when required.

Planning Considerations

b. Underground Utility Construction

The construction of most underground utility lines shall be subject to the following criteria: no more than 200 feet of trench are to be opened at one time (local criteria may be more restrictive); where consistent with safety and space considerations, excavated material is to be placed on the uphill side of trenches; trench dewatering (additional state/local permitting may be required) devices must discharge in a manner that will not adversely affect flowing streams, wetlands, drainage systems, or off-site property, and provide storm sewer inlet protection whenever soil erosion from the excavated material has the potential for entering the storm drainage system.

c. BMP Maintenance All BMPs shall be maintained and repaired as needed to assure continued performance. Sediment entrapment and inlet protection BMPs may require periodic replacement and all sediment accumulated behind them must be removed and disposed of properly. Sediment traps and basins will require periodic sediment removal when the design storage level is one-half full. All facilities must be inspected by the owner or owner’s representative following each heavy precipitation or snowmelt event that results in runoff.

d. Disposition Of Temporary Measures

All temporary erosion and sediment control measures must be removed within 30 days after stabilization.

e. Good Housekeeping,…