This manual is intended for use as a planning tool and design guidance document by the regulated and regulatory communities involved in stormwater quality management in the State of Connecticut.  The manual provides uniform guidance for developers and engineers on the selection, design, and proper application of stormwater best management practices (BMPs).  The manual will also assist local and state government officials (i.e., town engineers, planners, Planning and Zoning Commissions, Conservation Commissions, and Inland Wetlands Commissions, and Connecticut State agencies) design and review projects in a technically sound and consistent manner.

The information and recommendations in this manual are provided for guidance and are intended to augment, rather than replace, professional judgement.  The design practices described in this manual should be implemented by an individual with a demonstrated level of professional competence, such as a professional engineer licensed to practice in the State of Connecticut.  Design engineers, as well as those responsible for operation and maintenance, are ultimately responsible for the long-term performance and success of these practices.  However, the use of this manual is not restricted to engineers or technical professionals.  It is also intended for use by other individuals involved in stormwater and land use management for reviewing and recommending practices contained in the manual.

The manual is organized into two volumes, both contained in a single, comprehensive document.  The organization of the manual generally follows the recommended stormwater management planning process, which emphasizes preventive measures such as site planning and alternative site design, source controls, and pollution prevention over end-of-pipe structural controls.

Volume I provides an overview of the stormwater problem, approaches for preventing and mitigating stormwater impacts, and a description of site planning and source control practices for pollution prevention.  In addition to this chapter, other chapters in Volume I include:

Chapter Two – Why Stormwater Matters: The Impacts of Urbanization

This chapter introduces the concept of urban stormwater runoff and its impact on watershed hydrology, water quality, and ecology.  Chapter Two summarizes why stormwater management measures are necessary to protect receiving waters from the adverse impacts of uncontrolled stormwater runoff.

Chapter Three – Approaches for Preventing and Mitigating Stormwater Impacts

Chapter Three presents an overview of approaches for preventing and mitigating stormwater impacts through site planning and pollution prevention, stormwater quantity controls, construction erosion and sedimentation controls, and post-construction stormwater quality management.

Chapter Four – Site Planning and Design

Chapter Four addresses site planning concepts such as alternative site design and Low Impact Development.  These techniques can be incorporated into the design of new projects to reduce or disconnect impervious surfaces and retain and infiltrate stormwater on-site, thereby eliminating or reducing the need for structural stormwater quality controls.

Chapter Five – Source Control Practices and Pollution Prevention

Chapter Five describes source control and pollution prevention practices to limit the generation of stormwater pollutants at their source.  This chapter focuses on common municipal, residential, commercial, and industrial practices applicable to new and existing development such as street and parking lot sweeping, roadway deicing and salt storage, storm drainage system maintenance, illicit discharge detection and elimination, commercial and industrial pollution prevention, and lawn care and landscaping practices.

Volume II provides technical guidance on the selection, design, construction, and maintenance of structural stormwater treatment practices. Volume II also addresses procedures for developing a site stormwater management plan and design issues associated with stormwater retrofits for existing development. Volume II includes the following chapters:

Chapter Six – Introduction to Stormwater Treatment Practices

Chapter Six introduces structural stormwater treatment practices that can be used alone as primary treatment, as pretreatment or supplemental treatment practices, or in combination (i.e., treatment train approach). This chapter also describes general categories of recently developed, emerging, or potential future stormwater treatment devices and technologies, as well as criteria for evaluating the performance and applicability of new treatment practices.

Chapter Seven – Hydrologic Sizing Criteria for Stormwater Treatment Practices

Chapter Seven explains the procedures and applicability of sizing criteria for structural stormwater treatment practices to meet pollutant reduction, groundwater recharge and runoff volume reduction, and peak flow control requirements.  This chapter also includes guidance on the design of stormwater bypass structures and sizing examples for various types of stormwater treatment practices.

Chapter Eight – Selection Criteria for Stormwater Treatment Practices

Chapter Eight provides guidance on selecting appropriate structural stormwater treatment practices for a development site based on the requirements and needs of the site.  This chapter includes a recommended selection process and selection criteria.

Chapter Nine – Developing a Site Stormwater Management Plan

Chapter Nine describes how to prepare a site stormwater management plan for review by local and state regulatory agencies.  The chapter includes a recommended plan format and contents, and a completeness checklist for use by the plan preparer and reviewer.

Chapter Ten – Stormwater Retrofits

Chapter Ten describes techniques for retrofitting existing developed sites to improve or enhance the water quality mitigation functions of the sites.  Chapter Ten also discusses the conditions for which stormwater retrofits are appropriate and the potential benefits of stormwater retrofits.

Chapter Eleven – Design Guidance for Stormwater Treatment Practices

Chapter Eleven provides detailed technical design guidance for each of the stormwater treatment practices introduced in Chapter Six.  This chapter includes guidance on the design, construction, and maintenance of these practices, as well as summary information on selection and sizing criteria addressed in previous chapters.

Appendices

Appendices containing supplemental information on the design, construction, and maintenance of structural stormwater management practices are included at the end of Volume II. A glossary of terms used in the manual is also provided at the end of Volume II.

While providing detailed guidance on a number of recommended stormwater management practices and related topics, this document is not an exhaustive reference on each topic and does not address all aspects of stormwater management.  Additional technical guidance can be found in numerous other documents, many of which are referenced in this manual.  References and recommended additional sources of information are listed at the end of each chapter.

This manual is intended for use as a guidance document to assist developers and the regulated community in complying with existing local, state, and federal regulatory programs. The manual itself has no independent regulatory authority.  Rather, it establishes guidelines that are implemented through a framework of existing regulations.  Although this manual is non-regulatory in scope, it provides the technical basis for a comprehensive, statewide stormwater quality management strategy, including the consistent application of stormwater management practices throughout the state.

The Connecticut Department of Environmental Protection (DEP) historically has been a national leader in developing and implementing water quality protection programs and policies.  A number of federal and state regulatory programs are currently in place for stormwater quality management and water resource protection in the state. Consistent with a long-established tradition of home-rule-style government exerted by municipal authorities, many of these programs are implemented at the local level through local zoning, subdivision, and inland wetlands and watercourses regulations and ordinances. In addition, the State of Connecticut has been delegated authority from the federal government to implement federal regulations that pertain to water resources protection.  Table 1-1 summarizes existing regulatory programs that address management of stormwater discharges in Connecticut. Descriptions of these programs and their relationship to this manual follow Table 1-1.

Connecticut Clean Water Act

The Connecticut Clean Water Act (CCWA) of 1967 (P.A. 67-57) launched Connecticut’s modern water pollution control program.  Under the CCWA, as amended, DEP has the regulatory authority to:

• Abate, prevent or minimize all sources of water pollution, including nonpoint sources,
• Develop state water quality standards,
• Permit discharges, including stormwater discharges, to waters of the state, and
• Establish enforcement tools for pollution abatement and prevention.

This statute (Chapter 446k of the CGS) forms the authority for the DEP Bureau of Water Management’s Permitting, Enforcement and Remediation Division (PERD) to regulate discharges to surface waters, ground waters, and Publicly Owned Treatment Works (POTWs). Discharges to surface waters are regulated by DEP under both the CCWA and the federal NPDES Program, because Connecticut has been delegated authority to implement the federal NPDES Program.  Consequently, stormwater discharges are regulated under a series of general permits based on the type of activity generating the discharge.  The general permit program is authorized under CGS Section 22a-430b and is designed to authorize similar minor stormwater discharges by one or more applicants.  The regulated sources are divided into four major categories:

Commercial Activities

This general permit applies to discharges from any conveyance which is used for collecting and conveying stormwater and which is directly related to retail, commercial, and/or office services whose facilities occupy 5 acres or more of contiguous impervious surface and which are described in the SIC Codes 50’s and 70’s.

Industrial Activities

This general permit applies to discharges from any conveyance which is used for collecting and conveying stormwater and which is directly related to manufacturing, processing or material storage areas at designated categories of industrial facilities.

Construction Activities

This general permit applies to discharges of stormwater and dewatering wastewaters from construction activities which include, but are not limited to, clearing, grading, and excavation and which result in the disturbance of 5or more acres of total land area on a site. As described above, under Phase II of the NPDES Stormwater Program, construction activities disturbing between 1 and 5 acres are also regulated by DEP through a coordinated effort with municipalities under the Connecticut Erosion and Sedimentation Control Act.

Municipal Separate Storm Sewer Systems (MS4s)

This general permit regulates discharges of stormwater from small MS4s and other similar facilities located in urbanized areas. Separate general permits address stormwater discharges from small municipalities and other state and public facilities, as well as the Connecticut Department of Transportation.

Inland Wetlands and Watercourses Act

The Inland Wetlands and Watercourses Act of 1972, as amended, establishes authority for DEP and municipalities to adopt programs regulating construction and other activities affecting inland wetlands and watercourses, including impacts due to stormwater or stormwater-related activities.  The Wetlands Management Section of the DEP Inland Water Resources Division (IWRD) has responsibility for overseeing implementation of the Act and directly regulates the activities of Connecticut state agencies that are located in or may affect inland wetlands and watercourses.  As discussed in more detail below, local inland wetland agencies are responsible for regulating private and municipal work located in or affecting wetlands or watercourses within each Connecticut municipality.

Erosion and Sediment Control Act

The Soil Erosion and Sediment Control Act (CGS Sections 22a- 325 to 22a-329, inclusive)requires that the Council on Soil and Water Conservation develop guidelines for soil erosion and sediment control on land being developed. The latest version of these guidelines was released in April of 2002.  The goal of the guidance document is to reduce soil erosion from stormwater runoff, minimize nonpoint sediment pollution from land being developed, and conserve and protect the land, water, air and other environmental resources of the state.

Flood Management Certification

Under CGS Section 25-68b through 25-68h, inclusive, any state agency proposing an activity within or affecting a floodplain or impacting natural or man-made storm drainage facilities must submit a flood management certification application to DEP.

Stream Channel Encroachment

Stream channel encroachment lines have been established for approximately 270 linear miles of riverine floodplain throughout Connecticut.  Under CGS Sections 22a-342 through 22a-349a, DEP IWRD regulates the placement of encroachments and obstructions riverward of these encroachment lines.  Any activity that permanently alters the character of the floodplain or watercourse within these areas, including activities generating stormwater discharges, is subject to approval by DEP.

401 Water Quality Certification

Applicants for a federal license or permit for activities that may result in a discharge into navigable waters of the state, including stormwater discharges, must submit a water quality certification application to DEP.

Water Diversion Policy Act

The Water Division Policy Act of 1982 (P.A. 82-402, as amended) grants the DEP IWRD limited authority to regulate the withdrawal and use of groundwater and surface waters of the state, including stormwater diversions.  Under Section 22a-365 through 22a-379a of the CGS, permitting is required for any activity that causes, allows, or results in the withdrawal from or the alteration, modification, or diminution of the instantaneous flow of water. Diversions must be consistent with other state policies that deal with long-range planning, management and use of the water resources of the state, including the State Plan for Conservation and Development, Water Quality Standards, Flood Management Act, Water Supply Planning Process, Inland Wetlands and Watercourses Act, Aquifer Protection Act, and Endangered Species Act.

Dam Safety Program

The Dam Safety Section of the DEP IWRD is responsible for administration and enforcement of Connecticut’s dam safety laws under CGS Sections 22a-401 through 22a-411, inclusive. The Dam Safety Section regulates the construction, alteration, repair, and removal of dams, including stormwater impoundments through the use of embankments such as stormwater retention/detention ponds, stormwater wetlands, and infiltration basins.  Registration with the Dam Safety Section is required for all new stormwater impoundments.  A dam construction permit may also be required if the structure may endanger life or property in the event of failure or breaking away. Structures that pose a significant or high hazard to life or property are also subject to periodic inspections by DEP.

Connecticut Coastal Management Act

The Connecticut Coastal Management Act (CGS §§22a-90 through 22a-112, inclusive) establishes goals and policies for the protection of coastal resources.  Under CGS Sections 22a-98, the Commissioner of DEP must coordinate all regulatory programs under his jurisdiction with permitting authorities in the coastal area, including those related to wetlands and watercourses, stream channel encroachment, and the erection of structures or placement of fill in tidal, coastal, or navigable waters, to ensure that permits issued under such regulatory authority are consistent with coastal management goals and policies. The coastal area is defined by statutes [CGS §22a-94(a)] and encompasses the municipalities listed in Table 1-2. In addition, pursuant to CGS §22a-100(b), each state department, institution, or agency responsible for the primary recommendation or initiation of actions within the coastal boundary, which may significantly affect the environment, must also ensure that such actions are consistent with coastal management goals and policies and incorporate all reasonable measures mitigating any adverse impacts on coastal resources.  The coastal boundary is defined by statute [CGS §22a-94(b)].  Adverse impacts on coastal resources are also statutorily defined [CGS §22a-93(15)] and include degrading water quality through the significant introduction into either coastal waters or groundwater supplies of suspended solids, nutrients, toxics, heavy metals, or pathogens, all of which can be contained in stormwater.  In addition, degrading water quality through the significant alteration of temperature, pH, dissolved oxygen, or salinity is also included in the statutory definition of adverse impacts, and these impacts can also result from stormwater runoff. Coastal permitting and assistance to municipalities is administered through the DEP Office of Long Island Sound Programs (OLISP).

Table 1-2. Municipalities Within the Coastal Area

Tidal Wetlands Act

The Tidal Wetlands Act of 1969 (CGS §§ 22a-28 through 22a-35, inclusive) gives DEP authority to regulate activities in tidal wetlands.  The permitting program administered by OLISP requires that the applicant address possible impacts to coastal resources, including those associated with stormwater runoff, and discourages direct stormwater discharges to tidal wetlands.

Structures, Dredging and Fill Act

The Structures, Dredging, and Fill Act (CGS §§ 22a-359 through 22a-363f, inclusive) gives DEP the authority to regulate dredging, the erection of structures, and the placement of fill in tidal, coastal or navigable waters of the state waterward of the high tide line. The permitting program administered by OLISP requires that the applicant address possible impacts to coastal resources, including those associated with stormwater runoff, and discourages direct untreated stormwater discharges to tidal, coastal, or navigable waters.

Nonpoint Source Management Programs (pursuant to CWA Section 319 and CZARA Section 6217)

The Connecticut Nonpoint Source Management (NPS) Program is administered by the DEP Bureau of Water Management (BWM) Planning and Standards Division (PSD) and is a network of several federal, state, and local programs.  The NPS Program includes all of the components required under Section 319 of the Federal Clean Water Act. It establishes long- and short-term goals for the prevention and management of nonpoint sources of pollution, including those associated with urban runoff and stormwater.  EPA defines NPS pollution as that which is "caused by diffuse sources that are not regulated as point sources and are normally associated with precipitation and runoff from the land or percolation." EPA approved Connecticut’s upgraded Nonpoint Source Management Program in November 1999 (see Nonpoint Source Management Program at https://www.ct.gov/deep/lib/deep/water/nps/planupdate/ct_nps_plan_final.pdf.)

As described in the discussion of federal programs above, Section 6217 of the 1990 CZARA requires the development of a Coastal Nonpoint Pollution Control Program (CNPCP) to implement management measures to reduce or eliminate nonpoint source pollution within the coastal boundary.  The CNPCP is a networked program administered by OLISP with assistance from BWM and relies on other regulatory programs described in this section including state and local permitting authorities.

Aquifer Protection Area Act

The Aquifer Protection Act of 1989 requires the development of aquifer protection land use regulations applicable within DEP-approved aquifer protection areas (areas recharging large public water supply wells). As part of the proposed regulations, municipalities containing aquifer protection areas would also be required to adopt regulations, subject to approval by DEP, requiring permitting for all regulated activities within aquifer protection areas.  Under the proposed regulations, regulated activities within an aquifer protection area may require a stormwater management plan to assure that stormwater runoff generated by the proposed activity is managed in a manner to prevent pollution of ground water and surface water.

Source Water Assessment Program (SWAP)

The Connecticut Source Water Assessment Program (SWAP) was initiated in 1997 in response to the 1996 Amendments to the Federal Safe Drinking Water Act.  The Connecticut Department of Public Health (DPH) in partnership with DEP is responsible for the development of the SWAP, which is designed to assess and protect public drinking water supply sources in the state. The SWAP completes its work based upon an EPA-approved Work Plan, dated September 1999. The SWAP includes the delineation of a protection area surrounding the drinking water source, the identification of potential pollution sources within and around the protection area, and the determination of a water supply’s susceptibility to contamination.  The SWAP will build on existing surface water and wellhead protection programs administered by DPH and DEP.  As part of the program, DEP and DPH will recommend a variety of source protection strategies aimed at reducing potential impacts from non-point pollution sources including stormwater runoff to municipalities and water companies. Additional information on the SWAP can be found at http://www.dph.state.ct.us/BRS/WSS/swap.html.

Underground Injection Control (UIC) Program

The Federal Safe Drinking Water Act established the UIC program to provide safeguards so that injection (or infiltration) wells used for waste disposal do not endanger water quality, especially groundwater drinking sources. In Connecticut, the DEP Water Management Bureau has been given primacy for this program.  A well under the UIC Program is any well where the depth is greater than the largest surface dimension (this could include certain infiltration trenches with vertical pipe connections) that is used to discharge waste to the ground.  Historically the type of UIC wells used in Connecticut were “Class V” (not hazardous wastes), and were primarily used for disposal of commercial and industrial process wastewaters from floor and sink drains.  They were typically drywell type structures, and were most commonly used for automotive service drains.  In Connecticut these types of wells are no longer allowed, and groundwater discharges of wastes other than domestic sewage or clean water are not allowed to the ground in existing or potential groundwater drinking supply area. Stormwater structures such as infiltration drywells or trenches, which are susceptible to spills, leaks, or other chemical releases, especially at industrial or petro-chemical commercial sites, may be considered UIC wells.

Care must be taken to ensure that stormwater drywells or infiltration trenches do not threaten groundwater quality, especially drinking water sources. Later chapters in this manual provide guidance about sites where the use of stormwater infiltration structures should be avoided due to groundwater quality concerns, and sites where they could be used to recharge stormwater with pretreatment or other safeguards.

Public Health Code – Sanitation of Watersheds

Connecticut Public Health Code Section 19-13-B32i requires that stormwater discharges terminate at least one hundred feet from an established watercourse located within lands tributary to public drinking water supplies, including both surface and groundwater sources.  If such termination is not possible, discharges that terminate within 100 feet of a watercourse require review by the Department of Public Health. Discharges within 100 feet must include adequate flow energy dissipation and not adversely impact stream quality. This requirement applies to surface drinking water supply watershed areas (approximately 16.5 % of Connecticut’s land area), and to streams tributary to public drinking water supply wells.

State-Mandated Programs

Several of the state programs discussed above require implementation of municipal regulations and permitting processes, including:

• Inland Wetlands and Watercourses Act: CGS Section 22a-42(c) requires that each municipality establish an Inland Wetlands and Watercourses Agency and local regulations regulating private and municipal work located in or affecting wetlands or watercourses. The regulations must conform to model regulations developed by DEP and contain certain criteria and procedures for application review. The application must address measures to prevent or minimize pollution, including those associated with stormwater runoff.

• Erosion and Sediment Control Act:The Erosion and Sediment Control Act requires that municipalities adopt regulations requiring that a soil erosion and sediment control plan be submitted with any application for development within the municipality when the disturbed area of such development is more than one-half acre.
• Coastal Management Act/Coastal Site Plan Review: Under the CCMA, coastal municipalities are required to implement Connecticut’s Coastal Management Program through their existing planning and zoning authorities. Most activities within the coastal boundary, as defined by DEP according to CGS 22a-94, require municipal Coastal Site Plan Review (CSPR). In this review process, the applicant must describe the proposed project and identify coastal resources in the project area and potential impacts to those resources.  Local planning and zoning authorities must decide whether potential adverse impacts to water quality or other coastal resources are acceptable.  A description of stormwater management measures may be required depending on the size of a project and the municipality concerned.  CGS Section 22a-101 allows coastal municipalities to develop Municipal Coastal Programs, which are revisions to plans of conservation and development and zoning regulations to focus on the coastal resources and coastal management issues unique to each town.
• Municipal Planning/Zoning:Public Act 91-170 (codified in CGS §8-2(b) and CGS §8-35a) and Public Act 91-395 [codified in CGS §8-23(a)] require that the zoning regulations and plans of conservation and development for any municipality contiguous to Long Island Sound, and the regional plans of development of each region contiguous to Long Island Sound, be made with reasonable consideration for the restoration and protection of the ecosystem and habitat of Long Island Sound. These documents must also contain recommendations and practices to reduce hypoxia, pathogens, toxic contaminants, and floatable debris in Long Island Sound.

• Aquifer Protection Act:Under the proposed aquifer protection land use regulations, municipalities containing aquifer protection areas would also be directed to adopt regulations requiring local permitting for all regulated activities within aquifer protection areas. Under the proposed regulations, regulated activities within an aquifer protection area may require a stormwater management plan to assure that stormwater runoff generated by the proposed activity is managed in a manner to prevent pollution of ground water and surface water.

Municipal Planning/Zoning

Development projects and other activities subject to approval by municipal planning and zoning authorities are typically subject to review for potential impacts to environmental resources.  Depending upon the local regulations, stormwater quantity and/or quality may be regulated.  In addition, some municipalities have developed or are considering developing local stormwater quality ordinances.