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    City of Danbury

    The City of Danbury has enacted a Stormwater Ordinance in order to establish minimum stormwater management requirements and controls to protect and safeguard the general health, safety, and welfare of the public residing in watersheds within this jurisdiction.  The City of Danbury  is the permitting authority for all land disturbing activities and requires the land owner to maintain all on-site stormwater control facilities and all open space areas (e.g. parks or “green” areas) required by the approved stormwater control plan. The City of Danbury will only provide construction permits to projects that establish a plan to manage stormwater runoff occurring during the construction process. The City of Danbury, under the NPDES program, also has the authority to inspect properties for noncompliance and can issue a notice of violation (NOV) for any deficiency or infraction onsite. Property owners are responsible for the maintenance of any stormwater facilities or practices located on the property. The City of Danbury has the authority to inspect stormwater facilities and practices in order to ascertain that they are properly maintained and functioning.

    The City of Danbury has been issued a general permit for the discharge of stormwater into its stormwater system. This permit, General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems, was re-issued January 9, 2013 under the authority of Section 22a-430b of the Connecticut General Statutes. The permit requires the City of Danbury to develop a stormwater management plan (SWMP), with minimum control standards such as: public education and outreach on stormwater impacts; Public Involvement/Participation; Illicit discharge detection and elimination; Construction site stormwater runoff control; Post-construction stormwater management in new development and redevelopment; and Pollution prevention/good housekeeping for municipal operations.

    The City of Danbury primarily follows the stormwater regulations set forth by the Connecticut Department of Energy and Environment (DEEP) - and the aforementioned permit issued from the DEEP- however, Danbury has also adopted local zoning standards for stormwater drainage from residential, commercial, and industrial developments. Developments located in the City of Danbury's Aquifer Protection Area (APA) are subject to more intensive stormwater regulations, described in more detail below.

    Danbury Ordinance

    49-9.2. Prohibition of Illicit Connections. 

    (a) The construction, use, maintenance or continued existence of illicit connections to the MS4 is prohibited. 

    (b) This prohibition expressly includes, without limitation, illicit connections made in the past, regardless of whether the connection was permissible under law or practices applicable or prevailing at the time of connection. 

    (c) A person is considered to be in violation of this ordinance if the person connects a line conveying sanitary sewage to the MS4, or allows such a connection to continue. 

    (d) Improper connections in violation of this ordinance must be disconnected and redirected, if necessary, to an approved onsite wastewater management system or the sanitary sewer system upon approval of the Director. All costs associated with eliminating the improper connection and with redirecting flows in a manner approved by the Director shall be borne by the property owner. 

    (e) Any drain or conveyance that has not been documented in plans, maps or equivalent, and which may be connected to the MS4, shall be located by the owner or occupant of that property upon receipt of written Notice of Violation from the Director requiring that such locating be completed. Such notice shall specify a reasonable time period within which the location of the drain or conveyance is to be determined, that the drain or conveyance be identified as storm sewer, sanitary sewer or other, and that the outfall location or point of connection to the MS4, sanitary sewer system or other discharge point be identified. Results of these investigations are to be documented and provided to the Director.

    City of Danbury Zoning Regulations

    8.A.3. Erosion and Sedimentation Control Permits. 

    1. Permit Requirement. No person shall do any grading, stripping, excavating or filling or undertake any earth change unless a valid erosion and sedimentation control permit is received from the Health Director or his/her designee with the following exceptions:

    (1) any activity occurring on a regulated wetland or watercourse, where a permit is required from the Environmental Impact Commission; or, 

    (2) exemptions which are listed in this Section. 

    1. Permit Application. 

    An application obtained from the Planning Department shall be completed and submitted for each erosion and sedimentation control permit. The following plans and specifications shall accompany each application for an erosion and sedimentation control permit. [Rev. 04/30/2019] 

    (1) Erosion and sediment control plans and specifications prepared in accordance with, but not limited to, "The Erosion and Sediment Control Handbook," U.S. Department of Agriculture, Soil Conservation Service, Storrs, Connecticut and the 2002 Connecticut Guidelines for Soil Erosion and Sediment Control, DEP Bulletin 34, Connecticut Council on Soil and Water Conservation in cooperation with Connecticut Department of Environmental Protection, as may be amended. [Rev. 04/30/2019] 

    (2) An Operation and Maintenance Plan for all stormwater systems that will discharge to, or receive discharge from, the City of Danbury municipal stormwater system. Said Operation and Maintenance Plan shall include the requirement for short-term and long-term inspection and maintenance of stormwater basins and other relevant stormwater system components and the submission of an annual report documenting the inspection results and maintenance activities performed to be submitted to the Department of Health and Human Services. In the event that development disturbs greater than ½ acre of land and will not discharge to, or receive discharge from, the City of Danbury municipal stormwater system, the City may, at its discretion, require submission of an Operation and Maintenance Plan to ensure the performance and pollutant removal efficiency of stormwater basins and other relevant stormwater system components. [Eff. 04/30/2019]

    City of Danbury, Engineering Division General Information & Guide


    1. Pre-development and post-development runoff computations for the entire site based on a 25 year storm will be required. Where open channels, culve1ts and/or bridges are proposed or where open channels, culverts and bridges may be impacted by site improvements/development, the Engineering Division may require that these hydraulic facilities/stmctures be analyzed for 50, 100 and/or 500 year storm frequencies.
    2. Calculations for sizing the on and off site drainage systems (based on a 25 year storm) will be required.
    3. Either the Rational, TR-55 or TR-20 (where applicable) method is acceptable.
    4. Rights to drain from downstream property owner(s) will be required, if there is an increase in the rate of or volume of runoff discharged from the site, a change in the point of discharge of runoff from the site in question onto other property or if there is a decrease in runoff which has adverse effects downstream.
    5. The developer's engineer is to verify that surface runoff from any City road will not have a negative impact on the site. If runoff from a City road will impact the site, a drainage plan to handle this runoff is to be developed by the engineer for installation by the developer.
    6. Connections to existing systems:
    1. Calculations on the adequacy of the capacity of the existing downstream system will be required. If portions of the existing system are found to be inadequate, replacement of these portions of the existing system may be necessary.
    2. If connecting to a City system, the connection is to be made under the supervision of and to the satisfaction of the City's Highway Department.
    1. Retention Systems/Detention Systems/Drywells where proposed:
      1. Calculations (based on a 25 year storm) for the sizing of the storage required for the proposed development and of the outlet control are required.
      2. Percolation and deep hole tests are to be done and results submitted, if warranted.
      3. The installation of the system is to be done under the supervision of A State of Connecticut licensed engineer.
      4. After construction, the engineer who supervised the installation of the system is to submit to the City written certification that the system was installed as per the approved design.
      5. A reminder to the property owner that the system will remain a private one and that regular maintenance will be crucial to its continued functioning as intended is to be made.
      6. Adequate access to the system for maintenance purposes is to be provided.
      7. If the system is to be installed in a parking/driveway area, it is to be capable of handling minimum H-20 loads.
      8. A DEP dam permit may be warranted for a detention or retention pond.
    2. Floodplains..
    3. Anny Corps of Engineers approval is to be acquired, if warranted.
    4. Discharges are to be properly stabilized.
    5. Roof drains are to be shown on the plan.
    6. It is recommended that no portion (other than floor drains or underdrains) of a private on-site storm drainage system be located beneath a building or structure.
    7. If the development will discharge to a State of Connecticut storm drainage system, State Department of Transportation (DOT) approval will be required.


    (For developed sites in the AQUIFER PROTECTION AREA) 

    This document contains information obtained from, and prepared by, the State of Connecticut Department of Energy and Environmental Protection (“DEEP”). It is intended to assist you with the stormwater management plan requirements of the City of Danbury Aquifer Protection Area Program. When the City of Danbury Aquifer Protection Agency or the City of Danbury Aquifer Protection Area Regulations requires a stormwater management plan, the plan shall ensure that stormwater run-off generated by the regulated activity is managed in a manner so as to prevent pollution of ground water.

    Because many of the facilities in the Aquifer Protection Area have already registered for the DEEP General Permit Associated with Commercial Activity (GP-Commercial) or the General Permit for the Discharge of Stormwater Associated with Industrial Activity (GP-Industrial), those forms and the accompanying Stormwater Management Plan or Pollution Prevention Plan serve as the basis for the City of Danbury Aquifer Protection Agency Stormwater Management Plan (the “Plan”). Due to the sensitivity of aquifer protection area within the City, there are some special considerations beyond those in the general permits, so additional information is required in the form of a stormwater Supplement.

    The information required in the Supplement should guide the revision of an existing registered Stormwater Management Plan or Pollution Prevention Plan. Facilities without an existing stormwater general permit should complete a registration form for GP-Commercial and develop the associated stormwater management plan. Such plan should include information below and required for the Supplement.

    All stormwater management plans shall meet the requirements for the DEEP General Permit of the Discharge of Storm Water associated with a Commercial Activity (Commercial GP). Such requirements shall include:

    1. A Registration Form that provides facility information, indicates the type of activity, and identifies stormwater discharge information including the number and type of conveyance.

    2. A Stormwater Management Plan that includes measures for pollution prevention, pavement sweeping, outdoor storage and washing restriction, illicit discharge control, spill control/response, and maintenance and inspection of storm water structures. It shall also contain detailed information relative to the following:

    • The Pollution Prevention Team or individual responsible for implementation of the plan;
    • Identification of discharge points or potential pollution sources;
    • Housekeeping measures;
    • Spill control and response measures;
    • Maintenance and inspection provisions and checklists;
    • Employee training;
    • Regular compliance evaluations;
    • Future Considerations;
    • Record keeping requirements;
    • Monitoring requirements for industrial uses only;
    • Plan Certification (see Attachment A); and

    3. A Stormwater Supplement that addresses additional areas of concern to groundwater including the provision of measures necessary to prevent contaminated stormwater discharges/releases to the ground, application of stormwater discharge and treatment measures to protect groundwater quality, and encouragement of safe recharge of stormwater where it does not endanger groundwater quality. Additional management measures include: prevention of illicit discharges to stormwater discharged to the ground, provision of necessary impervious pavement in high potential pollutant release areas or “storm water hot spots” such as storage and loading areas, fueling areas, intensive parking areas and roadways, and discharge of paved surface runoff to aboveground type land treatment structures including surface drains, sheet flow surface swales, depressed grass islands, detention/retention and infiltration basins, and wet basins. These measures take advantage of natural treatment processes in soil and vegetation before discharge to the groundwater and promote natural aquifer recharge. The DEEP 2004 Connecticut Stormwater Quality Manual provides comprehensive stormwater guidance including potential groundwater concerns and is available on the DEEP’s website at

    While the emphasis of the Plan and Supplement should be to minimize groundwater quality impacts of the runoff, a plan should be balanced and the extent possible include a combination of approaches to protect all water resources concerns including surface water quality and water quantity changes between pre-development and post-development runoff rates and volumes where possible. Most alternative site design designs, low impact development, and green infrastructure techniques will benefit groundwater except for certain direct infiltration techniques.

    The Supplement shall provide the following information.

    A. The identification of additional stormwater and site features of concern to groundwater (as applicable):

    • Outline of buildings, sheds or other storage structures, pavement
    • Stormwater structures and conveyances to the ground- drainage flow direction, infiltration areas and structures, and treatment or controls
    • Location of fueling stations
    • Location of loading/unloading areas
    • Location of wastewater disposal systems- sewer line or septic system
    • Location of waste storage and disposal areas including: dumpsters, used oil storage tanks, and other waste storage
    • Location of liquid storage areas including: underground and above ground storage tanks, and their filling and discharging or distribution lines Location of any other outdoor structures or processing service areas that may impact groundwater or have materials exposed to precipitation.

    B. A description of methods to prevent illicit discharges to the stormwater system.

    Nothing but stormwater, uncontaminated groundwater seepage or permitted discharges are allowed into the stormwater system. Methods of discharge should be tested and analyzed to ensure that there are no unpermitted non-stormwater discharges at the facility. Testing methods should be documented and may include, but not be limited to, visual inspections of the facility and review of site plans, dry weather inspection of storm drains to ensure that there is no dry-weather flow, and dye or smoke testing if necessary. A testing schedule shall be identified. All plans should contain a statement that no washing of equipment or vehicles shall be permitted to take place outside where it can flow to the storm drain system. All washing must take place indoors, in an area where a permit has been obtained to discharge wastewater through an approved oil/water/grit separator to a municipal sewage treatment facility, or in an area where all wastewater discharges to a holding tank.

    C. An approved site plan and statement contained within the Stormwater Management Plan that ensures no there is no outside storage of hazardous materials.

    Outside storage of hazardous materials (including salt storage) is prohibited in the Aquifer Protection Area. All hazardous materials much be stored in a building or under a roof, on an impermeable surface that is protected from stormwater, inclement weather or hazards that can lead to a direct discharge into the ground. Regular inspection of all hazardous materials storage is required. Inspection schedules and reports shall be kept on site.

    D. A list of all runoff management practices.

    The Supplement shall list any runoff management practices used at the facility. Note appropriate descriptions or qualifications to the practices listed, such as the portion of the site affected. Runoff management practices may include catch basins, drainage swales, riprap channels or pools, detention/retention basins, infiltration basins or structures, impervious areas, sheet flow, biofilters or other measures used to manage/treat runoff. Management practices to be followed include directing runoff from paved surfaces to above-ground land treatment structures, surface drains, sheet flow, surface swales, depressed grass islands, detention/retention and infiltration basins, and wet basins. These practices provide an opportunity for volatilization of volatile organic compounds to the extent possible before the stormwater can infiltrate into the ground. Direct infiltration structures such as galleries, drywells, and leaching trenches do not allow for attenuation of salt or other soluble compounds that may be contained in parking lot runoff. New direct infiltration structures should not be installed and existing structures should be considered for replacement. If clean roof runoff can be segregated from stormwater, it is a good source of recharge to the aquifer. In this case, subsurface infiltration structures such as dry wells, galleries, or leaching trenches are appropriate and encouraged.

    While the emphasis is to minimize groundwater quality impacts of the runoff, a plan should be balanced and the extent possible include a combination of approaches to protect all water resources concerns including surface water quality, water quantity changes between predevelopment and post-development runoff rates and volumes. Most alternative site designs, low impact development, and green infrastructure techniques will be beneficial to groundwater except for certain direct infiltration techniques. Non-structural measures to dissipate and treat runoff are encouraged, including sheet flow from uncurbed pavement and vegetated swales/basins.

    If a stormwater collection system must be installed, it should discharge to an above-ground outlet point (swales, basins, channels, etc.) to prevent illicit discharges and fuel/chemical pollution releases to the ground.

    E. Identification and mitigation of existing subsurface infiltration devices in stormwater hot spots.

    Stormwater “hot spots” are areas or activities on the site with greater potential for high pollutant loads that may threaten groundwater quality. Examples of these include salvage areas, fueling facilities, dumpster or chemical storage areas, loading docks and large parking lots. In these areas, existing direct infiltration structures (galleries, dry wells, leaching trenches) are of particular concern as they can serve as a direct conduit for chemical pollutants to enter the groundwater and do not allow for attenuation of those chemical pollutants. Management of these stormwater hot spots should include measures to reduce potential impacts to groundwater such isolation of the “hot spot” by separating the activity or moving the activity to another location on the site. Examples include construction of a berm surrounding the activity to isolate it and redirect the stormwater runoff away from the infiltration device, construction of a swale to take the drainage from the hot spot away from the infiltration device, or relocation of an activity so that it does not drain to an infiltration structure. Stormwater discharge may also be pre-treated by modifying the infiltration device to include a grass or stone filter strip area around entrance, an oil-water separator, or media filters or inserts.

    The Plan and Supplement shall also include regular monitoring and inspection of the area by employees, the keeping of temporary spill control devices on site such as speedy dry and absorbent pads, and regular maintenance and cleaning of the drainage area and infiltration structure.

    City of Danbury Stormwater Documents

    City of Danbury Stormwater Website

    Danbury Zoning Regulations

    Danbury Ordinance