By: Michael Errickson, PE and DTC Civil Engineering Project Manager — If you work with buildings, especially if you have anything to do with their building process, you need to know the new requirements issued by the Department of Energy and Environmental Protection (DEEP) in their upcoming reissuance of the General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems (MS4), and how they are going to affect you.

The General Permit for the Discharge of Stormwater from Small Municipal Separate Storm Sewer Systems (MS4) is due for reissuance. Significant public input was part of the revision process including major concerns brought forth by the Connecticut Conference of Municipalities, Connecticut Council of Small Towns, and Connecticut Fund for the Environment. Now is a great time to review existing and revised requirements of the MS4 General Permit prior to reissuance.

What is a Small MS4?

Any municipally owned or operated means for stormwater conveyance (i.e. pipes, catch basins, manmade channels) located partially or entirely within a non-rural area that has at least 1,000 residents.

Why are MS4’s regulated?

Impervious areas such as parking lots and roadways are associated with dense population centers. Stormwater runoff from vehicle oil and grease drippings, excess fertilizer application, and pet waste seem inconsequential, but in fact concentrate as stormwater runoff is captured by catch basins and ultimately conveyed to a pipe outfall. The resulting stormwater discharge negatively impacts water quality of receiving waterbodies.

How does the MS4 Permit affect me?

Many municipalities in Connecticut already hold a MS4 General Permit registration. The revised permit modifies some of the existing conditions and adds others. Additional communities were included with the addition of the 1,000 resident threshold.

The MS4 permit reaches beyond municipal responsibilities. Several of the permit conditions will be imposed upon private development projects by local regulation.

Conditions of the Permit

A stormwater management plan must be prepared by the municipality and maintained as a living document, updated at least annually. The MS4 permit requires six minimum control measures within the plan including:

  1. Public Education and Outreach
    • Create a public education program targeting the consequences of stormwater runoff from pet waste, excess fertilizer application, herbicides, pesticides, impervious land cover, and illicit discharges.
    • The program should be tailored to specific pollutants identified in the MS4 watershed such as phosphorous, nitrogen, bacteria, mercury.
  2. Public Involvement/Participation
    • Provide an opportunity for the public to review and comment on the stormwater management plan. The goal of this measure is to gain public support and encourage public adoption of stormwater best management practices at home.
  3. Illicit Discharge Detection and Elimination (IDDE)
    • Develop a written IDDE program that creates legal authority of the municipality to prohibit and eliminate illicit discharges, find sources of illicit discharges, eliminate illicit discharges, and screen the MS4 area to prevent future illicit discharges.
    • Appendix B of the General Permit contains a protocol for identifying and eliminating illicit discharges. At a minimum, this protocol must be applied to areas of impervious cover greater than 11 percent, or stormwater discharges to impaired waters. The MS4 registrant must develop a priority list of sites for implementation of IDDE.
  4. Construction Site Stormwater Runoff Control
    • The permittee is required to implement and enforce a construction site stormwater runoff control program for soil disturbance totaling ½ acre or more. The municipal program must incorporate the 2002 Connecticut Guidelines for Soil Erosion and Sediment Control and the 2004 Connecticut Stormwater Manual.
    • Municipalities covered under the proposed General Permit must conduct inspections to inventory the number of privately owned retention, detention, and other basins discharging to MS4’s. Long-term maintenance plans must be created for these facilities, both public and private facilities contributing to the MS4 system.
  5. Post Construction Stormwater Management
    • This control measure requires the municipality to create an ordinance, bylaw, regulation, standard condition of approval, or other legal authority to require consideration of low-impact development (LID) and runoff reduction strategies prior to implementing traditional practices. LID practices must meet or exceed the 2004 Connecticut Stormwater Manual.
    • If the existing site directly connected impervious area (DCIA) is greater than 40% only ½ the water quality volume (WQV) is required to be retained and infiltrated on site.
    • New sites or existing sites with DCIA less than 40% shall retain and infiltrate the entire WQV.
    • A “fee bank” shall be created for sites where runoff reduction cannot be achieved due to site limitations such as high groundwater or bedrock. The site developer would pay a fee for use by the municipality for retrofit and reduction of directly connected impervious area elsewhere offsite.
    • Calculate directly connected impervious area for each MS4 outfall. Revise estimate in annual report as site development projects add of reduce DCIA.
  6. Pollution Prevention/Good Housekeeping
    • Requires maintaining a stormwater operation and maintenance manual and employee training.
    • Infrastructure must be rehabilitated and retrofitted as needed. Retrofit is defined as disconnecting DCIA from each outfall by retaining the water quality volume on site.
    • Tracking DCIA disconnection is required. Credit may be taken for disconnection project performed up to 5 years prior.
    • Prioritize and plan retrofits with an emphasis on areas with impervious cover of 11 percent or greater.
    • Municipally owned sites must comply with permit language regarding maintenance of:
      1. Parks and open space
      2. Pet waste management
      3. Waterfowl management
      4. Buildings and facilities
      5. Vehicles and equipment
      6. Parking lots
      7. Snow management practices
      8. Sweeping
      9. Leaf management
      10. Catch basin cleaning

Stormwater Quality Monitoring

The General Permit registrant is required to create an inventory of outfalls discharging into impaired waters and screen for pollutants including but not limited to nitrogen, phosphorus, and bacteria. Sampling for other parameters may be necessary if turbidity levels greater than 5 NTUs are identified. All monitoring shall be conducted within the first 6 hours of a rainfall event that occurs at least 48 hours after the preceding rainfall event.

Testing results may require follow up investigation of the contributing drainage area for source pollutants, implementation of additional best management practices, and prioritization of outfalls for future monitoring. Monitoring results must be presented in the annual report due April 1 of each year.

Planning for the Future

The revised MS4 General Permit contains several requirements that require adoption of local ordinance or regulation. This takes a considerable amount of time to draft language and approve within each municipality. Although the permit has not been reissued and minor changes can reasonably be expected, now is the time to begin the process of adopting such language.

Mapping efforts in conjunction with the 2000 and 2010 census to identify municipal separate storm systems within urbanized areas (greater than 1,000 residents) will consume time and funding as well.

This summary addresses the main points of the MS4 General Permit. Significant detail such as timelines for implantation of the six program elements should be review prior to reissuance of the General Permit to allow sufficient time for compliance.