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HomeMy WebLinkAbout2015-04-08 PACKET 05.6.M m Cottage Grove h ere Pride and Vc0 5perity Meet TO: Public Works Commission FROM: Ryan Burfeind, Project Engineer DATE: March 3, 2015 RE: MS4 Permit Requirements and Surface Water Management Plan Update Cottage Grove Stormwater Pond Maintenance Program Background On August 1, 2013, the Minnesota Pollution Control Agency (MPCA) issued a new Municipal Separate Storm Sewer System (MS4) Permit, which will be effective until July 31, 2018. This MS4 permit is what authorizes municipalities through Minnesota to discharge stormwater runoff to Waters of the State. As part of the permit, each municipality is required to maintain best manage- ment practices (BMPs) in six minimum control measure (MCM) categories. These categories include public education and outreach, public participation and involvement, illicit discharge detection and elimination (IDDE), construction site stormwater runoff control, post- construction stormwater management, and pollution prevention /good housekeeping for municipal operations. Cottage Grove was issued coverage under this new permit on March 17, 2014. Planning Commission Recommendation The Planning Commission held the public hearing on the proposed text amendments at their reg- ular meeting on February 23, 2015. A presentation giving an overview of the text amendments was given at the meeting. There were no public comments regarding the text amendments during the public hearing. The Planning Commission unanimously (5 -to -0 vote) recommended the City Council adopt the ordinance text amendments to City Code Titles 8 -4; Storm Water Illicit Dis- charge and Illicit Connections, and Title 11 -6 -12; Grading, Filling, or Excavation. Discussion Ordinance Text Amendments One of the requirements under this permit is for municipalities to ensure that their ordinances regarding IDDE, construction site stormwater runoff control, and post- construction stormwater management meet specific criteria. City Code Title 8 -4; Storm Water Illicit Discharge and Illicit Connections, covers IDDE; Title 11 -6 -12; Grading, Filling, or Excavation, covers construction site stormwater runoff control and post- construction stormwater management. To meet the require- ments in the MS4 permit, amendments to these two sections of the City Code are proposed. The updates related to IDDE are required to ensure the City has a regulatory mechanism that effectively prohibits non - stormwater discharges into the storm sewer system. Prior to this permit re- issuance, Cottage Grove had a fairly complex IDDE ordinance in place. As a result, few updates are needed to meet the new permit requirements. Public Works Commission MS4 Permit Requirements & Cottage Grove Stormwater Pond Maintenance Program March 3, 2015 Page 2 of 4 For construction site stormwater runoff control, the MS4 permit requires that the City's ordinance establish requirements for erosion and sediment controls that are at least as stringent as the MPCA's General Permit to Discharge Stormwater Associated with Construction Activity (CSW Permit). This includes requirements for installation, inspection, and maintenance of controls such as silt fence, catch basin inlet protection, and temporary sediment basins as well as requirements regarding turf establishment. Title 11 -6 -12 contains the City's requirements for erosion and sedi- ment controls; however, updates are required to make them as stringent as the MPCA CSW per- mit. These updates will not place any additional requirements on construction activities in Cottage Grove, as they are already regulated by the same requirements as part of the MPCA CSW permit. The final updates are related to post- construction stormwater management. The MPCA included in the MS4 permit specific requirements regarding the following items: 1. Discharge volume, total phosphorus, and total suspended solids for new development and redevelopment projects 2. Limitations on infiltration of stormwater 3. Exceptions for stormwater discharge volumes 4. Mitigation requirements for development activities when post- construction stormwater management requirements for total phosphorus and total suspended solids cannot be met onsite 5. Long -term maintenance requirements for structural stormwater BMPs. Several of these topics are currently covered in Section 3 and Section 7 of the City's Surface Water Management Plan (SWMP). In order to meet these new permit requirements, amendments to Section 3 and Section 7 of the SWMP are proposed and will be referenced in City Code Title 11 -6 -12. Stormwater Pond Maintenance Program Another aspect of the City's MS4 permit is the requirement to maintain our system of stormwater ponds. The City owns and maintains 121 stormwater ponds, which are designed to provide rate control and improved water quality. The water quality improvement is achieved by allowing sedi- ment and organic material to settle out of the stormwater once it enters the pond, reducing sedimentation of downstream waterbodies. In addition to reduced sedimentation, the phosphorus that is bonded to the particles will also be retained in the pond. Phosphorus is a nutrient that can cause algae blooms once it enters local lakes and rivers. Over time, build -up of sediment and organic matter will reduce the volume of the pond, and in turn reduce the treatment effectiveness. To ensure that ponds in the City continue to function as designed, maintenance on stormwater ponds is conducted annually. One aspect of the maintenance program is the work conducted by the Public Works Department. Public Works maintenance activities include removal of sediment around pond outlets, brush removal, mowing, and replacement of failing riprap. By completing this routine annual maintenance, the need for larger contracted maintenance projects is reduced. Below you can see a pond that was mowed by Public Works in 2013: Public Works Commission MS4 Permit Requirements & Cottage Grove Stormwater Pond Maintenance Program March 3, 2015 Page 3 of 4 In addition to the maintenance completed by Public Works, the City also hires a contractor to complete an annual pond maintenance project. This project includes work such as pipe repair, large amounts of sediment removal, tree clearing, and riprap replacement. The intent of this pro- ject is to bring ponds that are in worse condition back to their original design. In the past three years alone these projects have included work on 14 ponds, resulting in the removal of 1,970 cubic yards of sediment, removal and replacement of 422 cubic yards of failing riprap, replace- ment of 144 feet of damaged storm sewer pipe, and replacement of seven damaged storm sewer outlets. Below are before and after aerial photos of two ponds in the Highland Hills neighborhood that were included in the 2014 pond maintenance project. These projects included sediment removal, riprap removal and replacement, and tree removal. Before After Public Works Commission MS4 Permit Requirements & Cottage Grove Stormwater Pond Maintenance Program March 3, 2015 Page 4 of 4 Before After Recommendation Receive information on the ordinance text amendments to meet MS4 permit requirements and the Cottage Grove stormwater pond maintenance program.