The following are post construction stormwater treatment requirements.
(A) Permittees must develop a post construction stormwater management system that is at least as stringent as the current post construction stormwater management permit conditions (Minimum Control Measure 5) as required by the general stormwater small municipal separate storm sewer systems (MS4) permit issued to the city by the Minnesota Pollution Control Agency (MPCA).
(B) The Permittee shall take into consideration with their design sections of the city's current MS4 permit as follows:
(1) Post construction stormwater management.
(a) Post-construction stormwater management program. Prior to start of any construction activity, permittee shall develop and implement a post-construction stormwater management program that utilizes any combination of BMPs necessary to meet the following conditions on the site of a construction activity to the maximum extent practicable (MEP):
1. For new development projects, no net increase from pre-project conditions (on an annual average basis) of:
a. Stormwater discharge volume, unless precluded by the stormwater management limitations outlined in division (B)(1)(b) listed below.
b. Stormwater discharges of total suspended solids (TSS).
c. Stormwater discharges of total phosphorus (TP).
2. For redevelopment projects, a net reduction from pre-project conditions (on an annual average basis) of:
a. Stormwater discharge volume, unless precluded by the stormwater management limitations outlined in division (B)(1)(b) listed below.
b. Stormwater discharges of TSS.
c. Stormwater discharges of TP.
(b) Infiltration as stormwater treatment method. The use of infiltration as a stormwater treatment method is prohibited in the following areas:
1. Where industrial facilities are not authorized to infiltrate industrial stormwater under an NPDES/SDS industrial stormwater permit issued by the Agency.
2. Where vehicle fueling and maintenance occur.
3. With less than three feet of separation distance from the bottom of the infiltration system to the elevation of the seasonally saturated soils.
4. Where high levels of contaminants in soil or groundwater will be mobilized by the infiltrating stormwater.
(c) Infiltration as stormwater treatment method; restrictions.
1. The use of infiltration as stormwater treatment method will be restricted without a detailed engineering review, to achieve no post construction net increase in volume, TSS or TP when the infiltration device will receive discharges from, or be constructed in:
a. Areas of predominately Hydrologic Soil Group D (clay) soils.
b. Areas within a drinking water supply management area (DWSMA) as defined in Minn. Rule 4720.5100, subpart. 13.
2. The restrictions above do not preclude proposers of construction activity from infiltrating stormwater. Rather, the restrictions simply require that a higher level of design and review is needed.
3. The permittee may have a lesser volume reduction requirement than required division (B)(1)(a)1. and (B)(1)(a)2., above, if the project meets one of the prohibitions or restrictions listed above and if the owner or operator of the construction activity implements to the maximum extent practicable (MEP) other volume reduction techniques such as evapotranspiration, reuse/harvesting, conservation design, green roofs, etc. on site. If other volume reduction techniques are not used, documentation must be provided on why that decision was made.
(d) Linear projections, exception. For linear projects where the lack of right-of-way precludes the installation of volume control practices that meet the conditions for post-construction stormwater management listed above, the permittee may be allowed an exception. This exception will only be allowed if it is proven that a reasonable attempt was made to obtain right-of-way during the project planning process.
(e) Exceptions for stormwater discharge volume. The permittee may be allowed lesser volume control on the site of the original construction only under the following circumstances:
1. The owner and/or operator of a construction activity is precluded from infiltrating stormwater through a designed system due to any of the infiltration related limitations described above; and
2. The owner and/or operator of the construction activity implements, to the MEP, volume reduction techniques, other than infiltration, (e.g., evapotranspiration, reuse/harvesting, conservation design, green roofs, etc.) on the site of the original construction activity that reduces stormwater discharge volume, but may not meet the conditions for post-construction stormwater management in division (B)(1)(a)1. and (B)(1)(a)2., above.
(f) Mitigation.
1. Where TSS and TP has not been addressed on the site of the original construction activity, permittee may mitigate project areas in the following order of preference:
a. Locations that yield benefits to the same receiving water that receives runoff from the original construction activity.
b. Locations within the same Minnesota Department of Natural Resource (DNR) catchment area as the original construction activity.
c. Locations in the next adjacent DNR catchment area up-stream.
d. Locations anywhere within the city's jurisdiction.
2. Mitigation projects must involve the creation of new structural stormwater BMPs or the retrofit of existing structural stormwater BMPs, or the use of a properly designed regional structural stormwater BMP. This can include permanent stormwater ponding.
3. Routine maintenance of structural stormwater BMPs already required by this permit cannot be used to meet mitigation requirements of this part.
4. Mitigation projects shall be completed within 24 months after the start of the original construction activity.
5. The city shall determine, and document, who will be responsible for long-term maintenance on all mitigation projects of this part.
6. If the city receives payment from the owner and/or operator of a construction activity for mitigation purposes in lieu of the owner or operator of that construction activity meeting the conditions for post-construction stormwater management called out in this chapter, the city shall apply any such payment received to a public stormwater project, and all projects must be in compliance with this division (B)(1)(f), above.
(g) Wet sedimentation basins as a method of mitigation.
1. It is recognized that the vast majority of the city has Class D soils unsuitable for infiltration.
2. If permittee provides supporting documents that this is the case for the construction site and chooses to proceed with the installation of a wet sedimentation basin as a means of mitigation, the following requirements shall be met.
a. For new development projects in currently undeveloped areas: Wet sedimentation basins shall be constructed as required by the current MPCA CGP permit with the additional requirement that live storage in wet sedimentation basins shall be of sufficient size to retain the 100-year rain event for the watershed area and shall release stormwater runoff at a rate required by the current MPCA CGP permit.
b. For currently developed areas or re-development areas: Wet sedimentation basins shall be constructed as required by the current MPCA CGP permit.
c. Permittee shall submit to the city design calculations showing that the above criteria has been met for the construction site.
(h) Long-term maintenance of structural stormwater BMPs. Where BMP's are to remain in place post construction as part of the post-construction stormwater management, permittee shall comply with the following:
1. All BMPs shall be designed to minimize the need for maintenance, to provide easy vehicle (typically eight feet or wider) and personnel access for maintenance purposes, and to be structurally sound. All BMPs shall have a plan of operation and maintenance that assures continued effective removal of pollutants carried in storm water runoff. The city or City Engineer may inspect all public and private BMPs at any time. Inspection records will be kept on file at the city's office. It shall be the responsibility of the permittee to obtain any necessary easements or other property interests to allow access to the BMPs for inspection and maintenance purposes. The city shall retain enforcement powers for assuring adequate operation and maintenance activities through approval conditions, penalties, noncompliance orders and fees.
2. In the event that a structural stormwater BMP becomes less effective, new or improved structural stormwater BMPs must be implemented to ensure the conditions for post-construction stormwater management in division (B)(1)(a)1. and (B)(1)(a)2., above.
(i) Site plan review.
1. Prior to any construction activities taking place, permittee shall provide to the city two sets of legible copies of the site plan prepared to a scale appropriate to the site of the project and suitable for performing the review. The site plan shall include post-construction stormwater management BMPs.
2. Site plan approval issued under this chapter runs with the land and is a condition of plat or development approval. Any landowner or subsequent landowner of any parcel within the plat or development area must comply with the plan or any approval, condition, revision or modification of the plan. Failure to comply with this plan shall constitute a violation and subject the permittee, developer, and/or landowner to enforcement provisions, penalties and any applicable noncompliance fees.
(C) It is unlawful to initiate any land development activity, land disturbing activity, or other activities which may result in an increase in storm water quantities, degradation of storm water quality, or restriction of flow in any storm sewer system, open ditch or natural channel, storm water easement, water body, or wetland outlet within the jurisdiction of the city, without having first complied with the terms of this chapter.
(D) A processing and approval fee may be adopted by the City Council. This fee shall accompany all applications for site plan review and approval.
(E) Approval of any plan submitted under the provisions of this chapter shall expire one year after the date of approval unless construction has commenced in accordance with the plan. However, if prior to the expiration of approval, the Applicant makes a written request to the City for an extension of time to commence construction setting forth the reasons for the requested extension, the City may grant one extension of not greater than one year. The city shall make a decision on the extension within 30 days of receipt. Any plan may be revised following the same procedure for an original approval. The city may waive all or part of any applicable application fees if the revision is minor. Any denied or expired application may be resubmitted with additional information addressing the concerns contained within the denial or the reason why the original plan was allowed to expire. The resubmitted application shall be subject to all applicable fees and review time lines as if it were a new application.
(F) It shall be the applicant's responsibility to obtain any required permits from other governmental agencies having any jurisdictional authority over the work to be performed. Typically, such agencies include, but are not limited to the Buffalo-Red River Watershed District, Clay County, the Minnesota Department of Natural Resources, the Minnesota Department of Transportation, the Minnesota Pollution Control Agency, the State Historical Preservation Office, the U.S. Army Corps of Engineers, the U.S. Environmental Protection Agency, Federal Emergency Management Agency, the Minnesota Department of Health and others. The City may choose to obtain some of the required permits. The Applicant will be notified which permits are to be obtained by the city.
(G) Other than those outlined in the SWPPP or as required in section 2-01, any hydrologic models and/or design methodologies used to determine runoff conditions and to analyze storm water management structures and facilities, shall be approved in advance by the city or City Engineer. All storm water management plans, drawings, specifications, and computations for storm water management facilities submitted for review shall contain a validated seal and shall be signed by a professional engineer registered in the State of Minnesota. The requirement of having a professional engineer sign the documents may be waived by the city.
(H) The city for just cause upon 30-day notice may modify any city approval that was made regarding any storm water management plan proposed by the permittee. Just cause shall include but not be limited to:
(1) Promulgation of new federal, state or local regulatory requirements;
(2) Changes in the requirements of this chapter;
(3) Changes in the process used by the permittee or changes in discharge rate, volume, or character; and
(4) Changes in the design or capability of receiving storm water systems.
(I) Upon completion of all required construction activities, the permittee shall submit to the city record drawings to document any changes or material modifications to the original plan concept. The record drawings shall show the final configuration for all improvements as constructed. A professional engineer registered in the State of Minnesota shall certify the record drawings. If no significant or material changes occurred between the approved plan and final construction, the record drawings need not be submitted to the city. The permittee, however, is responsible to retain copies of said drawings and provide them to the city upon request. Failure to provide these drawings upon written request constitutes a violation of this chapter.
(Ord. 15-02, passed 2-9-2015)