CONSENT AGENDA - James Hafner, Stormwater Manager
Title
SECOND READING
AMENDING CHAPTER 34, ENVIRONMENT, ARTICLE XI, STORMWATER MANAGEMENT, DIVISION 2, STORMWATER MANAGEMENT PLAN, CODE OF ORDINANCES OF THE CITY OF BLAINE
Background
As of August 1, 2013, the Minnesota Pollution Control Agency (MPCA) revised and reissued the Municipal Separate Storm Sewer System (MS4) permit. In March 2014, the City of Blaine (the City) was extended coverage under the newly revised permit. In order to remain compliant, the City is required to update its stormwater related ordinances, policies and Stormwater Pollution Prevention Plan (SWPPP).
The City's stormwater and erosion control ordinances need minor revisions to ensure compliance with the MS4 permit requirements. These changes were first explained to Council at the January 22, 2015 Workshop. They consist of adding detail and specifics to measures already included in the ordinance. The result brings the ordinances into compliance but does not exceed what is necessary and does not raise the bar above the minimum requirements of the MS4 permit. Costs of compliance, whether to the City on its own projects or to contractors working within the City, will be minimal and in most cases will not add any additional cost.
To further explain the changes being proposed, reference is made here to a guidance document provided by the MPCA.
" The requirements for post construction stormwater treatment set forth in the Permit are narrative in nature and do not contain specific numeric standards, in order to allow MS4 permittees maximum flexibility in determining how their community will meet the treatment conditions. The MPCA expects MS4 permittees to adopt treatment requirements in their regulatory mechanism that are reflective of the narrative requirements found within the Permit."
Narrative requirements are defined as broad statements that establish goals and outcomes. The alternative is numeric standards which prescribe specific goals and standards. The MPCA MS4 permit is based on narrative standards which, as stated above, are intended to allow maximum flexibility.
The proposed language added to the City ordinance is taken from the MS4 permit and is only intended to clarify what was already in the ordinance as well as provide guidance in choosing BMPs that would meet the permit requirements. Previously, the ordinance only stated that stormwater volume management must be provided. The proposed language clarifies the components of stormwater that need to be managed, those being volume, total phosphorous (TP), and total suspended solids (TSS). This clarification helps the permittee choose the appropriate BMPs for their site conditions that will provide the best treatment for the parameters being regulated. Since the conditions of the permit are narrative in nature, simply choosing and installing the appropriate BMPs meets the intent of the permit. The fact that these are narrative standards implies no testing is necessary. The newly added language requested by Council clarifies that fact.
Ordinance No. 15-2306 was introduced for First Reading at the February 19, 2015 Council meeting. It was brought back to the March 19, 2015 Council meeting for second reading at which time it was postponed for minor changes. The language requested by Council to clarify that no testing will be required to prove either no net increase or a net reduction of pollutants has been added to the proposed ordinance amendment. This language is the bolded paragraph under Sec. 34-485 of the attached document illustrating the proposed changes to the ordinance.
Ordinance No. 15-2306 is being presented at this time for adoption.
Recommendation
By motion, adopt Ordinance No. 15-2306.
Body
THE CITY OF BLAINE DOES ORDAIN: (Added portions are underscored and deleted portions are shown in brackets with overstrike.)
DIVISION 2. - STORMWATER MANAGEMENT PLAN
Sec. 34-481. - General criteria.
A stormwater management plan shall be required of all new development, redevelopment and land disturbance projects greater than one acre in parcel size or part of a greater plan of development. This plan shall be designed to reduce and/or minimize the impervious area of the site, control the peak flow rate, and minimize the volume of stormwater runoff from the same as required in the LSWMP and these ordinances. Plans must be submitted to the City for review and approval prior to the start of construction. Each project will construct, implement and maintain all best management practices (BMP) that are deemed necessary to achieve the goals of this division, including post-construction stormwater management BMPs. Prior to the start of construction, all projects shall be in possession of any and all permits required for the project including, but not limited to:
(1) Watershed districts;
(2) City of Blaine;
(3) U.S. Army Corps of Engineers;
(4) National Pollutant Discharge Elimination System (NPDES); and
(5) Wetland restoration or mitigation plan approval.
Projects smaller than one acre in size are encouraged to implement BMPs that will promote infiltration and contribute to improved water quality.
Sec. 34-482. - Design standards.
Minimal [impact design standards] Impact Design Standards (MIDS) (see Minnesota Stormwater Manual) shall be followed to achieve the best stormwater management. The BMPs used should seek to mimic the natural hydrology, utilize pervious areas for stormwater treatment and to infiltrate stormwater runoff from driveways, sidewalks, rooftops, parking lots, and landscaped areas to the maximum extent practical to provide treatment for both water quality and quantity. The Minnesota Stormwater Manual ([Stormwater Steering Committee,]MN Pollution Control Agency), the Minnesota Urban Small Sites BMP Manual (Metropolitan Council), Local Road Research Board BMP Maintenance Guide, and Protecting Water Quality in Urban Areas (MPCA) are resources that provide guidance in achieving these goals.
(1) Implementation. Low impact development, [or] better site design, or Green Infrastructure design techniques are the preferred methods of achieving stormwater management. Mimicking the natural topography and land cover as they exist in the pre-developed condition to meet the standards and requirements of the city and other regulatory agencies shall be the first consideration.
(2) Recommended practices. Practices and methods used to achieve the intent of the above paragraph shall include, but not be limited to, the following:
a. Rain gardens;
b. Green roofs;
c. Bio-retention practices;
d. Pervious pavements or pavers;
e. Plots of native vegetation and/or buffers in place of sod;
f. Reforestation and revegetation;
g. Trees and tree box filters;
h. Reduction of impervious area;
i. Rain water harvesting.
(3) Other practices. Other traditional stormwater BMPs may be approved on a site by site basis to achieve the goals of water quality and quantity, and rate control. These practices shall conform to the standards outlined in the resources referenced above.
(4) [[Pre-treatment of runoff.]] Pre-treatment of runoff. All stormwater runoff shall be pre-treated prior to discharge to any surface water.
(5) Maintenance plan. A plan shall be established to maintain all temporary and permanent BMPs in a working and efficient condition. This may include removal of invasive species, sediment, debris, or any other foreign or obstructive object or condition that prevents the BMPs from performing as designed.
(6) Exemption. The mill and overlay or rehabilitation of a public roadway that does not create additional impervious surfaces; and sidewalk or trail projects are exempt from these stormwater requirements. These projects may be subject to other regulations.
Sec. 34-483. - Drainage.
Site alteration, grading, placement and installation of BMPs and other related activities shall be implemented in such a way that drainage from the site shall not exceed the pre-developed rates and will not adversely affect neighboring properties. Sections 33.16 and 33.17 of the Blaine City Zoning Ordinance shall also apply.
Sec. 34-484. - Calculations.
Hydrologic and hydraulic design calculations must be submitted for the pre-development and post-development conditions for the two-, ten-, and 100-year events as well as the ten-day snow melt event. Such calculations shall include:
(1) Description of the design storm frequency, intensity and duration;
(2) Time of concentration;
(3) Soil curve numbers or runoff coefficients;
(4) Peak runoff rates and total runoff volumes for each watershed area;
(5) Infiltration rates, where applicable;
(6) Culvert capacities;
(7) Flow velocities;
(8) Data on the increase in rate and volume of runoff for the design storms used; and
(9) Documentation of sources for all computation methods and field test results.
Sec. 34-485. - Volume control and pollutant management.
Stormwater volume management practices shall be the equivalent of infiltrating or retaining the first [one] 1.1 inches of precipitation over the impervious surface of the site. These practices should seek to utilize pervious areas for stormwater treatment and to infiltrate stormwater runoff from driveways, sidewalks, rooftops, parking lots and landscaped areas to the maximum extent practical to provide treatment for both water quantity and quality.
New Development projects shall achieve no net increase from pre-project conditions (on an annual average basis) of stormwater discharge volume; discharges of total suspended solids (TSS); and discharge of total phosphorus (TP).
Redevelopment projects shall achieve a net reduction from pre-project conditions (on an annual average basis) of stormwater discharge volume; discharges of total suspended solids (TSS); and discharge of total phosphorus (TP).
No pre- or post-construction testing will be required by the City of Blaine to determine the "no net increase" or "net reduction" requirements stated above. Using best management practices will be accepted as compliance.
The above requirements may be altered and alternative treatment BMPs approved under the following limitations:
(1) Infiltration techniques shall be prohibited when the infiltration structural BMP will receive discharges from or be constructed in areas:
a. where industrial facilities are not authorized to infiltrate industrial stormwater under an NPDES/SDS Permit;
b. where vehicle fueling and maintenance occur;
c. with less than 3 feet of separation from the bottom of the infiltration system to the elevation of the seasonally saturated soils or top of bedrock;
d. where high levels of contaminants in soil or groundwater will be mobilized by the infiltration of stormwater.
(2) Infiltration techniques will be restricted when the infiltration device will be constructed in areas:
a. with predominately Hydrologic Soil Group D soils;
b. within 1,000 feet up-gradient or 100 feet down-gradient of active karst features;
c. within a Drinking Water Source Management Area (DWSMA) as defined in the City's Wellhead Protection Plan;
d. where soil infiltration rates are more than 8.3 inches per hour.
If volume and pollutant management controls cannot be constructed on-site, off-site locations where the controls can be met must be identified.
Guidance for best management practices and standards for these mitigation processes should follow the Minimal Impact Design Standards (MIDS) Design Sequence Flowchart for flexible treatment options contained in the MN Stormwater Manual.
INTRODUCED AND READ in full the 19th day of February, 2015.
PASSED by the City Council of the City of Blaine this 16th day of April, 2015.