Farmington Storm Drainage Ordinance

CITY OF FARMINGTON

DAKOTA COUNTY,

MINNESOTA

ORDINANCE NO. 009-604

AN ORDINANCE AMENDING TITLE 11 OF THE FARMINGTON CITY CODE, THE SUBDIVISION ORDINANCE, CONCERNING

STORM DRAINAGE

THE CITY COUNCIL OF THE CITY OF FARMINGTON ORDAINS:

SECTION 1. Section 11-4-7 of the Farmington City code is amended by adding the underlined language and deleting the strikethrough language as follows:†

(A) All subdivision design shall incorporate adequate provisions for storm water runoff consistent with the Farmington storm water management plan, as amended, and be subject to review and approval of the city engineer and the City of Farmington Standard Detail Plates and Engineering Guidelines. At the time each plat or replat is approved, a connection charge shall be made for past, present or future storm sewer costs, payable in cash, and shall be deposited in the "city surface water management fund". The monies so collected will be used in accordance with the Farmington comprehensive drainage plan. Connection charges shall be determined as set forth in table 3, land use assessment rate, of the Farmington comprehensive drainage plan the City Fee Schedule. The cash payment may be deferred, at an interest rate determined by resolution of the City Council, to the time the first stage of development takes place, so long as the terms of deferment are set forth in a developer's agreement executed by the City and the owner of the plat.

SECTION 2. Section 11-4-7 (B) of the Farmington City code is amended by adding the underlined language and deleting the strikethrough language as follows:†

11-4-7 (B)(1): Post Construction Water Quality Criteria:

1. Post construction stormwater runoff quality measures shall meet the standard for the General Permit Authorization to Discharge Storm Water Associated With Construction Activity Under the National Pollutant Discharge Elimination System/State Disposal System Permit Program Permit MN R100001 (NPDES General Construction Permit) issued by the Minnesota Pollution Control Agency, August 1 2003 2008, as amended; except where more specific requirements are provided in paragraphs 2, 3, 4, and 5 below.

SECTION 3. Section 11-4-7 (C) of the Farmington City code is amended by adding the underlined language and deleting the strikethrough language as follows:†

11-4-7 (C)(1): Runoff Temperature Control Criteria:

1. Post construction runoff criteria for controlling temperature increases relies on the establishment of buffers as specified in the Buffer Standard; the prioritization of temperature sensitive BMPís such as infiltration and filtration, and the designation of temperature sensitive wet pond design approaches in the Post Construction Water Criteria above; and the control of runoff volume increases and the use of credits with the Runoff Volume Control Criteria below. No additional specific temperature criteria are incorporated since these other areas of the Standards emphasize approaches sensitive to runoff temperature. However, since these other areas of the Standards allow flexibility, and in some cases waivers: permit applications involving the creation of one or more acres of new impervious surface in the trout stream portions of the Vermillion River and its tributaries where such areas do not first drain to a waterbody with 10 or more acres of open water; a. must include a narrative description of the temperature sensitive practices incorporated; and,b. The LGU City or the VRWJPO may limit or deny waivers, or may require additional runoff temperature BMPís, if the LGU City or the VRWJPO finds that the site design does not minimize the potential for runoff temperature increases.

SECTION 4. Section 11-4-7 (D)(2) of the Farmington City code is amended by adding the underlined language and deleting the strikethrough language as follows:†

11-4-7 (D) Peak Runoff Rate Control Criteria

2. Runoff rates for proposed activities, and development shall:

(a) Not exceed existing runoff rates for the 1-year, and 10-year critical duration storm events.

(b) Be implemented by Cities and Townships the City such that peak runoff rate controls keep future peak flood flows for the Vermillion River 100-year, 4- day event from increasing above existing conditions peak flows. (While the VRWJPO works to develop numerical Standards at a subwatershed scale, the Standard will be implemented as follows: Runoff rates for proposed activities, and development shall not exceed the existing rate for the 100-year critical duration storm event.)

SECTION 5. Section 11-4-7 (E) of the Farmington City code is amended by adding the underlined language and deleting the strikethrough language as follows:†

11-4-7 (E): Runoff Volume Control Criteria:

1. Development that creates one acre or more of new impervious surface must incorporate volume control practices into the design sufficient to hold the runoff volume for the 2-year 24-hour storm at pre-development conditions. Determination of the necessary control volume to achieve this Standard can be completed by the LGU City on a regional basis and included in an approved Local Water Plan, or calculated on a site-by-site basis for each individual proposal.

2. Credits for site design are the preferred methods for meeting the Volume Control requirements and shall be considered prior to the design of infiltration or filtration facilities.

3. The water quality control volumes necessary to meet the NPDES General Construction Permit that are satisfied using infiltration or filtration technologies (filtration only on Type C and D soils) can count toward the Volume Control requirements of these Standards.

4. When using infiltration for volume control, infiltration volumes and facility sizes shall be calculated:

(a) Using the appropriate hydrological soil group classification and saturated infiltration rate shown below:

Hydrologic Soil Type A: 0.30 inches/hour

Hydrologic Soil Type B: 0.15 inches/hour

Hydrologic Soil Type C: 0.07 inches/hour

or,

(b) Using documented site specific infiltration or hydraulic conductivity measurements completed by a licensed soil scientist or engineer, or

(c) Using the method provided in the Minnesota Stormwater Manual Volume 2 (MPCA 2005) pages 18 through 21 of Chapter 12-INF, and b. The design shall consider the infiltration rates of the least permeable horizon within the first five feet below the bottom of the infiltration practice, and c. The system shall be capable of infiltrating the required volume in 72 hours.

5. Constructed infiltration facilities, such as infiltration basins and trenches:

(a) Can only be used if there is pretreatment of stormwater runoff designed to protect the infiltration system from clogging with sediment and to protect groundwater quality;

(b) Cannot be used within 400 feet of a municipal or other community supply well or within 100 feet of a private well unless specifically allowed by an approved wellhead protection plan;

(c) Cannot be used for runoff from fueling and vehicle maintenance areas and industrial areas with exposed significant materials;

(d) Cannot be used on areas with less than 3 feet vertical separation from the bottom of the infiltration system and the seasonal high water table;

(e) Cannot be used in Type D soils.

6. Infiltration areas must be fenced or otherwise protected from disturbance before the land disturbing activity starts.

7. Volume control amounts may be waived by the LGU City or the VRWJPO for sites with predominately Type C and D soils, or where a shallow water table prevents construction of infiltration systems, provided the following are met in order of decreasing preference:

(a) Credits and site design practices to minimize the creation of connected impervious surfaces are used to the extent practical.

(b) Underdrains are used to promote filtration instead of infiltration.

8. Vegetation used in conjunction with infiltration systems must be tolerant of urban pollutants, and the range of soil moisture conditions anticipated.

SECTION 6. Effective Date. This ordinance shall be effective upon its passage and publication according to law.

ADOPTED this 16th day of March, 2009, by the City Council of the City of Farmington.

CITY OF FARMINGTON

/S/: Todd Larson, Mayor

ATTEST:

/S/: Lisa Shadick

Administrative Services Director / Deputy City Clerk

SEAL

/S/: Joel Jamnik, City Attorney

3/26

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