New Madison Stormwater Ordinance moving forward

SUMMARY: DRAFT REVISIONS TO CHAPTER 37 (STORMWATER MANAGEMENT) OF THE MADISON GENERAL ORDINANCES

What are the existing stormwater requirements?

New development is currently required to meet the following:

1. Peak Detention – detain the 1-, 2-, 5-, 10-, and 100-year storm events such that the post development peak discharge rates (CFS – cubic feet per second) match the predevelopment peaks for each listed storm
2. Total Suspended Solids Control – reduce 80% of the TSS coming off the site in a post development condition
3. Infiltration – infiltrate 90% of the predevelopment average annual infiltration
4. Oil & Grease Control – treat the first 1⁄2” of parking lot or drive-through runoff with a capture device
5. Safely convey water downstream in an events exceeding the 100-year storm event

Redevelopment is currently required to meet the following:

1. Treat new parking areas to remove 60% TSS
2. Treat new parking to remove oil & grease from the first 1⁄2” of runoff

What is being proposed:

New development is proposed to be required to meet the following: (changes in red).

1. Peak Detention – detain the 1-, 2- ,5-, 10-, 100- and 200- year storm events such that the post development peak discharge rates (CFS – cubic feet per second) match the predevelopment peaks for each listed storm.
2. Total Suspended Solids Control – reduce 80% of the TSS coming off the site in a post development condition.
3. Infiltration – infiltrate 90% of the predevelopment average annual infiltration
4. Oil & Grease Control – treat the first 1⁄2” of parking lot or drive-through runoff with a capture device.
5. Safe Overflow – route the 100- and 500-year storm events through the development. Runoff from the 100-year event must stay in the Right of Way, while runoff from the 500-year may encroach on private property but cannot flood a structure. Elevations of key buildings will be set above the routed 500-year water elevation.

Redevelopment is proposed to be required to meet the following: (changes in red).

1. Treat new parking to remove 60% TSS
2. Treat new parking to remove oil & grease from the first 1⁄2” of runoff
3. If the proposed site has an impervious area (hard surface) that exceeds 80% of the existing site impervious area then:

a. Reduce the 10-year storm event peak discharge rate by 15% compared to existing conditions

b. Reduce the 10-year storm event site runoff volume by 5% compared to existing conditions

c. Reductions shall be completed using green infrastructure that captures at least the first 0.5″ of rain over the total site impervious area. Additional green or non-green best management practices (BMPs) may be used for volumes beyond the first 0.5” of rainfall if needed to comply with other requirements of this ordinance.

4. The following guidance shall be used in interpreting this code:

a. An intensive green roof with a media depth of 12” or more shall be considered pervious for the purpose of meeting the lot coverage described above and to result in no runoff during a 10-year design storm. This reduction may be used to offset volumes and rates for the remainder of the site. For storms exceeding the 10-year event the roof shall be considered to have a curve number (CN) of 68.

b. An extensive green roof with media depth of a minimum of 4” shall be considered to be pervious for the purpose of meeting the lot coverage described above. The runoff CN for this type of feature shall be considered to be a 76.

c. Pervious pavement designed to comply with the Wisconsin WDNR’s guidance for post construction stormwater practices shall be considered to be pervious for the purposes of meeting the percent lot coverage described above. The runoff CN for this type of feature shall be considered to be a 74.

d. Green Infrastructure includes, but is not limited to, the following practices: rainwater harvesting/reuse, rain gardens, bioretention systems, infiltration basins, planters that are connected to roof drainage, bioswales, permeable pavement, green roofs, and rain barrels.

Regardless of how or what Green Infrastructure features are used to meet the above requirements, they shall require the recording of a maintenance agreement for the features against the appropriate parcel.

MADISON STORMWATER ORDINANCE CHANGES

Someone did a really nice drafter’s analysis (assuming it’s correct) for the ordinance, the summary of the changes is as follows:

DRAFTER’S ANALYSIS:  This ordinance makes numerous changes to Chapter 37 of the Madison General Ordinances to update the City’s stormwater code.  To simplify the changes, the entire chapter is being repealed and recreated.  The notable changes are as follows, I bolded the relevant parts:

1.                     Sec. 37.04 amends the definition of redevelopment by increasing the land disturbance threshold from 4,000 square feet to 10,000 square feet, and exempting out parking lot resurfacing.  This is meant to address the unintended consequence of encouraging very small parking lots from being improved due to the need to add very expensive stormwater treatment methods.  Dane County is moving this to 20,000 square feet for similar reasons.

2.                     Sec. 37.05(4)(d) is being amended to allow for credits against the stormwater charge, based upon an approved Rate Adjustment and Credit Policy.

3.                     Section 37.05(6)(b) reorganizes and alters the design standards for privately financed additions to the public stormwater system, including:

a.                     Making compliance mandatory for new development, and a goal for redevelopment and/or infill development.

b.                     Culverts across streets at greenway crossings were previously required to be designed for the 25-year event.  This revision changes that to the 100-year event.

c.                     Overflow of the pipe and road system in the event of a 500-year storm event shall not impact any private habitable structures.  Site plans will also be reviewed to confirm that the proposed structure elevations are compliant with this design overflow requirement during a 500-year storm event.

4.                     Section 37.05(7)(a)2.a. reduces the peak volume of discharge subject to the surcharge fee for stormwater system connection permits from 225 gallons per minute to 100 gallons per minute.

5.                     Section 37.05(7)(b)5. requires that certain sites with private discharges into an enclosed depression be designed to mitigate the increased volume from include existing discharges during the 25 and 100 year storm events.

6.                     Section 37.05(7)(b)8 updates the remedial procedures available to the City in the event that a private storm sewer or best management practice is not being adequately maintained.

7.                     Section 37.05(9) updates language about crossings of the public stormwater system, including clarifying the City’s remedial authority where private drainage systems interfere with the public drainage system.

8.                     Section 37.08(1)(c) is being amended to require that phasing be considered when reviewing erosion control plans.

9.                     Section 37.08(4) updates erosion control plan performance standards to prevent or reduce certain types of sediment discharge, to ensure that rate or volumetric discharge doesn’t increase during construction, and to create implementation requirements for best management practices.

10.                     Existing language in Section 37.09 is being updated to make it uniformly refer to stormwater management plans, instead of also calling them reports.

11.                     Section 37.09(2)(e) is being amended to update requirements of a stormwater management plan’s runoff peak flow calculations, to require specific levels for pre and post development.

12.                     Section 37.09(2)(l) is being amended to require that buildings in flood prone areas be designed to provide a minimum flood protection to the 100-year event (instead of half a foot above the regional flood elevation).

13.                     Section 37.09(3) is being amended in several ways to update the stormwater management performance standards in a stormwater management plan.  Among the changes include:

a.                     In Subd. (b), clarifying when oil and grease controls are necessary;

b.                     In Subd. (c)1., updating the general runoff rate control requirements by requiring sites already subject to an approved plan at the plat or CSM level to meet new development standards to maintain predevelopment peak runoff rates for the 100-year and 200-year events;

c.                     In Subd. (c)2., requiring new development to meet the following requirements:  maintain predevelopment peak runoff rates for 1, 2, 5, 10, 100 and 200-year events, and to safely pass the 500-year event; factor in downstream system capacity to determine the safe capacity of the off-site drainage system; assure that the 100 year event flows through public right-of-ways and that if private property is to be flooded during a 500-year event, entrance elevations must be set to avoid flooding in this scenario; and requiring the use of green infrastructure to capture the first ½ inch of rainfall to meet the rate and volume reductions;

d.                     In Subd. (c)3., if redevelopment has proposed impervious cover that exceeds 80% of the existing impervious cover, the site is required to reduce peak runoff rates by 15% and reduce runoff volumes by 5% during a 10-year event by using green infrastructure to remove the first ½ inch of rainfall;

e.                     In Subd. (c)4., development or redevelopment in flood prone watersheds must comply with the detention and storage requirement identified in individual watershed plans, if on file.

f.                     In Subd. (c)5., if off-site discharge to private lands is to an enclosed depression, the applicant is require to mitigate the increased volume of discharge to include the 25 and 100-year storm events.

14.                     Section 37.11(1) is being amended to have the Board of Public Works set the erosion control permit fee and stormwater management permit fee. This change is consistent with other permits and fees and will allow easier adjustment of the fee to better recover the City’s costs incurred to administer the permit.

15.                     Section 37.11(2) allows a contractor who is responsible for completion of erosion control measures to take out a permit.

The ordinance in in the file called body in the attachments to the file. The body is 42 pages long.  And the red-lined version where you can see the changes – 6280 Chapter 27 (Full Red Line).pdf is 46 pages long.

350 Madison’s Community Climate Solutions team has several letters of support in the file (Benwitz, Mrozek, Kuntz, Peseri, Vedder-Shults, Chapman)

WHO PAYS FOR THIS?

The developers.  Here’s the fiscal note:

The proposed changes to Chapter 37 are not expected to have a direct fiscal impact on the City. Several of the regulatory changes will result in increased compliance costs for private sector entities associated with new development. The proposed regulatory changes may also result in increased staff time for review and approval of the new requirements, but this staff time would be recovered through charges for review to developers. No appropriation is required.

WILL IT MAKE A DIFFERENCE?

I guess we’ll see.