§ 86-408. Performance standards.

(a)

Responsible party . The responsible party shall comply with this section.

(b)

Storm water management plan . A written storm water management plan in accordance with section 86-410 shall be developed and implemented for each post-construction site.

(c)

Maintenance of effort . For redevelopment sites where the redevelopment will be replacing older development that was subject to post-construction performance standards of NR 151 in effect on or after October 1, 2004, the responsible party shall meet the total suspended solids reduction, peak flow control, infiltration, and protective areas standards applicable to the older development or meet the redevelopment standards of this article, whichever is more stringent.

(d)

Requirements . The storm water management plan required under sub. (b) shall include the following:

(1)

Total suspended solids . BMPs shall be designed, installed and maintained to control total suspended solids carried in runoff from the post-construction site as follows:

a.

BMPs shall be designed in accordance with Table 1 or to the maximum extent practicable as provided in subd. b. The design shall be based on an average annual rainfall, as compared to no runoff management controls.

Table 1 — TSS Reduction Standards

Development Type	TSS Reduction
New development	80 percent
In-fill development	80 percent
Redevelopment	40 percent of load from parking areas and roads

 

b.

Maximum extent practicable. If the design cannot meet a total suspended solids reduction performance standard of Table 1, the storm water management plan shall include a written, site-specific explanation of why the total suspended solids reduction performance standard cannot be met and why the total suspended solids load will be reduced only to the maximum extent practicable.

c.

Off-site drainage. When designing BMPs, runoff draining to the BMP from off-site shall be taken into account in determining the treatment efficiency of the practice. Any impact on the efficiency shall be compensated for by increasing the size of the BMP accordingly.

(2)

Water quantity and management of peak runoff .

a.

BMPs shall manage the volume, timing, and peak flow rate of runoff to prevent increases in the regional flood and stream bank erosion rates.

b.

These BMPs may be implemented either on-site or off-site as part of a regional stormwater device, practice or system. The BMP shall manage runoff from the post-construction site prior to discharge to waters of the state.

c.

When implemented on a regional basis, the BMPs implemented at a particular site shall comply with the findings of the relevant local or regional storm water management plan, rather than sections d. and e.

d.

The following peak runoff reductions are required:

1.

By design, BMPs shall be employed to maintain or reduce the one-year, 24-hour post-construction peak runoff discharge rates to the one-year, 24-hour pre-development peak runoff discharge rates, or to the maximum extent practicable.

2.

For the 50 percent/two-year, 24-hour design storm, BMPs shall be designed to either maintain or reduce the peak runoff discharge rates, to the maximum extent practicable, as compared to predevelopment conditions, or achieve a maximum runoff release rate of 0.15 cubic feet per second per acre, whichever is more stringent.

3.

i.

For development, runoff management shall prevent increases in the regional flood and stream bank erosion rates.

ii.

If demolition or construction during redevelopment will disturb an area larger than two acres, then the village shall reduce the runoff rate by the amount listed in Table 2 for the one percent/100-year and 50 percent/two-year storms, except as provided for in MMSD Chapter 13.11 (5) Rules.

Table 2 — Runoff Reduction Requirements

Area disturbed by demolition or construction	Reduction of the existing runoff release rate as of October 25, 2010.
Greater than 2 acres to 3.5 acres	10%
Greater than 3.5 acres to 5 acres	15%
Greater than 5 acres	20%

 

iii.

If redevelopment will add one-half acre or more of impervious surface, then the requirements of paragraph a. apply rather than paragraph b.

4.

The runoff curve numbers in Table 3 shall be used to represent the actual pre-development conditions. Peak discharges shall be calculated using TR-55 runoff curve number methodology, Atlas 14 precipitation depths, and the NRCS Wisconsin MSE3 precipitation distribution (for Milwaukee County). On a case-by-case basis, the Village Administrator may allow the use of TP-40 precipitation depths and the Type II distribution.

The NRCS calculated county-specific Atlas 14 precipitation depths and MSE3 and MSE4 precipitation distributions are available at:

http://www.nrcs.usda.gov/wps/portal/nrcs/detail/wi/technical/engineering/?cid=nrcs142p2_025417.

Table 3 — Maximum Pre-Development Runoff Curve Numbers

Runoff Curve Number	Hydrologic Soil Group
	A	B	C	D
Woodland	30	55	70	77
Grassland	39	61	71	78
Cropland	55	68	77	80

 

5.

For the one percent/100-year, 24-hour design storm, BMPs shall be designed to achieve a runoff release rate that is less than or equal to either:

i.

0.5 cubic feet per second per acre; or

ii.

A rate determined for the individual site that distributes runoff over the critical time sufficient to comply with subd. a.

e.

This subsection of the ordinance does not apply to any of the following:

1.

A post-construction site where the discharge is directly into a lake over 5,000 acres or a stream or river segment draining more than 500 square miles.

2.

Except as provided under section 86-408(c), a redevelopment post-construction site.

3.

An in-fill development area less than five acres.

(3)

Infiltration .

a.

Best management practices . BMPs shall be designed, installed, and maintained to infiltrate runoff in accordance with the following or to the maximum extent practicable:

1.

Low imperviousness . For development up to 40 percent connected imperviousness, such as parks, cemeteries, and low density residential development, infiltrate sufficient runoff volume so that the post-development infiltration volume shall be at least 90 percent of the pre-development infiltration volume, based on an average annual rainfall. However, when designing appropriate infiltration systems to meet this requirement, no more than one percent of the post-construction site is required as an effective infiltration area.

2.

Moderate imperviousness . For development with more than 40 percent and up to 80 percent connected imperviousness, such as medium and high density residential, multi-family development, industrial and institutional development, and office parks, infiltrate sufficient runoff volume so that the post-development infiltration volume shall be at least 75 percent of the pre-development infiltration volume, based on an average annual rainfall. However, when designing appropriate infiltration systems to meet this requirement, no more than two percent of the post-construction site is required as an effective infiltration area.

3.

High imperviousness . For development with more than 80 percent connected imperviousness, such as commercial strip malls, shopping centers, and commercial downtowns, infiltrate sufficient runoff volume so that the post-development infiltration volume shall be at least 60 percent of the pre-development infiltration volume, based on an average annual rainfall. However, when designing appropriate infiltration systems to meet this requirement, no more than two percent of the post-construction site is required as an effective infiltration area.

b.

Pre-development . The pre-development condition shall be the same as specified in Table 3 of the Peak Discharge section of this article.

c.

Source areas .

1.

Prohibitions . Runoff from the following areas may not be infiltrated and may not qualify as contributing to meeting the requirements of this section unless demonstrated to meet the conditions identified in section 86-408 (d)(3)f.:

i.

Areas associated with a tier 1 industrial facility identified in § NR 216.21 (2)(a), including storage, loading and parking. Rooftops may be infiltrated with the concurrence of the regulatory authority.

ii.

Storage and loading areas of a tier 2 industrial facility identified in § NR 216.21 (2)(b).

iii.

Fueling and vehicle maintenance areas. Runoff from rooftops of fueling and vehicle maintenance areas may be infiltrated with the concurrence of the regulatory authority.

2.

Exemptions . Runoff from the following areas may be credited toward meeting the requirement when infiltrated, but the decision to infiltrate runoff from these source areas is optional:

i.

Parking areas and access roads less than 5,000 square feet for commercial development.

ii.

Parking areas and access roads less than 5,000 square feet for industrial development not subject to the prohibitions under par. i.

iii.

Except as provided under section 86-408(c), redevelopment post-construction sites.

iv.

In-fill development areas less than five acres.

v.

Roads on commercial, industrial and institutional land uses, and arterial residential roads.

d.

Location of practices .

1.

Prohibitions . Infiltration practices may not be located in the following areas:

i.

Areas within 1000 feet upgradient or within 100 feet downgradient of direct conduits to groundwater.

ii.

Areas within 400 feet of a community water system well as specified in § NR 811.16(4) or within the separation distances listed in § NR 812.08 for any private well or non-community well for runoff infiltrated from commercial, including multi-family residential, industrial and institutional land uses or regional devices for one- and two-family residential development.

iii.

Areas where contaminants of concern, as defined in § NR 720.03(2), are present in the soil through which infiltration will occur.

2.

Separation distances .

i.

Infiltration practices shall be located so that the characteristics of the soil and the separation distance between the bottom of the infiltration system and the elevation of seasonal high groundwater or the top of bedrock are in accordance with Table 4.

ii.

Notwithstanding par. 2., applicable requirements for injection wells classified under ch. NR 815 shall be followed.

Table 4 — Separation Distances and Soil Characteristics

Source area	Separation distance	Soil characteristics
Industrial, commercial, institutional parking lots and roads	5 feet or more	Filtering layer
Residential arterial roads	5 feet or more	Filtering layer
Roofs draining to subsurface infiltration practices	1 foot or more	Native or engineered soil with particles finer than coarse sand
Roofs draining to surface infiltration practices	Not applicable	Not applicable
All other impervious source areas	3 feet or more	Filtering layer

 

3.

Infiltration rate exemptions . Infiltration practices located in the following areas may be credited toward meeting the requirements under the following conditions, but the decision to infiltrate under these conditions is optional:

i.

Where the infiltration rate of the soil measured at the proposed bottom of the infiltration system is less than 0.6 inches per hour using a scientifically credible field test method.

ii.

Where the least permeable soil horizon to five feet below the proposed bottom of the infiltration system using the U.S. Department of Agriculture method of soils analysis is one of the following: sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay, or clay.

e.

Alternate use . Where alternate uses of runoff are employed, such as for toilet flushing, laundry, or irrigation or storage on green roofs where an equivalent portion of the runoff is captured permanently by rooftop vegetation, such alternate use shall be given equal credit toward the infiltration volume required by this section.

f.

Groundwater standards .

1.

Infiltration systems designed in accordance with this section shall, to the extent technically and economically feasible, minimize the level of pollutants infiltrating to groundwater and shall maintain compliance with the preventive action limit at a point of standards application in accordance with ch. NR 140. However, if site specific information indicates that compliance with a preventive action limit is not achievable, the infiltration BMP may not be installed or shall be modified to prevent infiltration to the maximum extent practicable.

2.

Notwithstanding par. 1., the discharge from BMPs shall remain below the enforcement standard at the point of standards application.

g.

Pretreatment . Before infiltrating runoff, pretreatment shall be required for parking lot runoff and for runoff from new road construction in commercial, industrial and institutional areas that will enter an infiltration system. The pretreatment shall be designed to protect the infiltration system from clogging prior to scheduled maintenance and to protect groundwater quality in accordance with subd. f. Pretreatment options may include, but are not limited to, oil and grease separation, sedimentation, biofiltration, filtration, swales or filter strips.

h.

Maximum extent practicable . Where the conditions of subd. c. and d. limit or restrict the use of infiltration practices, the performance standard of section 86-408(d)(3) shall be met to the maximum extent practicable.

(4)

Protective areas .

a.

Definition . In this section, protective area means an area of land that commences at the top of the channel of lakes, streams and rivers, or at the delineated boundary of wetlands, and that is the greatest of the following widths, as measured horizontally from the top of the channel or delineated wetland boundary to the closest impervious surface. However, in this section, protective area does not include any area of land adjacent to any stream enclosed within a pipe or culvert, so that runoff cannot enter the enclosure at this location.

1.

For outstanding resource waters and exceptional resource waters, 75 feet.

2.

For perennial and intermittent streams identified on a U.S. Geological Survey seven and one-half-minute series topographic map, or a county soil survey map, whichever is more current, 50 feet.

3.

For lakes, 50 feet.

4.

For wetlands not subject to par. e. or f., 50 feet.

5.

For highly susceptible wetlands, 75 feet. Highly susceptible wetlands include the following types: calcareous fens, sedge meadows, open and coniferous bogs, low prairies, coniferous swamps, lowland hardwood swamps, and ephemeral ponds.

6.

For less susceptible wetlands, ten percent of the average wetland width, but no less than ten feet nor more than 30 feet. Less susceptible wetlands include: degraded wetland dominated by invasive species such as reed canary grass; cultivated hydric soils; and any gravel pits, or dredged material or fill material disposal sites that take on the attributes of a wetland.

7.

In pars. 4. to 6., determinations of the extent of the protective area adjacent to wetlands shall be made on the basis of the sensitivity and runoff susceptibility of the wetland in accordance with the standards and criteria in § NR 103.03.

8.

Wetland boundary delineation shall be made in accordance with § NR 103.08 (1m). This paragraph does not apply to wetlands that have been completely filled in compliance with all applicable state and federal regulations. The protective area for wetlands that have been partially filled in compliance with all applicable state and federal regulations shall be measured from the wetland boundary delineation after a fill has been placed. Where there is a legally authorized wetland fill, the protective area standard need not be met in that location.

9.

For concentrated flow channels with drainage areas greater than 130 acres, ten feet.

10.

Notwithstanding pars. 1. to 9., the greatest protective area width shall apply where rivers, streams, lakes and wetlands are contiguous.

b.

Applicability . This section applies to post-construction sites located within a protective area, except those areas exempted pursuant to subd. d.

c.

Requirements . The following requirements shall be met:

1.

Impervious surfaces shall be kept out of the protective area entirely or to the maximum extent practicable. If there is no practical alternative to locating an impervious surface in the protective area, the storm water management plan shall contain a written, site-specific explanation.

2.

Where land disturbing construction activity occurs within a protective area, adequate sod or self-sustaining vegetative cover of 70 percent or greater shall be established and maintained where no impervious surface is present. The adequate sod or self-sustaining vegetative cover shall be sufficient to provide for bank stability, maintenance of fish habitat, and filtering of pollutants from upslope overland flow areas under sheet flow conditions. Non-vegetative materials, such as rock riprap, may be employed on the bank as necessary to prevent erosion such as on steep slopes or where high velocity flows occur.

3.

BMPs such as filter strips, swales, or wet detention ponds, that are designed to control pollutants from non-point sources, may be located in the protective area.

d.

Exemptions . This section does not apply to any of the following:

1.

Except as provided under section 86-408(c), redevelopment post-construction sites.

2.

In-fill development areas less than five acres.

3.

Structures that cross or access surface water such as boat landings, bridges, and culverts.

4.

Structures constructed in accordance with § 59.692 (1v), Stats.

5.

Areas of post-construction sites from which the runoff does not enter the surface water, including wetlands, without first being treated by a BMP to meet the local ordinance requirements for total suspended solids and peak flow reduction, except to the extent that vegetative ground cover is necessary to maintain bank stability.

(5)

Fueling and maintenance areas . Fueling and vehicle maintenance areas shall have BMPs designed, installed, and maintained to reduce petroleum within runoff, so that the runoff that enters waters of the state contains no visible petroleum sheen, or to the maximum extent practicable.

(e)

General considerations for storm water management measures . The following considerations shall be observed in on-site and off-site runoff management:

(1)

Natural topography and land cover features such as natural swales, natural depressions, native soil infiltrating capacity, and natural groundwater recharge areas shall be preserved and used, to the extent possible, to meet the requirements of this section.

(2)

Emergency overland flow for all storm water facilities shall be provided to prevent exceeding the safe capacity of downstream drainage facilities and prevent endangerment of downstream property or public safety.

(f)

BMP location .

(1)

To comply with the performance standards required under section 86-408 of this article, BMPs may be located on-site or off-site as part of a regional storm water device, practice or system, but shall be installed in accordance with § NR 151.003, Wis. Adm. Code.

(2)

The village administrator may approve off-site management measures provided that all of the following conditions are met:

a.

The village administrator determines that the post-construction runoff is covered by a storm water management system plan that is approved by the village and that contains management requirements consistent with the purpose and intent of this article.

b.

The off-site facility meets all of the following conditions:

1.

The facility is in place.

2.

The facility is designed and adequately sized to provide a level of storm water control equal to or greater than that which would be afforded by on-site practices meeting the performance standards of this article.

3.

The facility has a legally obligated entity responsible for its long-term operation and maintenance.

(3)

Where a regional treatment option exists such that the village administrator exempts the applicant from all or part of the minimum on-site storm water management requirements, the applicant shall be required to pay a fee in an amount determined in negotiation with the village administrator. In determining the fee for post-construction runoff, the village administrator shall consider an equitable distribution of the cost for land, engineering design, construction, and maintenance of the regional treatment option.

(g)

Additional requirements . The village administrator may establish storm water management requirements more stringent than those set forth in this article if the village administrator determines that the requirements are needed to control storm water quantity or control flooding, comply with federally approved total maximum daily load requirements, or control pollutants associated with existing development or redevelopment.

(h)

Credit for removal of impervious surfaces .

(1)

Same site credit . The village administrator may use the removal of pavement, covered structures, or other impervious surfaces at the same property to calculate the net post construction impervious acreage and corresponding water quantity management duties to meet MMSD 13.11 requirements. The credit does not change the water quantity management requirements under subsection (d)(2)d.1. and 2.

Credit may equal, but not be larger than the acreage of impervious surfaces removed when runoff release rates and detention are the best management practices utilized at the site. When best management practices with a higher order of preference are utilized in lieu of detention, equivalent credit may be granted as determined by the village administrator with the concurrence of the MMSD. Credit for reducing impervious surfaces at a site, not utilized by the development on the site, belongs to the village administrator and may be banked for allocation to other development within the watershed under subsection (h)(2).

(2)

Dispersed site in same watershed credit. The village administrator may bank the removal of impervious surface, which individually must be one-half acre or more, within the same watershed, where the volume, timing and peak flow runoff will be distributed over the critical time sufficient to assure the level of protection provided by MMSD flood abatement projects will not be reduced. The village administrator may allocate banked credit to promote a policy of smart growth. The total acreage banked or allocated, or both, shall be reported, by watershed or sub-watershed, annually to the MMSD for concurrence. The credit does not change the water quantity management requirements under subsection (d)(2)d.1. and 2.

(Ord. No. 01-O-16, 3-21-2016)