(5) REQUIREMENTS. The plan required under
sub. (4) shall include:
(a)
Total
suspended solids. Best management practices shall be designed,
installed and maintained to control total suspended solids carried in runoff
from the post-construction site as follows:
1.
For new development, by design, reduce to the maximum extent practicable, the
total suspended solids load by 80%, based on an average annual rainfall, as
compared to no runoff management controls. No person shall be required to
exceed an 80% total suspended solids reduction to meet the requirements of this
subdivision.
2. For redevelopment,
by design, reduce to the maximum extent practicable, the total suspended solids
load by 40%, based on an average annual rainfall, as compared to no runoff
management controls. No person shall be required to exceed a 40% total
suspended solids reduction to meet the requirements of this
subdivision.
3. For in-fill
development under 5 acres that occurs within 10 years after October 1, 2002, by
design, reduce to the maximum extent practicable, the total suspended solids
load by 40%, based on an average annual rainfall, as compared to no runoff
management controls. No person shall be required to exceed a 40% total
suspended solids reduction to meet the requirements of this
subdivision.
4. For in-fill
development that occurs 10 or more years after October 1, 2002, by design,
reduce to the maximum extent practicable, the total suspended solids load by
80%, based on an average annual rainfall, as compared to no runoff management
controls. No person shall be required to exceed an 80% total suspended solids
reduction to meet the requirements of this subdivision.
5. Notwithstanding subds. 1. to 4., if the
design cannot achieve the applicable total suspended solids reduction
specified, the storm water management plan shall include a written and
site-specific explanation why that level of reduction is not attained and the
total suspended solids load shall be reduced to the maximum extent practicable.
Note: Pollutant loading models such as SLAMM,
P8 or equivalent methodology may be used to evaluate the efficiency of the
design in reducing total suspended solids. Information on how to access SLAMM
and P8 is available from the storm water coordinator in the runoff management
section of the bureau of watershed management at dnr.wi.gov.
(b)
Peak
discharge.1. By design, BMPs shall
be employed to maintain or reduce the peak runoff discharge rates, to the
maximum extent practicable, as compared to pre-development conditions for the
2-year, 24-hour design storm applicable to the post-construction site.
Pre-development conditions shall assume "good hydrologic conditions" for
appropriate land covers as identified in TR-55 or an equivalent methodology.
The meaning of "hydrologic soil group" and "runoff curve number" are as
determined in TR-55. However, when pre-development land cover is cropland,
rather than using TR-55 values for cropland, the runoff curve numbers in Table
2 shall be used.
Table 2 - Maximum Pre-Development Runoff Curve
Numbers for Cropland Areas
| Hydrologic Soil
Group | A | B | C | D |
| Runof f Curve
Number | 56 | 70 | 79 | 83 |
Note: The curve numbers in Table 2 represent
mid-range values for soils under a good hydrologic condition where conservation
practices are used and are selected to be protective of the resource
waters.
2. This paragraph
does not apply to:
a. A post-construction site
where the change in hydrology due to development does not increase the existing
surface water elevation at any point within the downstream receiving water by
more than 0.01 of a foot for the 2-year, 24-hour storm event.
Note: Hydraulic models such as HEC-RAS or
another methodology may be used to determine the change in surface water
elevations.
b. A
redevelopment post-construction site.
c. An in-fill development area less than 5
acres.
Note: The intent of par. (b) is to minimize
streambank erosion under bank full conditions.
(c)
Infiltration.
BMPs shall be designed, installed and maintained to infiltrate runoff to the
maximum extent practicable in accordance with the following, except as provided
in subds. 5. to 8.:
1. For residential
developments one of the following shall be met:
a. Infiltrate sufficient runoff volume so
that the post-development infiltration volume shall be at least 90% 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 1% of the project site is required as an effective
infiltration area.
b. Infiltrate
25% of the post-development runoff volume from the 2-year, 24-hour design storm
with a type II distribution. Separate curve numbers for pervious and impervious
surfaces shall be used to calculate runoff volumes and not composite curve
numbers as defined in TR-55. However, when designing appropriate infiltration
systems to meet this requirement, no more than 1% of the project site is
required as an effective infiltration area.
2. For non-residential development, including
commercial, industrial and institutional development, one of the following
shall be met:
a. For this subdivision only,
the "project site" means the rooftop and parking lot areas.
b. Infiltrate sufficient runoff volume so
that the post-development infiltration volume shall be at least 60% 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 2% of the project site is required as an effective
infiltration area.
c. Infiltrate
10% of the post-development runoff volume from the 2-year, 24-hour design storm
with a type II distribution. Separate curve numbers for pervious and impervious
surfaces shall be used to calculate runoff volumes and not composite curve
numbers as defined in TR-55. However, when designing appropriate infiltration
systems to meet this requirement, no more than 2% of the project site is
required as an effective infiltration area.
3. Pre-development condition shall be the
same as specified in par. (b).
Note: A model that calculates runoff volume,
such as SLAMM, P8 or an equivalent methodology may be used. Information on how
to access SLAMM and P8 is available from the storm water coordinator in the
runoff management section of the bureau of watershed management at
dnr.wi.gov.
4. 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. 8. Pretreatment options may include, but are not limited to, oil/grease
separation, sedimentation, biofiltration, filtration, swales or filter strips.
Note: To achieve the infiltration requirement
for the parking lots or roads, maximum extent practicable should not be
interpreted to require significant topography changes that create an excessive
financial burden. To minimize potential groundwater impacts it is desirable to
infiltrate the cleanest runoff. To achieve this, a design may propose greater
infiltration of runoff from low pollutant sources such as roofs, and less from
higher pollutant source areas such as parking lots.
5. Exclusions. The runoff from the following
areas are prohibited from meeting the requirements of this paragraph:
a. Areas associated with tier 1 industrial
facilities identified in s.
NR 216.21(2)
(a), including storage, loading, rooftop and
parking.
b. Storage and loading
areas of tier 2 industrial facilities identified in s.
NR 216.21(2)
(b).
Note: Runoff from tier 2 parking and rooftop
areas may be infiltrated but may require pretreatment.
c. Fueling and vehicle maintenance
areas.
d. Areas within 1000 feet
upgradient or within 100 feet downgradient of karst features.
e. Areas with less than 3 feet separation
distance from the bottom of the infiltration system to the elevation of
seasonal high groundwater or the top of bedrock, except this subd. 5. e. does
not prohibit infiltration of roof runoff.
f. Areas with runoff from industrial,
commercial and institutional parking lots and roads and residential arterial
roads with less than 5 feet separation distance from the bottom of the
infiltration system to the elevation of seasonal high groundwater or the top of
bedrock.
g. Areas within 400 feet
of a community water system well as specified in s.
NR 811.16(4) or within 100 feet of a
private well as specified in s.
NR 812.08(4) for runoff infiltrated from
commercial, industrial and institutional land uses or regional devices for
residential development.
h. Areas
where contaminants of concern, as defined in s.
NR 720.03(2), are present in the soil
through which infiltration will occur.
i. Any area where the soil does not exhibit
one of the following characteristics between the bottom of the infiltration
system and the seasonal high groundwater and top of bedrock: at least a 3-foot
soil layer with 20% fines or greater; or at least a 5-foot soil layer with 10%
fines or greater. This subd. 5.
i.
does not apply where the soil medium within the infiltration system provides an
equivalent level of protection. Subdivision 5. i. does not prohibit
infiltration of roof runoff.
Note: The areas listed in subd. 5. are
prohibited from infiltrating runoff due to the potential for groundwater
contamination.
6.
Exemptions. The following are not required to meet the requirements of this
paragraph:
a. Areas where the infiltration
rate of the soil is less than 0.6 inches/hour measured at the bottom of the
infiltration system.
b. Parking
areas and access roads less than 5,000 square feet for commercial and
industrial development.
c.
Redevelopment post-construction sites.
d. In-fill development areas less than 5
acres.
e. Infiltration areas during
periods when the soil on the site is frozen.
f. Roads in commercial, industrial and
institutional land uses, and arterial residential roads.
7. Where alternate uses of runoff are
employed, such as for toilet flushing, laundry or irrigation, such alternate
use shall be given equal credit toward the infiltration volume required by this
paragraph.
8.
a. Infiltration systems designed in
accordance with this paragraph 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.
b. Notwithstanding subd. 8. a., the discharge
from BMPs shall remain below the enforcement standard at the point of standards
application.
(d)
Protective areas.
1. In this paragraph, " 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 paragraph, "protective area" does not include any area of land
adjacent to any stream enclosed within a pipe or culvert, such that runoff
cannot enter the enclosure at this location.
a. For outstanding resource waters and
exceptional resource waters, and for wetlands in areas of special natural
resource interest as specified in s.
NR 103.04, 75 feet.
b. For perennial and intermittent streams
identified on a United States geological survey 7.5-minute series topographic
map, or a county soil survey map, whichever is more current, 50 feet.
c. For lakes, 50 feet.
d. For highly susceptible wetlands, 50 feet.
Highly susceptible wetlands include the following types: fens, sedge meadows,
bogs, low prairies, conifer swamps, shrub swamps, other forested wetlands,
fresh wet meadows, shallow marshes, deep marshes and seasonally flooded basins.
Wetland boundary delineation shall be made in accordance with s.
NR 103.08(1m). This paragraph does not
apply to wetlands that have been completely filled in accordance with all
applicable state and federal regulations. The protective area for wetlands that
have been partially filled in accordance with all applicable state and federal
regulations shall be measured from the wetland boundary delineation after fill
has been placed.
e. For less
susceptible wetlands, 10% of the average wetland width, but no less than 10
feet nor more than 30 feet. Less susceptible wetlands include degraded wetlands
dominated by invasive species such as reed canary grass.
f. In subd. 1. a., d. and e., 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 s.
NR 103.03.
g. For concentrated flow channels with
drainage areas greater than 130 acres, 10 feet.
2. This paragraph applies to
post-construction sites located within a protective area, except those areas
exempted pursuant to subd. 4.
3.
The following requirements shall be met:
a.
Impervious surfaces shall be kept out of the protective area to the maximum
extent practicable. The storm water management plan shall contain a written
site-specific explanation for any parts of the protective area that are
disturbed during construction.
b.
Where land disturbing construction activity occurs within a protective area,
and where no impervious surface is present, adequate sod or self-sustaining
vegetative cover of 70% or greater shall be established and maintained. 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.
Note: It is recommended that seeding of
non-aggressive vegetative cover be used in the protective areas. Vegetation
that is flood and drought tolerant and can provide long-term bank stability
because of an extensive root system is preferable. Vegetative cover may be
measured using the line transect method described in the university of
Wisconsin extension publication number A3533, titled "Estimating Residue Using
the Line Transect Method".
c. Best management practices such as filter
strips, swales or wet detention basins, that are designed to control pollutants
from non-point sources may be located in the protective area.
Note: Other regulations, such as ch. 30,
Stats., and chs.
NR 103, 115, 116 and 117 and their
associated review and approval process may apply in the protective
area.
4.
Exemptions. This paragraph does not apply to:
a. Redevelopment post-construction
sites.
b. In-fill development areas
less than 5 acres.
c. Structures
that cross or access surface waters such as boat landings, bridges and
culverts.
d. Structures constructed
in accordance with s.
59.692(1v),
Stats.
e. Post-construction sites
from which runoff does not enter the surface water, except to the extent that
vegetative ground cover is necessary to maintain bank stability.
Note: A vegetated protective area to filter
runoff pollutants from post-construction sites described in subd. 4. e. is not
necessary since runoff is not entering the surface water at that location.
Other practices necessary to meet the requirements of this section, such as a
swale or basin, will need to be designed and implemented to reduce runoff
pollutants prior to runoff entering a surface water of the state.
(e)
Fueling and vehicle maintenance areas. Fueling and vehicle
maintenance areas shall, to the maximum extent practicable, have BMPs designed,
installed and maintained to reduce petroleum within runoff, such that the
runoff that enters waters of the state contains no visible petroleum sheen.
Note: A combination of the following BMPs may
be used: oil and grease separators, canopies, petroleum spill cleanup
materials, or any other structural or non-structural method of preventing or
treating petroleum in runoff.
