Current through August 26, 2024
(1) REQUIREMENT.
BMPs shall be designed, installed, and maintained to infiltrate runoff in
accordance with the following or to the maximum extent practicable:
(a)
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.
(b)
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 2 percent of the
post-construction site is required as an effective infiltration area.
(c)
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 2 percent of the
post-construction site is required as an effective infiltration area.
Note: A histogram showing the relationship
between connected imperviousness and land use is available from the department
at dnr.wi.gov.
(2) PRE-DEVELOPMENT. Pre-development
condition shall be the same as specified in s.
NR 151.123(1), Table 2.
Note: A model that calculates runoff volume,
such as SLAMM, P8, or an equivalent methodology may be used. For performance
standards based on an average annual rainfall, specific rainfall files for five
geographic locations around the state may be used. Information on how to access
SLAMM and P8 and the rainfall files is available from the department's storm
water management program at dnr.wi.gov. Use the most recent version of the
model and the parameter files for Wisconsin users unless directed otherwise by
the regulatory authority.
(3) SOURCE AREAS.
(a)
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 of sub. (6):
1. Areas
associated with a tier 1 industrial facility identified in s.
NR 216.21(2)
(a), including storage, loading, and parking.
Rooftops may be infiltrated with the concurrence of the regulatory
authority.
2. Storage and loading
areas of a tier 2 industrial facility identified in s.
NR 216.21(2)
(b).
Note: Runoff from the employee and guest
parking and rooftop areas of a tier 2 facility may be infiltrated but runoff
from the parking area may require pretreatment.
3. Fueling and vehicle maintenance areas.
Rooftops of fueling and vehicle maintenance areas may be infiltrated with the
concurrence of the regulatory authority.
(b)
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:
1. Parking areas and access roads
less than 5,000 square feet for commercial development.
2. Parking areas and access roads less than
5,000 square feet for industrial development not subject to the prohibitions
under par. (a).
3. Except as
provided under s.
NR 151.121(5), redevelopment
post-construction sites.
4. In-fill
development areas less than 5 acres.
5. Roads in commercial, industrial, and
institutional land uses, and arterial residential roads.
(4) LOCATION OF PRACTICES.
(a)
Prohibitions.
Infiltration practices may not be located in the following areas:
1. Areas within 1,000 feet upgradient or
within 100 feet downgradient of direct conduits to groundwater.
2. Areas within 400 feet of a community water
system well as specified in s.
NR 811.16(4) or within the separation
distances listed in s.
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.
3. Areas where contaminants of concern, as
defined in s.
NR 720.03(2), are present in the soil
through which infiltration will occur.
(b)
Separation distances.
1. 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 3:
|
Table 3. 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
|
|
All Other Impervious Source Areas
|
3 feet or more
|
Filtering Layer
|
2.
Notwithstanding par. (b), applicable requirements for injection wells
classified under ch. NR 815 shall be followed.
(c)
Infiltration rate
exemptions. Infiltration practices located in the following areas may
be credited toward meeting the requirement under the following conditions, but
the decision to infiltrate under these conditions is optional:
1. 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.
2. Where the least permeable soil horizon to
5 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.
(5)
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.
(6)
GROUNDWATER STANDARDS.
(a) 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.
(b) Notwithstanding
par. (a), the discharge from BMPs shall remain below the enforcement standard
at the point of standards application.
(7) 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 sub. (6). Pretreatment options may
include, but are not limited to, oil and grease separation, sedimentation,
biofiltration, filtration, swales, or filter strips.
(8) MAXIMUM EXTENT PRACTICABLE. Where the
conditions of subs. (3) and (4) limit or restrict the use of infiltration
practices, the performance standard of s. NR 151.124 shall be met to the
maximum extent practicable.
