Water Quality
Management Policy
Adopted by the Commission
September 14, 1998
Revised: November 1998
Executive Summary
The lakes, rivers, ponds, streams,
and wetlands of the Bassett Creek Watershed are an important community asset. These
resources supply aesthetic and recreational benefits, in addition to providing wildlife
habitat and refuge. The Bassett Creek Water Management Commission recognizes a need to
assure adequate water quality in the water bodies in its jurisdiction, and has taken steps
to protect these resources.
Phosphorus and suspended sediment are recognized as
being particularly detrimental to the health of lakes and streams. As a result, the
Commission is requiring measures to reduce the influx of these pollutants to its water
bodies. Furthermore, to better plan its strategy, the Commission has identified projected
uses and corresponding water quality goals for each of the major water bodies in the
watershed.
Wherever possible, the Commission plans to make use
of regional treatment facilities to manage water quality. However, in addition to regional
treatment, sound water management practices must occur on the local level. To this end,
the Commission intends to review plans for construction activities within its jurisdiction
to ensure that water quality goals are met.
This document sets forth the Water Quality
Management Policy of the Commission. Part I of this document explains the rationale and
strategy of the Bassett Creek Water Management Commission in establishing its Water
Quality Management Policy. Part II describes the CommissionNs review process and its
specific requirements for construction activities within the watershed.
Part I: Rationale for the
Policy
1. Introduction
When natural areas are urbanized, stormwater runoff
from new roads, highways, industries and homes carries pollutants at above-natural rates
to adjacent water bodies. Numerous studies have documented the adverse water quality
impacts associated with converting land from its native, undisturbed state to urban land
uses. Outflow from urbanized areas accelerates the natural eutrophication of our lakes,
streams and rivers.
At the same time, an increased population density generally results
in an increased appreciation for the many benefits of urban lakes, rivers, wetlands, and
streams. This results in strong pressure to mitigate the impacts of urbanization, and to
reduce the effects of past water quality degradation.
The Bassett Creek Water Management Commission (Commission) is
mandated to manage the water resources of the watershed in order that the beneficial uses
of wetlands, lakes, and streams remain available to the community. Such uses may include
simple aesthetic appreciation, wildlife observation, swimming, boating, or others.
The Commission recognizes a public need for water quality protection
and improvement within its jurisdiction, and accepts water quality management as one of
its highest priorities. Part I of this document outlines the CommissionNs objectives with
regard to water quality in the Bassett Creek Watershed. Part II gives the standards
the Commission has adopted in seeking to meet these objectives. This policy was adopted by
the Basset Creek Water Management Commission at its September 14, 1994 meeting.
Revisions to the policy were adopted at the Commission=s December 18, 1997
meeting.
2. Objectives and Strategy
The expected use and corresponding desired water
quality for a particular water body may be quite different from those of another lake,
pond or stream. For example, a large lake in the midst of a residential area may be
expected to provide safe and healthful swimming for local citizens. Water quality in this
situation would need to be excellent. By contrast, the water quality expectations for a
small and relatively neglected pond in a predominantly commercial zone would be lower.
Realizing this distinction between water bodies, the Bassett Creek
Water Management Commission found it useful to classify water bodies according to their
expected use and corresponding required water quality. Table 1 shows the water
quality classifications adopted by the Commission. These classifications rank water bodies
by the water quality required to support either current, or desired future uses.
Table 1
Definition of Management Classifications
According to Desired Uses
| Level I |
Level I water bodies
fully support all water-based recreational activities including swimming, scuba diving and
snorkeling. |
| Level II |
Level II water
bodies are appropriate for all recreational uses except full body contact activities.
Recreational activities for these water bodies include: sailboating, water skiing,
motorboating, canoeing, wind surfing and jet skiing. |
| Level III |
Level III water
bodies will support fishing, aesthetic viewing activities and observing wildlife. |
| Level IV |
Level IV water
bodies are water resources generally intended for runoff management (i.e., stormwater
detention) and have no significant recreational use values. |
It can be seen that Level I water
bodies will require the highest water quality. Levels II, III, and IV water bodies require
successively lower water quality to support their intended use.
Using the system shown in Table 1, classifications for the major
water bodies within the Bassett Creek Watershed were decided upon by the Commissioners.
These classifications were based on public input, and resulted from consultation with the
staff and elected officials of the cities within the watershed.
For example, water quality goals for Medicine lake were set by the
Commission in 1974, after discussions of the effect of the lake's water quality on its
recreational use. The water quality that existed in Medicine Lake in 1974 was consistent
with the desired use. However, since 1974, the water quality of Medicine Lake has
deteriorated and future restorative measures will be needed to reach the water quality
goal. The management classifications for Medicine Lake and for the rest of the major water
bodies in the Bassett Creek Watershed are shown in Table 2.
Table 2
Management Classifications of
Major Water Bodies in Bassett Creek Watershed
| Main Stem |
Grimes Pond
N. Rice Pond
S. Rice Pond
Birch Pond
Wirth Lake
Westwood Lake
Bassett Creek (Mississippi River to Medicine Lake) |
Level III
Level III
Level III
Level III
Level I
Level II
Level III |
| North Branch |
Lost Lake
Northwood Lake
Bassett Creek Park Pond |
Level II
Level II
Level III |
Medicine Lake
Branch |
Parker's Lake
Turtle Lake
Crane Lake
Medicine Lake |
Level I
Level II
Level III
Level I |
Sweeney
Branch |
W. Ring
Pond
E. Ring Pond
Courtlawn Pond
Twin Lake
Sweeney Lake |
Level III
Level III
Level III
Level I
Level I |
Level I = Recreational (All
Activities)
Level II = Recreational (Non-Body Contact Activities)
Level III = Aesthetic Viewing
Level IV = Runoff Management
After classifying the water bodies of the Bassett Creek Watershed,
the Commission set specific water quality goals for each lake or stream, and analysis was
made of the steps that would be required to meet these goals. It became clear that the
water quality goals could not be met without taking measures to assure adequate water
quality in the subwatersheds draining to the water bodies. As a result, watershed
management, including review of land development, forms a major component of the
management program for the lakes and streams of the Bassett Creek Watershed.
The Commission's watershed management and land development policies
are directed mainly at controlling the amount of phosphorus that is carried in the runoff
from the watershed. High phosphorus levels in lakes lead to algal proliferation. An
abundance of algae reduces the clarity of the water, may result in impairment of fish
habitat, and can cause scum and odor problems. Water quality monitoring of Basset Creek
waters shows control of phosphorus levels to be the key to controlling algal growth.
Closely related to the reduction of phosphorus loads to the water
bodies is the control of suspended sediment inflows. Suspended sediment--fine particles of
soil, dust and dirt carried in moving water--results from stormwater runoff from streets
and parking lots, and abounds when erosion occurs. This sediment load clouds streams and
lakes, thereby disturbing aquatic habitats. It also is a major source of phosphorus, which
is frequently bound to the fine particles. As a result, many of the Commission's standards
are aimed at preventing or slowing the transport of fine soil, dust and dirt particles
into the streams and lakes.
To address its water quality concerns, an overall water quality
management plan is currently being developed by the Commission. The plan will identify
where regional basins can be developed in the watershed to meet the water quality goals
adopted by the Commission. The plan will also estimate the development cost of those
regional facilities. After adoption of the water quality plan and the capital improvement
plan by the Commission, property owners/developers in the watershed of those regional
facilities may be required to contribute to the cost of those regional facilities. Their
portion of the cost will be in proportion to their contribution of nutrients to the total
contribution of nutrients to the regional facility.
The Commission intends to use regional watershed treatment
facilities wherever possible to attain the water quality goals for the watershed. In
addition to regional treatment, however, implementation of Best Management Practices
(BMPs) will be required on construction sites throughout the watershed. Such practices are
seen as particularly important in areas of the watershed where regional detention
facilities have not been established or are not feasible.
To encourage water quality protection and the use of BMPs, the
Commission intends to review plans for construction activities within the Bassett Creek
Watershed in accordance with this policy. Activities within the subwatersheds will be
regulated according to the classification (Level I, II, III, etc.) of the receiving
water listed in Table 2.
General level-dependent requirements for stormwater treatment are
shown in Table 3. The treatments listed are intended to reduce phosphorus, suspended
sediment, and other pollutant loads carried by the stormwater runoff.
Table 3
General Requirements for Water Management
According to Management Classification
| |
Runoff Treatment |
|
Management
Classification |
Best Management
Practices |
Sediment-tation |
Skimming |
Nutrient
Removal |
| Levels I and II (Recreation) |
Required |
Required |
Required |
Required |
| Level III (Aesthetic Viewing) |
Required |
Required |
Required |
May be
Required |
| Level IV (Runoff Management) |
Required |
Not
Required |
Not
Required |
Not
Required |
| Wetlands (Types 2-8) |
Required |
Not
Required |
Not
Required |
Not
Required |
Particular requirements designed to
achieve the Commission's water quality goals are outlined in Part II of this document.
Part II of this document gives a complete listing of the water quality control standards
and design criteria that have been adopted by the Commission. Part II describes:
- Which projects will require a submittal for review.
- The nature of the review process.
- What exhibits will be required in the submittal.
- What the standards are for the required "Water Quality
Management Plan," in accord with the classification of the receiving water body.
- What the standards are for the required Erosion Control Plan.
- How a variance from the standards may be applied for.
Part II: Water Quality
Management Standards
1. Projects for Which Best
Management Practices Must be Considered
a. It is the policy of the Bassett Creek Water Management Commission
(Commission) to require that, prior to commencing construction or reconstruction of a
site, all persons, municipalities or other agencies proposing improvements, developments,
or redevelopments within the Bassett Creek watershed for residential, commercial,
industrial, institutional, or public uses shall submit information regarding the project
to the Commission in conformity with the requirements of this policy. They shall further
secure comments from the Commission regarding the conformance of the project to the
policies of the Bassett Creek Water Management Plan. [Note: an NPDES permit for
construction activity is required from the Minnesota Pollution Control Agency for projects
which disturb one or more acres of area.]
b. A commercial, industrial, institutional or public
development is defined as a project involving a site of more than 0.5 acres of
land where there is no existing commercial, industrial, institutional or public
development. A commercial, industrial, institutional or public expansion/addition is
defined as a project involving a site that was partially developed prior to adoption of
the Commission's Water Quality Policy (September 14, 1994) and
involves grading more than 0.5 acres of land. A commercial, industrial, institutional
or public redevelopment is defined as a project involving a site of more than
5 acres of land where the commercial, industrial, institutional, residential or
public development currently exists.
c. A residential development is defined as a project
involving a site of more than 2 acres and which contains four or more proposed living
units. A residential redevelopment is defined as a project involving more than
10 acres where there are four or more existing living units.
d. A road construction or reconstruction project involving a
site of more than 5 acres of land for which the site runoff is not currently
directed to an onsite or regional treatment facility. This policy results from the
Commission=s goal to eliminate direct discharges from roadways to a
Level I, II, or III water body, including Bassett Creek.
e. If the Commission has approved a municipal Stormwater Management
Plan for a municipality, or for a subwatershed within a municipality, the requirements of
this policy which are met by the municipal plan shall be deemed satisfied upon showing
compliance with the municipal plan.
2. Review Procedure
a. The Commission will review the developer's submittal only after
the applicant demonstrates that the project has received preliminary approval from the
municipality indicating compliance with existing municipal plans.
b. The Commission meetings are held the third Thursday of each
month. In order for a proposed project to be included on the agenda, plans should be
submitted to the Commission staff at least two weeks prior to the meeting date. Complex
projects may require additional review time.
c. Upon receipt of a submittal, the Commission staff will review the
submittal and prepare recommendations to the Commission. A memorandum describing each
project and the staff recommendations will be sent to the Commissioners approximately one
week before each meeting.
d. The Commission will review and comment upon the submittal at its
regularly scheduled meeting. The Commission will approve, conditionally approve, or reject
the submittal. A letter with its comments, including a list of deficiencies or required
modifications, will be sent to the municipality and the permit applicant.
3. Required Exhibits for
Submittal for Review
A submittal for review shall include two sets of
exhibits for Commission review, one set to be returned to the municipality with Commission
comments, and one set to be retained in the Commission files. The following exhibits shall
be included in a submittal:
a. A set of Project Plans, including at least:
(1) A scale drawing of the site showing property lines and
delineation of lands under ownership of the applicant.
(2) Proposed and existing stormwater facilities location, alignment
and elevation.
(3) Existing and proposed site contour elevations related to NGVD,
1929 datum.
(4) Construction plans and specifications of all proposed stormwater
management facilities.
b. A Runoff Water Quality Management Plan and Computations,
signed by a registered professional engineer, and meeting the minimum requirements
described in Paragraph 4 of these standards. Pond sizing and average depth calculations
must also be provided.
c. A final Erosion Control Plan meeting the requirements of
Paragraph 5 of these standards.
d. Completed Application Form and checklist of Best
Management Practices.
4. Runoff Water Quality
Management Plans--Minimum Standards
A Runoff Water Quality Management Plan shall include
the following items:
a. Delineation of the subwatersheds contributing runoff from
offsite, and proposed and existing subwatersheds onsite.
b. Delineation of existing onsite wetlands, marshes, and/or
floodplain areas.
c. Existing 5-year; and proposed post-development normal, 5-year and
100-year stormwater elevations for the site.
d. Stormwater runoff volume and rate analyses for existing and
proposed conditions for 5-year and 100-year storm events.
e. All hydrologic and hydraulic computations necessary to design the
proposed stormwater quality management facilities.
f. Documentation indicating conformance with an existing municipal
Stormwater Management Plan. If a municipal Plan does not exist, documentation indicating
that the municipality has reviewed the project.
5. Best Management
Practices--Minimum Standards
a. Best Management Practices--General. A checklist of Best
Management Practices such as those shown in Table 4 (see end of this document) shall
be submitted demonstrating that, to the maximum extent practical, the plan has
incorporated the structural and non-structural BMPs, as described in the book Protecting
Water Quality in Urban Areas (Minnesota Pollution Control Agency, 1989). A list of
other BMPs is given in Table 5 to illustrate the range of practices that minimize the
adverse effects of stormwater runoff on receiving waters.
b. Best Management Practices--Expansion/Addition Projects. For commercial,
industrial, institutional or public expansion/addition projects, the Commission
realizes that existing development may limit the type of best management practices that
can be implemented for the entire site. The most desirable best management practice is to
construct a permanent wet detention basin to serve the entire site. At a minimum, a wet
detention basin must be constructed to serve the expansion/addition and, if applicable,
the increased contributing drainage area of the basin. Other appropriate best management
practices will be required for the existing development if wet detention for the increased
contributing drainage area is not practical. The Commission will work with the project
applicant to assist with determining the appropriate temporary and permanent best
management practices to implement for the project.
c. Best Management Practices--Road Projects. Best management
practices must be considered to improve the quality of stormwater runoff from road
construction and reconstruction projects. The most desirable best management practice
is the construction of a permanent wet detention basin, if possible. The Commission
realizes that existing development and right-of-way constraints will limit the type of
best management practices that can be implemented. At a minimum, temporary measures will
be required to address erosion and sediment control during construction. The Commission
will work with the project applicant to assist with determining the appropriate temporary
and permanent best management practices to implement for the project. The project
applicant must submit a description of the evaluation process used to identify feasible
best management practices to be implemented on the project.
Examples of applicable construction (temporary) best management
practices include, but are not limited to:
- Silt fence/hay bales
- Temporary diversions
- Temporary stream crossings
- Catch basin inlet protection
Examples of permanent best management practices include, but are not
limited to:
- Detention basins (wet and dry); these can be formed along ditches
through the use of permeable check dams or weirs
- Infiltration
- Vegetated swales
- Slope erosion protection
- Streambank protection
- Filter strips
- Infiltration trenches
Grit chambers or sump manholes are another possible best management
practice for capturing sediment. They are less desirable best management practices because
of the need for frequent inspection and cleaning at least twice per year to be effective.
If either is proposed to be used, the project applicant will be required to submit a
maintenance schedule.
6. General Ponding Requirements
In general, it is the Commission's policy to manage
its water resources using the regional detention basin concept. However, where regional
basins have not been constructed or cannot be developed, sound water quality management
requires the use of onsite detention basins or other features to meet water quality goals
established for Bassett Creek watershed receiving water bodies.
a. Natural or excavated low areas will be used for the detention
basins. Generally accepted reservoir routing procedures using critical duration runoff
events shall be used for design of these areas and outlets.
b. The size and design of the onsite detention basin will depend on
the receiving water body's management category (see Table 2) and flow conveyance
capacity, the quantity of impervious surface within the development, and the degree to
which onsite infiltration of runoff is encouraged. Onsite detention basins shall be
designed based on the following:
(1) Water Quality Goals
Detention basin shall achieve pollutant removal efficiencies
equal to or greater than those obtained by implementing the criteria set forth by the
Nationwide Urban Runoff Program (NURP) and Protecting Water Quality in Urban Areas
(MPCA, 1989) with specific consideration to the receiving body water quality goals. Design
of onsite detention basins will depend, to some extent, on the Commission's water quality
goals for the receiving water. For example, if the receiving water body has a Level I
water quality goal, the detention basin discharging to that lake or stream must achieve
high pollutant removal efficiencies. A Level IV goal, by contrast, would not demand that
efficiencies be as high.
(2) Water Quantity Goals--Flow Conveyance Capacity
Onsite detention basins shall avoid or minimize
increases in predevelopment runoff rates to the greatest extent practical. The capacity of
the receiving body to convey and/or store the runoff shall also be considered so as to not
adversely affect water levels off the site.
(3) Alternatives to Onsite Ponds
Alternative water quality management features may be used where
onsite ponds are not feasible. Alternative features must be designed to provide water
quality benefits that equal or exceed design criteria outlined in existing Commission
policies.
7. Water Quality Pond Design
Criteria
Following is the detention basin design criteria that
must be met for each water quality management classification (Levels I, II, III,
etc.) based on the receiving water body. See Table 2 to determine the water quality
management classification of the receiving water body.
a. Level I Water Bodies and Streams
(1) The permanent pool ("dead storage") volume below the
principal spillway (normal outlet) shall be greater than or equal to the runoff volume
from a 2.5-inch, 24-hour storm over the project site, assuming full development. Under
special conditions, such as expansions to existing water quality ponds, the entire
contributing drainage area will need to be considered in computing the dead storage
volume, assuming full development of the drainage area.
(2) The permanent pool average depth (basin volume/basin surface
area) shall be > 4 feet, with a maximum depth of < 10 feet.
For small ponds (less than 3 acre-feet in volume) average depth shall be > 3 feet,
with a maximum depth of < 10 feet. An "effective
average depth" (basin "effective
volume"/basin "effective surface
area") may be calculated for ponds that include basin shelves.
The "effective volume" and
"effective surface area" are computed by extending the basin sideslopes below
the basin shelf, vertically, to the water surface.
(3) An emergency overflow (emergency outlet) must be in place and
adequate to accommodate the 100-year frequency critical duration rainfall event.
(4) Basin side slopes above the normal water level shall be no
steeper than 3:1 when possible, and preferably flatter. A basin shelf with a minimum width
of 10 feet and 1 foot deep below the normal water level is recommended to enhance
wildlife habitat, reduce potential safety hazards, and improve access for long-term
maintenance.
(5) To prevent short-circuiting, the distance between the major
inlets and normal outlet shall be maximized.
(6) The flood pool ("live storage") volume above the
principal spillway shall be such that the peak discharge rate from the 5-year frequency,
critical duration storm does not exceed the peak discharge for a similar storm under
predevelopment conditions.
(7) Extended detention of runoff from the more frequent (1-year to
5-year) storms shall be achieved through a principal spillway design which shall include a
perforated vertical riser, small orifice outlets, or a compound weir.
(8) The design must include effective energy dissipation devices
that reduce outlet velocities to 4 fps or less. These outlets shall consist of
stilling basins or other such devices that prevent erosion at all stormwater outfalls into
the detention basin, and at the basin outlet. Storm sewer outfalls must extend to the
detention basin or other receiving water body and must discharge at or below its normal
water elevation.
(9) Trash and floatable debris skimming devices shall be placed
on the outlet of all onsite detention basins to provide treatment up to the critical
duration 5-year storm event. Submerged inlets, permanent baffled weirs or similar devices
may be employed. Timber baffled weirs are discouraged. Velocities through the devices
shall be less than 0.5 fps. The top of submerged inlets shall be at least one foot
below the water surface.
(10) During construction of the basin, care shall be taken to
prevent the discharge of waterborne sediments to downstream water bodies.
b. Level II Water Bodies and Streams
(1) The permanent pool (dead storage) volume below the principal
spillway (normal outlet) shall be greater than or equal to the runoff volume from a
2.0-inch, 24-hour storm over the project site, assuming full development. Under special
conditions, such as expansions to existing water quality ponds, the entire contributing
drainage area will need to be considered in computing the dead storage volume, assuming
full development of the area.
(2) All other requirements as listed above for Level I water
bodies.
c. Level III Water Bodies and Streams
(1) The permanent pool ("dead storage") volume below the
principal spillway (normal outlet) shall be greater than or equal to the runoff volume
from a 1.5-inch, 24-hour storm over the project site, assuming full development. Under
special conditions, such as expansions to existing water quality ponds, the entire
contributing drainage area will need to be considered in computing the dead storage
volume, assuming full development of the area.
(2) All other requirements as listed above for Level I water
bodies.
d. Level IV Water Bodies and Streams
(1) Energy dissipation devices as described for Level I water
bodies, and any and all other practical measures needed to maintain the function and
character of the Level IV water body.
e. Wetlands (Type 2-8)
(1) Energy dissipation devices as described for Level I water
bodies, and any and all other practical measures needed to maintain the function and
character of the wetland.
8. Erosion Control Plans--Minimum
Standards
a. During construction where grading involves more than 200 cubic
yards of cut or fill, or disturbs more than 10,000 square feet, an Erosion Control
Plan shall meet the standards given in the Erosion and Sediment Control Manual
(Hennepin County Conservation District, 1989) and Protecting Water Quality in Urban
Areas (MPCA, 1989).
b. Erosion control plans submitted for review shall show proposed
methods of retaining waterborne-sediments onsite during the period of construction, and
shall specify methods and schedules to determine how the site will be restored, covered,
or revegetated after construction.
c. In addition, the project applicant shall:
(1) Provide specific measures to control erosion based on the grade
and length of the slopes on the site, as follows:
(a) Silt fences shall be placed along the toe of the slopes that
have a grade of less than 3 percent and are less than 400 feet long from top to toe.
The silt fences shall be supported by sturdy metal or wooden posts at intervals of
4 feet or less.
(b) Flow lengths up-slope from each silt fence shall not exceed
400 feet for slopes that have a grade of less than 3 percent.
(c) Silt fences shall be placed along the toe of the slopes that
have a grade of 3 to 10 percent and are less than 200 feet long from top to toe.
These fences shall be supported by sturdy metal or wooden posts at intervals of
4 feet or less.
(d) Flow lengths up-slope from each silt fence shall not exceed
200 feet for slopes that have a grade of 3 to 10 percent.
(e) Diversion channels or dikes and pipes shall be provided to
intercept all drainage at the top of slopes that have a grade of more than 10 percent and
are less than 100 feet long from top to toe. Silt fence shall be placed along the toe
of said slopes, and shall be supported by sturdy metal or wooden posts at intervals of
4 feet or less.
(f) Diversion channels or dikes and pipes shall be provided to
intercept all drainage at the top of slopes that have grades of more than 10 percent.
Also, diversion channels or diked terraces and pipes shall be provided across said
slopes if needed to ensure that the maximum flow length does not exceed 100 feet.
Silt fence shall be placed along the toe of said slopes, and shall be supported by sturdy
metal or wooden posts at intervals of 4 feet or less.
(2) Require that silt fences or hay bales, staked with at least two
sturdy metal or wooden posts per bail, be installed around each catch basin inlet on the
site and that this barrier remain in place until pavement surfaces have been installed.
(3) Ensure that flows from diversion channels or pipes are routed to
sedimentation basins or appropriate energy dissipators in order to prevent transport of
sediment to outflow conveyors and to prevent erosion and sedimentation when runoff flows
into the conveyors.
(4) Provide that site-access roads be graded or otherwise protected
with silt fences, diversion channels or dikes and pipes to prevent sediment from leaving
the site via the access roads. Each site-access road shall have coarse aggregate filter
berms with a minimum height of 2 feet above the adjacent roadway and with maximum
side slopes of 4:1.
(5) Require that soils tracked from the site by motor vehicles be
cleaned daily (or more frequently, as necessary) from paved roadway surfaces throughout
the duration of construction.
(6) Assure that silt fences and diversion channels or dikes and
pipes be deployed and maintained for the duration of site construction. If construction
operations interfere with these control measures, the silt fences, diversion channels or
dikes and pipes may be removed or altered as needed but shall be restored to serve their
intended function at the end of each day.
(7) Specify that disturbed areas be revegetated or mulched
permanently or temporarily if it can be reasonably anticipated that significant additional
grading will not occur within 30 calendar days. A schedule of significant grading
work will be required as part of the erosion and sedimentation control plan.
(8) Require that temporary or permanent mulch be disc-anchored and
applied at a uniform rate of not less than 2 tons per acre.
(9) Provide a temporary vegetative cover consisting of a suitable,
fast-growing, dense grass-seed mix spread at 1.5 times the usual rate per acre. If
temporary cover is to remain in place beyond the present growing season, two-thirds of the
seed mix shall be composed of perennial grasses.
(10) Provide a 4-foot wide sodded area along the curb line of all
streets adjacent to the site and along all property boundaries where runoff could leave
the site.
(11) Specify a permanent vegetation cover consisting of sod, a
suitable grass-seed mixture, or a combination thereof. Seeded areas shall be either
mulched or covered by fibrous blankets to protect seeds and limit erosion.
(12) Provide temporary onsite sedimentation basins whenever other
erosion and sedimentation control practices are inadequate. Onsite detention basins shall
be designed to achieve pollutant removal efficiencies equal to or greater than those
obtained by implementing the criteria set forth by the Nationwide Urban Runoff Program
(NURP), and Protecting Water Quality in Urban Areas (MPCA, 1989).
9. Variances from the Water
Quality Management Policy
a. Applications for variances shall be filed with the City where the
property being developed, redeveloped, or retrofitted is located and shall state the
exceptional conditions of the property and the peculiar and practical difficulties claimed
as a basis for a variance. The applicant shall state on the application the reasons for
requesting the variances, in accordance with all the requirements set forth in Section (c)
below.
b. All applications for variances shall be referred by the City to
the Bassett Creek Water Management Commission's Engineer, and shall be reviewed by the
Commission. In reviewing the application, the Commission shall take into consideration the
criteria, standards, and goals for maintaining and improving the quality of the
watershed's public waters.
To address the applicant's hardship or special situation, the
Commission may grant the variance, contingent upon conditions that the Commission may set
forth. Alternatively, the Commission may deny the request and set forth reasons for the
denial.
c. In granting variances, the Commission shall make a finding
showing that all of the following conditions exist:
(1) There are special circumstances or conditions affecting the
property such that the strict application of the provisions of these standards and
criteria would deprive the applicant of the reasonable use of its land.
(2) The variance is necessary for the preservation and enjoyment of
a substantial property right of the applicant.
(3) The granting of the variance will not be detrimental to the
public welfare or injurious to the other property in the territory in which the property
is situated.
(4) In applications relating to a use in the floodplain or within
the management envelope set forth in the management plan, the variance shall not allow a
lower degree of flood protection than the flood protection elevation stated in the
management standards.
(5) The granting of the variance will not be contrary to the intent
of taking all reasonable and practical steps to improve water quality within the
watershed.
10. Definitions
a. Road construction or reconstruction projects include any
project which results in the complete removal of the road surface, exposing the base,
and/or removal of the vegetated surface within the road right-of-way. Examples include
road widening projects, ditch work, road replacement and utility installation. Road
overlay projects and road resurfacing projects which do not disturb the road base will not
be covered by the requirements of this policy.
b. Commercial, industrial, institutional or public development
projects typically result in larger areas of impervious surface, typically in the
range of 60 to 80 percent imperviousness. Examples of these developments include
shopping malls, stores, schools, hospitals, and warehouses.
c. Residential development projects typically result in
smaller areas of impervious surface, typically in the range of 25 to 60 percent
imperviousness. Examples of these projects include single family home construction,
townhome construction and apartment building construction.
d. Commercial, industrial, institutional or public
expansion/addition projects are additions to existing projects for which approval of
the existing project was obtained prior to adoption of this water quality policy. Examples
of such projects include parking lot expansions/additions and building
expansions/additions.
e. Best Management Practices are the structural,
non-structural, and institutional controls used to improve the quality of stormwater
runoff. Tables 4 and 5 at the end of this section provide examples of common best
management practices. Additional best management practices may be found in Protecting
Water Quality in Urban Areas (MPCA, 1989).
f. Onsite or regional treatment facility is a stormwater
treatment basin designed to treat the stormwater runoff generated from either the project
site (onsite) or an area larger than the project site (regional).
g. Complex projects include projects that are 40 acres
or more, controversial, involve more than one property owner, require detailed hydrologic
or hydraulic modeling, require vast changes to infrastructure (such as stormwater
systems), include many wetland impacts, require extensive environmental review, or involve
many different land uses within the same development project.
h. Stormwater (management) facilities include storm sewer
pipes, ditches, ponds, infiltration basins, etc.
i. Critical duration runoff: Generally accepted reservoir
routing procedures using critical duration runoff events refers to the hydrologic methods,
usually computer models, used to determine flowrates and flood levels resulting from
stormwater runoff events. The event which results in the highest flood level or flowrate
is the critical duration event. Examples of such methods include TR-20, Hydrocad, SWMM,
HEC-1 and other approved watershed models.
Table 4
Checklist of Common
Best Management Practices (BMPs)
For Development or Re-Development
| Description
of BMP |
Was
BMP Used in Project? |
Location
Used or Basis for Nonusage: |
| Discharge Elimination BMPs |
1. Reduce area of impervious surface (pavement, roofs, etc.)
|
|
|
2. French drains and subsurface drains
|
|
|
3. Infiltration trench and dry well
|
|
|
4. Exfiltration trench
|
|
|
5. Porous pavement
|
|
|
6. Retention (infiltration) basin
|
|
|
| Stormwater BMPs |
7. Detention Basin with outlet protection
|
|
|
8. Extended detention basin
|
|
|
9. Wetland treatment area
|
|
|
10. Parking lot/rooftop runoff storage with outlet protection
|
|
|
11. Grit chambers/manholes
|
|
|
12. Diversion channel
|
|
|
| Floatable/Oil Removal
BMPs |
13. Floatable skimmer
|
|
|
14. Parking lot oil/grease separators
|
|
|
| Sediment Control BMPs |
15. Riprap or other storm drain outlet protection
|
|
|
16. Storm drain inlet protection
|
|
|
17. Slope stabilization and erosion control measures
|
|
|
18. Vegetated swale
|
|
|
| Nonstructural BMPs |
19. Street sweeping
|
|
|
20. Fertilizer management
|
|
|
21. Other (describe):
|
|
|
Table 5
Suggested Best Management Practices
Institutional Source Controls
- No Littering Ordinance
- Pet Feces Removal Ordinance
- Chemical Use/Storage Ordinance
- Recycling Programs
- Public Education Programs
- Vacant Lot Cleanup Ordinance
- Spill Prevention Ordinance
- Nonstructural Source Controls
- Program to Prevent Illicit Discharges
- Street Sweeping
- Cleaning of Storm Drains
Minor Structural Source Controls
- Diversion Channels
- Grass Swales
- Natural Channels to Reduce Erosion
- Vegetative Controls on Exposed Soils
- Storm Sewer Outlet Protection
- Slope Stabilization and Erosion Control Measures
- Riprap Protection
Minor Structural Discharge Elimination Methods
- Development and Maintenance of Recharge Areas
- Development and Maintenance of Porous Pavement
- French Drains and Infiltration Trench
Moderate Structural Controls for Floatables/Oils Removal
- Development and Maintenance of Parking Lot Oil/Grease
Separators
- Development and Maintenance of Parking Lot and Rooftop
Runoff Storage with Outlet Protection
Major Structural Controls for Floatables/Oils Removal
- Detention Basin with Outlet Skimmer
- Wetlands Treatment Area
Major Structural Controls for Floatables, Metals,
Microorganisms, and Nutrient Removal
- Lime Precipitation, Filters, and
Chlorination/Dechlorination to Detention Basins
- Lime Precipitation, Chlorination/Dechlorination to
Wetlands
|
