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Requirements for Improvements and Development Proposals
November 1998

Introduction

This document was prepared to assist developers and consultants to design and manage projects in accordance with the policies of the Bassett Creek Watershed Management Plan. Copies of the Plan, as adopted by the Bassett Creek Watershed Management Commission, may be obtained from Barr Engineering Company. The cost of the Bassett Creek Watershed Management Plan is $25.

Note: The Requirements for Improvements and Development Proposals were modified by the Bassett Creek Watershed Management Commission's 2004 Watershed Management Plan. Please refer to section 4.2.2.4 of the September 2004 BCWMC Watershed Management Plan (Second Generation Plan) for information on the BCWMC's nondegradation policy and Level I treatment standards required watershed-wide. 

The Requirements for Improvements and Development Proposals document includes the following:

1. Requirements for Improvements and Development Proposals

This section includes general submittal requirements as set forth in the Bassett Creek Water Management Plan.

2. Appendix: Water Quality Management Policy

The Appendix includes the Commission's Water Quality Management Policy adopted September 14, 1994. The policy outlines specific requirements for development and redevelopment proposals. Water quality requirements are primarily based on the area of the proposed site and the receiving water body of site runoff.

The types of projects that must be submitted to the Commission for review are described in Part A.

A. Review of Improvements and Development Proposals

In order to facilitate the management of the water resources of the watershed, cooperation between the Bassett Creek Water Management Commission, member municipalities and concerned citizens is important. Consistent with policies of the Commission and the Joint Powers Agreement, the Commission desires to be informed of improvements or land development proposals which may affect the water and related resources of the watershed. The Commission will provide information and assistance in the preliminary planning stages of these improvements or land development proposals; however, because of the increasing number of developments requiring review, a review procedure is necessary. The Commission will limit their formal review of improvements and development proposals until the City staff has completed their review and established that the improvement or development proposals conform to their local municipal ordinances and regulations. The Commission will then review the proposals and submit their comments and recommendations to the City and other appropriate governmental agencies prior to the final approval or disapproval of the City or other governmental agency.

All persons, municipalities or other agencies proposing improvements or developments within the Bassett Creek watershed shall submit sufficient information to determine the effect that their proposal may have on the water resources of the watershed within the following guidelines:

1. Floodplains

Any proposal which would consist of a major alteration of existing structures, erection of new structures, filling, floodway encroachment, activities considered incompatible with acceptable floodplain uses or be subject to damage by the 100-year flood, and is located below the management envelope included in the Bassett Creek Water Management Plan must be submitted for Commission review. This section shall apply to structures such as bridges, footbridges, culverts, and pipe crossings of any nature, including sanitary sewer, water supply, and electrical and telephone lines.

2. Artificial Storage Sites

Any proposal within the limits of the proposed artificial storage sites established by the Bassett Creek Water Management Plan that may be in conflict with the minimum requirements as outlined in the Plan shall be submitted for Commission review.

3. Lakes and Wetlands

Proposals that may affect the water surface elevation, outlet storage capability or shoreline, or be incompatible with existing or proposed land use around the lakes and wetlands in the Bassett Creek watershed shall be submitted for Commission review.

4. Water Resources

Proposals that would alter remaining protected water resources in the watershed, involve the discharge of industrial or other waste to any watercourse or storm sewer, require extensive land alteration, are directly tributary to the watercourses of the watershed, or may otherwise affect the existing water quality shall be submitted for Commission review. In addition, the Commission shall be informed of the proposed application of chemicals or other treatments to lakes and ponds in the watershed.

5. Diversion of Surface Water Runoff

Proposals to provide intra- or inter-watershed diversion which may affect flood levels, lakes levels, and minimum streamflows in the watershed shall be submitted for Commission review.

6. Land Use Changes

Proposed changes in land use, zoning, and municipal drainage plans which may require the modification of the Water Management Plan shall be submitted for Commission review.

7. Appropriations

Ground or surface water appropriations which may temporarily or permanently alter the existing ground and surface water levels in the watershed shall be submitted for Commission review.

8. Utility Crossings

The construction of utilities through or paralleling the creek which require disturbance of the bed or banks of the creek or the diversion of the creek shall be submitted for Commission review.

9. Permit Applications

One copy of all permit applications made to the Minnesota Department of Natural Resources for work in public waters including supporting documentation shall be submitted for Commission review.

10. Water Quality Management Policy

The Commission's Water Quality Management Policy outlines criteria for the design of water quality enhancement features. The policy is intended to insure that water quality objectives are achieved throughout the watershed. A project must be designed in accordance with the water quality policy, when the proposed site meets one of the following development or redevelopment criteria:

a. A commercial, industrial, institutional or public development project involving a site of more than 0.5 acres of land where there is not existing commercial, industrial, institutional or public development.

b. A commercial, industrial, institutional or public redevelopment 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 project involving a site of more than 2 acres and which contains four or more proposed living units.

d. A residential redevelopment project involving more than 10 acres where there are four or more existing living units.

11. Construction Erosion Control

When construction is proposed that will result in more than 200 cubic yards of cut or fill or more than 10,000 square feet of grading, an erosion control plan must be submitted for Commission review. Specific requirements for erosion control plans are included in this report.

B. Procedure for Review of Development Proposals

The following procedures have been established for review of development proposals by the Bassett Creek Water Management Commission:

1. 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.

2. 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.

3. 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 and applicant approximately one week before each meeting.

4. 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.

5. The applicant shall submit an application form and two sets of plans and specifications for Commission review, one set to be returned to the municipality with Commission comments and one to be retained in the Commission files. The application form must be signed by City staff.

6. Refer to Water Quality Management Policy for required exhibits, if applicable. The Water Quality Management Policy requires preparation and submittal of project plans and a runoff water quality management plan.

C. Floodplain Regulations

The floodplain of a stream can be defined as that area adjacent to a stream which is inundated during times of flood. More specifically, the Minnesota Floodplain Management Act of 1969 defines the floodplain as that area adjoining a watercourse which is subject to inundation by a flood of 100-year frequency. Under the provisions of this act, local governmental units are required to adopt floodplain management ordinances which will include "the delineation of floodplains and floodways, the preservation of the capacity of the floodplain to carry and discharge regional floods, minimization of flood hazards, and the regulation of the use of land in the floodplain." Under the provisions of the required ordinances, no major alteration to existing structures, no new fill and no floodplain use which would unreasonably constrict flood flows will be allowed in the floodplain unless further provisions are made to fully compensate any detrimental effects.

The floodplain in the Water Management Plan has been estimated assuming existing channel conditions and runoff resulting from a 100-year storm occurring over the ultimately urbanized watershed. It represents that area which is subject to floodplain regulations until municipalities have completed storage and channel improvements which are a part of this or subsequent phases of the Water Management Plan. At the present time, all of the municipalities in the Bassett Creek watershed have adopted floodplain management ordinances and are restricting development of floodplain areas.

The following policies regarding floodplain regulation within the Bassett Creek watershed have been adopted:

1. The floodplain of Bassett Creek is defined as that area lying below the 100-year flood elevations as shown in the Water Management Plan of the Commission, or as subsequently revised due to channel improvement, storage site development, or requirements established by appropriate state or federal governmental agencies.

2. No land use of a type which would be damaged by flood waters is permitted within the floodplain.

3. Allowable types of land use which are consistent with the floodplain, such as recreation areas, parking lots, excavations and storage areas, agriculture, and other open space uses, would be allowed only to the extent that they would not increase flooding. Permanent storage piles, fences, and other obstructions which would collect debris or provide restriction to flood flows are not allowed.

4. Filling will generally not be allowed within that floodplain established in the Water Management Plan. If any municipality desires to fill within the established floodplain, such filling will require the approval of the Commission and require provisions for compensating storage and/or channel improvement so that the flood level shall not be increased at any point along the channel due to the fill.

5. Expansion of existing non-conforming land uses within the floodplain will be prohibited unless they are fully floodproofed in accordance with existing codes and regulations.

D. Water Resources

1. Water Quality Management

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. The Water Quality Management Policy was adopted to protect, preserve, and manage the water resources in the Bassett Creek watershed. The policy is discussed in Part A and a copy of the policy is provided in the appendix.

2. Control of Streambank Erosion and Streambed Degradation

Streambank erosion and streambed degradation control measures must:

a. Be employed whenever the net sediment transport for a reach of stream is greater than zero or whenever the stream's natural tendency to form meanders directly threatens damage to structures, utilities or natural amenities in public areas.

b. Include effective energy dissipation devices or stilling basins to prevent streambank or channel erosion at all stormwater outfalls. Specifically:

i. Outfalls with outlet velocities of less than 4 fps that project flows downstream into the channel in a direction of 30° or less from the normal flow direction generally shall not require energy dissipators or stilling basins, but they may need some riprap protection.

ii. Energy dissipators shall be sized to provide an average outlet velocity of no more than 6 fps. If riprap is also used, the average outlet velocity may be increased to 8 fps.

iii. Riprap stilling basins shall not be used where outlet velocities exceed 8 fps.

c. Specify riprap consisting of natural angular stone suitably graded by weight for the anticipated velocities.

d. Provide riprap to an adequate depth below the channel grade and to a height above the outfall or channel bottom so as to ensure that the riprap will not be undermined by scour or rendered ineffective by displacement.

e. Specify that riprap be placed over a suitably graded filter material or filter fabric to ensure that soil particles do not migrate through the riprap and reduce its stability.

f. Require that streambank stabilization and streambed degradation control structures be submitted for review by the Commission. The review will consider the need for the work, the adequacy of design, unique or special site conditions, energy dissipation, the potential for adverse effects, contributing factors, preservation of natural processes, and aesthetics.

3. Grit Chambers

Grit chambers for presettlement of stormwater must:

a. Be designed and sized to provide theoretical settlement of a 0.3-mm grit particle in still water at 10°C (based on Stoke's Law).

b. Be designed to provide sufficient storage volume for the settled particles consistent with the maintenance schedule.

c. Include a device to diffuse inflow and provide a relatively uniform distribution of flow over the cross section of the chamber.

d. Provide convenient access for equipment and maintenance personnel to the chamber site and into the chamber itself.

e. Be inspected at least three times a year (spring, summer and fall) to determine the volume of stored grit, and be cleaned immediately whenever significant grit has accumulated or there is a likelihood that the chamber will be full of grit before the next scheduled inspection.

4. Regional Detention Basins

Regional detention basins must:

a. Conform to municipalities stormwater runoff criteria.

b. Have water quality features designed based on Level I management classification as set forth in the water quality management policy.

5. Sediment Collection and Nutrient Entrapment

Wetlands used for sediment collection and nutrient entrapment must conform to the criteria for onsite or regional detention basins (whichever are appropriate). In addition, these wetlands and detention basins must:

a. Detain stormwater runoff in the first 1-1/2 feet of stormwater storage depth for an average period of no less than 48 hours.

b. Provide an outlet structure capable of draining the wetland or basin substantially dry to permit harvesting of wetland vegetation and removal of sediment.

c. Be harvested every fall (usually before October 15) by cutting the vegetation and removing the cuttings to an approved disposal site.

E. Sediment Control

Sediment, in terms of volume, ranks above domestic sewage, industrial wastewaters and chemicals as a major contributor to water pollution. In addition to filling stream channels, ponds and lakes, sediment reduces the oxygen content of water and it carries adsorbed phosphorus into streams and lakes where the phosphorus often stimulates algal blooms.

As development of the Bassett Creek watershed continues, sediment concentration in runoff will increase due to construction activity, unless effective sediment control measures are implemented. Increased sediment concentrations are also associated with runoff from streets, parking lots and other impervious surfaces associated with development.

In order to protect the water resources of the Bassett Creek watershed from increased sediment and associated water quality problems, the Commission has established the following policies to encourage land use planning and development that minimizes sediment yield:

1. The use of onsite settling ponds and/or filter fabric (silt fence) to control the sediment in runoff from construction sites, land clearing or grading operations, is required on all projects as set forth in this document.

2. The sedimentation ponds will be cleaned on a regular interval determined by calculating the sediment yield expected from the tributary watershed and comparing it to the capacity of the pond.

3. Preservation and improvement of marsh areas for sediment removal by natural filtration is recommended as long as the natural intrinsic value of the wetland is not adversely affected.

4. The design of storm sewer, stream channel improvements and channel crossings must consider temporary erosion control and sediment reduction measures to be implemented during construction and permanent measures to eliminate erosion and reduce sediment production during operations.

F. Requirements for Construction Erosion and Sediment Control Plans

1. 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).

2. 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.

3. In addition, the project proposer shall:

a. Provide specific measures to control erosion based on the grade and length of the slopes on the site, as follows:

(1) 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.

(2) Flow lengths up-slope from each silt fence shall not exceed 400 feet for slopes that have a grade of less than 3 percent.

(3) 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.

(4) Flow lengths up-slope from each silt fence shall not exceed 200 feet for slopes that have a grade of 3 to 10 percent.

(5) 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.

(6) 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.

b. 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.

c. 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.

d. 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.

e. 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.

f. 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.

g. 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.

h. Require that temporary or permanent mulch be disc-anchored and applied at a uniform rate of not less than 2 tons per acre.

i. 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.

j. 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.

k. 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.

l. 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).

G. Minnesota Department of Natural Resources Regulations

The following rules and regulations regarding water resource management are enforced by the Department of Natural Resources.

1. Permit Application

Any project constructed below the ordinary high water mark (OHW) which alters the course, current, or cross-section of state protected waters or wetlands is subject to the regulatory jurisdiction of the Minnesota Department of Natural Resources (DNR). This includes filling, excavation, construction of structures, water level control and drainage projects.

For lakes and wetlands, the OHW is defined as the highest water level that has been maintained for a sufficient period of time to leave evidence upon the landscape. The OHW is commonly that point where the natural vegetation changes from being predominantly aquatic in nature, to predominantly terrestrial. For watercourses, the OHW is the elevation of the top of the bank of the channel.

Any work requiring a permit and commencing without a permit is a violation of state law and constitutes a misdemeanor punishable by fines of up to $700 and/or 90 days in jail. If there is a question about whether or not a particular lake, marsh, or stream is a protected water or wetland, copies of the DNR protected waters map are available for public inspection at the DNR Metro Region, Soil and Water Conservation District offices, and County Auditor offices.

To ensure equitable allocation and the conservation of surface and groundwater resources, appropriation permits are required for any withdrawal of water exceeding 10,000 gallons per day or a total of 1 million gallons.

2. Land Use

The DNR Division of Waters works with local officials in the administration of floodplain and shoreland zoning controls. Floodplain controls provide protection to the community and its residents from flooding up to a 100-year flood event. Shoreland controls provide for the wise development of lakeshore and streams by specifying such things as lot size, setback, structure height and septic requirements.

Questions concerning the DNR's role in water resource management should be directed to the DNR Division of Waters, Metro Region, 1200 Warner Road, St. Paul, Minnesota 55106 (651-772-7910).

Appendix: Water Quality Management Policy

Water Quality Management Policy

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 1 of this document explains the rationale and strategy of the Bassett Creek Water Management Commission in establishing its Water Quality Management Policy. Part 2 describes the Commission's review process and its specific requirements for construction activities within the watershed.

Part 1: Rationale for the Policy

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 1 of this document outlines the Commission's objectives with regard to water quality in the Bassett Creek watershed. Part 2 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.

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

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

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 of the district 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

Particular requirements designed to achieve the Commission's water quality goals are outlined in Part 2 of this document. Part 2 of this document gives a complete listing of the water quality control standards and design criteria that have been adopted by the Commission. Part 2 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 2: 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 or developments within the Bassett Creek watershed for residential, commercial, industrial, institutional, or public roadway 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 / 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

Refer to Section B for review procedure.

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 beset 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 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 to 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 entire contributing drainage area, 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 he 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 sideslopes 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 wetland.

(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

Refer to Section F for criteria.

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 project includes 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 vasts 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

Table 5
Suggested Best Management Practices

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