Nonpoint Source Pilot Projects

One of the primary goals of the Rouge Project’s Nonpoint source (NPS) pollution studies is to implement pilot storm water pollution control programs to test their applicability in southeast Michigan and nationwide. Data derived from the pilot NPS pollution control programs will serve as the basis for developing cost-effective NPS control practices that can be implemented on a watershed-wide basis. The following eight best management practices (BMP’s) were selected for implementation within the Rouge watershed.

Extended Detention Pond
Wet Detention Pond
Swale
Sand Filter
Multi-Chambered Treatment Train
In-line Quality Devices
Sedimentation Basin
Source Control
Reports

Extended Detention Pond Evaluation

BMP Description
A dry detention basin is an impoundment formed by constructing a dam or embankment or by a combination of excavation and an embankment with an outlet structure to detain surface runoff for periods of generally around 24 to 30 hours. The primary objective of an extended detention pond is to attenuate peak flows, which is accomplished by regulating the outflow peak discharge and storing flood volumes within the detention basin. An emergency spillway is designed to pass extreme events to protect the embankment/dam from damage. Extended detention basins can also be designed to provide water quality benefits by removing pollutants attached to settle able particulates. Generally, an extended detention pond is dry between storms.

Why is this BMP being tested?
This pilot BMP was selected for demonstration in order to evaluate the most prevalent type of BMP in the Rouge watershed: an existing extended dry detention pond with a standpipe/gravel filter outlet structure. This demonstration will provide information on the benefits and costs of this type of BMP, including operations and maintenance requirements. The information from this demonstration will be used to determine if existing design criteria for new structural BMPs should be modified, if existing BMPs should be retrofit to provide increased benefits, and what the costs of these actions may be. Water quantity and water quality benefits of watershed-wide applications of this type of BMP will be estimated and included in the final report.

Many communities in the Rouge River Watershed require storm water management BMPs for new development and extended detention ponds are the most common structural BMP employed in the watershed. However, many storm water ponds in the Rouge River Watershed provide peak flow attenuation only, and generally are not designed to provide water quality control. Because this type of detention pond is prevalent in the watershed, characterizing its performance is a necessary step in developing a watershed management plan for the Rouge River.

Site Characteristics
This BMP is an existing extended dry detention pond, which serves a drainage area of 18 acres developed primarily into multifamily condominiums. The extended dry detention water quality volume in the existing pond is 1.47 acre-feet, which provides 0.98 inches of storage over the entire drainage area. This volume is sufficient to capture the "first flush" of runoff from the drainage area. In addition, the hydraulic analysis performed on the site showed that the pond takes more than a day to completely drain after a storm event which allows opportunity for particulate matter to settle.

Design Characteristics
This pond was designed using the Oakland County Simplified Method (10-year Storm). These ponds are generally designed to briefly detain the drainage area runoff from a 10-year storm event (approximately 0.8 inches for residential land use), while allowing a peak outflow rate of 0.2 cubic feet per second (cfs) per acre of developed land.

Construction Considerations
This BMP pond was constructed by developers in 1987. The pond was not modified by the Rouge Project for this evaluation.

Operations and Maintenance Considerations
The RPO team performed the following routine operation and maintenance (O&M) activities during the evaluation period:

• Check outlet regularly for clogging.
• Check banks and bottom of pond for erosion and contact owner for correction if necessary.
• Check for sediment resuspension and contact owner for sediment removal if necessary.
• General site maintenance continues to be performed by the site owner.

The final report for this project will include recommendations for routine and non-routine O&M for this BMP. Costs and benefits will also be documented.

Preliminary Assessment of Benefits
Flow and water quality monitoring and sampling equipment was installed at this site from July, 1995 to 1997. Pollutant removal rates for TSS were up to sixty percent per event and for BOD up to thirty percent.

Costs
Capital costs for this BMP were borne by the developer in 1987 and are not available for reporting. Operations and maintenance costs are ongoing and will be summarized in the final report.

General Applicability of BMP

• Used when the objective is to attenuate peak flows and remove particulate pollutants through settling.
• Used typically in urbanized and agricultural areas.

Wet Detention Pond Evaluation

Description
This type of detention pond BMP has a permanent water pool. The objective of this BMP is to attenuate peak flows, by controlling the outflow peak discharge and storing flood volumes within the detention basin. An emergency spillway is designed to pass extreme events to protect the embankment from damage. Wet detention ponds can also be designed to provide water quality benefits by achieving a high level of particulate and some dissolved contaminant removals.

Why is this BMP being tested?
This pilot BMP was selected for demonstration in order to evaluate the long term pollutant removal efficiency of this type of BMP in the Rouge River Watershed. This demonstration will provide information on the benefits and costs of this type of BMP, including operations and maintenance requirements. The information from this demonstration will be used to determine if existing design criteria for new structural BMPs should be modified, if existing BMPs should be retrofit to provide increased benefits, and what the costs of these actions may be. Water quantity and water quality benefits of watershed-wide application of this type of BMP will be estimated and included in the final report.

Wet detention ponds in the Rouge River Watershed are generally designed to provide peak flow attenuation as dry detention ponds, but include a permanent pool which may provide some water quality benefits as well. In most cases permanent pool storage volume is established based on aesthetics rather than specific water quality design criteria. Consequently, the residence time in the permanent pool may not be sufficient to maximize pollutant removal efficiency in the pond.

Site Characteristics
This BMP is an existing wet detention pond which serves a drainage area of 85 acres consisting of primarily public land use (e.g., school, police department, civic center). The permanent pool volume for the existing pond is estimated at 7.8 acre-feet, or 1.1 inches over the entire drainage area. This value is equal to the required 1.1 inches which will provide an average two week residence time, based on local rainfall and hydrology.

Inflows to this pond are from one 42-inch pipe from the west, one 36-inch pipe from the northwest, and two small ditches from the north and northeast. The two ditches are expected to carry negligible flows and these flows will be field verified during wet weather. The outlet consists of one 15-inch pipe and an overflow structure, both draining to a 36-inch pipe at the southwest corner. The slope of the banks is approximately 4:1 with maintained grass. The vegetation growth in the pond is low. The pond is not fenced and is easily accessed from the Ella Mea Park.

Design Characteristics
This pond was designed using the methods recommended by the Oakland County Drain Commission (OCDC). Ponds designed using the OCDC criteria generally briefly detain the drainage area runoff from a 10-year storm event (approximately 0.8 inches for residential land use), while allowing a peak outflow rate of 0.2 cfs per acre of developed land.

Construction Considerations
This BMP pond was constructed by the city of Novi in 1983. The pond was not modified by the Rouge Project for this evaluation.

Operations and Maintenance Considerations
The RPO team will perform the following routine operation and maintenance (O&M) activities:

• Check pond for floatables and sediment build up and contact the city for removals.
• Check for spot erosion in banks and contact the city for correction if necessary.
• Check for mosquitoes.

The final report for this project will include recommendations for routine and non-routine O & M for this BMP. Costs and benefits will also be documented.

Assessment of Benefits
Flow and water quality monitoring and sampling equipment are expected to be installed in the spring 1996. Complete evaluation of the pond performance will be conducted after 15 to 20 storm events have been monitored and sampled.

General Applicability of BMP

• Used when the objective is to achieve high level of particulate and some dissolved contaminant removal.
• Used typically with large regional tributary areas.
• Used when passive recreation (e.g. bird watching, wildlife habitat) is desired.

Swale Evaluation

BMP Description
This BMP is a shallow broad-bottomed ditch in which dense grass growth is established. This grassy conveyance system provides storm water pollutant removal through physical filtration of runoff through the grass cover, and infiltration of runoff into the underlying soil.

Why is this BMP being tested?
This Rouge pilot BMP was selected for demonstration in order to monitor and evaluate the pollutant removal efficiency of a constructed grassy swale. This demonstration provided information on swale retrofit BMP benefits and costs, including operations and maintenance requirements. Also, a local highway runoff EMC database was established. This pilot BMP will better define long-term and seasonal pollutant removal efficiencies of swales. The information from this demonstration retrofit will be used to determine if existing design criteria for new swale BMPs should be modified, if existing BMPs should be retrofitted to provide increased benefits, and the estimated costs for these actions. Water quantity and water quality benefits of a watershed-wide application of this type of BMP will be estimated and included in the final report.

There is potential for swale retrofits within the Rouge River Watershed in new residential subdivisions and state and county road drainage facilities. Swale retrofits are also a potential in the Rouge River Watershed in existing roads and highways, right-of-ways and public facilities where swales currently exist, but may not have been designed for quality control.

Site Characteristics
The pilot swale was constructed within the I-696 right-of-way next to the intersection of I-696 and Minnow Pond Drain. The grassy swale is located at an existing storm sewer outfall that currently discharges untreated highway runoff directly to the Minnow Pond Drain. The drainage area to the proposed swale is approximately 2.4 acres.

Design Characteristics
The designed swale is 160 feet long at a slope of 2 percent or less, that should provide an average hydraulic residence time of more than 10 minutes. The swale width is four feet so it will not be difficult for incoming runoff to spread equally throughout the swale. The driving factors behind this design are to maximize effectiveness of filtration through the grass and infiltration into the soil, by minimizing flow depths and maximizing the residence time in the swale. The design will also include a diversion structure to bypass some of the runoff from extreme storm events directly into the Minnow Pond Drain. The diversion should protect the swale against erosion that could occur during high flow conditions.

The general design criteria used with this swale to provide effective removal of pollutants have been recommended by Horner, 1991 and FHWA, 1989. This general criteria is:

• Minimum hydraulic residence time of about 10 minutes for the average rainfall event.
• Maximum flow depth of 3 inches for the average rainfall event.
• Maximum swale width of 8 feet.
• Minimum swale length of 100 feet (for bottom slopes less than 2 percent) to 150 feet (for bottom slopes in excess of 2 percent).

Construction Considerations
This project required regrading the I-696 right-of-way to construct the swale, clearing and grubbing, adding topsoil and geofabric, construction of a diversion structure with riprap overflow to reroute large storms, restoration (seeding, fertilization, mulching) and installation of two monitoring flumes with approach channels at the upstream and downstream ends of the swale for water monitoring and sampling. Information regarding construction efforts and costs will be documented during construction and included in the final report.

Operation and Maintenance Considerations
Expected O & M requirements for this retrofit are as follows:

• Maintain an evenly spread flow by keeping the swale free of leaves, branches, rocks, litter and other debris which accumulates in swale. This shall be accomplished during a monthly visit to the site.
• Remove sediment from the swale deposited during high intensity storm events and mend channelized areas of the swale.
• Reseed any swale areas that have poor grass growth, as needed.

To maintain thicker and healthier grass, mowing of the swale area is required once or twice a month, depending on weather condition. Grass heights should be maintained around six to eight inches during the monitoring period. Grass clippings should be removed promptly from the swale and disposed of in such a way so that reentry into the receiving water is avoided.

Watering of the swale grass is required to keep the grass healthy. At least one watering visit per week is required, depending upon weather conditions.

The final report for this project will include recommendations for routine and non-routine O & M for this BMP. Costs and benefits will also be documented.

Assessment of Benefits
Water quality improvement evaluation for the selected pilot site will be added to the final report after the completion of the monitoring and assessment of this BMP.

General Applicability of BMP

• Used when the objective is to remove particulate pollutants through filtration.
• Used typically in urbanized subdivisions, roads and highway right-of-ways and agricultural areas.
• Limited to treating a few acres.

Sand Filter Evaluation

BMP Description
This BMP is a two-chambered linear concrete structure that improves water quality of runoff by providing sedimentation and filtration to the storm water runoff.

Why is this BMP being tested?
This Rouge pilot BMP was selected for demonstration in order to evaluate the incremental pollutant removal efficiency attributable to a linear sand filter. This demonstration will provide information on this retrofit BMP benefits and costs, including operations and maintenance requirements. The information from this demonstration retrofit will be used to determine if existing design criteria for new sand filter BMPs should be modified, if existing BMPs should be retrofitted to provide increased benefits, and the estimated costs of these actions.

This structure is currently not used in the Rouge River Watershed. Region V of the Environmental Protection Agency recommended a demonstration of sand filter technology in the Midwest region as part of the Rouge Project. Sand filters have been successfully implemented in the State of Delaware, and in such cities as Austin, Texas and Seattle, Washington; however, the nonpoint source literature reveals no information regarding sand filter performance in the Midwestern United States.

Applicability of sand filters in the watershed is considered to be substantial. Sand filters could be installed in fully-developed areas in which land for more conventional and less expensive BMPs is unavailable. Example locations could include small convenience stores, industrial sites, small tributaries to lakes, and other identified problem areas.

Site Characteristics
The site selected for this pilot BMP serves a 0.9 acre parking lot at two senior citizen housing complexes in the City of Wayne, Michigan. The drainage area to the filter is approximately 0.8 acres. This filter inflow is a sheet flow from the parking lot through a linear steel grating.

Design Characteristics
The filter consists of two chambers. The first chamber is a sedimentation chamber, and the second is the filtration chamber. Runoff enters the filter structure through grates located in the parking lot next to an existing curb. The runoff overflows the weir between the two chambers and passes through 18 inches sand filtration layer and a 4 inches gravel drain bed. A 4 inches perforated collector pipe runs along the length of the gravel layer to collect the filtered runoff. Geotechnical filter fabric is installed between the sand and the gravel layers. There is a clearwell chamber in the downstream side of the structure to capture the filtered runoff from the perforated pipe and the overflow runoff from the filter overflow weir.

The site and the filter was modeled using P8. The predicted total runoff volume "captured" depends on the storage volume above the filtration and sedimentation chambers, the area and the depth of the filtration material, and permeability of the filtration material. The available depth of storage volume above the filtering material on this site is 1.8 feet. The width of the two chambers was fixed at 2 feet each. The design filtering material permeability is 3.5 ft/day. This permeability value is recommended in the Texas, California and Virginia BMP manuals.

Analysis using the filter model was performed on three values of permeability to test the model sensitivity for total volume "captured" (i.e. passes through the sand filter) and TSS removal efficiency. Results of the P8 model runs are shown in the following tables. The first table shows the percent volume captured through the filter and the percent TSS removal efficiency by the filter using a 10-year rainfall record. The second table shows the percent volume captured through the filter and the percent TSS removal efficiency by the filter using several single design storms. Based on these results, the recommended sand filter size is 80 feet long and a width of 2 feet for each chamber. This size is chosen based on 60% volume captured through the filter and 80% TSS removal efficiency from the drainage area runoff and using a sand permeability of 3.5 ft/day.

Construction Characteristics
This project includes construction of the sand filter structure, connecting outlet to existing storm sewer manhole, minor paving and site restoration. The construction cost was approximately $100,000.

Operation and Maintenance Considerations
Expected Operation and maintenance requirements for this retrofit are as follows:

• The filtering material must be cleaned, and possibly replaced, when the treatment rate of the filter media becomes unacceptable due to clogging.
• Sedimentation chamber must be cleaned as required depending on the volume of sediments in the chamber.

The final report for this project will include recommendations for routine and non-routine O & M for this BMP.

Assessment of Benefits
Water quality improvement evaluation for the selected pilot site will be added to the final report after the completion of the monitoring and assessment of this BMP.

General Applicability of BMP

• The objective is to remove particulate pollutants through filtration.
• Placed underground.
• May require less space than other treatment control BMPs.
• Limited to treating a few acres.
• Used typically in parking lots.

Multi-Chamber Treatment Train Evaluation

Multi-Chambered Treatment Train

BMP Description
The multi-chamber treatment train is a three-chambered system. The first chamber is a grit chamber to remove the largest particles; the second chamber is for settling and absorption; the third chamber completes the process and consists of a filtration system.

Why is this BMP being tested?
This Rouge pilot BMP was selected for demonstration in order to evaluate the incremental pollutant removal efficiency attributable to the MCTTs recently constructed in Wisconsin. This demonstration provides information on this BMP's benefits and costs, including operations and maintenance requirements. The information from this BMP will be used to determine if existing design criteria for new sand filter BMPs should be modified, if existing BMPs should be retrofitted to provide increased benefits, and the estimated costs of these actions. Water quantity and water quality benefits of watershed-wide application of this type of BMP will be estimated and included in the final report.

This structure is currently not used in the Rouge River Watershed. Multi-Chamber Treatment Trains (MCTTs) have been implemented in the State of Alabama and recently constructed on two sites in Wisconsin.

Applicability of MCTTs in gas stations, small convenience stores and industrial sites in the watershed are possible if this structure is proven to be cost effective.

Design Characteristics
Preliminary research of the MCTT has been conducted by Dr. Robert Pitt of the University of Alabama at Birmingham. Dr. Pitt developed the MCTT in conjunction with a 319 grant from the United States Environmental Protection Agency which is being coordinated by Mr. Richard Field.

The MCTT is a three-chambered system. The first chamber is the catch basin chamber that acts as grit chamber to remove the largest particles, and will also include a small column of packing balls with a crosscurrent air flow to remove highly volatile components. The second chamber is the main settling chamber that includes a tube or plate settlers to enhance sedimentation. Sorbent pads are contained within the chamber to enhance the removal of the floatable hydrocarbons. A treatment period of 20 to 70 hours is suggested to settle finer particles and to control oil residues. The third chamber, the filtration chamber, contains mixed media sand and peat slow filter with a special sorption filter fabric layer. The goal of the MCTT is to have a 70% to 90% toxicity control in the main settling chamber.

The MCTT design process was already underway with the assistance of Dr. Pitt. The location of the MCTT within the city of Westland DPS yard storm sewer line was under evaluation. Depth of the storm sewer system and the drainage area contributing to each manhole inlet effects the sizing and location of the MCTT. The detailed design of this structure in Westland was halted because the city of Westland decided not to allow the construction at their DPS yard. The design of the MCTTs recently constructed in Wisconsin will be documented in the final report.

Preliminary results from the University of Alabama at Birmingham study show that the treatment unit is possibly providing substantial reductions in storm water toxicants (both in particulate and filtered phases), organics, and suspended solids. Slight increases in turbidity and color and about a unit in pH reduction also occurred during the filtration step. According to the study, the filter unit appears to be responsible for most of the toxicity reductions. However, the main settling chamber also resulted in substantial reductions in the dissolved toxicity fraction, total and dissolved COD, suspended solids, turbidity, and color. The catch basin/grit chamber also showed suspended solids reductions. In summary, the use of the MCTT is seen to be capable of reducing a broad range of storm water pollutants that have been shown to cause substantial receiving water problems.

Operation and Maintenance Considerations
Expected Operation and maintenance requirements for this retrofit are as follows:

• The filtering material must be cleaned, and possibly replaced, when the treatment rate of the filter media becomes unacceptable due to clogging.
• Sedimentation chamber must be cleaned as required depending on the volume of sediments in the chamber.

The final report for this project will include recommendations for O & M for this BMP. Costs and benefits will also be documented.

Assessment of Benefits
Water quality improvement evaluation for the selected pilot site will be added to the final report after the completion of the monitoring and assessment of this BMP.

General Applicability of BMP

• The objective is to remove particulate pollutants through settling, absorption and filtration.
• Must be placed underground.
• Requires space.
• Limited to treating a few acres.
• To be used typically in gas stations.

In-Line Quality Devices

BMP Description
In-line quality devices are storm sewer insert type devices which are used to catch sediments, filter, and absorb hydrocarbon products from the storm water runoff in the catch basin manhole structure before entering the storm sewer system.

Why is this BMP being tested?
This Rouge pilot BMP was selected for demonstration in order to evaluate a low cost storm inlet insert type devices in the Rouge Watershed. This demonstration will provide information on the benefits and costs of these devices, including operations and maintenance requirements. The information from these devices will be used to determine if existing design criteria should be modified and if existing storm sewer inlet manholes should be retrofitted with these devices to provide pollutant removals, and the estimated costs of these actions. Water quantity and water quality benefits of a watershed-wide application of this type of BMP will be estimated and included in the final report.

These devices are not used in the Rouge River Watershed. Unique designs of these devices were used in the States of Florida and Washington. Applicability of these devices in gas stations, small convenience stores and small parking lots in the watershed are possible due to their low cost.

Site Characteristics
The selected site for this pilot BMP is a gas station with a convenience store in Livonia, Michigan. The drainage areas for the two storm sewer inlets on site are 0.6 and 0.16 acres consecutively.

Design Characteristics
This BMP is considered to be a simple retrofit to improve storm water quality before it enters the storm sewer system. Catch basin insert type units were targeted for this type of BMP. These devices are presently manufactured and marketed by vendors around the United States and Canada. Most of vendors for these devices were located in Florida and Washington State due to the interest of these municipalities with this type of water quality improvement retrofit. Many vendors were contacted and thereafter the following four units were chosen for assessment:

Hydro-Cartridge: by Geotechnical Marine Corporation, Hialeah Gardens, Florida.
Stream Guard: by Foss Environmental, Seattle Washington.
Gully Washer: by Aqua-Net Incorporation Seattle, Washington.
Grate Inlet Skimmer Box: by Suntree Isles Incorporation Cape Canaveral, Florida.

The objective of these devices is to provide an insert type unit that could be installed in existing storm water inlet manholes by only lifting the inlet manhole cover and inserting the unit. Units are sized to fit in existing inlet manholes. These units consist of sediment material to capture solids and absorbent material to capture oil products. Overflow outlet is also provided to allow for large runoff to flow through.

Construction Considerations
Four devices were obtained from vendors and two are currently installed at the site. Construction and revisions to the site were not required. The installation of these devices were performed by the RPO team.

Operations and Maintenance Considerations
The RPO team performed the following operation and maintenance (O&M) activities:

• Regular check for sediment and record the frequency of sediment cleaning related to each device. Regular sediment check is important to avoid clogging.
• Check on absorbent material and replace when required.

The final report for this project will include recommendations for routine and non-routine O & M for this BMP. Costs and benefits will also be documented.

Assessment of Benefits
The devices were in operation from October 1995 to June 1997. Results are shown below:

In-line Quality Devices Sediment Removal Summary

In-line Quality Devices Oil Adsorption Summary

Costs
A cost summary is shown below:

In-line Quality Devices Capital Cost Summary
(1995 costs)

General Applicability of BMP

• The objective is to remove particulate pollutants through settling, absorption and filtration.
• Placed in storm sewer inlet manholes.
• Does not require new site construction.
• Limited to treating a few acres.
• To be used typically in gas stations, small convenience stores and small parking lots.

General Limitations of BMP

• May require more frequent maintenance.
• Storm water quality volume is small.
• Dissolved pollutants are not captured.
• Clogging potential if not maintained properly.

Sedimentation Basin Evaluation

Description
Sedimentation basins (or regional detention basin) are usually considered to be structures that are strategically located to serve a number of individual developments. The basin is an impoundment formed by constructing a dam or embankment, or by a combination of excavation and an embankment with an outlet structure to detain first flush surface runoff for periods of generally around 24 hours. This basin operates similarly to an extended detention pond, but is designed to capture the first flush flow only and divert flood flows away from the basin. The primary objective of the sedimentation basin is to provide water quality benefits by removing pollutants attached to settle able particulates from the first flush volume captured by the basin.

Why is this BMP being tested?
Useful information associated with the analysis of a first flush sediment pond such as the one proposed for the City of Novi would include sediment deposition rates, operations and maintenance requirements, pollutant removal efficiency, capital costs, and operation and maintenance costs. A detailed analysis could be performed to establish guidelines in preventing sedimentation and disruption of existing wetland systems downstream from construction activities. Information obtained could be used as the basis for a comprehensive Rouge River Watershed soil erosion and sedimentation program similar to that implemented in Maryland.

The regional pond concept has been used in several applications throughout the Rouge River Watershed. The city of Novi, a rapidly-developing community, implemented a Storm water Master Plan in 1983 which was based on the regional detention pond concept. Since the implementation of the master plan, many regional detention ponds have been constructed within the city.

Although the regional approach to storm water detention was once encouraged in the Rouge River Watershed by local regulatory officials, these facilities are now discouraged. Officials believe that the regional concept results in wetland deterioration due to storm water sediment loadings. Monitoring data and/or documented qualitative data to substantiate these beliefs are not currently available.

Application of the first flush sedimentation pond in the Rouge River Watershed would be possible in areas where regional ponds are or will be used for water quantity control, and additional localized water quality control is desirable. For new developments in which both water quantity and water quality control are desired, a wet pond or an extended detention dry pond may be constructed, and a separate first flush sedimentation pond would not be necessary.

Site Characteristics
The sedimentation pond is constructed at the downstream end of a 53 by 34 inch storm sewer pipe that discharges into a regional detention pond. The tributary area consists of 93 acres of residential land (which is currently about 80 percent developed) and three acres of road drainage with overall 30 percent impervious area. Details on pond configuration are identified in the design characteristics section below.

Design Characteristics
The first flush sedimentation pond in the City of Novi was designed by the consulting firm of J.C.K. and Associates Inc. The MDNR has reviewed the design and issued a permit for construction of this project. The RPO has also reviewed the design and agreed that the design was acceptable.

The storm sewers draining to the sediment basin are designed to handle the 100-year storm event, based on peak flows calculated using the Rational Method. The sewer capacities were estimated using Manning's Equation.

The sedimentation basin is sized for three times the runoff volume from the mean rainfall event (0.21 inches). This event is applied to the impervious tributary area only, and a runoff coefficient of 0.95 is assumed. Given the impervious upstream area of 28 acres, and the values above, the required water quality volume is 1.40 acre-feet, which corresponds to 0.6 inches of storage per impervious acre in the drainage area.

Inflow to the basin discharges from a 53 by 34 inch storm sewer pipe. The pond captures the first flush of runoff and allows flows in excess of this first flush volume to bypass the sediment basin through a diversion structure. The bypass prevents scouring and resuspension of collected sediments in the sediment basin. A forebay and an underdrain system are also provided to enhance sedimentation. A 6-inch perforated PVC outlet is provided for a 24-hour drawdown of the water quality volume. The detention period of 24 hours should provide enough time for settling of the particulate matter conveyed by the storm water runoff. In addition, an oil/water separator is proposed directly upstream of the sedimentation basin.

Construction Considerations
This pond in will be constructed by the City of Novi in the spring of 1996. The pond will not modified by the Rouge Project for this evaluation. Information regarding the construction efforts conducted by the City of Novi and pond costs will be documented and included in the final report.

Operations and Maintenance Considerations
The City of Novi will perform the following routine operation and maintenance (O&M) activities:

• Check banks and bottom surface of basin for erosion.
• Check the volume of sediment accumulated and possibility of resuspension.

The final report for this project will include recommendations for routine and non-routine O & M for this BMP. Costs and benefits will also be documented.

Assessment of Benefits
Water quality improvement evaluation for this sedimentation ponds will be added to the final report after the completion of the monitoring and assessment of this BMP. The efficiency performance for this pond should be similar to an extended detention pond.

Costs
Capital costs for this BMP will be borne by the City of Novi and will be documented after bid opening in early 1996. Operations and maintenance costs will be summarized in the final report.

General Applicability of BMP

• Used when the objective is to remove particulate pollutants through settling.
• Used typically in areas where considerable new construction is performed upstream of the pond.
• Used typically to protect downstream wetlands or development from high sediment deposits.

Reports from Products Catalog for Rouge NPS Pilot Projects (Structural)

NPS-SR06.00 - Specifications and Contract Documents for I-696/Minnow Pond Drain Swale Retrofit Construction

NPS-SR10.00 - Cost Estimating Guidelines: Best Management Practices and Engineering Controls

NPS-TPM37.00 - Operational And Maintenance Manual

NPS-TPM40.00 - BMP#1: Extended Detention Pond Evaluation For Period July 15, 1995 - December 31, 1995

NPS-TPM45.00 - Analysis of Existing Detention Ponds in the Rouge River Watershed

NPS-TPM46.00 - Guidelines for Conducting a Detention Pond Inventory

NPS-TM27.00 - Middle Rouge Detention Basin Inventory

NPS-TM31.00 - Pilot Structural Best Management Practice Site Selection and Assessment

NPS-TR03.00 - Nonpoint Source Data Assessment and Field Investigation

NPS01A-TR02.01 - Pilot Best Management Practice Projects (319 Grant)

NPS-TMP59 - Evaluation of On-line Media Filters
in the Rouge River Watershed

Please address all comments and suggestions about the contents of this Web page to rougeweb@co.wayne.mi.us.

The Rouge River National Wet Weather Demonstration Project is funded, in part, by the United States Environmental Protection Agency (EPA) Grants #XP995743-01, -02, -03, -04, -05, -06, -08 and C-264000-01.