City of Roseville, MI Article IV Stormwater Systems

[Adopted 6-28-2019 by Ord. No. 1311[1]]

[1] Editor's Note: This ordinance repealed former Art. IV, Stormwater Systems, adopted 10-28-2014 by Ord. No. 1274.

§ 256-50 Construction plan design standards for stormwater systems.

Unless otherwise noted, the following design standards and requirements apply to construction plans submitted for review by the City of Roseville for all types of developments or drain-related construction activities.

§ 256-51 Prevention, control, and reduction of stormwater pollutants by use of best management practices.

A. With this article, the City adopts the requirements identifying best management practices for any activity, operation, or facility which may cause or contribute to pollution or contamination of stormwater, the storm drain system, or waters of the state. The owner or operator of a commercial or industrial establishment shall provide, at their own expense, reasonable protection from accidental discharge of prohibited materials or other wastes into the municipal separate storm sewer system (MS4) or watercourses through the use of these structural and nonstructural BMPs.

B. Further, any person responsible for a property or premises, which is, or may be, the source of an illicit discharge, may be required to implement, at said person's expense, additional structural and nonstructural BMPs to prevent the further discharge of pollutants to the municipal separate storm sewer system. Compliance with all terms and conditions of a valid NPDES permit authorizing the discharge of stormwater associated with industrial activity, to the extent practicable, shall be deemed compliance with the provisions of this section. These BMPs shall be part of a stormwater pollution prevention plan (SWPPP) as necessary for compliance with requirements of the NPDES permit.

C. "Reasonable protection" for the purposes of this article shall mean the installation, operation and maintenance of the required structural and/or nonstructural BMPs, implementation and documentation of the BMPs operation and maintenance procedures and practices; and pollution prevention and good housekeeping (P2/GH) procedures and practices necessary for the establishment to comply with state and federal stormwater regulations.

§ 256-52 General requirements.

The following general stormwater management requirements apply to all new developments and redevelopments in the City of Roseville.

A. The design process shall begin by identifying sensitive areas located on the site and laying out the site to protect the sensitive areas.

B. Best management practices. Best management practices (BMPs) that reduce the amount of stormwater runoff and improve water quality are required and shall be designed on a site-specific basis. Rate and volume reduction BMPs shall be used to protect open channel storm drains. All BMPs shall be included on the plans and will be subject to review and approval by the City of Roseville, the Macomb County Public Works Office (MCPWO) and the Michigan Department of Environment, Great Lakes and Energy (EGLE formerly MDEQ), or the authorized state regulatory agency, as necessary for permits.

(1) During construction, all sites that disturb one or more acres of land, or are located within 500 feet of waters of the state, BMP usage shall be monitored and recorded in the weekly soil erosion sedimentation control (SESC) reports. In such cases, weekly SESC reports shall also be required during construction.

(2) Land uses with potential for significant pollutant loading ("hot spots"), including but not limited to gas stations, commercial vehicle maintenance and repair, auto recyclers, recycling centers, and scrap yards, will require BMPs which address regulation of the specific hazard as determined by the MCPWO or the City Engineer. In such cases, weekly SESC reports shall also be required.

(3) The developer/owner shall include a long-term operation and maintenance schedule for all permanent BMPs. A maintenance agreement between the developer/owner and the City is necessary for permanent BMPs which shall include but not be limited to: inspection of structural or vegetative BMPs, performance of maintenance and corrective actions when BMPs are neglected by the owner, and deed restrictions. All such maintenance agreements shall be binding on the property and shall remain in effect in the event the property ownership is transferred or sold.

C. On-site management of stormwater is required first and foremost, unless site constraints consistent with the flow chart preclude this approach.

D. Stormwater shall be managed using four standards: channel protection, flood control, water quality, and pretreatment to protect both water resources and real property.

E. Channel protection control system shall be provided on all new developments connecting to an open drain to protect the drain's channel and banks from erosion due to the increased flow. Direct discharges to the Macomb County Public Works Office drains are generally governed by MCPWO design standards. Open drains within the City of Roseville jurisdiction shall be protected by incorporating a restricted flow of the channel protection volume. It is required that the postdevelopment project site runoff volume and peak flow rate must be maintained at or below predevelopment levels for all storms up to the two-year, twenty-four-hour event. "Predevelopment level" means the runoff flow volume and rate for the last land use prior to the planned new development or redevelopment. Compliance with this requirement is determined by calculating the existing ("predevelopment") and postdevelopment runoff volume and rate for the two-year and smaller storm events. The method is described in the Department of Environmental Quality (DEQ) publication, Computing Flood Discharges for Small Ungaged Watersheds, dated July 2003 (updated January 22, 2010).

(1) If it is demonstrated using the Alternative Approach Flowchart (Exhibit A[1]) that the development cannot meet the required channel protection performance standard, the development may propose incorporation of green infrastructure [i.e., rain gardens, green (vegetated) roofs, permeable pavement, impervious cover removal, use of trees, etc.] This includes instances where site conditions (e.g., space limitations or tight soils that prevent infiltration, or soil or groundwater contamination, "hot spots") challenge or prohibit feasibility of maintaining the project site's predevelopment runoff levels for all storms up to the two-year, twenty-four-hour event. Green infrastructure shall be allowed under all circumstances consistent with the flowchart. Review of these proposals will be consistent with the SEMCOG Low Impact Development Manual for Michigan, 2008 or current standards.

[1] Editor's Note: Exhibit A is on file in the City offices.

F. Flood control shall be provided for all sites through retention or detention. On-site detention or retention of stormwater is required of all new developments or redevelopments to maintain the peak outflow to a rate similar to the predevelopment runoff rate. On-site flood control may be reduced or waived for direct discharges to large lakes and rivers if the developer demonstrates no negative impacts, or if provided in a regional facility with adequate upstream infrastructure.

G. Overland flow routes and the extent of high water levels for the 100-year storm shall be identified for all sites.

H. Water quality treatment shall be provided for all sites. A minimum treatment volume equal to one inch of runoff from the project site is required. A minimum volume of 900 cubic feet per acre is required for directly connected disturbed pervious areas (i.e., lawns). BMPs shall be designed to reduce postdevelopment solids loadings by 80% or to not exceed solids loadings of 80 milligrams per liter. Developments that disturb less than one acre, and are not part of a larger common plan of development or sale, may be exempted from the City's water quality treatment standards as approved by the City Engineer.

I. Pretreatment is required for infiltration, filtration and detention BMPs for ease of maintenance and to protect BMP integrity and preserve longevity.

J. Stormwater discharges from activities with a high risk for an accidental spill of pollutants (stormwater hot spots) shall provide spill containment.

K. The design maximum release rate, volume or concentration of stormwater discharged from a site shall not exceed the capacity of existing infrastructure or cause impairment to the off-site receiving area. Evaluation of the existing outlet must be performed and an adequate outlet must be provided.

L. The use of many decentralized low-impact development (LID) BMPs is not mandated but is encouraged on private sites.

M. Unless otherwise noted, hydraulic and hydrologic calculations (including rainfall volumes and distributions) shall be based on current EGLE standards (i.e., NOAA Atlas 14) and procedures in place at the time of application.

N. Construction plans for a phased development shall show the existing and/or proposed drainage systems for all prior phases of the development, unless the drainage system for the current phase is entirely independent of the prior phases. Furthermore, drainage plans for a phase of a development must not be dependent upon work planned to be performed in a future phase.

O. Plans shall include a grading plan showing existing and proposed topographic contour lines and proposed finish floor and basement floor elevations.

P. All existing natural or man-made watercourses shall be shown on the plans. The proposed changes to the site must not interfere with common law natural flow rights. Existing watercourses must be preserved or relocated, or the flow otherwise accommodated by the proposed plans. Provisions for the maintenance of the watercourse must be included in the deed restriction or an equivalent legally binding agreement. EGLE and/or the Army Corps of Engineers may also require permits for changes made to such watercourses.

Q. No construction activities shall be allowed without approval of the City of Roseville Building Official in a 100-year floodplain as determined by the City of Roseville.

R. The cover sheet of the plans shall include a "permit status table" indicating the status of all permits being obtained.

S. If an established drain is involved, construction plans shall include a note indicating that "All work performed in the right-of-way of an established drain shall require a permit from the Drain Commissioner."

T. The engineer's seal shall be affixed to all sheets of the construction plans.

U. Unless the storm sewers are to be owned and maintained by a single private entity (i.e., municipal or commercial development, manufactured housing community, etc.), all storm sewers shall be located within an easement. The minimum easement width for a storm sewer shall be 12 feet centered on the sewer center line. City Engineer may require a larger easement as necessary for access and to facilitate maintenance and future repairs. The dedication of the easement shall be required prior to acceptance of the continuous maintenance and service by the City.

V. Privately maintained storm infrastructure, including but not limited to pipes, stormwater detention facility, water treatment units, bioswales, etc., will require a maintenance agreement.

W. All existing and proposed on-site drainage easements shall be clearly shown.

X. No public right-of-way runoff shall be routed through private storm sewer unless approved by City Engineer. All storm sewer intended to be public (i.e., road drainage), shall be within a public right-of-way except as may be necessary to outlet said public storm sewer to another public sewer.

§ 256-53 Established drains.

A. No construction activities shall be allowed without approval from the Macomb County Public Works Office for any development directly discharging to an established county drain. All work within the right-of-way of the established drain is subject to the design standards and requirements of the Macomb County Public Works Office.

B. If an established county drain is involved, construction plans shall include a note indicating that "All work performed in the right-of-way of an established drain shall require a permit from the Macomb County Public Works Office."

C. Where drainage is discharged to an established drain, such outlets shall be so designed as to enter the drain at an angle of 90° or less, as determined by the upstream center line.

§ 256-54 Storm sewers.

A. Plans shall show boundaries and acreages of catchment areas contributing runoff to each proposed or existing catch basin and/or inlet. Runoff from off-site tributary areas must be accommodated in design or rerouted.

B. The required discharge capacity for each reach of sewer shall be determined by the Rational Method.

(1) A ten-year design storm shall be used such that rainfall intensity, I = 175/(T + 25), where T = time of concentration in minutes.

(2) The runoff coefficient, C, shall be in conformance with normal design practice. Where a weighted average coefficient is employed, the computations shall be submitted for review.

(3) Minimum C-coefficients for various finish surfaces are as follows:

Finish Surface	Minimum C-coefficient
Water surface	1.00
Impervious pavement and roofs	0.90
Dense graded stone and pavers	0.80
Open graded stone	0.60
Lawns	0.35
Other surface C-coefficients	Subject to approval by City Engineer

(4) The following averaged C-coefficients may be used in lieu of weighted coefficient for proposed developments:

Development	Averaged C-coefficients
Single-family residential	0.35
Multifamily residential	0.55
Commercial	0.85
Industrial	0.90

C. A complete set of storm sewer design calculations shall accompany every set of construction plans submitted for review.

(1) Sewer capacities shall be based on the Manning Equation for full flow velocity. With Manning's "n" coefficient as follows:

Pipe Material	"n" Coefficient
Smooth lined, metal, PVC or HDPE pipe	0.011
Reinforced concrete pipe	0.013
Corrugated, metal, PVC, or HDPE pipe	0.024
Other pipe material	n-coefficients subject to approval by City Engineer

(2) Energy losses from friction shall be based on calculated design storm peak discharges and velocities, not Manning design (i.e., full-pipe) capacities.

(3) Energy losses from friction shall be based on typical Manning "n" roughness values as approved by the City Engineer.

(4) Energy losses through manholes and other appurtenances shall be included in the design calculations or reflected in friction losses through use of conservative Manning "n" roughness values as approved by the City Engineer.

D. The storm sewer pipe shall have a minimum diameter of 12 inches when constructed in a public right-of-way or easement.

E. Minimum allowable pipe velocity shall be 2.5 feet per second (except where the minimum diameter requirement makes this unachievable). Desirable pipe velocity range shall be four to eight feet per second. Maximum allowable pipe velocity shall be 10 feet per second.

F. Hydraulic grade lines for the ten-year storm shall be calculated and shown as a part of all storm sewer profiles. In no case shall the elevation of the hydraulic grade line exceed the elevation of a point lying one foot below the rim elevation of a manhole, catch basin or inlet. The hydraulic grade line upstream of a detention or retention storage facility shall be calculated assuming the design high water elevation (e.g., full detention basin) or 8/10 height of pipe, whichever is higher.

G. The storm sewer plan and profile drawing shall show the following data:

(1) Proper identification and numbering of manholes, catch basins and inlets.

(2) Invert and casting elevations for all structures.

(3) Pipe length (C/L to C/L to structures).

(4) Pipe diameter.

(5) Pipe slope.

(6) Pipe class or designation.

(7) Detail of trench construction and type of backfill material.

H. Generally, manholes shall be placed not more than 400 feet apart for sewers less than 30 inches diameter and 600 feet apart for larger sewers.

I. The minimum inside diameter of all manholes, catch basins and inlets shall be 48 inches, with the following exception: Inlet structures from which water will be discharged directly into a catch basin may be 24 inches inside diameter. The depth of such inlets shall be no greater 5.0 feet and no less than 3.5 feet from the top of frame and cover to the invert.

J. Manholes and inlet structures may be constructed of brick, manhole block, precast concrete (ASTM C478) or cast-in-place concrete.

K. All manhole block or brick structures shall be plastered on the outside with one to 2.5 mix of portland cement mortar, 1/2 inch thick. No calcium chloride or other chemical shall be added to lower the freezing point of the mortar, as the strength of the mortar may be lessened.

L. Inlet structures in the public street right-of-way shall be spaced a maximum of 400 feet apart (or a maximum of 400 feet on either side of a high point). The spacing and/or number of inlet structures required to accommodate the design flows in streets and in private drives and parking areas shall be based on a maximum of one cubic foot per second per 90 square inches of opening in an inlet or catch basin cover.

M. All storm sewer pipe, manholes, catch basins, and inlets shall meet MDOT specifications.

N. Generally, drops of over 2.0 feet at manholes, from invert of higher pipes to lower pipes, shall be avoided.

O. Joints in concrete pipe having a diameter of 30 inches or larger shall be pointed up on inside with mortar after backfilling has been completed.

P. Where drainage is discharged to an established drain or natural watercourse, such outlets shall be so designed as to enter the drain or watercourse at an angle of 90° or less, as determined by the upstream center line. Preformed end sections, grouted riprap or specially designed outlet structures will be required.

Q. Unless the storm sewers are to be owned and maintained by a single private entity (i.e., municipal or commercial development, manufactured housing community, etc.), all storm sewers shall be located within an easement. The minimum easement width for a storm sewer shall be 12 feet centered on the sewer center line.

R. All existing and proposed on-site drainage easements shall be clearly shown.

S. To account for energy losses, at structures a flow change of direction of greater than 45°, a 0.10 foot drop shall be added from the upstream to downstream pipes. Approval from City Engineer is required to waive the requirement for sites where existing conditions do not provide adequate storm depth to facilitate the drop.

T. At structure with a change of pipe size, the 8/10th elevation, or obvert of the pipes shall align. Approval from City Engineer is required to waive the requirement for sites where existing conditions do not provide adequate storm depth to facilitate the drop.

U. Storm sewers shall have a minimum of 3 1/2 feet of cover from the finished surface to the horizontal center line, where existing conditions allow. City Engineer may approve less cover where existing conditions restrict cover.

V. An end section with prefabricated bar screen shall be installed on the end of all storm sewers 12 inches in diameter or larger. Openings of the bar screen shall be no more than six inches on center.

W. All connections of storm sewers shall be at structure (i.e., manhole, catch basins etc.) locations. Blind taps or wye connections are not allowed with the exception of sump pump connections per the City's Stormwater Detail Sheet. All sump pumps shall be directed, via an enclosed three-inch diameter minimum pipe, to the storm system.

§ 256-55 Open channels.

A. The peak ten-year flow in each reach of open channel shall remain within the banks of the channel. Off-site tributary area shall be included in the design, or the off-site tributary runoff shall be rerouted around the channel.

B. The values of Manning's "n" shall be no less than 0.040 except where the channel is smooth and paved, in which case an "n" value of 0.013 to 0.022 shall be used.

C. The maximum velocity for grass-lined channels shall not exceed five feet per second. Where the above velocity is exceeded, the channel shall be protected by cobble paving or other means to prevent scour.

D. The minimum acceptable nonsiltation velocity should be 1.5 feet per second.

E. Unless the open channels are to be owned and maintained by a single private entity (i.e., industrial/commercial development, manufactured housing community, etc.), all open channels shall be located within an easement. Open channels shall have a minimum right-of-way of 40 feet plus top width of channel centered on the center line. A consistent right-of-way width shall be maintained along the entire reach of channel on the proposed site. A minimum width of 20 feet must be maintained from the top-of-bank to the edge of the right-of-way to allow for maintenance. The above minimum width shall govern generally; however, wider rights-of-way may be required at the discretion of the City Engineer.

F. Side slopes of open channels shall normally be no steeper than one vertical to three horizontal. Where conditions dictate steeper side slopes, consideration should be given to slope paving and fencing. The final decision in such matters rests with the City Engineer.

G. All existing and proposed on-site drainage easements shall be clearly shown on the plans.

§ 256-56 Culverts.

A. All culverts should be labeled on the plans as "existing," "proposed," or "to be extended."

B. Plans shall show boundaries and acreages of tributary areas contributing runoff to each proposed or existing culvert on the proposed site.

C. Proposed or extended culverts must be approved by the City Engineer. Proposed or extended culverts may also require the approval of the Macomb County Road Commission, the Macomb County Public Works Commission, the Michigan Department of Environmental Quality and/or the Michigan Department of Transportation (MDOT).

D. The Rational Method shall be used to determine the peak design flow for the culvert, if the tributary area to the culvert is less than 20 acres. For larger tributary areas, the SCS Method shall be used. The runoff coefficients used should be consistent with those in standard engineering practice, as approved by the City Engineer, and selected to reflect the future land use of the tributary area.

E. All culverts shall be designed with consideration of both inlet and outlet control conditions. Calculations of the ten-year and 100-year headwater elevations for all culverts thus designed shall accompany the final plans.

(1) The ten-year headwater elevation of each culvert shall not exceed an elevation one foot below the road or driveway center line elevation. The backwater shall not extend beyond the limits of the proprietor's property.

(2) The 100-year headwater elevation of each culvert may overtop the road or driveway center-line elevation, but must remain below proposed finish floor elevations of all nearby existing and proposed structures.

(3) The tailwater elevation assumed for each culvert should be estimated as the normal depth of the peak flow in the downstream channel, unless the tailwater is influenced by the headwater of another downstream culvert or the confluence of another watercourse.

F. Wing walls, headwalls, end sections, and all other culvert extremities shall be designed to ensure the stability of the surrounding soil and to meet the requirements of other governing agencies (e.g., Macomb County Road Commission, MCPWO, MDOT, EGLE), if applicable.

G. Roadways over culverts or bridges may be required to be paved or designed in such a way as to prevent the erosion of road material into the established drain or watercourse.

H. The following data shall be provided for all proposed or extended culverts:

(1) Length.

(2) Diameter.

(3) Invert elevations.

(4) Material type.

(5) Protection for culvert ends.

I. Riprap must be provided for all culverts in established drains or significant watercourses. The riprap provided for the protection of culvert ends shall:

(1) Extend at least one culvert diameter upstream of the culvert inlet and at least four culvert diameters downstream of the culvert outlet;

(2) Extend across the bottom of the channel and up the banks of the channel to at least the elevation of the crown of the culvert;

(3) Be inlayed such that it does not cause an obstruction in the watercourse; and

(4) Have a minimum dimension no smaller than that consistent with HEC-11 Design Guidelines for Rock Riprap and MDOT standards. (A conservative guideline for water depths less than three feet would be to use eight-inch-diameter riprap for flow velocities up to six feet per second, and sixteen-inch-diameter riprap for flow velocities up to 11 feet per second.)

J. Minimum diameter for a driveway or crossroad culvert shall be 18 inches or equivalent pipe arch.

K. The pipe used in culverts shall meet MDOT specifications and Macomb County Road Commission standards.

§ 256-57 Bioretention.

A. A bioretention system consists of a soil bed planted with native vegetation located above an underdrained sand layer. It can be configured as either a bioretention structure or a bioretention swale. Stormwater runoff entering the bioretention system is filtered first through the vegetation and then the sand/soil mixture before being conveyed downstream by the underdrain system. Runoff storage depths above the planting bed surface are typically shallow. The adopted TSS removal rate for bioretention systems is 90%.

B. Bioretention systems are used to remove a wide range of pollutants, such as suspended solids, nutrients, metals, hydrocarbons, and bacteria from stormwater runoff. They can also be used to reduce peak runoff rates and increase stormwater infiltration when designed as a multistage, multifunction facility.

(1) Predesign site evaluation.

(a) For infiltration trench and structure practices, a minimum field infiltration rate (fc) of 0.52 inch per hour is required; lower rates preclude the use of these practices. For surface sand filter and bioretention practices, no minimum infiltration rate is required if these facilities are designed with a "day-lighting" underdrain system; otherwise these facilities require a 0.52 inch per hour rate.

(b) Feasibility testing is to be conducted to screen unsuitable sites, and reduce testing costs. A soil boring is not required at this stage. However, a designer or landowner may opt to engage concept design borings at his discretion, without feasibility testing.

(c) Initial testing involves either one field test per facility, regardless of type or size, or previous testing data, such as the following:

[1] On-site septic percolation testing, within 200 feet of the proposed BMP location, and on the same contour which can establish initial rate, water table and/or depth to bedrock;

[2] Geotechnical report on the site prepared by a qualified geotechnical consultant; or

[3] Natural Resources Conservation Service (NRCS) County Soil Mapping showing, an unsuitable soil group such as a hydrologic Group D soil in a low-lying area.

(d) If the results of initial feasibility testing as determined by a qualified professional show that an infiltration rate of greater than 0.52 inch per hour is probable, then the number of concept design test pits shall be per the following Table D-1 (Exhibit B[1]). An encased soil boring may be substituted for a test pit, if desired.

[1] Editor's Note: Exhibit B is on file in the City offices.

(2) Design criteria.

(a) Storage volume, depth, and duration. Bioretention systems shall be designed to treat the runoff volume generated by the stormwater quality design storm (two-year). The maximum water depth during treatment of the stormwater quality design storm shall be 12 inches in a bioretention structure and 18 inches in a bioretention swale. The minimum diameter of any outlet or overflow orifice is 2.5 inches. The bottom of a bioretention system, including any underdrain piping or gravel layer, must be a minimum of one foot above the seasonal high groundwater table. The planting soil bed and underdrain system shall be designed to fully drain the stormwater quality design storm runoff volume within 72 hours.

(b) Permeability rates. The design permeability rate through the planting soil bed must be sufficient to fully drain the stormwater quality design storm runoff volume within 72 hours. This permeability rate must be determined by field or laboratory testing. Since the actual permeability rate may vary from test results and may also decrease over time due to soil bed consolidation or the accumulation of sediments removed from the treated stormwater, a factor of safety of two shall be applied to the tested permeability rate to determine the design permeability rate. Therefore, if the tested permeability rate of the soil bed material is four inches/hour, the design rate would be two inches per hour (i.e., four inches per hour/two). This design rate would then be used to compute the system's stormwater quality design storm drain time.

(c) Planting soil bed. The planting soil bed provides the environment for water and nutrients to be made available to the vegetation. The soil particles can absorb some additional pollutants through cation exchange, and voids within the soil particles can store a portion of the stormwater quality design storm runoff volume. The planting soil bed material should consist of 10% to 15% clays, a minimum 65% sands, with the balance as silts. The material's pH should range from 5.5 to 6.5. The material shall be placed in twelve-inch to eighteen-inch lifts. The total depth or thickness of the planting soil bed should be a minimum of three feet. As noted above, the design permeability rate of the soil bed material must be sufficient to drain the stormwater quality design storm runoff volume within 72 hours. Filter fabric should be placed along the sides of the planting soil bed to prevent the migration of soil particles from the adjacent soil into the planting soil bed.

(d) Vegetation. The vegetation in a bioretention system removes some of the nutrients and other pollutants in the stormwater inflow. The use of native plant material is recommended for bioretention systems wherever possible. The goal of the planting plan should be to simulate a forest-shrub community of primarily upland type. In general, trees should dominate the perimeter zone that is subject to less frequent inundation. Shrubs and herbaceous species that are adapted to moister conditions and expected pollutant loads should be selected for the wetter zones. The number of stems per acre should average 1,000, with tree spacing of 12 feet and shrub spacing of eight feet.

(e) Sand layer. The sand layer serves as a transition between the planting soil bed and the gravel layer and underdrain pipes. It shall be a minimum thickness of 12 inches and consist of clean medium aggregate sand (AASSHTO M-6/ASTM C-33 or MDOT Class II). To ensure proper system operation, the sand layer must have a permeability rate at least twice as fast as the design permeability rate of the planting soil bed.

(f) Underdrain. The underdrain piping must be rigid Schedule 40 PVC pipe. The portion of drain piping beneath the planting soil bed and sand layer must be perforated. All remaining underdrain piping, including cleanouts, must be nonperforated. All joints must be secure and watertight. The underdrain piping must connect to a downstream storm sewer manhole, catch structure, channel, swale, or ground surface at a location that is not subject to blockage by debris or sediment and is readily accessible for inspection and maintenance. Blind connections to downstream storm sewers are prohibited.

(g) Overflows. All bioretention systems must be able to safely convey system overflows to downstream drainage systems. The capacity of the overflow must be consistent with the remainder of the site's drainage system and sufficient to provide safe, stable discharge of stormwater in the event of an overflow.

(h) Tailwater. The hydraulic design of the underdrain and overflow systems, as well as any stormwater quantity control outlets, must consider any significant tailwater effects of downstream waterways or facilities. This includes instances where the lowest invert in the outlet or overflow structure is below the flood hazard area design flood elevation of a receiving stream.

(i) Maintenance. The following requirements must be included in the system's maintenance plan.

[1] General maintenance.

[a] All bioretention system components expected to receive and/or trap debris and sediment must be inspected for clogging and excessive debris and sediment accumulation at least four times annually as well as after every storm exceeding one inch of rainfall. Such components may include bottoms, trash racks, low-flow channels, outlet structures, riprap or gabion aprons, and cleanouts.

[b] Sediment removal should take place when the structure is thoroughly dry. Disposal of debris, trash, sediment, and other waste material should be done at suitable disposal/recycling sites and in compliance with all applicable local, state, and federal waste regulations.

[2] Vegetated areas.

[a] Mowing and/or trimming of vegetation must be performed on a regular schedule based on specific site conditions. Grass should be mowed at least once a month during the growing season. Vegetated areas must be inspected at least annually for erosion and scour. Vegetated areas should also be inspected at least annually for unwanted growth, which should be removed with minimum disruption to the planting soil bed and remaining vegetation.

[b] When establishing or restoring vegetation, biweekly inspections of vegetation health should be performed during the first growing season or until the vegetation is established. Once established, inspections of vegetation health, density, and diversity should be performed at least twice annually during both the growing and nongrowing seasons. The vegetative cover should be maintained at 85%. If vegetation has greater than 50% damage, the area should be reestablished in accordance with the original specifications and the inspection requirements presented above.

[c] All use of fertilizers, mechanical treatments, pesticides and other means to assure optimum vegetation health should not compromise the intended purpose of the bioretention system. All vegetation deficiencies should be addressed without the use of fertilizers and pesticides whenever possible.

[3] Structural components. All structural components must be inspected for cracking, subsidence, spalling, erosion, and deterioration at least annually.

§ 256-58 Infiltration.

A. An infiltration structure is a facility constructed within highly permeable soils that provides temporary storage of stormwater runoff. An infiltration structure does not normally have a structural outlet to discharge runoff from the stormwater quality design storm. Instead, outflow from an infiltration structure is through the surrounding soil. An infiltration structure may also be combined with an extended detention structure to provide additional runoff storage for both stormwater quality and quantity management. The adopted TSS removal rate for infiltration structures is 80%.

B. Infiltration structures are used to remove pollutants and to infiltrate stormwater back into the ground. Such infiltration also helps to reduce increases in both the peak rate and total volume of runoff caused by land development. Pollutant removal is achieved through filtration of the runoff through the soil as well as biological and chemical activity within the soil.

(1) Predesign site evaluation.

(a) Infiltration structures can present some practical design problems. When planning for an infiltration structure that provides stormwater quality treatment, consideration should be given to soil characteristics, depth to the groundwater table, sensitivity of the region, and runoff water quality. Specifically, infiltration structures must not be used in the following locations:

[1] Industrial and commercial areas where solvents and/or petroleum products are loaded, unloaded, stored, or applied or pesticides are loaded, unloaded, or stored.

[2] Areas where hazardous materials are expected to be present in greater than "reportable quantities" as defined by the United States Environmental Protection Agency in the Code of Federal Regulations at 40 CFR 302.4.

[3] Areas where infiltration structure use would be inconsistent with an NJDEP approved remedial action work plan or landfill closure plan.

[4] Areas with high risks for spills of toxic materials such as gas stations and vehicle maintenance facilities.

[5] Areas where industrial stormwater runoff is exposed to source material. "Source material" means any material(s) or machinery, located at an industrial facility that is directly or indirectly related to process, manufacturing, or other industrial activities, that could be a source of pollutants in any industrial stormwater discharge to groundwater. Source materials include, but are not limited to, raw materials, intermediate products, final products, waste materials, by-products, industrial machinery and fuels, and lubricants, solvents, and detergents that are related to process, manufacturing, or other industrial activities that are exposed to stormwater.

[6] Areas where their installation would create a significant risk for basement seepage or flooding, cause surficial flooding of groundwater, or interfere with the operation of subsurface sewage disposal systems and other subsurface structures. Such adverse impacts must be assessed and avoided by the design engineer.

(b) Infiltration structures must be configured and located where their construction will not compact the soils below the structure. In addition, an infiltration structure must not be placed into operation until the contributing drainage area is completely stabilized.

[1] General setback requirements for infiltration structures:

[a] Soil absorption systems for Title 5 systems: 50 feet.

[b] Private wells: 100 feet.

[c] Public wells: 150 feet.

[d] Public reservoir, surface water sources for public water systems and their tributaries: 400 feet.

[e] Other surface waters: 50 feet.

[f] Property lines: 10 feet.

[g] Building foundations: greater than 10 feet to 100 feet, depending upon soil types and infiltration structure type.

(c) Soils are perhaps the most important consideration for site suitability. In general, county soil surveys can be used to obtain necessary soil data for the planning and preliminary design of infiltration structures. For final design and construction, soil tests are required at the exact location of a proposed structure in order to confirm its ability to function without failure.

[1] Tests should include:

[a] Determination of the textural classification.

[b] Permeability of the subgrade soil at and below the bottom of the proposed infiltration structure.

[2] The recommended minimum depth for subgrade soil analysis is five feet below the bottom of the structure or to the groundwater table. Soil permeability testing can be conducted in accordance with the standards for individual subsurface sewage disposal systems.

(2) Design criteria.

(a) Storage volume, depth, and duration.

[1] An infiltration structure must be designed to treat the total runoff volume generated by the structure's maximum design storm. This may either be the groundwater recharge or stormwater quality design storm, depending upon the structure's proposed use. An infiltration structure must also fully drain this runoff volume within 72 hours. Runoff storage for greater times can render the structure ineffective and may result in anaerobic conditions, odor, and both water quality and mosquito breeding problems. The bottom of the infiltration structure must be at least two feet above seasonal high water table or bedrock. For surface structures, this distance must be measured from the bottom of the sand layer. The structure bottom must be as level as possible to uniformly distribute runoff infiltration over the subgrade soils.

[2] To enhance safety by minimizing standing water depths, the vertical distance between the structure bottom and the maximum design stormwater surface in surface infiltration structures should be no greater than two feet. Construction of an infiltration structure must be done without compacting the structure's subgrade soils. Excavation must be performed by equipment placed outside the structure whenever possible. This requirement should be considered when designing the dimensions and total storage volume of an infiltration structure. It is important to note that the use of infiltration structures is recommended only for the stormwater quality design storm and smaller storm events. Use of infiltration structures for larger storm events and the requirements by which such structures are to be designed, constructed, and maintained should be reviewed and approved by all applicable reviewing agencies.

(b) Permeability rates.

[1] The minimum design permeability rate of the soils below an infiltration structure will depend upon the structure's location and maximum design storm. The use of infiltration structures for stormwater quality control is feasible only where soil is sufficiently permeable to allow a reasonable rate of infiltration. Therefore, infiltration structures designed for storms greater than the groundwater recharge storm can be constructed only in areas with Hydrologic Soil Group A and B soils.

Maximum Design Structure Location	Minimum Design Permeability Rate (inches/hour)
Groundwater recharge subsurface	0.2
Groundwater recharge surface	0.5
Stormwater quality surface and subsurface	0.5

[2] In addition to the above, the design permeability rate of the soil must be sufficient to fully drain the infiltration structure's maximum design storm runoff volume within 72 hours. This design permeability rate must be determined by field testing. [See § 256-57B(1), Bioretention, predesign site evaluation.] Since the actual permeability rate may vary from test results and may also decrease over time due to soil bed consolidation or the accumulation of sediments removed from the treated stormwater, a factor of safety of two must be applied to the tested permeability rate to determine the design permeability rate. Therefore, if the tested permeability rate of the soils is four inches per hour, the design rate would be two inches per hour (i.e., four inches per hour/two). This design rate would then be used to compute the structure's maximum design storm drain time.

(c) Bottom sand layer. To help ensure maintenance of the design permeability rate over time, a six-inch layer of sand must be placed on the bottom of an infiltration structure. This sand layer can intercept silt, sediment, and debris that could otherwise clog the top layer of the soil below the structure. The sand layer will also facilitate silt, sediment, and debris removal from the structure and can be readily restored following removal operations. The sand layer must meet the specifications of a MDOT Class II sand. This must be certified by a certified testing lab.

(d) Overflows. All infiltration structures must be able to convey overflows to downstream drainage systems in a safe and stable manner. The capacity of the overflow must be consistent with the remainder of the site's drainage system and sufficient to provide safe, stable discharge of stormwater in the event of an overflow.

(e) Subsurface infiltration structures. A subsurface infiltration structure is located entirely below the ground surface. It may consist of a vault, perforated pipe, and/or stone bed. However, due to the greater difficulty in removing silt, sediment, and debris, all runoff to a subsurface infiltration structure must be pretreated. This pretreatment must remove 80% of the TSS in the runoff from the structure's maximum design storm.

(f) Basis of design.

[1] The design of an infiltration basin is based upon Darcy's Law:

Q = KIA

Where:
Q	=	The rate of infiltration in cubic feet per second (cfs)
K	=	The hydraulic conductivity of the soil in feet per second (fps)
I	=	The hydraulic gradient
A	=	The area of infiltration in square feet (sf)

[2] From the variables shown in the figure below:

Average Hydraulic Gradient = D_avg/d

Minimum Hydraulic Gradient = D₁/d

Maximum Hydraulic Gradient = D₂/d

(g) Maintenance. The following requirements must be included in the system's maintenance plan.

[1] General maintenance. All infiltration structure components expected to receive and/or trap debris and sediment must be inspected for clogging and excessive debris and sediment accumulation at least four times annually as well as after every storm exceeding one inch of rainfall. Such components may include bottoms, riprap or gabion aprons, and inflow points. This applies to both surface and subsurface infiltration structures. Sediment removal should take place when the structure is thoroughly dry. Disposal of debris, trash, sediment, and other waste material should be done at suitable disposal/recycling sites and in compliance with all applicable local, state, and federal waste regulations.

§ 256-59 Detention storage facilities.

A. Detention storage facilities are designed to detain runoff for a short period of time and then release it to a watercourse where it returns to the hydrologic cycle. The objective of detention storage is to regulate the released runoff rate and to reduce the impact on downstream drainage systems. Detention storage should not be confused with retention storage (i.e., retention basins), a facility with no engineered outlet (other than an emergency-type outlet) designed to hold runoff for a considerable length of time. The water in a retention basin is not discharged to surface water, although it may infiltrate into the ground, evaporate, or be consumed by plants.

B. In keeping with common law natural flow rights and the Michigan Drain Code,[1] concentrated discharges of stormwater (such as the outflow from a detention facility) or increased surface water runoff over property owned by others must be pursuant to a valid right-of-way, easement, or other written permission from all property owners affected. The outflow from a detention facility is considered to be such a concentrated discharge of stormwater.

[1] Editor's Note: See MCL § 280.1 et seq.

C. All forms of detention storage shall meet the following criteria:

(1) On-site detention (or retention, see § 256-60, Retention basins, below) of stormwater is required of all new developments or redevelopments to maintain the peak outflow to a rate similar to the predevelopment runoff rate or to a discharge rate approved by the City Engineer. In no case shall the outflow from a site exceed the capacity of the receiving watercourse to accept the flow. In the case where the alternative of extended detention is approved, the channel protection volume shall be held for 48 hours or released at the one-year/twenty-four-hour discharge rate.

(2) For development sites greater than five acres, the detention basin volume shall be determined for the 100-year flood volume from all tributary area, including off-site area.

(a) The tributary area shall include all acreage contributing runoff to the detention storage facility, including any off-site tributary area in its existing state, whether developed or undeveloped.

(b) The following equations shall be used to determine the 100-year detention volume:

Q_a = Allowable release rate, cfs

Q_o = Q_a/(A C)

Where:
A	=	Tributary area in acres
C	=	Weighted runoff coefficient
Detention time in minutes, T = -25 + sqrt (10,312.5/Qo)
Storage volume per impervious acre, Vs = 16,500 T/(T + 25) — 40 Qo T
Required detention volume in cubic feet, V = Vs x A x C

(3) For development sites five acres and less, the detention basin volume shall be determined for the ten-year flood volume from all tributary area, including off-site area.

(a) The tributary area shall include all acreage contributing runoff to the detention storage facility, including any off-site tributary area in its existing state, whether developed or undeveloped.

(b) The following equations shall be used to determine the ten-year detention volume:

Q_a = Allowable release rate, cfs

Q_o = Q_a/(A C)

Where:
A	=	Tributary area in acres
C	=	Weighted runoff coefficient
Detention time in minutes, T = -25 + sqrt (6,562.5/Qo)
Storage volume per impervious acre, Vs = 10,500T/(T+25) - 40 Qo T
Required detention volume in cubic feet, Vs x A x C

(4) If the site is located near the downstream end of a watercourse or drainage district, the City Engineer may require that the proprietor's engineer generate and submit hydrographs of the outflow from the existing site and from the proposed site (i.e., detention facility) and a hydrograph of the flow in the receiving watercourse to verify that the detained outflow would not result in an increase in the peak flow in the receiving watercourse. If the detained outflow would result in an increase in the peak flow in the receiving watercourse, then stormwater detention is not an acceptable stormwater management option. Retention of stormwater or other stormwater management design approved by the City Engineer must be provided. See § 256-60, Retention basins, for design requirements.

(5) Portions of the developing site may be allowed to drain unrestricted (i.e., not through a detention facility) if either of the following conditions are met:

(a) The areas draining unrestricted are not being disturbed or altered by the construction, such that they will maintain their existing drainage characteristics and patterns.

(b) The areas draining unrestricted are being disturbed or altered but will be permanently stabilized to prevent erosion and will not contain any impervious surface postconstruction. In this case, the unrestricted flow must be draining to a receiving watercourse with valid rights-of-way, or else written agreement from the affected property owners would have to be obtained per common law natural flow rights and the Michigan Drain Code.[2] In addition, the postconstruction peak 100-year flow from these areas should be calculated and deducted from the total allowable peak flow from the detention facility (Q_a). The detention outlet(s) should be designed to restrict the basin outflow(s) to this reduced allowable peak flow rate.

[2] Editor's Note: See MCL § 280.1 et seq.

(6) Where the detention facility is to be equipped with a pump discharge, the proprietor shall be required to furnish design data on pump(s) and discharge force main so that the capacity of the system can be verified. These data will include system curve calculations, the pump performance curves, and a profile of the system piping. The pumping station should be able to release the first flush volume over approximately 24 hours, the bankfull flood volume over 24 to 48 hours, and the 100-year flood volume at a rate not to exceed 0.15 cfs/ac of tributary area. A backup generator will be required to ensure the operation of the pumping station in the event of power loss. The City discourages the use of pumped outlets and will not accept responsibility for damages due to power failure, pump malfunction, or acts of God that result in storm conditions that exceed the design conditions of the pump station.

(7) An agreement for acceptance and maintenance of the detention facility, if executed by the proprietor, shall be submitted to the City of Roseville prior to final approval. The agreement both as form and content shall be subject to the approval of the City.

D. Detention basins. A detention basin is a form of detention storage where the stormwater is detained aboveground as surface water. In addition to the general requirements indicated above in § 256-58, detention basins shall meet the following requirements:

(1) Detention volume in a gravity-outlet detention basin must be located:

(a) Above the invert of the lowest row of orifices in the outlet standpipe;

(b) Above the elevation of the dry weather base flow in the receiving watercourse;

(c) Above the elevation of the groundwater table. Soil boring data used to determine the groundwater table elevation shall be submitted with the plans.

(2) The detention basin outlet shall consist of a vertical standpipe with multilevel orifices to control the release of stormwater from the basin, including the first flush volume, bankfull flood volume, and 100-year flood volume (or ten-year flood volume for sites less than five acres).

(a) The standpipe shall not be less than 36 inches in diameter.

(b) The standpipe shall contain multiple rows of orifices (i.e., holes) to control the release of the first flush runoff volume, the bankfull flood volume, and the 100-year flood volume (or ten-year for sites less than five acres).

[1] First flush orifices shall be located at the elevation of the basin floor (or permanent pool water level, if a wet basin).

[2] Additional bankfull flood orifices shall be at the elevation of the first flush volume in the basin, where the first flush volume is calculated as the first one-inch of runoff over the site, or Vff (cf) = 3630 x A(acres) x C, where C is the runoff coefficient.

[3] Additional 100-year (or ten-year for sites less than five acres) flood control orifices shall be located at the elevation of the bankfull flood volume in the basin, where the bankfull flood volume is calculated as the rainfall from a 1.5-year storm, or Vbf (cf) = 8170 x A (acres) x C.

(3) To promote improved filtering of runoff sediment from smaller, more frequent storm events, the bankfull flood and first flush volumes shall be based on the developing tributary site area only, and not include off-site tributary area.

(a) Orifices should not be less than one-inch in diameter or greater than four inches in diameter.

(b) The top of the standpipe shall consist of a grating at or above the design (high) water level to serve as an overflow mechanism, in addition to the overflow spillway/berm.

(c) The standpipe shall be encased in stone extending to the design (high) water level to allow for filtering of the stormwater prior to discharge from the basin. The encasement stone size shall be large enough so as not to plug or pass through the orifices in the standpipe.

(d) The standpipe shall contain a sediment sump with a depth of at least one foot.

(e) Double standpipes (e.g., a thirty-six-inch-diameter inner standpipe within a forty-eight-inch-diameter outer standpipe) are encouraged. Double standpipes are believed to be less prone to blockages of the control orifices, and therefore require less maintenance. The inner standpipe should contain the appropriate number and configuration of orifices to provide the controlled release of the first flush volume, the bankfull flood volume, and the 100-year (or ten-year for sites less than five acres) flood volume. The outer standpipe should contain at least several times the orifice area as the inner standpipe over the entire height of the standpipe, such that the head loss across the outer standpipe orifices is negligible.

(f) The outlet pipe extending from the standpipe to the receiving watercourse shall be sized to convey the calculated 100-year (or ten-year for sites less than five acres) peak inflow to the detention basin.

(g) The location of the outlet pipe extending downstream of the standpipe shall be indicated on a profile drawing of the receiving watercourse, whether or not the receiving watercourse is an established drain. The receiving watercourse profile shall extend at least from the upstream end of the site to the downstream end of the site.

(4) A sediment sump shall be provided within the basin, below the lowest orifice elevation but above the groundwater table, to provide for sediment accumulation.

(a) The volume of the sump shall be equivalent to the first flush volume, or one-inch of runoff over the site area. (Sump Volume, cf = V_ff = 3630 x A x C.)

(b) Appropriate precautions shall be taken to protect public safety and to ensure that the sump does not constitute a nuisance.

(5) All detention basins must have standpipe overflow grates and spillway berms for emergency overflow at the high water level.

(a) The standpipe overflow grate and spillway must provide adequate capacity to overflow the peak 100-year (or ten-year for sites less than five acres) basin inflow with no more than one-foot of head (i.e., water level must not exceed the one-foot of freeboard).

(b) Downstream of the overflow spillway, the stormwater overflow must be directed (either by overland flow or via a swale or ditch) to the receiving watercourse.

(6) A minimum of one foot freeboard shall be provided above the design high water elevation.

(7) The side slopes shall not be steeper than six feet horizontal to one-foot vertical. Slope protection shall be provided as necessary. Basin side slope elevation contours shall be shown on the plans.

(8) Unless the detention basin contains a permanent pool, the bottom of all detention basins shall be graded in such a manner as to provide positive flow to the outlet. A minimum bottom slope of 1% shall be provided.

(9) A twelve-foot-wide minimum access easement shall be provided for all detention basins, as measured from the top of bank.

(10) A twenty-five-foot-wide minimum setback from property lines shall be provided for all detention basins, as measured from the top-of-bank.

(11) Detention basin configurations where stormwater must back up into the basin (i.e., stormwater enters the conveyance system downstream of the basin) will not be permitted.

(12) Multiple detention basins serving a single development should function independently. If the outflow from one basin passes through another basin before being discharged to the receiving watercourse, a full hydraulic analysis (i.e., a computer model simulation) will be required to ensure that the system functions satisfactorily.

(13) If at any time the detention basin is to function as a sediment basin (for use during the construction phase), an outlet filter shall be provided. Such an outlet filter is to be designed in accordance with criteria established by the Macomb County Public Works office. Such use of a detention pond shall be considered a temporary measure only. The proprietor shall be responsible for sediment removal upon completion of construction.

(14) Detention basins shall meet all local ordinances and/or requirements for "ponds."

E. Underground storage. Underground storage is a form of detention storage where the stormwater is detained in underground pipes. Like a detention basin, the water is released at a controlled rate to a receiving watercourse. In addition to the general requirements indicated above in § 256-59, underground detention facilities shall meet the following requirements:

(1) Detention volume in an underground detention facility shall be located above the elevation of the dry weather baseflow in the receiving watercourse and above the elevation of the groundwater table. Soil boring data used to determine the groundwater table shall be submitted with the plans.

(2) To minimize sedimentation in the downstream drainage district, sediment shall be removed from the stormwater before water enters the underground storage facility (e.g., in first flush forebay or within the catch basins using removable filtration inserts).

(3) The pipe material used for the underground storage facility shall have an expected life of at least 50 years.

(4) Access manholes shall be provided along the underground storage facility to allow for maintenance.

(5) A minimum of one foot of freeboard shall be provided between the design hydraulic grade line in the underground storage facility and the rim elevations of all access manholes.

(6) A twenty-five-foot-wide setback from property lines shall be provided for all underground storage facilities.

(7) An access easement shall be provided to and above the underground storage facility.

(8) No permanent structures shall be constructed above the underground storage facility.

F. Parking lot surface storage is a form of detention storage where the stormwater is detained in the parking lot surface creating temporary flooding of the parking lot. Like a detention basin, the water is released at a controlled rate to a receiving drain. In addition to the general requirements indicated above in § 256-59, parking lot surface storage shall meet the following requirements:

(1) Storage elevation must be less than one foot from the finish floor elevation of the nearest building.

(2) Storage depth shall not exceed 12 inches at any location of the parking lot.

§ 256-60 Retention basins.

A "retention basin" is a facility with no engineered outlet (other than an emergency-type outlet) designed to hold runoff for a considerable length of time. The water in a retention basin is not discharged to a natural watercourse, although it may be consumed by plants, evaporate, or infiltrate into the ground. A retention basin should not be confused with a "detention basin," a facility designed to detain runoff for a short period of time and then release it to a watercourse.

A. On-site retention (or detention; see § 256-59, Detention storage facilities) is required of all new developments or redevelopments to prevent an increase in peak flows downstream in the drainage district.

(1) Retention basins are an acceptable stormwater management practice on sites where the soil has an infiltration rate of at least 0.52 inch per hour and a clay content of less than 30% (per recommendations in Guidebook of Best Management Practices for Michigan Watersheds). The required storage volume of a retention basin is that of the runoff from a 100-year design storm as determined using the SCS Method. On sites with soils having a lower infiltration rate and/or higher clay content, the City Engineer may allow retention basins with storage volume for the runoff from two consecutive 100-year design storms.

(2) Retention basins shall accommodate runoff from off-site areas that drain onto/across the developing site. An exception to this rule would be if off-site runoff were to be routed around the site to a receiving watercourse, if done in a manner such that runoff from the developing site would not contribute to this off-site flow. If the off-site flow were to be concentrated from overland flow to a point discharge into a receiving watercourse without valid rights-of-way, written agreement from the affected property owners would have to be obtained per common law natural flow rights and the Michigan Drain Code.[1]

[1] Editor's Note: See MCL § 280.1 et seq.

B. One foot of freeboard shall be provided above the design high water elevation.

C. Retention volume must be provided above the elevation of the groundwater table. Soil boring data used to determine the groundwater table elevation shall be submitted with the plans.

D. All retention basins must have a spillway for emergency overflow at the high water level.

(1) The spillway must provide adequate capacity to overflow the peak 100-year basin inflow with no more than two feet of head (i.e., water level must not exceed the two feet of freeboard).

(2) The plans must identify where the overflow would be directed to flow or stored in the event of an overflow.

E. The side slopes shall not be steeper than six feet horizontal to one foot vertical unless fenced in accordance with City requirements. Slope protection shall be provided as necessary. Basin side slope elevation contours shall be shown on the plans.

F. A twelve-foot-wide access easement shall be provided to and around all retention basins.

G. An agreement for acceptance and maintenance of the retention basin system, if executed by the proprietor, shall be submitted to the City of Roseville prior to final approval. The agreement both as form and content shall be subject to the approval of the City.

H. If at any time during the construction period the retention basin is to function as a sediment basin, the proprietor shall be responsible for sediment removal prior to completion of construction. (See Macomb County Public Works Office for requirements regarding soil erosion and sedimentation control during construction.)

§ 256-61 Wetlands and low-lying areas.

A. In order to help in analyzing site hydrology and the predevelopment runoff rate, soil types, the normal groundwater table, and an accurate delineation of wetlands must be provided as part of preliminary plats/plans. The City Engineer may require confirmation of the absence or presence of regulated wetlands from EGLE through its wetland assessment program. Construction activities to be performed within a regulated wetland may require a permit from the EGLE.

B. Any regulated wetlands or other wetlands that will be part of the drainage system shall be designated as a common area and placed within a conservation easement.

C. If existing wetlands or low-lying areas are to be used for stormwater storage, all requirements under either § 256-59D, Detention basins, or § 256-60, Retention basins, would apply, depending on whether the wetlands/area would have an outlet.

D. If any disturbed or impervious surfaces will drain into an existing wetland or low-lying area, calculations may be required to be submitted indicating that the wetland will accommodate runoff from a 100-year design storm without exceeding the finished grade elevation of any adjacent existing or proposed structure.

E. If a wetland will be used for stormwater storage, a sediment forebay shall be provided upstream of the wetlands to reduce the stormwater velocity and encourage sedimentation. Additionally, a permit from the EGLE may be required.

§ 256-62 Oil separators.

Oil must be removed from stormwater as appropriate prior to discharge to a receiving watercourse. The City Engineer will consider means of oil removal on a case-by-case basis.

§ 256-63 First flush basins and sediment collection units.

When standalone BMPs such as permanent first flush basins and prefabricated sediment collection units are proposed or required for a specific site, the following design standards shall apply:

A. A settling pond (first flush pond) is a means to detain the first flush volume so that a minimum of 80% of the TSS settle to the bottom of the pond.

B. A settling pond may be standalone or adjacent to a detention pond as a settling forebay.

C. The bankfull volume is calculated as the rainfall from a 1.5-year storm while the first flush volume is calculated as the first one inch of runoff from the on-site impervious tributary area, or

V_ff (cf) = A x C x 3630 cf/ac-impervious

D. The outlet of a first flush basin or sediment collection unit shall be designed to release the first flush volume over 24 to 36 hours.

E. The outlet of a first flush basin or sediment collection unit shall not be submerged by the receiving watercourse at a ten-year design level.

F. The first flush basin or sediment collection unit shall contain a bypass structure and/or berm to allow the ten-year peak flow to bypass without hydraulic interference.

§ 256-64 Discharge requirements.

A. Discharge prohibitions.

(1) Prohibition of illegal discharges.

(a) No person shall discharge or cause to be discharged into the municipal separate storm sewer system (MS4) or watercourses any materials, including but not limited to pollutants or waters containing any pollutants, that cause or contribute to a violation of applicable water quality standards, other than stormwater.

(b) The commencement, conduct or continuance of any illegal discharge to the storm drain system is prohibited except as described as provided in § 256-64A(2).

(2) The following discharges if identified as not being a significant contributor to violations of water quality standards (WQS) are excluded from discharge prohibitions established by this article:

(a) Waterline flushing and discharges from potable water sources.

(b) Landscape irrigation runoff, lawn watering runoff, and irrigation waters.

(c) Diverted stream flows and flows from riparian habitats and wetlands.

(d) Rising groundwaters and springs.

(e) Uncontaminated groundwater infiltration and seepage.

(f) Uncontaminated pumped groundwater, except for groundwater cleanups specifically authorized by NPDES permits.

(g) Foundation drains, water from crawl space pumps, footing drains, and basement sump pumps.

(h) Air-conditioning condensation.

(i) Waters from noncommercial car washing.

(j) Street wash water.

(k) Dechlorinated swimming pool water from single-, two-, or three-family residences. (A swimming pool operated by the permittee shall not be discharged to a separate storm sewer or to surface waters of the state without NPDES permit authorization from the EGLE).

(l) Discharges or flows from firefighting activities if identified as not being significant sources of pollutants to waters of the state.

(m) Discharges specified in writing by the authorized enforcement agency as being necessary to protect public health and safety.

(n) Dye testing is an allowable discharge, but requires a "Notice of Intent to Treat" under the General Rule 97 Certification of Approval to be obtained from EGLE prior to the commencement of the test.

(o) The prohibition shall not apply to any nonstormwater discharge permitted under an NPDES permit, waiver, or waste discharge order issued to the discharger and administered under the authority of the Federal Environmental Protection Agency, provided that the discharger is in full compliance with all requirements of the permit, waiver, or order and other applicable laws and regulations, and provided that written approval has been granted for any discharge to the storm drain system.

B. Prohibition of illicit connections.

(1) The construction, use, maintenance or continued existence of illicit connections to the storm drain system is prohibited.

(2) This prohibition expressly includes, without limitation, illicit connections made in the past, regardless of whether the connection was permissible under law or practices applicable or prevailing at the time of connection.

(3) A person is considered to be in violation of this article if the person connects a line conveying sewage to the MS4, or allows such a connection to continue.

§ 256-65 Inspection and monitoring requirements.

Monitoring of discharges.

A. Applicability.

(1) This section applies to all facilities that have stormwater discharges, facilities associated with industrial activity, and those having construction activity.

B. Access to facilities.

(1) The City of Roseville shall be permitted to enter and inspect facilities subject to regulation under this article as often as may be necessary to determine compliance with this article. If a discharger has security measures in force which require proper identification and clearance before entry into its premises, the discharger shall make the necessary arrangements to allow access to representatives of the City.

(2) Facility operators shall allow the City ready access to all parts of the premises for the purposes of inspection, sampling, examination and copying of records that must be kept under the conditions of an NPDES permit to discharge stormwater, and the performance of any additional duties as defined by state and federal law.

(3) The City shall have the right to set up on any permitted facility such devices as are necessary and/or required by the MS4 permit to conduct monitoring and/or sampling of the facility's stormwater discharge.

(4) The City has the right to require the discharger to install monitoring equipment as necessary. The facility's sampling and monitoring equipment shall be maintained at all times in a safe and proper operating condition by the discharger at its own expense. All devices used to measure stormwater flow and quality shall be calibrated to ensure their accuracy.

(5) Any temporary or permanent obstruction to safe and easy access to the facility to be inspected and/or sampled shall be promptly removed by the operator at the written or oral request of the City and shall not be replaced. The costs of clearing such access shall be borne by the operator.

(6) Unreasonable delays in allowing the City access to a permitted facility is a violation of a stormwater discharge permit and of this article. A person who is the operator of a facility with a NPDES permit to discharge stormwater associated with industrial activity commits an offense if the person denies the authorized enforcement agency reasonable access to the permitted facility for the purpose of conducting any activity authorized or required by this article.

(7) If the City has been refused access to any part of the premises from which stormwater is discharged, and he/she is able to demonstrate probable cause to believe that there may be a violation of this article, or that there is a need to inspect and/or sample as part of a routine inspection and sampling program designed to verify compliance with this article or any order issued hereunder, or to protect the overall public health, safety, and welfare of the community, then the City may seek issuance of a search warrant from any court of competent jurisdiction.

§ 256-66 Enforcement; illicit discharge elimination plan and total maximum daily load.

A. Notice of violation. Whenever the City of Roseville or other enforcing agency finds that a person has violated a prohibition or failed to meet a requirement of this article, the authorized enforcement agency may order compliance by written notice of violation to the responsible person. Such notice may require without limitation:

(1) The performance of monitoring, analyses, and reporting;

(2) The elimination of illicit connections or discharges;

(3) That violating discharges, practices, or operations shall cease and desist;

(4) The abatement or remediation of stormwater pollution or contamination hazards and the restoration of any affected property;

(5) Payment of a fine to cover administrative and remediation costs; and

(6) The implementation of source control or treatment BMPs.

B. If abatement of a violation and/or restoration of affected property is required, the notice shall set forth a deadline within which such remediation or restoration must be completed. Said notice shall further advise that, should the violator fail to remediate or restore within the established deadline, the work will be done by a designated governmental agency or a contractor and the expense thereof shall be charged to the violator.

C. The City of Roseville Illicit Discharge Elimination Plan and Total Daily Maximum Load, as amended from time to time, and as adopted via resolution by the City of Roseville City Council, is hereby incorporated herein by reference.[1]

[1] Editor's Note: Said plan is on file in the City offices.