In order to control Post-Construction water quality damage and damage to public and private lands, the owner of each development area shall be responsible for developing a Post-Construction Storm Water Management Plan.
(a) This plan will be combined with the Construction Site Conservation Plan and the Riparian Setback and Wetland Setback Plans that are also developed for the site.
(b) This plan will contain a description of controls appropriate for each construction operation covered by these regulations, and the operator will implement such controls in a timely manner.
(c) The BMPs used to satisfy the conditions of these regulations shall meet the standards and specifications in the current edition of the Ohio Rain Water and Land Development manual, ODOT Post-Construction storm water standards, or other manual that is acceptable to the Community Engineer or Ohio EPA.
(d) The plan must make use of the practices that preserve the existing natural condition to the Maximum Extent Practicable (MEP).
(e) To meet the Post-Construction requirements of this regulation, the Post-Construction Water Quality Plan must contain a description of the Post-Construction Best Management Practices (BMPs) that will be installed during construction for the site and the rationale for their selection. The rationale must address the anticipated impacts on the channel and floodplain morphology, hydrology, and water quality.
(f) This plan will identify the person or entity responsible for continued maintenance of all vegetative and/or mechanical BMPs for both the construction and Post-Construction phases of the development.
(g) Long-term maintenance requirements and schedules of all BMPs for both the construction and Post-Construction phases of the development will be identified.
(h) This plan will contain long-term maintenance inspection schedules, including the printed name and contact point of the Post-Construction landowner (e.g., president of the homeowners association, store manager, apartment complex manager, etc.).
(i) This plan will identify the person or entity financially responsible for maintaining the permanent inspection and maintenance of permanent storm water conveyance and storage structures and other conservation practices.
(j) The method of ensuring that funding will be available to conduct the long-term maintenance and inspections of all permanent storm water, soil erosion and sediment control and water quality practices will be identified.
(k) The Post-Construction Plan will also contain the following information depending on the size of the development sites as well as any additional information required by the community engineer:
(1) Development Sites Smaller than Five Acres: A development site that will disturb one (1) or more, but less than five (5) acres of land and is not a part of a larger common plan of development or sale which will disturb five or more acres of land shall identify:
A. Storm Water Issues: A statement as to how the decreased storm water quality that will be caused by the planned development project will be handled
B. Description of Measures: A description of the BMPs that will be installed during the construction process to control pollutants in storm water discharges that will occur after construction operations have been completed.
C. Upland Areas: Structural measures placed on upland areas to the degree attainable.
D. Map: A map of the entire site showing the overall development.
E. Riparian and/or Wetland Setback: All riparian and wetland setback areas will be identified on the plans. They will also be marked in the field prior to the start of construction.
F. BMPs: Best Management Practices used in the Post-Construction Water Quality Plan may include but are not limited to:
1. Permanent Storm Water Detention ponds that provide extended detention of the water volume.
2. Flow attenuation by use of open vegetated swales and natural depressions
3. Onsite infiltration of runoff
4. Sequential systems that combine several practices
5. Permanent conservation easements, preferably with the easement being held by a third party with no vested interest in ever seeing the property developed
6. Natural Channel Design for drainageways
7. Bioengineering in drainageways
8. Recreating floodplains
9. Chemical and biological filters in storm sewer inlets
10. Sand Filters
11. Allowing roof water from buildings to run across lawn areas to remove pollutants
12. Onsite sewage disposals system replacement or conversion to sanitary sewers
13. Low Impact Development Design
14. Countryside Development Design meeting the criteria of the Western Reserve Resource Conservation and Development Area.
15. Aquatic benches in Retention Basins and ponds.
G. Technical Basis: The plans will contain a rational statement utilized to select the BMPs used to control pollution and to maintain and protect water quality.
(2) Development Sites 5 Acres or Larger: A development site that disturbs five (5) or more acres of land or will disturb less than five (5) acres, but is a part of a larger common plan of development or sale, which will disturb five (5) or more acres of land shall identify:
A. Storm Water Detention: The Post-Construction BMP(s) chosen must be able to detain storm water runoff for protection of the stream channels, stream erosion control, and improved water quality.
B. Structural BMPs: Structural (designed) Post-Construction storm water treatment practices shall be incorporated into the permanent drainage system for the site.
C. Properly Sized BMPs: The BMP(s) chosen must be sized to treat the water quality volume (WQv) and ensure compliance with Ohio’s Water Quality Standards in OAC Chapter 3745-1.
1. The WQv shall be equivalent to the volume of runoff from a 0.75-inch rainfall and shall be determined according to one of the two following methods:
2. Through a site hydrologic study approved by the local municipal permitting authority that uses continuous hydrologic simulation and local long-term hourly precipitation records or
3. Using the following equation:
a. WQv = C * P * A / 12 where: WQv = water quality volume in acre-feet C = runoff coefficient appropriate for storms less than 1 inch (see Table 1) P = 0.75 inch precipitation depth A = area draining into the BMP in acres
Table 1 Runoff Coefficients Based on the Type of Land Use
Land Use | Runoff Coefficient |
Industrial & Commercial | 0.8 |
High Density Residential (>8 dwellings/acre) | 0.5 |
Medium Density Residential (4 to 8 dwellings/acre) | 0.4 |
Low Density Residential (<4 dwellings/acre) | 0.3 |
Open Space and Recreational Areas | 0.2 |
(4) Where the land use will be mixed, the runoff coefficient should be calculated using a weighted average. For example, if 60% of the contributing drainage area to the storm water treatment structure is Low Density Residential, 30% is High Density Residential, and 10% is Open Space, the runoff coefficient is calculated as follows (0.6)(0.3) + (0.3)(0.5) + (0.1)(0.2) = 0.35.
(5) An additional volume equal to 20 percent of the WQv shall be incorporated into the BMP for sediment storage and/or reduced infiltration capacity. The BMPs will be designed according to the methodology included in the Ohio Rainwater and Land Development manual, ODOT Post-Construction storm water standards, or other manual that is acceptable to Ohio EPA. .
(6) BMPs shall be designed such that the drain time is long enough to provide treatment, but short enough to provide storage available for successive rainfall events as described in Table 2 below
Table 2: Target Draw Down (Drain) Times for Structural Post-Construction Treatment Control Practices
Best Management Practice | Drain Time of WQv |
Infiltration | 24 - 48 hours |
Vegetated Swale and Filter Strip | 24 hours |
Extended Detention Basin (Dry Basins) | 48 hours |
Retention Basins (Wet Basins)* | 24 hours |
Constructed Wetlands (above permanent pool) | 24 hours |
Media Filtration, Bioretention | 40 hours |
• Provide both a permanent pool and an extended detention volume above the permanent pool, each sized at 0.75 * WQv
(7) The owner may request approval from the Village Engineer to use alternative structural Post-Construction BMPs if the owner can demonstrate, in a way that is acceptable to Ohio EPA rules and regulations, that the alternative BMPs are equivalent in effectiveness to those listed in Table 2 above. The use of alternative or vender supplied Post-Construction BMPs should be limited to redevelopment projects where justification is provided that the traditional BMPs in Table 2 are technically and economically infeasible.
(8) Construction activities shall be exempt from this condition if it can be demonstrated that the WQv is provided within an existing structural Post-Construction BMP that is part of a larger common plan of development or sale or if structural Post-Construction BMPs are addressed in a regional or local storm water management plan.
(9) For redevelopment projects (i.e., developments on previously developed property), Post-Construction practices shall either ensure a 20 percent net reduction of the site impervious area, provide for treatment of at least 20 percent of the WQv, or a combination of the two.
(10) Site Description:
A. The prior land uses of the site
B. The nature and type of construction activity (e.g., low density residential, shopping mall, highway, etc.)
C. Total area of the site and the area of the site that is expected to be disturbed (i.e., grubbing, clearing, excavating, filling or grading, including off-site borrow, fill or spoil areas and off-site utility installation areas)
D. Amount of the impervious area and percent imperviousness created by the construction activity
E. Name and/or location of the immediate receiving stream or surface water(s) and the first subsequent named receiving water and the major river watersheds in which it is located.
(11) A vicinity sketch locating:
A. The development area
B. The larger common plan of development or sale
C. All pertinent surrounding natural features within 200 feet of the development site including, but not limited to:
D. Water resources such as wetlands, springs, lakes, ponds, rivers and streams (including intermittent streams with a defined bed and bank)
E. Conservation Easements
F. Other sensitive natural resources and areas receiving runoff from the development
(12) The existing and proposed topography shown in the appropriate contour intervals as determined by the community engineer (generally one-foot contours are used).
(13) The location and description of existing and proposed drainage patterns and facilities, including any allied drainage facilities beyond the development area and the larger common plan of development or sale.
(14) Existing and proposed watershed boundary lines, direction of flow and watershed acreage.
(15) The person or entity responsible for continued maintenance of all permanent vegetative and/or mechanical Post-Construction water quality conservation practices (BMPs).
(16) The location of any existing or planned riparian and/or wetland setback areas on the property. (Ord. 3329. Passed 5-16-07.)