The Storm Water Management Plan will also contain the following information.
(a) Construction activities which do not include the installation of any impervious surface (eg. soccer fields), abandoned mine reclamation activities, wetland mitigation, etc. or such activities regulated by the State of Ohio are not required to comply with this section.
(b) General Requirements: All Storm Water Management Plans must contain the following information pertaining to post-construction water quality control:
(1) A description of the post-construction BMP(s) that will be installed during the 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.
(2) Detail drawings must be provided for all post-construction BMP(s).
(3) Structural post-construction BMPs cannot be installed within a State surface water (eg. wetland or stream) unless it is authorized by a Clean Water Act Section 401 quality certification and/or Clean Water Act Section 404 permit.
(4) This Plan must also include a document identifying the person or entity that will serve as the Post-Construction operator who will be financial responsible for maintaining the perpetual inspection and maintenance of the permanent storm water conveyance and storage structures and practices.
(5) This plan must contain maintenance responsibilities; routine maintenance tasks; schedule for inspection and maintenance and any necessary legally binding maintenance easements and agreements.
(c) 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:
(1) 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.
(2) 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.
(3) Upland Areas: Structural measures placed on upland areas to the degree attainable.
(4) Map: A map of the entire site showing the overall development.
(5) 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.
(6) BMPs: Best Management Practices used in the Post-Construction Water Quality Plan may include but are not limited to:
A. Permanent Storm Water Detention ponds that provide extended detention of the water volume
B. Flow attenuation by use of open vegetated swales and natural depressions
C. Onsite infiltration of runoff
D. Sequential systems that combine several practices
E. Permanent conservation easements, preferably with the easement being held by a third party with no vested interest in ever seeing the property developed
F. Natural Channel Design for drainage ways
G. Bioengineering in drainageways
H. Recreating floodplains
I. Chemical and biological filters in storm sewer inlets
J. Sand Filters
K. Allowing roof water from buildings to run across lawn areas to remove pollutants
L. Onsite sewage disposals system replacement or conversion to sanitary sewers
M. Impact Development Design: Countryside Development Design meeting the criteria of the Western Reserve Resource Conservation and Development Area & Aquatic benches in Retention Basins and ponds.
(7) 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.
(d) 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:
(1) 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.
A. Structural BMPs: Structural (designed) Post-Construction storm water treatment practices shall be incorporated into the permanent drainage system for the site.
B. 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. The WQv shall be equivalent to the volume of runoff from a 0.75-inch rainfall and shall be determined according to the following method / equation:
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) or the following formula: C=0.858i3 - 0.78i2 +0.04where i= fraction of post-construction impervious area where 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 |
C. 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.
D. 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. .
E. The BMPs listed in Table 2 below shall be considered standard BMPs approved for general use. However, communities with a regulated MS4 may limit the use of some of these BMPs. 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 and avoid the creation of nuisance conditions. The outlet structure for the post-construction BMP must bot discharge more than the first half of the WQv or EDv in less than one-third of the drain time. BMPs shall be designed as further described in Table 2 below:
Table 2 Runoff Coefficients Based on the Type of Land Use
Best Management Practice | Drain Time of WQv |
Infiltration Basin^ | 24-48 hours |
Enhanced Water Quality Swale | 24 hours |
Dry Extended Detention Basin* | 48 hours |
Wet Extended Detention Basin** | 24 hours |
Constructed Wetland (above permanent pool)+ | 24 hours |
Sand & Other Media Filtration | 40 hours |
Bioretention Cell^ | 40 hours |
Pocket Wetland# | 24 hours |
Vegetated Filter Strip | 24 hours |
*Dry Basins must include forebay and micropool each sized at 10% of the WQv;
**Provide both a permanent pool and an EDv above the permanent pool, each sized at 1.75;
*WQv
+Extended detention shall be provided for the full WQv above the permanent water pool;
^The WQv shall completely infiltrate within 48 hours so there is no standing or residual water in the BMP;
#Pocket wetlands must have a wet pool equal to the WQv, with 25% of the WQv in a pool and 75% in marshes. The EDv above the permanent pool must be equal to the WQv.
F. The owner may request approval from the Building Commissioner 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.
1. The permitee may request approval from Ohio EPA to use alternative methods to satisfy conditions in this permit if the permittee can demonstrate that the alternative methods are sufficient to protect the overall integrity of the receiving stream and the watershed. Upon approval of the Ohio EPA, alternative methods will be approved or denied by the Building Commissioner based upon the City Engineer's recommendation and on a case-by-case basis.
G. 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.
H. 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.
I. A municipally operated regional storm water BMP can be used as a post-construction BMP provided that the BMP can detain the WQv from the entire drainage area and release it over a 24-hour period upon written permission from the City's Engineer.
J. IF APPLICABLE AS AN ALTERNATE: The construction of new roads and roadway improvement projects by public may implement post-construction BMPs in compliance with the current version of the Ohio Department of Transportation's "Location and Design Manual, Volume Two Drainage Design" that has been accepted by Ohio EPA. Approval from the City Engineer shall be acquired if using this as an alternative.
(Ord. 70-12. Passed 11-13-12.)