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 City 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 and should consider all future anticipated uses of the site.
(F) Structural post-construction BMPs cannot be installed within a state surface water (e.g., wetland or stream) unless it is authorized by a Clean Water Act § 401, being 33 U.S.C. § 1341 water quality certification and/or Clean Water Act § 404, being 33 U.S.C. §§ 1251 et seq. permit.
(G) 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.
(H) Long-term maintenance requirements and schedules of all BMPs for both the construction and post- construction phases of the development will be provided as a stand alone document to the post construction operator and the community.
(I) 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, and the like). All reports must be retained for a minimum of five years and made available to the city for inspection.
(J) This plan will identify the person or entity that will serve as the post-construction operator who will be financially responsible for maintaining the perpetual inspection and maintenance of permanent storm water conveyance and storage structures and other conservation practices. The plan must identify and provide a mechanism to require transfer of responsibilities in the event the property is sold and a means of notification to the city prior to transfer.
(K) 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.
(L) Maintenance plans must ensure that pollutants collected within structural post-construction practices, be disposed of in accordance with local, state and federal regulations.
(M) Maintenance plans must include legally binding perpetual maintenance easements and agreements. Easement documents must provide for community access.
(N) 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 City Engineer.
(1) Development Sites Smaller than Five Acres. A development site that will disturb one or more, but less than five 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 continue after construction operations or will be employed 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 and including drainage areas and patterns;
(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. On-site 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. On-site 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; and
15. Aquatic benches in retention basins and ponds.
(g) Technical Basis. The plan will contain a statement of the rationale utilized to select the BMPs used to control pollution and to maintain and protect water quality.
(2) Development sites five acres or larger. A development site that disturbs five or more acres of land or will disturb less than five acres, but is 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 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.
1. The BMP(s) chosen must be sized to treat the water quality volume (WQv) and ensure compliance with the state’s water quality standards in O.A.C. 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 equation:
2. WQ
v
= C * P * A / 12 where: WQ
v
= water quality volume in acre-feet; C = runoff coefficient appropriate for storms less than one inch (either using Table 1 or the following formula: C = 0.858i - 0.78i
2
+ 0.774i + 0.04 where i = fraction of post-construction impervious area); P = 0.75 inch precipitation
depth; and A = area draining into the BMP in acres.
Table 1: Runoff Coefficients Based on the Type of Land Use | |
Land Use | Runoff Coefficient |
High Density Residential (>8 dwellings/acre) | 0.5 |
Industrial & Commercial | 0.8 |
Low Density Residential (<4 dwellings/acre) | 0.3 |
Medium Density Residential (4 to 8 dwellings/acre) | 0.4 |
Open Space and Recreational Areas | 0.2
|
(d) 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;
(e) An additional volume equal to 20% 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;
(f) 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 not discharge more than the first half of the WQv
in less than one-third of the drain time;
Table 2: Target Drain Times for Structural Post-Construction BMPs | |||
BMPs Suitable for Drainage Areas > 5 Acres | BMPs Suitable for Drainage Areas < 5 Acres | ||
Table 2: Target Drain Times for Structural Post-Construction BMPs | |||
BMPs Suitable for Drainage Areas > 5 Acres | BMPs Suitable for Drainage Areas < 5 Acres | ||
Best Management Practice | Drain Time | Best Management Practice | Drain Time |
Dry extended detention basin* | 48 hours | Infiltration basins^ | 24-48 hours |
Wet extended detention basin** | 24 hours | Bioretention cells | 40 hours |
Constructed wetlands+ | 24 hours | Sand and other media filters | 40 hours |
Infiltration basins^ | 24-48 hours | Enhanced water quality swales | 24 hours |
Pocket wetlands# | 24 hours | ||
Vegetated filter strips | 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 0.75 WQ
v. | |||
+ 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 WQ
v
with 25% of the WQ
v
in a pool and 75% in marshes. The ED
v
above the permanent pool must be equal to the WQ
v
.
| |||
(g) The owner may request approval from the City 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;
(h) 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. 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 Community Engineer;
(i) For redevelopment projects (i.e., developments on previously developed property), post- construction practices shall either ensure a 20% net reduction of the site impervious area, provide for treatment of at least 20% of the WQv, or a combination of the two. Where projects are a combination of new development and redevelopment, the total WQv that must be treated shall be calculated by a weighted average based on acreage, with the new development at 100% WQv and redevelopment at 20% WQv;
(j) Site description:
1. The prior land uses of the site;
2. The nature and type of construction activity (e.g., low density residential, shopping mall, highway, and the like);
3. Total area of the site, area drained 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);
4. Amount of the impervious area and percent imperviousness created by the construction activity; and
5. 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. Provide a volume of flow and if applicable a water quality designation of the stream or wetland.
(k) A vicinity sketch locating:
1. The development area;
2. The larger common plan of development or sale; and
3. All pertinent surrounding natural features within 200 feet of the development site including, but not limited to:
a. Water resources such as wetlands, springs, lakes, ponds, rivers and streams (including intermittent streams with a defined bed and bank);
b. Conservation easements; and
c. Other sensitive natural resources and areas receiving runoff from the development.
(l) The existing and proposed topography shown in the appropriate contour intervals as determined by the City Engineer (generally one-foot contours are used);
(m) 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;
(n) Existing and proposed watershed boundary lines, direction of flow and watershed acreage;
(o) The person or entity responsible for continued maintenance of all permanent vegetative and/or mechanical post-construction water quality conservation practices (BMPs); and
(p) The location of any existing or planned riparian and/or wetland setback areas on the property.
(Ord. 17-05, passed 2-7-2005; Ord. 102-10, passed 8-23-2010)