(a) SMPs are intended to provide information on all soil erosion, sediment and runoff control activities and best management practices (BMPs) to be used and incorporated on the site both during and after site development. This information includes, but is not limited to, site grading, stormwater management facilities and practices, erosion, sediment and runoff control information, maintenance plans, and other measures that focus on managing the effects of earth disturbing activities that occur as a result of site development.
(b) No earth disturbing activity subject to regulation under this chapter shall be undertaken for any land disturbance equal to or greater than one acre without an approved Site Development Plan as required under Section 1272.03 and a stormwater management plan (SMP) as required under this section. The stormwater management plan may be amended if there is a change in design, construction, operation, or maintenance which has a significant effect on the potential for the discharge of pollutants to the surface waters of the State or if the SMP proves to be ineffective in achieving the general objectives of controlling the pollutants in stormwater discharge associated with construction activity.
(c) Each SMP shall provide site designs that meet the performance standards required by this section.
(d) A SMP shall specifically include all the following:
(1) The minimum elements required in the Site Development Plan described in this chapter.
(2) The contents of the Stormwater Pollution Prevention Plan (SWP3) required by Ohio EPA Permit No. OHC000003 and incorporated herein by reference. (Attaching a copy of the current Ohio Environmental Protection Agency's NPDES construction general permit may be helpful.)
(3) A determination of runoff coefficients for both the pre-construction and post construction site conditions.
(4) For all disturbances of five or more acres of land (or less than five acres, but part of a larger common plan of development or sale which will in total disturb five or more acres of land), a description of post construction BMP(s) chosen and designed to detain and treat a water quality volume (WQv) equivalent to the volume of runoff from a 0.75-inch rainfall in accordance with the methodology outlined in Ohio EPA Permit Number OHC000003, Part III.G.2.e Large Construction Activities. When a combination of impervious area reduction and stormwater quality control facilities are used, ensure a twenty percent net reduction of the site impervious area, provide for a treatment of at least twenty percent of the WQv, or a combination of the two.
(5) Post construction 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 A. The developer must provide the Village Engineer with written approval from the Ohio EPA to use any post-construction BMP not listed in Table A.
Table A Target Draw Down (Drain) Times for Structural Post-Construction Treatment Control Practices | |
Stormwater control measure (SCM) | Drain time of WQv |
Infiltration | 24 B 48 hours |
Extended detention basin (dry basins) | 48 hours |
Extended detention basin (permeable pavement) | 24 hours |
Retention basins (wet basins) | 24 hours* |
Constructed wetlands (above permanent pool) | 24 hours |
Media filtration, bioretention | 24 hours |
* Provide both a permanent pool and an extended detention volume above the permanent pool, each size at 0.75 * WQv. | |
(6) For all disturbances of more than one acre 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, a description of measures that will be installed during the construction process to control pollutants in stormwater discharges that will occur after construction operations have been completed. Structural practices must comply with the requirements of the Ohio Environmental Protection Agency (EPA) Permit No. OHC000003: Authorization for Stormwater Discharges Associated with Construction Activity under the National Pollutant Discharge Elimination System (NPDES) Part m.G.2.e.
(7) An implementation schedule which describes the sequence of major construction operations (e.g., grubbing, excavating, grading, utilities and infrastructure installation) and the implementation of erosion, sediment and stormwater management practices or facilities to be employed during each operation of the sequence.
(8) A detail drawing of a typical individual lot showing standard individual lot erosion and sediment control practices.
(9) A detailed description of the stormwater controls to be incorporated into the SMP and explaining how such controls meet or exceed the appropriate performance standards required by this chapter.
(10) A detailed maintenance plan that describes procedures for inspections, cleaning, maintenance, repair, and replacement needed to ensure the continued performance of control practices by the managing organization responsible for implementing the SMP. Such plans must ensure that pollutants collected within structural post construction practices, be disposed of in accordance with local, State, and Federal regulations.
(11) A site map including:
A. Limits of earth-disturbing activity of the site including associated offsite borrow or spoil areas.
B. Soil types on the site, including locations of unstable or highly erodible soils.
C. Existing and proposed elevations and contours. A delineation of drainage watersheds expected during and after major grading activities as well as the size of each drainage watershed, in acres.
D. Existing and planned locations of buildings, roads, parking facilities and utilities.
E. The location of all erosion and sediment control practices, including areas likely to require temporary stabilization during site development.
F. Sediment and stormwater management basins, noting their sediment settling volume and contributing drainage area. Site map should include required and provided sediment storage and dewatering volumes and the weir length or skimmer size as applicable.
G. Permanent stormwater management practices to be used to control pollutants in stormwater after completion of the construction project.
H. Areas designated for the storage or disposal of solid, sanitary, and toxic wastes, including dumpster areas, cement truck washout areas, and vehicle fueling and maintenance.
I. The location of designated construction entrances where vehicles will access the site.
J. The location of any in-stream activities, including stream crossings.
K. Surface water locations of springs, wetlands, streams, lakes, water wells, etc., on or within 100 feet of the site, and including the boundaries of wetlands or stream channels and first subsequent named receiving water(s) the permittee intends to fill or relocate for which the permittee is seeking approval from the Army Corps of Engineers and/or Ohio EPA.
(12) A copy of the written notification from the director of the Ohio EPA that the developer or permittee has been granted permit coverage and is authorized to discharge stormwater associated with construction activity under the conditions of the permit and a copy of the Ohio EPA permit under which the permittee has been granted coverage or a copy of the permit requirements.
(13) The permitee's Ohio EPA facility permit number.
(14) The identity of all subcontractors engaged in activities that could impact stormwater runoff.
(15) Signatures from all of the identified subcontractors indicating that they have been informed and understand their roles and responsibilities in complying with the SMP.
(16) Determination of post-development runoff.
A. Each SMP shall include a comparison that quantifies the volume and rate of runoff from the site by subdrainage areas for pre-development conditions and proposed conditions. This evaluation shall be prepared according to methods prescribed in the current edition of Rainwater and Land Development or other appropriate sources. The evaluation shall:
1. Show delineation and sequence of subdrainage units which comprise the area proposed for development.
2. Indicate the hydraulic length of slope per individual subdrainage unit and the length of the natural or manmade watercourse which accommodates the surface runoff from each subdrainage unit.
3. Indicate within the legend the average percent slope, erosion factor (K) and runoff curve number (CN) per the individual subdrainage areas.
4. Include a hydrograph using the TR55, Type II Rainfall Distribution Pattern over a twenty-four-hour period for the following return intervals: 1-, 2-, 5-, 10-, 25-, 50-, and 100-year storms. Hydrographs for each of the recurrence intervals shall be produced for both the existing and proposed conditions.
5. The twenty-four-hour rainfall depths in Table B shall be utilized to quantify the stormwater runoff for the existing and proposed conditions.
Table B Sectional Mean Frequency Distributions for Storm Period of 24-Hours and Recurrence Intervals of 1 Year to 100 Years in Ohio | |
Return Period (years) | Rainfall (inches) for given recurrence interval |
1 | 2.00 inches |
2 | 2.40 inches |
5 | 2.98 inches |
10 | 3.46 inches |
25 | 4.16 inches |
50 | 4.74 inches |
100 | 5.36 inches |
Source: NOAA Atlas 14, Precipitation Frequency Estimates, Extracted Feb. 2011 | |
(17) Calculations for the design of stormwater management facilities shall demonstrate the following for each subdrainage unit:
A. The peak rate of runoff from the critical storm and all more frequent storms occurring on the site does not exceed the peak rate of runoff from a one year frequency, twenty-four-hour storm occurring on the same site under pre-development conditions.
B. Storms of less frequent occurrence (greater return periods) than the critical storm, shall have a proposed peak rate of runoff less than the existing peak rate of runoff.
C. The overflow spillway elevation shall be set one foot above the 100-year storm elevation and the surrounding berm elevation shall set minimally one foot higher than the overflow spillway.
(18) Calculation of a critical storm for each subdrainage unit of the site shall be determined as follows:
A. Calculate by appropriate hydrologic methods, such as the NRCS Technical Release 55 (TR55) the total volume of runoff from a one-year frequency, twenty-four-hour storm occurring on the development area before and after development.
B. From the volumes determined in above, determine the percentage increase in volume of runoff due to the proposed development, and using this percentage, select the twenty-four-hour critical storm from Table C.
Table C 24-Hour Critical Storm Runoff Rate | ||
If the percentage of increase in runoff volume is: | ||
Equal to or greater than | And less than | The critical storm runoff rate will be limited to: |
0 | 10 | 1 year |
10 | 20 | 2 years |
20 | 50 | 5 years |
50 | 100 | 10 years |
100 | 250 | 25 years |
250 | 500 | 50 years |
500 | - | 100 years |
C. The Village Engineer shall approve or reject any calculation method based on its technical validity for the given situation. Downstream capacity may further reduce maximum discharge requirements.
(e) Stormwater Management Facility Design Criteria.
(1) Runoff from all drainage area tributary to the stormwater management facility must be conveyed to the facility for all design storms up to and including the 100-year storm.
(2) A vehicular access drive and permanent easements must be provided from a public roadway to the outlet control device as approved by the Village Engineer.
(3) Attempt to preserve and/or improve the existing natural drainage by utilizing practices such as protecting existing vegetative buffer strips, phasing of construction operations in order to minimize the amount of disturbed land at any given time, and designation of tree preservation areas or other protective clearing and grubbing practices. Post-construction stormwater practices shall provide perpetual management of runoff quality and quantity so that a receiving stream's physical, chemical, and biological characteristics are protected and ecological functions are maintained.
(f) Stormwater Basins.
(1) The outlet structure and/or riser shall be located in the embankment for maintenance purposes.
(2) An emergency spillway is to be provided on all stormwater basins. Emergency spillways must be designed to convey flood flows safely past the embankment, and shall be designed in accordance with NRCS standards and specifications. The emergency spillway shall have a 100-year design storm capacity unless exempted in writing by the Village Engineer.
(3) All embankments shall be designed in accordance with the specifications in the current edition of the Ohio Rainwater and Land Development manual, the NRCS Field Office Technical Guide for Cuyahoga County, and the Ohio EPA standards.
A. All pond grading shall have a maximum slope of 3:1 and shall incorporate safety features to ensure public safety.
B. The primary spillway opening shall be constructed so as to not permit access to the public and other non-maintenance personnel.
(g) Off-Site Stormwater Control Facilities.
(1) Exceptions to requiring permanent on-site runoff control on the site may be considered by the Village Engineer provided the applicant can prove that:
A. The intent and standards of this chapter for runoff control can be best achieved by the utilization of off-site stormwater control facilities.
B. Runoff from the site can be conveyed to off-site stormwater facilities in a manner and by means which satisfy or surpass the standards of this chapter.
C. The applicant has ownership of or the right to use the off-site facility in question.
(h) Underground Storm Water Control Facilities.
(1) Underground storm water control facilities may be constructed to provide storm water management for development sites as approved by the Village Engineer.
(2) Voids in the stone aggregate around underground pipes or chambers are not to be included in the volume calculations for underground detention storm water management facilities.
(Ord. 2014-119. Passed 2-11-15; Ord. 2017-31. Passed 5-10-17; Ord. 2022-38. Passed 5-11-22.)