(a) Storm water management (SWM) plans are intended to provide critical information on all soil erosion 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, storm water management facilities and practices, erosion 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. Said plan shall be prepared, signed, and sealed by a licensed professional engineer authorized in the State of Ohio.
(b) Each SWM plan shall provide site design that meets the performance standards presented in Section 1295.05 and provide practical treatment for both water quality and quantity of storm water from the site as appropriate.
(c) In general, SWM plans need to address:
(1) Erosion and sediment control. Provide measures to ensure that earth-disturbing activities at the site during and after development will be managed in a manner that will minimize increased erosion and sedimentation from the site resulting in impacts to water quality and that meet the performance standards specified in Section 1295.05.
(2) Runoff control. Providing measures to ensure that the rate of surface water runoff from the development site during and after construction will approximate the predevelopment conditions and that meet the performance standards specified in Section 1295.05.
(d) A SWM plan shall specifically include all the following:
(2) The contents of the storm water pollution prevention plan (SWP3) required by the Ohio EPA's NPDES Construction Activity Permit #OHC000003 and incorporated here by reference. The contents of the storm water management (SWM) plan include, but are not limited to:
A. A determination of runoff coefficients for both the pre-construction and post construction site conditions.
B. 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 (see Ohio EPA Construction Activity Permit for Methodology).
C. 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 storm water discharges that will occur after construction operations have been completed.
D. An implementation schedule which describes the sequence of major construction operations (i.e., clearing, grubbing, excavating, filling, grading, utilities, and infrastructure installation, etc.) and the implementation of erosion, sediment and storm water management practices or facilities to be employed during each operation of the sequence.
E. A detail drawing of a typical individual lot showing standard individual lot erosion and sediment control practices.
F. A detailed description of the storm water controls to be incorporated and how these meet or exceed the appropriate performance standards presented in Section 1295.05.
G. A detailed maintenance plan that describes procedures (e.g. inspections) needed to ensure the continued performance of control practices and the responsible party (i.e., homeowner association, site owner and/or applicant, etc.). Such plans must ensure that pollutants collected within structural post-construction practices be disposed of in accordance with local, state, and federal regulations.
H. A site map including:
1. Limits of earth-disturbing activity of the site including associated offsite borrow or spoil areas.
2. Soil types on the site, including locations of unstable or highly erodible soils.
3. Existing and proposed contours. A delineation of drainage watersheds expected during and after major grading activities as well as the size of each drainage watershed, in acres.
4. Existing and planned locations of buildings, roads, parking facilities and utilities.
5. The location of all erosion and sediment control practices, including areas likely to require temporary stabilization during site development.
6. Sediment and storm water management basins noting their sediment settling volume and contributing drainage area.
7. Permanent storm water management practices to be used to control pollutants in storm water after construction operations have been completed (as applicable).
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. Permanent conservation easements, preferably with the easement being held by a third party with no vested interest in ever seeing the property developed.
e. Natural channel design for drainageways.
f. Bioengineering in drainageways.
g. Recreating floodplains.
h. Chemical and biological filters in storm sewer inlets.
i. Sand filters.
j. Allowing roof water from buildings to run across lawn areas to remove pollutants.
k. Onsite sewage disposals system replacement or conversion to sanitary sewers.
l. Low impact development design.
m. Aquatic benches in retention basins and ponds.
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.
8. Areas designated for the storage or disposal of solid, sanitary, hazardous and/or toxic wastes, including but not limited to dumpster areas, cement truck washout areas, and vehicle fueling and maintenance areas.
9. The location of designated construction entrances where vehicles will access the site.
10. The location of any in-stream activities, including stream crossings.
11. A copy of the Ohio EPA NPDES permit shall be included and referenced on the SWM plan.
(e) Determination of Post Development Runoff.
(1) Each SWM plan shall include an evaluation of pre-development conditions together with impacts during construction (disturbed) and post-development impacts that quantify the volume and rate of runoff from the site by subdrainage areas. This evaluation shall be prepared according to methods prescribed in the latest edition of Rainwater and Land Development or other appropriate sources. The evaluation shall:
A. Show delineation and sequence of subdrainage units which comprise the area proposed for development.
B. 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.
C. Indicate within the legend the average percent slope, erosion factor (K) and runoff curve number (CN) per individual subdrainage unit for a 24-hour storm of a one-year frequency.
D. Include a hydrograph for a 24-hour storm of the critical frequency to be controlled and all calculations made pertinent to evaluate the effects of the proposed development on the pre-development runoff conditions of the site.
(2) Calculations for the design of storm water 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, 24-hour storm occurring on the same site under pre-development conditions.
B. Storms of less frequent occurrence than the critical storm, up to the 100-year storm shall have its peak runoff rates no greater than 0.25 CFS per contributing drainage acre unless otherwise approved by the Municipal Engineer.
(3) Detention volume shall be no less than 0.167 acre-feet per contributing drainage acre unless otherwise approved by the Municipal Engineer.
(4) 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, 24-hour storm occurring on the development area before, during and after development.
B. From the volumes determined in division A. above, determine the percentage increase in volume of runoff due to the proposed development, and using this percentage, select the 24-hour critical storm from the following table:
24-Hour Critical Storm Runoff Rate |
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 Municipal 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.
(5) Off-site storm water control facilities. Exceptions to requiring permanent on-site runoff control on the site may be considered by the Municipal Engineer provided the site owner and/or 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 storm water control facilities.
B. Runoff from the site can be conveyed to offsite storm water facilities in a manner and by means which satisfy or surpass the standards of this chapter.
C. The site owner and/or applicant has ownership of or the right to use the off-site facility in question.
(f) Storm water management (SWM) plan submission review and action.
(1) The site owner and/or applicant is encouraged to have a pre-submission meeting with the municipality.
(2) The site owner and/or applicant's submission of two sets of the SWM plan, and other supporting data required by this regulation, to the municipality initiates the review process.
(3) The SWM plan shall be reviewed by the Municipal Engineer to:
A. Verify background information furnished by the site owner and/or applicant and evaluate the proposed development in relation to existing site conditions.
B. Assess the SWM plan in relation to the performance standards and requirements of this chapter.
(4) Upon submission of the SWM plan the municipality shall complete a review and shall either:
A. Approve the SWM plan as submitted by the site owner and/or applicant;
B. Conditionally approve the SWM plan and require the submission of additional and/or revised information by the site owner and/or applicant, in order to fully meet the intent and standards of this chapter; or
C. Disapprove the SWM plan based upon a written review noting the reasons.
(5) Action by the municipal approval authority and the authorized agent(s) approving or disapproving the SWM plan is a final order for purposes of judicial review.
(Ord. 13-030. Passed 10-15-13; Ord. 21-021. Passed 11-16-21.)