(a) Stormwater Management Plans (SMPs) are intended to provide 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, pad elevation certification, stormwater 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.
(b) Each SMP shall provide site designs that meet the Performance Standards presented in Section 921.03 and provide practical treatment for both water quality and quantity of stormwater from the site as appropriate.
(c) In general, SMPs need to address:
(1) Erosion and sediment control. Providing measures to insure that earth disturbing activities at the site during and after development will be managed in a manner that will not result in increased erosion and sedimentation from the site resulting in impacts to water quality and that meet the Performance Standards specified in Section 921.03
.
(2) Runoff control. Providing measures to insure that the quantity of surface water runoff from the development site during and after construction will mimic the pre-development conditions and that meet the Performance Standards specified in Section 921.03
.
(1) The minimum elements required in the Site Development Plan described in Section 921.04(c)(1) to (4).
(2) The contents of the Storm Water Pollution Prevention Plan (SWP3) required by the Ohio EPA’s NPDES Construction Activity Permit #OHC000002 and incorporated here by reference (a copy of this permit is included in Appendix A). This Plan may be submitted as developed for the Ohio EPA, in conjunction with the other requirements of subsection (d) hereof. The contents of the Ohio EPA’s SWP3 include, but are not limited to:
A. A description of prior land uses at the site.
B. Existing data describing the soils on the site and, if available, the quality of any discharge from the site.
C. A determination of runoff coefficients for both the pre-construction and post construction site conditions.
D. For all large earth-disturbing activities (involving the disturbance of five or more acres of land or will disturb less than five acres, but part of a larger common plan of development or sale which will 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).
E. For all small earth-disturbing activities (which 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), a description of measures that will be installed during the development process to control pollutants in storm water discharges that will occur after construction operations have been completed.
F. An implementation schedule which describes the sequence of major construction operations (i.e., grubbing, excavating, grading, utilities and infrastructure installation) and the implementation of erosion, sediment and storm water management practices or facilities to be employed during each operation of the sequence.
G. For subdivided developments where the SWP3 does not call for a centralized sediment control capable of controlling multiple individual lots, a detail drawing of a typical individual lot showing standard individual lot erosion and sediment control practices.
H. A detailed description of the stormwater controls to be incorporated and how these meet or exceed the appropriate Performance Standards presented in Section 921.03. This shall include the identification of which entity (developer, contractor, owner) is responsible for implementation of each individual control (e.g., contractor A will clear land and install perimeter controls and contractor B will maintain perimeter controls until final stabilization).
I. A detailed maintenance plan that describes procedures (e.g. inspections) needed to ensure the continued performance of control practices. Such plans must ensure that pollutants collected within structural post-construction practices, be disposed of in accordance with local, state, and federal regulations.
J. A Site Map that includes:
1. Limits of earth-disturbing activity of the site including associated off-site 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.
8. 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.
9. The location of designated construction entrances where vehicles will access the site.
10. The location of any in-stream activities, including stream crossings.
(3) Copies of pertinent Notices of Intent (NOI), permits, public notices and letters of authorization must be included with SMP submissions. These may include, but are not limited to, Ohio EPA NPDES Permits authorizing storm water discharges associated with construction activity, Ohio EPA Phase II Stormwater Permits, Section 401 and 404 Clean Water Act Permits, Ohio EPA Isolated Wetland Permit, and Ohio Dam Safety Law Permits.
(4) Supplemental requirements as provided in subsection (f) hereof.
 To ensure consistency between State and local requirements and to reduce duplication of effort this model requires the minimum SWP3 requirements of Ohio’s Construction Activity General Permit (subsection (d)(2) hereof), in addition to local supplemental requirements (subsection (f) hereof). This allows applicants to use the SWP3 information developed for the State to be used toward fulfillment of the local requirements of this model. |
(e) Stormwater discharge to critical areas with sensitive resources (i.e. wetlands, steep slopes, scenic river designation, recharge areas, etc.) shall be subject to additional criteria, or shall need to utilize or restrict certain stormwater practices.
(f) Supplemental Requirements.
(1) Determination of post development runoff.
A. Stormwater runoff shall not be diverted from its existing watershed.
B. Each SMP shall include an evaluation of pre-development conditions together with during, and post-development impacts that quantifies 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:
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 individual subdrainage unit for a 24-hour storm of a one-year frequency.
4. Include a hydrograph for a 24-hour storm of the critical frequency to be controlled as determined according to subsection (f)(1)D hereof and all calculations made pertinent to evaluating the effects of the proposed development on the pre-development runoff conditions of the site.
C. Calculations for the design of stormwater management facilities shall demonstrate the following for each subdrainage unit:
1. 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 (1) year frequency, twenty-four (24) hour storm occurring on the same site under pre-development conditions.
2. Storms of less frequent occurrence than the Critical Storm, up to the 100 year storm shall have its peak runoff rates no greater than the peak runoff rates from equivalent storms under pre-development conditions. Consideration of the 1, 2, 5, 10, 25, 50, and 100 year storms in design and construction will be considered meeting this standard.
D. Calculation of a critical storm for each subdrainage unit of the site shall be determined as follows:
1. Calculate by appropriate hydrologic methods, such as the NRCS Technical Release 55 2, the total volume of runoff from a one year frequency, 24 hour storm occurring on the development area before, during, and after development.
[
2 Urban Hydrology for Small Watersheds, Technical Release 55. 1986. Natural Resources Conservation Service.]
2. From the volumes determined in subsection (f)(1)D.1.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 this table:
If the percentage of increase in volume of runoff is
(see chart below):
% Equal To or Greater Than | % Less Than | The Critical Storm for Peak Rate Control |
- | 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 |
E. The City of Fairborn’s City Engineer (authorized agent) shall approve or reject any calculation method based on its technical validity for the given situation.
(2) Off-site stormwater control facilities. Exceptions to requiring permanent on-site runoff control on the site shall be considered by the City of Fairborn Planning Commission and the authorized agent(s) 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 satisfies or surpasses the standards of this chapter).
C. The applicant has ownership of or the right to use the off-site facility in question.
(g) Stormwater Management Plan Submission, Review and Action.
(1) The applicant is encouraged to have a pre-submission meeting with the City of Fairborn ‘s City Engineer (authorized agent).
(2) Submission of two (2) sets of the SMP and other supporting data required by this regulation to the Planning Commission of the City of Fairborn and its authorized agent (City Engineer) completes the applicant’s responsibilities and initiates the review process.
(3) The SMP shall be reviewed by the City of Fairborn Planning Commission and/or its authorized agent (City Engineer) to:
A. Verify background information furnished by the applicant and evaluate the proposed development in relation to existing site conditions.
B. Assess the SMP in relation to the Performance Standards and requirements of this chapter.
(4) Upon submission of the SMP, the City of Fairborn Planning Commission and the authorized agent (City Engineer) shall complete a review of the SMP by the next regularly scheduled Planning Commission meeting, provided that the applicant has submitted all information required at least 20 working days prior to a regularly scheduled meeting.
(5) The City of Fairborn Planning Commission shall either:
A. Approve the SMP as submitted by the applicant; or
B. Conditionally approve the SMP and require the submission of additional and/or revised information by the applicant, in order to fully meet the intent and standards of this chapter; or
C. Disapprove the SMP.
(6) Revisions to conditionally approved SMPs shall be prepared and submitted by the applicant to the City of Fairborn Planning Commission and/or its authorized agent (City Engineer) for review.
(7) Action by the City of Fairborn Approval Authority and the authorized agent (City Engineer) approving or disapproving the SMP is a final order for purposes of judicial review.
(Ord. 7-09. Passed 3-2-09.)