(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, 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 1195.03 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 ensure 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 1195.03.
(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 1195.03.
(d) If a SMP is required under Section 1195.02(h) such plan shall specifically include all the following and be included with the final construction document submission:
(1) The minimum elements required in the Site Development Plan described in Section 1195.04(c)(1)A.-D.
(2) The contents of the Storm Water Pollution Prevention Plan (SWP3) required by the Ohio EPA’s NPDES Construction Activity Permit #OHC000002 and incorporated herein by reference. This plan may be submitted as developed for the Ohio EPA, in conjunction with the other requirements of Section 1195.05(d). 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 which will disturb less than five acres, but are 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 are not 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 stormwater 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 stormwater 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 1195.03. 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 stormwater management practices to be used to control pollutants in stormwater 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 stormwater 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 (h) hereof.
(g) Stormwater discharge to critical areas with sensitive resources (i.e. wetlands, steep slopes, scenic river designation, recharge areas, etc.) may be subject to additional criteria, or may need to utilize or restrict certain stormwater practices.
(h) Supplemental Requirements.
(1) Determination of Post Development Runoff.
A. 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, 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 and all calculations made pertinent to evaluating the effects of the proposed development on the pre-development runoff conditions of the site.
B. 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 their 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.
C. 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 552 , total volume of runoff from a one-year frequency, 24-hour storm occurring on the development area before, during, and after development.
2. From the volumes determined in subsection (h)(1)C.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:
% 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 |
_________________________
2Urban Hydrology for Small Watersheds, Technical Release 55. 1986. Natural Resources Conservation Service.
D. The Municipal Manager’s Office shall approve or reject any calculation method based on its technical validity for the given situation.
(2) Off-Site Stormwater Control Facilities.
A. Exceptions to requiring permanent on-site runoff control on the site may be considered by the Municipal Manager’s Office provided the applicant can prove that:
1. The intent and standards of this chapter for runoff control can be best achieved by the utilization of off-site stormwater control facilities.
2. 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.
(3) Stormwater Management Plan Submission, Review and Action.
A. The applicant is to have a pre-submission meeting with the Municipal Manager’s Office as part of the preliminary plan approval process.
B. Submission of two (2) sets of the SMP and other supporting data required by this regulation to the Municipal Manager’s Office completes the applicant’s responsibilities and initiates the review process.
C. The SMP shall be reviewed by the Municipal Manager’s Office to:
1. Verify background information furnished by the applicant and evaluate the proposed development in relation to existing site conditions.
2. Assess the SMP in relation to the Performance Standards and requirements of this chapter.
D. The Municipal Manager’s Office shall either:
1. Approve the SMP as submitted by the applicant; or
2. Disapprove the SMP with comments.
E. Action by the Municipal Manager’s Office approving or disapproving the SMP is a final order for purposes of judicial review. (Ord. 08-80. Passed 12-1-08.)