(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 or earth-disturbing activities that occur as a result of site development. Said plan shall be prepared and stamped by a licensed professional engineer authorized in the State of Ohio. To minimize duplication, storm water pollution prevention plans developed to meet the requirements of Ohio EPA Permit No. OHC00005 may be coordinated and combined with requirements of this section to serve as the applicant's SWM Plan.
(b) Each SWM plan shall provide site design that meets the Performance Standards presented in Section 1082.05 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 1082.05.
(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 1082.05
.
(3) Non-structural preservation methods. Preserving existing natural conditions as much as feasible, in accordance with Ohio EPA Permit No. OHC00005, Part III.G.2.a.
(4) Post construction storm water management practices. Providing practices which offer perpetual management of runoff quality and quantity; ensure stream functions are maintained; and ensure receiving stream's physical, chemical, and biological characteristics are protected in accordance with Ohio EPA Permit No. OHC00005, Part III.G.2.e.
(5) Maintenance. Providing a description of maintenance procedures needed to ensure the continued performance of control practices as described in division (d)(2)G. of this section.
(6) Inspections. Providing procedures for inspection of all on-site controls as specified in Section 1082.08(h), Compliance Responsibility, Internal Inspections.
(d) A SWM Plan shall specifically include all the following:
(1) The minimum elements required in the Site Development Plan described in Section 1082.06(b).
(2) The contents of the Storm Water Pollution Prevention Plan (SWP3) required by Ohio EPA Permit No. OHC00005 and incorporated herein 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 0.90-inch rainfall (in accordance with the methodology outlined in Ohio EPA Permit No. OHC00005, Part III.G.2.e Large Construction Activities). 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 1082.07(d)(2)B. The developer must provide the City Engineer with written approval from the Ohio EPA to use any post-construction BMP not specifically authorized under Ohio EPA Permit No. OHC00005 or listed in Table 1082.07(d)(2)B.
Table 1082.07(d)(2)B. Target Draw Down (Drain) Times for Structural Post-Construction Treatment Control Practices
Target Draw Down (Drain) Times for Structural Post-Construction Treatment Control Practices | |
Best Management Practice (BMP) | Drain Time of WQV |
Infiltration | 24 - 48 hours |
Vegetated Swale and Filter Strip | 24 hours |
Extended Detention Basin (Dry Basins) | 48 hours |
Retention Basins (Wet Basins)* | 24 hours |
Constructed Wetlands (above permanent pool) | 24 hours |
Media Filtration, Bioretention | 40 hours |
* Provide both a permanent pool and an extended detention volume above the permanent pool, each size at 0.90* WQV. | |
C. For all disturbances of more than one acre but less than five acres of land and are 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. Structural practices must comply with the requirements of the Ohio EPA Permit No. OHC00005, Part III.G.2.e.
D. 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.
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 1082.05.
G. A detailed maintenance plan that describes the frequency and type of procedures (i.e., inspection, cleaning, maintenance, repair, and replacement) needed to ensure the continued performance of control practices and the party (e.g., a homeowners' association or the City of Vermilion) that will be responsible for implementing this plan. Such plans must ensure that pollutants collected within structural post-construction practices be disposed of in accordance with local, state, and federal regulations.
1. EXCEPTION: The developer shall have the option of owning the Storm Water Management Control Facility or dedicating it to the City of Vermilion along with the other City utilities. The City may elect to accept the Storm Water Management Control Facility with additional requirements before the facility shall be dedicated:
a. A survey plat of all the lands to be dedicated to the City shall be submitted for approval and acceptance. All preparation and recording fees for said plat shall be the developer's responsibility.
b. The dedicated land shall include a minimum of twenty foot wide access to the facility from the closest public right-of-way. A minimum fifteen foot wide concrete or asphalt drive to support maintenance vehicles shall be installed to provide access at the developer's expense.
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 and elevations. 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.
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.
11. Surface water locations including springs, wetlands, streams, lakes, water wells, etc., on or within 200 feet of the site, 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.
I. 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 storm water 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.
J. The permittee shall reference its Ohio EPA Facility Permit Number on the SWM plan.
K. An Inspection and Maintenance Agreement for Storm Water Best Management Practices. The Agreement shall be substantially in the form of Attachment A to Ordinance 2017-16.
(e) Determination of Post Development Runoff.
(1) Each SWM plan shall include a comparison that quantifies the volume and rate of runoff from the site by sub-drainage areas for pre-development conditions and proposed conditions. This evaluation shall be prepared according to methods prescribed in Rainwater and Land Development or other appropriate sources. The evaluation shall:
A. Show delineation and sequence of sub-drainage units which comprise the area proposed for development.
B. Indicate the hydraulic length of slope per individual sub-drainage unit and the length of the natural or man made watercourse which accommodates the surface runoff from each sub-drainage unit.
C. Indicate within the legend the average percent slope, erosion factor (K) and runoff curve number (CN) per individual sub-drainage areas.
D. Include a hydrograph utilizing TRSS, "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. Hydro-graphs for each of the recurrence intervals shall be produced for both the existing and proposed conditions.
E. The twenty-four-hour rainfall depths in Schedule 1082.07(e)(1)E. shall be utilized to quantify the storm water runoff for the existing and proposed conditions.
Schedule 1082.07(e)(1)E. Sectional Mean Frequency Distributions for Storm Period of 24-Hours and Recurrence Intervals of 1 Year to 100 Years in Ohio Return Period (years)
Return Period (years) | Rainfall (inches) for given recurrence interval |
1 | 1.98 in. |
2 | 2.44 in. |
5 | 3.06 in. |
10 | 3.55 in. |
25 | 4.35 in. |
50 | 5.08 in. |
100 | 5.92 in. |
SOURCE: Huff, Floyd A., and James R. Angel. Rainfall Frequency Atlas of the Midwest. Illinois State Water Survey, Champaign, Bulletin 71, 1992.
(2) Calculations for the design of storm water management facilities shall demonstrate the following for each sub-drainage 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 than the critical storm, up to the 100-year storm shall have its proposed peak runoff rates no greater than the pre-development peak runoff rate for that storm event.
(3) Detention volume shall be no less than 0.167 acre-feet per contributing drainage acre unless otherwise approved by the City Engineer.
(4) Calculation of a critical storm for each sub-drainage unit of the site shall be determined as follows:
A. Calculate by appropriate hydrologic methods, such as the TRSS, 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 division (4)A. 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 the following table:
Table 1082.07(e)(4)B: Twenty-Four Hour Critical Storm Runoff Rate
If the percentage of increase in runoff volume is: | The Critical Storm Runoff Rate will be Limited to: | |
Equal to or greater than | And Less Than | |
0 | 10 | 1 year |
10 | 20 | 2 years |
20 | 50 | 5 years |
50 | 100 | 10 years |
250 | 500 | 50 years |
500 | -- | 100 years |
C. The City 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 City 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 storm water control facilities.
B. Runoff from the site can be conveyed to off-site storm water 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.
(f) Storm Water Management (SWM) Plan Submission, Review and Action.
(1) The applicant is encouraged to have a pre-submission meeting with the City Engineer.
(2) Submission of two sets of the SWM plan and other supporting data required by this regulation to the City Engineer complete the applicant's responsibilities and initiates the review process.
(3) The SWM plan shall be reviewed by the 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 SWM plan in relation to the performance standards and requirements of this chapter.
(4) Upon submission of the SWM plan the City Engineer shall complete a review and shall either:
A. Approve the SWM plan as submitted by the applicant; or
B. Conditionally approve the SWM plan 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 SWM plan based upon a written review noting the reasons.
(5) Action by the City Approval Authority and the authorized agent(s) approving or disapproving the SWM plan is a final order for purposes of judicial review.
(Ord. 2017-16. Passed 5-15-17; Ord. 2022-23. Passed 5-9-22.)