In order to control Post-Construction water quality damage and damage to public and private lands, the owner of each development area shall be responsible for developing a Post-Construction Storm Water Management Plan (PCSWP).
(a) The PCSWP plan will be combined with the Construction Site Conservation Plan and the Riparian Setback and Wetland Setback Plans that are also developed for the site.
(b) The PCSWP plan will contain a description of controls appropriate for each construction operation covered by these regulations, and the operator will implement such controls in a timely manner.
(c) The PCSWP plan will list TMDLs applicable for the site and demonstrate that appropriate stormwater control measures (SCMs) have been selected to address these TMDLs.
(d) The PCSWP plan will include a site description identifying:
(1) The prior land uses of the site
(2) The nature and type of construction activity (e.g., low density residential, shopping mall, highway, etc.)
(3) Total area of the site and the area of the site that is expected to be disturbed (i.e., grubbing, clearing, excavating, filling or grading, including off-site borrow, fill or spoil areas and off-site utility installation areas)
(4) Amount of the impervious area and percent imperviousness created by the construction activity
(5) Name and/or location of the immediate receiving stream or surface water(s) and the first subsequent named receiving water and the major river watersheds in which it is located.
(6) A vicinity sketch locating:
A. The development area
B. The larger common plan of development or sale
C. All pertinent surrounding natural features within 200 feet of the development site including, but not limited to:
1. Water resources such as wetlands, springs, lakes, ponds, rivers and streams (including intermittent streams with a defined bed and bank)
D. Conservation Easements
E. Other sensitive natural resources and areas receiving runoff from the development
F. The existing and proposed topography shown in the appropriate contour intervals as determined by the city engineer (generally one-foot contours are used).
G. The location and description of existing and proposed drainage patterns and facilities, including any allied drainage facilities beyond the development area and the larger common plan of development or sale.
H. Existing and proposed watershed boundary lines, direction of flow and watershed acreage.
I. The location of any existing or planned riparian and/or wetland setback areas on the property.
(e) The SCMs used to satisfy the conditions of these regulations shall meet the standards and specifications in the current edition of the Ohio Rain Water and Land Development manual, or other manual that is acceptable to the City Engineer or Ohio EPA.
(f) The PCSWP plan must make use of the practices that preserve the existing natural condition to the Maximum Extent Practicable (MEP).
(g) To meet the Post-Construction requirements of this regulation, the Post-Construction Water Quality Plan must contain a description of the Post-Construction SCMs that will be installed during construction for the site and the rationale for their selection. The rationale must address the anticipated impacts on the channel and floodplain morphology, hydrology, and water quality.
(h) Structural post-construction SCMs cannot be installed within State surface water (e.g., wetland or stream) unless it is authorized by a Clean Water Act Section 401 water quality certification and/or Clean Water Act Section 404 Permit.
(i) The PCSWP plan will identify the person or entity responsible for continued maintenance of all vegetative and/or mechanical SCMs for both the construction and Post-Construction phases of the development.
Long-term maintenance requirements and schedules of all SCMs for both the construction and Post-Construction phases of the development will be provided as a stand alone document to the Post-Construction operator and the City. The PCSWP plan will contain long-term maintenance inspection schedules, including:
(1) The printed name and contact point of the Post-Construction landowner (e.g., president of the homeowners association, store manager, apartment complex manager, etc.)
(2) The person or entity that will serve as the Post-Construction operator who will be financially responsible for maintaining the perpetual inspection and maintenance of permanent storm water conveyance and storage structures and other conservation practices.
(3) The method of ensuring that funding will be available to conduct the long-term maintenance and inspections of all permanent storm water, soil erosion and sediment control, and water quality practices will be identified.
(j) Maintenance plans must ensure that pollutants collected within structural Post-Construction practices be disposed of in accordance with local, state, and federal regulations.
(k) Maintenance plans must include legally binding perpetual maintenance easements and agreements. Easement documents must provide for City access.
(l) Unless specifically exempted, all activities associated with post-construction stormwater management must comply with all portions of Ohio EPA Permit No OHC000005 or the most recent Ohio EPA General Permit Authorization for Storm Water Discharges Associated with Construction Activity Under the National Pollutant Discharge Elimination System.
(m) For all construction activities that will disturb two or more acres of land or will disturb less than two (2) acres that are part of a larger common plan of development or sale which will disturb two (2) or more acres of land, the post construction BMP(s) chosen shall be able to manage storm water runoff for protection of stream channels, stream stability, and water quality. The BMP(s) chosen must be compatible with site and soil conditions. Structural post-construction storm water treatment practices shall be incorporated into the permanent drainage system for the site.
(1) The BMP(s) chosen must be sized to treat the water quality volume (WQv) and ensure compliance with Ohio's Water Quality Standards in OAC Chapter 3745-1. The WQv shall be equivalent to the volume of runoff from a 0.90-inch rainfall and shall be determined using the following equations:
A. WQv = Rv * P * A / 12 (Equation 1) where: WQv = water quality volume in acre-feet; Rv = the volumetric runoff coefficient calculated using equation 2; P = 0.90 inch precipitation depth; A = area draining into the BMP in acres
B. Rv = 0.05 + 0.9i (Equation 2) where: i = fraction of post-construction impervious surface
(2) An additional volume equal to twenty percent (20%) of the WQv shall be incorporated into the BMP for sediment storage. Ohio EPA recommends BMPs be designed according to the methodology described in the most current edition of the Rainwater and Land Development manual or in another design manual acceptable for use by Ohio EPA.
(3) The BMPs listed in Table 1a and 1b are approved for use within the City of Lorain. BMPs shall be designed such that the drain time is long enough to provide treatment but short enough to provide storage for successive rainfall events and avoid the creation of nuisance conditions. The outlet structure for the post-construction BMP shall not discharge more than the first half of the WQv in less than one-third of the drain time. The WQv is the volume of storm water runoff that must be detained by a post-construction practice as specified by the most recent edition of the Rainwater and Land Development manual.
Table 1a Extended Detention Post-Construction Practices with Minimum Drain Times
Extended Detention Practices | Minimum Drain Time of WQv |
Wet Extended Detention Basin 1,2 | 24 hours |
Constructed Extended Detention Wetland 1,2 | 24 hours |
Dry Extended Detention Basin 1,3 | 48 hours |
Permeable Pavement - Extended Detention 1 | 24 hours |
Underground Storage - Extended Detention 1,4 | 24 hours |
Sand & Other Media Filtration - Extended Detention 1, 5 | 24 hours |
1. The outlet structure shall not discharge more than the first half of the WQv in less than one-third of the drain time.
2. Provide a permanent pool with a minimum volume equal to the WQv and an extended detention volume above the permanent pool equal to 1.0 x WQv.
3. Dry basins must include a forebay and a micropool each sized at a minimum of 0.1 x WQv and a protected outlet, or include acceptable pretreatment and a protected outlet.
4. Underground storage must have pretreatment for removal of suspended sediments included in the design and documented in the SWP3. This pretreatment shall concentrate sediment in a location where it can be readily removed. For non-infiltrating, underground extended detention systems, pretreatment shall be 50% effective at capturing total suspended solids according to the testing protocol established in the Alternative Post Construction BMP Testing Protocol.
5. The WQv ponding area shall completely empty between 24 and 72 hours.
Table 1b Infiltration Post-Construction Practices with Maximum Drain Times
A. Infiltration Practices | B. Maximum Drain Time of WQv |
Bioretention Area/Cell 1,2 | 24 hours |
Infiltration Basin 2 | 24 hours |
Infiltration Trench 3 | 48 hours |
Permeable Pavement - Infiltration 3 | 48 hours |
Underground Storage - Infiltration 3,4 | 48 hours |
1. The outlet structure shall not discharge more than the first half of the WQv in less than one-third of the drain time.
2. Provide a permanent pool with a minimum volume equal to the WQv and an extended detention volume above the permanent pool equal to 1.0 x WQv.
3. Dry basins must include a forebay and a micropool each sized at a minimum of 0.1 x WQv and a protected outlet, or include acceptable pretreatment and a protected outlet.
4. Underground storage must have pretreatment for removal of suspended sediments included in the design and documented in the SWP3. This pretreatment shall concentrate sediment in a location where it can be readily removed. For non-infiltrating, underground extended detention systems, pretreatment shall be 50% effective at capturing total suspended solids according to the testing protocol established in the Alternative Post-Construction BMP Testing Protocol. 5. The WQv ponding area shall completely empty between 24 and 72 hours.
(4) Post-construction practices shall be sized to treat 100% of the WQv associated with their contributing drainage area. If there is an existing post-construction BMP that treats runoff from the disturbed area and the BMP meets the post-construction requirements of this permit, no additional post-construction BMP will be required. A regional storm water BMP may be used to meet the post-construction requirement if: (1) the BMP meets the design requirements for treating the WQv; and (2) a legal agreement is established through which the regional BMP owner or operator agrees to provide this service in the long term. Design information for such facilities such as contributing drainage areas, capacities, elevations, outlet details and drain times shall be included in the SWP3.
(5) Small Construction Activities. For all construction activities which result in a disturbance less than two (2) acres, a post-construction practice shall be used to treat storm water runoff for pollutants and to reduce adverse impacts on receiving waters. If limiting factors exist which would prohibit the project going forward should Table 1a and 1b practices be required, the applicant must provide a justification in the SWP3 as to why the use of these practices are not feasible and present an alternative practice, the utilization of which is subject to Engineer approval.
(6) Transportation Projects. The construction of new roads and roadway improvement projects by public entities (i.e., the state, counties, townships, cities, or villages) may implement post-construction BMPs in compliance with the current version (as of the effective date of this permit) of the Ohio Department of Transportation's "Location and Design Manual, Volume Two Drainage Design" that has been accepted by Ohio EPA as an alternative to the conditions of this permit.
(7) Offsite Mitigation of Post-Construction. The City of Lorain shall allow offsite mitigation of post-construction requirements if authorized by Ohio EPA under Part III.G.2.e of permit OHC000005. Prior to plan approval by the City of Lorain, evidence of Ohio EPA approval for offsite mitigation must be submitted to the City Engineer.
(8) Previously Developed Areas - For a previously developed area, one or a combination of the following two conditions shall be met:
A. A twenty percent (20%) net reduction of the site's volumetric runoff coefficient through impervious area reduction with soil restoration or replacing impervious roof area with green roof area (for these purposes green roofs shall be considered pervious surface) or,
B. Treatment of twenty percent (20%) of the WQv for the previously developed area using a practice meeting Table 4a/4b criteria.
(9) Where there is a combination of redeveloped areas and new development, a weighted approached shall be used with the following equation:
A. WQv = P * A * [(Rv1*0.2) + (Rv2 - Rv1)] / 12 (Equation 3) where: where P = 0.90 inches; A = area draining into the BMP in acres; Rv1 = volumetric runoff coefficient for existing conditions (current site impervious area); Rv2 = volumetric runoff coefficient for proposed conditions (post-construction site impervious area)
(10) Post-construction practices shall be located to treat impervious areas most likely to generate the highest pollutant load, such as parking lots or roadways, rather than areas predicted to be cleaner such as rooftops.
(11) Runoff Reduction Practices. The size of structural post-construction practices used to capture and treat the WQv can be reduced by incorporating runoff reducing practices into the design of the site's drainage system. The approach to calculate and document runoff reduction is detailed in the Rainwater and Land Development Manual. BMP-specific runoff reduction volumes are set by specifications in the Rainwater and Land Development Manual for the following practices:
A. Impervious surface disconnection
B. Rainwater harvesting
C. Bioretention
D. Infiltration basin
E. Infiltration trench
F. Permeable pavement with infiltration
G. Underground storage with infiltration
H. Grass swale
I. Sheet flow to filter strip
J. Sheet flow to conservation area
If utilized, evidence of accurate Runoff Reduction Practice utilization must be submitted to the City for review prior to plan approval.
(12) In order to promote the implementation of green infrastructure, the City of Lorain may consider the use of runoff reducing practices to demonstrate compliance with Section 1531.07(m) for areas of the site not draining into a common drainage system of the site, e.g., sheet flow from perimeter areas such as the rear yards of residential lots, low density development scenarios, or where the permittee can demonstrate that the intent of pollutant removal and stream protection, as required in Section 1531.07(m) is being addressed through non-structural post-construction BMPs. Consideration shall be based upon review and approval by Ohio EPA.
(13) The City of Lorain may consider the use of alternative BMPs if all OHC000005 permit conditions for such alternatives are met and approved by Ohio EPA. Consideration shall be based upon review and approval by Ohio EPA. (Ord. 167-19. Passed 12-16-19.)