(A) Minimum requirements. All development or redevelopment disturbing at least one acre must include provisions to preserve or minimize impacts to predevelopment site hydrology and topography to the maximum extent practicable through runoff pollution prevention techniques. In addition to runoff pollution prevention measures, storm water treatment BMPs shall be incorporated into Plan Design as needed to meet the performance criteria in § 154.03.
(B) Runoff pollution prevention.
(1) Storm water management begins with thoughtful design. Site planning that integrates comprehensive storm water management from the outset is the most effective way to reduce and prevent pollution and flooding. Good site planning can also reduce the size and cost of structural solutions; when BMP storm water structures are proposed only at the final stages of design and construction, the result is often unnecessarily large and costly facilities. Planning ahead can prevent the need for large structures.
(2) Site planning practices. With careful site planning, developers and municipalities can reduce the amount of impervious area created by pavement and roofs and thus reduce the volume of runoff and associated pollutants requiring control. Practices that could be considered:
(a) Select site designs that preserve or minimize impacts to predevelopment site hydrology and topography;
(b) Protect environmentally sensitive areas;
(c) Practice conservation development;
(d) Use cluster development;
(e) Create open space;
(f) Maximize the flow path from inflow points to outflow points;
(g) Provide underdrain systems, where applicable;
(h) Reduce hydraulic connectivity of impervious surfaces;
(i) Practice rooftop greening;
(j) Relax frontage and setback requirements;
(k) Modify sidewalk standards;
(l) Modify driveway standards;
(m) Use alternative cul-de-sac designs;
(n) Use alternative parking lot surfaces.
(C) Stormwater treatment BMPs.
(1) Types of treatment BMPs. A variety of BMPs are effective in (1) filtering storm water, (2) reducing the speed at which it leaves a site, and (3) reducing the volume of runoff. These three actions are critical to reducing non-point-source water pollution and protecting downstream water bodies. Some types of storm water treatment BMPs are:
(a) Retention systems:
(b) Detention systems;
(c) Infiltration systems;
(d) Filtration systems;
(e) Constructed wetlands;
(f) Alternative outlet designs.
(2) Location and regional treatment options.
(a) All storm water storage facilities shall be constructed within a dedicated storm water storage easement which meets the following standards:
1. The boundary of the maximum water surface elevation of any storm water storage facility resulting from a post-development 100-year return period storm shall define the minimum dedicated storm water storage easement. Such storm water storage easement shall be bounded by not less than a 25-foot horizontal width combined utility/drainage easement to separate the storm water storage facility from any building or structure. A variance for locating any utility, building or structure within the said boundary or any building or structure within the said separation area may be granted for good cause as determined by the Administering Authority, such as allowances for underground storm water storage or for installation of community amenities.
2. The maximum water surface elevation of any storm water storage facility resulting from a post-development 100-year return period storm shall be at least two feet lower than the lowest ground floor or lowest unprotected basement opening of any building located on any property which uses the storm water storage facility as a drainage outlet.
3. Storm water storage facilities that rely on man-made berms of any kind to store storm water shall be provided with an automatic non- mechanical emergency bypass drainage device (overflow weir, and the like) capable of passing the flow resulting from a post-development 100-year return period storm without causing failure of the man-made berms or ponding greater than two feet above the maximum water surface elevation resulting from a post-development 100-year return period storm.
4. Only the dedicated storm water storage easements may be used for storm water storage facilities. Any portion of a residential lot, combined utility/drainage easements, utility easements, and traffic rights-of-way do not qualify for use as storm water storage facilities.
(b) BMPs may be located on-site or off-site as part of a regional storm water device, practice or system.
(c) The Administering Authority may approve off-site management measures provided that all of the following conditions are met:
1. The Administering Authority determines that the post-construction runoff is covered by a storm water management system plan that is approved by the local public agency and that contains management requirements consistent with the purpose and intent of this chapter.
2. The off-site facility meets all of the following conditions:
a. The facility is in place.
b. The facility is designed and adequately sized to provide a level of storm water control equal to or greater than that which would be afforded by on-site practices meeting the performance standards of this chapter.
c. The facility has a legally obligated entity responsible for its long-term operation and maintenance.
(d) Where a regional treatment option is utilized such that the Stormwater Board may exempt the applicant from all or part of the minimum on-site storm water management requirements, the applicant shall be required to pay a fee in an amount determined in negotiation with the Stormwater Board. In determining the fee for post-construction runoff, the Stormwater Board shall consider an equitable distribution of the cost for land, engineering design, construction and maintenance of the regional treatment option.
(Ord. 2010-BCC-13, passed 4-19-10) Penalty, see § 154.99