The SWPPP shall include provisions for stormwater quality BMPs that are designed to achieve the following design/performance objectives.
(A) Reduce total suspended solids (TSS) from the first flush as defined by land use characteristics and contributing area; or, capture and treatment of at least one-half inch precipitation applied over the contributing area.
(B) Reduce or buffer increases in storm runoff temperature caused by contact with impervious surfaces.
(C) Stormwater detention/retention facilities shall be designed to address the rate at which flow is released over the entire runoff discharge period and the volume of discharge over the critical design-storm period. The outlet structure shall be designed as a v-notch weir or other multiple stage configurations capable of controlling the discharge rates for the two, ten and 100-year design-storm events.
(1) The Indiana Drainage Handbook or the Indiana Stormwater Quality Manual should be reviewed and considered when preparing the SWPPP.
(2) The county reserves the right to develop or adopt other guidance documents to serve as design and implementation standards. Other guidance documents distributed by the county should be reviewed and considered when preparing the SWPPP. These documents may be applied as standards by which designs are to be prepared and controls implemented. The county shall have authority to implement this chapter by appropriate regulations, guidance or other related materials. In this regard, technical, administrative or procedural matters may be modified as needed to meet the objectives defined herein, so long as such modifications as to technical, administrative or procedural matters are not contrary or beyond the intent of the objectives defined above.
(a) Regulations, guidance or other related materials that may be given authority by this chapter may include, but are not limited to: best management practice (BMP) manuals, design regulations and requirements, submittal checklists, review checklists, inspection checklists, certifications, stormwater management manuals and operation and maintenance manuals.
(b) Materials may include information deemed appropriate by the county including guidance and specifications for the preparation of grading plans, selecting environmentally sound practices for managing stormwater, minimum specifications and requirements, more complete definitions and performance standards.
(c) The above referenced documents shall not in any way require specific commercially available products; however, they may refer to performance specifications, class of devices, construction or management practice.
(d) The above referenced documents may restrict or prevent the use of specific products, techniques or management practices (that are to be accepted by the public or are deemed to have a negative impact on public infrastructure or the MS4) that have been identified as unacceptable for performance, maintenance or other technically based reasons.
(e) Documents referenced above may be updated periodically to reflect the most current and effective practices and shall be made available to the public; however, the failure to update the manual shall not relieve any applicant from the obligation to comply with this chapter, and shall not prevent the county from imposing the most current and effective practices.
(D) Soil bioengineering, “green” and other “soft” slope and stream bank stabilization methods shall receive preference over rip rap, concrete and other hard armoring techniques. “Hard” alternatives shall only be permitted when their necessity can be demonstrated given site-specific conditions.
(E) Retention: supportive data must be submitted to justify the type of facility selected. If the facility is designed to retain (volume control) all or a significant portion of runoff (as opposed to temporarily detain), then appropriate soils analyses findings shall be submitted to the county. This submission shall also discuss the impacts the facility will have on local karst topography as found through a geotechnical investigation of the site. The facility may be designed to infiltrate runoff to groundwater rather than transmit it downstream under conditions up to a ten-year storm event. It must be able to bypass all other storms up to a 100-year event with a discharge rate equivalent to or less than pre-development conditions without negatively impacting the 100-year floodplain above or below the site. If data indicates that the facility can not retain a significant portion of the runoff (95%), then the facility must be sized to detain runoff.
(F) Detention facilities may, and are encouraged to, be designed to serve multiple purposes. For example, runoff may be detained under wet-weather conditions, but also serve as common or recreational areas during dry-weather conditions. Where multi-purpose facilities are provided, or where flat grades or poorly draining soils are encountered, provisions for adequate low-flow stormwater management system may be required. Where the retention/detention facility is planned to be used as a lake, pond or stormwater quality management practice with a permanent pool, water budget calculations shall be performed and submitted to demonstrate that an adequate pool is expected during dry summer months.
(G) A licensed professional engineer shall stamp all plans for construction. This shall include all proposed improvements or modifications to existing or new stormwater infrastructure and other related improvements or modifications.
(H) The county reserves the right to require superseding or additional treatment criteria or objectives for specific pollutant(s) as necessary to meet overall stormwater quality management program objectives or directives under a watershed improvement or Total Maximum Daily Load (TDML) program.
(Ord. 2006-7, passed 5-18-2006)