Performance principles
Sec. 18.12. Performance principles.
The contents of the SWPPP shall clearly demonstrate how the principles, outlined below, have been met in the design and are to be accomplished by the proposed development project.
(1) Pursue Low Impact Design (LID) to the maximum extent possible. LID site planning and design strategies must be used to the maximum extent possible in order to reduce the generation of water runoff volumes for both new and redevelopment projects. In the event any of the following LID strategies are rejected as infeasible at a site, the specific rationale for rejection must be provided by the applicant. LID design includes the following:
a. Protect as much undisturbed open space as possible to maintain predevelopment hydrology and allow precipitation to naturally infiltrate into the ground.
b. Maximize the protection of natural drainage areas, streams, surface waters, and wetlands;
c. Minimize land disturbance including clearing and grading;
d. Minimize soil compaction;
e. Provide low-maintenance landscaping that encourages retention and planting of native vegetation and minimizes the use of lawns, fertilizers, and pesticides;
f. Minimize impervious surfaces;
g. Minimize the decrease in the “time of concentration” from pre-construction to post construction, where “time of concentration” means the time it takes for runoff to travel from the hydraulically most distant point of the drainage area to the point of interest within a watershed;
h. Infiltrate precipitation as close as possible to the point it reaches the ground using vegetated conveyance and treatment systems;
i. Break up or disconnect the flow of runoff over impervious surfaces; and
j. Provide source controls to prevent or minimize the use of exposure of pollutants into stormwater runoff at the site in order to prevent or minimize the release of those pollutants into stormwater runoff.
(2) The site selected shall show due regard for natural drainage characteristics and topography.
(3) To the extent possible, steep slopes shall be avoided.
(4) The grade of slopes created shall be minimized.
(5) Post-development runoff rates should not exceed pre-development rates, consistent with other storm water requirements which may be in effect. Any increase in storm water runoff shall be retained and recharged as close as feasible to its place of origin by means of detention ponds or basins, seepage areas, subsurface drains, porous paving, or similar technique.
(6) Original boundaries, alignment, and slope of watercourses within the project locus shall be preserved to the greatest extent feasible.
(7) In general, drainage shall be directed away from structures intended for human occupancy, municipal or utility use, or similar structures.
(8) All drainage provisions shall be of such a design and capacity so as to adequately handle storm water runoff, including runoff from tributary upstream areas which may be outside the locus of the project.
(9) Drainage facilities shall be installed as early as feasible during construction prior to site clearance, if possible.
(10) Fill located adjacent to watercourses shall be suitably protected from erosion by means of rip-rap, gabions, retaining walls, vegetative stabilization, or similar measures.
(11) Temporary vegetation and/or mulching shall be used to protect bare areas and stock-piles from erosion during construction; the smallest areas feasible shall be exposed at any one time; disturbed areas shall be protected during the non-growing months, November through March.
(12) During the growing season, April through October, permanent vegetation shall be placed immediately following fine grading.
(13) Trees and other existing vegetation shall be retained whenever feasible; the area beyond within the dripline shall be fenced or roped off to protect trees from construction equipment.
(14) Construction wastes will be managed to reduce the potential for stormwater runoff to mobilize them and contaminate surface or ground water. The storage, disposal, or use as fill of material containing asphalt, concrete, construction debris or stumps, even if determined to be non-hazardous, is prohibited.
(15) All areas damaged during construction shall be resodded, reseeded, or otherwise restored. Where soil compaction has occurred through storage of materials or use of equipment, soil infiltration shall be restored through use of soil amendments or other means. Monitoring and maintenance schedules, where required, shall be predetermined.
(16) All controls installed or used to achieve compliance with this SWPPP must be properly operated and maintained at all times.
(17) Sediment controls, stormwater measures, and other controls shall protect downstream water bodies from adverse water quality and quantity impacts resulting from the construction activities.
(18) Groundwater recharge: Stormwater must be recharged to maintain baseflow at predevelopment recharge levels to the maximum extent practicable.
(19) Water quality: Stormwater runoff from a site must be adequately treated before discharge.
(20) Pollution prevention: All development sites require the use of source control and pollution prevention measures to minimize the impact that the land use may have on stormwater runoff quality. ARTICLE VI. ENFORCEMENT