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CITY OF EVERETT STORMWATER MANAGEMENT MANUAL
<br /> polluted runoff. Examples are storage of liquid chemicals,waste oils, and solvents in portable containers
<br /> such as drums; loading and unloading of liquids from trucks; and painting, finishing, and coating
<br /> activities. A sump or holding tank serves to provide spill containment until the liquids can be pumped out
<br /> and properly disposed of. If the activity produces large amounts of runoff,this BMP will not be very
<br /> effective because the stray contaminants will overflow the sump or pass through the sump before
<br /> collection and disposal are possible. To prevent run-on,the area should be enclosed with a berm, curb,.or
<br /> dike. The following implementation information is intended for situations where this BMP can be
<br /> effective.
<br /> A designated activity area should be paved and sloped to drain to a central collection point. A sump,
<br /> vault,or holding tank should be installed underneath this collection drain. Some materials, such as
<br /> gasoline, can react with asphalt pavement and break it down,releasing additional pollutants. If the area is
<br /> not yet paved and materials are present which may react with asphalt,the area must be paved with
<br /> concrete. If the area is already paved with asphalt, an asphalt sealant can be applied which can aid in
<br /> preventing pavement degradation. Whichever paving material is used,the paved surface must be free of
<br /> gaps and cracks.
<br /> The sump or holding tank should have a capacity large enough to contain the entire volume of a potential
<br /> spill.
<br /> The cost of constructing a sump and the disposal of accumulated contents can be high, so businesses
<br /> should consider whether other allowable alternative BMPs can be used.
<br /> Commercial services that pump sumps and holding tanks are listed in the Yellow Pages of the phone
<br /> directory under Environmental and Ecological Services.
<br /> BMPs S.4, S.5, and S.7 in this chapter present information on covering activities and run-on prevention.
<br /> 4.2.6 S.6 Surround the Activity Area with a Curb, Berm, or Dike, or Elevate the
<br /> Activity
<br /> This set of BMP options can be an effective means for prevention of stormwater run-on to an activity
<br /> area. In addition,a curb,berm,or dike can be used for containment of spills in the activity area, or for
<br /> containment of contaminated activity runoff. Generally,a containment BMP is most applicable to spill
<br /> control situations;that is, sites where runoff is relatively clean,but occasional spills may occur.
<br /> If a curb, dike, or berm is used to prevent stormwater run-on to a covered activity area,and the activity
<br /> area is paved or otherwise impermeable,the berm should be placed underneath the covering so that rain
<br /> will not pond inside it. Stormwater run-on can also be prevented by elevating the activity with a platform
<br /> or other type of pedestal.
<br /> Containment may be achieved with concrete curbing,an earthen berm, a tub such as a plastic wading
<br /> pool, or some other dike material, depending on the activity, its size, and resources available. Activities
<br /> that require more space and therefore cannot be contained with a tub may need to be surrounded by a
<br /> curb, dike, or berm. Aboveground storage tanks of liquids, storage of chemicals or wastes in numerous
<br /> drums, and stockpiling of fertilizer are examples of activities that can be contained effectively in this
<br /> manner. As the activity area gets larger,containment with an earthen berm can probably be provided less
<br /> expensively than concrete curbing.
<br /> If a curb,berm, or dike is used for runoff containment,and other containment sizing regulations(such as
<br /> Fire Codes,Ecology or Snohomish Health District restrictions)do not apply, it should function so that all
<br /> stormwater runoff from rain events up to the 6-month storm is contained in the immediate activity area
<br /> until properly disposed of later. This approach is applicable for activities that involve liquid material •
<br /> storage, and that may consequently incur spills. It is also applicable to stockpile areas where runoff is
<br /> Volume IV— Source Control
<br /> 4-4
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