Page 30 - Section4.2.1-SWPPPCutSheet-FiltrexxStormWaterBlanket

The Filtrexx ® Rain garden is a storm water best management practice (BMP) that utilizes soil, plants, and microbes to flter, retain, and infltrate storm water runoff from developed sites . Rain gardens are an important component of Low Impact Development (LID) strategy because it is relatively simple, inexpensive, effective and aesthetically attractive. Filtrexx ® GrowingMedia tm is an important component of a successful Rain garden installation.

Rain gardens can be used on any site utilizing a variety of design techniques. Optimum designs allow: Rain garden facility located in close proximity to source of runoff; Rain garden facilities to be dispersed uniformly throughout site; each Rain garden facility to collect runoff from sub-drainage area of 1 ac. or less (max of 2 ac); a large enough area to accommodate the Rain garden facilities within required setbacks; high infltration, stabile, well structured in-situ soils. Rain garden can be installed on sites that do not meet all criteria, but it can be diffcult and/or less successful. Key components of Rain garden systems include:

• Pretreatment – It is important to flter excess debris and sediment from runoff before it reaches Rain garden system to minimize maintenance. • Flow Entrance – It is best to allow water to sheet fow directly into the facility, where concentrated

fows enter through a curb cut or pipe it is important to dissipate the velocity of the runoff with stone, rip rap, or similar method. • Ponding Area – Surface storage of runoff is accommodated in ponding area. Acceptable depth: 3 in -12 in (75-300mm), 6 in (150mm). • Plant Materials – Plants in a Rain garden facility help to bind and uptake pollutants, remove water through evapo-transpiration, encourage infltration, and create an aesthetically pleasing landscape feature.

• Mulch – The mulch layer is an important medium for the adsorption and fltering of pollutants, as well as protecting the soil from eroding and drying out. A 3 in (75mm) blanket of Filtrexx ® FilterMedia tm is recommended for this application. • Planting Soil – The soil in a Rain garden facility is specifcally designed to flter pollutants, infltrate water, and support plant growth. The soil must have a minimum infltration rate of 2 in (50mm)/hr. A mixture of 75% coarse construction sand (grain size 0.02 in – 0.04 in [0.5-1.0mm]) and 25% Filtrexx ® GrowingMedia tm is recommended for this application. • Underdrain with Pea Gravel Diaphragm – An underdrain is necessary when in-situ soils have infltration rate of < 1 in/hr in order to ensure that the facility drains properly. A perforated pipe surrounded w/ a 6-9 in (150-225mm) layer of pea gravel leading to