Frequently Asked Questions
Bioslope media or bioslope mix is best purchased by the loose, bulk ton and delivered in a dump truck or dump trailer. Planning is critical to either place the material into the system directly or store in a manner (i.e. on concrete/asphalt) to prevent contaminants from being mixed with the bioslope media prior to installation.
Bio-slopes are designed to treat sheet flow from adjacent impervious surfaces such as roads. Stormwater sheet flow moves off of the roadway, sometimes through another filter treatment, over a bio-slope. Runoff is filtered through the bio-slope and the bio-slope media. The bio-slope media is composed a combination of coarse aggregate and permeable soil particles with high water retention capability. Bioslope mix may include aggregates, perlite, dolomite, and gypsum. The dolomite and gypsum components help treat stormwater and act as a buffer for acidic pH conditions and provide treatment for heavy metals. Perlite aids in the treatment of particulates, metals, and nutrients with it primary function being to retain moisture. Treated runoff exits the bioslope system through a granular drain backfill material and sometimes with a perforated drain pipe. The overall effect filters stormwater to reduce the amount of runoff and improve water quality from runoff.
According to the Georgia Stormwater Manual (https://atlantaregional.org), “Bioslopes (also referred to as ecology embankments) are water quality best management practices that use a permeable engineered soil media to capture and treat stormwater runoff from adjacent paved areas. Bioslopes are typically installed along embankments or other slopes and designed to treat sheet flow stormwater runoff.
Bioslopes are designed with limited longitudinal slopes to force the flow to be slow and uniform, thus allowing for particulates to settle and limiting the effects of erosion. Once infiltrated into the highly permeable engineered soil layer, an underdrain is typically used to remove the treated stormwater from the embankment or slope. Larger flow rates, from less frequent storm events, in the form of sheet flow bypass the engineered soil media by overtopping and continuing down the embankment or slope.
Usually, bioslopes are installed parallel to roads and right of ways just off the shoulder. They are useful as stormwater management practices when the downslope area is limited in space to treat stormwater with other practices such as bioswales or bioretention basins. GDOT (Georgia Department of Transportation) projects, county, and city municipalities include bioslopes as part of their design plan.
Aggregate and soil suppliers, like River Sand, Inc., have facilities and stockpiles of materials to blend bioslope media. Most small landscaping yards do not blend products or have the capability to blend accurately. Many large rock or stone quarries only provide aggregates and not engineered soil blends or the QA/QC protocols to back them up.