Extended Performance of Media Filter Drains: New Media

There are numerous linear best management practices used by many state departments of transportation (DOTs) for highway runoff treatment. An example of one type is a media filter drain (MFD) which is a trench filled with aggregate and three active ingredients: dolomite, gypsum, and perlite (MFDs are also called Ecology embankments or bioslopes). Initial research on MFDs predicted that their life spans were at least10 years. Recent studies indicate that for dissolved zinc and copper metal removal, the life span may exceed 20 years. The dissolved concentrations of these metals are of issue as higher concentrations in receiving waters can impact many aquatic species, particularly some cold water fish such as salmon. This study extended the life further in laboratory tests for MFDs made with media with slightly higher amounts of active ingredients. Zinc and copper removal remained high. However, some possible channeling was suspected with slightly lower removal rates after long periods without moisture.