Modified Media Filter Drain Mix with Alternate Aggregate Grading

The media filter drain (MFD) or Ecology Embankment is a best management practice (BMP) approved to treat copper and zinc in highway runoff in many states. High levels of these metals may impact coldwater aquatic species in receiving waters. The MFD was originally based on a gradation of aggregate no longer readily available in Washington State and this research investigated substituting the original aggregate specification with a more widely available AASHTO Grading No. 8, which has slightly fewer fines. Results indicate that the MFD is effective at removing dissolved copper and zinc using the alternate aggregate specification in the MFD mix. Column experiments were used to show that the alternate MFD mix had a higher median removal rate than a suite of typical stormwater control BMPs for both dissolved zinc and copper, qualifying it as an enhanced treatment method. In addition, it was shown that the MFD mix design can be loaded with dissolved metals for at least 14 years with no loss in performance, even when subjected to larger storms. MFDs built with a wider range of aggregate gradations may be more economical in other regions based on standard aggregate gradations available.