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93/07/95 09:41 V503 224 7820 1VOODWARD —CLYDE 41009/012 • vegetative techniques, and thin clay soils along with a need to protect groundwater eliminated the use of infiltration facilities. Studies have been completed to date at four sites in Texas, and two more studies are in progress. Other monitoring studies are in pragggss in Texas, Delaware, Florida, Virginia and the District of Columbia. Dr. Schueler's article in Techniques is an excellent guidance overview for sand filters, along with the City of Austin's Environmental Criteria Manual, Section 1.6 (February 1991) and Earl Shaver's guidance on sand filter inlet designs: Sand Filter Design for Water Quality Control (1991). Basic design guidance using a Darcy's Law approach is contained in the Stormwater Management Manual for the Puget Sound Basin (February 1992). The design information uses the 6- month, 24 -hour storm event as the criteria for sizing sand filters; the City may need to adapt this to Eugene based on whatever design storm recommendation/standard is selected. A number of other good reference materials are listed in Schueler's Techniques article which could be utilized as guidance_ (note: WCC is currently obtaining, and will be reviewing each, to refine these recommendations prior to finalizing this memorandum)_ Since the state of the practice on sand filters is evolving rapidly, it is recommended that one staffperson at the City become the key contact with other agencies conducting the performance studies. This individual should keep the City staff informed of changes and provide updated reference guidance material as needed. The arrival of additional monitoring information over the next two years should help to define, and hopefully standardize, the most effective design concepts. The compost facility is a relatively new experimental concept developed by W & H Pacific Consultants of Portland, OR. To date, there is one known manufacturer and about thirty leaf compost systems have been installed to treat runoff from small sites in the Pacific Northwest. Leaf compost was chosen over compost derived from yard waste because the latter had problems with nutrients and other pollutants readily Leaching out of the filter media. Some performance data from a prototype system has recently become available, although much has yet to be learned about long -term performance. The life of the compost in the filter varies, depending on the supplier. As it decomposes, there is the potential for the filter to begin gradually releasing nutrients and dissolved metals to the downstream storm drain system. The available information on leaf compost filters is presented in W. Stewart's report Compost Stormwater Treatment System (draft, 1992). Recently the California Department of Transportation (Caltrans) announced that it would be constructing many compost facilities for treatment of runoff from transportation corridors. S1945042na\task0200 \onsite controls \techmcm.ck 8