Cost issues   After extensive testing, the authors selected leaf compost as the ideal medium. It was available from a city compost system at $10 per cubic yard. Compost derived from yard wastes (rich in hemic) met many criteria, but failed leaching tests.     The pollutant removal performance of the prototype was computed based on flow composite monitoring of seven storm events (Table 1). The system provides excellent removal of sediment, particulate nutrients, organic carbon, hydrocarbons, and some heavy metals.