An improved trench drain filter and modular system therefor for intercepting and treating run off water in a trench drain before discharge into a drainage system. The filter elements include a perforated pipe covered with one or more layers of geotextile material, which is, in turn, covered with a permeable fabric membrane. In a preferred embodiment a pouch containing an absorbent agent is disposed within the pipe upstream of the discharge point, and in another embodiment a multi-filter modular unit is provided, the unit including a plurality of filter elements disposed in an enclosure having fluid flow control baffles to direct fluid to and through the filter elements.