The operational flow rate needs to provide the predetermined contact time for both adsorption and filtration and at the same time be ... granule on 15" of gravel ...

Vicdom Sand and Gravel was started in 1976, but the company's roots date back to 1956 when brothers Domenic and Victor Giordano started Giordano Sand and Gravel. Today, the company is known as Vicdom Sand and Gravel, with several sand and gravel pits and a limestone quarry in southern Ontario.
Second, a retaining wall must have properly compacted backfill. Backfill refers to the dirt behind the wall. In order to provide proper drainage, at least 12 inches of granular backfill (gravel or a similar aggregate) should be installed directly behind the wall. Compacted native soil can be used to backfill the rest of the space behind the wall.