Gray Water Systems for Subsurface Landscape Irrigation

Infiltration Galleys

• Infiltration galleys are the simplest system if you require subsurface distribution. An infiltration galley is an open space underground where water drains and soaks in. Create the space by placing infiltrators, half pipes, box troughs or half drums into an appropriately sized trench, open side down. Size the galley so that the average surge will cover the entire floor with 1 1/2 inches of water and the maximum gray water surge will not completely fill the galley.

Branched Drain System

• A branched drain system splits the gray water flow, and contains and covers it in a mulch basin. Gray water exits the house to a double ell fitting that splits the flow into additional pipes. Split each flow again before emptying into a mulch basin or subsurface chamber. Conceal a free flow outlet in a mulch basin with rocks. The bottom of the basin or chamber should be at least 4 inches below the outlet pipe to prevent clogging.

Pumice Wick

• A pumice wick filters and absorbs gray water, then distributes it more evenly over a larger area. To make a pumice wick dig a 10 inch wide, 17 inch deep trench that drops half an inch for every 10 feet. Line it with landscape fabric, put 4 inches of pumice rock in the bottom and place 3-inch perforated pipe on top of the pumice. Fill the trench so the pumice is 10 to 12 inches deep, cover it with landscape fabric and finish filling the trench with soil. Drain the gray water into the perforated pipe. The end of the pipe should flow out into a mulch basin or gallery.

Sub-Surface Drip

• The most complex subsurface gray water system is a septic tank to subsurface drip system. These commercially available systems includes a settling and anaerobic digestion tank, effluent filter, secondary treatment, effluent pump, drip filter and subsurface drip distribution. Secondary treatment is expensive but necessary to avoid clogging the drip system. Proper operation and regular maintenance are important for these systems. The cost is prohibitive for most single households but functional for multi-family or institutional systems.