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Healthcare Provider Information |
Address:
Garrett Co. Health Dept.
1025 Memorial Drive
Oakland, MD 21550
Main Phone:
301-334-7777
or 301-895-3111
FAX: 301-334-7701
See department pages for individual phone numbers
E-Mail Webmaster
Drainfield Trench
Cross Section
- Length - specified in permit (crossovers are not counted)
- Depth - 2 feet (unless otherwise specified).
- Width - 2 feet.
- Maximum slope of trenches - 4 inches per 100 feet.
- Minimum trench separation (center to center) - 8 feet (10 feet is recommended).
- Stone used in drainage trenches must be #2 or #57 (#6) screened stone without fines. (Crusher run is unacceptable.) The suggested gravel or rock size is ¾ or 2 ½ in. (1.8 to 6.4 cm) in diameter. The rock should be durable and resistant to slaking and dissolution. A hardness of 3 or greater on the Moh's Scale of Hardness is suggested. Rock that can scratch a copper penny without leaving any residual rock meets this criterion. The media should be washed to remove all fines that could clog the infiltrative surface.
- A minimum of 6 inches of gravel must be placed under the 4 inch perforated drainage pipe. This 4-inch pipe must then be covered by a minimum of 2 inches of gravel, which results in a minimum of 12 inches of gravel in each drainage trench.
- Only one line of 4 inch perforated pipe is to be placed in each trench. Pipe perforations should face down.
- Before backfilling, a strip of untreated building paper, hay or straw the width of the trench must be placed on top of the gravel. This will prevent soil infiltration when backfilling.
- If a sewage disposal system is to be installed on sloped land, a CROSSOVER SYSTEM OR A STANDPIPE SYSTEM should be installed.
- On flat land a CLOSED LOOP SYSTEM or DISTRIBUTION BOX SYSTEM should be installed. Contact Environmental Health Services for instructions.
NOTE: Approximately 4 inches in drain field length are lost for every two pieces of perforated pipe joined together. This equals a loss of 3 feet in length per 100 feet installed.