1. (a)

   1. (1) Low pressure distribution allows an absorption area or secondary treatment filter to be dosed evenly across the entire area.
   2. (2) The discharge assembly of LPD systems consists of small diameter piping with orifices drilled at predetermined intervals through which effluent is dosed to the absorption area or secondary treatment filter.

   3. (3)

      1. (A) All LPD systems shall meet the following requirements.
      2. (B) See Appendix G, figure 10.

2. (b)

   1. (1) Piping in LPD systems shall be constructed of Schedule 40 PVC pipe.
   2. (2) Joints or connections shall be primed and welded with the appropriate chemical agents.

3. (c)

   1. (1) Orifices may range in size from one-eighth inch (1/8”) to three-sixteenths inch (3/16”).

   2. (2) Orifices shall be:

      1. (A) Centered in the pipe;
      2. (B) Pointed up or down; and
      3. (C) Shielded.
   3. (3) For soils with high hydraulic conductivity, the orifice spacing shall not exceed twenty-four inches (24”).
   4. (4) For soils with moderate hydraulic conductivity, the orifice spacing shall not exceed forty-eight inches (48”).
   5. (5) Orifices shall not be installed within twelve inches (12”) of the manifold pipe.
   6. (6) LPD applications require an authorized effluent filter.

4. (d)

   1. (1) In situations where the LPD manifold discharge assembly is located at a lower elevation than the pump, a one-quarter inch (1/4”) siphon-breaker hole shall be drilled in the pump effluent line or vacuum breaker above the high-water level to prevent siphoning.
   2. (2) An extra two (2) gallons per minute shall be added to the system flow rate to accommodate the siphon-breaker hole.
5. (e) The squirt height, also referenced as, distal pressure, distal height, or residual head or height, shall not be less than five feet (5’).
6. (f) The dose volume shall not exceed one-half (1/2) gallon per orifice.

7. (g)

   1. (1) Plastic or brass valves, either globe or gate, shall be installed between the manifold and distribution laterals in order to facilitate orifice head adjustment.
   2. (2) Control valves shall be encased in readily accessible valve boxes or similar encasement.

8. (h)

   1. (1) A ninety-degree (90°) electrical sweep with threaded cleanout or valve shall be installed at each end of the laterals for maintenance.
   2. (2) Cleanouts shall be encased in readily accessible valve boxes or similar encasement.

9. (i)

   1. (1) LPD absorption trenches shall contain a minimum of eight inches (8”) of gravel and four inches (4”) of cover above the gravel bed.
   2. (2) Authorized gravel substitutes may be used in LPD design.
   3. (3) See Appendix G, figure 3.

Codification Notes: “PVC” means polyvinyl chloride.