1504.5 Irrigation, Disposal Field and Mulch Basin Con-

struction. Irrigation fields, disposal fields and mulch basins used in gray water systems shall comply with this section. Gray water systems may contain either an irrigation field or a dis- posal field or a combination of both. This section is not intended to prevent the use of other methods of gray water irri- gation or disposal approved by the Enforcing Agency.

[BSC-CG] Irrigation design shall be verified in accor- dance with the California Green Building Standards Code (CALGreen), Chapter 5, Division 5.3.

[HCD 1] Irrigation design shall be verified in accor- dance with the California Green Building Standards Code (CALGreen), Chapter 4, Division 4.3.

1504.5.1 Mulch Basin. A mulch basin may be used as an irrigation or disposal field. Mulch basins shall be sized in accordance with Table 1504.2 and of sufficient depth, length and width to prevent ponding or runoff during the gray water surge of a clothes washer, bathtub or shower. Mulch must be replenished as required due to decomposi- tion of organic matter. Mulch basins will require periodic maintenance, reshaping or removal of dirt to maintain surge capacity and to accommodate plant growth and pre- vent ponding or runoff. 1504.5.2 Irrigation Field. The provisions of this section are not intended to prevent the use of any appropriate material, appliance, installation, device, design or method of construction. If an alternate design is not available, the following provisions may be used as guidance in the design of a gray water irrigation field: (1) Filters used in gray water irrigation systems shall be

as specified by the manufacturer’s installation instruc- tions for the design flow rate and intended use. The filter backwash and flush discharge shall be contained and disposed of into the building sewer system, septic tank or, with approval of the Enforcing Agency, a sep- arate mini-leachfield sized to accept all the backwash and flush discharge water. Filter backwash water and flush water shall not be used for any purpose. Sani- tary procedures shall be followed when handling filter backwash and flush discharge or gray water. (2) Emitters shall be designed to resist root intrusion

and shall be of a design recommended by the man- ufacturer for the intended gray water flow and use. (3) Each irrigation zone shall be designed to include no

less than the number of emitters specified in Table 1504.5.5, or through a procedure designated by the Enforcing Agency. Minimum spacing between emit- ters in any direction shall be sufficient to prevent surfacing or runoff. (4) The system design shall provide user controls, such

as valves, switches, timers and other controllers, as appropriate, to rotate the distribution of gray water between irrigation zones.

ALTERNATE WATER SOURCES FOR NONPOTABLE APPLICATIONS

(5) All drip irrigation supply lines shall be polyethylene

tubing or PVC Class 200 pipe or better and Sched- ule 40 fittings. All joints shall be pressure tested at 40 psi (276 kPa), and shown to be drip tight for five min- utes, before burial. All supply piping shall be cov- ered to a minimum depth of two (2) inches (51 mm) of mulch or soil. Drip feeder lines can be poly or flex- ible PVC tubing and shall be covered to a minimum depth of two (2) inches (51 mm) of mulch or soil. (6) Where pressure at the discharge side of the pump

exceeds 20 psi (138 kPa), a pressure-reducing valve able to maintain downstream pressure no greater than the maximum operating pressure of the installed tubing, emitters, or other components shall be installed downstream from the pump and before any emission device. (7) When an irrigation system utilizes a pump, and dis-

charges water at a point higher than the pump, a backwater valve shall be installed downstream of the pump to prevent back siphonage of water and soil. 1504.5.3 Disposal Field. The provisions of this sec- tion are not intended to prevent the use of any appropri- ate material, appliance, installation, device, design or method of construction. If an alternate design is not available, the following provisions may be used as guid- ance in the design of a gray water disposal field: (A) Disposal systems shall be not less than three (3)

inches (80 mm) in cross sectional dimension and shall be constructed of perforated high-density poly- ethylene pipe, perforated ABS pipe, perforated PVC pipe, leaching chambers or other approved materi- als, provided that sufficient openings are available for distribution of the gray water into the trench area. Material, construction, and perforation shall be in compliance with the appropriate absorption field’s drainage standards and shall be approved by the Enforcing Agency. (B) Filter material, clean stone, gravel, slag, or similar

filter material acceptable to the Enforcing Agency, varying in size from three-quarter ( ³ ∕ 4) inch (19.1 mm) to two and one-half (2 ¹ ∕ 2) inches (64 mm) shall be placed in the trench to the depth and grade required by this section. The perforated section shall be laid on the filter material in an approved man- ner. The perforated section shall then be covered with filter material to the minimum depth required by this section. The filter material shall then be cov- ered with untreated building paper, straw, or similar porous material to prevent closure of voids with earth backfill. No earth backfill shall be placed over the filter material cover until after inspection and acceptance. Exception: Manufactured leaching chambers shall be installed in compliance with the manufacturer’s installation instructions. (C) Disposal fields shall be constructed in accordance

with Table 1504.5.3.

2022 CALIFORNIA PLUMBING CODE 311

(D) When necessary on sloping ground to prevent exces-

sive line slopes, disposal lines shall be stepped or installed on the contour lines of the slope. The lines between each horizontal leaching section shall be made with approved water-tight joints and installed on natural or unfilled ground.

TABLE 1504.5.3 SUBSOIL IRRIGATION FIELD CONSTRUCTION

For SI units: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 inch per foot = 83.3 mm/m 1 Manufactured leaching chambers shall be installed in compliance with the manufacturer’s installation instructions.

TABLE 1504.5.5 SUBSURFACE IRRIGATION DESIGN

CRITERIA FOR SIX TYPICAL SOILS

For SI units: 1 gallon per day = 0.000043 L/s

• The estimated gray water discharge per day shall be determined in accordance with Section 1503.8 of this code.