1504.5 Irrigation, Disposal Field and Mulch Basin

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

TABLE 1504.2

DESIGN OF SIX TYPICAL SOILS

For SI units: 1 square foot = 0.0929 m [2], 1 gallon per day = 0.000043 L/s

316 2025 CALIFORNIA PLUMBING CODE

ALTERNATE WATER SOURCES FOR NONPOTABLE APPLICATIONS

[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 dur- ing the gray water surge of a clothes washer, bathtub or shower. Mulch must be replenished as required due to decomposition of organic matter. Mulch basins will require periodic maintenance, reshaping or removal of dirt to maintain surge capacity and to accommodate plant growth and prevent ponding or runoff.

1504.5.2 Irrigation 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 irrigation field:

(1) Filters used in gray water irrigation systems shall be as specified by the manufacturer’s installation instructions 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 Enforc- ing Agency, a separate 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. Sanitary 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.

(5) All drip irrigation supply lines shall be polyethylene tubing or PVC Class 200 pipe or better and Schedule 40 fittings. All joints shall be pressure tested at 40 psi (276 kPa), and shown to be drip tight for five minutes, before burial. All supply piping shall be covered to a minimum depth of two (2) inches (51 mm) of mulch or soil. Drip feeder lines can be poly or flexible PVC tub- ing 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.

(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.

ALTERNATE WATER SOURCES FOR NONPOTABLE APPLICATIONS

TABLE 1504. 5.3

SUBSOIL IRRIGATION FIELD CONSTRUCTION

DESCRIPTION	MINIMUM	MAXIMUM
Number of drain lines per valved zone_1_	1	–
Length of each perforated line_1_	–	100 feet
Bottom width of trench_1_	12 inches	24 inches
Spacing of lines, center to center_1_	4 feet	–
Depth of earth covers of lines	10 inches	–
Depth of filter material cover of lines	2 inches	–
Depth of filter material beneath lines_1_	3 inches	–
Grade of perforated lines level	level	3 inches per 100 feet

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

TYPE OF SOIL	MAXIMUM EMITTER DISCHARGE (gallons per day)	MINIMUM NUMBER OF EMITTERS PER GALLON OF ESTIMATED GRAY WATER DISCHARGE PER DAY* (gallons per day)
Sand	1.8	0.6
Sandy loam	1.4	0.7
Loam	1.2	0.9
Clay loam	0.9	1.1
Silty clay	0.6	1.6
Clay	0.5	2.0

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.