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1504.1 General
Irrigation or disposal fields shall be permitted to have one or more valved zones. Each zone shall be of a size to receive the gray water anticipated in that zone.
1504.2 Required Area of Subsurface Irrigation Fields, Subsoil Irrigation Fields, and Mulch Basins
The minimum effective irrigation area of subsurface irrigation fields, subsoil irrigation fields, and mulch basins shall be determined by Table 1504.2 for the type of soil found in the excavation, based upon a calculation of estimated gray water discharge under Section 1503.8. For a subsoil irrigation field, the area shall be equal to the aggregate length of the perforated pipe sections within the valved zone multiplied by the width of the proposed subsoil irrigation field.

TABLE 1504.2
DESIGN OF SIX TYPICAL SOILS
TYPE OF SOIL MINIMUM SQUARE FEET OF IRRIGATION AREA PER 100 GALLONS OF ESTIMATED GRAY WATER DISCHARGE PER DAY MAXIMUM ABSORPTION CAPACITY IN GALLONS PER SQUARE FOOT OF IRRIGATION/LEACHING AREA FOR A 24-HOUR PERIOD
Coarse sand or gravel 20 5.0
Fine sand 25 4.0
Sandy loam 40 2.5
Sandy clay 60 1.7
Clay with considerable sand or gravel 90 1.1
Clay with small amounts of sand or gravel 120 0.8
For SI units: 1 square foot = 0.0929 m2, 1 gallon per day = 0.000043 L/s
1504.3 Determination of Maximum Absorption Capacity
The irrigation field and mulch basin size shall be based on the maximum absorption capacity of the soil and determined using Table 1504.2. For soils not listed in Table 1504.2, the maximum absorption capacity for the proposed site shall be determined by percolation tests or another method acceptable to the Authority Having Jurisdiction. A gray water system shall not be permitted, where the percolation test shows the absorption capacity of the soil is unable to accommodate the maximum discharge of the proposed gray water irrigation system.
1504.4 Groundwater Level
No excavation for an irrigation field, disposal field, or mulch basin shall extend within 3 feet (914 mm) vertical of the highest known seasonal groundwater level, nor to a depth where gray water contaminates the groundwater or surface water. The applicant shall supply evidence of groundwater depth to the satisfaction of the Authority Having Jurisdiction.
1504.5 Subsurface and Subsoil Irrigation Field Design and Construction
Subsurface and subsoil irrigation field design and construction shall be in accordance with Section 1504.5.1 through Section 1504.7.3. Where a gray water irrigation system design is predicated on soil tests, the subsurface or subsoil irrigation field or mulch basin shall be installed at the same location and depth as the tested area.
1504.5.1 Subsurface Irrigation Field
1504.5.2 Minimum Depth
Supply piping, including drip feeders, shall be not less than 2 inches (51 mm) below finished grade and covered with mulch or soil.
1504.5.3 Filter
Not less than 140 mesh (105 microns) filter with a capacity of 25 gallons per minute (gpm) (1.58 L/s), or equivalent shall be installed. Where a filter backwash is installed, the backwash and flush discharge shall discharge into the building sewer or private sewage disposal system. Filter backwash and flush water shall not be used.
1504.5.4 Emitter Size
Emitters shall be installed in accordance with the manufacturer's installation instructions. Emitters shall have a flow path of not less than 1200 microns (µ) (1200 µm) and shall not have a coefficient of manufacturing variation (Cv) exceeding 7 percent. Irrigation system design shall be such that emitter flow variation shall not exceed 10 percent.
1504.5.5 Number of Emitters
The minimum number of emitters and the maximum discharge of each emitter in an irrigation field shall be in accordance with Table 1504.5.5.

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.
1504.5.6 Controls
The system design shall provide user controls, such as valves, switches, timers, and other controllers, to rotate the distribution of gray water between irrigation zones.
1504.5.7 Maximum Pressure
Where pressure at the discharge side of the pump exceeds 20 pounds-force per square inch (psi) (138 kPa), a pressure-reducing valve able to maintain downstream pressure not exceeding 20 psi (138 kPa) shall be installed downstream from the pump and before an emission device.
1504.6 Mulch Basin Design and Construction
A mulch basin shall comply with Section 1504.6.1 through Section 1504.6.4.
1504.6.1 Single Family and Multi-Family Dwellings
The gray water discharge to a mulch basin is limited to single family and multi-family dwellings.
1504.6.2 Size
Mulch basins shall be of sufficient size to accommodate peak flow rates and distribute the total amount of estimated gray water on a daily basis without surfacing, ponding or runoff. Mulch basins shall have a depth of not less than 10 inches (254 mm) below finished grade. The mulch basin size shall be based on the maximum absorption capacity of the soil and determined using Table 1504.2.
1504.6.3 Minimum Depth
Gray water supply piping, including drip feeders, shall be not less than 2 inches (51 mm) below finished grade and covered with mulch.
1504.6.4 Maintenance
The mulch basin shall be maintained periodically to retain the required depth and area, and to replenish the required mulch cover.
1504.7 Subsoil Irrigation Field
1504.7.1 Minimum Pipe Size
Subsoil irrigation field distribution piping shall be not less than 3 inches (80 mm) diameter.
1504.7.2 Filter Material and Backfill
Filter material, clean stone, gravel, slag, or similar material acceptable to the Authority Having Jurisdiction, varying in size from 3/4 of an inch (19.1 mm) to 21/2 inches (64 mm) shall be placed in the trench to the depth and grade in accordance with Table 1504.7.3. The perforated section of subsoil irrigation field distribution piping shall be laid on the filter material in an approved manner. The perforated section shall then be covered with filter material to the minimum depth in accordance with Table 1504.7.3. The filter material shall then be covered with porous material to prevent the closure of voids with earth backfill. No earth backfill shall be placed over the filter material cover until after inspection and acceptance.
1504.7.3 Subsoil Irrigation Field Construction
Subsoil irrigation fields shall be constructed in accordance with Table 1504.7.3. Where necessary on sloping ground to prevent excessive line slopes, irrigation lines shall be stepped. The lines between each horizontal leaching section shall be made with approved watertight joints and installed on the natural or unfilled ground.

TABLE 1504.7.3
SUBSOIL IRRIGATION FIELD CONSTRUCTION
DESCRIPTION MINIMUM MAXIMUM
Number of drain lines per valved zone 1
Length of each perforated line 100 feet
Bottom width of trench 12 inches 18 inches
Spacing of lines, center to center 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 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
1504.8 Gray Water System Color and Marking Information
Pressurized gray water distribution systems shall be identified as containing nonpotable water in accordance with Section 601.3 of this code.
1504.9 Other Collection and Distribution Systems
Other collection and distribution systems shall be approved by the local Authority Having Jurisdiction, as allowed by Section 301.3 of this code.
1504.9.1 Higher Requirements
Nothing contained in this chapter shall be construed to prevent the Authority Having Jurisdiction from requiring compliance with higher requirements than those contained herein, where such higher requirements are essential to maintaining a safe and sanitary condition.
1504.10 Testing
Building drains and vents for gray water systems shall be tested in accordance with this code. Surge tanks shall be filled with water to the overflow line prior to and during the inspection. Seams and joints shall be left exposed, and the tank shall remain watertight. A flow test shall be performed through the system to the point of gray water discharge. Lines and components shall be watertight up to the point of the irrigation perforated and drip lines.
1504.11 Maintenance
Gray water systems and components shall be maintained in accordance with Table 1501.5.

Related Code Sections

1504.0 Alternate Water Sources for Nonpotable Applications, Subsurface Irrigation System Zones
system design is predicated on soil tests, the subsurface or subsoil irrigation field or mulch basin shall be installed at the same location and depth ...
1504.10 Alternate Water Sources for Nonpotable Applications, Testing
through the system to the point of gray water discharge. Lines and components shall be watertight up to the point of the irrigation perforated ...