R317-401-6. Irrigation Fields

(a) Each irrigation zone shall have a minimum effective irrigation area for the type of soil and absorption characteristics.

(b) The area of the irrigation field shall be equal to the aggregate length of the perforated pipe sections within the irrigation zone times the width of the proposed trench. The required square footage shall be determined as follows:

TABLE 3

Subsurface Irrigation Field Design

Soil Characteristics Subsurface Irrigation Field area

                         Loading, gallons of graywater per

                         day per square foot

Coarse Sand or gravel 5

Fine Sand 4

Sandy Loam 2.5

Sandy Clay 1.6

Clay with considerable

sand or gravel 1.1

Clay with sand or gravel 0.8

TABLE 4

Drip Irrigation System Design

Soil Characteristics Drip Irrigation System

                         Maximum Minimum

                         emitter number of

                         discharge, emitters

                                    per gallon

                         gallons per day of

                         per day graywater

Coarse Sand or gravel 1.8 0.6

Fine Sand 1.4 0.7

Sandy Loam 1.2 0.9

Sandy Clay 0.9 1.1

Clay with considerable

sand or gravel 0.6 1.6

Clay with sand or gravel 0.5 2.0

(c) No irrigation point shall be within two vertical feet of the maximum groundwater table. The applicant shall supply evidence of ground water depth to the satisfaction of the local health department.

(d) Subsurface drip irrigation system.

(i) Minimum 140 mesh (115 micron) filter with a capacity of 25 gallons per minute, or equivalent filtration, sized appropriately to maintain the filtration rate, shall be used.

(ii) The filter backwash and flush discharge shall be captured, contained and disposed of to the sewer system, septic tank, or, with approval of the local health department, in a dry well 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 of graywater.

(iii) Emitters recommended by the manufacture shall be resistant to root intrusion, and suitable for subsurface and graywater use.

(iv) Each irrigation zone shall be designed to include no less than the number of emitters specified in this rule.

(v) Minimum spacing between emitters should be 14 inches in any direction, or as recommended by the manufacturer.

(vi) The system design shall provide user controls, such as valves, switches, timers, and other controllers as appropriate, to rotate the distribution of graywater between irrigation zones.

(vii) All drip irrigation supply lines shall be:

(A) polyethylene tubing or PVC class 200 pipe or better and schedule 40 fittings;

(B) With solvent-cemented joints, inspected and pressure tested at 40 pounds per square inch and shown to be drip tight for five minutes, before burial; and

(C) buried at a minimum depth of six inches. Drip feeder lines can be polyethylene or flexible PVC tubing and shall be covered to a minimum depth of six inches.

(viii) Where pressure at the discharge side of the pump exceeds 20 pounds per square inch, a pressure-reducing valve able to maintain downstream pressure no greater than 20 pounds per square inch shall be installed downstream from the pump and before any emission device.

(ix) Each irrigation zone shall include a flush valve/anti-siphon valve to prevent back siphonage of water and soil.

(e) Subsurface Irrigation Field

(i) Perforated sections shall be a minimum three-inch diameter and shall be constructed of perforated high-density polyethylene pipe, perforated ABS pipe, perforated PVC pipe, or other approved materials, provided that sufficient openings are available for distribution of the graywater in the trench area. Material, construction and perforation of the piping shall be in compliance with the requirements of the International Plumbing Code.

(ii) Clean stone, gravel, or similar filter material acceptable to the local health department, and varying in size from 3/4 inch to 2 1/2 inches, shall be placed in the trench to the depth and grade required by this section. Perforated sections shall be laid on the filter material. The perforated sections shall then be covered with filter material to the minimum depth required by this section. The filter material shall then be covered with landscape filter fabric or similar porous material to prevent closure of voids with earth backfill.

(iii) No earth backfill shall be placed over the filter material cover until after inspection and approval of the local health department.

(iv) Subsurface Irrigation fields shall be constructed as follows:

TABLE 5

Subsurface Irrigation Field Construction Details

Description Minimum Maximum

Number of drain lines

 per subsurface irrigation zone one ---

Length of each perforated line, feet --- 100

Bottom width of trench, inches 6 18

Total depth of trench, inches 12 ---

Spacing of lines, center to center, feet 4 ---

Depth of earth cover

 on top of gravel, inches 4 ---

Depth of filter material

 cover over lines, inches 2 ---

Depth of filter material

 beneath lines, inches 3 ---

Grade of perforated lines,

 Inches per 100 feet Level 4

(f) Construction, Inspection and Testing

(i) Installation shall conform to the equipment and installation methods described in the approved plans.

(ii) The manufacturer of all system components shall be properly identified.

(iii) Surge tanks shall be filled with water to the overflow line prior to and during construction inspection. All seams and joints shall be left exposed and the tank shall remain watertight.

(iv) The irrigation field shall be installed in the area which has soils similar to the soils which have been evaluated, and has absorption rate corresponding to the given soil classification.

(v) A graywater stub-out may be allowed for future construction, provided it is capped prior to the connection to the installed irrigation lines and landscaping. Stub-out shall be permanently marked: GRAYWATER STUB-OUT, DANGER UNSAFE WATER.

(vi) A flow test shall be performed throughout the system, from surge tank to the point of graywater irrigation. All lines and components shall be watertight.