The system shall be sized in accordance with the sum of the output of all water sources connected to the subsurface irrigation system. Where graywater collection piping is connected to subsurface landscape irrigation systems, graywater output shall be calculated according to the gallons-per-day-per-occupant number based on the type of fixtures connected. The graywater discharge shall be calculated by the following equation:
A = Number of occupants:
Residential—Number of occupants shall be determined by the actual number of occupants, but not less than two occupants for one bedroom and one occupant for each additional bedroom.
Commercial—Number of occupants shall be determined by the International Building Code.
B = Estimated flow demands for each occupant:
Residential—25 gallons per day (94.6 lpd) per occupant for showers, bathtubs and lavatories and 15 gallons per day (56.7 lpd) per occupant for clothes washers or laundry trays.
Commercial—Based on type of fixture or water use records minus the discharge of fixtures other than those discharging graywater.
C = Estimated graywater discharge based on the total number of occupants.
The surface grade of all soil absorption systems shall be located at a point lower than the surface grade of any water well or reservoir on the same or adjoining lot. Where this is not possible, the site shall be located so surface water drainage from the site is not directed toward a well or reservoir. The soil absorption system shall be located with a minimum horizontal distance between various elements as indicated in Table 1402.3. Private sewage disposal systems in compacted areas, such as parking lots and driveways, are prohibited. Surface water shall be diverted away from any soil absorption site on the same or neighboring lots.
LOCATION OF SUBSURFACE IRRIGATION SYSTEM
|ELEMENT||MINIMUM HORIZONTAL DISTANCE|
|Storage tank (feet)||Irrigation disposal field (feet)|
|Lot line adjoining private property||5||5|
|Streams and lakes||50||50|
|Public water main||10||10|
For SI: 1 foot = 304.8 mm.
The total absorption area required shall be computed from the estimated daily graywater discharge and the design-loading rate based on the percolation rate for the site. The required absorption area equals the estimated graywater discharge divided by the design-loading rate from Table 1403.1.1.
DESIGN LOADING RATE
|PERCOLATION RATE (minutes per inch)||DESIGN LOADING FACTOR (gallons per square foot per day)|
|0 to less than 10||1.2|
|10 to less than 30||0.8|
|30 to less than 45||0.72|
|45 to 60||0.4|
For SI: 1 minute per inch = min/25.4 mm, 1 gallon per square foot = 40.7 L/m2.
Distribution piping shall be not less than 3 inches (76 mm) in diameter. Materials shall comply with Table 1403.2. The top of the distribution pipe shall be not less than 8 inches (203 mm) below the original surface. The slope of the distribution pipes shall be not less than 2 inches (51 mm) and not greater than 4 inches (102 mm) per 100 feet (30 480 mm).
|Polyethylene (PE) plastic pipe||ASTM F405|
|Polyvinyl chloride (PVC) plastic pipe||ASTM D2729|
|Polyvinyl chloride (PVC) plastic pipe with a 3.5-inch O.D. and solid cellular core or composite wall||ASTM F1488|
For SI: 1 inch=25.4 mm.