| (D) Lateral depth and vertical separation. All drainfield
laterals shall be between 18 inches and three feet deep. There shall
be a minimum vertical separation distance of one foot from the bottom
of the excavation to a restrictive horizon, and a minimum vertical
separation of two feet from the bottom of the excavation to groundwater.
(E) Media. Each dosing pipe shall be placed with the
drain holes facing down and placed on top of at least six inches of
media (pea gravel or media up to two inches measured along its greatest
dimension).
(F) Pipe and hole size. The distribution (dosing) and
manifold (header) pipe shall be 1.25 - 1.5 inches in diameter. The
manifold may have a diameter larger than the distribution pipe, but
shall not exceed 1.5 inches in diameter. Distribution (dosing) pipe
holes shall be 3/16 - 1/4 inch in diameter and shall be spaced five
feet apart.
(G) Pump size. Pumped effluent drainfields shall use
at least a 1/2 horsepower pump.
(H) Backfilling. Only Class Ib, II, or III soils as
described in §285.30(b)(1)(A) of this title shall be used for
backfill.
(c) Proprietary disposal systems.
(1) Gravel-less drainfield piping. Gravel-less pipe
may be used only on sites suitable for standard subsurface sewage
disposal methods. Gravel-less pipe shall be eight-inch or ten-inch
diameter corrugated perforated polyethylene pipe. The pipe shall be
enclosed in a layer of unwoven spun-bonded polypropylene, polyester,
or nylon filter wrap. Gravel-less pipe shall meet ASTM F-667 Standard
Specifications for large diameter corrugated high density polyethylene
(ASTM D 1248) tubing. The filter cloth must meet the same material
specifications as described under subsection (b)(1)(E) of this section.
(A) Planning parameters. Gravel-less drainfield pipe
may be substituted for drainline pipe in both absorptive and ET systems.
When gravel-less pipe is substituted, media will not be required.
ET systems shall be backfilled with Class II soils only. All other
planning parameters for absorptive or ET systems apply to drainfields
using gravel-less pipe.
(B) Installation. The connection from the solid line
leaving the treatment tank to the gravel-less line shall be made by
using an eight or ten-inch offset connector. The gravel-less line
shall be laid level, the continuous stripe shall be up, and the lines
shall be joined together with couplings. A filter cloth must be pulled
over the joint to eliminate soil infiltration. The gravel-less pipe
must be held in place during initial backfilling to prevent movement
of the pipe. The end of each gravel-less line shall have an end cap
and an inspection port. The inspection port shall allow for easy monitoring
of the amount of sludge or suspended solids in the line, and allow
the distribution lines to be back-flushed.
(C) Drainfield sizing. To determine appropriate drainfield
sizing, use a drainfield width of W = 2.0 feet for an eight-inch diameter
gravel-less pipe, and an excavation width of W = 2.5 for a ten-inch
gravel-less pipe.
Attached Graphic
(2) Leaching chambers. Leaching chambers are bottomless
chambers that are installed in a drainfield excavation with the open
bottom of the chamber in direct contact with the excavation. The ends
of the chamber rows shall be linked together with non-perforated sewer
pipe. The chambers shall completely cover the excavation, and adjacent
chambers must be in contact with each other in such a manner that
the chambers will not separate. To obtain the reduction in drainfield
size allowed in subparagraph (A)(i) and (ii) of this paragraph for
excavations wider than the chambers, the chambers shall be placed
edge to edge.
(A) The following formulas shall be used to determine
the length of an excavation using leaching chambers.
(i) The following formula is used for leaching chambers
without water saving devices and the excavation is the same width
as the chamber.
Attached Graphic
(ii) The following formula is used for leaching chambers
with water saving devices and the excavation is the same width as
the chamber.
Attached Graphic
(iii) The following formula is used for leaching chambers
without water saving devices and the excavation width is greater than
the width of the chamber.
Attached Graphic
(iv) The following formula is used for leaching chambers
with water saving devices and the excavation width is greater than
the width of the chamber.
Attached Graphic
(B) Leaching chambers shall not be used for absorptive
drainfields in Class Ia or IV soils. Leaching chambers may be used
instead of media in ET systems, low-pressure dosed drainfields, and
soil substitution drainfields; however, the size of the drainfield
shall not be reduced from the required area.
(C) Backfill covering leaching chambers shall be Class
Ib, II, or III soil.
(3) Drip irrigation. Drip irrigation systems using
secondary treatment may be used in all soil classes including Class
IV soils. The system must be equipped with a filtering device capable
of filtering particles larger than 100 microns and that meets the
manufacturer's requirements.
(A) Drainfield layout. The drainfield shall consist
of a matrix of small-diameter pressurized lines, buried at least six
inches deep, and pressure reducing emitters spaced at a maximum of
30-inch intervals. The pressure reducing emitter shall restrict the
flow of effluent to a flow rate low enough to ensure equal distribution
of effluent throughout the drainfield.
(B) Effluent quality. The treatment preceding a drip
irrigation system shall treat the wastewater to secondary treatment
as described in §285.32(e) of this title unless the drip irrigation
system has been approved by the executive director as a proprietary
disposal system without the use of secondary treatment.
(C) System flushing. Systems must be equipped to flush
the contents of the lines back to the pretreatment unit when intermittent
flushing is used. If continuous flushing is used during the pumping
cycle, the contents of the lines must be returned to the pump tank.
(D) Loading rates. Pressure reducing emitters can be
used in all classes of soils using loading rates specified in §285.91(1)
of this title. Pressure reducing emitters are assumed to wet four
square feet of absorptive area per emitter; however, overlapping areas
shall only be counted once toward absorptive area requirements. The
loading rate shall be based on the most restrictive soil horizon within
one foot of the pressure reducing emitter. When solid rock is less
than 12 inches below the pressure reducing emitter, the loading rate
shall be based on Class IV soils.
(E) Vertical separation distance. There shall be a
minimum of one foot of soil (with less than 60% gravel) between the
pressure reducing emitter and groundwater and six inches between the
pressure reducing emitter and solid rock, or fractured rock. For proprietary
disposal systems that do not pretreat to secondary treatment, there
shall be two feet of soil (with less than 30% gravel) between the
groundwater and pressure reducing emitter and one foot of soil between
solid rock or fractured rock and the pressure reducing emitter.
(F) Labeling or listing. All drip irrigation system
devices shall either be labeled by the manufacturer as suitable for
use with domestic sewage, or be on the list of approved devices maintained
by the executive director according to §285.32(c)(4) of this
title.
(4) Approval of proprietary disposal systems. All proprietary
disposal systems, other than those described in this section, shall
be approved by the executive director before they may be used. Proprietary
disposal systems shall be approved by the executive director using
the procedures established in §285.32(c)(4)(B) of this title.
(d) Nonstandard disposal systems. All disposal systems
not described or defined in subsections (b) and (c) of this section
are nonstandard disposal systems. Planning materials for nonstandard
disposal systems must be developed by a professional engineer or professional
sanitarian using basic engineering and scientific principles. The
planning materials for paragraphs (1) - (5) of this subsection shall
be submitted to the permitting authority and the permitting authority
shall review and either approve or disapprove them on a case-by-case
basis according to §285.5 of this title (relating to Submittal
Requirements for Planning Materials). Electrical wiring for nonstandard
disposal systems shall be installed according to §285.34(c) of
this title (relating to Other Requirements). Upon approval of the
planning materials, an authorization to construct will be issued by
the permitting authority. Approval for a nonstandard disposal system
is limited to the specific system described in the planning materials
for the specific location. The systems identified in paragraphs (1)
- (5) of this subsection must meet these requirements, in addition
to the requirements identified for each specific system Cont'd... |
