| (G) Drainfields on irregular terrain. Where the ground
slope is greater than 15% but less than 30%, a multiple line drainfield
may be constructed along descending contours as shown in §285.90(5)
of this title. An overflow line shall be provided from the upper excavations
to the lower excavations. The overflow line shall be constructed from
solid pipe with an SDR of 35 or stronger, and the excavation carrying
the overflow pipe shall be backfilled with soil only.
(H) Drainfield plans. A number of sketches, specifications,
and details for drainfield construction are provided in §285.90(4)
and (5) of this title.
(2) Evapotranspirative (ET) system. An ET system may
be used in soils which are classified as unsuitable for standard subsurface
absorption systems according to §285.31(b) of this title with
respect to texture, restrictive horizons, or groundwater. Water saving
devices must be used if an ET system is to be installed. ET systems
shall only be used in areas of the state where the annual average
evaporation exceeds the annual rainfall. Evaporation data is provided
in §285.91(7) of this title.
(A) Liners. An impervious liner shall be used between
the excavated surface and the ET system in all Class Ia soils, where
seasonal groundwater tables penetrate the excavation, and where a
minimum of two feet of suitable soil does not exist between the excavated
surface and either a restrictive horizon or groundwater. Liners shall
be rubber, plastic, reinforced concrete, gunite, or compacted clay
(one foot thick or more). If the liner is rubber or plastic, it must
be impervious, and each layer must be at least 20 mils thick. Rubber
or plastic liners must be protected from exposed rocks and stones
by covering the excavated surface with a uniform sand cushion at least
four inches thick. Clay liners shall have a permeability of 10 -7
centimeters/second or less, as tested by a certified soil laboratory.
(B) ET system sizing. The following formula shall be
used to calculate the top surface area of an ET system.
Attached Graphic
(C) The owner of the ET system shall be advised by
the person preparing the planning materials of the limits placed on
the system by the Q selected. If the Q is less than required by §285.91(3)
of this title, the flow rate shall be included as a condition to the
permit, and stated in an affidavit properly filed and recorded in
the deed records of the county as specified in §285.3(b)(3) of
this title (relating to General Requirements).
(D) Backfill material. Backfill material shall consist
of Class II soil as described in §285.30 of this title. All drainlines
must be surrounded by a minimum of one foot of media. Backfill shall
be used to fill the excavation between the media to allow the backfill
material to contact the bottom of the excavation.
(E) Vegetative cover for transpiration. The final grade
shall be covered with vegetation fully capable of taking maximum advantage
of transpiration. Evergreen bushes with shallow root systems may be
planted in the disposal area to assist in water uptake. Grasses with
dormant periods shall be overseeded to provide year-round transpiration.
(F) ET systems. ET systems shall be divided into two
or more equal excavations connected by flow control valves. One excavation
may be removed from service for an extended period of time to allow
it to dry out and decompose biological material which might plug the
excavation. If one of the excavations is removed from service, the
daily water usage must be reduced to prevent overloading of the excavation(s)
still in operation. Normally, an excavation must be removed from service
for two to three dry months for biological breakdown to occur.
(G) ET system plans. A number of sketches for ET system
construction are provided in §285.90(4) and (5) of this title.
(3) Pumped effluent drainfield. Pumped effluent drainfields
shall use the specifications for low-pressure dosed drainfields described
in subsection (d)(1) of this section, with the following exceptions.
(A) Applicability. If the slope of the site is greater
than 2.0%, pumped effluent drainfields shall not be used. Pumped effluent
drainfields may only be used by single family dwellings.
(B) Length of distribution pipe. There shall be at
least 1,000 linear feet of perforated pipe for a two bedroom single
family dwelling. For each additional bedroom, there shall be an additional
400 linear feet of perforated pipe. No individual distribution line
shall exceed 70 feet in length from the header.
(C) Excavation width and horizontal separation. The
excavated area shall be at least six inches wide. There shall be at
least three feet of separation between trenches.
(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
Cont'd... |
