| (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)(5) 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 in this section.
(1) Low-pressure dosed drainfield. Effluent from this
type of system shall be pumped, under low pressure, into a solid wall
force main and then into a perforated distribution pipe installed
within the drainfield area.
(A) The effluent pump in the pump tank must be capable
of an operating range that will assure that effluent is delivered
to the most distant point of the perforated piping network, yet not
be excessive to the point that blowouts occur.
(B) A start/stop switch or timer must be included in
the system to control the dosing pump. An audible and visible high
water alarm, on an electric circuit separate from the pump, must be
provided.
(C) Pressure dosing systems shall be installed according
to either design criteria in the North Carolina State University Sea
Grant College Publication UNC-S82-03 (1982) or other publications
containing criteria or data on pressure dosed systems which are acceptable
to the permitting authority. Additionally, the following sizing parameters
are required for all low-pressure dosed drainfields and shall be used
in place of the sizing parameters in the North Carolina State University
Sea Grant College Publication or other acceptable publications.
(i) The low-pressure dosed drainfield area shall be
sized according to the effluent loading rates in §285.91(1) of
this title and the wastewater usage rates in §285.91(3) of this
title. The effluent loading rate (Ra) in the formula in §285.91(1)
of this title shall be based on the most restrictive horizon one foot
below the bottom of the excavation. Excavated areas can be as close
as three feet apart, measured center to center. All excavations shall
be at least six inches wide. To determine the length of the excavation,
use the following formulas, where L = excavation length, and A = absorptive
area.
(I) If the media in the excavation is at least one
foot deep, the length of the excavation is L = A/(w+2) where:
(-a-) w = the width of the excavation for excavations
one foot wide or greater; or
(-b-) w = 1 for all excavations less than one foot
wide.
(II) If the media in the excavation is less than one
foot deep, the length of the excavation is L = A/(w + 2H), where H
= the depth of the media in feet and:
(-a-) w = the width of the excavation for excavations
one foot wide or greater; or
(-b-) w = 1 for all excavations less than one foot
wide.
(ii) 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 the greatest
dimension).
(iii) Geotextile fabric meeting the criteria in subsection
(b)(1)(E) of this section shall be placed over the media. The excavation
shall be backfilled with Class Ib, II, or III soil.
(iv) There shall be a minimum of one foot of soil (with
less than 30% gravel) between the bottom of the excavation and solid
or fractured rock. There shall be a minimum of two feet of soil (with
less than 30% gravel) between the bottom of the excavation and groundwater.
(2) Surface application systems. Surface application
systems include those systems that spray treated effluent onto the
ground.
(A) Acceptable surface application areas. Land acceptable
for surface application shall have a flat terrain (with less than
or equal to 15% slope) and shall be covered with grasses, evergreen
shrubs, bushes, trees, or landscaped beds containing mixed vegetation.
There shall be nothing in the surface application area within ten
feet of the sprinkler which would interfere with the uniform application
of the effluent. Sloped land (with greater than 15%) may be acceptable
if it is properly landscaped and terraced to minimize runoff.
(B) Unacceptable surface application areas. Land that
is used for growing food, gardens, orchards, or crops that may be
used for human consumption, as well as unseeded bare ground, shall
not be used for surface application.
Cont'd... |
