| 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.
(C) Technical report. A technical report shall be prepared
for any system using surface application and shall be submitted with
the planning materials required in §285.5(a) of this title. The
technical report shall describe the operation of the entire on-site
sewage facility OSSF system, and shall include construction drawings,
calculations, and the system flow diagram. Proprietary aerobic systems
may reference the executive director's approval list instead of furnishing
construction drawings for the system.
(D) Effluent disinfection. Treated effluent must be
disinfected before surface application. The effluent quality in the
pump tank must meet the minimum required test results specified in §285.91(4)
of this title. All new disinfection equipment shall be listed as approved
dispensers or disinfection devices for wastewater systems by National
Sanitation Foundation (NSF) International or by an ANSI accredited
testing institution under ANSI/NSF Standard 46, or approved by the
executive director. After January 1, 2016, all new disinfection equipment
shall be listed as disinfection devices for wastewater systems by
NSF International or by an ANSI accredited testing institution under
ANSI/NSF Standard 46, or approved by the executive director. Installation
of disinfection devices on new systems shall be performed by a licensed
installer II. Tablet or other dry chlorinators shall use calcium hypochlorite
properly labeled for wastewater disinfection. The effectiveness of
the disinfection procedure will be established by monitoring either
the fecal coliform count or total chlorine residual from representative
effluent grab samples as directed in the testing and reporting schedule.
The frequency of testing, the type of tests, and the required results
are shown in §285.91(4) of this title. Replacement of disinfection
devices on existing systems may be considered an emergency repair
as described in §285.35 of this title (relating to Emergency
Repairs) and shall be performed by either a licensed installer II,
a licensed maintenance provider, or a registered maintenance technician.
(E) Minimum required application area. The minimum
surface application area required shall be determined by dividing
the daily usage rate (Q), established in §285.91(3) of this title,
by the allowable surface application rate (Ri = effective loading
rate in gallons per square foot per day) found in §285.90(1)
of this title or as approved by the permitting authority.
(F) Landscaping plan. Applications for surface application
disposal systems shall include a landscape plan. The landscape plan
shall describe, in detail, the type of vegetation to be maintained
in the disposal area. Surface application systems may apply treated
and disinfected effluent upon areas with existing vegetation. If any
ground within the proposed surface application area does not have
vegetation, that bare area shall be seeded or covered with sod before
system start-up. The vegetation shall be capable of growth, before
system start-up.
(G) Uniform application of effluent. Distribution pipes,
sprinklers, and other application methods or devices must provide
uniform distribution of treated effluent. The application rate must
be adjusted so that there is no runoff.
(i) Sprinkler criteria. The maximum inlet pressure
for sprinklers shall be 40 pounds per square inch. Low angle nozzles
(15 degrees or less in trajectory) shall be used in the sprinklers
to keep the spray stream low and reduce aerosols. If the separation
distance between the property line and the edge of the surface application
area is less than 20 feet, sprinkler operation shall be controlled
by commercial irrigation timers set to spray between midnight and
5:00 a.m.
(ii) Planning criteria. Circular spray patterns may
overlap to cover all irrigated area including rectangular shapes.
The overlapped area will be counted only once toward the total application
area. For large systems, multiple sprinkler heads are preferred to
single gun delivery systems.
(iii) Effluent storage and pumping requirements.
(I) For systems controlled by a commercial irrigation
timer and required to spray between midnight and 5:00 a.m., there
shall be at least one day of storage between the alarm-on level and
the pump-on level, and a storage volume of one-third the daily flow
between the alarm-on level and the inlet to the pump tank.
(II) For systems not controlled by a commercial irrigation
timer, the minimum dosing volume shall be at least one-half the daily
flow, and a storage volume of one-third the daily flow between the
alarm-on level and the inlet to the pump tank.
(III) Pump tank construction and installation shall
be according to §285.34(b) of this title.
(iv) Distribution piping. Distribution piping shall
be installed below the ground surface and hose bibs shall not be connected
to the distribution piping. An unthreaded sampling port shall be provided
in the treated effluent line in the pump tank.
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