|(a) General requirements.
(1) All disposal systems in this section shall have
an approved treatment system as specified in §285.32(b) - (d)
of this title (relating to Criteria for Sewage Treatment Systems).
(2) All criteria in this section shall be met before
the permitting authority issues an authorization to construct.
(3) The pipe between all treatment tanks and the pipe
from the final treatment tank to a gravity disposal system shall be
a minimum of three inches in diameter and be American Society for
Testing and Materials (ASTM) 3034, Standard dimension ratio (SDR)
35 polyvinyl chloride (PVC) pipe or a pipe with an equivalent or stronger
pipe stiffness at a 5% deflection. The pipe must maintain a continuous
fall to the disposal system.
(4) The pipe from the final treatment tank to a gravity
disposal system shall be a minimum of five feet in length.
(5) Except for drip irrigation tubing, pipe under internal
pressure within any part of an on-site sewage facility system shall
meet the minimum requirements of ASTM Schedule 40.
(6) Pipe that crosses drainage easements shall be sleeved
with ASTM Schedule 40 pipe; the pipes shall be buried at least one
foot below the surface, or buried less than one foot and encased in
concrete; the outside pipe shall have locater tape attached to the
pipe; and markers shall be placed at the easement boundaries to indicate
the location of the pipe crossing. Crossings shall be designed and
constructed in a manner that protects the pipe and the drainage way
(b) Standard disposal systems. Acceptable standard
disposal methods shall consist of a drainfield to disperse the effluent
either into adjacent soil (absorptive) or into the surrounding air
through evapotranspiration (evaporation and transpiration).
(1) Absorptive drainfield. An absorptive drainfield
shall only be used in suitable soil. There shall be two feet of suitable
soil from the bottom of the excavation to either a restrictive horizon
or to groundwater.
(A) Excavation. The excavation must be made in suitable
soils as described in §285.31(b) of this title (relating to Selection
Criteria for Treatment and Disposal Systems).
(i) The excavation shall be at least 18 inches deep
but shall not exceed a depth of either three feet or six inches below
the soil freeze depth, whichever is deeper. Single excavations shall
not exceed 150 feet.
(ii) In areas of the state where annual precipitation
is less than 26 inches per year (as identified in the Climatic Atlas
of Texas, (1983) published by the Texas Department of Water Resources
or other standards approved by the executive director), the maximum
permissible excavation depth shall be five feet.
(iii) Multiple excavations must be separated horizontally
by at least three feet of undisturbed soil. The sidewalls and bottom
of the excavation must be scarified as needed. When there are multiple
excavations, it is recommended that the ends be looped together.
(iv) The bottom of the excavation shall be not less
than 18 inches in width.
(v) The bottom of the excavation shall be level to
within one inch over each 25 feet of excavation or within three inches
over the entire excavation, whichever is less.
(vi) If the borings or backhoe pits excavated during
the site evaluation encounter a rock horizon and the site evaluation
shows that there is both suitable soil from the bottom of the rock
horizon to two feet below the bottom of the proposed excavation and
no groundwater anywhere within two feet of the bottom of the proposed
excavation, a standard subsurface disposal system may be used, providing
the following are met.
(I) The depth of the excavation shall comply with clause
(i) of this subparagraph.
(II) The rock horizon shall be at least six inches
above the bottom of the excavation.
(III) Surface runoff shall be prevented from flowing
over the disposal area.
(IV) Subsurface flow along the top of the rock horizon
shall be prevented from flowing into the excavation.
(V) The sidewall area will not be counted toward the
required absorptive area.
(VI) The formulas in clause (vii)(I) - (III) of this
subparagraph shall be adjusted so that no credit is given for sidewall
(VII) No single pipe drainfields on sloping ground
as shown in §285.90(5) of this title (relating to Figures) or
no systems using serial loading shall be used.
(vii) The size of the excavation shall be calculated
using data from §285.91(1) and (3) of this title (relating to
Tables). The soil application rate is based on the most restrictive
horizon along the media, or within two feet below the bottom of the
excavation. The formula A = Q/Ra shall be used to determine the total
absorptive area where:
(I) The absorptive area shall be calculated by adding
the bottom area (L x W) of the excavation to the total absorptive
area along the excavated perimeter 2(L+W), (in feet) multiplied by
(II) The length of the excavation may be determined
as follows when the area and width are known.
(III) For excavations three feet wide or less, use
the following formula, or §285.91(8) of this title to determine
(B) Media. The media shall consist of clean, washed
and graded gravel, broken concrete, rock, crushed stone, chipped tires,
or similar aggregate that is generally one uniform size and approved
by the executive director. The size of the media must range from 0.75
- 2.0 inches as measured along its greatest dimension except as noted
in clause (i) of this subparagraph.
(i) If chipped tires are used:
(I) a geotextile fabric heavier than specified in subparagraph
(E) of this paragraph must be used; and
(II) the size of the chipped tires must not exceed
three inches as measured along their greatest dimension.
(ii) Soft media such as oyster shell and soft limestone
shall not be used.
(C) Drainline. The drainline shall be constructed of
perforated distribution pipe and fittings in compliance with any one
of the following specifications:
(i) three- or four-inch diameter PVC pipe with an SDR
of 35 or stronger;
(ii) four-inch diameter corrugated polyethylene, ASTM
F405 in rigid ten foot joints;
(iii) three- or four-inch diameter polyethylene smoothwall,
(iv) three- or four-inch diameter PVC ASTM D2729 pipe;
(v) three- or four-inch diameter polyethylene ASTM
F892 corrugated pipe with a smoothwall interior and fittings; or
(vi) any other pipe approved by the executive director.
(D) Drainline installation requirements. The drainline
shall be placed in the media with at least six inches of media between
the bottom of the excavation and the bottom of the drainline. The
drainline shall be completely covered by the media and the drainline
perforations shall be below the horizontal center line of the pipe.
For typical drainfield configurations, see §285.90(5) of this
title. For excavations greater than four feet in width, the maximum
distance between parallel drainlines shall be four feet (center to
center). Multiple drainlines shall be manifolded together with solid
or perforated pipe. Additionally, the ends of the multiple drainlines
opposite the manifolded end shall either be manifolded together with
a solid line, looped together using a perforated pipe and media, or
(E) Permeable soil barrier. Geotextile fabric shall
be used as the permeable soil barrier and shall be placed between
the top of the media and the excavation backfill. Geotextile fabric
shall conform to the following specifications for unwoven, spun-bounded
polypropylene, polyester, or nylon filter wrap.
(F) Backfilling. Only Class Ib, II, or III soils as
described in §285.30 of this title (relating to Site Evaluation)
shall be used for backfill. Class Ia and IV soils are specifically
prohibited for use as a backfill material. The backfill material shall
be mounded over the excavated area so that the center of the backfilled
area slopes down to the outer perimeter of the excavated area to allow
for settling. Surface runoff impacting the disposal area is not permitted
and the diversion method shall be addressed during development of
the planning materials.
(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.
(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.