| (ii) On sites with 2% slopes or less, the area credited
toward the minimum required basal area sizing includes all areas below
the distribution system as well as the side slope area on all side
slope areas greater than six inches deep.
(G) Mounds shall only be installed on sites with less
than 10% slope.
(H) The toe of the mound is considered the edge of
the soil absorption system.
(I) The side slopes must be no steeper than three to
one.
(J) There must be at least six inches of backfill over
the distribution media and the mound shall be crowned to shed water.
(4) Soil substitution drainfields. Soil substitution
drainfields may be constructed in Class Ia soils, highly permeable
fractured rock, highly permeable fissured rock, or Class II and III
soils with greater than 30% gravel.
(A) A soil substitution drainfield must not be used
in Class IV soils or Class IV soils with greater than 30% gravel.
Class III or IV soil shall not be used as the substituted soil in
a soil substitution drainfield. There must be at least two feet of
substituted soil between the bottom of the media and groundwater.
(B) A soil substitution drainfield is constructed similar
to a standard absorptive drainfield except that a minimum two foot
thick Class Ib or Class II soil buffer shall be placed below and on
all sides of the drainfield excavation. The soil buffer must extend
at least to the top of the media. The two-foot buffer area along the
sides of the excavation is not credited as bottom area in calculating
absorptive area. However, the interface between the media and the
substituted soil is credited as absorptive area.
(C) Soil substitution drainfields must be designed
to address soil compaction to prevent unlevel disposal. It is recommended
that low-pressure dosing be used for effluent distribution. The edge
of the substituted soil is considered the edge of the soil absorption
drainfield in determining the appropriate separation distances as
listed in §285.91(10) of this title.
(D) Class Ia soils do not provide adequate treatment
of wastewater through soil contact. A soil substitution drainfield
may be constructed in Class Ia soils in order to provide adequate
soil for treatment. Absorptive area sizing must be based on the textural
class of the substituted soil and must follow the formulas in subsection
(b)(1)(A)(vii)(I) of this section.
(E) Highly permeable fractured and fissured rock, which
contains soil in the fractures and fissures, does not provide adequate
treatment of wastewater through soil contact. A soil substitution
drainfield can be constructed in this permeable fractured and fissured
rock in order to provide adequate soil for treatment. Absorptive area
sizing must be based on the most restrictive textural class between
either the native soil residing in the fractures or fissures or the
substituted soil. The sizing must follow the formulas in subsection
(b)(1)(A)(vii)(I) of this section.
(F) Class II and III soils with greater than 30% gravel
do not provide adequate treatment of wastewater through soil contact.
A soil substitution drainfield can be constructed in Class II or III
soils with greater than 30% gravel in order to provide adequate soil
for treatment. Absorptive area sizing must be based on the most restrictive
textural class between either the non-gravel portion of the native
soil or the substituted soil. The sizing must follow the formulas
in subsection (b)(1)(A)(vii)(I) of this section.
(5) Drainfields following secondary treatment and disinfection.
Subsurface drainfields following secondary treatment and disinfection
may be constructed in Class Ia soils, fractured rock, fissured rock,
or other conditions where insufficient soil depth will allow septic
tank effluent to reach fractured rock or fissured rock, as long as
the following conditions are met.
(A) Drainfield sizing.
(i) If the unsuitable feature is Class Ia soil, the
disposal area sizing shall be based on the application rate for Class
Ib soil. Some form of pressure distribution shall be used for effluent
disposal.
(ii) If the unsuitable feature is fractured or fissured
rock, the system sizing should be based on the application rate for
Class III soil. Some form of pressure distribution system shall be
used for effluent disposal.
(B) Effluent disinfection. Treated effluent must be
disinfected as indicated in §285.32(e) of this title before discharging
into the drainfield.
(C) Other requirements. The affidavit, maintenance,
and testing and reporting requirements of §285.3(b)(3) of this
title and §285.7(a) and (d) of this title (relating to Maintenance
Requirements) apply to these systems.
(6) All other nonstandard disposal systems. The planning
materials for all non-standard disposal systems not described in paragraphs
(1) - (5) of this subsection shall be submitted to the executive director
for review according to §285.5(b)(2) of this title before the
systems can be installed.
|
| Source Note: The provisions of this §285.33 adopted to be effective February 5, 1997, 22 TexReg 1114; amended to be effective June 13, 2001, 26 TexReg 4115; amended to be effective August 29, 2002, 27 TexReg 7917; amended to be effective August 3, 2006, 31 TexReg 6013; amended to be effective September 11, 2008, 33 TexReg 7536; amended to be effective December 27, 2012, 37 TexReg 9947 |
