Figure: 30 TAC §285.91(13)
TABLE XIII: DISPOSAL AND TREATMENT SELECTION CRITERIA
ON-SITE SEWAGE FACILITY(9) (OSSF) | SOIL TEXTURE OR FRACTURED ROCK(10) (MOST RESTRICTIVE CLASS ALONG MEDIA(1) or 2 FEET BELOW EXCAVATION) |
MINIMUM DEPTH TO GROUNDWATER | MINIMUM DEPTH TO RESTRICTIVE HORIZON(1) |
Disposal Method
(section) Treatment |
Class Ia | Class Ib, II(8) or III(8) | Class IV | Fractured Rock | MEASURED FROM
BOTTOM OF MEDIA(7) |
MEASURED
FROM
BOTTOM OF MEDIA(7) |
Absorptive
drainfield(2) (285.33(b)(1))Septic tank |
U | S | U | U | 2 feet | 2 feet |
Absorptive
drainfield(2) Secondary treatment |
S(5) | S | U | S(5) | 2 feet | 2 feet |
Lined E-T(2)
Septic tank |
S | S | S | S | N/A | N/A |
Lined
E-T(2) Secondary treatment |
S | S | S | S | N/A | N/A |
Unlined
E-T(2) Septic tank |
U | S | S | U | 2 feet | 2 feet |
Unlined
E-T(2) Secondary treatment |
S(5) | S | S | S(5) | 2 feet | 2 feet |
Pumped Effluent
Drainfield(3) Septic tank |
U | S | S | U | 2 feet | 1 foot |
Leaching
chamber(2) Septic tank |
U | S | U | U | 2 feet | 2 feet |
Leaching
chamber(2) Secondary treatment |
S(5) | S | U | S(5) | 2 feet | 2 feet |
Gravelless
pipe(2) Septic tank |
U | S | U | U | 2 feet | 2 feet |
Gravelless
pipe(2) Secondary treatment |
S(5) | S | U | S(5) | 2 feet | 2 feet |
Drip Irrigation
Septic tank/ filter |
U | S | S | U | 2 feet | 1 foot |
Drip Irrigation Secondary treatment/ filter |
S(5) | S | S | S(5) | 1 foot | 6 inches |
Low Pressure Dosing
Septic tank |
U | S | S | U | 2 feet | 1 foot |
Low Pressure
Dosing Secondary treatment |
S(5) | S | S | S(5) | 2 feet | 1 foot |
Mound
(4) Septic tank |
S | S | S | S | 2 feet | 1.5 feet |
Mound(4) Secondary treatment |
S | S | S | S | 2 feet | 1.5 feet |
Surface application
Secondary treatment |
S(6) | S(6) | S(6) | S(6) | N/A | N/A |
Surface application
Non-standard treatment |
S(6) | S(6) | S(6) | S(6) | N/A | N/A |
Soil
Substitution(2) Septic tank |
S | S | U | S | 2 feet | 2 feet |
Soil
Substitution(2) Secondary Treatment |
S | S | U | S | 2 feet | 2 feet |
S = Suitable
U = Unsuitable
(1) An absorptive drainfield may be
used, if a rock horizon is at least 6 inches above the bottom of the excavation,
see §285.33(b)(1).
(2) If the
slope in the drainfield area is greater than 30% or is complex, the area is
unsuitable for the disposal method.
(3) Can only be installed in an area where the slope is less
than or equal to 2.0%.
(4) Can only be installed in an area where the slope is less
than 10%.
(5) Requires
disinfection before disposal. A form of pressure distribution shall be used for
effluent disposal in fractured or fissured rock.
(6) Requires vegetation cover and
disinfection.
(7) When no
media exists, measure from the bottom of the excavation or pipe, whichever is
less.
(8) May require gravel
analysis for further suitability analysis (see
§285.30(b)(1)(B)).
(9) If
OSSF is located within a Flood Hazard, see §285.31(c)(2) for special planning
requirements.
(10) Includes
fissured rock.
All OSSFs require surface drainage
controls if slope is less than 2%.