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%.