1. (a) Soil analysis procedures. At least two soil borings or two backhoe pits shall be taken in opposite ends of the area to be used for soil absorption systems. In the areas of high soil variability the permitting authority may require additional borings and backhoe pits. These borings or backhoe pits shall be excavated to the depth of two feet below the proposed excavation or to a restrictive horizon whichever is less. The type and size of an OSSF shall be determined on the basis of the most restrictive soil class located anywhere within two feet of the bottom of the proposed excavation. Evaluation of these borings and overall site evaluation shall be performed by individuals currently certified as a site evaluator. Characteristics including soil texture, soil structure, soil drainage, and soil depth shall be evaluated.

2. (b) Soil texture analysis. The soil classes shall be determined by a general texture analysis in accordance with §285.91(6) of this title (relating to Tables).

   1. (1) Soil Class Ia. Sandy texture soils which contain more than 30% gravel. This class is considered unsuitable with respect to texture.
   2. (2) Soil Class Ib. Sandy soils which contain less than or equal to 30% gravel. This class is be considered suitable with respect to texture.
   3. (3) Soil Class II. This class is considered suitable with respect to texture.
   4. (4) Soil Class III. This class is considered suitable with respect to texture.
   5. (5) Soil Class IV. This class is considered unsuitable with respect to texture.

3. (c) Soil structure analysis. Soils determined to be in Class Ib or Class II soils are generally considered suitable as to structure. In Class IV soils structure analysis need not be performed. Three soil structures significant to the movement of sewage effluent through Class III soils are blocky, platy, and massive.

   1. (1) Massive soil structure. A massive soil structure is considered unsuitable with respect to structure.
   2. (2) Blocky soil structure. A blocky soil structure is considered suitable with respect to structure.
   3. (3) Platy soil structure. A platy soil structure is considered unsuitable with respect to structure.
4. (d) Soil depth analysis. The depth of soils classified suitable as to texture and structure shall be at least 24 inches below the bottom of the proposed disposal area when standard ground absorption systems are to be utilized. Soils without at least 24 inches of suitable soil beneath the proposed drainfield shall be considered unsuitable.
5. (e) Restrictive horizons evaluation. Dense clay subsoils, rock and plugged laminar soils are considered to be restrictive horizons. They can be recognized by an abrupt change in texture from a sandy or loamy surface horizon to a clayey subsoil or rock like material which an auger will not penetrate. Soils in which restrictive horizons are less than 24 inches below the bottom of the proposed drainfield shall be considered unsuitable.
6. (f) Groundwater evaluation. The presence of groundwater shall be determined by a site evaluator. Any soil profile that is indicative of high water tables within 24 inches below the bottom of the proposed drainfield shall be considered unsuitable.
7. (g) Topography. Uniform slopes under 30% are considered suitable with respect to topography. When slopes are less than 2.0%, provisions shall be made to insure good surface drainage of rainfall or runoff from covering the soil absorption field. The drainfield excavation shall follow the contour of the ground. Soil absorption systems shall not be located in a depression or in areas of complex slope patterns where slopes are dissected by gullies and ravines.
8. (h) Flood hazard. No new OSSFs or substantial improvements to existing OSSFs shall be allowed in the regulated floodway, determined from either Federal Emergency Management Agency (FEMA) maps or a flood study prepared by a professional engineer registered in Texas. Any sites within the 100-year floodplain, determined from either FEMA maps or flood studies prepared by a professional engineer registered in Texas, shall be subject to special planning requirements to indicate that the location of the OSSF will not result in damage to the OSSF or result in contamination from the OSSF during flooding. Any planning materials submitted under this subsection shall indicate how possible tank flotation is eliminated.

9. (i) Determination of over-all site suitability. The following criteria shall determine if the site can be utilized for standard subsurface disposal methods without need of any significant modification of the site. Section 285.91(5) of this title (relating to Tables) summarizes soil and site criteria for construction of a standard treatment and disposal system.

   1. (1) If all of the soil or site criteria categories are determined to be suitable, standard subsurface disposal methods may be utilized.
   2. (2) If the site and soil evaluation proves to be suitable, the size of the subsurface absorption system may be calculated using data in §285.91(5) of this title (relating to Tables). Unsuitable sites must use appropriate proprietary or non-standard systems.
   3. (3) If one or more of the soil or site criteria categories are evaluated as unsuitable, standard subsurface disposal methods cannot be utilized. However, the site may still be utilized for standard on-site wastewater treatment by using non-standard sub-surface disposal methods, except as noted in §285.33(a)(2) of this title (relating to Criteria for Sewage Disposal Systems).

Source Note:The provisions of this §285.30 adopted to be effective February 5, 1997, 22 TexReg 1114.