1. (a) Land planning and site evaluation. Land developments and land subdivided for building construction which will utilize OSSFs for sewage disposal shall be evaluated for overall site suitability and this submittal shall be reviewed and approved by the permitting authority prior to approval being granted for subdivision of the property. The following items shall be evaluated:

   1. (1) Residential lot sizing.

      1. (A) General considerations. The failure of an OSSF may be caused by a large number of circumstances, including inadequate soil percolation, improper construction, planning, installation, and misuse. The single most important factor concerning public health problems resulting from these failures is the residential dwelling density which is primarily a function of lot size. The failure of an OSSF in a highly populated area is the fundamental cause of public health hazards resulting from on-site sewage disposal. Failure of an OSSF provides a medium for the transmission of disease and the fact that many people are in the vicinity causes concern over the spreading of disease. OSSFs using soil absorption for effluent disposal are more likely to malfunction in high population density situations because the soil available to absorb or evaporate the effluent is limited. The failure of an absorption system on a small lot can be financially disastrous to the owner because the lot may not contain sufficient room to construct a new absorption field in a new location.
      2. (B) Platted or unplatted subdivisions served by a public water supply. Subdivisions of single family dwellings platted or created after January 1, 1988, and served by a public water supply but utilizing individual OSSF methods for sewage disposal, shall provide for individual lots having surface areas of at least 1/2 acre, or shall have site-specific sewage disposal plan submitted by a registered professional engineer or registered sanitarian and approved by the permitting authority. The location of an OSSF under this paragraph shall be in accordance with §285.91(10) of this title (relating to Tables). In no instance shall the area available for such systems be less than two times the design area.
      3. (C) Platted or unplatted subdivisions served by individual water systems. In subdivisions platted or created after January 1, 1988, for single family dwellings where each lot maintains an individual water supply well and an OSSF, the sewage disposal plan shall show the approved well location and a sanitary control easement around the well within a 100-foot radius in which no subsurface sewage system may be constructed. A watertight sewage unit or lined evapotranspiration bed with leak detection capability may be placed closer to the water well than 100 feet, provided the permitting authority has granted a variance. To minimize the possibility of the transmission of waterborne diseases due to the pollution of the water supplied for domestic use, each lot in a subdivision shall contain no less area than one acre, or shall have site-specific planning materials prepared by a registered professional engineer or a registered sanitarian and approved by the permitting authority. In no instance shall the area available for such systems be less than two times the design area.
   2. (2) Manufactured housing communities or multi-unit residential developments served by a central sewage collection system for on-site disposal. Manufactured housing communities or multi-unit residential developments which are owned and controlled by a person which rents or leases space may utilize smaller lots than stated in paragraph (1)(A) and (1)(B) of this subsection provided a sewage disposal plan addressing replacement area is submitted to the permitting authority and approved. Developments of this type which connect living units to a sewage collection system for on-site disposal, must provide planning materials for the system prepared by a registered professional engineer or registered sanitarian. The total anticipated sewage production for such property shall not exceed 5,000 gallons per day from the connected homes and the OSSF must conform to the definition of OSSFs in §285.2 of this title (relating to Definitions).
   3. (3) Site evaluation. The subdivided property must be evaluated for soil suitability in accordance with §285.30 of this title (relating to Site Evaluation).

2. (b) Approval of existing small lots or tracts. Existing small lots or tracts, subdivided prior to January 1, 1988, and not conforming to the minimum lot size requirements, may be approved for an OSSF provided the following conditions are met:

   1. (1) Minimum separation distances in §285.31 of this title (relating to Separation/ Setback Requirements) are maintained; and
   2. (2) The site has been evaluated by the site evaluator in accordance with §285.30 of this title (relating to Site Evaluation).
3. (c) Review of subdivision or development plans. Persons proposing residential subdivisions, manufactured housing communities, multi-unit residential developments, business parks, or other similar uses and utilizing OSSFs for sewage disposal must submit planning materials for these developments to the permitting authority. The planning materials must include an overall site plan, topographic map, 100-year floodplain map, soil survey, location of water wells, and complete report detailing the types of OSSFs to be considered and their compatibility with area wide drainage and groundwater. A comprehensive drainage and 100-year floodplain impact plan must also be included in these planning materials. Planning materials shall also address potential replacement areas. A response to the submitted planning material from the permitting authority will be provided within 45 days of receipt.

Source Note:The provisions of this §285.4 adopted to be effective February 5, 1997, 22 TexReg 1114.