1. (a) Disposal processes--standard. The effluent discharged from an approved treatment process requires further handling to render it safe from a public health standpoint. Acceptable standard disposal methods shall consist of a drainfield to disperse the effluent into adjacent soil (absorptive) or into the surrounding air through evapotranspiration (evaporation and transpiration).

   1. (1) Absorptive drainfield. An absorptive drainfield is an excavation constructed in suitable soil. A porous media (crushed rock, stone, etc.) is then placed in the excavation and perforated pipe (drainline) placed in the media and connected to the outlet of the treatment system. The media is covered with a permeable geotextile fabric and the remainder of the excavation backfilled with previously removed soil. The top of the excavation area is seeded with plants or grasses, where vegetation is sustainable, to aid in water elimination. The following considerations must be met for approval of an absorptive drainfield:

      1. (A) Excavation. The excavation must be constructed in suitable soils as described in §285.30 of this title (relating to Site Evaluation). The excavation shall not exceed a depth of three feet or six inches below the soil freeze depth, whichever is the larger. However, in areas of the state where annual precipitation is less than 26 inches of rainfall per year (as identified in the Climatic Atlas of Texas, (1983) published by the Texas Department of Water Resources and suitable soils (Class Ib, II, or III) lie below unsuitable soil caps, the maximum permissible excavation shall be five feet. Multiple excavations must be separated horizontally by at least three feet of undisturbed soil. After excavation the excavated surfaces (sidewalls and bottom) must be scarified as needed. The bottom of the excavation shall be not less than 18 inches in width and level to within one inch over each 25 feet of excavation. The size of the excavation shall be calculated using data from §285.91(8) of this title (relating to Tables). The formula A = Q/Ra shall be used to determine drainfield area where:
         Attached Graphic
         

         1. (i) The usable surface area shall be calculated by adding the excavation bottom area to the total excavated perimeter (in feet) multiplied by one foot (bottom area + perimeter X 1.0).
            Attached Graphic
            
         2. (ii) The length of the excavation may be determined as follows when the area and width are known:
            Attached Graphic
            
         3. (iii) For excavations three feet wide or less use the following formula or §285.91(8) of this title (relating to Figures) to determine L:
            Attached Graphic
            

      2. (B) Porous media. The porous media shall consist of clean, washed and graded gravel, broken concrete, rock, crushed stone, chipped tires, or similar aggregate that is generally one uniform size ranging from 0.75-2.0 inches as measured along its greatest dimension.

         1. (i) The permitting authority may consider and approve on a case-by-case basis the use of chipped tire sizes greater than 0.75-2.0 inches along the greatest dimension.
         2. (ii) When chipped tires are used in conjunction with geotextile fabric, a heavier duty geotextile fabric must be utilized to minimize fabric punctures and eliminate fabric tears due to protruding steel belt remnants.
         3. (iii) Soft media such as oyster shell and soft limestone will not be approved.

      3. (C) Drainline. The drainline shall be constructed of perforated distribution pipe and fittings in compliance with the following specifications:

         1. (i) Three or four inch diameter polyvinyl chloride pipe with a standard dimension ratio (SDR) of 35 or less.
         2. (ii) Four inch diameter corrugated polyethylene, ASTM F405 in rigid ten foot joints only.
         3. (iii) Three or four inch diameter polyethylene smoothwall, ASTM F810.
         4. (iv) Any other pipe approved by the executive director.
      4. (D) Installation Requirements. The drainline shall be placed in the porous media with at least six inches of media between the bottom of the excavation and the bottom of the drainline. The drainline shall be completely covered by the porous media and the drainline perforations shall be below the horizontal center line of the pipe. Single drainlines shall not exceed 150 feet, see §285.90(5) of this title (relating to Figures). The drainlines shall be placed parallel to each other and parallel to the longest horizontal dimension of the excavation. For excavations greater than three feet in width, the maximum separation distance between parallel drainlines shall be four feet (center to center). Multiple drainlines shall be manifolded together with solid or perforated pipe. The opposite ends of multiple drainlines shall be manifolded together with solid line or looped together using perforated line and bedding. If drainfield is not to be looped, end caps must be used.
      5. (E) Permeable soil barrier. A permeable soil barrier shall be placed between the top of the porous media and the excavation backfill. Geotextile fabric shall be used for the permeable soil barrier. Geotextile fabric shall conform to the following specifications for unwoven, spun-bounded polypropylene, polyester or nylon filter wrap:
         Attached Graphic
         
      6. (F) Backfilling. Backfilling is the process of replacing the soil removed during excavating back into the drainfield and on top of the geotextile fabric. Only Class Ib or II soils as described in §285.30(b) and (c) of this title (relating to Site Evaluation) shall be used for backfill. Rock and high shrink swell clays are specifically prohibited for use as a backfill material. The backfill material shall be mounded over the excavated area so that the center of the excavation slopes down to the outer perimeter to allow for settling. The excavated area may be bermed or drainage swales may be used to divert surface runoff from the site.
      7. (G) Drainfields on irregular terrain. Where topography or ground slope is greater than 15% but less than 30% slope for the construction of a level single drainfield, multiple long narrow drainfields may be constructed along descending contours. An overflow line shall be provided from the upper excavations to the lower excavations. This overflow line shall be constructed from solid pipe with an SDR of 35 or less and the excavation carrying the overflow pipe shall be backfilled with soil only.
      8. (H) Drainfield plans. A number of approved sketches, specifications and details for drainfield construction are provided in §285.90(4) and (5) of this title (relating to Figures).

   2. (2) Evapotranspirative drainfield (ET). An ET drainfield is a standard disposal process which may be used in soils which are classified as unsuitable in §285.30 of this title (relating to Site Evaluation) with respect to texture, structure, restrictive horizons and ground water. Water saving devices must be utilized in all structures for which ET beds are recommended. ET drainfields are generally constructed in accordance with the specifications for absorptive drainfields with the following exceptions:

      1. (A) Liners. An impervious liner must be used between the excavated surface and the constructed drainfield in all Class Ia soils classified as unsuitable due to the possibility of ground water contamination. Liners are also required for Class IV soils with seasonal ground water tables which penetrate the excavation. Liners shall be constructed from impervious rubber or plastic material having a thickness of 20 mils or greater per layer. Reinforced concrete, gunite, and compacted and tested clay (one foot thick or more) may also be used for liner material. Liners shall be constructed in such a manner as to have a permeability of 10[sup]-7[/sup] cm/sec or less as tested by a certified soil laboratory. Rubber or plastic liners must be protected from rocks and stones (when exposed) by covering the excavated surface with a uniform sand cushion at least four inches thick.
      2. (B) ET drainfield sizing. The following formula shall be used to calculate the top surface area of a constructed ET drainfield:
         Attached Graphic
         
      3. (C) Backfill material. Backfill material shall consist of soil Class II as described in §285.30 of this title (relating to Site Evaluation). Excavations containing two or more drainlines may eliminate the porous media between the drainlines to allow the backfill material to contact the bottom of the excavation. This construction procedure will enhance the wicking action of the soil and improve water transfer. The porous media shall extend at least one foot beyond the edge of the drainline horizontally.
      4. (D) Vegetative cover for transpiration. The final grade shall be covered with vegetation fully capable to take maximum advantage of transpiration, depending on the season and the site's location. Evergreen bushes having shallow root systems may be planted in the drainfield to assist in water uptake. Grasses with dormant periods shall be overseeded to provide year-round transpiration.
      5. (E) Multiple ET drainfields. ET drainfields shall be divided into two or more separate units connected by flow control valves. One of the units may be removed from service for an extended period of time to allow it to dry out and decompose biological material which might tend to plug the drainfield. If one of the units is removed from service, the daily water usage must be reduced to prevent overloading of the units still in operation. Normally, a unit must be removed from service for two to three dry months for biological breakdown to occur.
      6. (F) Geographical location. ET drainfields shall only be used in those areas of the state where the annual average evaporation exceeds the annual rainfall. As the annual rainfall approaches the annual evaporation, the required ET drainfield size becomes very large and expensive to construct (see data in §285.91(7) of this title (relating to Tables)).
      7. (G) ET drainfield plans. A number of approved sketches for ET drainfield construction are provided in §285.90(4) and (5) of this title (relating to Figures).

   3. (3) Pumped effluent drainfield. Pumped effluent drainfields must utilize low pressure dosed drainfield specifications described in subsection (c)(1) of this section, with the following exceptions:

      1. (A) Applicability. Pumped effluent drainfields may only be utilized by single family dwellings and not commercial or institutional structures.
      2. (B) Length of drainfield. There shall be at least 1,000 linear feet of perforated drain pipe for a two bedroom single family dwelling. For each additional bedroom, there shall be an additional 400 linear feet of perforated drain pipe. No individual lateral may exceed 70 feet in length.
      3. (C) Trench width and horizontal separation. Trenches shall be at least six inches wide. There shall be at least three feet of separation between trenches.
      4. (D) Lateral depth and vertical separation. All drainfield laterals shall adhere to a depth range from 1.5 feet to 3 feet. There shall be at a minimum vertical separation distance of 2.0 foot from the bottom of the excavation to a restrictive horizon or to ground water.
      5. (E) Porous media. Each dosing pipe shall be placed with the drain holes facing down and placed on at least six inches of porous media (pea gravel or larger) between the bottom of the excavation and pipe.
      6. (F) Pipe and hole size. Lateral drain pipe shall use 1.25-1.5 inch diameter line. Manifolds or headers shall use 1.25-1.5 inch diameter line, where the manifold or header lines must have a diameter as large or larger than the lateral line diameter. Lateral drain pipe hole sizes shall be 3/16-1/4 inch diameter spaced 5 feet apart.
      7. (G) Pump size. Pumped effluent drainfields shall utilize at least a 1/2 horsepower pump.
      8. (H) Topography. When slopes are greater than 2.0%, pumped effluent drainfields shall not be used.

2. (b) Disposal processes--proprietary.

   1. (1) Gravel-less drainfield piping. Gravel-less pipe may be used only on sites suitable for standard subsurface sewage disposal methods. Gravel-less pipe is available in eight-inch or ten-inch diameter corrugated perforated polyethylene pipe. The pipe is enclosed in a layer of unwoven spun-bonded polypropylene, polyester or nylon filter wrap. Gravel-less pipe shall meet American Society for Testing and Materials, ASTM F-667 Standard Specifications for large diameter corrugated high density polyethylene (ASTM D 1248) tubing. The filter cloth must meet the same material specifications as described under subsection (a)(1)(E) of this section.

      1. (A) Planning parameters. Gravel-less drainfield pipe may be substituted for pipe in both absorptive or ET drainfields. When gravel-less pipe is substituted, the porous media around conventional pipe will not be required. ET drainfields shall be backfilled with Class II soils only. Gravel-less pipe shall not be used for absorptive drainfields in Class IV soils. All other planning parameters for absorptive or ET drainfields apply to gravel-less pipe.
      2. (B) Installation. The proper installation of adequate construction materials is vitally important to the success of gravel-less drainfield systems. Materials include gravel-less pipe, backfill, end caps, offset connectors and filter cloth. All connections from the house to the septic tank shall be in accordance with §285.34(a) of this title (relating to Other Requirements). The connection from the septic tank to the gravel-less line shall be made by using an eight or ten-inch offset connector. It is important that the gravel-less line be laid level with the continuous stripe up, and joined with couplings. The filter cloth must be pulled over the joint to eliminate soil infiltration. The gravel-less pipe must be held in place during initial backfilling to prevent movement of the pipe in the excavation. The end of each gravel-less line shall have an end cap and inspection port installed. An inspection port is required because the amount of sludge or suspended solids in the line can be easily monitored and the distribution lines can be back-flushed.
      3. (C) Drainfield Sizing. Eight inch diameter gravel-less pipe shall use W = 2.0 feet and ten inch gravel-less pipe shall use W = 2.5 feet for absorptive drainfield sizing.

   2. (2) Leaching chambers. Leaching chambers are bottomless chambers which are planned for installation in a drainfield excavation with the open bottom of the chamber in direct contact with the excavation. The chambers are linked together with sewer pipe (no perforations) in such a manner as to completely cover the excavation with adjacent chambers in contact with each other. Other special conditions for leaching chambers are as follows:

      1. (A) The excavation may be reduced by 40% from the value calculated using §285.91(1) of this title (relating to Tables). The following formula may be used for excavations utilizing leaching chambers:
         Attached Graphic
         
      2. (B) These chambers shall not be used for absorptive drainfields in Class Ia or IV soils.
      3. (C) Backfill covering leaching chambers should be Class Ib, or II soil.

   3. (3) Drip Irrigation. A drip irrigation system consist of small diameter pressurized lines directly buried in the soil to a nominal depth of six inches. The lines contain pressure reducing emitters spaced at 30 inch maximum intervals. The purpose of the pressure reducing emitter is to restrict the flow of effluent from the pipe into the surrounding soil to a very low rate. This distribution method promotes uniform wetting of the soil in the root zone of surface vegetation. Since the near surface root zone of plants will absorb water, even in Class IV soils, this type of system may be used for on-site disposal in these soils. The system must be equipped with a filtering device capable of filtering to 100 microns and meet drip irrigation (pressure emitter) manufacturer requirements.

      1. (A) Drainfield layout. The drainfield shall consist of a matrix of lines and emitters arranged in almost any configuration where the layout would ensure equal distribution throughout the drainfield. The system must be equipped with a mechanism to flush from the drainfield back to the treatment unit.
      2. (B) Effluent quality. Treatment preceding this disposal process shall treat the wastewater to a degree to preclude plugging of the emitters. This quality shall be determined by the executive director.
      3. (C) System maintenance. Ongoing maintenance contracts in accordance with the maintenance provisions of §285.7 of this title (relating to Additional Application Requirements for Surface Irrigation Systems) shall be required for all emitter systems. Systems must be equipped to flush the system back to the treatment unit.
      4. (D) Loading Rates. Pressure emitters can be used in all classes of soils using loading rates as specified in §285.91(1) of this title (relating to Tables). Emitters are assumed to wet four square feet of absorptive area per emitter, however, overlapping areas shall only be counted once toward absorptive area requirements.
      5. (E) There shall be a minimum of 1 foot of soil between the drip emitter and ground water or solid or fractured rock.
      6. (F) No device associated with a drip irrigation system shall be installed which has not been labelled by the manufacturer as suitable for use with domestic sewage or is on an approved list of the executive director in accordance with §285.32(b)(5) of this title (relating to Treatment processes-proprietary).
   4. (4) Testing and monitoring of proprietary disposal systems. All proprietary disposal systems other than those described in this section shall be approved by the executive director prior to their use in the state. Proprietary systems shall be approved by the executive director utilizing the procedures established in §285.32(b) of this title (relating to Criteria for Sewage Treatment Systems).

3. (c) Disposal processes--non-standard. Non-standard disposal processes are all systems, components and materials not described as standard and not marketed for sale in the state as a proprietary item. The permitting authority may at its option review and either approve or disapprove the planning materials on a case-by-case basis. Planning criteria will be derived from basic engineering analysis and scientific investigation of the proposed disposal process.

   1. (1) Low pressure dosed drainfield. A low pressure dosing system consists of an approved treatment system as specified in §285.32 of this title (relating to Criteria for Sewage Treatment Systems). Effluent from this system is pumped, under low pressure, into a solid wall force main and then into a perforated distribution pipe which is installed within the drainfield area.

      1. (A) The effluent pump in the pump tank must be capable of an operating range that will assure that effluent is delivered to the most distant point of the perforated piping network, yet not be excessive to the point that "blow-outs" occur.
      2. (B) A start/stop switch or timer must be included in the system to control the dosing pump. A high water alarm, on an electric circuit separate from the pump, must be provided.

      3. (C) Drainfield criteria. Pressure dosing systems may be installed in accordance with design criteria in the North Carolina State University Sea Grant College Publication UNC-S82-03 (1982) or other publications containing criteria or data on pressure dosed systems which are acceptable to the permitting authority. The following parameters are required for all low pressure subsurface drainfields:

         1. (i) The low pressure dosed drainfield area shall be sized in accordance with §285.91(1) of this title (relating to Tables). Use 3 square feet of wetted area per linear foot of dosing pipe for all excavated areas less than one foot wide.
         2. (ii) Each dosing pipe shall be placed with the drain holes facing down and placed on at least 6 inches of porous media (pea gravel or larger) between the bottom of the excavation and pipe.
         3. (iii) Geotextile fabric shall be placed over the porous media and the excavation filled with Class Ib or II soil.
         4. (iv) There shall be a minimum of one foot of soil between the bottom of the excavation and solid or fractured rock. There shall be a minimum of two feet of soil between the bottom of the excavation and ground water.

   2. (2) Surface irrigation systems. Surface irrigation methods include, but are not limited to, spray irrigation, landscape irrigation or any other method of applying treated effluent onto the surface of the ground.

      1. (A) Types of wastewater treatment. The treatment system shall consist of any standard, proprietary, approved aerobic units or non-standard treatment methods described in §285.32 of this title (relating to Criteria for Sewage Treatment Systems) and meeting the following effluent criteria:
         Attached Graphic
         
      2. (B) Acceptable surface application areas. Acceptable land for surface application will include generally flat terrain (land less than or equal to 15% slope) covered with grasses, evergreen shrubs, bushes, trees or landscaped beds containing mixed vegetation. Sloped land may be acceptable if properly landscaped and terraced to minimize runoff.
      3. (C) Unacceptable surface application areas. Land which cannot be used for surface irrigation includes land for growing food, gardens, orchards or crops which may be used for human consumption. Additionally, effluent shall not be applied to unseeded bare ground under any circumstances.
      4. (D) Minimum required application area. The minimum surface application area required shall be determined by dividing the daily usage rate (Q) as established in §285.91(3) of this title (relating to Tables) by the allowable surface irrigation application rate (Ri) found in §285.90(1) of this title (relating to Figures) or as approved by the permitting authority.
         Attached Graphic
         

      5. (E) Uniform application of effluent. Distribution pipes, sprinklers, flow channels and other application methods/devices must provide uniform distribution of treated effluent. The application rate must be adjusted so as not to produce runoff.

         1. (i) Sprinkler criteria. When sprinklers are used as the application method, the maximum inlet pressure shall be 40 pounds per square inch. Low angle nozzles (13 degrees or less in trajectory) shall be used in the sprinklers to keep the spray stream low and reduce aerosols. Sprinkler operation shall be controlled by commercial irrigation timers, when property line setbacks are less than 20 feet.
         2. (ii) Sprinkler head requirements. Circular spray patterns may overlap to cover all irrigated area including rectangular shapes. However, the overlapped area will be only counted once toward the total application area. For large systems, multiple sprinkler heads are preferred to single gun delivery systems.
         3. (iii) Effluent storage requirements. Storage requirements and pump tank construction and installation shall be in accordance with §285.34(b) of this title relating to Other Requirements). A sampling port shall be provided in the treated effluent line in the pump tank.
   3. (3) Mound systems. A mound drainfield is an absorptive drainfield constructed above the native soil surface. A scarified interface (for absorptive mounds) between the native soil, a porous media around the distribution pipe, the distribution piping, and a topsoil cover are all components of the mound system. The depth of the material between the distribution pipe and the restrictive horizon or ground water shall be at least two feet. The preferred constructed shape is a long narrow rectangle, with the long dimension laid out along a contour. Effluent shall be pressure dosed into the distribution piping to ensure equal distribution and to control application rates. Planning criteria for mound construction may be as specified in the North Carolina State University Sea Grant College Publication UNC-SG-82-04 (1982), the United States Environmental Protection Agency's On-site Wastewater Treatment and Disposal Systems Design Manual (1980) or any technical publication containing mound system criteria and acceptable to the executive director. Shallow placement of the pressure distribution pipe is recommended to reduce mound height.
   4. (4) Soil substitution drainfields. Soil substitution drainfields may be constructed in Class Ia soils, fractured rock, fissured rock, or other conditions of high permeability where septic tank effluent could rapidly reach ground water without undergoing adequate treatment through soil contact. A soil substitution drainfield is constructed similar to a standard absorptive drainfield with one exception. The exception consists of a 24-inch thick Class Ib, Class II or Class III soil buffer placed below and on all sides of the drainfield excavation to an elevation less than the top of the porous media. The Class Ib, Class II or Class III soil acts as a filter medium to remove contaminants from the wastewater prior to its contacting the highly permeable natural ground. Class IV soils may not be utilized for soil substitution. Disposal areas shall be sized based on the textural class of the substituted soil. It is recommended, but not mandatory, that low pressure dosing be used for effluent distribution.

   5. (5) Drainfields Following Approved Aerobic Units, 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, fissured rock, or a restrictive horizon before undergoing adequate treatment through soil contact.

      1. (A) Drainfield Sizing.

         1. (i) If the unsuitable feature is Class Ia soils, the disposal area sizing should be based on the application rate for Class Ib soils. It is recommended, but not mandatory, that some form of pressure distribution be used for effluent disposal.
         2. (ii) If the unsuitable feature is insufficient soil depth to fractured or fissured rock, the system sizing should be based on the application rate for Class III soils. It is recommended, but not mandatory, that some form of pressure distribution system be used for effluent disposal.
      2. (B) Maintenance Requirements. The maintenance requirements of §285.7(c)-(g) of this title (relating to Additional Application Requirements for Surface Irrigation Systems) apply to these systems.

Source Note:The provisions of this §285.33 adopted to be effective February 5, 1997, 22 TexReg 1114.