(a) Unless otherwise directed by the commission, a remedial investigation as approved by the executive director shall be completed before the executive director's selection of the remedial action, except for removals and preliminary site investigations in accordance with §335.346 of this title (relating to Removals and Preliminary Site Investigations).
(b) A similar study may be approved by the executive director as an appropriate alternative to the performance of a full remedial investigation when necessary to avoid delay, to make more effective use of resources or when such similar study is sufficient to adequately characterize a site.
(c) The contents of the remedial investigation as approved by the executive director, will depend on the particular circumstances of each specific facility. Under any remedial investigation, however, sufficient information must be collected and evaluated to allow the executive director to select an appropriate remedial action.
(d) A remedial investigation may include the following, as appropriate to a particular facility, for the purpose of allowing the executive director to select an appropriate remedial action:
  (1) investigations of surface water and sediments necessary to characterize hydrologic features such as surface drainage patterns, areas of erosion and sediment deposition, surface waters, floodplains, and actual or potential hazardous substance migration routes within these areas. Properties of surface and subsurface sediments, which would influence the type and rate of hazardous substance migration or affect the ability to implement alternative remedial actions, shall be characterized;
  (2) investigations to adequately characterize the nature and extent of hazardous substances in the soils encompassing the facility. Properties associated with the soils, which would influence the type and rate of hazardous substance migration or affect the ability to implement alternative remedial actions, shall be characterized;
  (3) investigations of hydrogeology and geology to adequately characterize the nature and extent of hazardous substances in the groundwater and the features which affect the fate and transport of those hazardous substances. This should include, but is not limited to, the physical properties and distribution of bedrock and unconsolidated materials, groundwater flow rate and gradient for contaminated and potentially contaminated aquifers, groundwater divides, areas of groundwater recharge and discharge, and location of public and private groundwater wells;
  (4) information regarding local climatological characteristics which are likely to affect the hazardous substance migration such as: rainfall patterns; frequency of storm events; temperature variations; prevailing wind direction; and wind velocity;
  (5) an ecological risk assessment;
  (6) descriptions of the location, quantity, horizontal and vertical extent, concentrations and sources of hazardous substances. Information on the physical and chemical characteristics and the toxicological effects of hazardous substances shall be provided, if available; and
  (7) a feasibility study.
(e) Protective concentration levels shall be developed in accordance with Chapter 350, Subchapter D of this title (relating to Development of Protective Concentration Levels).
(f) A workplan for a remedial investigation shall be submitted to the executive director for final review and possible modifications and shall include the following:
  (1) a sampling and analysis plan covering all sampling activities to be undertaken in accordance with the remedial investigation;
  (2) a quality assurance project plan to ensure the integrity of all samples taken in accordance with the remedial investigation;
  (3) a health and safety plan to describe steps to be taken to assure the health and safety of all personnel engaged in implementing the remedial investigation; and
  (4) an implementation schedule for all aspects of the remedial investigation.
(g) Treatability studies may be required as necessary to provide information to evaluate remedial action alternatives.
(h) In evaluating the acceptability of a remedial investigation, the executive director may require the utilization of published agency and EPA technical guidance documents.
(i) A health and safety plan shall be prepared that addresses the protection of on-site personnel and the public from potential hazards associated with implementing the remedial investigation at a particular facility.
(j) A report shall be prepared at the completion of the remedial investigation and submitted to the executive director for review, possible modification, and final approval.
(k) The selection of the remedial alternative shall be made according to the process outlined in the guidance document "Presumptive Remedies for Soils at Texas State Superfund Sites" or other applicable presumptive remedy documents, unless the executive director determines that a feasibility study must be conducted.
(l) The remedial action for a particular facility shall be selected based on the remedial alternative that the executive director determines to be the lowest cost alternative which is technologically feasible and reliable, effectively mitigates and minimizes damage to the environment, and provides adequate protection of the public health and safety and the environment.
(m) All engineering evaluations, plans, and specifications included in the feasibility study or similar study must be prepared and submitted in accordance with the Texas Engineering Practice Act.
(n) All engineering and geoscientific information submitted to the agency shall be prepared by, or under the supervision of, a licensed professional engineer or licensed professional geoscientist, and shall be signed, sealed, and dated by qualified professionals as required by the Texas Engineering Practice Act and the Texas Geoscience Practice Act and the licensing and registration boards under these acts.

Source Note: The provisions of this §335.348 adopted to be effective September 9, 1991, 16 TexReg 4624; amended to be effective July 22, 1998, 23 TexReg 7369; amended to be effective September 23, 1999, 24 TexReg 7426; amended to be effective September 1, 2003, 28 TexReg 6915