Chapter 4: Design

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Section 1: Overview

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Goals

As described in the FHWA Interim Guidance Summary regarding hazardous materials in project development, the following goals should be considered during design:

One of the main goals of the design process is to provide as much information as possible to TxDOT consultants and the district's advanced project development, environmental, and right-of-way staff regarding design details (such as locations of excavations and de-watering requirements). This disclosure will allow the most thorough environmental site assessment possible. As preliminary design requirements are finalized, assumptions made during project planning for the initial site assessment may need to be re-evaluated.

Due to the increased costs associated with hazardous materials management, information regarding known or possible hazardous material concerns should be integrated into the project coordination, alignment selection, and decision-making processes.

If contamination cannot be avoided, or cleaned up prior to construction, the project designer, in conjunction with ENV division staff, should develop procedures, plan notes, specifications and plan details to address contamination concurrent with construction.

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Procedure Overview

This chapter provides guidance for those rare cases when contamination cannot be avoided or cleaned up prior to construction. For example, in situations where soil and groundwater contamination is widespread, cleanup could potentially take years; it may not be feasible to delay construction until cleanup is complete. Also, in some situations it may be cost-prohibitive to clean an area to non-contaminated levels. In such a case the corrective action plan may call for a risk-based closure, which allows contaminated soil and groundwater to remain in place. However, special handling considerations may be necessary if the contamination is encountered during construction.

For the most part, TxDOT’s preparation and work activities regarding contamination issues during construction are preventive, not corrective actions.

The following are some terms relevant to design, and their definitions:

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  • Corrective Action: Cleanup, removal or stabilization of contaminated soil and/or groundwater as required by environmental regulations. The goal of corrective action is typically to obtain regulatory closure of the affected site.
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  • Preventive Action: Cleanup, removal, or stabilization of contaminated soil, and/or groundwater as required prior to or during construction or maintenance projects. In contrast with corrective action, preventive action is concerned primarily with worker safety, as well as ensuring that the existing contamination problem is not aggravated by the project.
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  • Aggravate: To contribute to or cause further releases into the environment, resulting in exacerbation of existing soil or groundwater pollution by:
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    • removing contaminated soil or groundwater by excavation or pumping and improperly handling, storing, or discharging the soil or groundwater,
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    • creating pathways for contaminant migration, and;
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    • obstructing ongoing or impending corrective actions.
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  • Specialty Contractor: A contractor with the training, experience and equipment necessary to perform construction-related services within contamination zones. Specialty contractors perform work in areas where Occupation Safety and Health Administration (OSHA) training requirements and/or pollution liability concerns prevent the general contractor from performing such work. Underground storage tank removal contractors constitute a large statewide pool of potential specialty contractors.
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  • Soil and Groundwater Management Plan (SGMP): A project-specific, written document that becomes a special provision of the Plans, Specifications, and Estimates (PS&E) for a project that details specific locations where contamination may be encountered during construction, and specific requirements to be followed by the construction contractor when working in those locations.

Environmental regulatory considerations drive many decisions during the design of a project within a contaminated area. Work involving contamination during construction is usually concerned with preventive action, rather than corrective action. Examples include installation of migration-proof pipe/utility trenches within contamination zones, as well as removal of a petroleum storage tank during construction in compliance with the Texas Commission on Environmental Quality (TCEQ) regulations.

This guidance provides the framework around which effective and economic measures for dealing with hazardous materials contamination during project design can be established. If contaminated or potentially contaminated areas cannot be avoided within a proposed construction site, several options for handling construction are available to project designers. These options should be carefully considered to make the most appropriate decision early in the project development stage. Preventive action of contaminated areas should only be incorporated into the PS&E when justification can be provided for not avoiding the site, or when preventive action of the contaminated material cannot reasonably be accomplished in a separate contract prior to the roadway construction contract.

Petroleum-contaminated soils are the most widespread form of contamination encountered by TxDOT in highway construction activities. The ability to resolve problems associated with petroleum contamination quickly and at relatively low cost is a significant factor in the feasibility of many projects. The standard procedures presented in this section are best suited to this type of contamination, although they may also be used to address other contaminant types.

The procedures outlined below should be followed to determine how to proceed on projects with potential hazardous material contamination.

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  1. Coordinate as early as possible with the Hazardous Materials Management Section of ENV when contamination is suspected to be encountered on a project.
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  2. Provide enough detail and adequate information to determine how to avoid or minimize work in contaminated areas. Environmental site assessments and investigations are driven by the project design and should.
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  3. Analyze design and construction considerations/factors to determine the most efficient and cost-effective way to develop and implement a preventive action plan.
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  4. Develop the PS&E to incorporate any necessary contract provisions once a method for preventive action has been chosen,

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