Launch Slideshow

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By the book

By the book

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    Contractors tunneling under a roadway: These workers are operating under a contractor-provided health and safety plan. Appropriate personal protection equipment and forced-air ventilation of the excavation tunnel was specified in the contract. Photos: City of Dallas

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    Proper stockpiling of contaminated soil: Note the proper stormwater fencing at this Dallas Water Utilities project; stockpiled soils are located on and covered with plastic.

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    The below map is an example of a Dallas Water Utilities GIS search showing locations of regulated facilities with the potential for contaminant releases that could impact the utility's rights of way. Blue circles: city-permitted monitoring wells. Green diamonds: Voluntary Cleanup Program sites. Red diamonds: Leaking Petroleum Storage Tank Program sites. Orange shields: registered dry cleaners. Map: City of Dallas requires developers

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    A probable unacceptable condition: The surrounding natural color of soil in this soil column is contrasted by the dark, stained affected soil.

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    Unacceptable condition: Nonaqueous phase liquid (NAPL, or free-phase product) is present on the surface water at the bottom of a utility excavation. Free-flowing fuel, obviously discolored groundwater with a rainbow “sheen,” and strong odors exist at this project.


Developing a soil and groundwater management plan

Unlike the Sustainable Development and Construction strategy, which addresses single-site developments, the water utility needed a broad-scale approach for the city's entire water distribution system (i.e., the water mains). It needed a comprehensive plan that could easily be used by all staff engineers and subcontractors to protect the public water supply, as well as workers performing upgrades and installations.

The utility contracted Terracon Consultants Inc. to develop a thorough and prescriptive soil and groundwater management plan (SGMP). Terracon's goal was to create a 15- to 20-page plan that would include the necessary technical information, background, and specifications to ensure the safety of the water supply pipelines, while also remaining simple and user-friendly for civil engineers unfamiliar with technical environmental issues.

The utility also chose to use its internal Geographic Information System (GIS) to assist with screening criteria as part of the new procedures. To help project engineers identify potentially contaminated areas during planning stages on all pipeline projects, the following layers are used (see the map on page 30):

  • City-permitted monitoring sites
  • Voluntary Cleanup Program sites
  • Leaking petroleum storage tanks
  • Registered dry cleaners
  • Areas with a Municipal Setting Designation (MSD; identifies properties with groundwater that's not potable)
  • Known landfills (existing, closed, permitted, and unpermitted).

    The soil and groundwater management plan had to account for contaminants that could come into contact with various types of water piping and associated gaskets. DWU engineers evaluated degradation thresholds (the concentration of a particular contaminant that impairs the proper operation of a particular material, such as a polyvinyl chloride or polyethylene pipe) to determine a conservative approach to protecting the city's pipelines. They used the resulting information to devise a plan that:

  • Instructs utility personnel on how to obtain environmental information through available in-house resources, and how to retain a consultant to assist in evaluating the potential for a pipeline right of way to contain contaminated soils and/or groundwater. Procedures include measures to take to obtain available Phase I environmental site assessments that are completed as part of right-of-way acquisitions, and how to conduct regulatory searches or reviews of regulatory files. If issues are identified, the plan provides step-by-step instruction on ordering subsurface investigations to evaluate and characterize contaminated soils and groundwater located within the pipeline right of way.
  • Presents protocol for evaluating known contaminant concentrations on a scale of low, high, or unacceptable contaminant conditions, as defined by risk-based protective concentration levels used by the Texas Commission on Environmental Quality. Low and high conditions take into consideration piping and gasket materials requirements for the pipeline, trench design parameters, construction parameters, and waste management requirements. Unacceptable contaminant conditions include the presence of free-phase product within the proposed pipeline corridor. The free-phase product must be removed from utility pipeline corridors or the pipeline must be relocated outside of the free-phase product plume. (For examples, see images on page 31.)
  • Details steps to prepare summary documentation of contaminant conditions in the work area, which are then given to contractors to ensure that proper health and safety practices are followed during construction. Procedures for the proper handling of contaminated soil and groundwater during construction activities (i.e., stockpiling and covering contaminated soils on plastic, and containerizing contaminated groundwater) are also included.
  • Provides information on the training requirements (40-hour OSHA Hazardous Waste Operations training; HAZWOPER) for contractor personnel tasked with excavating contaminated soils and ground-water. Thus, the utility department's bid documents can include requirements for properly trained construction personnel (see image on page 29). Additionally, if contaminated media are known to exist, the contractor is required to provide its own soil and ground-water management plan to ensure that proper handling procedures are followed.

    To ensure that the management plan is used by all employees — and isn't just another dust-collecting manual sitting on a shelf — Terracon conducted presentations for both engineers and field staff. The engineering staff presentation included a thorough review of procedures and how the plan should be used in the planning and design of pipelines. The field staff presentation was tailored with information specific to inspections and procedures that staff would be observing in the field during construction.

    The manual also includes several case studies and site scenarios to help personnel understand how the document works, and how to proceed under the new procedures. The water utility department plans to update the manual continually over time to keep procedures fresh and accurate.

    — Sallman (jbsallman@terracon.com) is a principal with engineering consulting firm Terracon, in their Dallas office.

    WHY USE A SOIL AND GROUNDWATER MANAGEMENT PLAN?

    A wide variety and mixture of contaminants exist in shallow soils and groundwater along rights of way and major thoroughfares where water utilities are typically located. These contaminants can interact with both water pipes and piping gaskets, degrading or weakening the pipeline materials. Contaminant damage to water piping may cause premature failure of the water piping or gaskets (especially for pressurized piping), resulting in potential unsafe drinking water supply, service interruptions, costly repairs, and untold damage to a department's public image.

    Discovering contaminated soils and/or groundwater during the construction phase of utility upgrades typically results in schedule delays and large cost overruns. But by following established procedures to identify contaminated areas during the infrastructure planning stage prior to installation allows for proper planning and cost evaluation of the issues.


    WEB EXTRA

    To access DWU's soil/groundwater management plan, click here.