Ninyo & Moore Geotechnical and Environmental Sciences Consultants.

Ninyo & Moore provides geotechnical engineering, engineering geology, geophysics, hydrogeology, soil and materials testing, and environmental services.
3202 East Harbour Drive Phoenix, AZ
Phone: 602.243.1600

Water Treatment Plant

Water Treatment Plant
Scope of Work:
  • PCB Assessment and Remediation

Ninyo & Moore began working with a Water District (District) in 1992 to conduct Phase I and II Environmental Site Assessments (ESAs) of rights-of-way, facilities, properties, and acquisition/trade properties; conduct closures and investigations of underground storage tanks (USTs); and provide other miscellaneous services under several contracts. One example project includes several iterations of construction material sampling for two water treatment plants to assess the possible presence of polychlorinated biphenyls (PCBs) in concrete near polysulfide sealant-filled joints in sedimentation basins. Ninyo & Moore’s services were conducted in support of the District’s efforts to rehabilitate mechanical systems in sedimentation basins at the plants that had exceeded their design lives. Based on the results of Ninyo & Moore’s PCB assessment work, the District engaged in extensive negotiations with the United States Environmental Protection Agency (EPA). Those negotiations, supported by a sampling and analysis plan prepared by Ninyo & Moore, resulted in an EPA-approved Toxic Substances Control Act (TSCA) Risk-Based Disposal remediation plan for removal and disposal of PCB-containing sealant and nearby concrete in the basins prior to rehabilitation. The plan also included provisions for monitoring basin contents (partially treated water and sediment) following repair and return to service, as well as contingencies for additional testing and concrete encapsulants, if needed. This project is being considered by the EPA as the standard for all similar water basin remediation projects.

Project Challenge: For the first Plant, remediation of the PCB-impacted concrete was performed inside a fully enclosed, negative pressure enclosure (NPE), containment structure. That work was very expensive and time consuming because the 100-foot by 500-foot basin was divided into five separate zones that were remediated sequentially so that the individual NPEs would be of a manageable size. Working in the negative-air enclosures also exposed workers to greater health risks due to wearing air-purifying respirators and high levels of heat stress.

Innovative Solution: A significant benefit that Ninyo & Moore delivered to the District during the work for the second plant was testing and evaluation of vacuum-shrouded equipment (VSE); such as needle guns, scabblers, and saws. Ninyo & Moore identified equipment manufacturers and designed pilot testing protocols to evaluate the VSE performance. VSE performance was evaluated based on the rate of remediation (i.e., concrete removal) and the ability to capture airborne particulates and, hence, control worker exposure. Concrete sampling and industrial-hygiene sampling before, during, and after the pilot test demonstrated that the desired objectives could be achieved using VSE methods for remediation. As a result of the support that Ninyo & Moore provided, approximately $1 million in savings was realized by the District during the cleanup of each basin by implementing the procedures validated by the pilot test.

Services: Ninyo & Moore’s services included coordination and negotiation with the EPA; PCB assessment; remediation design; District bidding support; preparation of a post-remediation and analysis plan; evaluation of remediation via VSE (resulting in significant cost savings); remediation monitoring, industrial hygiene sampling, and testing; safety oversight; close-out reporting; and post-remediation basin water and sediment sampling.