Tetra Tech has been supporting RCRA closure activities for lined retention basins at numerous power generating stations in southern California since 2001. Closure demonstration is being used to limit or terminate environmental liability from previous releases of boiler cleaning solutions at the retention basins. Closure certification has been demonstrated at the Long Beach, San Bernardino, Highgrove, and Etiwanda facilities. Closure is in progress for five other facilities (El Segundo, Mandalay, Alamitos, Ormond Beach, and Huntington Beach). For these projects, Tetra Tech is assessing human health and ecological risks associated with chemicals in soil and groundwater to demonstrate achievement of closure performance standards.

For the human health risk assessments, Tetra Tech is conducting exposure analyses, environmental fate and transport analysis, a toxicity assessments, and risk characterization. The ecological risk assessments incorporate site-specific biological characterization and determination of the exposure pathways by which biota may be exposed to chemicals of concern. In-depth statistical evaluations of chemical concentration data for soil and groundwater are being conducted to identify applicable background data and gain concurrence with the Department of Toxic Substances Control.