Risk Screening, Evaluation And Assessment

Risk Assessment for Site Closure, Hanford, California

Major Oil Company

Client had previously disposed refinery liquid wastes and sludge in a surface impoundment at a municipal landfill. The impoundment was subsequently covered with soil, and the landfill was closed. The impoundment area was sold to a private landowner. Trinity completed site characterization following Regional Water Quality Control Board (RWQCB) direction.
Risk assessment was utilized in view of the limited extent of impacts and lack of environmental or human receptors in vicinity of site.

Client goal was to determine cost-effective path to closure for this site.

Trinity developed a site conceptual model based on previously-performed site characterization. The site conceptual model included developing a list of chemicals of concern using RBCA Tier 1 and California Environmental Screening Levels.
Based on the site conceptual model, Trinity used RISC4 model to evaluate vadose-zone and saturated-zone fate and transport of chemicals of concern. Site data and conservative assumptions were input to the fate and transport model.
The fate and transport model indicated no chemicals of concern would reach the theoretical receptor within 100 years. Therefore, no additional risk assessment was conducted

Trinity’s report included an evaluation of costs of remediation by excavation, and the presentation of the site modeling approach, input parameters, and results.
Client and property owner are negotiating a deed restriction to prevent future development or groundwater supply well installation within the former impoundment area.
Submittal of the report to the RWQCB is pending.