Risk Assessment Support, IR Sites 1, 2, 11 and 13, Naval Auxiliary Landing Field (NALF), San Clemente Island, CA.

For this task order, GCE provided risk assessment support for Installation Restoration (IR) Sites 1, 2, 11 and 13. A Remedial Alternative Analysis (RAA) was compiled for IR Sites 11 and 13, and a Residual Risk Technical memorandum was compiled for all four sites.

This Screening-level Ecological Risk Assessment (SLERA) Refinement was conducted for Installation Restoration (IR) Site 11 and IR Site 13, two former surface waste disposal sites at the NALF located on San Clemente Island (SCI), California. The nature and extent evaluation was focused on improving the delineation of elevated metal concentrations at IR Sites 11 and 13 based on comments received from the regulatory agencies requesting additional delineation be conducted around specific soil samples with elevated metals at IR Site 11 and IR Site 13. These additional data, in conjunction with SLERA-specific data, were also used to refine the ecological risk assessment (ERA) for IR Sites 11 and 13 and to provide risk management recommendations for these two sites.

The SLERA refinement was conducted for plants (IR Site 13) and the Bell’s sparrow (IR Sites 11 and 13), a listed species consistently identified in previous studies as the most sensitive bird or mammal receptor at NALF SCI. The plant risk refinement included: plant toxicity evaluation based on tissue residue analysis; and evaluating plant uptake of metals across a broad range of soil concentrations.

The Bell’s sparrow risk refinement consisted of two independent evaluations that incorporated multiple lines of evidence:

  1. Measuring metal exposure and potential risk to Bell’s sparrows by collecting blood samples and a blood toxicity evaluation; and
  2. Refining the Bell’s sparrow dose model evaluation by:
  • Replacing modeled tissue exposure point concentrations (EPCs) used to estimate dietary exposure with site-specific tissue data;
  • Evaluating the bioavailability of metals ingested by the Bell’s sparrow with physiologically-based extraction tests (PBET); and
  • Refining the incidental ingestion rate of the Bell’s sparrow to be more representative of its feeding habits.

Additional delineation of elevated arsenic and lead was conducted at IR Site 11 and both are now considered adequately delineated. An additional delineation of elevated arsenic, cadmium and lead was also conducted at IR Site 13 and the findings also indicate that no additional delineation is warranted at IR Site 13. This study addressed uncertainties identified in the IR Sites 11 and 13 ESI/SSA regarding elevated metal delineations and potential risk to plant and avian ecological receptors from those metals. Based on the results of the evaluations presented, elevated metals were considered adequately bounded and potential risk to ecological receptors was characterized as acceptable with a high degree of confidence. Based upon these findings, no further action was recommended for IR Sites 11 and 13.

At the conclusion of the SLERA, a Remedial Risk Alternative Analysis was compiled for use in a Focused Feasibility Study for IR Sites 11 and 13. The ultimate remedy will be Land Use Controls.

To move all four sites towards closure using Land Use Controls, a Residual Risk Assessment Memorandum was prepared for IR Sites 1, 2, 11, and 13 to update older human health and ecological risk assessments at the request of the Los Angeles Regional Water Quality Control Board and its supporting agencies the US Fish and Wildlife Service, and the California Department of Fish and Wildlife – Office of Spill Prevention and Response.