Risk Sciences

Gradient prepared comments on proposed changes to critical areas ordinances for wetlands and fish and wildlife habitat conservation areas in a Western State. Our comments focused on the consistency of the proposed changes with existing regulations and regulatory guidance, the use of best available science, and the need for and effectiveness of the proposed measures.

Gradient critically reviewed the technical materials supporting proposed effluent limit guidelines (ELGs) under the Clean Water Act for steam electric power generation utilities. US EPA proposed ELG changes for several parameters, including arsenic, selenium, and mercury. We assessed the completeness and validity of the analyses performed by US EPA to support the rule-making effort, including considerations of toxicity, fate and transport in the environment, and cost analysis of potential impoundment failure risks.

Gradient developed a risk-based discharge limit for the pesticide methoprene used at a New Zealand company's wastewater treatment plant. We based our site-specific discharge limit on a post-discharge dispersion model, current knowledge of methoprene toxicity, and effective treatment while remaining protective of the receiving water environment.

Gradient evaluated technical approaches for developing Alternate Concentration Limits (ACL) for groundwater to surface water discharge from a chemical manufacturing facility located next to a large river. We evaluated the relative sensitivity of benthic versus pelagic aquatic organisms for key chemicals of concern at the site, and reviewed current state of the science on mixing of groundwater with surface water in the hyporheic zone.

Gradient evaluated the basis for a proposed natural resource damage (NRD) settlement offer at a Great Lakes Superfund site. Using benchmarking analysis techniques, we quantitatively compared NRD settlements at other sediment sites to our client's offer. Our analysis considered the nature and extent of the ecological harm, as well as the role of our client's releases in causing the harm. Our work aided settlement negotiations.

As part of a review of the effectiveness of a Superfund remedy, Gradient reviewed historical metal and PCB fish tissue data and coordinated additional fish tissue sampling in a pond at an old landfill. The data were used to model bioaccumulation risks and evaluate population-level effects in fish, higher trophic level ecological receptors, and human health.