Development and Application of Tools to Assess and Understand the Relative Risks of Regulated Chemicals in Indirect Potable Reuse Projects:The Montebello Forebay Groundwater Recharge Project

Principal Investigators and Project Managers
Margaret H. Nellor, P.E., Nellor Environmental Associates, Inc.
Jeffrey Soller, Soller Environmental, LLC

Tools to Assess and Understand the Relative Risks of Indirect Potable Reuse and Aquifer Storage & Recovery Projects
Volume 1A

The overall objective of the project is to use existing risk assessment tools to develop new information that can be used by sponsors of indirect potable reuse projects to evaluate and explain the relative human health risks related to the use of recycled water.

The project is comprised of three tasks. In Task 1, quantitative relative risk assessments are being conducted for two different groundwater recharge projects in Southern California based on chemicals that are currently regulated or under consideration for regulation. In Task 1a, the subject of this report, a quantitative relative risk assessment is conducted on a long-standing program in the Montebello Forebay that has a monitoring system that includes wells that produce water with and without a recycled water component. Task 1b addresses the Chino Basin Groundwater Recharge Project, in which recycled water has been recently introduced, and a separate report has been prepared for that asessment.

For both groundwater recharge projects, relative human health risks will be used as a metric to evaluate the potential human health issues associated with using recycled water to replenish local groundwater rather than traditional comparisons to drinking water standards. This approach does not assess the absolute risk from ingestion of water at the tap but rather compares the relative risk of various recharge scenarios.

There are numerous practical applications of the work presented in this report that can be applied to other indirect potable reuse projects to assess their relative safety with respect to human health for regulated contaminants of potential concern. Moreover, additional information on “acceptable” concentrations in drinking water is being developed by other components of this project and by other ongoing research projects. The benefit to public agencies of this report is the ability to focus on specific source control and/or treatment options as necessary and appropriate based on the results of a relatively straightforward and modest analysis rather than having to conduct more resource-intensive health effects studies, including epidemiology studies. Moreover, these quantitative relative risk analyses could be coupled with public outreach efforts to support ongoing and/or planned indirect potable reuse operations.

(2011, 49 pages, 06-018-1A)