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Western Geographic Science Center


Developing an Adaptive Management Approach Using Offsets for Reducing Mercury Loadings to the Sacramento River Watershed

Water quality trading and offsets are being developed to improve policy- maker’s and regulator’s ability to assess non–point source impacts in watersheds and to evaluate the efficacy of using market-incentive programs for preserving environmental quality. Offset programs allow facilities facing higher pollution control costs to meet their regulatory obligations by making pollution reductions elsewhere at a lower cost. Research is being conducted by the U.S. Geological Survey (USGS) Western Geographic Science Center (WGSC) in collaboration with Stanford University developing an adaptive management approach (AMA) to help wastewater treatments plants decide whether offsets can meetMethyl Mercury traveling up the food chain their discharge permit requirements for mercury (Hg) Total Maximum Daily Loads (TMDL) cost-effectively in the Sacramento River Watershed. The intent of the AMA is to use empirical data and subjective judgment from real-life environmental and economic conditions to provide TMDL decision-makers with a strong scientific and technical basis for making offset decisions. An efficient AMA requires both a scientific basis and methods to translate that science into a regulatory decision framework under a variety of political and economic conditions.

Physical, chemical, and biological processes for Hg in aquatic environments are quite complex and contain uncertainties for identifying the ecosystem dynamics. Although a number of various deterministic models and empirical models have been developed for Hg, the uncertainty of these underlying scientific processes may produce similarly large uncertainties in the decision-making process. USGS research is focusing on using alternative econometric and statistical methods to explicitly state and reduce these uncertainties so that they are better incorporated in policy decision-making. The USGS WGSC approach consists of applying probabilities using a Bayesian Probability Network (BPN) which integrates information of varying rigor and detail into a simple model of a complex system. The relationships are identified and quantified using historical data, physical process-based models, conceptual models, and expert judgment. Thus, they are conceptual rather than mechanistic models, intended to represent a coherent set of beliefs and knowledge about a system rather than the physical processes themselves. This network structure provides an integrated approach to uncertainty analysis and allows easy updating of prediction and inference when new observations of model variables are made.

Based upon this work, USGS WGSC will apply this framework in the Cache Creek watershed (sub-basin of the Sacramento River Watershed) as a hypothetical case to aid decision-making for wastewater treatment plants and industrial facilities for meeting discharge permit requirements. The objective of the AMA is for the decision-maker, for instance, a permitted discharger, to use the alternative statistical methods based on probabilistic relationships between mitigation decisions and load reductions, to predict the impacts of a remediation (offset) project on Hg load at the point of compliance as well as mitigation costs.

Gold and Mercury Mines in the Sacramento River WatershedThis research project seeks to critically analyze society’s use of science and statistics within a stakeholder framework to produce an optimal methodology for water quality analysis. The purpose of the research is not to prescribe specific offset decisions for point sources or policy decisions for regulatory bodies pronouncing offsets as a suitable water quality policy. The intent is to develop a decision support framework using empirical data that incorporate actual issues and environmental conditions to provide TMDL decision-makers (regulators and permitted-facilities) with a strong scientific and technical basis for making water quality decisions. The methods employed through this research will provide local, regional, and federal decision-makers an understanding of whether discharge permit requirements can be met through offsets (environmentally, cost-effectively, and legally) for persistent, bio–accumulative toxics like Hg. In addition, this research will provide alternative statistical methods for TMDL and water quality analyses explicitly stating the uncertainty of economic and scientific results

Published Reports

Preliminary Preview for a Geographic and Monitoring Program Project: A Review of Point Source–Nonpoint Source Effluent Trading/Offset Systems in Watersheds

Remediation Control Strategies and Cost Data for an Economic Analysis of a Mercury Total Maximum Daily Load in California

Incorporating Uncertainty into Mercury-Offset Decisions with a Probabilistic Network for National Pollutant Discharge Elimination System Permit Holders: An Interim Report

Point of Contact: Bill Labiosa


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