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One of the biggest current challenges facing regulatory agencies in the development of effluent limits in discharge permits for wastewater treatment plants and wasteload allocations in total maximum daily loads (TMDLs) is how to regulate loads and concentrations of legacy bioaccumulative pollutants, like mercury, when the permitted discharge is an extremely small portion of the overall watershed load. After a wastewater treatment plant has implemented all possible infrastructural and programmatic mercury control measures, what is a reasonable mercury mass limit for a regulated discharge into a waterbody that is still over its assimilative capacity for mercury? The concept of a mass offset program is one alternative that is being explored. In a mass offset program, municipal treatment plants develop and implement watershed load reduction projects, such as sediment controls or mine site restorations, that remove much more mercury from the system than is introduced by the discharge of treated municipal effluent. This is a novel concept for managing bioaccumulative pollutants, so the first step is to evaluate whether a mass offset program for mercury is feasible.

The process of evaluating the feasibility of a mercury offset program for the Sacramento watershed is described in this paper. The environmental context for the program includes a description of the watershed, the mining legacy, and current mercury loads to the San Francisco Bay-Delta. A brief overview is provided of the regulatory context under which the program would be implemented including basin plans, fish advisories, mercury TMDLs, methyl mercury water quality criteria, wildlife criteria, and federal trading policy.

The SRCSD is utilizing the stakeholder process to develop the mercury offset program feasibility study. A group of regulators, permit holders, scientists, and land use managers have worked since October 2002 to define feasible program objectives and the regulatory framework within which the program can operate. Working meetings have focused on:

Identification of potential mercury load reduction projects, selection criteria reflecting feasible projects, and a resulting short list of potentially feasible mercury load reduction projects.

Crediting framework including offset ratios, reconciliation and banking, and agreements.

Legal questions and regulatory challenges including liability issues, credit eligibility and approaches to NPDES permitting.

Bioavailability study work plan panel discussion designed to develop appropriate management questions to identify sources of “magic” mercury.

Outreach and Education as the most effective activity to reduce risk from mercury exposure in the near term relative to the time horizon (decades to centuries) envisioned to determine effectiveness of mercury load reduction in the SRW on fish tissue concentrations in the Delta.

Remaining challenges include crafting compatible TMDLs and NPDES permits to allow offsets to occur, providing incentives to minor sources to pursue offset opportunities, and building a better understanding of mercury behavior in the environment.
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Document Type: Research Article

Publication date: 2004-01-01

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