SWCRB Proposal for New Beneficial Uses and Mercury Water Quality Objectives
February 16, 2017
On January 3, 2017 the California State Water Resources Control Board (SWRCB) released a draft proposal for designating new beneficial uses and developing mercury water quality objectives. The sweeping proposal could significantly impact NPDES permittees, including wastewater treatment facilities, individual industrial NPDES permittees, municipalities, operators of reservoirs and lakes, and industries regulated under the State’s Industrial General Permit for stormwater by imposing stringent numeric effluent limitations for mercury and limiting the use of mixing zones. The proposed new beneficial use categories will impose high fish consumption rates, which will in turn drive TMDL targets and NPDES permit limits to lower future levels for a range of additional water quality constituents, including DDT, PCBs, and dioxin/furan compounds. SWRCB will seek responses to the proposal at a public hearing on February 7. Written comments are due by noon on February 17 with adoption targeted for May.

How Exponent Can Help

Exponent is already collaborating with a number of clients and coalitions to address this proposal and working to bring it to the attention of a broader array of stakeholders. Exponent representatives who attended the SWRCB staff workshop on January 9, which provided a public forum to discuss the proposals and their implementation, are prepared to support organizations interested in reviewing and commenting on the proposal and to help coordinate responses across impacted constituents.

Exponent’s interdisciplinary team of scientists has expertise in all aspects of water quality, including expertise in the behavior of mercury in the environment. Our human health and ecological scientists have a deep understanding of the derivation of water quality standards to protect human health, fish, and wildlife, and the appropriate use of exposure assumptions and toxicity data in deriving water quality criteria. Exponent environmental scientists and engineers have extensive experience in analysis of surface water quality and contaminant transport, and we have evaluated dispersion and fate of discharges from wastewater outfalls, water quality conditions in receiving waters, basin-wide impacts of nonpoint source runoff, and impacts of natural and man-made hydrologic changes on water quality.

About the Proposal

Key features of the state’s proposal include three new state-wide beneficial use definitions concerning traditional tribal and cultural use, tribal subsistence fishing use, and subsistence fishing use by others. The subsistence fishing uses set default fish consumption rates, which can be superseded by site-specific rates, and which are substantially higher than the fish consumption rates assumed for the general population. Normally, new beneficial uses must be designated in basin plans before being applied, but here the proposal states that both subsistence uses can affect listing and permit limits now if they are “existing uses,” even if not designated in a basin plan.

New proposed mercury water quality objectives would apply to all waters of the state except open ocean waters. Fish tissue objectives for human health and protection of wildlife range from 0.03 to 0.2 mg/kg, depending on consumption levels and fish sizes. Proposed NPDES effluent limitations for publicly owned treatment works and other types of discharges range from 1 ng/L to 12 ng/L (parts-per-trillion). For industrial dischargers, the action level for mercury changes from 1,400 ng/L to 300 ng/L. For MS4 dischargers, the proposal requires mercury control measures and gives regional boards discretion to substitute additional measures. These mercury objectives and limitations may not be achievable, and even if they could be achieved, proposed effluent limitations may not change mercury concentrations in receiving waters or fish, because other sources are so significant.

For more information, view the full proposal on the SWRCB website.

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