Yosemite National Park (El Portal) Wastewater Studies Complete
May 8, 2014

The Yosemite El Portal Wastewater Treatment Facility must meet strict water quality requirements to comply with its discharge permit. The plant treats wastewater from Yosemite National Park recreational areas and the community of El Portal, CA, and then discharges the treated, high quality effluent to the Merced River within the park. AES, with assistance from Pacific EcoRisk Laboratories, prepared a Water-Effects Ratio (WER) Study which was conducted to support renewal of the Yosemite/El Portal discharge permit. The WER Study assessed the toxicity of copper in a mixture of the plant’s treated effluent and water from the Merced River and determined the appropriate copper limits to protect the environment. The Regional Water Board concurred with the findings of the WER Study and updated the plant’s discharge requirements accordingly.

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