Complete a treatability study of a hypolimnetic oxygenation system to remediate lake sediment and biota contaminated with mercury in clear lake, CA

The U.S. Environmental Protection Agency (EPA) Region 9 awarded a $1.25 million Project Grant to the University of California, Davis under the Superfund State, Political Subdivision, and Indian Tribe Site-Specific Cooperative Agreements program (CFDA 66.802) on October 1, 2025. The grant funds a treatability study and pilot implementation of a Hypolimnetic Oxygenation System (HOS) to remediate mercury-contaminated sediments and biota in Clear Lake, California. The contamination originates from historic mining activities at the adjacent Sulphur Bank Mercury Mine Superfund site. The project will operate through December 31, 2027.

UC Davis will deliver four primary services: site preparation and infrastructure installation for the liquid oxygen injection system in the Oaks Arm, including construction of concrete pads, fencing, solar power systems, and conveyance piping; predictive modeling using meteorological data to determine optimal oxygen injection timing to prevent methylmercury formation and harmful algal blooms; project management and stakeholder coordination across contractors and researchers; and comprehensive reporting and documentation. The project includes a sub-award to Universidad De Granada, which will contribute computational modeling support. By injecting oxygen into the lake bottom during anoxic periods, the project seeks to improve water quality and reduce both methylmercury formation and harmful algal blooms through a two-year operational and monitoring phase.

Description

The purpose of this cooperative agreement is to complete a treatability study of a hypolimnetic oxygenation system to remediate lake sediment and biota contaminated with mercury in clear lake, CA. Clear lake is california's second largest freshwater lake but is severely impaired by mercury contamination from historic mining activities at the adjacent sulphur bank mercury mine superfund site. By injecting oxygen into the bottom of the lake during key anoxic events, EPA seeks to improve water quality and reduce both methyl mercury formation and harmful algal blooms. The project will involve the construction of an HOS pilot system in the oaks arm and the operation of the system for two years. This assistance agreement provides full federal funding in the amount of $1,250,000. Refer to terms and conditions. Activities:task 1: land site preparation this includes site preparation work for the installation of the liquid oxygen injection system. Work will include construction of a concrete pad, fencing, lighting, WI-FI, solar panel and batter for system controls, clearing and grubbing, purchasing conveyance piping for oxygen injection, and digging a trench for conveyance piping to enter the lake. Task 2: modeling UC davis has developed a method to predict when and for how long low dissolved oxygen levels occur in the lake using basic meteorological information such as air temperature, relative humidity, solar radiation, wind speed, and lake surface temperature. This task will fund modeling efforts to inform when oxygen injection is needed to prevent methyl mercury formation in the lake. This task will fund the use of these models during the monitoring and operation phases of the project. Task 3: project management this task provides staff time for UC davis to coordinate amongst the numerous stakeholders, contractors, and researchers involved in the project. This task will also cover staff time for all grant administration requirements. Task 4: reporting this task will be used to fund all grant reporting requirements for tasks 1-3. Subrecipient:a subaward is proposed to the university of spain granada to hire a graduate student under the supervision of DR. Alicia corteacute; s to assist with task 2, modeling. The student and DR. Cortes will work on developing a mercury biogeochemical model to evaluate the effectiveness of the HOS treatment system. Outcomes:this project seeks to improve water quality in clear lake by reducing harmful mercury concentrations in surface water and fish and mitigating harmful algal blooms. Clear lake is a source of drinking water for 18 different water utilities that collectively serve about 60% of all lake county residents. Seven federally recognized native american tribes toxic surround the lake and use IT for subsistence and cultural activities. The lake is also popular withs sportfisherman, which generates tourism revenue. Algal blooms and mercury pollution threaten the health of clear lake and are a major impediment to the local economy of lake county. Improving these conditions has the potential to protect a critical drinking water source as well as revive a struggling rural economy. The main anticipated deliverables for this cooperative agreement are: - a site that is fully prepped for installation of a hypolimnetic oxygenation system including a concrete pad, trench for conveyance piping, fencing, solar and battery for controls, WIF-FI, lights, etc. -purchase materials for the hypolimnetic oxygenation system including anchors and conveyance piping. -development and use of various mercury, nutrient and hydrodynamic models to predict anoxic conditions and inform when, how much, and for how long oxygen should be injected into the lake. -effective collaboration amongst multiple stakeholders including local, state, and tribal governments. This project is a great example of cooperative federalism and is funded by several sources including an EPA communi