NEPA Environmental Assessment for a Dairy Anaerobic Digester Project


This confidential Dairy Anaerobic Digester Project consists of the construction of an anaerobic digester facility that converts cow manure to biogas, a mixture of methane, carbon dioxide, and hydrogen sulfide, with an accompanying gas upgrading system to produce renewable natural gas (RNG) for injection into the local gas supply pipeline. The facility will utilize two types of digesters, continuously stirred tank reactors (CSTRS) and an anaerobic lagoon to digest scrape and flush manure. The proposed biogas facility is being designed and implemented with the goal of developing an environmentally beneficial project which converts previously uncaptured methane generated from cow waste to a usable fuel source. This project meets the owners sustainability initiatives and goals. The project has many environmental advantages including reduction of odor, greenhouse gas emission, volatile organic carbon (VOC) emissions, and potential hydrogen sulfide (H2S) emissions due to capture and treatment.

The facility would be built on farmland that is located in Arizona. The Dairy covers approximately 350 acres approximately 50 miles southwest of Phoenix, Arizona. The dairy is supported by its own adjacent 7,000-acre farm which supplies feedstock.


The Dairy applied for financing for the anaerobic digestion facility under the Rural Energy for America Program (REAP). The U.S. Department of Agriculture (USDA), Rural Development (RD) is the federal agency that is responsible for reviewing and approving projects applying for financing through this program. Accordingly, the decision to approve or deny the financing is considered a Proposed Action under the National Environmental Policy Act (NEPA). The Proposed Action thereby required an Environmental Assessment (EA), analyzing the potential environmental impacts of the Proposed Action to determine whether a Finding of No Significant Impact (FONSI) is warranted or if additional environmental analysis will be conducted.

The anaerobic digester facility includes a natural-gas fired boiler, gas upgrading system, and backup flare that would result in emissions of Criteria Air Pollutants designated under the Clean Air Act. Accordingly, the dairy is required to apply for a Non-Title V Air Permit in accordance with the applicable county air pollution control regulations.


Montrose Environmental prepared a NEPA EA for this dairy in support of the financing application process. The air quality analysis within the EA utilized the air emissions estimates generated by Montrose Environmental in support of the Air Permit Application. The EA determined that the project would not result in significant adverse effects to the environment.

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