Project Summary

Hoyle Tanner has completed the preliminary engineering study for upgrade of the South Woodstock WWTF. The WWTF is a 50,000 gpd package conventional activated sludge facility that has not been upgraded since 1966. Redundancy is currently not provided for process tankage including aeration basin and secondary clarifier. Therefore, these process units cannot be taken offline for tank inspection or repair. The facility is required to nitrify and denitrify with an effluent Total Nitrogen (TN) limit in the NPDES permit. Additionally, a portion of the WWTF site is located in the Regulatory Floodway, creating significant limitations on siting of new process tankage. 

For upgrade of the WWTF, three process alternatives were considered: Sequencing Batch Reactor (SBR), Membrane Bioreactor (MBR), and submerged attached growth bioreactor (SAGB). The alternatives were evaluated based on a life-cycle cost analysis and non-monetary factors. The recommended alternative is an SBR process with an innovative equipment layout, allowing all process equipment to be accessed from above the water line. This allows for a two tank SBR process without pre-equalization to meet the Vermont DEC SBR design guidelines that require either a three tank SBR process or a two-tank process with pre-equalization. This innovative approach saves the capital cost of construction of additional tankage and allows a lower cost alternative to fit within the site constraints. 

This project is designed and bid with construction scheduled to begin in Spring 2022 with completion in Fall 2023.