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By: Luke Heikkila, Municipal Senior Engineering Technician, Bolton & Menk

Along the rugged shoreline of Lake Superior lies the City of Two Harbors, Minnesota, a community known for its historic charm, scenic beauty, and vibrant tourism. With a population of just under 3,600, the city welcomes thousands of visitors each summer, drawn by its lighthouses, hiking trails, and proximity to the North Shore’s natural wonders. But behind this beautiful setting, Two Harbors faced a growing infrastructure challenge that would ultimately lead to one of the largest projects ever taken on by the city.

The issue began brewing, quite literally, with the rise of Castle Danger Brewery. Founded in 2011, the brewery quickly became a cornerstone of the local economy and a major player in Minnesota’s craft beer scene. Producing more than 20,000 barrels of beer annually, Castle Danger’s success brought pride to the community but also placed an unexpected burden on the city’s aging wastewater treatment facility (WWTF). Originally built in 1957 to accommodate a population of 4,000, the WWTF was ill-equipped to handle the industrial waste stream generated by the brewery, which rivaled that of a city three times the size of Two Harbors.

Without a significant industrial user (SIU) agreement or a pretreatment program in place, the facility began experiencing operational strain and permit violations. The situation reached a critical point on July 9, 2018, when a combination of factors led to 13 effluent violations in a single day. Operators were forced to divert domestic wastewater into the equalization basin for overnight treatment, and the secondary clarifiers were overwhelmed with sludge. The severity of the situation was clear to those working at the plant, who struggled to maintain operations with outdated equipment and limited capacity.

In response, city leaders partnered with Bolton & Menk to develop a comprehensive solution that addressed both the immediate challenges and long-term needs of the facility. The first step was to establish an SIU agreement and implement a pretreatment program with Castle Danger Brewery. Fieldwork was conducted to identify pollutant sources and recommend best management practices, ranging from simple changes like halting yeast disposal through drains to more substantial investments such as installing a centrifuge. Brewery byproducts were redirected to local farms for use as cattle feed or sent to the Western Lake Superior Sanitary District (WLSSD) for treatment, significantly reducing the load on the Two Harbors WWTF.

Simultaneously, the city embarked on a full-scale upgrade of the treatment facility. The improvements included the installation of a new mechanical bar screen and grit separator, a transition from conventional aeration to extended aeration, and enhancements to the tertiary treatment system to improve mercury removal and manage high-flow events. The biosolids process was modernized by replacing lime cake application with liquid storage and drum thickening. Additional upgrades included a new laboratory, operator facility, office space, chlorine contact tank, and energy efficiency improvements.

Collaboration from all parties was not just beneficial, it was vital, given the project’s scale and complexity. Castle Danger Brewery played a key role in securing funding, joining the city in lobbying efforts at the state and federal levels. Public engagement was also central to the project, with utility meetings guiding design decisions to ensure the facility complemented the town’s tourist-friendly aesthetic. The final design featured coordinated sight lines, nautical-themed fencing, and architectural elements that reflected the community’s character.

The results were immediate and impressive. Following a 3.5-inch rainfall, the equalization tank received only 100,000 gallons of overflow, compared to the previous volume of 1 to 2 million gallons. Mercury discharge limits were met, biosolids were managed more effectively, and odors from screenings were significantly reduced thanks to a new washing system. Superintendent Randy Hedin noted that operations have stabilized, and the facility is now well-equipped to support both seasonal population increases and future growth.

The Two Harbors WWTF project stands as a model of innovation and collaboration. From navigating the town’s first SIU agreement to securing $30 million in funding, the journey reflects the evolving nature of wastewater operations and the critical role of community partnerships in driving success. In a town where tourism and industry coexist, the ability to adapt and invest in sustainable infrastructure ensures that Two Harbors remains not only a beautiful destination but a thriving community.