Wastewater Treatment Facility Upgrade
The City of Viroqua wastewater treatment system has evolved through the City’s history, from small filters in low areas of the City, to the original trickling filter secondary treatment plant built in the 1940s on the City’s northwest side. In 1977-1978, the treatment system was moved to the existing site, northwest of the previous facility. The treatment system consisted of primary clarifiers and two CanTex activated sludge package plant trains. The trains, designated East and West, included aeration, reaeration, clarifiers, chlorine contact, and aerobic digestion contained in one circular basin. The treatment system site also contained a 670,000 gallon holding pond for flow equalization and sludge drying beds. The control building housed office and laboratory space, a chlorine room, a standby generator, aeration blowers, and a sludge pump.
In 1994, the facilities were upgraded to include a new anaerobic digester, sludge storage tank, leachate and septage receiving facilities and new aeration equipment. In 1999, the biological treatment process was modified to incorporate enhanced biological phosphorus removal (BPR) and back-up alum feed system to comply with new phosphorus limits. Additional modifications were made in 2002 including, addition of a digester supernatant tank, a mechanical screen (replacing influent comminutors), effluent UV treatment, fine bubble diffused aeration, a submersible nitrate recycle pump and new RAS/WAS pumps.
The Springville Branch of the Bad Axe River has been the receiving waterbody for all the iterations of Viroqua wastewater treatment system. In 2006, the Wisconsin Department of Natural Resources (WDNR) began what ended up being nearly a decade of conversations with Viroqua, about this intermittent tributary losing water to the ground. As a result, many studies were performed on this stretch of the intermittent stream. A 2007 Effluent Outfall Investigation prepared by Davy Engineering suggested that about 83% of the receiving stream flow is lost between the WWTF discharge point and the Springville Spring, 2 miles downstream. Additional studies, by the WDNR and by Town & Country Engineering in 2013, corroborated these findings, although thought that lost flow was believed to be considerably less than 83% on average.
In 2015, Viroqua Utilities teamed with Town and County Engineering to complete a Facility Plan. This plan started with the need to resolve the losing stream issue but was also intended to review the wastewater treatment facility as a whole. The facility was facing three major issues. 1. Aging infrastructure and equipment, 2. Poor energy and treatment efficiency and 3. New regulatory compliance issues.
As a part of a $9.93 Million facility upgrade project, a $2 Million outfall extension project was constructed in 2018. This included approximately 2 miles of 12 inch “force main” that flows by gravity to the outfall structure located upstream of the Springville Branch.
Viroqua Utility commenced a $9.93 Million upgrade to the wastewater treatment facility in 2017, with engineering from Town and Country Engineering. The City received multiple grants and principal forgiveness including $2.024 million from Rural Development, $650,000 from Clean Water Fund, and $15,500 from Focus on Energy; with the remaining funds coming in the form of low interest loans from Rural Development and the Clean Water Fund.
After two years of construction and a year to readjust to a new and more flexible way of operating, the Viroqua wastewater facility is realizing huge improvements to operation. The Utility continues to work with Town and Country Engineering and is also working with Greg Paul, Op2Myz, to push the upgraded facility to its full potential. In the past year, the Utility was able to easily meet the City’s Multi–Discharger Variance (MDV) interim phosphorus limit of 0.8 mg/L and has been below the goal of 0.2 mg/L nearly all year long, which reduces annual MDV payments. While the Utility is still working on optimizing the system and ensuring consistency in treatment, it appears the facility upgrades have provided the tools necessary to achieve these goals.
Wastewater Treatment Facility Upgrade and Outfall Relocation FAQ
Q. What does the upgrade involve?
A. In short the upgrade involves replacing worn and outdated equipment, improving treatment capability and efficiency and relocating the effluent outfall.
Q. How much does this cost?
A. The upgrades to the wastewater treatment facility will cost $8 Million and the outfall will cost $2 Million. The city will receive $2.7 Million dollars in grant money from the WDNR and USDA.
Q. What does “effluent” mean?
A. “Effluent” means treated municipal wastewater.
Q. What does “relocating the effluent outfall” mean?
A. The current outfall discharges to the headwaters of the Springville Branch of the Bad Axe River. It has been determined that 20-30% of the water in the stream makes it to the Springville site. The remaining 70-80% of the flow goes into the fracture bedrock underground. The Wisconsin Department of Natural Resources is requiring the City ensure that the effluent bypasses the water losing area of the fractured bedrock and continues to be surface flow. As such the City is moving a discharge point 2 miles downstream past the losing area.
Q. How much water comes out of the outfall?
A. The current plant peak weekly flow is around 350,000 gallons per day. That is total volume in a 24hr period. This equals about 245 gallons per min or 0.5 cubic feet per second. This translates into less flow than 6 standard 5/8” garden hoses at 40 psi.
Q. What does the relocation mean for effluent quality?
A. Moving the outfall downstream means that the City must meet more stringent effluent requirements. The current limit for Biochemical Oxygen Demand (BOD, i.e. organic load) will be reduced. The City will also have limits for new parameters, temperature and ammonia. Across the State phosphorus effluent limits are decreasing over the next 5 years. As a result of the relocation of the outfall the City will be required to decrease the phosphorus loading even further than required at the current location. The City will continue to have limits for total suspended solids, fecal coliform, pH and dissolved oxygen.
Q. Did the City explore other options to the outfall relocation?
A. Yes, there were three main options explored. 1. No relocation but treating effluent to near drinking water quality standards. 2. Grouting the fractured bedrock zone. 3. Using a pipeline to relocate the outfall. WDNR required strict compliance to drinking water quality standards for option 1, no relocation, making it economically unrealistic. The WDNR deemed option 3, outfall relocation, verses option 2 as the most environmentally sound and viable long term option.
