> News+Events > Features > Water

Upgrade begins at Blue Lake Wastewater Treatment Plant in Shakopee

A $200 million, six-year upgrade of the Metropolitan Council’s Blue Lake Wastewater Treatment Plant in Shakopee begins in September.

Goals of the construction include:

• Enhanced pollutant removal
• Improved safety and reliability
• Replacement of aging equipment and support systems
• Reduced energy usage
• Increased capacity to serve area growth

The plant currently serves approximately 275,000 people in 28 southwest-metro-area communities — from Maple Plain on the north and Waconia on the west, to Minnetonka, Eden Prairie and Shakopee on the east and Prior Lake on the south. The upgrades will meet the increasing needs of the plant’s service area, which is projected to grow to some 420,000 people by the year 2030.

Here’s a look at some of the planned improvements.

Phase I – Removing more phosphorus

Phosphorus is an essential element for sustaining life, but if too much remains in the clean water the plant discharges to the river, it could promote excessive algae growth and degrade water quality. Construction is scheduled to start in September on mechanical modifications to existing treatment tanks that will increase the amount of phosphorus removed from the wastewater.

The plant has voluntarily removed phosphorus for several years. The additional removal will help the plant consistently stay within a clean-water-discharge permit limit of 1 milligram per liter on an annual average; the limit is set to begin in October 2008.

During this phase, the plant also will build a new exhaust stack for a heat-drying process that turns wastewater solids into fertilizer pellets. Increasing the stack from the current 100 feet to 170 feet is aimed at reducing odors.

Phase II – Improving the flood-control levee

Before additional facilities can be built, the plant’s flood-control levee needs to be expanded and rehabilitated. Modest expansions will be done on two sides of the plant. The rehabilitation work involves removing trees that have grown along the approximately 4,000-foot levee. One of the lessons learned from Hurricane Katrina is that trees growing in levees can leave open channels when the trees and roots die, allowing flood water to enter and weaken the structure.

The tree loss will be offset by planting approximately 300 trees in a 40-acre buffer space on the west side of the plant property. An adjacent 5-acre tract will become a restored prairie.

This phase also includes increasing the number and capacity of wells used for groundwater pumping during floods to protect the structural stability of the plant, and installing stormwater holding ponds. The majority of the work will be done between this fall and late 2008; the tree planting will follow later in the project, and prairie restoration will be done in Phase IV.

Phase III – Making disinfection safer

Like other plants operated by the Council’s Environmental Services Division (MCES), Blue Lake is now faced with replacement of its aging disinfection system. And like the other plants, its gaseous chlorine disinfection system will be replaced with a safer and more secure liquid bleach system.

The new system will use liquid sodium hypochlorite to kill the vast majority of pathogenic bacteria that remain in this final stage of the treatment process. Then liquid sodium bisulfite will be added to neutralize any remaining residual chlorine in the water, which otherwise could adversely impact aquatic organisms in the river.

Another key improvement in the third phase will be adding facilities to remove more ammonia nitrogen from the wastewater. This will ensure that the total amount of ammonia nitrogen remaining in the treated wastewater and discharging to the river does not exceed current loadings, despite future increases in the volume of wastewater that will be treated.

Other improvements in this phase will include replacement and rehab of:

• Heating, ventilation and air conditioning equipment
• Process control systems
• Pumps
• Air compressors

The area in the plant where septage haulers empty their tank trucks will be redesigned and relocated for improved load monitoring and security. Construction of this phase is planned for 2009-2010.

Phase IV – Augmenting the solids handling process

Anaerobic digesters are used at MCES’s Empire Plant in Dakota County to kill pathogens in wastewater solids so they can be applied to farmland. The same type of facilities will be installed at the Blue Lake Plant to augment the existing heat-drying equipment. As they break down the solids, the digesters will produce enough methane gas to supply upward of 70 percent of the fuel needed to run the heat dryer, which now runs on natural gas.

The digesters will reduce the volume and mass of the solids so that the existing dryer will have capacity through 2020. The digesters also will provide solids handling capability when the dryer is down for maintenance. Construction of this phase is planned for 2010-2011.

Phase V – Adding treatment tanks to handle greater flows

The final phase, slated for construction in 2011-2013, is when more treatment tanks will be built to actually expand the plant to handle the next two decades of increases in wastewater flows. The current average annual flow of approximately 28 million gallons per day is projected to increase to approximately 40 million gallons per day by the year 2030. Existing treatment tanks also will be rehabilitated, and extensions are planned for a tunnel system that provides operations and maintenance access to much of the treatment equipment.

After the expansion, the Blue Lake Plant will be the second largest wastewater treatment plant in the state. MCES’s Metro Plant on the Mississippi River in St. Paul is the largest; it has the capacity to treat 251 million gallons of wastewater daily.

The plant will continue operating throughout the project. This is the third round of major improvements to the plant since it opened in 1971.