Expanding the Capacity of a Controlled Discharge Lagoon System
The Iowa Woodward Resource Center’s wastewater treatment facility was experiencing incoming hydraulic loads that exceeded the capacity of its controlled discharge lagoon system. As a result, the treatment system was struggling to achieve wastewater storage requirements of 180 days.
Controlled discharge lagoon systems are commonly utilized by smaller, rural communities in parts of the Midwest. All wasterwater is held in large storage ponds or lagoons for a minimum of six months, as natural processes treat and clean the wastewater over time. Once the wastewater reaches a safe level, it’s discharged in controlled amounts that comply with water quality standards to ensure stewardship of the natural environment.
This project began with a review of existing and future treatment requirements, an analysis of existing facilities, and an evaluation of lagoon alternatives. During the investigation, it was determined that efforts to reduce inflow and infiltration, along with a significant expansion of the three-cell controlled discharge lagoon, would be necessary to meet treatment requirements long-term.
The removal of roof drains and downspouts on buildings in the area was key to eliminating the sources of inflow and infiltration (I/I). Excess water flowing into sanitary sewer pipes from groundwater and stormwater is referred to as I/I. Inflow is stormwater rapidly flowing into sewers through prohibited connections. Examples include: roof drains and downspouts, fountain drains, sump pumps, and storm drain cross-connections, along with manhole covers and larger defects within a sanitary sewer system. To address additional inflow sources, manholes within the project area were also repaired or replaced depending on their condition.
Infiltration is groundwater that seeps more slowly into sewer pipes through holes, cracks, joint failures, and faulty connections. Targeted sections of the collection system were lined to improve performance and avoid infiltration.
The existing influent lift station was upgraded. This included replacing two 400 gallon-per-minute (gpm) influent pumps with 800 gpm pumps controlled by Variable Frequency Drives (VFD). The pump station was also equipped with larger force main piping to achieve capacity needs.
A significant amount of earthwork was necessary to increase hydraulic capacity with a new primary lagoon cell. New control structures were also included with the project to help manage water flows.
Key project accomplishments include:
- Reduced inflow and infiltration (I/I)
- Increased pump station capacity
- Improved structures
- Increased hydraulic capacity