A quick guide to Iowa wastewater facilities design standards

Iowa wastewater facilities design standards were adopted in the late 1970s and early 1980s. Today, the Iowa Department of Natural Resources (DNR) supplements these specifications with the 10 States Standards to help municipalities design or upgrade Publicly-Owned Treatment Works (POTWs) in the state. However, the detailed design standards for POTWs can be difficult for municipalities to understand and navigate. Here is a guide providing an overview of the Iowa wastewater facilities design standards.

Key features in Iowa wastewater facilities design standards

When municipalities build or upgrade a wastewater treatment facility, the Iowa DNR has the final say. To ensure DNR approval for wastewater facility construction, municipalities should examine the following key aspects of Iowa wastewater facilities design standards.

Separation distance

A POTW should be positioned at least 1,000 feet from the nearest inhabitable structures, including residences and commercial buildings. To prevent drinking water contamination, the treatment plant should be established 1,000 feet from public shallow wells and should maintain a distance of 400 feet from public deep wells and private wells.

Quality of effluent

Because a POTW must meet the effluent limitations in the operation permit, design engineers should obtain effluent limitations for various options while preparing the facilities plan. In most cases, the discharge permit includes a Carbonaceous Biochemical Oxygen Demand (CBOD) limit, Total Suspended Solids (TSS) limit, ammonia limit, E. coli limit, dissolved oxygen limit and pH limit. Depending on a community's specific industries and/or receiving stream, the discharge permit may include effluent limits for various metals such as copper.

Type of treatment

Design flows and loadings

Determining design flow and loadings represents a critical step in planning a new or expanded wastewater treatment plant. Justifications for new values for design flows and loadings for a new or upgraded treatment plant often rely on historical flow data and the projected 20-year population increase.

Iowa wastewater plant design standards suggest a design flow of 100 gallons per person per day. However, with increased infiltration and inflow into the sewer system, this design value is not always adequate. Municipalities can request a variance from the recommended design flows and loadings when designing a treatment plant for the community. All design flows and loadings, including variances, must be approved by the DNR.

Power source and equipment reliability

POTWs should maintain two separate and independent sources of electric power, which most often is an emergency power generator. In case of a power outage, the backup emergency power can provide power necessary to continue to provide minimum treatment . Additionally, all major pieces of equipment, including tanks, pumps and UV disinfectant systems, should possess redundant equipment so treatment can be maintained should a piece of equipment break down.

This overview of the Iowa wastewater facilities design standards can help you understand some of the considerations when planning for a new or upgraded POTW. The Iowa wastewater facilities design standards seldom change, however, water quality standards change more frequently and can result in changing effluent limits. You need experts to assist in preparing a Facility Plan to ensure whether the plan proposed by your municipality complies with DNR's design and water quality standards.

As a municipality in Iowa, you might need to implement additional treatments or adopt the latest technologies to meet water quality-based effluent limits.

Water quality-based effluent limits

• Ammonia: The most recent revision in water quality standards by the Iowa DNR has led to stringent ammonia limits in wastewater effluent. To meet the revised standards, POTWs with lagoon-based systems have adopted various methods for ammonia removal from the wastewater, including a Submerged Attached Growth Reactor (SAGR), covered aerated lagoons and/or addition of a polishing reactor for the tertiary treatment of wastewater.

• E.coli: E. coli is an indicator organism tested to determine the overall levels of microorganisms in the effluent. Reduction in E. coli is necessary in many wastewater effluents to protect recreational use of the receiving stream. Reducing E. coli can be accomplished through chlorination or ultraviolet (UV) disinfection.
• Total nitrogen and phosphorus limits: The total nitrogen and total phosphorus limits are likely to be included in the water quality standards soon.Treatment plants with an average design flow of more than 1 million gallons per day have total nitrogen and total phosphorus limits on new permits. The majority of treatment plants in Iowa have smaller capacities and have not faced these limits yet.

Municipalities can face an uphill task when preparing a Wastewater Treatment Facility Plan to accommodate changing effluent limits. To help ensure your municipality achieves DNR approval while addressing design challenges with innovative solutions, partner with an experienced engineering and environmental consulting firm.

Fehr Graham has been providing end-to-end assistance on wastewater engineering to wide-ranging communities since the 1970s. Our knowledge of Iowa's design standards, permitting process and funding requirements can help you significantly improve outcomes throughout the design and construction phases of wastewater treatment plants.