EVALUATING WASTEWATER TREATMENT ALTERNATIVES FOR SMALL COMMUNITIES WITH LAGOONS

Water Protection Program fact sheet
10/2015
Division of Environmental Quality Director: Ed Galbraith
PUB02587

Addressing infrastructure is a challenge facing communities across the United States.  In 2012, an assessment by the Missouri Department of Natural Resources and the U.S. Environmental Protection Agency estimated that $9.6 billion in capital investments will be needed to address Missouri’s wastewater infrastructure needs over the next 30 years.  Repair or replacement of infrastructure that is at or near the end of its useful life is a critical responsibility for community leaders.  Recent wastewater treatment requirements for ammonia mean that many lagoon systems also need treatment upgrades and this will require additional cost to ensure compliance.

Consider Regionalization
“Regionalization” refers to independent public bodies, such as cities or counties, and possibly private entities working together to share responsibility for providing wastewater services to their residential, commercial, and industrial customers.  When people work together through regionalization of wastewater services, public utilities often benefit from reduced capital and operational costs, and increased economies of scale.  There are two ways that communities can regionalize:

Negotiating the inter-local agreement or contract between the regional partners may be a challenge. The political relationships between the local parties and the fairness of the agreement to all parties must be carefully negotiated. Even in communities committed to cooperation, negotiating the contract is a time consuming job, and getting adequate involvement and buy-in will take time and patience.

Why regionalization makes sense
“Economies of scale” is the phrase used to explain why it costs less overall to build or operate one larger facility than two small facilities.  Certain construction costs, such as permits, equipment mobilization and engineering design costs, apply regardless of the size of treatment plant.   The other financial advantage of regional facilities is they simply have more customers to share the burden of paying the bills. Administrative and operational costs don’t vary much with the size of the plant. No matter how many connections the system has, the clerk needs to send out bills and balance the books and the operator needs to monitor flow and manage system operation. This means each ratepayer in a larger system pays a lower bill for operating the treatment plant.   In some areas, a regional partnership with a centralized treatment facility works best.   In other places, smaller decentralized treatment systems that are centrally operated may work better. A comprehensive evaluation is necessary to determine if regionalization is right for your community. 

Evaluating Wastewater Treatment Alternatives for Small Communities with Lagoons
Hundreds of Missouri towns and cities with centralized wastewater collection systems utilize wastewater lagoons to treat wastewater.  In 2005, Missouri adopted EPA water quality criteria for ammonia, and many National Pollutant Discharge Elimination System (NPDES) operating permits in the state now contain ammonia limits.  Since 2013, there is a new national water quality criteria for ammonia that will require more effective removal of ammonia and result in lower ammonia limits. Because lagoons typically are not effective in removing ammonia from wastewater, many cities, towns and system owners must now decide how they will meet the new requirements.  The following comparison of wastewater technology options is provided to help small communities understand the range of alternatives available when treatment system upgrades are needed*. 

Convert to No Discharge System Using Lagoon with Land Application

Retrofit Lagoon for Ammonia Treatment

Construct Alternate Sewer System

Construct Mechanical Plant

Description

Land application is the controlled application of wastewater from the lagoon to a vegetated land surface with a fixed or movable sprinkler distribution system.  Microbes in the soil break down the pathogens in wastewater effluent.  The nutrients and the water in partially treated wastewater contribute to the growth of a wide variety of crops and the maintenance of pasture.  Cost estimates vary depending upon the population served, amount of flow and how much land is needed for proper application of wastewater effluent.

Lagoons may be modified to remove certain pollutants from effluent prior to discharge to the receiving stream by installing an enhanced treatment technology.  Common types of lagoon retrofits include installing a lagoon cover and polishing reactor or a gravel filter.  Some technologies will use the entire lagoon system without adjusting the cells themselves, while others will be constructed using a portion of the existing lagoon footprint and retrofitting the system to add air or improve final settling.

Alternate systems can consist of nontraditional sewer collection systems and a pretreatment facility followed by soil absorption of the effluent. System configuration and cost is highly variable based on the demand and physical area.  This type of system can be an environmentally sound, financially responsible solution to address wastewater for a sparsely populated or very small community where a conventional central treatment system is not practical or affordable.

Sewage is transported away from homes in sewers to a central plant where it is treated.  Mechanical plants move wastewater through a series of tanks, along with other components such as pumps, blowers, and screens, and control flow with mechanical instruments. Treated effluent is then discharged into a receiving stream. Common types of mechanical plants in small Missouri towns are extended aeration package plants, sequencing batch reactors, and extended aeration oxidation ditches. 

Fit with Possible Future RegulatoryChanges

Wastewater is applied to land rather than discharged; therefore, effluent limits are not required within the NPDES permit. If future regulatory changes occur that further limit the amount of pollutants discharged from permitted systems, those additional limits will not apply to a system permitted as a no discharge land application treatment system.

The technology is designed to treat wastewater to meet effluent limits in the NPDES permit in effect at the time of the system’s design.  If future regulatory changes occur that further reduce the amount of pollutants the system may discharge, the facility would likely need to modify the system (at additional cost) to meet those additional NPDES permit requirements.

Wastewater is contained within septic tanks and applied to the soil; effluent limits are not required within a NPDES permit. If future regulatory changes occur that further limit the amount of pollutants that effluent from a permitted system can contain, those additional limits will not apply to a clustered septic system that does not discharge. 

A mechanical plant is designed to treat wastewater to meet effluent limits in the NPDES permit in effect at the time of the system’s design.  If future regulatory changes occur that further reduce the amount of pollutants the system may discharge, the facility would likely need to be modify (at additional cost) to meet those additional NPDES permit requirements.

System Capital Cost*  

Moderate
$$ - $$$

Moderate
$$ - $$$$

Moderate
 $$ - $$$ †

High
$$$$ †

Land Requirement

Large land requirement: must either acquire land or sign long-term land lease. 

Land requirement is minimal to moderate.

Land requirement is moderate for septic installation and soil absorption field.

Minimal to moderate land requirement.

Staffing Requirements

Requires extensive management by a fairly skilled licensed operator to operate and maintain the system and meet all operational, monitoring and reporting requirements.

Requires extensive management by a skilled licensed operator to operate and maintain the system and meet all operational, monitoring and reporting requirements.  The permit will require the operator maintain a higher certification level.

Requires vigilant maintenance to ensure proper operation, and may not require a licensed operator.

Requires extensive management by a skilled licensed operator to operate and maintain the system and meet all monitoring and reporting requirements.  The permit will require the operator maintain a higher certification level.

 

Operation & Maintenance Cost

$-$$$

Low to moderate overall operating cost due to decreased sampling required because this is a non-discharging system; although careful and attentive operation and maintenance is necessary for a land application system.

$$-$$$$

Moderate to high operating costs due to increased sampling requirements, higher system energy demand and the need for extensive management by a skilled operator.

$

Low overall operating cost, decreased sampling cost, fewer operator hours.  Overall operation and maintenance cost may be retained by the continuing authority, with individuals responsible for operating their own septic tanks.

$$-$$$$

Moderate to high operating costs due to increased sampling requirements,   higher system energy demand and the need for extensive management by a skilled operator.

Future upgrade need for new regulatory requirements

Minimal cost anticipated because this type of system will have no pollutant limits for effluent.

Moderate to high cost anticipated because system is likely to need modification or retrofit.

Minimal cost anticipated because this type of system will have no pollutant limits for effluent.

Moderate to high cost anticipated because system is likely to need modification or retrofit.

It may be right for your community if…

  • Your small population is stable or declining. 
  • Land for wastewater effluent irrigation is available for lease or acquisition.
  • Land acquisition cost may be offset by agricultural revenues.
  • Your small population is stable or growing slightly.
  • Land for construction of this wastewater effluent treatment solution is available for lease or acquisition.
  • Your population is small or declining; or the population is small now but future development is anticipated that will increase the population.  
  • The area consists of a small number of potential connections.
  • Your population is not notably small and/or the population is growing.
  • Land for wastewater effluent irrigation is not available for lease or acquisition.

*This is not a comprehensive list of technologies and assumes facilities are designed, constructed, operated and maintained properly.   Permit holders should not rely solely on this document when making treatment technology decisions; it is important to consult closely with an experienced Missouri registered professional engineer in selecting a treatment solution. A discussion of the ammonia criteria and potential treatment technology in included in Publication 2481 at http://dnr.mo.gov/pubs/pub2481.htm.

**Actual costs vary depending on site- specific parameters.

†For communities currently served by a lagoon, an additional cost will be properly closing the existing lagoon.

There is no one-size-fits all approach to providing infrastructure that will always produce optimal results. In some areas of the state, local geology and land use are not compatible with a permitted no discharge lagoon and land application, while in other areas land application may be the perfect answer for a rural community surrounded by farm land.  Regional partnerships, too, must be carefully considered to ensure a plan is established that fits the needs of each involved community and as well as the regional geography.   

Wastewater treatment and drinking water infrastructure are some of the most valuable assets owned by a city or town, and have a significant impact on the community’s health, economy and overall well-being.   Community benefits that follow infrastructure maintenance and upgrades include:

The Department of Natural Resources encourages communities to review the long-term needs of their community when evaluating wastewater solutions. 

The department offers financial assistance to municipalities, counties, public sewer or water districts, political subdivisions or instrumentalities of the state with a population of less than 10,000 to help fund site-specific facility plans and engineering reports that evaluate the costs and feasibility of alternatives.  Visit the department’s Community Assistance webpage to find a Community Services Coordinator in your region to assist you at www.dnr.mo.gov/assistance, or call 800-361-4827.