What Is a Cluster System?

According to U.S. EPA: "A cluster (or community) decentralized wastewater treatment system is under some form of common ownership and collects wastewater from two or more dwellings or buildings. It conveys the wastewater to a treatment and dispersal system located on a suitable site near the dwellings or buildings. It is common to find cluster systems in places like rural subdivisions."

Image from U.S. Environmental Protection Agency

Cluster systems transport wastewater from a small number of homes (typically 2-10) via alternative sewers to either a conventional treatment plant or to a pretreatment facility followed by soil absorption of the effluent. Cluster systems can be financially sound, environmentally friendly solutions for small community wastewater problems, where conventional central treatment systems are not practical or affordable and where individual onsite systems are inappropriate because of site or soil limitations. 

The advantages of cluster systems are the lower average cost, flexibility in land use, less complex operation and maintenance for the community, and non-discharging, decentralized wastewater treatment systems can provide an environmentally sound alternative for small or disadvantaged communities.

The main disadvantage of cluster systems is the amount of operation and maintenance needed. While it is typically not complicated, alternative sewers have septic tanks that need to be inspected and pumped and mechanical parts and controls that use electricity. Since cluster systems are located onsite, workers are required to travel to individual homes or businesses. This type of decentralized wastewater system requires more frequent maintenance, which can be costly if anything is malfunctioning. 

Another key thing to keep in mind is that cluster systems require a somewhat complex organizational structure in order to make community decisions like fee collection and continuing education of homeowners about wastewater issues. The cooperation of homeowners using the cluster system is much more important than with municipal systems since smaller systems are less resilient and less tolerant of periodic large flows or larger than normal loadings of household chemicals than in large systems, where these peaks are averaged out over a very large user base.

Featured Videos: Onsite Wastewater Systems

According to the US Census Bureau, one in four homes in the U.S. is served by an onsite wastewater system. Our first featured video this week explores some of these onsite options and then explains in simple terms how each of these systems work in different soil conditions and what it takes to maintain them. In the end, the video shows how the cost-effectiveness of septic systems can often more than outweigh the cost of a centralized system for many smaller communities. 

Wondering how to find the funding to get these types of decentralized systems off the ground? Our second video this week explores how innovative partnerships and Clean Water State Revolving Funds can be used for exactly these kinds of projects.