Learning to Think Small

Rural communities face key challenges in upgrading wastewater infrastructure. Land-based technologies can be part of the solution.

Learning to Think Small

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Small communities face the same basic water infrastructure issues as large cities do. The difference is that they are more challenged to find the funding to make needed improvements and updates.

Dr. A.R. “Bob” Rubin has spent decades helping smaller communities deal cost-effectively with issues around wastewater treatment and stormwater.  He is a professor emeritus at North Carolina State University in biological and agricultural engineering and has worked extensively with the Water Environment Federation on rural water quality and wastewater management. He has also worked with the U.S. EPA on small and decentralized treatment systems, including solutions that revolve around individual and cluster septic systems.

In Rubin’s work, a small community is defined as one with a population of 10,000 or less, or a Standard Metropolitan Statistical Area (SMSA) with a population of 50,000 or less. (An SMSA is defined as a region that consists of a city and surrounding communities that are linked by social and economic factors.)

Rubin was part of an Ask the Experts panel at WEFTEC Connect last October on “Planning Approaches to Sustainable and Resilient Infrastructure for Small Communities – One Chance for Success!” He talked about wastewater solutions for smaller towns in an interview with Treatment Plant Operator. 

What is the fundamental difference between large and small communities as it relates to meeting water infrastructure challenges?

Rubin: They’ve got the same public health and environmental issues. The difference between the two is the ability to get funding and the ability to pay the bills. In your state, for example, Green Bay and Madison have huge tax bases. They are vibrant communities. You have people moving in. You have got a growing workforce and a growing tax base. But in a community with, say 1,000 people, many are retirees on fixed incomes. People are leaving.

Where does that leave smaller communities in seeking infrastructure funding?

Rubin: They have two choices. They can increase the tax rate, or increase the tax base. In small communities, both of those are a challenge. In large communities, they don’t have to increase the tax rate, because they continue to increase the tax base.

What is your basic approach to dealing with these issues?

Rubin: My approach is natural — using appropriate technology and natural systems whenever possible. That is not to say natural systems are always the only solution. In many instances site and soil conditions may limit potential for use of a natural system, and a mechanical system must be used. This approach suggests a comprehensive options assessment as a necessary part of any design plan.

As a practical matter, what does that mean?

Rubin: It means using collection technologies such as small-diameter gravity and low-pressure sewers, with land-based treatment technologies, as part of a managed program.

What kinds of land-based treatment options are there? And why are they appropriate for smaller communities?

Rubin: They include constructed wetlands, spray irrigation and drip irrigation — using the land. If you’re working in a small community, there is a lot of land. In downtown Chicago there is not a lot of land, but in rural communities, there is an abundance of land. So take advantage of that land and use it as a treatment mechanism.

Are you referring to communities that already have centralized collection and treatment, or those that do not?

Rubin: Both. If they already have a system and it’s regulated under the NPDES program, by law they are supposed to upgrade that system every five years when their permit is reissued. A lot of small community systems haven’t been upgraded. And now with the Total Maximum Daily Load approach, the federal and state governments are imposing phosphorus limits on permits. Natural systems are really good for removing phosphorus.

For operators used to big-pipe sewers, how would you describe a small-diameter low-pressure sewer system?

Rubin: A pressure sewer system is a septic tank or pump tank in everybody’s yard, and a connection to a 4-, 6- or 8-inch-diameter pipe that is flowing full. It’s like a water system in reverse. In addition to the pressure sewer, small-diameter gravity systems are an excellent option where the slope is conducive to that option. They are essentially watertight, so inflow and infiltration is maintained at a minimum. There are design programs available for such systems from effluent pump and grinder pump manufacturers.

What’s an example of an infrastructure project for a small community with a troubled wastewater system?

Rubin: I am working with a town in North Carolina with fewer than 1,000 people. They have a gravity sewer and an aerobic treatment plant. In heavy rain events, the collection system completely fills, and the aerobic plant overflows into the adjoining stream. We’re looking to upgrade their system to reduce I&I as much as we can with lining and by eliminating some connections that served an old industrial area that is no longer there. Then we’ll upgrade the plant, move it to a higher location, and put in some flow equalization so that they can accommodate those peak events. You may ask why not convert to a natural system. The answer is that although suitable soils are available in the area, converting to a land-based system would be more costly than repairs to the existing mechanical system. That’s what is planned; it has not been funded yet. 

How can communities secure funding for projects like this?

Rubin: The U.S. Department of Agriculture Rural Development program. I can go to my local Rural Development office. I can talk to their Rural Development coordinator and say, “We need a small planning grant for our community.” I can get up to $25,000 to $30,000 for a planning grant. With that I can determine the collections, treatment and management needs.

What happens after the planning has been completed?

Rubin: We can put together an engineered report that lists all the costs and I can apply for a low-interest loan. The money from Rural Development goes to a local bank, which then loans the money to do the infrastructure project.

What about grants for infrastructure projects?

Rubin: There is money available through the U.S. Department of Housing and Urban Development, as community development grants. And grant is the operative word. There are low-interest loans, but low-income, high-need communities should first be looking for sources of grants available through the federal government. Some states also have grant programs to help promote rural development.

So this is about communities with centralized infrastructure that is out of date and needs to be upgraded cost-effectively?

Rubin: Yes and no. It could also be a small community that is using onsite wastewater systems, where those systems are malfunctioning, and there are issues with shallow water tables or shallow bedrock, and where upgrading those systems could cause public health or environmental problems. In those cases we have gone in with collection and treatment systems that will alleviate that onsite wastewater problem.

So in those cases everyone has a septic tank, but the wastewater is piped to one central land-based treatment system?

Rubin: Yes, or it could be to treatment systems dispersed through the community. Is it best for everything to go to a single location, or is it possible to use multiple community drainfields? Every system is unique.

What about a community with a big-pipe system that is reaching end of life and now is facing phosphorus limit and a costly upgrade?

Rubin: It may be that they could continue to use that existing infrastructure. Line the collection system so that it’s structurally more sound, and add on something like a constructed wetland. We have good design data for natural systems. WEF has three manuals of practice that include sections on natural systems. The EPA has publications on the design of land-based treatment technologies.

Where else can community leaders go for information and advice?

Rubin: They can go to their state university extension service, or to the Natural Resource Conservation Service and the Soil Conservation Service. Yes, those entities deal with agriculture, but removing nutrients from drainage lines going through farm fields is not all that different from removing nutrients from domestic wastewater.

What are the key advantages of land-based treatment technologies?

Rubin: In most cases, there is no direct discharge to a stream, so the community is no longer in the NPDES program – they are in a state nondischarge program. The water goes either into the soil and flows laterally to a stream, or the water goes to deeper groundwater, in which case it recharges the aquifer and makes that water available to any down-gradient water user. 

Is that water adequately treated by passing through the soil?

Rubin: Oh, yes, flowing through 2 to 3 feet of soil removes 99.9% of the pollutants, or more. In 1 foot of good, loamy soil, from 99% to 99.9% of bacteria and viruses are removed. After 3 feet of soil, the number is down to nondetect.

Do all of these land-based treatment methods require some level of pretreatment?

Rubin: Yes. Even a septic tank is a pretreatment system. A septic tank will remove about 30% of BOD and 50-60% of solids. It’s a really good pretreatment device. With a primary treatment lagoon, you can remove, depending on the temperature, anywhere from 50% to 75% of the pollutants. All of these pretreatment technologies work well.

What are the disadvantages of land-based treatment systems?

Rubin: Public perception is probably the biggest disadvantage. There can be odors. And part of a land-based treatment system is nutrient management. I design land treatment system to assimilate the nutrients that are contained in the wastewater. If we change the crop, the nutrient uptake changes.

So in summary, would you say that smaller communities can do themselves a lot of good by thinking outside the box?

Rubin: Yes, and by getting up-to-date information, and that starts with talking to local experts. There is lots of technical information out there, and it’s not all engineering oriented. The quest starts with finding out what’s appropriate in your area.

So what’s the bottom line about small communities and dealing with these infrastructure issues?

Rubin: As long as we have people, we’re going to need a water supply, and we’re going to have to deal with sewage. As long as we have impermeable surfaces and runoff, we will have to deal with stormwater. And as long as we throw things away, we will have to deal with solid waste. Those environmental infrastructure issues are not going away.  


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