Field of Drains

A precast septic system shared by seven homes gives a developer the flexibility to maximize green space and profit.

By David Holzel

Folks who live in $700,000 homes still put their trousers on one leg at a time. And just like everyone else, they still need a system to dispose of wastewater. The 2-year-old Brantwood development in semi-rural western Howard County, Md., is outside the public sewer service area. So the homes in the development instead use precast concrete septic systems.

Located in the fast-growing corridor between Baltimore and Maryland's Washington D.C. suburbs, Howard County shares the predicament of many fast growing outer suburbs around the country as it tries to balance demand for growth with preservation of open spaces. Brantwood's developer faced such a tradeoff when it came time to design a waste-removal system.

The building material was never in doubt. The engineer, the contractor and even the county officials prefer precast concrete for its ease of assembly, durability and watertightness. The twist at Brantwood was the installation of a shared septic system that removes the effluent from seven of the neighborhood's 120 homes to a common drain field. The remaining homes in the neighborhood will use individual septic systems.

The shared system "works like a traditional septic system, only larger," says Nancy Mayer, president of Mayer Brothers, the precast company that produced Brantwood's system.

The gravity-run system cost about $70,000 to build. It includes two 3,000 gallon and two 2,500-gallon precast concrete septic tanks to gather and separate the waste. These tanks are larger than the usual 1,000- and 1,500-gallon receptacles used for individual systems. A precast distribution box -- measuring nearly 10 feet by 6 feet by 2 feet and weighing 4,800 pounds -- channels the effluent to 18 outlets running downhill to a 70,000-square-foot drain field. Speed levelers, composed of a dial inserted between the distribution box and each of the 4-inch PVC pipes that lead to the drain field, control the flow.

"And it works great," says Jeff Welty, deputy bureau chief for the Howard County Bureau of Utilities. Welty maintains Brantwood's shared septic system, which is county owned and operated under state law.

"In many Maryland counties, cluster zoning is seen as the ideal world to preserve as much farmland as possible," Welty says. So developers reduce lot sizes from three acres to one and cluster the homes on part of the property.

While one acre is still a lot of ground to cover with a lawnmower, it might not be enough space for a septic system, which requires 10,000 square feet -- about a quarter of an acre -- to do its business. The chance of there being no suitable drain field on a lot that size is considerable, Welty says. "That's what drove this whole [shared] system."

Developer John Liparini, president of Brantly Development Group, says the shared septic option allowed him to make full use of Brantwood's acreage. "In this case, we were able to save a home site," he says. "Zoning requirements would have made us build one less home otherwise."

There are four active shared systems in Howard County, and another three or four are being considered, Welty says.

The system was delivered in August 2000 and took about a day to set up in wet conditions. The contractor, CCS Inc., had a crane in place to move the concrete boxes, which the precaster trucked to the site.

"We opted to start digging the hole the day before and left everything open overnight," says Leonard Skein, the project's utility superintendent. "In two or three hours everything was set in place. We had the rest of the day to vacuum test the structures for watertightness and backfill."

To ensure that the structures were watertight, the precaster had cleaned the surfaces that were to be joined and applied a primer, then placed a butyl mastic sealant between the joints.

Skein says he has worked on septic systems made of brick or poured-in-place concrete. Those systems often develop holes, he says. "Plus you can't set up in one day, and you have to work around the weather." Those are two disadvantages precast concrete doesn't share.

"Precast is the only way to go," he says. "If we can get it precast, that's the way we prefer it."

From an engineering standpoint, a shared septic system is advantageous because of its efficiency of scale, according to Anish Jantrania, a technical services engineer at the Virginia Department of Health, who has designed on-site systems. "On a single-family home [system] you're not using the technology efficiently."

The inefficiency isn't apparent at Brantwood, Jantrania says, because the shared system is small and gravity driven. But imagine a more complex system, one run by an electric pump. "You could have seven homes and seven pumps, or seven homes and one pump. With a shared system you would be using less electricity and your operating costs would be lower."

For a developer, a shared system makes sense when it allows him to build additional houses. "It's an expense issue," John Liparini says. "A shared system is a little more expensive."

An individual septic system costs $4,000-$5,000 to install, he says. Shared systems like the one at Brantwood cost about $10,000 per home. While the per unit cost is double that of an individual system, the fact that he was able to build an additional house more than made up for the higher cost, he says.

Precast concrete itself plays a role in holding down cost. "Precast is so much quicker," says Mark Niemann, project manager for contractor CCS. "Your labor savings is 50 percent. So even if your material cost is higher, it's more than offset by the lower cost of labor."

And unlike the rusted steel septic tanks that precast often replaces, concrete isn't likely to deteriorate with age. "Concrete increases in strength over time," says Mayer. "That system will outlast any of us who built it."

With the twin pressures of residential development and preservation of green space likely to continue in semi-rural areas like western Howard County, shared septic systems may become a more common choice. Add precast concrete construction to the mix and you have a durable, watertight, labor-saving system that won't send profits down the drain.

Project Profile

Project: Brantwood subdivision, Howard County, Md.

Developer: Brantly Development Group, Columbia, Md.

Engineers: LDE Inc., Columbia, Md.

Precast Company: Mayer Brothers, Inc., Elkridge, Md.

MD SHA
Approved Plant
Baltimore City, Howard County WBE