N.C. STATE RESEARCH EFFORT LEADS TO APPROVAL OF NEW SEPTIC SYSTEM

A "triple whammy" of heavy clay, rock and shallow water tables have long presented serious obstacles to siting septic tanks in many areas of North Carolina where sewer hookups are not available.

A new type of septic system that could be used in some places where conventional septic systems can not will be available to the state soon, thanks to the efforts of North Carolina State University researchers.

The effort to approve the use of pressure-dosed sand-filter pretreatment systems was initiated by a citizens' advisory committee in Chatham County. More than nine years ago, the advisory committee to the Chatham County Center of the North Carolina Cooperative Extension Service asked for alternatives to conventional systems amidst frustration over difficulties of obtaining permits for septic systems. Extension agents requested help from soil scientists at N.C. State, including Dr. Mike Hoover, soil science Extension specialist.

"This effort represents the best of what the university can do and how the Extension network serves the university and the citizens of the state," Hoover said.

In Chatham County, as in many areas of the state, the county health department could not issue septic permits for a large amount of land there because of soil conditions. N.C. State soil scientists knew that an alternative had to be found.

"We have acres and acres of land, but it's not deep enough," said Jimmy Collins, head of environmental health for the Chatham County Health Department.

Hoover, along with Dr. Aziz Amoozegar, soil science professor, and graduate student assistants, explored a number of options, including the pressure-dosed sand filters that had been used successfully in other states. Working with the Chatham County Health Department, they set up three demonstration sites to see how well the system would operate in Chatham County.

Pressure-dosed sand-filter pretreatment systems are not new. They have been used successfully in other states for many years. Until now, the systems have not been available for regular use in North Carolina. Sand filters that were not pressure-dosed were used here 25 years ago, but those quickly tended to become saturated and clog.

The pressure-dosed sand filters attach to a septic tank and pump tank, and provide additional treatment for effluent before it is released into a drain field in the soil. Effluent is pumped through the filter about six times each day, giving the filter time to "rest" between doses. Aerobic bacteria in the filters can destroy pathogens that are filtered through the sand.

"We call this a filter, but it is much, much more than a filter. This is truly a biological treatment unit. Aerobic bacteria that become attached to the sand attack other bacteria and viruses in the sewage effluent as it flows through the filter," Hoover said.

After several years of demonstration, the soil scientists sent their findings to the On-Site Wastewater Section of the state Division of Environmental Health, Department of Environment, Health and Natural Resources. Later, the Chatham County Commissioners asked Hoover to write a proposal to state regulators on the use of pressure-dosed sand filters. In addition to the Chatham County data, Hoover included information from a demonstration project conducted by the Craven County Health Department that included pressure-dosed sand filters, as well as other research data from across the country.

The state has approved three types of pressure-dosed sand filters for use in North Carolina. One type is buried beneath the ground, and the others allow some access to the filter for maintenance. A drain field to receive the treated effluent is required for all these systems.

The Type A filter is a buried, pressure-dosed, single-pass sand filter, meaning that effluent passes through the filter one time. The filter will be buried beneath the ground and lined with a heavy-duty plastic that will not allow water in or out. The filter bottom consists of four inches of gravel and a four-inch collection pipe that flows to the drain field.

On top of the gravel is a 24-inch layer of sand covered with more gravel. One-inch distribution pipes running through the gravel bring effluent to the sand surface from the pump tank. The entire filter is covered with a sandy soil that will allow air to reach the underground filter. Type A filters cover the largest surface area of the three systems and require less maintenance, but will cost more to install than other systems.

Type B is a free-access, pressure-dosed, single-pass filter, that allows access to the top layer of sand for maintenance. This type of filter requires less sand, a depth of only 18 inches, and a smaller surface area than Type A, but may require more frequent maintenance. Sand may have to be periodically replaced in some of these filters.

Type C, a free-access, pressure-dosed, recirculating filter, is similar to type B, but requires 24 inches of sand depth and covers the smallest surface area of the three types. After each pass through the Type C filter, 75 percent of the effluent is returned to the system and reapplied to the filter. When it reaches the drain field, effluent will have been treated about four times.

An added advantage of the Type C filter is that it converts the nitrate form of nitrogen into nitrogen gas that is absorbed into the atmosphere. In nitrogen-sensitive water basins, this could serve as a helpful way of reducing nitrates from septic systems by 50 percent.

"All of these sand-filter pretreatment systems can provide a tremendous improvement in quality of treatment we get in septic systems located in North Carolina's sensitive-receiving environments," Hoover said.

"This is an extra measure of public health protection for on-site systems in challenging soil conditions. Many of the public health concerns about failing septic systems recently in the news can be significantly reduced through the used of systems such as pressure-dosed sand filters."

Hoover is quick to add that these pretreatment systems will not be a "cure-all" for all areas where conventional septic systems cannot be sited. A licensed soil scientist must verify that the system will work on a particular site, and the system design must be engineer-approved. All these systems must be monitored at least twice a year by a certified operator.

Initially, the costs for this type of system may be high, Hoover said, but he hopes that costs will come down as contractors become more familiar with installing the systems. Lower costs would make these systems available to a broader group of homeowners.

Jimmy Collins of the Chatham County Health Department believes that the systems will cost about $10,000 initially. He is looking into pre-fabricated kits for these systems available in other states.

This summer, Hoover plans to hold training programs to teach contractors how to install these systems. The training will be conducted by installers who have experience with pressure-dosed sand filters. For more information on training, contact your county center of the Cooperative Extension Service.