WHILE there has long been criticism of septic tank owners for not maintaining and protecting these systems, septic tanks are now under attack as a primary source of nitrogen pollution to the Chesapeake Bay.
Each new person in the Bay watershed generates 8 pounds of nitrogen a year; that's an extra 24 million pounds annually deposited in the bay by 2020, if population projections are valid.
Nitrogen can be effectively removed in larger sewage treatment plants. But traditional septic systems -- built for sanitation, not water pollutant removal -- can't do the job. Most of the nitrogen finds its way through soil and underground water into surface water, such as the Bay and tributaries.
Newer single-home septic systems can remove about 60 percent of the nitrogen waste. But those systems cost two to three times more than a traditional $3,000 septic system, plus $200 or so yearly for maintenance of pumps and electrical connections.
More than a third of the houses in Maryland have septic systems.
A governor's task force has been looking at ways to reduce nitrogen discharge from septics. The most obvious solution is to require the costly nitrogen removal process for any new or replacement septic system. To minimize opposition, the panel proposes this step only for undefined "areas of special concern," with the worst nitrogen concentrations.
Septics are often the only choice available for homes too far from existing public sewage lines. Once built, operating costs are usually cheaper than municipal sewage charges, an incentive to resist hookup to a central system. They can recharge underground reservoirs, slowly dispersing the waste water, unlike treatment plants that dump into rivers.
But septics only have a life of 20 or so years before they must be rebuilt or replaced. The septic tank should be pumped every two or three years to protect the system; surveys show over 40 percent of Maryland owners don't do so.
More older septic systems are reaching their life's end. But higher replacement costs imposed by the state could discourage action until sewage backs up into homes. The task for the state and the bay watershed is to more accurately calculate the cost-benefit of these advanced septic systems before requiring them anywhere.