After many months of debate, the Board of Health has passed a regulation that will require the installation of "denitrification" septic systems for any new construction or homes with failed septic systems that are 500 feet from wetlands or water bodies.

The regulation, approved earlier this month, updates an existing Board of Health regulation, which requires the same for new construction within 150 feet of bodies of water.

Denitrification septic systems are designed to remove nitrogen from wastewater. The regulation requires that the systems discharge 19 milligrams or less of nitrogen per liter of wastewater discharge on an annual average.

To compare, a standard "Title 5" septic system allows approximately 28 to 35 milligrams of nitrogen per liter of wastewater discharge on an annual average.

Late last year, the Board of Health got an earful from engineers and residents who were concerned that the regulation would be too costly to property owners.

The Board of Health compromised, and added language to the regulation that allows for property owners to apply for a variance -- both for new construction and existing systems -- that would essentially allow a waiver of the requirements. Approval of variances is at the discretion of the Board of Health.

"The Board of Health found that these new regulations are achievable, and have demonstrated to effect a measurable benefit to our coastal waterways," Board of Health Chair Frank DeFelice said in a statement. "We enacted the regulations after two full years of consultation with local experts, state regulators, and our residents."

Still, some stakeholders who have been involved in the debate are not thrilled.

"If you're going to comply with the regulation, you've basically doubled the cost for a septic system," argues John Churchill of Wareham-based JC Engineering. "If we're going to save the client money, we have to ask for a variance. If [the Board of Health members] deny it, we have to redesign for a nitrogen-reducing septic system."

Churchill said that a conventional system typically costs homeowners $10,000 for engineering, etc. He estimated that it will cost homeowners $20,000 to comply with the regulation.

Churchill also argues that there is "ambiguity in the regulation," including whether or not it applies to existing commercial development in the same way it applies to existing homes.

"They're almost regulating homes instead of septic system," Churchill said.

Churchill said he hasn't seen enough evidence that nitrogen is a problem in Buzzards Bay.

The problem with nitrogen, which is naturally present in human waste and found in fertilizers, is that it makes things grow. When nitrogen pollutes waterways, invasive species such as algae grow out of control and use up the oxygen, which in turn causes fish, shellfish, and other marine life to die.

"What's the maximum load that causes the eel grass to dissipate and causes the overabundance? Churchill asks. "If we have a problem, can anybody tell me when the last fish kill was?"

But the Board of Health is satisfied with the regulation, which officials noted is supported by the Buzzards Bay Coalition, a nonprofit that works to protect and restore the bay, which is a staunch advocate for tougher nitrogen regulations in Wareham.

The new regulation only affects properties with on-site wastewater treatment systems — not users of the town's sewer system. The approval comes after years of discussions about how to reduce nitrogen in Wareham's waterways.

In October, 2010, a bylaw that required that developers contribute no new nitrogen to the watershed was passed by Town Meeting, but later repealed after officials found that the bylaw was essentially unenforceable.