CHINA — Even the best septic system won’t last forever.

That was the main message Tuesday from a group of experts assembled by Code Enforcement Officer Scott Pierz. The experts offered advise to Planning Board members, who are aiming to revise the town’s septic system compliance ordinance.

Even so, a properly designed and installed system that is pumped every five years or so and is not abused should last 15 or 20 years. It should not, for example, be used beyond its designed capacity.

Pierz invited Jim Jacobsen from the state’s subsurface wastewater disposal unit, home inspector Ron Rodrigue and several local licensed site evaluators to provide qualified information in helping planning board members.

The board hopes to present a revised ordinance to voters in June, along with the ballot question, presented by petition, asking to repeal the existing program.

Now, all systems in the shoreland zone must be inspected by the end of 2014. Those systems that fail must be replaced and those that pass must be re-inspected every four years.

Most of the experts who spoke Tuesday suggested eliminating the re-inspection requirement, calling it unnecessary.

Several of the experts, however, agreed with Rodrigue’s recommendation that a septic system inspection must happen when a property changes hands.

They were doubtful about expanding China’s program from the shoreland zone to the entire town, partly because of the difficulty of enforcing a town-wide system.

Subsurface disposal rules are designed to clean wastewater before it gets to a lake or to groundwater, not to keep it out, Jacobsen said. The only way to keep wastewater out of other water is to create a municipal collection system and then discharge the treated water into a river.

Systems installed before 1974, they agreed, were not designed to current standards and have exceeded a reasonable life span. Any septic system that old and within 250 feet of a lake should be inspected, Jacobsen and others advised.

There was no consensus on the cost of such inspections. Rodrigue said up to $250 was reasonable; site evaluator David Rocque agreed for a newer system, but said inspecting an older one might cost more.

Rocque added “biomat” to the Planning Board’s vocabulary. The biomat is a layer of bacteria along the bottom of the leach field that helps finish treating wastewater. Without a biomat, water leaks through the bottom, while too thick a biomat causes water to pool on the ground above the field.

In other business, Planning Board members had one application on Tuesday’s agenda. They scheduled a Feb. 14 public hearing on Thadius Barber’s application to amend the subdivision that includes Fieldstone Quick Stop and the mini-mall north of it by dividing the parcel in two.

Barber said he intends the subdivision to be only on paper; he does not plan to sell either property.