AUBURN — The City Council signaled its support for new septic design standards in the Lake Auburn watershed Tuesday, pointing to possible approval on May 2.

The workshop discussion Tuesday came after the Planning Board gave a favorable recommendation last week, tying its recommendation to several measures aimed at monitoring development and water quality.

Mayor Jason Levesque said Wednesday that the council may also consider amending the ordinance to require existing homes in the watershed to update systems, setting a timeline and funding mechanism for replacements.

The city has been eyeing changes to its septic design standard for several months stemming from a recent study of Lake Auburn. While the update would improve upon wastewater treatment in the watershed, it has also raised questions over its effect on new housing development.

The study, which was given to officials late last year, said the septic standard used in the Lake Auburn Watershed Overlay District has limited development on a significant part of the watershed by “effectively prohibiting the use of innovative and alternative septic system and leach field designs.”

City staff has said that because Auburn’s standard does not allow for alternative soils to be used in designs, some properties simply cannot meet the standard in order to install a system, which has restricted development, but that the design itself is not yielding the best results.

While the update is expected to allow some level of new development, city staff believes the new standard will create a “net benefit” to the lake by requiring better performing septic systems, and officials are looking to extend that requirement to existing property owners.

Those questioning the move, like Councilor Rick Whiting, agree that the septic standard should be changed, but say the effort should also be tied to halting any additional development in the watershed.

In order to address development fears, the Planning Board recommended that several conditions be placed on the update, which were supported by the council Tuesday. One of them is to change the allowed density in the watershed overlay district from one unit per acre to one unit per three acres.

Eric Cousens, director of Planning and Permitting, said Tuesday that while the change “may open up some lots that were previously unbuildable,” moving to one unit per three acres will limit the amount of new development.

Other conditions include establishing a monitoring system in the watershed after the change is in place, with the stipulation that if water quality degradation is found after monitoring, a moratorium on development would kick in.

Whiting, as well as Councilor Belinda Gerry, said they’re concerned about making a change that could allow development, and then having to potentially correct the mistake if water quality worsens because of it.

Those in favor of the change argued that existing conditions of septic systems and phosphorus sources from the upper watershed are the major contributors to water quality issues. Staff has said that 275 of a total 321 systems are “grandfathered” under the existing septic rules.

“The biggest fear here isn’t three or four new homes being built, it’s over 275 potentially-failing (septic) systems,” Levesque said.

There were several tense exchanges between Whiting and Levesque on Tuesday, including a disagreement over the need for further expert analysis. Whiting said Auburn should be consulting with lake experts like Bates professor Holly Ewing, “rather than politicians, and appointees of politicians creating policies they don’t really understand.”

Levesque said the $100,000 study was conducted by experts in the field, with recommendations on issues like the septic design, that has been discussed for years.

“We can’t place the blame of new development as the source of all evil and not address something that hasn’t been addressed for decades,” he said.

Levesque argued that the septic ordinance should also include language that requires existing homes to update septic systems, with a mechanism for funding the replacements over “a prescribed period of time.” He suggested that the cost of such a requirement should fall to the Lake Auburn Watershed Protection Commission, which is funded jointly between the Auburn Water District and the city of Lewiston.

The council seemed open to the additional language, with Councilor Ryan Hawes saying all homes in the watershed “need to be held to the same standards.”

In a letter to the council Monday, the Lake Auburn Watershed Protection Commission did not take a formal stance on the specific septic proposal, but said the commission “does not support any changes in definitions and/or standards that would increase development of lands located within the physical boundaries of the Lake Auburn Watershed Overlay District.

“The existing standards and definitions are currently required to prevent water pollution associated with increased development and to prevent irreparable harm to the purity of the public water supply, which would threaten the existing filtration waiver,” the letter said.