AUBURN — The Planning Board gave a favorable recommendation Tuesday to a proposed change that would increase minimum lot sizes from one to three acres in the watershed, sending the issue to the City Council for consideration in November.

But, the decision did not come without public scrutiny as the proposal is closely tied to one that would also update the septic design standard in the watershed, which has been part of the larger local debate over water quality protections at Lake Auburn.

The proposal to lower the allowed density came in response to concerns that the updated septic ordinance would allow for more residential development.

The new septic rules, if approved, would allow property owners to utilize alternative soils in designing septic systems — something that has not been allowed in the watershed, but has also restricted development.

The City Council voted to table a vote on the septic design issue in June in order for the Planning Board to consider a shift to larger lot sizes.

City officials and staff believe that the two changes together can improve water quality at the lake while limiting the number of buildable lots, but many residents are not convinced that the changes will limit development and won’t cause unintended consequences.

The hearing Tuesday brought out several members of the public who hoped to comment on both issues, but many who came to discuss the proposed septic design changes were told that it was mistakenly labeled as a public hearing on the board’s agenda.

The board had already forwarded a favorable recommendation on the septic proposal, but with the condition that it also coincide with the density change, as well as a more robust water quality monitoring program. Many said because the two changes are closely linked, comments on both were germane to the discussion.

Eric Cousens, director of Planning and Permitting, said according to updated data from the city’s consultant FB Environmental, the zone change would result in a net reduction of buildable lots. He said the consultant’s modeling estimates 38 new lots in the watershed over the next 25 years under both the septic and density changes, and 41 new lots without any changes.

Josh Nagine, a Lewiston resident and Planning Board member, said any new buildings in the watershed will result in stormwater runoff from properties. Like others, he urged the city to table both the new septic design standard and rezoning “until relevant and enduring protections are put in place to curb unchecked development and protect Lake Auburn from what may become a one-time gold rush for a few individuals with the possibility of irreversible damage to the quality of our shared drinking water.”

Lewiston resident Julia Harper said during public comment that the modeling should be updated to take into consideration LD 2003, the state legislation meant to increase housing density in most areas.

“The modeling prepared does not take into account any of that,” she said.

Others urged the board to listen to a recent recommendation from the Lake Auburn Watershed Protection Commission, which asks city officials to hold off on the changes until a peer review of the FB Environmental report can be completed.

Planning Board Chairman Evan Cyr, who is also chair of the Lake Auburn Watershed Protection Commission, said the board was merely making a recommendation, “not an official action or final decision.”

“Also, I don’t see how lowering the density could have any negative effect on the watershed by itself,” he said.

Several Auburn residents, including Jim Wellehan, also said they didn’t believe there has been sufficient evidence presented yet to prove that water quality will not be negatively impacted.

Planning Board member Brian Dubois, who voted in favor of the recommendation, argued that “somewhere along the line, we’ve confused development with protecting our water source.”

“We have expert counsel, staff, and professionals that have given us a road map on how to protect it,” he said. “It’s not how we can expand development, it’s protecting the water source.”

Dubois also believes that “doing nothing is more costly for water quality.”

Board member Riley Bergeron, whose initial motion to table the recommendation failed, said he didn’t think waiting a few more weeks for LAWPC’s peer review would make a difference.

The board voted 5-2 to send a favorable recommendation on the density change.