Palo Alto residents have deep concerns about what's happening above the city's shallow aquifer -- namely, the millions of gallons of water that get pumped out of the ground every time someone in the area wants to build a basement.

On Wednesday night, a City Council committee waded into the complex issue of groundwater pumping by passing a slew of new requirements aimed at tightening the spigot and encouraging builders to adopt a less wasteful approach.

The new rules, which the council's Policy and Services Committee endorsed Wednesday night, build on the regulations that the council approved last year. They will also likely serve as a preamble to even more stringent regulations in 2018. Provided the full council adopts the committee's recommendations, starting in April contractors engaged in what's known as "dewatering" will have to demonstrate their ability to fill a truck in 10 minutes, limit pumping in residential areas to 10 weeks, offer to water trees and plants in neighboring properties, conduct pumping tests to gauge how much water is getting discharged and provide bi-weekly reports to the city.

In addition, the committee agreed to look at a more significant changes down the road, including ways to get people to adopt construction techniques that would significantly lessen the amount of water that needs to get pumped out.

The effort to beef up water-pumping regulations was inspired a grassroots movement that sprung up around the Old Palo Alto neighborhood, where most of the projects occur, and gradually spread to the wider community. While basement pumping is far from new, as several council members pointed out Wednesday, the issue has recently risen to the surface thanks to a combination of a statewide drought, the growing number of dewatering projects and the fact that most of them are in close to proximity to each other.

In 2015, there were 14 projects that required dewatering because they were located near Palo Alto's "shallow aquifer," according to Public Works staff. This year, there were eight, staff reported. Between them, these projects involved the pumping of about 140 million gallons of water, enough to supply all of the city's water needs for more than 17.5 days (Palo Alto currently uses about 8 million gallons per day).

Last year, the council responded to spreading community concern by adopting a slew of new rules, including a requirement that applicants supply a "statement of effects" of the groundwater pumping on nearby buildings and that they supply fill stations to recapture non-potable groundwater and allow it to be used for things like irrigation and construction cleanup.

While these rules will apply for the 2017 dewatering season, which runs from April 1 to Oct. 31, the city has more sweeping ambitions for 2018 and beyond. On Tuesday night, the council committee agreed that the most effective mitigation is incentivizing people to change the way they pump water.

The proposal was championed by local architect Dan Garber, who has spent the past year analyzing the dewatering problem together with Keith Bennett, founder of the citizens group Save Palo Alto's Groundwater. On Wednesday, residents wearing stickers with the group's name filled up (and spilled out of) the conference room during the committee's deliberation and about two dozen addressed the council. They urged a broad range of solutions, from a moratorium on groundwater pumping to a fee for each gallon of water discharged into the city's storm drains.

"We want effective regulations that minimize the waste of groundwater for all projects that commence in 2018 and beyond and we want improvements in the current process that make meaningful reduction in groundwater pumped in 2017 while obtaining accurate data to guide regulations in 2018 and onward," Bennett told the committee.

While some residents lamented the high number of basement projects, the committee agreed that the problem isn't really the basements, which Councilwoman Liz Kniss noted have been getting built for generations (her house, built in 1929, has one, she noted). She said she doesn't want to get basements to "get a bad name."

"It's about water," Kniss said. "Are we wasting water and how can we conserve it?"

Others agreed. Garber noted that most basement builders today use "broad-area dewatering strategies," which generally means building wells and then pumping the water out of the ground to enable excavation. Because of the nature of Palo Alto's soil, this often results in the surfacing of millions of gallons of water.

The alternative to this, he said, is a more localized approach which uses a cut-off wall to separate the basement area from the rest of the soil and only pumps out the water inside the cut-off wall. Garber recommended that the city consider two paths on developing dewatering regulations: one for builders who use the broad-area approach and the another for those willing to go the localized route. The idea, he said, is to provide incentives for builders to use the latter approach.

The council committee agreed wholeheartedly and voted 2-1 to make the near-term changes and to explore incentives for encouraging cut-off walls that would take effect in 2018. Even Councilman Tom DuBois, who voted against the motion, only did so because he felt it doesn't go far enough. In addition to all the things in the proposal, DuBois said the city should explore establishing a moratorium on basement pumping and imposing a fee for each gallon discharged. His two colleagues, Kniss and Vice Mayor Greg Scharff, both felt this would be going to far.

Among the changes that the committee recommended is a pump test. This was inspired by staff's recognition that the studies that contractors submitted to the city last year were by and large inaccurate. A new report from Public Works staff noted that they predicted "lower flow rates than occurred."

"The calculations were not well supported and were not readily verifiable," the report stated. "Evidence from community members suggests that the very low predicted groundwater drawdown levels may have been substantially exceeded."

Phil Bobel, assistant director of Public Works, said the pump test verifications will help address these inaccuracies. He also supported the idea of waiving the requirement for a study altogether for projects that rely on advanced construction techniques such as cut-off walls to minimize the water impact. While the city is unlikely to actually require localized solutions, it could create performance standards that would strongly incentivize builders to use such techniques.

"We're probably moving toward advanced construction techniques, but we don't have other cities that have done it, we haven't done it ourselves on residential properties," Bobel said. "We need to make sure that before we regulate, that this option is real and there aren't unintended consequences."