New, large basements that dip into the shallow aquifer that underlies much of Palo Alto are the main offenders, according to residents worried about the trend.
These basements require the removal of five to 10 million gallons of groundwater, accomplished with pumps — channeling water into the storm drain system — that run nonstop for three to more than six months, according to Bob Morris, a senior project manager with the city's Public Works Department.
And an average basement takes about 200 tons of concrete, Chief Building Official Larry Perlin has said. Concrete has come onto environmentalists' radar recently due to its energy-intense manufacturing process and greenhouse-gas emissions.
The numbers may sound high, but some people, including Public Works Department staff, say the pumping process doesn't have any long-term effects on either groundwater or the project's neighbors.
Morris said only five to 10 residential basements require dewatering each year, although the number of basements constructed is growing.
In 2001, the city's building department issued 23 permits for single-family houses with basements, Perlin said. That figure dropped to 17 in 2003 and peaked at 36 in 2006, with 32 permits issued last year.
"It would appear that there's a slight upward trend," Perlin said, adding that it might also be a sign of the improving economy.
The issue bubbled up to the City Council during its recent review of new green-building requirements. On an 8-0 vote (with Councilman John Barton conflicted out) on May 12, the council asked the Planning and Transportation Commission and city staff to examine the city's basement policies.
"I don't have enough information to say groundwater pumping is necessarily terrible, but it seems very suspicious to me," Vice Mayor Peter Drekmeier said.
When the Planning and Transportation Commission reviewed the green-building program in April, Chairwoman Karen Holman was the sole "no" vote, primarily because it didn't encompass basement issues.
"I'm not saying eliminate basements. Let's evaluate what the impacts are of what we're doing," Holman said. "If you're dewatering three million gallons off a site, it's hard to make the leap that there's no impact to that."
These basements might be killing trees, causing ground to sink and wasting usable water, neighbors to basements have said, writing letters to the council and circulating e-mails on the topic. The pumps can be loud, the storm-drain system already struggles during the winter and the city should be rewarding resource conservation, not projects that rely on tons of environmentally costly concrete, basement critics say.
"We have had problems with sinkholes in our yard after the basement construction behind us, as well as problems with doors and windows not working as well as they should," Councilman Jack Morton's wife, Mary Ellen Morton, wrote in an e-mail to the Weekly.
"At the time of the construction, I watered almost daily since the continuous pumping of water, which went on for over a year, seemed to draw water from my yard," she said.
Fighting basement dewatering has become a full-time passion for Old Palo Alto neighborhood resident, and native Palo Altan, Jody Davidson.
She said her quest began when she spotted a hose in her neighborhood continually pumping water into the storm drain.
"I just wondered innocently, 'Wow, all this water,'" Davidson said.
Her scientific background came in handy when she began researching the many effects of water removal.
"When you start withdrawing that much water, things are going to happen," she said.
Trees do rely on the water, the pumping can compound flooding and risk salt-water intrusion and it affects the stability of the land, she said. In addition, water does move between the city's shallow and deep aquifers, Davidson said, noting she received that information from a hydrologist.
But, perhaps most importantly, the city shouldn't be wasting such a critical resource, she said.
Palo Altans once drank from groundwater and they may need to again, she said.
"This water can be used in the event of a catastrophe," Davidson said.
To prove her point, she commissioned costly testing of water pumped from near the intersection of Bryant Street and Santa Rita Avenue. The tests came back clean, she said.
"I drank it to prove my point, without boiling," Davidson said.
For months, Davidson has been interviewing experts and researching the issue, hoping to convince policymakers and city staff members that basements don't belong in Palo Alto.
The homeowners usually don't realize the many negative ramifications of basements, she said.
When she tells them, as politely as she can, their faces fall, Davidson said.
To analyze the effects of dewatering, the city commissioned EIP Associates, a Sacramento-based firm, to study the method in 2004. Despite neighbors' concerns, the consultants concluded that dewatering for residential basements does not have negative effects on the groundwater supply or cause other problems.
Two aquifers, separated by a largely impermeable layer, underlie Palo Alto, the report states.
The lower aquifer is used for groundwater supplies and fit for drinking, while the upper aquifer, seven to 15 feet down, is largely contaminated with runoff containing chemicals and other materials, city staff members have said.
The aquifer below Palo Alto holds 350,000 acre-feet of water, the report states, citing the Santa Clara Valley Water District.
Even prolonged pumping would only have a "temporary, small and very localized" effect on the shallow aquifer, the report states.
"There would be no effect on the deep aquifer."
Basement excavations have caused problems if the dig's sides were improperly supported, but dewatering itself hasn't caused any land to subside, according to Perlin and Public Works Director Glenn Roberts.
The city requires builders to submit a dewatering plan, test the level of water and ensure it isn't contaminated, Morris said. Inspectors check on the pumps, hoses and tanks involved to ensure they are operating properly, he said.
"After the dewatering, the groundwater level reestablishes itself," Morris said.
He said the pumping only removes water about 20 feet away from the basement itself.
The Public Works Department is also considering banning dewatering in the winter when the city's storm-drain system is full, Morris said.
And Planning Arborist Dave Dockter says the dewatering doesn't hurt trees.
"Temporary dewatering is not going to have an adverse effect on Palo Alto's trees, generally," Dockter said.
Trees' roots dive 4 to 5 feet down, above even the shallow aquifer, Dockter said. They need oxygen-containing soil and draw on water primarily from irrigation, he said.
And in Palo Alto's dense clay soil, water doesn't travel laterally very far, restricting the effect dewatering would have on neighboring trees, he said.
Dockter admits he too was skeptical about the effects of pulling millions of gallons of water out of the ground.
"Conceptually, it kind of makes sense. In looking and evaluating, it is not the case," Dockter said, adding that he has studied the issue and consulted with the foremost authorities on urban tree roots.
Residential basement dewatering has never killed a tree in Palo Alto, he said.
"People are reacting on a visceral level; the science isn't there," Councilman Pat Burt said.
He does want the city to investigate the effects of basements, but he said the issue isn't "an acute concern."
Holman said she believes EIP Associates didn't have a complete understanding of the growing popularity of basements, however.
Full basements aren't permitted in the city's flood plain, which covers more than 4,000 properties, according to city estimates.
But about 50 percent of new Palo Alto houses have basements and three houses, in the flatlands, even have two-story basements, Holman said.
Although expensive to construct, basements are popular largely because their square footage doesn't contribute to the limit on the house's size set by height restrictions and its lot size, several council members have pointed out.
Some Palo Alto residents are calling for a basement ban, but that isn't the goal of Holman, Drekmeier or Councilwoman Yoriko Kishimoto.
"We should determine which areas in Palo Alto are suitable for basements," Drekmeier said.
Land is too expensive to eliminate basements, Kishimoto said.
"We just have to sort out all the issues," she said. "The land-use decisions of Palo Alto should be based on a thorough understanding of our ecosystem."
The Public Works Department plans to present a report on basements to the council June 2.
A planning-commission discussion is also planned, Holman said.