Advocates say the chance of an accident is slim.

Yet there would be some small level of danger if state and local authorities sanction a plan to store 7.5 billion cubic feet of natural gas thousands of feet below a neighborhood in south Sacramento.

That's one of the conclusions of a new draft environmental impact report on a natural gas company's proposal to use a cavernous rock formation about 3,800 feet below ground as a natural gas holding tank southwest of the former Sacramento Army Depot.

The document prepared for the California Public Utilities Commission notes that leaks, although unlikely, could occur in a populated area.

"There is insufficient information to conclude categorically that stored gas would not migrate to the overlying groundwater aquifer or ground surface," the EIR says. If that were to occur, there could be "groundwater impacts, health effects and potentially flash fires or explosions."

Among other "significant and unavoidable" impacts are that some pipeline segments also have a potential, albeit unlikely, for release of natural gas with resulting fire and explosion.

"The gas does not explode unless it's contained in a room or a building," said Donald Russell, president of Sacramento Natural Gas Storage, which is pursuing the project. "And there are no buildings near or over the pipeline or the wellhead itself."

The nearly 800-page EIR is filled with such technical language, listing impacts that can be avoided along with those that cannot.

It is the document that many in the neighborhood – along with attorneys and local elected officials – will scrutinize before giving their responses.

The state PUC must find there is a public convenience and necessity for the project to go forward.

The applicant also must get a permit from the city of Sacramento.

Most of the environmental impacts can be mitigated, and the report identifies alternative sites for underground storage and for interconnection pipelines.

Even the unavoidable impacts associated with potential leakage could be eased with extensive ongoing monitoring and testing, the report says.

But already there is resistance.

Some residents in the Avondale-Glen Elder neighborhood atop a portion of the 379-acre underground storage site have voiced concerns about the potential for leakage.

And Sacramento City Councilman Kevin McCarty said Monday that because the land is populated with about 700 homes and a number of businesses, assessing public safety will be paramount.

"We want to be very diligent to make sure that it is safe," McCarty said. "From what research I've done, this is unprecedented, to go into an urban area and re-pump gas back into an abandoned (cavern)" that has been abandoned for decades.

The Florin gas field previously held natural gas, but that was extracted by several companies until 1987, when the supply was depleted.

Russell of Sacramento Natural Gas Storage countered that the practice of returning to reuse such storage sites is not uncommon.

"We've got about a half dozen similar underground natural gas storage projects in depleted reservoirs located beneath urban areas," Russell said.

He said the company will present that information when the EIR is discussed.

He also said that a portion of the report shows a greater potential for some problem than company officials believe is possible. Russell cited an example of what he said is the draft's "flawed" data concerning pipeline pressure.

"We will submit our comments pointing out the flaws," he said.

The company also needs signed agreements from the residents and business owners whose land sits atop the proposed gas storage field to, in essence, rent the space beneath their properties.

The company is offering $500 signing bonuses and ongoing annual payments.

The project is aimed at establishing a natural gas storage facility for Northern California that is strategically located, providing a 30-day supply in the event of disruption of service from the main supply pipeline that serves the area.

The Sacramento Municipal Utility District has signed up to store gas at the site, and Russell has said other customers are expected to sign up as well.

Tina Thomas of the land-use law firm of Remy Thomas Moose & Manley, which is providing pro bono legal help on behalf of area homeowners along with Legal Services of Northern California, said the firm will submit its comments to the state PUC.

"We're going to look at it with an eye on compliance with the California Environmental Quality Act," Thomas said.

"We'll be looking at whether they have adequately analyzed the impact, the feasibility, the mitigation measures, and whether they have looked at a reasonable range of alternatives."

Call The Bee's Loretta Kalb, (916) 321-1073.