Cleaning up gasoline contamination at the downtown Santa Fe site for a new District Court complex will take two to three years and cost about $5 million, officials said Thursday.

Construction of the courthouse and an underground garage stalled last spring after workers discovered a plume of pollution thought to have been left by gas stations once located in the area.

Officials from the New Mexico Environment Department and Santa Fe County outlined the cleanup process during a meeting Wednesday at the construction site on Montezuma Avenue between Cerrillos Road and Sandoval Street.

Crews currently are building a massive "grout curtain" around the footprint for the planned structure.

The 22-foot-high concrete wall, which will begin about 20 feet below the surface, is designed to keep water and hydrocarbons from entering the site.

Once the wall is complete, the county will begin remediation work within the walled area. Contaminated soil — which must be removed to make room for the bottom floor of a two-level underground parking garage — will be trucked to a landfill at Rio Rancho. Uncontaminated soil will be brought into replace it.

Contaminated water will be treated on site and discharged into an infiltration gallery, a gravel-filled trench that will allow the water to seep back into the ground. If there is more water than what can be handled by the infiltration gallery, it would be discharged into the nearby Santa Fe River. Santa Fe County is awaiting approval of the permit that would allow the discharge into the riverbed. Discharged water will be tested daily to make sure it meets groundwater quality standards.

When that process is complete, construction on the $38 million courthouse building will finally start.

In the meantime, the New Mexico Environment Department will conduct its own effort to remediate the land around the building site.

That process will entail putting up two structures — one on the north end of the plume near the Law Enforcement Complex that houses the District Attorney's Office and one on the southeast corner of the site near the Albuquerque Journal North building — which will house equipment.

The state's clean-up method will involve drilling into the ground and vacuuming gasoline fumes to the surface where they will be burnt off into the atmosphere. That process will take place in buildings constructed for that purpose. The machine that burns the fumes will have venting stacks that will protrude from the equipment structures and release the exhaust from the spent fuel about 10 feet above the roofs of existing buildings in the area.

Consultants said Wednesday said some noise and fumes will be part of that process, which will last two or three years. The money to pay for the $4 million cost of the decontamination will come from the state's Corrective Action Fund.

The county's portion of the clean-up cost will be about $1 million. Santa Fe County plans to pursue a $350,000 grant (partially from federal economic-stimulus money) to defray that cost.

The courthouse building is expected to be completed by May 2012.

Contact Phaedra Haywood at 986-3068 or phaywood@sfnewmexican.com.