In a short letter to the administrator of the Environmental Protection Agency, Sen. Barbara Boxer has demanded to know how the federal agency will keep people from being exposed to the metals and radioactive isotopes mixed into the huge waste pile at a former metals recycling plant in Oxnard.

The EPA recently recommended that Halaco Engineering's more than 40-acre site next to Ormond Beach be included on the national list of Superfund cleanup sites. The California Democrat's letter comes as the agency is taking public comments on the proposed listing. Public comment ends May 7.

"Given the amount and type of dangerous wastes, the facility's history of violations, uncontrolled human exposures, and off-site contamination, EPA must immediately determine the extent of the threat and do everything possible to clean up and protect public health," she said in the letter, noting that last summer, there was "evidence of rampant trespass" at the abandoned facility.

The now-bankrupt company operated at the site for 40 years. It halted operations in 2004, leaving behind 750,000 cubic yards of waste in a slag heap covering more than 28 acres, in some places higher than 40 feet, and laden with lead, arsenic, barium, cadmium and beryllium. The waste is also sprinkled with radioactive isotopes like thorium and cesium. Last week, federal workers found some of that radioactive material along a berm near the wetlands next to the facility, resulting in the closure of the wetlands at the end of Perkins Road.

Rob Wise, EPA's on-scene coordinator working to stabilize the site, said he and his crew have posted "no trespassing" signs and reinforced a fence. Crews have been out with bulldozers pulling back the edge of the waste pile so that it does not move into the adjacent wetlands, and plan to cover the material with a natural fiber to ensure that dust or runoff doesn't move off the site.

The $4.5 million stabilization project will be finished at the end of April and should protect the waste for about three years while officials figure out how to clean it up in the most cost-effective and safest way possible, he said.

As for the radioactive thorium, Wise said workers will dig it out and move it to the waste pile, where it will be buried. Last week, he learned from former Halaco officials that the thorium likely wound up there during the 1960s, when the company pumped waste from its facility directly into the Oxnard Industrial Drain, which bisects the property. It stopped doing that in 1970, Wise was told.

Marvin Burns, an attorney representing former Halaco owners, wrote Gov. Arnold Schwarzenegger in December opposing the Superfund listing. Halaco had been unfairly targeted by regulatory agencies while other neighboring industrial businesses were left alone, Burns said in the letter.

Those businesses are "all spewing out enormous quantities of waste every day," Burns said. "We are confident those plants discharge hazardous substances each day ‘above background' as the EPA letter complains about Halaco. So far as we know, no one has attacked those other businesses with the intensity that attacks on Halaco have been made."