ESCONDIDO -- Removing the hazardous chemicals spilled last week on Interstate 15 near Deer Springs Road has turned out to be more intractible than originally thought, a spokesman for the California Department of Fish and Game said Wednesday.

The crux of the problem, said Robin Lewis, is the persistence of trivalent chromium, which laboratory analysis indicates is present at levels sufficient to injure or kill most of the aquatic life in the streambed that meanders along the eastern edge of Champagne Boulevard.

"We've got to get the chromium down," he said. "We just got our preliminary numbers back today and they indicate we still have some cleaning to do."

The streambed was lined with large stones, boulders and poured concrete several years ago, he said; the concrete is as much as six feet thick in places.

"We're toying with the idea of just putting in a layer of new cement and entombing what's there," he said.

Moviegoers who saw Erin Brockovich will remember the hazards associated with hexavalent chromium. Trivalent chromium is less dangerous, but an unsafe environmental contaminant nevertheless, he said.

He predicted completion of the cleanup by the end of next week.

Contact staff writer Edmond Jacoby at (760) 739-6675 or ejacoby@nctimes.com.