Ground Near San Marcos Dump Safe, Study Shows : Environment: County must now show proof that expansion of the landfill would do no harm.

Environmental studies released Tuesday showed no surface or underground seepage from North County’s only trash dump.

Superior Court Judge James R. Milliken halted expansion of the San Marcos landfill in September, ordering the county to show that there is no present pollution or any danger of future pollution from the landfill if the dump is expanded.

County supervisors have approved doubling the capacity of the San Marcos landfill, which will reach capacity early in 1992. The new sections of the dump would have lined basins to prevent leaching of materials into the soils, but the existing landfill section, which would be raised to 900 feet elevation, has no such protection.

Edward Severson, county public works engineer, said that the draft environmental study released Tuesday would be subjected to 30 days of public comment before being presented to the Board of Supervisors on Dec. 17. Judge Milliken has ordered the county to show proof by Dec. 2 that the expansion would do no environmental harm.

In the supplemental study, 10 additional monitoring wells were drilled around the San Marcos landfill to check on subsurface contamination. Plans also call for all surface runoff to be contained by a perimeter drain that would direct the water to on-site detention basins. The containment basins would be capable of containing runoff from a 100-year flood, a rainfall that meteorologists estimate would occur only once a century.

If runoff from the landfill surpassed the storage capacity, a pumping system would be developed to handle additional flows, the supplemental report stated.

With approval of the landfill expansion, the San Marcos site should be capable of handling the North County’s trash at least until the 21st Century, the report stated.

In addition to the Superior Court approval, the expansion plan also requires a permit from the Regional Water Quality Control Board.