ABSTRACT
From July 1985 to August 1986 Thums Long Beach Company disposed of waste drilling muds and cuttings in San Pedro Basin of the Southern California offshore area. Higher costs for onshore disposal had made ocean disposal economical during a multi-well drilling program. Ocean dumping was discontinued due to a decline in drilling activity.
Ocean dumping was conducted according to conditions of a U.S. Environmental Protection Agency (EPA) Ocean Dumping Permit for disposal of specific types and amounts of drilling muds and cuttings. A dumpsite specifically for muds and cuttings was designated by the EPA and is located 16 miles from Long Beach Harbor in water depth of 3000 feet. The disposed material consisted of water-based drilling mud and formation cuttings. The drilling mud was similar to Generic Mud #7, one of eight generic muds established by EPA for use in the National Pollutant Discharge Elimination System permit program. The cuttings were from unconsolidated sandstone and shale formations. Disposal of muds and cuttings was via a specially designed barge that can hold up to 6000 barrels of waste material. The muds and cuttings were blended together when loaded onto the barge and the, slurry was pumped overboard through a hose that extended below the water surface.
Ocean monitoring was conducted at the dumpsite during the three year permit period. Ocean monitoring included seafloor sampling and testing, water sampling from surface to 3000 feet, continuous water column profiling, and field verification of the discharge plume model. Results of the water quality and benthic monitoring program show that ocean dumping operations conducted by Thums in San Pedro Basin appear to have had no significant impact on the marine environment. Results of the discharge plume verification study show that the plume was rapidly dissociated and diluted below detection limits.
