BEACH AGITATION FOR CRUDE OIL REMOVAL FROM INTERTIDAL BEACH SEDIMENTS1

Abstract

ABSTRACT The Arco Anchorage crude oil spill in Port Angeles Harbor, Washington, on December 21, 1985 resulted in oil contamination of approximately 7,000 feet of sheltered beach along the south side of Ediz Hook. The oil penetrated into coarse-grained beach sediments within much of the intertidal zone. Typical oil penetration depths ranged from 2 to 12 inches, Hydrocarbon concentrations in beach sediments six weeks after the spill ranged from 50 to 20,000 ppm with a mean of 2,900 ppm (total weight basis). A beach agitation program was implemented to remove the oil trapped within pore spaces in the beach sediments. Various equipment was evaluated for beach agitation purposes, including raking machinery, rippers, and jetting apparatus. A bulldozer operating in shallow water with ripper teeth and a water jet system was found to be most effective. Beach agitation was accomplished in segments with each work area isolated by containment booms and sorbent materials. Oil liberated by beach agitation was recovered by sorbents, rope skimmers, and a vacuum truck. By this method, the entire 7,000 feet of affected beach was treated in six weeks. Chemical analysis of beach sediments before and after the beach agitation program indicated that the technique was very successful in removing the oil held in soil pore spaces. More than 74 percent of the crude oil was removed from areas of heavy beach contamination. Residual oil concentrations from less than 50 to 7,500 ppm remained following the beach agitation program, with a mean post-agitation oil concentration of 550 ppm. This oil, mostly adsorbed to soil particles, is not readily removed by agitation and is expected to decrease in concentration over time.