Experimental Design and the Retention of Oil on Arctic Test Beaches

Abstract

Oil was laid down in a series of experiments at CHapaet t, Baffin Island, N.W.T., on pairs of control plotisn the upper intertidal zonea t four beach sites, each with a different wexapvoe sure, and on backshore pairs of control plaott stw o sites.T he control plots were established as a bfoars is comparison with a serioef si ntertidal shorelinec leanup experiments. Sites with different wave-energy exposures were selected itno porrodveird e a range of energy level environments anda lso a variety of intertidal sediment characteristicTs.h e experimental design of this phasoef the project attemptedt o reproduce conditions similar to those that would result from a large spiella.c hA tl ocation one plot was oiled with an aged Lagomedio crude oil and the other with an emulsion of water in aged crude oil. Replication of total hydrocarbon (t-h) analytical results within and between plots initially proved difficult due to the variabilityo f grain size and to the presence of pooled oilo n the beach surface. Although the subsequent collectiono f large (2.4 1) composited samples reduced this elemoefn vt ariability in the td-ha ta sets, changes through timoer differences between plots were considered significant only if these were in the range ofo rodneer of magnitude or greater. At the gravel beach sites the initial retention of oil on the intertidal emulsion plots was considerably less than on the aged oil plots, probably as a result of the different adhesion properties, viscosity and density of the emulsified oil. Observations and measurements indicate that there was a maximum loading of oil that ist o b beeli e av e fdu nctiono f (1) the sizeo f sediments and of the surface interstitial spaces; (2) the surface properties of the sediment particles (including wetness and dryness of the surface()3; ) the level of the water table; and( 4) the type and volume of the oil. On the most oefx tphoes feodu r intertidal locationso ver 99% of the spilled oil was removed from the surface of the plots within4 8 h. This removal was due to the mechanical energy of wave acatniodn t o sediment redistribution (erosion). At the more sheltered sites, oil was removed by rising tides after application of the oil. Rates of oil removal from the two sheltered beaches varied independently of wave exposure. Observations and analytical results indicate athftaetr seven or eight days dispersion ande dge effects became significant on the intertidal plots. Data from the intertidal plots, therefore, were consitdoe redp licate patchyo il contamination and were not representatoivf el arge natural spill situations beyond one week after the oil was laidd own