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6.0 Impact Considerations Version :27.10.4 <br /> Mixed Sand and Gravel Beaches <br /> • Description <br /> • Because of the mixed sediment sizes on these moderately sloping beaches, <br /> there may be zones of pure sand, pebbles, or cobbles. <br /> . There can be large-scale changes in the sediment distribution patterns <br /> depending upon season, because of the transport of the sand fraction offshore <br /> during storms. <br /> . Desiccation and sediment mobility on exposed beaches cause low densities of <br /> attached animals and plants. <br /> . The presence of attached algae, mussels, and barnacles indicates beaches that <br /> are relatively sheltered, with the more stable substrate supporting a richer biota. <br /> • Predicted Oil Behavior <br /> • During small spills, oil will be deposited along and above the high-tide swash. <br /> . Large spills will spread across the entire intertidal area. <br /> • Oil penetration into the beach sediments may be up to 50 cm; however, the <br /> sand fraction can be quite mobile, and oil behavior is much like on a sand beach <br /> if the sand fraction exceeds about 40 percent. <br /> • Burial of oil may be deep at and above the high-tide line, where oil tends to <br /> persist, particularly where beaches are only intermittently exposed to waves. <br /> . In sheltered pockets on the beach, pavements of asphalted sediments can form <br /> if oil accumulations are not removed, because most of the oil remains on the <br /> surface. <br /> Response Considerations <br /> • Remove heavy accumulations of pooled oil from the upper beachface. <br /> . All oiled debris should be removed; sediment removal should be limited as much <br /> as possible. <br /> • Low-pressure flushing can be used to float oil away from the sediments for <br /> recovery by skimmers or sorbents. High-pressure spraying should be avoided <br /> because of potential for transporting contaminated finer sediments (sand) to the <br /> lower intertidal or subtidal zones. <br /> • Mechanical reworking of oiled sediments from the high-tide zone to the upper <br /> intertidal zone can be effective in areas regularly exposed to wave activity. <br /> However, oiled sediments should not be relocated below the mid-tide zone. <br /> • In-place tilling may be used to reach deeply buried oil layers in the mid-tide zone <br /> on exposed beaches. <br /> Shell Supply and Distribution 6-41 Stockton Terminal FRP <br /> ©2019 Witt 0' Brien's Revision Date:October, 2019 <br />