Ghost Shrimp Bioturbation and Effective Contaminated Sediment Cap Design

Abstract

Ghost shrimp are deep burrowing crustaceans whose activities are commonly identified as a potential obstacle to the effective isolation of contaminants at sediment capping or confined aquatic disposal remediation projects. Although many individual capping projects have addressed or discussed this issue and incorporated site-specific design elements to protect against potential ghost shrimp bioturbation, there has been no thorough review of ghost shrimp natural history relative to its implications for capping design in general. Due to this information gap past cap designs have often been unnecessarily conservative in several design elements, particularly cap thickness. This paper reviews the current understanding of ghost shrimp natural history on the west coast of North America including preferred habitat types and bioturbation activities. From this information, cap design criteria and guidelines to protect against ghost shrimp bioturbation are presented that can be applied to a variety of capping situations. Design criteria and guidelines include: required cap thickness in various situations, water depths and environments that often have high rates of ghost shrimp bioturbation, and cap materials that reduce or prevent ghost shrimp burrowing activities or maximum depths. For cap thickness guidelines, the importance of differentiating between bioturbation that causes significant sediment turnover and observations of maximum ghost shrimp burrowing depths is also discussed. Natural history information is also used to better define reasonable requirements for long term monitoring of ghost shrimp presence and activities at capping projects.