The approximately 750-acre island supports 11.6 billion cubic feet of LNG storage, a regasification plant, two domestic distribution pipelines, a 44-acre Ship Slip and 33-acre Turning Basin in the Savannah River, and two 120-acre dredge material containment areas (DMCAs). The salt marsh restoration was required in order to meet environmental mitigation requirements for expansion of one DMCA in order to achieve the long-term (minimum 25 years) of planned disposal capacity for maintenance dredging operations.

In order to maintain disposal capacity for the DMCAs, dike raisings to a finished height of 62 feet (mean low water) are ultimately required. In order to maintain stability of these dikes, the DMCAs require horizontal expansion of counterweights. The planned counterweight extension however necessitated the filling of 6.11 acre of tidally influenced salt marsh ditch. With no source of third-party mitigation available for the salt marsh ditch impacts, Geosyntec proposed that SLNG pursue permittee-responsible on-site mitigation for salt marsh ditch impacts. This path required our team to develop a credit calculation methodology using a hydrogeomorphic assessment methodology (HGM) that assesses the form and function of the resources to be impacted and a reference tidal salt marsh on the island in order to develop a compensatory mitigation ratio for determining the size of the required mitigation area.