Mitigating For Construction Impacts Of An Offshore Pipeline In The Gulf Of Mexico

The Gulfstream Natural Gas Pipeline System (Gulfstream) has undergone four phases of development and is designed to deliver environmentally preferable natural gas to fuel new electric generating capacity throughout peninsular Florida in the United States. Phase I of Gulfstream's 726-mile pipeline originates onshore in the states of Mississippi and Alabama, crosses the Gulf of Mexico, and makes landfall in the state of Florida. AECOM, under contract to Gulfstream, has monitored post-construction disturbance and re-colonization of sessile epifauna/epiflora onto the disturbed pipeline, spoil mound, and anchor strike areas where hard-bottom habitat was encountered. During the permitting of Phase I of the pipeline, recovery of impacted offshore hard-bottom communities was conservatively predicted to take 100 years due to the lack of information about offshore pipeline construction impacts at the time. Previously published monitoring data for this project has revealed that within less than five years, the community structure had recovered in equivalence to non-impacted areas, and has already met the defined criteria of recovery (80-percent similarity to non-impacted hard-bottom areas). This information was used in support of determining the appropriate amount of habitat creation that would be required to mitigate for hard-bottom impacts during construction of Phase IV of the pipeline, an offshore lateral to the Phase I line. The purpose of this paper is to provide an overview of how the data from Phase I was used to provide an explanation as why the impacts appear to be less than initially expected, lessons learned concerning the appropriate assessment methods for determining post-construction impacts, and an interpretation of appropriate mitigation habitat. Most importantly, the paper also demonstrates how the type of information that was collected following Phase I can be applied to mitigation assessment methods and the defining of mitigation requirements