Subsidence Survey

Mont Belvieu is the main transport hub for liquefied petroleum gas (LPG) in the U.S., and it contains the largest storage area in the world. Due to its geographic location, it is linked to an expansive network of pipelines, facilities, and refineries in the region. Within the Mont Belvieu area is Barbers Hill Salt Dome, a critical underground storage facility for LPG since 1951. In 2013, Fenstermaker was hired by WSP USA to perform a First Order Class II Level Survey on monuments and wells located on the Barbers Hill Salt Dome. The purpose of this survey was to provide accurate survey elevations to determine subsidence rates for the Dome.  The survey consists of obtaining elevations on one hundred forty-five existing monuments and one hundred fifty-eight wellheads. 

Before our crews access the project site, Fenstermaker’s field crews complete site-specific safety programs designed to provide general facility information, identify facility hazards, and also educate them on what precautions to get given a specific incident.

Once the safety training is complete, Fenstermaker field teams utilize digital level and RTK/GPS survey technology to complete the project. This extensive survey consists of over 62 miles of level loops with an average closure of 0.002 feet. Because of the large areas we are required to cover for this project, 3 to 4 field crews are utilized over approximately 6 weeks in order to collect the required information. This data was cataloged and compared to previous years’ elevations and analyzed by WSP U.S.A. to determine subsidence rates for the Barbers Hill Salt Dome.  These monitoring surveys are performed yearly and have been conducted since 1987.