Case Study of Use of Offshore Wells for Monitoring Submarine Groundwater Discharge, Indian River Bay, Delaware

A project to characterize the physical and chemical attributes of submarine groundwater discharge (SGD) has developed and tested techniques and materials for drilling and installation of standard and multi-channel wells in offshore locations in Indian River Bay, Delaware.  Key requirements for these wells are that they remain in place and accessible for the 3 year duration of the project and that exposure to hazards of the open water environment is minimized.  Difficulties caused by shallow water depth, recreational boat traffic, and fishing activity affected drilling procedures and wellhead design.

Project staff have now drilled, logged, installed, and sampled 4 standard and 8 7-channel wells to depths of nearly 20 m below bottom in water depths up to 1.3 m and distances up to 225 m from the shore of Indian River Bay.  Downhole geophysical logs and well samples have documented the presence of a vertical salinity profile that crosses two salinity interfaces: saline (30-45 mS) to fresh (1-3 mS) at depths of 2-6 m below bottom and fresh to saline at depths of 9 to 13 m below bottom.  Physical and chemical measurements in an additional 14 wells installed onshore are being used to characterize the flow field and geochemistry of the freshwater system.  This work is integrated with broader project efforts to characterize SGD that include experiments using marine and land-based geophysics, seepage meters, pore-water samplers, geochemical analysis, and numerical simulation.