Borrow Area 1 Geotechnical Investigation for the Town of Hillsboro Beach, Florida

Core borings collected in February 2009 were combined with older data sets and a recent sub-bottom seismic survey to characterize the remaining sand resources in Borrow Area 1 (BA1) at the north end of Broward County, FL. The resources are medium to fine carbonate rich sands of a medium gray color. Sub-bottom profiles verified with the core borings were used to establish the isopach of clean sands in the borrow area. A potential of 1.12 million cubic yards of sand remain in sections at the north end, along the east side of the BA1, and in a section at the south end. The overburden of sand lies above a continuous limestone surface and varies in depth from 5 to 10 feet or greater. The central, west side of BA1 is a largely exposed limestone surface or a thin layer of sand above the limestone. A stratigraphic model constructed from the core borings provides a visualization of clean sand layers above a continuous limestone layer. The model demonstrates that rock rubble within the clean sand is a vertically restricted layer well above the limestone and is not a continuous lithified unit. It is recommended that the isopach data be used to design borrow cuts that are restricted to sections of BA1 containing 5 feet or more of sand over the limestone surface..