Subsurface geology and hydrogeology of downtown Honolulu with engineering and environmental implications

he construction of high-rise buildings and other engineering structures in the downtown Honolulu area requires detailed site investigations prior to design and construction. This includes soil borings, environmental assessments, and groundwater measurements. As a result, much data on the subsurface geology of downtown Honolulu exists, but it is spread among individual consulting firms and various government agencies. The purpose of this study is to compile the existing data and interpret the subsurface geology, engineering geology, hydrogeology, and environmental problems within the study area.;This study commenced with collecting and interpreting 2,276 soil boring logs from consulting firms in Honolulu, along with the Groundwater Index database and environmental databases from the State of Hawaii. The subsurface materials are classified into nine categories: fill, lagoonal (low-energy) deposits, alluvial deposits, coralline debris, coral ledges, cinders, tuff, basalt, and residual soil or weathered volcanics. The study area is divided into 157 quadrangles (1000' x 1000'). The subsurface conditions within each quad are described in detail, and nine cross-sections are presented for further clarification of the subsurface geology. Foundation bearing layers and buried alluvial channels are mapped. Environmental problems and groundwater data are summarized in the form of tables and maps.;The coral ledges, tuff, and basalt are the most suitable foundation bearing layers within the caprock. The coral ledges, coralline debris, coarse-grained lagoonal sediments, and cinder sands are characterized by higher hydraulic conductivities than the other materials that comprise the caprock. However, the caprock as a whole is characterized by much lower hydraulic conductivities than the underlying Koolau basalt that is the main aquifer for the island. The caprock groundwater is brackish, non-potable, and highly vulnerable to contamination. Petroleum hydrocarbons and heavy metals from leaking underground storage tanks are the primary soil and groundwater contaminants. Caprock groundwater is generally found within...