REPORT DOCUMENTATION FORM University of Hawai'i at Manoa
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REPORT DOCUMENTATION FORM WATER RESOURCES RESEARCH CENTER University of Hawai'i at Manoa I SERIES 2COWRR NUMBER Project Report PR-99-05 FIELD-GROUP 08-D,08-E 3TITLE 4 REPORT DATE October 1998 Subsurface geology and hydrogeology of 5 NO. OF downtown Honolulu, with engineering and PAGES xii + 225 environmental implications 6NO. OF 7NO.OF TABLES 13 1 FIGURES 25 8 AUIHOR(S) 9GRANT AGENCY Sue A. Finstick U.S. Department ofthe Interior Geological Survey 10 CONTRACT NUMBER 14-08-0001-G2015 II DESCRIPTORS: subsurface mapping, engineering geology, hydrology IDENTIFIERS: subsurface geology, subsurface hydrology, environmental implications, downtown Honolulu, Oahu, Hawaii 12 ABSTRACT (PURPOSE, METHOD. RESULTS, CONCLUSIONS) In the downtown Honolulu area, detailed site investigations are required prior to the design and construction of high-rise buildings and other engineering structures. Hence, over the years, numerous soil borings, environmental assessments, and groundwater measurements have been conducted. As a result, much data on the subsurface geology of downtown Honolulu exists, but it is spread out among individual consulting firms and various governmental agencies. The purpose ofthis study is to compile the existing data and interpret the subsurface geology, engineering geology, hydrogeology, and environmental problems within the downtown Honolulu area. This study commenced with collecting and interpreting data from 2,276 soil boring logs from consulting firms in Honolulu, along with data from the Groundwater Index database and environmental databases maintained by the State ofHawaii. 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 (l,000 feet x 1,000 feet each). 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 tables and maps. Coral ledges, tuff, and basalt are the most suitable foundation-bearing layers within the caprock. Coral ledges, coralline debris, coarse-grained lagoonal sediments, and cinder sands are characterized by higher hydraulic conductivities than 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 forms the main aquifer for the island. The caprock groundwater is not only brackish and nonpotable but also 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 ±5 feet of sea level. Dewatering is often necessary at sites involving the construction of basements. 2540 Dole Street· Honolulu, Hawai'i 96822· U.S.A.· (808) 956-7847 AUTHOR: Sue A. Finstick Department of Geology and Geophysics 2525 Correa Road Honolulu, Hawaii 96822 Current address: Department of Physical Science 351 West Center Street Science Complex 309 Southern Utah University Cedar City, Utah 84720 $30.00/copy Please make remittance in U.S. dollars from a U.S. bank or international money order to: Research Corporation of the University ofHawaii Mail to: Water Resources Research Center . University of Hawai'i at Manoa 2540 Dole St., Holmes Hall 283 Honolulu, Hawai'i 96822 • U.S.A. Attn: Publications Office NOTE: Please indicate PR-99-05 on check or money order for our reference. SUBSURFACE GEOLOGY AND HYDROGEOLOGY OF DOWNTOWN HONOLULU, HAWAI'I, WITH ENGINEERING AND ENVIRONMENTAL IMPLICATIONS Sue A. Finstick Project Report PR-99-0S October 1998 Project.Completion Report for "Subsurface Geology/Hydrology of Downtown Honolulu: Engineering and Environmental Implications, Phases I and II" Funding Agency: U.S. Department of the Interior Geological Survey Grant No.: 14-08-0001-G2015 Principal Investigator: Frank L. Peterson WATER RESOURCES RESEARCH CENTER University of Hawai'i at Manoa Honolulu, Hawai'i 96822 The activities on which this report is based were financed in part by the Department of the Interior, U.S. Geological Survey (grant no. 14-08-0001-G2015), through the Hawai'i Water Resources Research Center. The contents of this publication do not necessarily reflect the views and policies of the Department of the Interior, nor does mention of trade names or commercial products constitute their endorsement by the United States Government. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author and do not necessarily reflect the views of the Water Resources Research Center at the University of Hawai'i at Manoa. ABSTRACT In the downtown Honolulu area, detailed site investigations are required prior to the design and construction of high-rise buildings and other engineering structures. Hence, over the years, numerous soil borings, environmental assessments, and groundwater measurements have been conducted. As a result, much data on the subsurface. geology of downtown Honolulu exists, but it is spread out among individual consulting firms and various governmental 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 downtown Honolulu area. This study commenced with collecting and interpreting data from 2,276 soil boring logs from consulting firms in Honolulu, along with data from the Groundwater Index database and environmental databases maintained by the State of Hawai'i. 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 (1,000 feet x 1,000 feet each). 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 tables and maps. Coral ledges, tuff, and basalt are the most suitable foundation-bearing layers within the caprock. Coral ledges, coralline debris, coarse-grained lagoonal sediments, and cinder sands are characterized by higher hydraulic conductivities than other.materials that comprise the caprock. However, the caprock as a whole is characterized by much lower hydraulic conductivities than the underlying Ko'olau basalt that forms the main aquifer for the island. The caprock groundwater is not only brackish and nonpotable but also 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 ±5 feet of sea level. Dewatering is often .necessary at sites involving the construction of basements. v ACKNOWLEDGMENTS This study could not have been completed without the cooperation of the consulting firms of Geolabs Hawaii, Dames & Moore, Ernest K. Hirata and Associates, and Hawaii Geotechnical Group. In addition, the State of Hawai'i's Department of Health and Department of Land and Natural Resources and the City and County of Honolulu's Board of Water Supply, Department of Transportation Services, and Department of Public Works, all provided assistance. To all, I express my sincere thanks. Furthermore, I thank Professor Frank Peterson, who initiated this project and provided guidance for all phases of the project; the Hawai'i Water Resources Research Center for grant funding for the project; April Kam and Nancy Hulbirt for the drafting; Karen Tanoue for report editing; Patricia Hirakawa for preparing the camera-ready copy; and GRG Corporation of Wheatridge, Colorado,for providing me with Stratifact, the software package used for analysis and presentation ofdata. vi GLOSSARY 'a 'a rough, jagged type oflava adobe . a stiff gray-brown clay that is moderately to highly expansive alluvium stream-deposited sediments beachrock well~cemented coralline sand that formed in the intertidal zone blue lava rock, blue rock a hard, slightly weathered, moderately fractured, vesicular dark-gray basalt caprock coastal plain sediments and post-erosional volcanics of southeastern Oahu clinkers rough or jagged fragments of lava; characteristic of the top and bottom of an 'a'a flow 'ewa to go in the direction of 'Ewa* (generally to the west of Honolulu) harbor muds, harbor sediments thick sequences oflagoonal deposits in situ formed or deposited in place kya thousands of years ago lagoonal deposits dark-colored, fine-grained, low~energy sediments that formed in a shallow body of water makai on the sea side, toward the sea, in the direction of the sea* marl clayey coral mauka inland, upland, toward the mountain* mudrock local driller's term for tuff . palwelwe smooth, unbroken type of lava* peat partly decayed vegetation puka hole*; void puka puka rock highly vesicular basalt river-washed tuff rounded fragments of tuff river gravel, stream gravel, gravel-sized rock fragments that have been abraded and rounded by stream river-washed gravel action saprolite a residual soil formed by in situ weathering of