WRRCTR No.129 Underground Residence Times and Chemical Quality of Basal Groundwater in Pearl Harbor and Honolulu Aquifers, O'ahu, Hawai'i

Information on the large-scale movement and origin of groundwater in southern Oahu was obtained by examining the natural isotopic and chemical composition of water samples. Six basal groundwater systems (Pearl Harbor, Moanalua, Kalihi, Beretania, Moiliili, and Waialae) were studied and are discussed in this report. The experimental data base comprises the analyses of 84 groundwater samples, 2 surface water samples, and 49 rain-water samples for the following parameters, radiocarbon (l4C), carbon 13 (13C), tritium (3H), major ions, nitrate, silica, and pH. These data were supplemented with isotope and chemical data obtained in previous studies and selected data from the literature. Carbon isotope data, radiocarbon and carbon 13, on basal groundwater samples were evaluated with respect to "recharge reference" values. The latter were established on the basis of isotope analyses of water samples obtained from inland sources, such as tunnels tapping high-level dike compartments or wells located close to the mountains. Tritium data on basal groundwater samples were evaluated with respect to values for local rainfall and the recharge reference. Radiocarbon dating was used as an index of age to identify those groundwaters whose underground transit or residence times are in excess of about 200 years. Radiocarbon and tritium were used to identify young water, less than 20 yr old, through the detection of artificially high radiocarbon and tritium activities resulting from atmospheric testing of nuclear weapons during the past two decades. Underground residence times of basal waters in the Kalihi, Beretania, and Moiliili systems are quite long compared to the residence times of the other systems. Rain water infiltration in regions of high elevations located far inland is a definite source for most of the recharge to these systems. Basal water in the Waialae system has a short residence time compared to the other Honolulu systems. Moanalua basal waters were not uniform in their isotopic and chemical characteristics and indicated very long as well as very short residence times. Basal water in the western, inland portion of the Pearl Harbor system is similar in underground residence time to that in the Kalihi, Beretania, and Moiliili systems but water in the eastern and seaward portions is characterized by short residence times and, in many cases, the presence of young water. Many regions in this basal water system and, in part1cular, the eastern part, show the presence of transition-zone water, return irrigation water, and caprock-type water, either singularly or in some combination. Simple mixing models utilizing several suitable chemical parameters made it possible to determine the possible origins of water present in the discharge of a selected source or the presence of a particular type of water in the discharge of several sources located within a few miles of each other.Board of Water Supply, C&C of Honolulu; Oahu Sugar Co., Ltd.; Naval Facilities Engineering Command, U.S. Navy; and the Div. of Water and Land Development, State of Hawaii Grant/Contract No. 14-31-0001-381

WRRCTR No. 53 Tritium and Radiocarbon in Hawaiian Natural Waters: Part I

A field investigation was undertaken to establish the present tritium and radiocarbon activity levels of natural waters found in various parts of the island of Oahu. The instrumentation required for the radiocarbon analysis was assembled and workable procedures were developed. Monthly rainwater samples obtained from rain gages on the Koolau Range contained seasonally fluctuating tritium concentrations which are well in excess of the natural abundance level. Excess concentrations were also found for the tritium and radiocarbon content of surface waters from three separate sources. These excess concentrations are the result of fallout from atmospheric nuclear explosions. Samples from nine tunnels, which tap various Koolau dike compartments, contained tritium activities ranging from the current rainwater levels down to the pre-nuclear explosion levels. Most samples showed radiocarbon activities comparable to pre-explosion atmospheric C02 levels. Two samples, however, showed excess radiocarbon. Samples from wells and shafts tapping basal water in the Honolulu area generally showed little or no tritium and their radiocarbon concentrations were lower than those of the dike-water samples. Makiki, Booth, and Roseapple Springs, which discharge perched water, exhibited tritium levels slightly in excess of the contemporary rain water levels. Nuclear explosion radiocarbon was present at Makiki Spring whereas it was absent at Booth Spring. Correlations between radiocarbon and chloride content were found for samples from Central Oahu and the Pearl Harbor area. The magnitude of both constituents were moreover a function of the distance between the sample source and Pearl Harbor. Three multiple depth samples from well T-133 at Ewa Beach showed very low radiocarbon content. These results can be evidences of radioactive decay of the radiocarbon thus indicating very long residence times of these waters. Exchange reactions between the water-carbonates and the radiocarbon-free aquifer carbonates can lead to the same results however. The discovery of a linear relationship between the radiocarbon activity and chloride contents of these samples indicates that chemical exchange reactions have taken place.OWRR Project No. B-016-HI, Grant Agreement No. 14-31-0001-3271 The programs and activities described herein were supported in part by funds provided by the United States Department of the Interior as authorized under the Water Resources Act of 1964, Public Law 88-379

WRRCTR No. 65 Tritium Measurement of Natural Waters on Oahu, Hawaii: A Preliminary Interpretation (Sampling Perio: July 1969 to June 1970)

Water samples collected from various surface and sub-surface sources on the island of Oahu were analyzed for tritium levels. Tritium activity levels in twenty-five monthly rainwater samples show a seasonal dependence with a maximum in the summer (18.5 to 23 TU) and a minimum in the winter (12 TU). Samples from two surface-water reservoirs had activities of 13.2 and 19.7 TU reflecting contemporary rainwater which is their major source of recharge. Four streams in the Pearl Harbor area showed "rainwater" tritium levels when sampled at high flow. At low flow, two of the streams had low tritium levels indicating ground-water discharge into the stream, while the tritium activity of the other two streams was conparable to rainwater. Tritium activity higher than that of contemporary rainwater (22-38 TU) was exhibited by samples from two springs which discharge perched water, while samples from three wells and two shafts in the Honolulu area showed very little or no tritium activity. Multiple-depth samples obtained from wells in the Pearl Harbor area showed correlations between tritium activities, depths of sampling, and chloride concentrations.OWRR Project No. A-021-HI , Grant Agreement No. 14-31-0001-3011 The programs and activities described herein were supported in part by funds provided by the United States Department of the Interior as authorized under the Water Resources Act of 1964, Public Law 88-379

WRRCTR No.34 Some Measurements of the Tritium Content in the Natural Waters of Southern Oahu, Hawaii

An analysis was made of the tritium content of samples from various sources of surface and subsurface waters of the island of Oahu. Twenty rainwater samples collected from various rain gages located on the Koolau Range over a period of four months showed an activity between 16.3 and 28.2 tritium units. Samples from four streams in the Pearl Harbor area ranged from 14.5 to 21.3 tritium units, while samples from two springs and five wells in this same area all showed an activity below 5 tritium units. The instrumentation consisted of an electrolysis enrichment apparatus, a vacuum distillation unit and a liquid scintillation counter. A detailed description is given of the various parts of the electrolysis apparatus and the vacuum distillation unit. Both the enrichment and counting procedures are reviewed as well as the calibration of these systems.U.S. Department of the Interior Grant/Contract No. 14-01-0001-1630; A-016-H