WRRCTR No.126 Groundwater Resources of Kwajalein Island, Marshall Islands

Abstract

To evaluate the long-term sustainable yield of the Kwajalein groundwater body, and also to investigate methods of optimum development of this resource, a total of 23 observation wells was constructed, from which the thickness, areal extent, and quality of the Kwajalein groundwater lens was monitored. During the past year, freshwater storage in the lens has averaged 1.02 x 10^6 m^3 (270 mil gal) and has fluctuated more than 20% in response to recharge and discharge events. Because of the short period of record presently available and the large seasonal fluctuations, it has not been possible to determine if long-term changes in lens storage are occurring, and this can be determined only after a longer period of data becomes available. Recharge was also evaluated and during the July 1978 to June 1979 period, recharge to the fresh groundwater lens was estimated to be 8.93 x 10^5 m^3 (236 mil gal) which is 52% of the precipitation during this period. In addition, the areal distribution of recharge was found to be quite uneven with some areas adjacent to paved surfaces receiving recharge at rates as much as four times greater than other areas. A concentrated effort was made to evaluate sustainable yield; however, the length of record presently available is simply too short to provide an accurate measure of sustainable yield for the Kwajalein groundwater body. It appears almost certain, however, that sustainable yield is greater than the present rate of annual pumpage (1.25 x 10^5 m^3 [33 mil gal] during the 1978-1979 pumping year), and rough estimates indicate that it may exceed 1.89 x 10^5 m^3 /yr (50 mil gal/yr). To more precisely define the Kwajalein sustainable yield, it is recommended that the lens monitoring program established during this study be continued for at least the next few years.