Report Number: 1
Year: 1976

Groundwater Resources of Guam: Occurrence and Development

No abstract was published. A slightly revised, abridged version of the Preface follows.

Since 1964, the Government of Guam has been engaged in the development of groundwater to supply the domestic needs of the island's civil sector. Demand has grown in excess of projections, requiring intensive effort on the part of the public utility agency and its subcontractor to satisfy the increasing call for water, especially in the northern part of the island. The government's actions to meet demand have generally been based on careful consideration of the nature of groundwater, but the pace of development has been too rapid to devote time to the comprehensive documentation and evaluation of groundwater resources based on the last decade's working experience. Without a probing evaluation of the extent and exploitability of the island's groundwater, speculation often replaces rational analysis as the instrument of decision-making, leading to inefficient investments and irreparable damage to the resource.

Based on information which has accumulated in the last decade, this technical report evaluates the island's groundwater resources, particularly northern Guam, in a manner which provides a utilitarian framework for decision-making by government agencies concerned with water supply. The following points are investigated:

  1. Review and critique available literature on water resources and their development on the island of Guam; relate recommendations of previous reports to status of knowledge at the time they were written.
  2. Review past groundwater development (prior to start of GovGuam's activities in 1964) and historical water usage.
  3. Describe and analyze of groundwater resources and the environments in which they occur, including analyses of climate, geology, aquifer properties, sustainable yields, water quality, contaminant concerns, extent of available groundwater, etc.
  4. Based on findings from #3, evaluate of means of resource development in order to maximize sustainable yields within reasonable technical and economic constraints.
  5. Review and critique current development practices, including location of production wells.
  6. Recommend standards of development.
  7. Propose sustainable methods of providing groundwater for future growth.

The scope of work funded by the contract with the public utility agency also included:

  1. Preparation of water level and salinity maps of northern Guam representing at least 2 periods of measurement, and interpretation of hydraulic gradient/direction, lens properties, location of hydrologic discontinuities which my compartmentalize the aquifer, and changes in regional water levels related to saltwater intrusion.
  2. Identification and evaluation of hydrologic stresses such as pumping, tides and recharge, and correlation with changes in fresh water head.
  3. Comparison of current data with historical records of water levels, rainfall, tides and pumping to identify and describe lens response to long-term stresses.
  4. Identification of areas of thick limestone aquifer containing fresh water under "true lens" conditions, as well as areas of shallow bedrock which might prevent lens formation or variation in groundwater response to hydrologic stresses.
  5. Description of occurrence and behavior of fresh water lens and other groundwater bodies as reflected by areas of present pumping and natural discharge.
  6. Description of subsurface conditions controlling groundwater occurrence and movement.
  7. Description and investigation of recharge, especially in pumped areas.
  8. Recommendations for siting new production wells and better management practices.
  9. Determination of need and suitable sites for deep, multiple-tube wells in order to monitor the change in the configuration of the lens.
  10. Design of long-term water data monitoring network.
  11. Characterization of groundwater geochemistry.
John F. Mink