GHS Annual Report 2017

N. C. Habana, Y. S. Kim, K. K. Bautista, and J. W. Jenson

Guam Hydrological Survey (GHS)

The GHS program management, WERI Director,and Research Affiliate has reorganized the program management to include undergraduate research assistant support.The undergraduate research assistants slot to be filled will assist the program management,supporting web development as GHS mandate part of data repository, access, and distribution.The Research Affiliate will utilize an undergraduate research assistant to manage data and field assistance. The Guam Hydrologic Survey office and computer hydro-laboratory at WERI had been remodeled to improve GHS functionality. Designated storage space and worktable has been built to organize and prepare valuable field equipment. Workstations and work space have been configured properly for research assistants in the environmental science program.A Guam geologic rock display section was built to improve collection and organization of the island’s rock inventory.This area is also designed as a small geology laboratory. GHS provides limited stipends for research by graduate students working on their MS degree in Environmental Science and partial summer salaries to WERI faculty advising those students. It also pays for undergraduate field and lab assistants working on water resources projects on Guam, and the salary of one full-time Research Affiliate is charged with operating and managing WERI’s information database, the hydrology laboratory, and preparation and update of routine reports and presentations. The program activities in this report begins with GHS Research Projects followed by CWMP Research Projects. The GHS section is organized into four sections: Northern Guam Lens Aquifer (NGLA)database, NGLA map series, Sustainable management, and Workshops.

GHS Research Projects

Research projects are grouped into four sections: database, maps, sustainable management, and outreach. The database organizes a borehole database, which is the basis of subsurface information, and a water resources library. It also includes the collection and organization of pertinent meteoric, hydrologic, and water quality data. The maps often summarize the data analysis, and it is truly an indispensable tool for water resource management. Sustainable management is a multi-faceted approach to quality sustainable water resource. The workshops provide training and outreach to our interagency partners. 

Northern Guam Lens Aquifer Database

The Borehole Database

Drilling and drill logs
Drilling and drill logs

The primary source of facts below the surface of the Northern Guam Lens Aquifer comes from borehole records. Technical Report 141, Bendixson et al., was a major feat in collecting and thoroughly organizing the subsurface factual information. It set a standard means of documenting and placing information in a most simple and logical arrangement. The filing system, table listing, and information categorization is easily updatable. Now, the database is available on the internet for anyone to access (, see also GHS CWMP Online section).  The Guam Hydrologic Survey mandates interagency cooperation with Guam Environmental Protection Agency (GEPA) such that new deep drillings into the aquifer will be properly and thoroughly documented/recorded and submitted the Guam Hydrologic Survey. The cooperation positions WERI to work closely with drillers in assessing the geology and hydrologic potentials in pursuit of optimal production wells. Downhole video is now being used to find the most productive porous media in the borehole to determine the best placement and screening recommendations.   One of the priorities of the PL24-247 is maintenance and routine update of the Guam hydrological database and routine trend analyses of the data.  In response, is the ongoing project pertaining to the management and data analyses of the Northern Guam Aquifer Database. WERI Technical Report 141 is thus the first of a set of three related technical reports that provide basic information essential for successful development and management of the NGLA. In preparing the database over 4,000 pages of documents were scanned and organized into individual electronic folders for each of the 525 wells documented so far. These include 20 exploratory wells, 115 observation/monitoring wells, 212 drinking water wells, 39 agricultural/industrial wells, and 104 storm water management wells. Each well folder is electronically linked to its corresponding record in a Microsoft Excel® spreadsheet and webpage, which contains key engineering and hydrogeological data. To organize, classify, and relate the enormous amount of disparate data required development of a classification system for the data. The technical report is thus designed as a user’s manual for the database, providing a detailed description of the indexing system, along with definitions and conventions adopted or devised; data complexities, nuances, limitations; and assumptions and choices made in interpreting and classifying data. 

The database is also the primary data source for WERI’s topographic map of the basement rock beneath the aquifer, which is described in the second report in the series, Technical Report 142, Topography of the Basement Rock beneath the Northern Guam Lens Aquifer and its implications for Groundwater Exploration and Development. Creation of the map employed the latest data screening and spatial analysis techniques to evaluate 697 records, from which 173 control points were applied to the map. The new map updates the boundaries of the aquifer’s six groundwater basins and provides for more accurate demarcation within each basin of its basal zone, where freshwater is underlain by saltwater; para-basal zone, where freshwater is underlain by basement rock below sea level; and supra-basal zone, where conduits and discontinuous patches of freshwater are underlain by basement rock above sea level. The new map also incorporates new insights regarding groundwater occurrence gained from the broad-ranging 2010 Exploratory Drilling Program funded by Naval Facilities Engineering Command Pacific. The report concludes with recommendations regarding groundwater exploration, aquifer development, and maintenance and improvement of the basement map. With the compilation of additional data, including well locations and water table contours, the basement map has been re-designated as the Northern Guam Lens Aquifer Map. 

The NGLA Trilogy: Technical Reports 141 (aquifer borehole database), 142 (aquifer map) and 143 (aquifer salinity database).

GHS Support of Rehabilitation of GWA Wells

GWA is currently rehabilitating 10 wells that have long been out of service for various reasons: 

  • A Series wells: A-2, A-7, A-12 
  • D Series well: D-3, D-5, D-17, D-18 
  • F Series wells: F-17, F-18 
  • M Series wells: M-9 

The well rehabilitation program plan is to install newly drilled wells at the same facility, generally less than 20 feet from the original borehole. Valuable new information on aquifer properties and well design is being gathered, and new approaches to drill logging, geologic and hydrologic evaluation are being practiced. Video logs of the borehole records will now be available and accessible in GHS aquifer database. Borehole records (documents, drill logs, pump tests, videos, and geologic descriptions) will now be available online for the professional community to access. During the preparation stage, the borehole database online was instrumental in bringing together WERI scientists, GWA engineers, the drillers, and supporting engineering consultants and to assess and interpret subsurface information, helping promote the success of the well rehabilitation program. 

Northern Guam Lens Aquifer Map Series

By far the most important tool for successfully locating new wells that will deliver sufficient volumes of high-quality water from the Northern Guam Lens Aquifer is an accurate and precise set of maps on which basic data can be assembled. The updated mapping of the volcanic basement rock that forms the floor of the aquifer (Vann et al., 2014) was a major breakthrough for developing the Northern Guam Lens Aquifer Map.  

Northern Guam Lens Aquifer Map

The volcanic rock beneath the water-bearing limestone partitions the aquifer into semi-contiguous subterranean catchments, or basins. On the slopes of the basement rock standing above sea level, where the base of the aquifer thus lies above sea level, downward percolating fresh water becomes concentrated in basement valleys and at the base of the slopes, where it enters the lip of the fresh water lens. The rim of fresh water thus concentrated along the boundary of the volcanic basement and the water-table near sea level is underlain by volcanic rock rather than sea water. This para-basal water is thus fresher, thicker and much less vulnerable to salt-water contamination than the basal water downstream, which floats on the underlying sea water and becomes progressively thinner and saltier until it discharges at coastal springs and seeps. Water flowing down the flank of the volcanic slopes above sea level, designated supra-basal water, is the freshest of the water in the aquifer and is completely invulnerable to contamination by sea water. The first detailed map of the basement topography was produced as part of the 1982 Northern Guam Lens Study. Beginning in 1998, with the establishment of the Guam Hydrologic Survey by the 24th Legislature, WERI began updating and revising the 1982 map based on new data and insights acquired by exploratory drilling, the emplacement of new monitoring wells, and other data obtained incidental to ongoing local aquifer development and military installation environmental remediation projects. Most recently, the exploratory drilling program undertaken by the US Navy in 2010 in support of the anticipated military build-up provided additional new control on the elevation of the basement in crucial locations. Moreover, the new Guam Groundwater Availability Study led by the USGS Pacific Islands Water Science Center, in collaboration with WERI, provided additional funding to update the database that supports the map. 

Outcrop on the summit of Mt Alutom, which gives its name to the entire unit of basement rock beneath the limestone plateau of northern Guam.

An accurate map of the basement topography is an essential prerequisite for building accurate and reliable groundwater models, which is one of the goals of the groundwater availability study. WERI first published the updated basement map in 2014, along with WERI Technical Report 142, which describes the supporting data, explains how the data were interpreted in developing the map, and highlights the map’s strengths and limitations. The aquifer map is actually a composite set of maps, which shows the basement topography as a component of aquifer geology, along with surface topography and structural features, and the locations of drinking-water production wells and aquifer observation and monitoring wells. The map is available on line and an essential tool for environmental scientists, hydrogeologists, engineers, regulators, and policy-makers for protection and sustainable management of the aquifer. 

Northern Guam Lens Aquifer map

Ongoing and Planned Work on the Hydrologic Map Set of the Northern Guam Lens Aquifer

The Northern Guam Lens Aquifer is Guam’s primary source of freshwater, and if managed properly will continue to supply the island’s daily water needs for generations to come. It is also a very complex hydrogeologic system. No single map can characterize this aquifer. Rather, a multi-layer analysis is required to describe, model, and manage the groundwater system. The development of a set of hydrogeologic maps that captures each of the components—while also providing a means for showing their inter-relationships—is of basic and utmost importance for successful exploration, development, and management of the aquifer. The creation of an up-to-date map of the basement topography (as described above) has provided the first step toward an integrated, multi-layered hydrologic map. The current map includes not only updates of the boundaries of the aquifer’s six groundwater basins, but also provides for more accurate and detailed demarcation within each basin of its three groundwater zones: basal, para-basal, and supra-basal. The 2013 update incorporated new insights gained from the 2010 Exploratory Drilling Program funded by Naval Facilities Engineering Command Pacific (AECOM Technical Services Inc., 2011), and the 2013 Guam Groundwater Availability Study (Gingerich, 2013; Gingerich and Jenson, 2010). The 2013 update also shows no-pumping water-table simulation from the modeling study to estimate the phreatic surface, hydraulic gradients, flow lines, and basin boundaries. The modeled lens geometry shows the estimated location of boundaries of the para-basal zone. Drill-logs and contours of supra-basal waters (ICF Technology, 1995) were also incorporated in the map. Occurrence of surface streams over the Hagåtña Basin and adjacent terrain were also included. Semi-transparent surface hill-shading provides a surface elevation perspective of the limestone plateau. Other hydrologic features that can be added to the current map or included in complementary maps in the set include hydraulic conductivities, geologic features, soils, porosities, pumping effects, land cover, and rainfall distribution. Priority is being given to the following, as research funding becomes available: 

LiDAR image of sinkholes and surface depressions (Haputo Bay area).
Sinkholes and Closed Contour Depressions

The first priority is a map of the sinkholes on the aquifer surface, which are elements of its natural surface drainage system. Spatial analysis of LiDAR-based digital elevation model allows a precise determination of closed contour depressions on the limestone plateau. Mapping these depressions and their relationships to other hydrologic and geologic features will be a major contribution to determining the distribution of recharge between fast vertical conduit flow channels and slow percolation through the bedrock. This is important for accurately modeling aquifer recharge and predicting potential contaminant entry and flow paths. 

Septic tanks and sewer lines, and wells
Wastewater System

Development on the surface of the NGLA is raising concerns over possible wastewater contamination, as residential and business wastewater discharged at the surface and near-surface may be a threat to the freshwater lens below. Increased and denser development may intensify wastewater discharge. The NGLA map and the layover of the wastewater system provides a useful assessment tool for contaminant transport. It was recently used in the initial assessment of PFOS (Perfluorooctane-sulfonic acid) contaminant source potential. The map may also be useful to determine prioritization of sewer systems. The wastewater system map over the NGLA map will help planners manage future development and reduce wastewater contamination. 

Sustainable Management of Guam's Water Resources

The Northern Guam Lens Aquifer (NGLA) provides 90% of Guam’s drinking water. The anticipated addition of US Marine Corps activities will require additional production, while ongoing economic growth will increase demand as well. Policy-makers and water managers have begun asking “what is the absolute maximum volume of water that could be sustainably withdrawn from the aquifer?” Answering such a question requires identifying (1) the natural limits on aquifer recharge, storage, and water quality imposed by climatic and geologic conditions, (2) , but doing it for an ideal production system, i.e., one that is constructed and operated so as to achieve the maximum possible production for a given standard of quality.

Numerical modeling to simulate effects of different extraction systems.

Assessing the Natural Limits on Aquifer Production

This study is directed at estimating the maximum potential capacity of the NGLA, i.e., the capacity that ultimately could be achieved by an ideal production system, given what we currently know or must assume about the natural limiting conditions. Recent modeling has incorporated the current state of knowledge regarding natural conditions and constraints. The current phase of the modeling project simulates maximum yield from the para-basal zone—the optimum location in the aquifer. In the next phase, estimates of maximum potential capacity can be made by exploring scenarios to evaluate the effects of changes in well depths, addition of new wells, and changes in pumping rates. This study will thus help provide some estimates of the absolute upper limits of production that could, in principle, be achieved by an optimum system. These will provide ultimate baselines against which to make economic evaluations of future options for holistic sustainable management of the aquifer. Upper limits to production, however, must be measured in terms of the quality of groundwater associate with a given production target, however. In island aquifers, the salinity of the water increases (thus the quality decreases) as production increases. The ongoing modeling study is thus directed at quantifying the trade-off between quantity and quality, which can ultimately be expressed as an assay function or assay curve. One of the objectives of the modeling study is thus to identify the assay curves for hypothetical alternative future production systems.

Notion assay curve for a coastal/island aquifer.


Sustainable development and management of Guam’s water resource is more than about hydrology. Next phase research requires analysis of production and quality will apply graphing assay curves. Determining limits to development will involve an economic assessment of alternative technology that may shift the assay curves into greater capacity. 

GHS Workshop Series

The military buildup and ongoing economic growth anticipated on Guam over the next decade has raised concerns regarding sustainable management of Guam’s groundwater resources. Besides educating policy-makers and agency heads, it is also essential that island water resource professionals and educators be equipped with an accurate and up-to-date understanding of the essential characteristics of the island’s aquifer and the factors that must be considered to frame and implement sustainable management practices. Professional people, including working-level technical professionals in the water resources industry, university instructors, and school teachers, have extremely limited time to engage in instructional opportunities. The GHS has thus developed a series of short-course workshops for local water resource professionals and educators. Instructional content can be tailored to specific audiences, but can include the following: 

Instruction and media organization is supported by the GHS website containing the instructional materials plus additional references and links to other relevant and useful resources, and forums for maintaining continuing educational interaction and information-sharing. 

Comprehensive Water Monitoring Program (CWMP)

The United States Geological Survey (USGS) has monitored Guam’s water resources since 1951. Unfortunately, during the 1990s they were forced to downsize this program because matching support from the Government of Guam was discontinued. This resulted in the abandonment of all deep monitoring wells needed to monitor saltwater intrusion in the north, and most of the stream gages in the south by the mid-1990s. In 1995, the USGS closed its field office at US Naval Base Guam, but continued to run a limited monitoring program (out of its Saipan and Honolulu offices). In August, 1998 the CWMP was made a permanent part of WERI’s program when the legislature enacted PL 24-247. This resulted in the refurbishment of the deep monitoring wells and a renewed program of water resource monitoring on Guam. The intent of PL 24-161 was to restore, and then to expand, as needed, the discontinued monitoring program in order to help Guam manage and safeguard all of its freshwater resources, now and in the future. Under PL 24-161, WERI/UOG and the USGS entered into a memorandum of understanding to administer and fund this program on a 50/50 cost-sharing basis. The CWMP is a permanent investment in Guam’s future. The loss of a hydrologic observation program has proven to be detrimental. Good hydrologic research studies and support for water management decision essentially require consistent and accurate data. Gaps in data can limits a really good analysis and interpretation. This was experienced in the modeling of the NGLA (Gingerich 2013), where more information in the Agafa Gumas basin could have greatly improved the accuracy of the simulation. The interest and value is now well recognized in the preparation for the expansion of groundwater monitoring with the addition of eight new observation wells (Appendix II). 

CWMP Research Projects

The CWMP program collects pertinent hydrologic data and applies analysis and interpretation. The analysis and interpretation is conducted in research projects that will contribute to the status our water resources and new findings. The CWMP program is organized into two components, the monitoring program and data analysis. 

Monitoring (Observation) Programs

The monitoring/observation program is improving. USGS-WERI continues to work as a team in collecting well hydrologic information. The Guam Water Resources Development Group and the Technical Experts Group are also currently discussing and preparing for installation of eight new observation wells. WERI and Guam Waterworks Authority (GWA) established cooperation in a Memorandum of Understanding, where GWA shares the monthly water production report and quarterly well water chloride concentration data. Wastewater-nitrogen data are now being logged in two production wells in the Yigo area.

Interagency Cooperation Agreements

Interagency cooperation and knowledge networking is very important for sustainably managing our water resources. GWA has a memorandum of understanding with WERI, an agreement to share their production, chloride, and other water quality data. The agreement further strengthens our long history of partnership in all efforts to improve water production and wastewater management. Guam Environmental Protection Agency MOU with WERI is soon to follow. 

USGS-WERI Observation Well Data Collection

USGS Pacific Island Water Science Center (PIWSC) and WERI are cooperators in the CWMP. PIWSC, with WERI researchers and research assistants, make quarterly (or when considered necessary, e.g., extreme climatic events, refined observance) well data collection (see observation well map).

Sites for proposed new wells, NW Field DW1 and AAFB DW1, in the Andersen and Agafa Gumas Aquifer Basins.

New Deep Observation Wells for the NGLA

In August 2016, the Guam Water Resources Development Group and Technical Experts Group agreed to stand up a field team to visit the tentative sites (marked by open circles in the maps below) within the general locations (marked by orange polygons) proposed by WERI and USGS for each of the eight new deep observation wells to be installed in the aquifer, and designate at each location a suitable site at which to drill each well (green circles with black dots). The team was led by WERI Senior Hydrogeologist, Dr. John Jenson, and included technical staff and consultants from Guam Waterworks Authority (GWA), Naval Facilities Engineering Command Marianas (NAVFACMAR), and the 36th Civil Engineering Squadron (36 CEV) Environmental Flight. Team members received training on Munitions and Explosives of Concern (MEC) on 13 Oct and 16 Nov 2016, and deployed to the field on 28, 29, and 30 Nov, and 20 Dec 2016. The report (Appendix II) was prepared and submitted to GWA, NAVFACMAR, and 36 CEV, with considerations and recommendations for each selected site. 

Nitrogen-Baseline Data

GPS coordinates of the designated well sites.

Preliminary inquiries have suggested that contaminants from anthropogenic sources are showing up in the NGLA. Much more baseline data are needed, though, to determine if the problem is greater in zones with sewer collection lines or in zones that rely on household septic tanks. Furthermore, from the current data it is not known if ammonium and nitrate levels in the environment are changing with time. Results do show, though, that ammonium is nearly absent in the groundwater, indicating that biologically induced nitrification is occurring in the environment. The presence of low levels of nitrate corroborate this, though there is no clear indication yet that denitrification is occurring. It is essential that these issues be studied before actions are taken to extend sewer collection lines or even build new wastewater plants in Northern Guam. In addition, the effectiveness of septic tanks is also an issue of concern. As an alternative to traditional septic tanks, consideration is increasingly given to use of single-family prefabricated, packaged treatment units. These units could serve to reduce the potential of contamination reaching the water table, and indeed test results of effluent from a prefab-unit on island show far cleaner discharge as compared to a conventional septic tank. Further comparative testing is to be conducted. 

Hourly nitrate-N and ammonium-N data at Well Y-3

Data Analysis-Interpretation Research

Thesis Project: Freshwater lens responses to influential natural elements (Dougher et al.)

This research project analyzes historical observation well and local meteorological data to examine the response of lens to natural elements (e.g., climatic cycles, tide, recharge) in the Yigo-Tumon Basin. The Yigo-Tumon Basin is the largest of the aquifer’s six basins, supplying 18 mgd, or 56% of the total production of 33 mgd from the NGLA (July 2016, GWA, Joe Garrido). Time-series data from the 35-year records for two salinity-profiling wells in the basin are being analyzed to gain insights into the timing, rates, and magnitudes of changes in lens thickness in response to seasonal, inter-annual, and episodic (storm) variations in rainfall. The study will thus help to identify the conditions and quantify associated parameters that determine the proportion of rainfall captured as recharge. Findings will support the development of effective sustainable management practices, including appropriate policy and management responses to storms and droughts. Improved understanding of observed lens dynamics will also help to improve the reliability of our groundwater models. The quantity of groundwater available for extraction can be measured in terms of the freshwater lens thickness. Lens thickness can be measured directly from well salinity profiles and inferred indirectly from water levels. The lens thins or thickens in response to storage changes from recharge and water withdrawal (production). The amount of recharge that replenishes the aquifer depends primarily on seasonal and inter-annual changes in rainfall. This project is evaluating how the volume of water stored in the freshwater lens responds seasonal changes in rainfall, isolated storms, and El Niño Southern Oscillation (ENSO) events and typhoons. 

Multi-variable time series analysis of lens thickness, observation Well EX-7

Thesis Project: Salinity Trends in the Yigo-Tumon Basin (Miller et al.)

This project with the Guam Hydrologic Survey continues the process of updating the production well and chloride concentration database for the NGLA. Its purpose is to examine the Yigo-Tumon basin for historical trends and potential influences on salinity. The Yigo-Tumon basin accounts for over half (17 mgd) of the production of the total production (36 mgd) from the aquifer’s six basins. The analysis focuses on natural influence/causes of salinity in production wells in the Yigo-Tumon Basin. We aim, in particular, to test the hypothesis that seasonality and the El Nino Southern Oscillation have a significant influence on the salinity in the wells. The Yigo-Tumon basin dataset is of major interest due to the area’s primacy in production volumes and demand. The knowledge gained from this work help to determine and suggest sustainable management practices for municipal water production the Yigo-Tumon basin. Understanding the NGLA response to the seasonal cycle will allow planners to plan new well configurations with greater confidence and to determine appropriate production rates for active wells with the overall goal to maximize production and better understand the risks associated with additional development in the Yigo-Tumon Basin. 

State of the Climate 2015-16 (Lander)

To read the full report, click here


FY 2017 Expenditures for GHS and CWMP