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GeoInsighter Fall 2002 Newsletter

USGS Seacoast Water Availability Assessment Project Begins

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A massive water resource assessment project has begun in the rapidly growing New Hampshire Seacoast Region that aims to characterize the availability and sustainability of water resources. The 3-year, 1.5 million dollar study is a cooperative effort between the United States Geological Survey (USGS), the New Hampshire Department of Environmental Services (NHDES), the NH Office of State Planning (NHOSP), and 42 Seacoast towns. USGS and NHOSP data show that the area has grown by 35 percent over the last 20 years, and this growth, coupled with the impact of a recent drought, has fueled fears that water demand in the region could soon exceed supply. Reports of reduced stream flows, declining water tables, drying wetlands, quantity impacts to water supply wells, and salt water intrusion heighten these fears. The study aims to address whether these fears are justified by inventorying Seacoast water usage/water resources and by refining the understanding of bedrock aquifer hydrogeology. 

Much of the study is aimed at consolidating water resource data that already exists and filling in data gaps where important information is needed. Water resource data for stratified drift aquifers in the Seacoast region were compiled in 1992 through a cooperative study by the USGS and the NHDES that was completed for the Exeter, Lamprey, and Oyster River Basins. While the 1992 study focused on mapping the river courses and stratified drift deposits, this new study aims to map all of the surficial geologic deposits to create seamless surficial geologic coverage. Much of the geologic mapping will be conducted by the New Hampshire Geologic Survey (NHGS), and this information will be transferred into an easily accessible geographic information system (GIS) data layer. This mapping will obviously be useful to many land use and planning groups active in the Seacoast region. 

Another goal of the study is to develop a comprehensive network of ground water and surface water gauging points throughout the Seacoast region that will provide a baseline for evaluating trends in water usage and availability. Historical ground water monitoring well information will be obtained from the extensive NHDES database of waste sites and water resource projects. This database will be inventoried to find monitoring wells that can provide reliable baseline water level data. Acceptable wells will generally be located upgradient from waste sites and will be located outside the influence of water supply wells and remediation systems. Identified wells will be coupled with appropriate monitoring wells installed by the USGS during the stratified drift aquifer studies completed in 1992; 63 monitoring wells were installed as part of the previous study. These monitoring wells will be sampled monthly to evaluate long-term ground water level trends, and one synoptic gauging event is planned to provide a snapshot view of the regional water table. 

Five surface water gauges were installed during the earlier stratified drift study, and this new study includes five additional gauging stations in stream basins currently experiencing considerable development pressure. According to Ted Diers of the NHOSP, new gauging locations include the Winnicut River, Issinglass River, Taylor River (Hampton), Piscassic River, and the North River (a tributary to the Lamprey River). 

To better characterize water usage, the study includes a comprehensive review of withdrawal registration records. According to current NHDES water supply regulations, facilities that use more than 20,000 gallons per day averaged over any 7-day period or 600,000 gallons in any 30-day period must register and report their monthly water use. The NHDES believes that the compliance rate for this reporting is low, and the study aims to collect data that may be currently under-reported. Information on water withdrawals and discharge locations will be compiled in the New England Water-Use Data System (NEWUDS) maintained by the USGS. 

The USGS plans to develop a ground water flow computer model as a way to compile hydrogeologic, hydrologic, and water usage information and to forecast water availability and water sustainability. Ground water flow modeling is viewed as the only way to assess and simulate the interaction of all components of the water budget including ground water flow and stream flow, municipal and domestic water use, and water discharges. Hydrogeologists commonly use ground water flow models to simulate future ground water flow systems, but flow models covering areas as large as the New Hampshire Seacoast (830 square miles) are rare. Also, while computer flow models work relatively well in stratified drift aquifers, their application to bedrock aquifers, an important water resource in the Seacoast, is limited due to the complex nature of ground water flow in these aquifers. The USGS plans an iterative approach to develop this complex model. A small pilot model has already been prepared for the area immediately south of Great Bay and this model will be expanded to cover most of the area east of the Swampscott River. This expanded pilot model will be compiled with the help and oversight of an advisory committee that aims to focus on model objectives and model inputs. If this pilot effort is successful, the model will be expanded to include the entire Seacoast study area.

Funding for this project is coming from a variety of sources. The USGS accounts for 50 percent of the project budget, with the remaining 50 percent (approximately $800,000) being shared by Congress, the United States Environmental Protection Agency, the NHOSP, and local communities. The total tab to the community is approximately $125,000, and Ted Diers of the NHOSP reports that most of the 42 participating communities have chipped in already. If the project goes as planned, local planning boards, area consultants, and developers will be able to address future water resource concerns using good technical data and sound science derived through this study.

David A. Maclean, L.S.P., L.E.P.
damaclean@geoinc.com

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