Hydrogeology of stratified-drift aquifers and water quality in the Nashua Regional Planning Commission Area, south-central New Hampshire

Water-Resources Investigations Report 86-4358




The Nashua Regional Planning Commission area in south-central New Hampshire is a 12-community area that is experiencing increases in population and in demands for water supply. The study area is underlain by 129 sq mi (40% of the area) of stratified drift which, where sufficiently saturated and permeable, form the most productive aquifers in the area. Eight towns use the stratified-drift aquifers for municipal water supply. The saturated thickness of stratified drift in the study area ranges from 0 or < 20 ft near aquifer boundaries to more than 100 ft in the Souhegan and Merrimack River valleys. The transmissivity of stratified drift ranges from < 2,000 sq ft/day throughout much of the area to more than 8,000 sq ft/day in the communities of Amherst, Brookline, Hollis, Hudson, Litchfield, Merrimack, Milford, Nashua, and Pelham. Directions of groundwater flow are generally from valley walls to surface waters, which act as drains for the stratified drift aquifers. The estimated total yield of community water-supply systems in the study area (surface and groundwater combined) is 22 mgd (million gallons per day). Analytical modeling indicates that an additional 12 mgd could be obtained from six aquifers located in the communities of Amherst, Litchfield, Merrimack, Milford, and Pelham. Other aquifers in the area, not modeled in the study, could also provide increased amounts of water especially where yields could be augmented by induced recharge of surface water. Groundwater quality in the study area is characterized by naturally elevated levels of iron (Fe) and manganese (Mn). Of 32 wells sampled, 7 exceeded EPA recommended drinking water limits for both Fe and Mn, and 3 wells exceeded the Mn limit only. The average total dissolved solids concentration for 32 samples was 121 mg/L. Groundwater in the area is slightly corrosive; pH 's ranged from 5.0-7.3. Groundwater contamination has been detected at two ' Superfund ' sites in the study area located in Milford and Nashua. At both sites, contamination of groundwater has caused the shutdown of municipal and private water supply wells. The widespread effect of applying highway deicing chemicals on groundwater quality is reflected by sodium (Na) concentrations that average 24 mg/L throughout the study area. At 11 of 32 sites sampled, EPA recommended limits for Na (20 mg/L) was exceeded. (Author 's abstract)

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Hydrogeology of stratified-drift aquifers and water quality in the Nashua Regional Planning Commission Area, south-central New Hampshire
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Water-Resources Investigations Report
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U.S. Geological Survey,
101 p. :ill., maps (some col.) ;28 cm.