Click here to return to USGS publications
Geohydrology and Water Quality of Stratified-Drift Aquifers in the Lower Merrimack and Coastal River Basins, Southeastern New Hampshire
U.S . GEOLOGICAL SURVEY
Water-Resources Investigations Report 91-4025
Prepared in cooperation with the
NEW HAMPSHIRE DEPARTMENT OF ENVIRONMENTAL SERVICES WATER RESOURCES DIVISION 'iEOHYDROLOGY AND WATER QUALITY OF STRATIFIED-DRIFT AQUIFERS '-N THE LOWER MERRIMACK AND COASTAL RIVER BASINS, :SOUTHEASTERN NEW HAMPSHIRE
,~y Peter J . Stekl and Sarah M. Flanagan
T.J.S . GEOLOGICAL SURVEY
"Vater-Resources Investigations Report 91-4025
Prepared in cooperation with the NEW HAMPSHIRE DEPARTMENT OF ENVIRONMENTAL SERVICES WATER RESOURCES DIVISION
Bow, New Hampshire 1992
U.S . DEPARTMENT OF THE INTERIOR
MANUEL LUJAN, JR., Secretary
U .S. GEOLOGICAL SURVEY
Dallas L. Peck, Director
For additional information, write to: Copies of this report can be purchased from:
Chief, NH-VT Office U.S . Geological Survey U .S . Geological Survey Books and Open-File Reports Section 525 Clinton Street Box 25425 Bow, New Hampshire 03304 Federal Center, Bldg. 810 Denver, CO 80225
CONTENTS Page Abstract ...... 1 Introduction ...... 2 Purpose and scope ...... 2 Description of the study area ...... 2 Previous investigations ...... 5 Approach and methods ...... 5 Numbering system for wells, test holes, and springs ...... 7 Acknowledgments ...... ...... 7 Geologic setting ...... 7 Bedrock ...... 7 Surficial deposits ...... 8 Geohydrologic setting ...... 11 Occurrence of ground water ...... 11 General description and water-yielding characteristics of the lithologic units ...... 12 Stratified drift ...... 12 Till ...... 16 Bedrock ...... 16 Geohydrology of stratified-drift aquifers ...... 17 Description of aquifer boundaries ...... 22 Recharge, discharge, and direction of ground-water flow ...... 22 Flow ...... 22 Recharge ...... 25 Discharge ...... 26 Water table and direction of ground-water flow ...... 26 Aquifer characteristics ...... 30 Saturated thickness ...... 30 Storage coefficient ...... 33 Transmissivity and hydraulic conductivity ...... 33 Evaluation of water availability and simulation of ground-water flow ...... 34 Description and conceptualization of model ...... 35 Description of analytical method ...... 37 Windham-Cobbetts Pond aquifer ...... 38 Boundary conditions ...... 38 Aquifer parameters ...... 38 Application of numerical model ...... 41 Sensitivity analysis ...... 41 Application of analytical method ...... 46 Well-capture area ...... 46 Kingston-Powwow River aquifer ...... 46 Boundary conditions ...... 49 Aquifer parameters ...... 49 Application of numerical model ...... 49 Sensitivity analysis ...... 49 Application of analytical method ...... 52 Well-capture area ...... 52 Locations and descriptions of selected stratified-drift aquifers ...... 53 Derry-Island Pond aquifer ...... 53 Windham-Cobbetts Pond aquifer ...... 54 Kingston-Powwow River aquifer ...... 54 North Hampton-Knowles Pond aquifer ...... 55
CONTENTS (continued) Page Greenland aquifer ...... 55 Ground-water quality ...... 56 Physical and chemical properties ...... 58 Total dissolved solids ...... 58 Specific conductance ...... 58 pH ...... 58 Alkalinity ...... 58 Calcium, magnesium, and hardness ...... 59 Sodium ...... 59 Chloride ...... 59 Sulfate ...... 60 Iron and manganese ...... 60 Trace elements ...... 60 Organic compounds ...... 61 Contamination sources ...... 61 Summary and conclusions ...... 66 References ...... 68 Glossary ...... 72 Appendix: Geohydrologic sections based on seismic-refraction data ...... A-1
PLATES
(Plates are in pocket at back) Plates 1-3. Maps showing aquifer boundaries, data-collection locations, altitudes of the water table, hazardous-waste sites, and concentrations of major chemical constituents for stratified-drift aquifers in the lower Merrimack and Coastal River basins, southeastern New Hampshire in the: 1 . Western section . 2. Central section . 3 . Eastern section.
4-6. Maps showing saturated thickness, transmissivity, and materials of stratified-drift aquifers in the lower Merrimack and Coastal River basins, southeastern New Hampshire : 4. Western section. 5. Central section. 6. Eastern section .
7. Maps showing: A. Initial water-table configuration used for the Kingston-Powwow River simulation. B. Finite-difference grid used to discretize the Kingston-Powwow River aquifer. C. Drawdown resulting from pumping eight hypothetical wells completed in the Kingston-Powwow River aquifer at a combined rate of 4.0 million gallons per day for 180 days. D. Calculated water-table configuration based on simulated drawdown after 180 days of pumping in the Kingston-Powwow River aquifer.
iv
ILLUSTRATIONS Page Figure 1. Map showing location of the lower Merrimack and coastal rivers basins, southeastern New Hampshire ...... 3 2. Map showing western, central, and eastern map plates of the lower Merrimack and coastal rivers basins ...... 4 3. Sketch showing high-resolution, continuous seismic-reflection-profiling system ...... 6 4. Idealized geohydrologic block diagram showing distribution of geologic units and ground-water flow ...... 10 5. Idealized geohydrologic section showing unconfined and confined aquifers...... 15 6-9. Geohydrologic sections showing: 6. Valley train in southern Windham ...... 18 7. Outwash plain in Kingston ...... 19 8. Kame delta in North Hampton ...... 20 9. Kame delta in Kensington and Seabrook ...... 21 10. Sketch showing ground-water flow and water-level drawdowns at a pumped well near an impermeable boundary ...... 23 11. Sketch showing ground-water flow and water-level drawdowns at a pumped well near a recharge boundary ...... 23 12. Water-level fluctuations typical of fluctuations in wells completed in stratified-drift aquifers in elevated kame plains...... 24 13. Seismic-reflection profile (A) and cross section (B) of Cobbetts Pond, Windham, interpreted from seismic-reflection data...... 31 14. Seismic-reflection profile (A) and cross section (B) of Island Pond, Derry, interpreted from seismic-reflection data...... 32 15-17. Maps showing: 15. Finite-difference grid used to discretize the Windham-Cobbetts Pond aquifer .... 39 16. Initial water table for the Windham-Cobbetts Pond simulation ...... 40 17. Drawdown resulting from pumping five hypothetical wells completed in the Windham-Cobbetts Pond aquifer after pumping at a combined rate of 0.64 million gallons per day for 180 days ...... 42 18 . Graph showing effects of varying hydraulic conductivity on results at hypothetical well D from the Windham-Cobbetts Pond model ...... 43 19 . Graph showing effects of varying specific yield and duration of pumping on results at hypothetical well D from the Windham-Cobbetts Pond model ...... 44 20. Diagram showing method of determining potential yield of aquifer from the 7-day, 10-year low-flow estimate at an ungaged stream site ...... 47 21 . Map showing calculated water-table configuration based on simulated drawdown after 180 days of pumping from the Windham-Cobbetts Pond aquifer ...... 48 22. Graph showing effects of varying hydraulic conductivity and streambed conductance on results from the Kingston-Powwow River model ...... 50 23. Graph showing effects of varying specific yield and duration of pumping on results from the Kingston-Powwow River model ...... 51 24. Map showing locations of hazardous-waste sites ...... 57 Al-A17 . Geohydrologic sections based on seismic-refraction data for: ...... A-1 Al . Londonderry a-a', b-b', and c-c' ...... A-2 A2. Londonderry d-d', Windham e-e', and f-f' ...... A-3 A3. Windham g-g', h-h', and i-i' ...... A-4 A4 . East Kingston j-j' and Kingston k-k' and 1-1' ...... A-5 A5. Kingston m-m', n-n', and o-o' ...... A-6 A6. Kingston p-p', q-q', and r-r' ...... A-7 A7 . Kingston s-s', t-t', and u-u' ...... A-8
ILLUSTRATIONS (continued) Page A8. Kingston v-v', w-w', and x-x' ...... A-9 A9. Kingston y-y', z-z', and as-aa' ...... A-10 A10. Kingston bb-bb', cc-cc', and dd-dd' ...... A-11 All. Newton ee-ee', ff-ff', and gg-gg' ...... A-12 A12. Plaistow hh-hh' and ii-ii' and Greenland jj-jj' ...... A-13 A13. Greenland kk-kk'and Kensington 11-11' and mm-mm' ...... ...... A-14 A14. Kensington nn-nn' and oo-oo' and Newington pp-pp' ...... ,...... , A-15 A15. Newington qq-qq' and North Hampton rr-rr' and ss-ss' ...... A-16 A16. Rye tt-tt' and Seabrook uu-uu' and vv-vv' ...... ...... , A-17 A17. Seabrook ww-ww' ...... A-18
TABLES Page Table 1. Two-character town codes used as prefixes in the numbering system for wells, test holes, and springs ...... 8 2. Maximum well yields for major water-supply wells ...... 13 3. Low-flow measurements at miscellaneous sites ...... , 27 4. Hydraulic conductivity estimated for lithologies in stratified drift in southeastern New Hampshire ...... 34 5. Summary of aquifer-evaluation results showing sensitivity of model parameters ...... 45 6. Classification of hardness of water ...... ...... .__, ...___. ... ,...... 59 7. Summary of results of water-quality analyses ...... ,...... 62
CONVERSION FACTORS AND VERTICAL DATUM
Multiply By To obtain
Length inch (in.) 25.4 millimeter foot (ft) 0.3048 meter mile (mi) 1.609 kilometer
Area square mile (mil) 2.590 square kilometer
Volume gallon (gal) 3.785 liter million gallons (Mgal) 3,785 cubic meter cubic foot (ft3) 0.02832 cubic meter
Flow foot per second (ft/s) 0.3048 meter per second cubic foot per second (ft3/s) 0.02832 cubic meter per second cubic foot per second per 0.01093 cubic meter per second square mile [(ft3/s)/mi2] per square kilometer gallon per minute (gal/min) 0.06309 liter per second gallon per day (gal/d) 3.7854 liter per day million gallons per day 0.04381 cubic meter per second (Mgal/d) million gallons per day 1,460 cubic meter per second per square mile per square kilometer [(MgaVd)/mi`]
HvdraulicConductivity foot per day (ft/d) 0.3048 meter per day
Transmissivit square foot per day (ft2/d) 0.09290 square meter per day
Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929--a geodetic datum derived from a general adjustment ofthe first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929.
Geohydrology and Water Quality of Stratified-Drift Aquifers in the Lower Merrimack and Coastal River Basins, Southeastern New Hampshire
By Peter J. Stekl and Sarah F. Flanagan
ABSTRACT estimated for an aquifer in Windham near Cobbetts Pond and for an aquifer in Kingston along the Pow- wow River by use of a method analogous to superposi- Communities in the lower Merrimack River tion in conjunction with a numerical ground-waterflow basin and coastal river basins of southeastern New model. The potential yield is estimated to be 0.6 Hampshire are experiencing increased demands for million gallons per day for the Windham-Cobb etts water because of a rapid increase in population. The Pond aquifer and 4.0 million gallons per day for the population in 1987 was 225,495 and is expected to Kingston-Powwow River aquifer . Contributing increase by 30 percent during the next decade. As of recharge area for supply wells is estimated to be 1.6 1987, five towns used the stratified-drift aquifers for square miles in the Windham-Cobbetts Pond aquifer municipal supply and withdrew an estimated 6 mil- and 4.9 square miles in the Kingston-Powwow River lion gallons per day. Four towns used the bedrock aquifer. aquifer for municipal supply and withdrew an average samples from 30 wells indicate of 1.6 million gallons per day. Analyses of water that the water quality in the basins studied isgenerally Stratified-drift deposits cover 78 of the 327 suitable for drinking and other domestic purposes. square miles of the study area . These deposits are Concentrations of iron and manganese exceeded the generally less than 10 square miles in areal extent, U.S. Environmental Protection Agency's (USEPA) and their saturated thickness ranges front less than 20 and the New Hampshire Water Supply Engineering feet to as much as 100 feet. Transinissivity exceeds secondary maxintuna contaminant levels 4,000 square feet per day in several locations . Bureau's samples. With one exception, Stratified-drift aquifers in the eastern part are for drinking water in 20 compounds at all predominantly small ice-contact deposits surrounded concentrations of volatile organic Supply and by marine sediments or till of low hydraulic conduc- wells sampled met New Hampshire Water . At tivity . Stratified-drift aquifers in the western part con- Engineering Bureau's drinking-water standards sist of ice-contact and proglacial deposits that are one well, trichloroethylene was detected at a con- large in areal extent and are commonly in contact centration of 5.7 micrograms per liter. with stuface-water bodies . Ground-water contamination has been detected Five stratified-drift aquifers, in the towns of at several hazardous-waste sites in the study area. Derry, Windham, Kingston, North Hampton, and Currently, 5 sites are on the USEPA's National Greenland, have the greatest potential to supply addi Priority List of superfund sites, 10 sites are Resource tional amounts of water. Potential yields and con- Conservation and Recovery Act of 1976 sites, and 1 tributing areas of hypothetical supply wells were site is a Department ofDefense hazardous-waste site . INTRODUCTION and the coastal rivers basin, which include Berry Brook, Winnicut River, Taylor River, and Hampton Falls River that flow directly into Great Bay or the Southeastern New Hampshire has undergone a Atlantic ocean (fig. 1) . rapid increase in population in the past few decades . Population in the region increased by more than 39 percent from 1970 through 1987, when it reached 228,495 . The population is projected to increase at Purpose and Scope an average annual rate of 3.32 percent by the end of the century (New Hampshire Office of State Plan- ning, written commun., 1989) . Economic develop- The purpose of this ment has increased in southeastern New Hampshire report is to (1) describe the hydrologic and geologic because of its proximity to metropolitan Boston. characteristics of the This growth, accompanied by industrial expansion, stratified-drift aquifers--areal extent, saturated thickness, and transmissivity ; ground-water increased energy needs, and changes in land use, has levels; general directions of ground-water steadily increased the demands for potable water flow and yield of stratified drift and contributing for and has stressed existing municipal water supplies . areas selected aquifers after prolonged pumping; Currently, this area depends on ground water as its (2) describe general geohydrology of till primary source of water . The increased stress on and bedrock and water use and water-yielding this resource from a growing population has created characteristics of the bedrock aquifer; and occasional shortages in water quantity and deteri- (3) document ground-water oration of water quality. quality in the stratified-drift aquifers. Extensive ground-water contamination has oc- This investigation focused on but was not curred at five hazardous-waste sites, and the migra- limited to collection, compilation, and evaluation of tion of contaminants has prevented development of data from stratified-drift aquifers. Some water yield productive aquifers in some areas. Water quality in data was also collected and evaluated for the the shallow stratified-drift aquifers is of a concern bedrock aquifer. Two stratified-drift aquifers, in because depth to water is typically 20 ft or less, and Windham near Cobbetts Pond and in Kingston along the highly permeable surficial materials above the the Powwow River, have the greatest potential to supply water table offer little protection from seepage of additional ground water. A superposition modeling contaminants into ground water. Development of technique was used to estimate yields of new public water supplies is needed to satisfy cur- these two aquifers and to delineate the size of the rent and future demands. Additional ground-water contributing areas after 180 days of pumping. data are needed to facilitate development of water supplies and protection of water quality. To meet this need for ground-water data, the Description of the Study Area U.S . Geological Survey (USGS), in cooperation with the New Hampshire Department of Environmental Services, Water Resources Division, began a 10-year program in 1983 to provide detailed maps of The study area, in southeastern New Hamp- stratified-drift aquifers statewide. Maps that show shire (fig. 2), is east of the Merrimack River and aquifer boundaries, water-table altitudes, general extends from the towns of Londonderry to New directions of ground-water flow, saturated thick- Castle. Beaver Brook, Little River, Spicket River, ness, and aquifer transmissivity are being compiled and Powwow River are the largest drainage sub- on a scale of 1 in. equals 2,000 ft. The study also basins (fig. 1) . For the purpose of discussion in this provides statewide data on background water quality report, the area has been divided into three subareas in stratified-drift aquifers . Detailed geohydrologic (western, central, and eastern), and two map plates information is provided in the reports for use by (at the back of the report) are used to present regional and local planners in making maximum use geohydrologic information on each subarea (fig. 2) . of existing ground-water resources and in locating The study area of 327 mi`, is underlain by stratified- and developing new resources . This report drift aquifers (78 mi), marine deposits (69 mi), and describes stratified-drift aquifers for the Beaver till deposits (180 mi) . Many towns with a municipal Brook, Spicket River, Powwow River, and Little water supply rely completely or partly on ground River subbasins of the lower Merrimack River basin water for that supply.
Merrimac f i M Powwow River River . --\ ~ subbasin `sub- ..J Beaver f-* \ c, basin; Brook y 1 .~ subbasin ~ . Little River,' .. Snicket River /" subbasin '~ subbasin f - / MASSACHUSETTS
20 40 60 MILES
0 20 40 60 KILOMETERS
EXPLANATION 0 5 10 MILES DRAINAGE DIVIDE I 0 5 10 KILOMETERS STATE BOUNDARY COUNTY BOUNDARY TOWN BOUNDARY LAND AND OCEAN BOUNDARY
Figure 1.--Location of the lower Merrimack and coastal rivers basins, southeastern New Hampshire .
EXPLANATION
MAP PLATE BOUNDARY DRAINAGE DIVIDE STATE BOUNDARY COUNTY BOUNDARY TOWN BOUNDARY LAND AND OCEAN BOUNDARY
WESTERN MAP CENTRAL MAP PLATES 1 and 4 PLATES 2 and 5
('I \\ HAMPTO N 'I
HAMPTON' \ I FALLS
SOUTH SEABROOK HAMPTON, I HAMPSTEAD 11 I / \ / NEWTON
--~. N . -v
0 5 10 MILES
0 5 10 KILOMETERS
Figure 2.--Western, central, and eastern map plates of the lower Merrimack and coastal rivers basins. Previous Investigations program and from lithologic data collected from auger holes. Available subsurface data on stratig- raphy, saturated thickness, ground-water levels, and Regional investigations include two basic-data aquifer-test results were compiled. Data were ob- reports for wells and springs in southeastern New tained from published and unpublished sources of Hampshire (Bradley and Peterson, 1962; Weigle and the U.S. Geological Survey, New Hampshire Depart- Kranes, 1966), an interpretive report on ground- ment of Environmental Services, New Hampshire water resources (Bradley, 1964), and an evaluation Department of Transportation, well-drilling con- of water resources and the extent of ground-water tractors, towns, and local residents . Flanagan and contamination at a stratified-drift aquifer underly- Stekl (1990) have summarized data collected for this ing Pease Air Force Base (Bradley, 1982). study. Other studies on water resources and hazard- Data points were plotted on base maps, and ous-waste sites from several towns have been done about 1,400 site entries were added to the Geological by private consultants and a State agency. Camp Survey's computerized Ground-Water Site Inven Dresser & McKee, Inc. (1966, 1973) assessed water tory (GWSI) data base . The GWSI data base allows resources in the town of Derry. NUS Corporation retrievals for specific data requirements. For ex- (1985, 1986) investigated ground-water contamina- ample, retrievals can be restricted to data for wells tion at a commercial repair garage in Londonderry finished in a particular type of aquifer or wells from and ground-water contamination at the Auburn a specific geographical area. Each well is cross ref- Road Landfill in Londonderry. New Hampshire erenced to a well-identification number, latitude and Water Supply and Pollution Control Division longitude, original driller, and owner. (NHWSPC) (1985a, 1985b) investigated ground- Seismic-refraction profiling, a surface geophys- water contamination at the Coakley Landfill in ical method for subsurface exploration, was done at North Hampton and ground-water contamination at 49 sites (pls. 1-4) for a total distance of 10.0 mi to the Duston Road area in Salem. Goldberg-Zoino map depths to water table and bedrock and to es- and Associates (1986) investigated ground-water timate saturated thickness of aquifers. A 12-chan- contamination at the Ottati and Goss site in nel, signal-enhancement seismograph was used to Kingston. Roy F. Weston, Inc. (1986) investigated record arrival times of refracted waves generated ground-water contamination at Pease Air Force from the ignition of a two-component explosive Base in Portsmouth . Leggette, Brashears, & (Haeni, 1986a) . Altitudes of geophones and shot Graham, Inc. (1987) evaluated recharge areas to points on each seismic line were determined by water-supply wells owned by the Hampton Water leveling to a common datum. Seismic data were in- Works Company that service the towns of Hampton terpreted with a computer program (Scott and and North Hampton. others, 1972) that incorporates time delay and ray- Previous maps of stratified-drift aquifers in tracing methods . Data from nearby test holes were southeastern New Hampshire by the USGS include used to verify the results of the computer-generated reconnaissance maps at a scale of 1:125,000 for the profiles. lower Merrimack River basin (Cotton, 1977a) and Continuous seismic-reflection profiling--a the Piscataqua and other coastal river basins (Cot- geophysical method for investigating stratigraphy ton, 1977b) . Surficial-geology maps for parts of the below surface-water bodies--was done at Cobbetts study area are available through the Cooperative and Island Ponds (pls . 1 and 2). The profiles aid in Geologic Mapping Program (COGEOMAP)--a mapping fine and coarse-grained layers in the cooperative program between various states and the aquifer, the continuity of the aquifer, and depth to Geologic Division of the USGS . For New bedrock (Haeni, 1986b) . Seismic-reflection profiles Hampshire, the New Hampshire Department of En- are generated by towing a displacement-type sound vironmental Services, Office of the State Geologist, source and a hydrophone streamer across the water is the cooperator in this program . surface at a constant speed and monitoring the reflected signal (fig. 3) . Sound energy generated the water Approach and Methods from the sound source travels through column as outgoing seismic waves and into the sub- bottom materials. This energy or seismic wave is The areal extent of stratified-drift aquifers was sensitive to changes in the acoustic impedance of the delineated from published and unpublished surfi- underlying stratigraphic units and is reflected back cial-geology maps provided by the COGEOMAP to the surface (Haeni, 1986b) . Acoustic impedance
Boat Hydrophone cable Sound source t2-.A= iw,;S
Not to scale
Figure 3.--High-resolution, continuous seismic-reflection-profiling system. of stratigraphic layers is a product of a material's Numbering System for Wells, Test Holes, density and the velocity at which sound travels and Springs through that material. The reflected signals return to the hydrophones at the water surface and are then Numbers assigned by the USGS to wells, test filtered, amplified, and displayed graphically on the holes, and springs consist of a two-character town allow interpretation of aquifer chart recorder to designation (table 1), a supplemental letter desig and bedrock depths. Lithologic data stratigraphy nation ("A" for test holes done for geohydrologic from nearby wells and test holes were used as control purposes with no casing set, "B" for test holes done points to check the interpretation of the reflection primarily for constructional purposes, "S" for profiles. and "W" for all wells with a casing set), (pls . 1-3) springs, Test drilling was done at 66 locations sequential number within each town . For grain size, stratigraphy, and a to determine sediment example, the first well in the town of Atkinson is depth to bedrock, and ground depth to water table, ARW-1. water quality . A 6-inch-diameter, hollow-stem auger was used for test drilling. Split-spoon samples of subsurface materials collected at specific depths Acknowledgments were used to evaluate the grain-size characteristics identify the stratigraphic sequence of materials and appreciation to comprising the aquifers. Thirty-eight test holes The authors wish to express drillers, consult- cased with a 2-inch-diameter polyvinyl-chloride State and municipal officials, well of the area who (PVC) pipe and slotted screens were used to make ing engineers, and residents and granted access to ground-water-level measurements and collect provided useful information gratefully acknow- ground-water-quality samples. their properties. The authors by the staff Surface-water-discharge measurements were ledge the interest and support extended Rockingham Planning Commission. made at 16 sites during low flow when the surface of the water is primarily ground-water discharge. These low-flow measurements indicate quantities of ground water potentially available from aquifers. Hydraulic conductivities of aquifer materials GEOLOGIC SETTING were estimated from grain-size-distribution data from 61 samples of stratified drift . Transmissivity Bedrock was estimated from well logs by assigning hydraulic conductivity to specific well-log intervals, multiply- ing by the saturated thickness of the interval, and Metamorphic rocks of sedimentary and vol- summing the results. Additional transmissivity canic origin underlie the lower Merrimack River values were obtained from an analysis of specific- basin at depths of 0 to 120 ft. The regional struc capacity and aquifer-test data. tural pattern has a northeast-southwest trend and Long-term aquifer yields and contributing is defined by three major tectonic features: the areas to hypothetical supply wells were estimated by Massabesic anticlinorium along the western application of a method that is analogous to super boundary; the Merrimack trough, which occupies position and incorporates a ground-water-flow most of the basin ; and the Rye anticlinorium, model developed by McDonald and Harbaugh which extends along the coastal boundary and in- (1988) . This method was applied to two aquifers cludes towns from Portsmouth to Hampton (Lyons judged to have the best potential for providing addi- and others, 1982) . tional ground-water supplies. The Rye Gneiss of Precambrian age con- Samples of ground water from 26 test wells and tains the oldest rocks in southeastern New 4 municipal wells were collected in March and Hampshire and most commonly consists of August 1987 for analysis of common inorganic, or coarse-grained gneiss, quartzites, and schists. ganic, and volatile organic constituents. Methods The metamorphic rocks of these formations are for collecting and analyzing the samples are intruded by small lenticular bodies of granite, described by Fishman and Freidman (1989) . The pegmatite, and diabase aligned parallel to the water-quality results from the well samples were regional structural trend (Billings, 1956) . The used to characterize background water quality in the Merrimack Group of pre-Silurian age underlies stratified-drift aquifers. most of the study area and is divided into the Table 1.--Two-character town codes used as prefixes in the numbering system for wells, test holes, and springs
Town Code Town Code
New Hampshire Atkinson AR Newington NI Danville DC Newton NQ Derry DF North Hampton NS East Kingston EA Plaistow PW Exeter EX Portsmouth PX Greenland GT Rye RY Hampton HE Salem SA Hampton Falls HF Sandown SD Hampstead HD Seabrook SG Kensington KF South Hampton SL Kingston KT Stratham SS Londonderry LR Windham WP New Castle NE
Massachusetts Merrimac MR Salisbury SB
Kittery, Eliot, and Berwick Formations' (Lyons and Surficial Deposits others, 1986) . The Merrimack Group consists of schists, calc-silicate rocks, and quartzites, and the The surficial deposits are characteristic of the grade of metamorphism increases irregularly from two physiographic provinces in the study area: the east to west toward the Massabesic anticlinorium, coastal lowlands, which include the area east of the which extends from about the western town border Spicket River drainage basin, and the southeastern of Londonderry to the Seacoast (Lyons and others, New Hampshire uplands, which include the Spicket 1982) . basin and areas farther west. Topography east of the All formations are folded and faulted . Large Spicket River drainage basin is generally less than faults are oriented parallel to the regional northeast- 200 ft above sea level; the area is largely a broad flat southwest strike of the bedrock. The Portsmouth coastal plain underlain by unconsolidated glacial fault is one of the large faults and forms the Rye- and marine deposits. Except in some high hills, sur- Gneiss Kittery-Form ation contact for about 9 mi ficial deposits in this area were affected by marine (Novotny, 1969). Smaller faults strike northwester- inundation and beach processes that reworked older ly, cut across the regional structural grain, and do glacial deposits. Unique to this region are zones of not dislocate rocks more than a few tens of feet . coarse-grained glacial drift that underlie fine-
The stratigraphic nomenclature of bedrock units used in this report is that of the New Hampshire Geological Survey (Lyons and others, 1986) and does not necessarily follow usage of the U.S. Geological Survey. grained marine deposits in some localities. Where the ice melted, deposited by processes that involve this stratigraphic relation is present and the underly- repeated mudflows and sorting by meltwater) . Most ing coarse-grained deposits are thick, confined basal till has an oriented fabric and is fine-grained, aquifers have the potential to supply large quantities compact, and fissile. The thickness of basal till of ground water. In contrast, the uplands to the west ranges from 0 to 15 ft, but is much thicker in stream- have high ridges, steep slopes, and distinct valley lined elongate ridges, termed drumlins. Examples walls incised in bedrock. Marine deposits are ab- of drumlins are found in Kensington and South sent, and the shape of the bedrock surface is the Hampton. The thickness of till in one drumlin in primary control on the distribution of glacial sedi- Kensington exceeds 220 ft. Ablation till has more ments. sand and is less compact than basal till, lacks fissility Till, stratified drift, and marine deposits or consistent fabric, and contains lenses of silt, sand, primarily comprise the surficial deposits in the study or gravel. This till is found everywhere in the upland area. These deposits, which control the storage and areas and coastal lowland ridges and probably movement of ground water in the subbasins of the averages about 40 ft in thickness . study, are discussed in the context of their geologic Glaciofluvial and glaciolacustrine stratified origin (fig. 4) . drift cover 24 percent of the study area. Glacio- Unconsolidated deposits of Pleistocene and fluvial stratified drift consists of sorted, stratified Holocene age cover the bedrock throughout most of sand and gravel deposited by glacial meltwater southeastern New Hampshire . During late Wiscon streams. Glaciolacustrine drift is also found and sin time in the Pleistocene Epoch (approximately consists of well-sorted, stratified, and commonly 13,000 to 20,000 years ago) the entire region was laminated fine sand, silt, and clay deposits formed in covered by a vast continental glacier (Boudette, the standing water of lakes and ponds. An example 1990) . As the glacier advanced and its front melted, of these glaciolacustrine deposits are the laminated a fairly continuous blanket of unsorted material, couplets of silt and clay, as much as 60 ft thick, called till, was spread over the bedrock . beneath the bottom of Island Pond in the town of Proglacial stratified-drift deposits were formed Derry. next when meltwater flowing in channels or tunnels, Glaciofluvial and glaciolacustrine stratified derived to or under the ice, transported sediment drift can be grouped into two broad genetic types-- from melting ice to sites of deposition from till or ice-contact and proglacial stratified drift--which are margin. Stratified drift near or beyond the ice distinguished by the abundance of stagnant or deposited against or on top of melting ice formed detached ice in the original depositional environ- ice-contact deposits. As the ice sheet melted, sea ment. Ice-contact stratified drift consists of sediment level rose in relation to the land surface and flooded deposited on or against decaying ice. Proglacial part of the present coastal area. Sand, silt, and clay stratified drift is deposited by or in meltwater were deposited in large estuaries or bays similar to beyond the margin of a glacier. Generally, sorting present-day Great Bay and the Piscataqua River. and texture among sands and gravels is more Since deglaciation, the land uplifted and sea level uniform in a proglacial environment than in an ice- retreated to its current position. The sand, silt, and contact environment . Sand and gravel deposited in clay sediments are marine deposits as indicated by ice-contact position commonly contains inter- marine fossils found in sediment exposures . The an thick lenses of silt and fine sand, which were fine-grained marine deposits partly cover ice-con- bedded the temporary lakes near tact deposits, till, or bedrock . deposited in quiet parts of ice-contact deposits Ice was probably near the coast when the sea stagnant ice. The thickness of flooded part of coastal New Hampshire . The ice in the study area ranges from 0 to 80 ft . continued to melt and supplied outwash, which Many prominent topographic features among graded to the level of shore deposits in the flooded the lowlands of the basin are composed of ice-con- areas. tact and proglacial stratified drift that can be further Till is the predominant surficial material and classified on the basis of the landform in which they covers 55 percent of the study area. Till--an un- occur. Landforms composed of ice-contact glacio- sorted, unstratified mixture of rock fragments--con fluvial stratified drift include ice-channel fillings, sists of particles ranging in size from clay to boulders kame plains, kame terraces, and kame deltas. Char- and is present either as basal till (debris deposited acteristic features are ice-contact slopes, collapsed beneath the ice and compressed by its weight) or as surfaces, and kettles that formed in the deposits as ablation till (debris entrained within the ice and, as the supporting ice melted away.
Drainage divide Western uplands
Drumlin Upland valley Upland karne terrace 1 largely unsaturated Till-mantled bedrock hill Eastern coastal lowlands
Outwash
EXPLANATION RECHARGE TO BEDROCK ISCHARGE FROM STRATIFIED DRIFT GEOLOGIC UNIT A Infiltration of precipitation through till in uplands Seepage to river Inflow to the basin from circulation through bedrock D2 Ground-water evapotranspiration where the water table is shallow RECHARGE TO STRATIFIED DRIFT Till G 3 Underflow downvalley through stratified Precipitation on valley floor, which infiltrates to drift (not shown) . River and streams water table unless diverted as evapotranspiration or storm runoff from pavement or saturated soil Stratified drift 4 Pun-page from well screened in stratified D Runoff from adjacent hillsides at shallow depth drift Fractured bedrock through sandy till, through soil horizons and (or) as surface rivulets DISCHARGE FROM BEDROCK Marine deposits 5 Pumpage from well that intersects E Natural seepage losses from small tributaries not fractures incised to the water table table 6 Outflow from the basin from circulation ...... Water F Lateral and upward flow from bedrock through bedrock ---i Direction of ground-water flow G Induced infiltration from rivers near large-capacity wells where the water table is lowered by pumping Fault
Figure 4.--Idealized geohydrologic block diagram showing distribution of geologic units and ground-water flow (Modified from Randall and others, 1988a, fig. 1) . Ice-channel fillings are linear ridges of sand Marine deposits cover 21 percent of the surface and gravel deposited in meltwater streams confined and are found only in the eastern section. (This by stagnant ice. Eskers are generally a curvilinear percentage refers to those parts where marine type of ice-channel filling deposited in confined tun- deposits are actually at the surface or overlain by nels in or under the ice . The largest ice-channel outwash or beach deposits too thin to map or filling, in the town of Plaistow, is a linear southeast- analyze.) They consist of fine-grained sand, silt, and trending ridge about 5.5 mi long with occasional clay deposited in shallow estuaries and tidal areas breaks caused by sand and gravel mining and during the later stages of deglaciation when sea level postglacial erosion. The shape and orientation of rose and much of the valleys and lowlands was inun- the ridge indicates deposition between stagnating dated. Thin outwash and beach deposits typically tongues of ice or in a large fracture in the ice overlie the fine-grained marine deposits in the east- (crevasse) . Kame terraces--flat-topped masses of ern part . In some areas, marine deposits, up to 90 ft sand and gravel deposited by meltwater between a thick, overlie permeable ice-contact deposits and act receding or stagnant ice tongue and the valley wall-- as confining layers . are present in the western section. The entire thick- ness of many kame terraces is above the grade of GEOHYDROLOGIC SETTING modern streams; therefore, the bulk of the sand and gravel is unsaturated. Kame deltas typically have a flat-topped triangular shape and were built onto or Occurrence of Ground Water against glacial ice . These deltas are the most widespread landforms of stratified drift in the east- ern section. Most of the deltas in the area graded to Water occurs beneath the land surface in two estuaries or open marine waters. Foreset beds of the different zones. In the upper or unsaturated zone, which usually extends from a few inches to several deltas are commonly well-sorted sands that are tran- tens of feet below the land surface, the openings are sitional downslope to silts and clays of marine origin. filled with air and water. In the lower or saturated Locally, these deposits have been modified by beach zone, the interconnected openings contain only processes. water . The surface that divides these two zones is Landforms composed of proglacial stratified the water table. The water table rises when recharge drift in the area include valley trains and outwash exceeds the sum of withdrawal, discharge to streams, plains. A valley train consists of stratified drift and evapotranspiration from the saturated zone, and that fills a valley from wall to wall and was formed declines when the converse is true. In general, the by the deposition of sediment-laden meltwater water table is a subdued replica of the land surface; draining from a glacier upvalley (Flint, 1971) . The however, it commonly is deepest beneath hills and is most extensive valley train is in the Beaver Brook at or near the surface in the lowlands. valley. Although large in area, this valley train is Lithology also controls the configuration and less than 40 ft thick, and numerous interbedded fluctuation of the water table . For example, in layers of silt interrupt the vertical continuity of upland or lowland till, the water table is at or within sand and gravel. a few feet of the land surface every spring but Outwash plains are similar to valley trains but declines considerably during dry summers. In are not confined by valley walls. They are the largest coarse-grained stratified drift, the water table slopes landforms of stratified drift in the study area and are gently toward streams regardless of the season or generally thicker and more extensive inland than on topographic irregularities and tends to be slightly the coast. Outwash deposits are finer textured and above the grade of the nearest perennial stream. At better sorted, as a result of their distance of many eskers, kame terraces, and kame deltas that transport, than ice-contact deposits. Outwash form ridges, depths to water can be several tens of deposits consist primarily of loose medium- or fine- feet. In areas where outwash overlies lacustrine or grained sand but include some fine and coarse marine deposits, the topography is low and flat, the materials . The deposits become fine grained water table is typically several feet above the top of downward, often grading into marine and estuarine the fine-grained sediments if they are above stream deposits . An extensive outwash plain locally grade. reworked by beach processes is found in Kingston Ground water is present in unconfined and con- and Newton where thick deposits of sand and gravel fined aquifers in the study area. Where water par- exceed 120 ft in places. tially fills the aquifer and the upper surface of the saturated zone is at atmospheric pressure, ground deposited in sequences that are graded to a par- water is unconfined. The most extensive aquifers in ticular base level--generally thickest near the ice- the study area are unconfined. Ground water is contact slope, and thinnest and interrupted by commonly confined under hydrostatic pressure in bedrock outcrops near the till contact. The proximal the eastern part where stratified-drift and bedrock end of a sequence is characterized by poorly sorted aquifers are locally buried beneath relatively imper- and poorly stratified deposits containing lenses of meable silt and clay. Examples of high-yield wells till (flow till) that form the ice-contact faces of kame that produce water from confined aquifers are the terraces, kame deltas, and heads of outwash. These Sherburne well in Portsmouth (PXW-4) and gravel- features commonly supply small amounts of water to pack wells 3 (SGW-44) and 4 (SGW-65) in Seabrook wells because of the poorly sorted materials and the (table 2). absence of thick saturated intervals. Water levels in wells finished in the unconfined An example of the head of outwash is found aquifers will rise to the water table and fluctuate between 140 and 150 ft elevation, in the town of slowly as the volume of stored water changes. In Newton less than 1,000 ft southeast of the intersec contrast, ground water in confined aquifers is under tion between Amesbury and Bear Hill Roads (pl. 2) . hydrostatic pressure and water levels in wells will Much of this ridge of stratified drift is unsaturated rise above the top of the aquifer (fig. 5). and consists of very poorly sorted pebble-cobble- gravel material that has a low water-bearing capacity. The distal end of the sequences is charac- Description and WaterYielding General terized by well-stratified, moderately well-sorted Characteristics of the Lithologic Units deposits that comprise most of the ice contact and (or) proglacial landform. These deposits of well- The lower Merrimack and Coastal River basins sorted sand and gravel allow rapid flow of ground are underlain by three general types of geologic units water and are capable of large well yields where the that can yield useable quantities of water to properly saturated interval is sufficiently thick. Examples of constructed wells and, therefore, can be considered these deposits are the kame plain near Route 1 north aquifers: stratified drift, till, and crystalline bedrock. of the town of Hampton (pl. 3) and the kame delta These geologic units, however, differ greatly in their that underlies Pease Air Force Base in the town of ability to store and transmit water. Newington (pl. 3) . Both aquifers serve as primary sources of the public water supply. In fine-grained marine Stratified Drift some areas, deposits overlie ice-contact deposits or overlap the peri- meters of such deposits . For example, the Sher Stratified-drift deposits constitute the most ex- burne well in Portsmouth is drilled to a depth of 50 ft tensive and productive aquifer in the region. Cur- into a confined aquifer . The top 20 ft consists of silt rently, 79 percent of ground water withdrawn from and clay of marine origin that form a confining layer high-capacity wells in the basin is pumped from wells and the bottom 30 ft consists of highly permeable screened in the stratified-drift aquifer . Towns sand and gravel that forms the productive zone in a served by high-yield, gravel-packed wells finished in confined aquifer. Because of the confinement by the stratified-drift aquifer include Hampton, North marine deposits, recharge to the ice-contact Hampton, Portsmouth, Rye, and Seabrook (table 2) . deposits from precipitation and runoff is greatly The maximum well yield from 19 gravel-packed wells reduced . averages 377 gal/min and ranges from 125 to 900 gal/min. Maximum thickness of ice-contact deposits in- The yield from gravel-packed wells represents maxi- ferred from seismic data is 100 ft and from well logs mum yield for the well technology used at each site; is 78 ft; well yields range from 3 to 900 gal/min. therefore, the yields of these wells (table 2) are useful Proglacial deposits comprising valley trains and approximations of the withdrawal rates that can be outwash plains are generally finer grained, more expected from the aquifers. homogeneous, and better sorted than ice-contact The most productive high-yield stratified-drift deposits, and consist primarily of sand with small deposits are ice-contact and proglacial (valley train amounts of gravel and silt . Many of the valley trains, and outwash) deposits. Ice-contact deposits exhibit in the western part of the study area, have well- abrupt changes in stratification and grain size that sorted sand interbedded with layers of silt and clay cause large variations in the water-bearing charac- that formed from temporary glacial ponds that oc- teristics of the deposits. Ice-contact sediments are cupied the valleys. Gravel-packed wells developed
12 Table 2 .--Maximum well yields for major water-supply wells
[ft, feet ; gal/min, gallons per minute ; --, no data available; User : SNHWC, Southern New Hampshire Water Company; DPW, Department of Public Works; HWWC, Hampton Water Works Company; AFB, Air Force Base . Type of well : DVN, driven ; GPW, gravel-packed well ; BrW, open-hole bedrock well .]
User Type Depth Maximum Well Latitude Longitude or Other of of well identi- owner identifier well well yield fier (ft) (gal/min)
DERRY
DFW-79 42 52'19" 71 18'35' , SNHWC Maple Hills BrW 200-825 270 (3 wells)
GREENLAND
GTW- 1 43 01'501' 70 49'46" Portsmouth DPW Greenland well #5 GPW 60 450
HAMPTON
HEW- 3 42 57'27" 70 49'35" HWWC White's Field GPW 50 400 HEW- 6 42 57'12" 70 49'38" HWWC Scammon GPW 50 490 HEW- 7 42 56'30" 70 48'56" HWWC Ryder GPW 45 350 HEW-24 42 57'21" 70 49'30" HWWC Sicard GPW 63 625
LONDONDERRY
LRW-144 42 53'03" 71 21'38" SNHWC Birchville BrW 250-788 33 .5 (5 wells) LRW-145 42 53'54" 71 25'54" SNHWC Brook Park BrW 150-620 29 .6 (4 wells)
NEWINGTON
NiW- 8 43 05'08" 70 50'45" Pease AFB MMS No . 2 BrW 170 29 NiW- 9 43 05'13" 70 50'41" Pease AFB MMS No . 1 BrW 130 28 NiW- 50 43 04'43" 70 51'29" Pease AFB Loomis well BrW 300 15 NiW- 51 43 06'42" 70 49'01" C .H .Sprague & -- BrW -- 20 .8 (2 Sons Co . wells)
NORTH HAMPTON
NSW- 8 42 57'31" 70 49'2411 HWWC Marston Springs GPW 44 150 NSW- 27 43 00'05" 70 51'48" HWWC BRW #13 BrW 318 350 NSW- 31 43 00'09" 70 51'55" HWWC Coakley GPW 55 200 NSW- 70 43 00'01" 70 51'43" HWWC Crenshaw GPW 46 350
PORTSMOUTH
PXW- 2 43 04'3411 70 49'13' , Pease AFB Haven GPW 66 900 PXW- 4 43 03'34" 70 47'22" Portsmouth DPW Sherburne GPW 45 450 PXW- 5 43 03'26" 70 47'53" Portsmouth DPW Portsmouth well #1 GPW 63 350 PXW- 47 43 03'5611 70 48'19" Pease AFB Harrison GPW 46 .3 150 PXW- 49 43 03'34" 70 48'24" Pease AFB Smith GPW 67 430
Table 2.--Maximum well yields for major water-supply wells--Continued
User Type Depth Maximum Well Latitude Longitude or Other of of well no . owner identifier well well yield (ft) (gal/min)
RYE
RYW- 12 42 59 12711 70 46'2311 HWWC Jeness Beach GPW 21 125 RYW- 38 42 59'53" 70 47 1 17" Rye Water Dist . Garland GPW 49 400 RYW- 45 42 59'41" 70 47'18" Rye Water Dist . BRW #5A BrW 500 260
SALEM
SAW-207 42 45'34" 71 14 ,43" BCI Inc., Turner BrW 460 416 Salem DPW SAW-208 42 46'23" 71 15'291' BCI Inc., Donigan BrW 250 240 Salem DPW
SEABROOK
SGW- 1 42 53 137" 70 54 ,47" Seabrook DPW GPW #1 GPW 54 350 SGW- 2 42 53 ,37" 70 54 , 51" Seabrook DPW GPW #2 GPW 49 250
SGW- 44 42 53'15" 70 54 , 07" Seabrook DPW GPW #3 GPW 98 350 SGW- 65 42 53'12" 70 53'59" Seabrook DPW GPW #4 GPW 83 400 SGW- 89 42 54 , 17" 70 54 , 59" Seabrook DPW Brw #1 BrW 500 200
SGW- 90 42 54'20" 70 54 , 53" Seabrook DPW BrW #2 BrW 500 350 SGW- 91 42 54'21" 70 54'59" Seabrook DPW BrW #3 BrW 500 500 SGW- 92 42 53'59" 70 54 , 54 1, Seabrook DPW BrW #4 BrW 400 305
WINDHAM
WPW-273 42 48'00" 71 16 , 01" SNHWC W .& E . BrW 345-941 90 (2 wells) WPW-274 42 46'20" 71 18'39" SNHWC Golden Brook DVN 46 100 (2 wells)
Wells finished Wells finished in confined aquifer in unconfined aquifer (artesian wells) (water-table wells)
EXPLANATION SATURATED THICKNESS U Unconfined aquifer C Confined aquifer
0 WATER LEVEL IN WELL
Figure 5.--Idealized geohydrologic section showing unconfined and confined aquifers. in these deposits yield as much as 300 gal/min; how- These breaks in the otherwise solid rock are the con- ever, where coarse sand and gravel overlie thicker duits for ground-water flow and control both the move- deposits of fine-grained sand, silt, and clay, less than ment and storage capacity of water in bedrock. 300 gal/min is expected. Toward the coast, progla- Storage capacity is generally small because the frac- cial deposits thin, probably because the marine tures are narrow and widely spaced. The orientation, waters they were deposited in became progressively width, and number of water-bearing fractures also dif- shallower as relative sea level declined and marine fers from place to place, making systematic exploration sediments accumulated . Thinning of deposits also for large production wells difficult. If two wells are occurred with the retreat of the ice sheet northward. adjacent to each other, different fractures may be in- Outwash in the basin contains generally well- tersected . As a result, one well may yield an ample sorted, coarse-grained deposits with large pore supply of water at depth, whereas the other, even spaces . In many places, a veneer of outwash though drilled to a lesser depth than the first, may yield deposits overlies thick marine deposits; these out- a comparatively small supply. For the most part, how- wash deposits form a thin aquifer with small storage ever, crystalline bedrock is a reliable source of water capacity. Where outwash deposits have a large for both domestic and municipal supplies. saturated thickness, properly constructed, gravel- Information from 94 bedrock wells drilled in packed wells have large yields . Maximum thickness the towns of Greenland, Newington, and Portsmouth of these deposits is in the outwash plain at Kingston. (Stewart, 1968) indicate that the average well drilled Maximum depth to bedrock, determined by seismic- is a domestic well 118 ft deep, up to 6 in . in diameter, refraction, is about 120 ft and, from well logs, is 90 ft . and yielding 13 gal/min. On the basis of these and Currently, high-capacity production wells have not similar data collected from drillings in New England, been drilled in this deposit. the following assumptions were made: crystalline rocks generally yield only small amounts of water to wells and water Till is obtained from vertical fractures that typically pinch out at a depth of 300 ft because of lithostatic pressure (Hodges, 1969) . Till consists of a mixture of grain sizes ranging Data collected for this study from recent drill- from clay to boulders. Because it is dense and contains ings of bedrock municipal wells, however, indicate a large proportion of fine-grained particles, till is con that the crystalline bedrock aquifer beneath the sidered a poor aquifer and normally will not yield region can sustain high yields to properly located enough water to meet municipal, industrial, or com- wells. The maximum yield from eight bedrock mercial needs. Historically, large-diameter wells dug municipal water-supply wells ranges from 200 to in till have provided water for domestic and agricul- 500 gal/min and averages 328 gal/min (table 2) . All tural use, but these wells are shallow (less than 30 ft but one of these high-capacity bedrock wells exceeds deep) and generally yield only a few gallons per 300 ft in depth, and all exceed 8 in. in diameter. In minute. Many wells fail to meet current demands each of these wells, maximum yields were obtained during dry summers when the water table lowers and by drilling to greater depths than previously thought water storage decreases. Layers or lenses of stratified necessary . The rate of ground-water withdrawal sand and gravel are present at places in ablation till from bedrock municipal wells is estimated to be and, where these layers are saturated, more reliable 1 .6 Mgal/d--a rate equal to 21 percent of the ground long-term well yields can be expected. In contrast, water pumped from all public-water-supply wells in basal till is more compact and denser than ablation till the study area. The largest quantities of recoverable and produces a smaller water yield . Because the yield water are found where the bedrock is extensively from the till aquifer is seasonally inadequate to meet fractured or brecciated as a result of the intersection modern domestic demands, the trend is toward the of several fractures and (or) faults (Daniel, 1987) . drilling of bedrock wells. The brecciated zones associated with the north- east- and northwest-trending faults are potential for Bedrock areas providing above-average well yields. Al though the locations of several large northeast- trending faults have been shown on bedrock geology All rocks in the study area have been subjected maps (Billings, 1956; Novotny, 1969; Lyons and to uplift, weathering, and erosion, which have others, 1986), additional information on the struc- resulted in the widening of fractures and the forma tural fabric of the bedrock is necessary to prospect tion of new openings, such as stress-relief fractures . for large yields from bedrock aquifers.
16 GEOHYDROLOGY OF STRATIFIED- characteristics and, where saturated thicknesses DRIFT AQUIFERS are large, would yield large supplies of water to wells . Kame-delta deposits penetrated by well NSW-69 consist of exceptionally clean, well- Stratified drift is subdivided on plates 4-6 into washed coarse-grained sand and pebble gravel four categories on the basis of grain size. These that has a 70-ft saturated thickness. Low rates of categories are (1) coarse-grained material (sand recharge to the aquifer are considered the primary and gravel) with a median particle diameter pre- limit on the productivity of this and many other dominantly larger than 0.0049 in .; (2) fine-grained coastal aquifers . This deposit, like similar kame material (very fine sand, silt, and clay) with a median plains and deltas in the eastern part of the study particle diameter predominantly smaller than area, is small in areal extent; thus recharge from 0.0049 in.; (3) coarse-grained deposits that overlie precipitation is limited. fine-grained deposits; and (4) fine-grained deposits Present at the aquifer margins and within the (including marine) that overlie coarse-grained aquifer section are marine deposits of silt and clay deposits. that are relatively impermeable and do not yield The coarse-grained deposits in the central Pow- usable quantities of water to wells . Where the wow River valley, Derry-Island Pond area, the Gold- marine sediments border the aquifer perimeter en Brook valley, and the isolated kame plains and and extend the full saturated thickness, as in the deltas in Portsmouth-Newington, North Hampton- northwestern end of the section, lateral recharge Hampton, and Kensington (pls. 4-6) constitute some to the aquifer as ground-water discharge from of the most important aquifers in the basin. Of these neighboring uplands is restricted. The deposit is areas, the aquifers at Powwow River, Golden Brook not bordered by land significantly higher in eleva- only valley, and the Derry-Island Pond area are the tion and, therefore, recharge from upland runoff is their maxi- ones not currently developed at or near negligible. In addition, the hydraulic connection yield wells. mum potential to between Cornelius Brook and the aquifer is poor valley- Coarse-grained deposits are part of a because of the presence of marine impermeable train sequence in the Golden Brook valley of sediments in the streambed . Aquifers hydraulical- Windham. The stratigraphy of these proglacial ly isolated from streams can serve as storage reser- deposits is characterized by coarse sand and gravel voirs that can be tapped during late summer overlying very fine to medium sand (fig. 6) . The without causing a serious maximum thickness of these deposits (60 ft) is deter- periods of drought that normally would result mined from seismic-refraction surveys in the area. depletion of streamflow made from aquifers that border Present flow regulation at Golden Brook causes the if withdrawals are sustained by induced infiltration of stream to go dry during parts of the year, and, there- a river and are fore, the brook cannot be considered a reliable river water. source of water to recharge the deposits. In some localities, sand and gravel is buried Geohydrologic section B-B' (fig. 7), which ex- beneath the marine sediment. Geohydrologic sec- tends northwest-southeast across the axis of the tion D-D' (fig. 9) shows that Seabrook municipal Powwow River, shows a striking contrast between wells SGW-44 and SGW-65 are completed in coarse- the level outwash and the irregular bedrock surface. grained sand and gravel, which underlies 20 to 40 ft Seismic-refraction data indicate maximum depths to of fine-grained sand and clay. The contact between bedrock of 125 ft. The outwash-plain deposits are the base of the marine deposits and the underlying generally well-sorted and permeable ; therefore, sand and gravel is gradational at these wells . Con- water is believed to flow easily between this aquifer tacts are typically gradational where clay overlies and the Powwow River and nearby Great Pond. The ice-marginal deposits, deposited as submarine fans aquifer and surface-water bodies are interdepen- and deltas (Thompson and others, in press) in a dent and together comprise a water system that is high-energy environment that prevailed when capable of a high yield to wells completed in the meltwater currents flowed from the nearby ice mar- aquifer . gin. To the northwest, the vertical and horizontal Geohydrologic section C-C' (fig. 8) shows fine- contact between the marine sediments and the sand to coarse-grained sand and gravel underlying a kame and gravel is more abrupt and probably is erosional. delta in North Hampton that is interbedded with A 20-ft-thick layer of ice-contact sand and gravel discontinuous layers of marine sediments . The sand forms an aquifer confined above and below by sedi- and gravel deposits have excellent water-bearing ments.
17
Y 0 A' L0 ma
0 1000 2000 FEET EXPLANATION 0 200 400 600 METERS COARSE SAND AND GRAVEL VERTICAL EXAGGERATION X19 VERY FINE TO MEDIUM SAND
DATUM IS SEA LEVEL TILL BEDROCK --- CONTACT-APPROXIMATELY LOCATED DASHED WHERE INFERRED WPW-38 IDENTIFICATION W NUMBER
Figure 6.--Geohydrologic section A-A' showing the valley train in southern Windham. Line of section is shown on plate 1.
F- y Seismic-refraction data used for control a-- -I!_ Lo 'a
EXPLANATION