GEOHYDROLOGY AND WATER QUALITY OF STRATIFIED-DRIFT AQUIFERS IN THE BELLAMY, COCHECO, AND SALMON FALLS RIVER BASINS, SOUTHEASTERN NEW HAMPSHIRE By Thomas J. Mack and Sean M. Lawlor U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 90-4161 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, Copies of this report can write to: be purchased from: Chief, NH-VT Office U.S. Geological Survey U.S. Geological Survey Books and Open-File Reports Section Water Resources Division Federal Center 525 Clinton Street Box 25425 Bow, NH 03304 Denver, CO 80225 CONTENTS Page Abstract..................................................................... 1 Introduction ................................................................. 1 Purpose and scope .......................................................... 2 Previous investigations ...................................................... 2 Acknowledgments .......................................................... 4 Approach and methods ......................................................... 4 Geohydrologic units ........................................................... 12 Stratified drift ............................................................. 12 Till ...................................................................... 14 Bedrock .................................................................. 14 Geohydrology of stratified-drift aquifers ........................................... 14 Aquifer boundaries ......................................................... 15 Recharge, discharge, and direction of ground-water flow ........................... 15 Saturated thickness and storage .............................................. 16 Hydraulic conductivity and transmissivity ...................................... 17 Aquifer characteristics, by river basin .......................................... 18 Bellamy and lower Cocheco .............................................. 18 Middle Cocheco ........................................................ 21 Upper Cocheco ......................................................... 21 Ela .................................................................. 21 Lower Salmon Falls .................................................... 21 Middle Salmon Falls .................................................... 23 Upper Salmon Falls and Branch .......................................... 25 Isinglass .............................................................. 27 Simulation of ground-water flow and effects of pumping ........................... 27 Flow model of the New Durham aquifer .................................... 27 Model grid and boundaries ........................................... 27 Aquifer hydraulic properties .......................................... 29 Recharge and discharge ............................................. 29 Calibration ........................................................ 29 Sensitivity analysis ................................................. 32 Simulation of pumping at hypothetical wells ............................ 34 Flow model of the Farmington aquifer ...................................... 42 Model grid and boundaries ........................................... 42 Aquifer hydraulic properties .......................................... 42 Recharge and discharge ............................................. 42 Calibration ........................................................ 43 Sensitivity analysis ................................................. 45 Simulation of pumping at hypothetical wells ............................ 48 Water quality ................................................................ 48 Common and trace constituents ............................................... 55 Organic constituents ........................................................ 56 Hi CONTENTS (Continued) Page Summary and conclusions ...................................................... 56 Selected references ............................................................ 58 Glossary .................................................................... 63 Appendix: Geologic sections interpreted from seismic-refraction data .................. A-l PLATES (Plates are in map jacket) Plates 1-3. Maps showing aquifer boundaries, data-collection locations, and altitudes of water table in the: 1. Southeastern area. 2. Southwestern area. 3. Northern area. 4-6. Maps showing saturated thickness of stratified drift and transmissivity in the: 4. Southeastern area. 5. Southwestern area. 6. Northern area. ILLUSTRATIONS Page Figure I. Index map showing location of study area (Bellamy, Cocheco, and Salmon Falls River basins) southeastern New Hampshire ............... 3 2. Diagram showing seismic-reflection operation and ray paths .................... 5 3. Geologic sections interpreted from seismic-reflection data for: a. Dover Point and Bellamy River, Dover, a-a' ............................ 7 b. Bow Lake, Strafford, b-b' ........................................... 8 c. Salmon Falls River at Town House Road, Milton, c-c'..................... 9 d. Great East Lake, Wakefield, d-d' ..................................... 10 e. Great East Lake, Wakefield, e-e' ..................................... 11 4. Diagram showing seismic-refraction operation and ray paths .................... 12 5. Block diagram showing a valley-fill aquifer ................................... 13 iv ILLUSTRATIONS (Continued) Page Figure 6. Block diagram showing a glacioestuarine deltaic aquifer ........................ 13 7. Hydrograph of water level in well NFW-23 in New Durham and in well RHW-6 in Rochester ........................................ 16 8. Geologic section through the: a. Hoppers aquifer in Dover and Rochester, A-A' .......................... 20 b. Farmington aquifer, B-B' ........................................... 22 c. New Durham aquifer, C-C' .......................................... 23 d. Milton Three Ponds aquifer, D-D' .................................... 24 e. Branch River valley of Wakefield, E-E' ................................ 25 f. Great East Lake to Lake Ivanhoe, Wakefield, F-F ........................ 26 9. Map showing model grid and cell types for the New Durham aquifer .............. 28 10. Simulated water-table configuration in the New Durham stratified-drift aquifer .... 31 11. Effects of varying the model input on computed heads for the New Durham aquifer .. 33 12-16. Maps showing simulated water-table configuration in the New Durham aquifer when wells: 12. NFW-53 is pumped at 0.25 million gallons per day ..................... 35 13. NFW-53 is pumped at 0.50 million gallons per day ..................... 36 14. NFW-52 is pumped at 0.25 million gallons per day ..................... 37 15. NFW-52 is pumped at 0.50 million gallons per day ..................... 38 16. NFW-52 and NFW-53 are pumped at 0.25 and 0.50 million gallons per day . 39 17. Map showing model grid and cell types for the Farmington aquifer ............... 41 18. Simulated water-table configuration in the Farmington stratified-drift aquifer ...... 44 19. Effects of varying model input on computed heads for the Farmington aquifer ...... 46 20-23. Maps showing simulated water-table configuration in the Farmington aquifer when well: 20. FAW-73 is pumped at 0.25 million gallons per day ...................... 49 21. FAW-71 is pumped at 0.25 million gallons per day ...................... 50 22. FAW-71 is pumped at 0.50 million gallons per day ...................... 51 23. FAW-73 and FAW-71 are pumped at 0.25 million gallons per day ......... 52 TABLES Page Table 1. Two-character town codes used as prefixes in the numbering system for wells and borings ................................................. 4 2. Relation of mean horizontal hydraulic conductivity to mean grain size ............. 18 3. Average saturated thickness and estimated transmissivity and horizontal hydraulic conductivity according to published reports ...................... 19 4a. Relation of model-calculated and measured heads in the final calibrated steady-state model for the New Durham aquifer ........................... 30 4b. Model-calculated steady-state water budget for average conditions in the New Durham aquifer ................................................. 30 5. Changes in model-calculated heads during sensitivity testing of the New Durham aquifer model............................................ 32 6. Effects of simulated steady-state pumping on water levels in the New Durham aquifer and on flow in the Ela and Merrymeeting Rivers .................... 40 la. Relation of model-calculated and measured heads in the final calibrated steady-state model for the Farmington aquifer ............................ 43 7b. Model-calculated water budget for steady-state conditions in the Farmington aquifer .................................................. 43 8. Changes in model-calculated heads during sensitivity testing of the Farmington aquifer model ............................................. 45 9. Effects of simulated, steady-state pumping on water levels and streamflow in the Farmington aquifer ............................................. 47 10. Summary of results of water-quality-sample analyses .......................... 53 11. Volatile organic compounds in water samples from 21 wells