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GEOHYDROLOGY of the HOCKESSIN AREA with EMPHASIS on the COCKEYSVILLE AQUIFER By

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GEOHYDROLOGY of the HOCKESSIN AREA with EMPHASIS on the COCKEYSVILLE AQUIFER By State of Delaware DELAWARE GEOLOGICAL SURVEY Robert R. Jordan, State Geologist BULLETIN NO. 19 John H. Talley, Editor GEOLOGY AND HYDROLOGY OF THE COCKEYSVILLE FORMATION NORTHERN NEW CASTLE COUNTY, DELAWARE GEOLOGY OF THE COCKEYSVILLE FORMATION by Kenneth D. Woodruff and Margaret 0. Plank GEOHYDROLOGY OF THE HOCKESSIN AREA WITH EMPHASIS ON THE COCKEYSVILLE AQUIFER by William H. Werkheiser University of Delaware Newark, Delaware 1995 State of Delaware DELAWARE GEOLOGICAL SURVEY Robert R. Jordan, State Geologist BULLETIN NO. 19 John H. Talley, Editor GEOLOGY AND HYDROLOGY OF THE COCKEYSVILLE FORMATION NORTHERN NEW CASTLE COUNTY, DELAWARE GEOLOGY OF THE COCKEYSVILLE FORMATION by Kenneth D. Woodruff and Margaret 0. Plank GEOHYDROLOGY OF THE HOCKESSIN AREA WITH EMPHASIS ON THE COCKEYSVILLE AQUIFER by William H. Werkheiser University of Delaware Newark, Delaware 1995 CONTENTS Page Page ABSTRACT . ..... ..... ........... .................. I Gravity and Magnetics .... ........................... 22 Structural Relations in the Mill Creek Dome .. ..... .... 22 INTRODUCTION by John H. Talley........ .......................... .. .. 2 SUMMARY AND CONCLUSIONS ...... ..... ......... ... 23 Purpose and Scope . 2 GEOHYDROLOGY OF THE HOCKESSIN AREA Locations of Study Areas . 2 WITH EMPHASIS ON THE COCKEYSYILLE AQUIFER Acknowledgments . 4 by William H. Werkheiser ........ ..................... 26 GEOLOGY OF THE COCKEYSYILLE FORMATION INTRODUCTION ..... .................. ... ... .. ... 26 by Kenneth D. Woodruff and Margaret 0. Plank . 4 GEOHYDROLOGY ....................................... 28 INTRODUCTION . 4 Geohydrologic Framework and Regional Setting . 4 Ground-Water Occurrence ................ ... .... 28 Previous Work . 6 Cockeysville Aquifer ................ ............ .... 32 Methods of In vesti gation . 6 Boundaries ............................................ 32 Field Mapping . 6 Recharge ..... ... ... ................... .. .. ....... 32 Test Drilling . 6 Discharge ... ..... ...... .......... ................. 35 Geophysical Logging . 6 Flow Directions and Water Levels .................... 35 Gravity Survey . 6 Water Quality . .. ... .. .... ....................... .... 39 Petrographic Analysis . 7 Occurrence of Chemical Constituents .... .... ....... 40 ROCK UNITS OF THE STUDY AREA . 8 Evidence for Ground-Water Flow Between Aquifers .. 42 Geologic Units Adjoining Cockeysville Formation . 8 Water Budgets ................ ......... .. ............. 43 Baltimore Gneiss . 8 Mill Creek Basin . .. ... ........ ......... .. ............ 43 Setters Formation . 9 Ground-Water Budget for the Stressed Part Wissahickon Formation . 9 of the Cockeysville Aquifer ......................... 46 Cockeysville Formation . 11 Effect of Reduced Recharge on the Ground-Water Field Description .................. ... ............... 11 Budget for the Cockeysville Aquifer ................ 47 Mapping ...... .. .................................... 11 SUMMARY AND CONCLUSIONS .. .. ................... 47 Lithology . 12 Petrography . 14 REFERENCES CITED . ..... .............. .... ... ...... 48 Fractures and Solution Cavities . ...... .... ........... 14 APPENDICES ... .... .... .... .... .. .. ...................... 5 1 Weathered Zone ...... ...... .. ..... ....... ... 15 I. Conversion factors, vertical datum. STRUCTURAL GEOLOGY ............. .... ........... 16 and abbreviated water-quality uni ts .. ........... ... 51 Hockessin-Yorklyn Area . 16 2. Map coordinates for rock samples Borehole Data . 17 used for modal analyses ...... ... .. ... ... .. ...... 51 Field Observations . 18 3. Records of wells in the Gravity and Magnetics .... .......... ................. 18 Hockessin and Pleasant Hill areas ............ ..... 5 1 Pleasant Hill Area ..... ... .. .. .. ... ... ............ 18 4. Chemical analyses of ground and Borehole Data . 18 surface water in the Hockessin area ..... ..... ..... 56 ILLUSTRATIONS Plate I. Geologic map of the Pleasant Hill-Hockessin area ... ... .................... ............... .. ... ... .. ............... Pocket Page Figure I . Map showing locations of study areas . 3 2. Map showing location of study area for the geohydrology portion of the study . 5 3. Map showing location of wells and test holes drilled in support of this investigation . 7 4. Diagram showing Wi ssahickon-Cockeysville contact south of Hockessin . 11 5. Gamma-ray logs from well s in the Cockeysville Formation .. .. ................ ........................................... 12 6. Selected geophysical logs and lithology from test hole Bb35- I 6 . .. .. .. 13 7. Acoustic televiewer log of a portion of well Bb33-26 .. ............................................ ............. ......... 15 8. Acoustic televiewer log of a portion of well Bb34-35 . .......................... ............ ...... ... ............ .. 15 9. Acoustic televiewer log of a portion of well Bb44-22 ................. .. ............. ........ .. ... ...... ... ........ 16 10. Temperature logs in well Bb33-28 . ............ .. ................. ..................... ... ... ................. .. .. .. 16 11. Thickness of weathered zone in the Cockeysville Formation ................. .. ................... ......................... 17 12. Basic scheme for structural relations in the Delaware-Pennsylvani a Piedmont ..... ....................... ............... 18 13. Map showing locations of cross-sections . 19 14. Schematic cross-sections A-A'. B-B'. C-C', and D-D' in the Hockessin and Pleasant Hill areas ... .................... ..... 20 15. Descriptive and gamma-ray logs. composite for test holes Bb44-22 and Bb44-30 . ............... ......... ..... ...... .... 21 16. Bouguer gravity map of the Hockessin area .... .. ....... ... ................................ .......... .................. 22 17. Gravity model across the Hockessin-Yorklyn area .... ... ... ......... ...... ............... .......... ...... .... ..... .... 23 18. Aeromagnetic map of the study area ..................... ..................................... ... ........ ................. 24 19. Generalized geologic map of the Mill Creek dome .... .... ....... .. ....................... ...... .. ... ..... ...... 25 20. Graph showing precipitation at Wilmington, Delaware, 1961-90 ...... ......... .............. ... ......................... 26 21. Map showing well locations in the Hockessin area ............................. ... ...... .. .............. .... ...... 27 22. Graph showing ground-water withdrawals in the Hockessin area, 1975-90 . ... .. ......... ... ... .. .... .................. 28 23. Map showing data-collection sites in the Hockessin area ................. .... ..... ....... .. ................. ...... ..... 29 24. Graphs showing caliper logs for wells in the Cockeysville aquifer ..... ...... ..................... ... ... ... ..... ..... 30 25. Generalized hydrogeologic section of the Hockessin area .............. ... .. ............. ..... ............ ........... 3 1 26-30. Maps showing: 26. Stream discharge on June 27, 1990, and October 3, 1990 . ...... ... ... ............................. ....... .............. 33 27. Stream discharge on April 4, 1991 ........ .... .... ..... .. ....... ... ............................. ... .................. 34 28. Water-level altitudes in aquifers underlying White Briar ..... .......................................... .. ... ... ........ 36 29. Water-level altitudes in aquifers in the Hockessin area, November 14-16, 1990 ............................ .. .. ... ........ 37 30. Water-level altitudes in the Cockeysville aquifer, 1955 ....................................... .. ......................... 38 31-36. Graphs showing: 3 1. Water levels in observation wells .... ................. .............. .... ............... ... ..................... ... 39 (A) in the unstressed part of the Cockeysville aquifer . ... ..... ... ...... .......................... .......................... 39 (B) in the stressed part of the Cockeysville aquifer ....................................... .. ... ......................... 39 32. WaterlevelsinobservationwellBb43- 13, 1977-90 ...... .. ... .. ....... .................................... ................ 39 33. Water levels in observation well Bb34-40, 1979-90 ............................ ........................................ .. 39 34. Water levels in observation wells near pumped wells ... .................................. .............. .................. 40 35. Tri linear diagram for ground water from the Hockessin area ................................................................ 41 36. Box plots showing alkalinity, hardness. dissolved solids, and strontium concentrations in water from aquifers in the Hockessin area ................ ... ........... .. ............................................... 42 37-40. Graphs showing: 37. Relation of sum of cation concentrations to chloride concentrations ............ .................... .. .............. 42 38. Relation of sum of cation concentrations to strontium concentrati ons ...... ... ................................... .. ..... 43 39. Discharge of Mill C reek at Mill Creek Road at Hockessin, 1990 ................................................ ... .... .... 44 40. Annual recharge lO the Cockeysvi lie aquifer, 1978-90 ................................................................. .... 4 7 TABLES Page Table 1. Rocks of the Delaware Piedmont .. ............................................. ....... ............................... ...... 8 2. Modal analyses of the Baltimore Gneiss
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