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Pete McLaughlin, Amanda Lawson, and Jaime Tomlinson

Aquifer mapping in Kent and Sussex Counties, Delaware: A key to understanding groundwater sources A Presentation to the 2013 Region 3 Source Water Protection Meeting June 6, 2013. Pete McLaughlin, Amanda Lawson, and Jaime Tomlinson Delaware Geological Survey, University of Delaware.

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Pete McLaughlin, Amanda Lawson, and Jaime Tomlinson

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  1. Aquifer mapping in Kent and Sussex Counties, Delaware: A key tounderstanding groundwater sources A Presentation to the 2013 Region 3 Source Water Protection MeetingJune 6, 2013 Pete McLaughlin, Amanda Lawson, and Jaime Tomlinson Delaware Geological Survey, University of Delaware

  2. Where Source Water Protection Meets Geology • Your challenge: Identifying drinking water sources and protecting these source waters from contaminants • An understanding the source aquifer and groundwater flow within it allows delineation of source water assessment boundaries • An understanding of subsurface geology is necessary to accurately characterize the ground water source • Key geologic aspects: • Aquifer delination (geographic, depth) • Aquifer hydrologic characteristics • Nature of associated confining units

  3. Starting Premise Accurate Understanding of Aquifer Geology is essential to Accurate Understanding of Groundwater Occurrence Geology controls where the groundwater is, where it goes, and how much we get

  4. The Idea: A Project • Identify and delineate the aquifers of southern Delaware (Kent and Sussex Counties) the are sources of public drinking water • Determine where these aquifers are used as drinking water sources and the magnitude of withdrawals • Conducted by DGS, supported by DNREC

  5. Objectives and Background • Aquifers of Southern Delaware • Water Use in Southern Delaware Outline

  6. Goal: To establish an up-to-date summary of the groundwater resources of Kent and Sussex Counties, Delaware Incentives: The last comprehensive report on ground-water availability and aquifers in Sussex County was published more than 40 years ago (Sundstrom and Pickett, 1968) Reported aquifers in state, federal, and SWAPP databases are not always correct Benefit: The results of this work will support source water protection, well permitting, and water supply planning programs in Delaware

  7. Kent + Sussex Groundwater Use MGD Data from USGS (http://water.usgs.gov/watuse/data/2005/ )

  8. Kent + Sussex Population Data from USGS (http://water.usgs.gov/watuse/data/2005/ )

  9. Kent + Sussex Groundwater Use + 13? MGD if 130K population growth in 2030 PLUS more irrigation MGD

  10. Objectives Primary purpose: Updated summary of the ground-water resources of Kent and Sussex Counties, Delaware, in two parts: • Aquifer geology: • to compile geological cross-sections highlighting the correlation of aquifers • to construct structural contour and isopach maps of the aquifers • to acquire new data in areas where geological control is lacking, including new drilling and geophysical logging • Hydrology: • to compile data on water use in Sussex County, • to characterize the hydrologic characteristics of each aquifer, • summarized these within the updated aquifer framework.

  11. Objectives Recent related work: • Confined aquifer mapping for Kent County (McLaughlin and Velez, 2006) • Unconfined aquifer mapping for Sussex County (Andres and Klingbeil, 2006) Strategy: • use selected, high-quality data; • establish carefully documented methodologies for estimation/interpretation where high-quality data are lacking; • identify issues where a lack of adequate data indicates a need for further study (project will not address organizational/ quality control issues of all potentially available data).

  12. Geology&Hydrology

  13. Geology: Formations

  14. Geology: Aquifers

  15. Geology Methods & Data • Stratigraphic picks for tops and bottoms of aquifers (and formations) • Assembled stratigraphic picks database of 14000 records plus another 2300 records of sites where picks not made or were redacted • Stratigraphic picks database includes app. 6600 wells with stratigraphic picks and records of app. 2100 others evaluated but not suitable for picks

  16. Geology Methods & Data • Dense coverage of picks in Delaware • Extended picks into MD and NJ to minimize edge effects at borders

  17. GeologyMethods & Data • Drilled test holes at 10 locations where availability of confined aquifer data was sparse • Holes ranged from 600 to 840 ft depth • Cuttings sample were collected, lithologic logs were created, and geophysical logs (gamma-multipoint electric) were recorded • Benefit: High quality deep confined aquifer picks

  18. Unconfined Aquifer Methods & Data • New picks for Kent County; for Sussex used data and maps of A&K-2006 • Utilized geophysical logs, geologist logs, and driller logs • maximize data volume given degree of local variation • Well ranking system • 1 = Geophysical log and a descriptive log • 2 = Geophysical log only • 3 = Descriptive log only • 4 = Poor quality log • 5 = Unable to make pick

  19. Unconfined Aquifer Methods & Data • Can we take single driller logs face value? • Aim for consistency, esp. with geologist & geophysical logs example: block Md42

  20. Unconfined Aquifer Methods & Data Created Kent County unconfined aquifer grids Reviewed drillers logs in detail, aggressive accept/reject approach emphasizing consistency Elevation of Base Unconfined grid created using Radial Basis Function method in ArcGISGeostatistical Analyst Unconfined Thickness grid computed from surface DEM and base elevation grid Final grids corrected for 3-dimensional constraints (topography) Created a K-S unconfined grid by stitching new Kent unconfined elevation grid and existing A&K-2006 Sussex unconfined elevation grid

  21. Unconfined AquiferElevation Grid:Kent County

  22. Unconfined aquifer & geology • Common scattered beds of clayey silt • Silt to fine sand over medium to coarse sand in upper 5-25’ • Rare discontinuous clayey silt beds • Heterogeneous coarse to fine sand, gravelly sand, and pebble gravel

  23. Unconfined Aquifer, Sussex County Klingbeil and Andres, 2006 • Thickness map • Elevation of base • Transmissivity map • > 4200 data points • Used drillers’ and geophysical logs

  24. Unconfinedaquifer • Thickness map • Elevation of base • > 1600 data points • Splice with Sussex map

  25. UnconfinedaquiferKent + Sussex

  26. Confined Aquifer Methods & Data • Picks mostly from geophysical logs, a smaller number from lithologic logs with high-confidence data • Depths converted to elevation by subtracting from well elevation • significant elevation data QC required • Values exported from stratigraphic database and imported into ArcGIS as point data

  27. Confined Aquifer Methods & Data • Gridding utilized Radial Basis Function (multiquadric) method in ArcGIS Geostatistical Analyst • Used 100 m grid resolution • Grids made for each confined aquifer of: • top aquifer from picks • base aquifer from picks • aquifer thickness by grid math

  28. Confined Aquifer Methods & Data Grid QC work • Grids checked against intersection with overlying and underlying surfaces • in some cases, dummy or projected values used to ensure non-intersecting grid position in sparse data areas • Grid surfaces are cut-away where overlying surface occurs lower • most significant case: base of unconfined aquifer occurring below top of base of a confined aquifer, which means normally confined sand unit is not confined there

  29. Mount Laurel aquifer

  30. Rancocas aquifer

  31. Piney Point aquifer

  32. Lower Calvert sand sand unit below the Cheswold sand

  33. Cheswold sand

  34. Example of how to represent an aquifer in 3D contextCheswold sand somewhat simplified represented to updip limit of presence regardless of elevation of base unconfined accurate in 3 dimensions not represented on grid where based unconfined is lower

  35. “Federalsburg” sand

  36. Frederica sand

  37. Milford sand

  38. middle Choptank sand

  39. upper Choptank sand

  40. Manokin aquifer

  41. Manokin aquifersimplified, unconfined not accounted for

  42. Manokinaquifersubcrop Implications for Recharge andSource Water Protection

  43. Pocomoke aquifer

  44. Pocomoke aquifersimplified, unconfined not accounted for

  45. Pocomokeaquifersubcrop Implications for Recharge andSource Water Protection

  46. GroundwaterUse

  47. Groundwater Use Methods & DataGroundwater Use Calculations Public Industrial Domestic Livestock Irrigation Metered/ Reported for big systems + Estimated For smaller systems Assumed usage rates per user type X Population or size of facility served Metered/ Reported Estimated Irrigated acres X Estimated water use by crop type and soils calibrated to Known usage for metered irrigation Estimated Population outside public-served areas X socioeconomic-based per capita coefficient Calibrated to Known usage in similar public served areas Estimated Livestock populations X Average water use/type of livestock

  48. Compilation of Water Use Data Theoretically: • Reported Water Use (large users, allocations) • large public • industrial & thermoelectric • irrigation (ag & golf course) • Non-Reported Water Use (smaller users) • smaller public • domestic self-supplied • livestock • lawn self-supplied • other minor types

  49. Groundwater Use Data Well location data • DGS WATSYS Oracle database, includes multiple regular dumps of DNREC well database • SWAPP database dump used for list/locations/depths of public wells

  50. Groundwater Use Data2004-2008 Water Use Database with ~42,000 records and 930+ wells

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