State of Delaware DEPARTMENT OF NATURAL RESOURCES & ENVIRONMENTAL CONTROL John A. Hughes, Secretary Ground-water-quality survey of the Indian River Bay watershed, Sussex County, Delaware: Results of sampling, 2001-03 Prepared by Joshua W. Kasper and Scott A. Strohmeier Reviewed and approved by John T. Barndt, P.G. 2007 Document No. 40-08-05/07/03/01 _______________________ Division of Water Resources, Water Supply Section, Ground-Water Protection Branch State of Delaware Ruth Ann Minner, Governor Department of Natural Resources and Environmental Control John A. Hughes, Secretary Division of Water Resources Kevin C. Donnelly, Director Disclaimer Mention of trade or product names in this report is for descriptive purposes only and does not imply endorsement by the Department of Natural Resources and Environmental Control. Suggested citation Kasper, J.W., and Strohmeier, S.A., 2007, Ground-water-quality survey of the Indian River Bay watershed, Sussex County, Delaware: Results of sampling, 2001-03: Delaware Department of Natural Resources and Environmental Control Document No. 40-08-05/07/03/01, 57 p. Contents Introduction..................................................................................................................................... 1 Purpose and scope...............................................................................................................2 Acknowledgements............................................................................................................. 2 Description of study area ................................................................................................................ 2 Land use.............................................................................................................................. 2 Hydrogeology ..................................................................................................................... 3 Recharge potential ..............................................................................................................4 Methods of study............................................................................................................................. 4 Description of well network................................................................................................ 4 Ground-water-sample collection and laboratory analysis................................................... 5 Quality assurance and quality control................................................................................. 7 Data analysis ....................................................................................................................... 8 Results and discussion.................................................................................................................... 9 General ground-water quality ............................................................................................. 9 Major-ion chemistry.......................................................................................................... 14 Nutrient results.................................................................................................................. 16 Nitrate ................................................................................................................... 17 Ammonia............................................................................................................... 23 Phosphorus............................................................................................................ 23 Summary and conclusions ............................................................................................................ 26 References..................................................................................................................................... 27 Figures 1. Map showing the location of the Indian River Bay watershed.................................................. 1 2. Map of the Indian River Bay watershed showing sample locations and 1997 land-use classifications and pie chart showing areal percentages of 1997 land-use classifications.......................................................................................... 3 3. Map of the Indian River Bay watershed showing sample locations and recharge-potential classifications and pie chart showing areal percentages of recharge-potential classifications ................................................................................... 5 4. Percentile diagram of sample depth distribution, frequency histogram of sample depth, and frequency histogram of well classification ........................................... 6 5. Frequency histogram of project analyte qualification ............................................................. 12 6. Map showing sampled wells with nitrate concentrations above the Primary Maximum Contaminant Level for public water-supply systems...................................... 13 7. Map showing sampled wells with iron concentrations above the Secondary Maximum Contaminant Level for public water-supply systems...................................... 14 8. Piper diagram showing major-ion chemistry for all samples with complete chemical analyses.............................................................................................................. 15 9. Piper diagram showing major-ion chemistry for samples with nitrate concentrations less than 0.4 milligrams per liter and complete chemical analyses.............................................................................................................. 16 i 10. Piper diagram showing major-ion chemistry for samples with nitrate concentrations greater than 10 milligrams per liter and complete chemical analyses.............................................................................................................. 17 11. Scatter plot of calcium plus magnesium versus nitrate for samples under oxidizing conditions.......................................................................................................... 18 12. Frequency histogram of nitrate detections............................................................................. 18 13. Map showing nitrate concentration ranges ............................................................................ 19 14. Map of intermediate watersheds of the Indian River Bay watershed and percentile diagram of nitrate distributions for each of those watersheds.......................... 20 15. Scatter plot of nitrate versus sample depth ............................................................................ 21 16. Percentile diagram of nitrate distributions versus sample depth ........................................... 21 17. Percentile diagrams showing nitrate and ammonia distributions for oxidizing and reducing conditions.................................................................................... 21 18. Percentile diagrams showing nitrate and ammonia distributions for each recharge-potential setting ......................................................................................... 22 19. Frequency histogram of ammonia detections ........................................................................ 23 20. Frequency histogram of phosphorus detections..................................................................... 24 21. Scatter plot of phosphorus versus sample depth.................................................................... 24 22. Percentile diagram showing phosphorus distributions for oxidizing and reducing conditions.................................................................................... 24 23. Percentile diagram showing phosphorus distributions for each recharge-potential setting. ........................................................................................ 24 24. Map showing phosphorus concentration ranges..................................................................... 25 Tables 1. Project analytes, analytical methods, and related information. ................................................. 8 2. Statistical summary of ground-water-quality data for the Indian River Bay watershed .......................................................................................................................... 10 Appendices 1. Maps showing locations of wells sampled in grids A thru J.................................................... 30 2. Well details and ground-water-quality data for the Indian River Bay watershed, 2001-03........................................................................................................... 43 3. Summary of duplicate data for the Indian River Bay watershed, 2001-03.............................. 56 4. Summary of equipment blank data for the Indian River Bay watershed, 2001-03.................. 57 ii Ground-water-quality survey of the Indian River Bay watershed, Sussex County, Delaware: Results of sampling, 2001-03 By Joshua W. Kasper and Scott A. Strohmeier INTRODUCTION collected samples during 2001-03 from wells completed in the Columbia aquifer, which also is The Indian River Bay (IRB) watershed recognized as the unconfined or water-table aquifer located in Sussex County, Delaware (Figure 1), in the Coastal Plain of Delaware (Andres, 1987; contains a coastal lagoon, tidal and non-tidal streams, Talley, 1988). Primary project objectives were to (i) and ponds that are enriched with nitrogen (N) and assess and document the current distribution of major phosphorus (P).