Santa Barbara County Groundwater Characterization Project: Santa Ynez River Valley Groundwater Basin Riley Haas, Heal the Ocean Howard Kolb, PE, Central Coast Regional Water Quality Control Board James Bishop, PG, Central Coast Regional Water Quality Control Board Heal the Ocean Central Coast Regional Water Quality Control Board June 18, 2019 Santa Barbara County Groundwater Characterization Project: i Santa Ynez River Valley Groundwater Basin Santa Barbara County Groundwater Characterization Project: ii Santa Ynez River Valley Groundwater Basin Table of Contents Executive Summary ................................................................................................................... 1 1. Introduction ......................................................................................................................... 3 I. Study Area ...................................................................................................................... 4 2. OWTS Risk Assessment ..................................................................................................... 6 I. Introduction ..................................................................................................................... 6 II. OWTS Risk Assessment Methods ................................................................................... 7 III. OWTS Risk Assessment Results and Discussion .......................................................10 3. Groundwater Quality Overview ..........................................................................................11 I. Groundwater Quality Overview Introduction ...................................................................11 II. Groundwater Quality Overview Methods ........................................................................12 III. Groundwater Quality Overview Results and Discussion ..............................................17 Lompoc Plain subbasin ......................................................................................................17 Lompoc Terrace subbasin ..................................................................................................21 Lompoc Upland subbasin ...................................................................................................26 Santa Rita subbasin ...........................................................................................................30 Santa Ynez subbasin .........................................................................................................34 IV. Domestic Wells at Risk ...............................................................................................39 4. OWTS Impacts in the Santa Ynez Subbasin ......................................................................39 I. OWTS Impacts Introduction ............................................................................................39 II. OWTS Impacts Methods ................................................................................................40 III. OWTS Impacts results and Discussion .......................................................................41 Nitrate concentrations and land use ...................................................................................41 Nitrate Concentration Trend Analysis .................................................................................44 OWTS Impacts Statistical Model ........................................................................................48 Conclusions ..............................................................................................................................50 References ...............................................................................................................................53 Appendix A: Tables ...................................................................................................................56 Appendix B: Figures ..................................................................................................................71 Appendix C: Maps .....................................................................................................................75 Santa Barbara County Groundwater Characterization Project: iii Santa Ynez River Valley Groundwater Basin Figures and Maps Figure 1. Santa Ynez River Valley Groundwater subbasin boundaries. ...................................... 4 Figure 2. OWTS density in the Santa Ynez River Valley groundwater basin. ............................ 8 Figure 3. Risk of groundwater contamination by OWTS in the Santa Ynez River Valley groundwater basin. ...................................................................................................................11 Figure 4. Lompoc Plain groundwater subbasin boundary. .........................................................18 Figure 5. Lompoc Terrace groundwater subbasin boundary......................................................22 Figure 6. Lompoc Upland groundwater subbasin boundary.......................................................27 Figure 7. Santa Rita groundwater subbasin boundary. ..............................................................31 Figure 8. Santa Ynez groundwater subbasin boundary. ............................................................35 Figure 9. Map of land use and mean nitrate concentration. .......................................................43 Figure 10. Map of wells with statistically significant trends in concentration through time. ......46 Figure 11. Scatter plots for all wells within the Santa Ynez subbasin with statistically significant trends in nitrate concentration through time. .............................................................................47 Figure 12. Results of regression analysis. ................................................................................50 Figure 13. Box-and-whisker plots of the median arsenic concentration. ....................................71 Figure 14. Box-and-whisker plots of the median iron concentration...........................................72 Figure 15. Box-and-whisker plots of the median hexavalent chromium concentration ...............72 Figure 16. Box-and-whisker plots of the median manganese concentration ..............................73 Figure 17. Box-and-whisker plots of the median nitrate concentration. ......................................73 Figure 18. Box-and-whisker plots of the median sulfate concentration. .....................................74 Figure 19. Box-and-whisker plots of the total dissolved solids concentration. ............................74 Figure 20. Arsenic trend map. ...................................................................................................76 Figure 21. Hexavalent chromium trend map. .............................................................................77 Figure 22. Iron trend map. .........................................................................................................78 Figure 23. Manganese trend map. ............................................................................................79 Figure 24. Nitrate trend map. ....................................................................................................80 Figure 25. Sulfate trend map. ....................................................................................................81 Figure 26. TDS trend map. ........................................................................................................82 Figure 27. Arsenic impaired well map. ......................................................................................83 Figure 28. Hexavalent chromium impaired well map. ................................................................84 Figure 29. Iron impaired well map .............................................................................................85 Figure 30. Manganese impaired well map. ................................................................................86 Figure 31. Nitrate impaired well map. ........................................................................................87 Figure 32. Sulfate impaired well map. .......................................................................................88 Figure 33. TDS impaired well map. ...........................................................................................89 Figure 34. Average domestic well depth map. ...........................................................................90 Santa Barbara County Groundwater Characterization Project: iv Santa Ynez River Valley Groundwater Basin Tables Table 1. Santa Ynez River Valley Groundwater subbasin Descriptions. ..................................... 5 Table 2. Pollutants of concern and respective benchmarks for drinking water ...........................13 Table 3. Groundwater quality objectives....................................................................................13 Table 4. Number of wells from each GeoTracker GAMA dataset. .............................................14 Table 5. Results of regression analysis. ....................................................................................49 Table 6. Ratings and weights for the different parameters used in the OWTS risk model. .........57 Table 7. Select information on wells in the Santa Ynez subbasin with statistically significant changes in concentration through time.. ....................................................................................58