Scientific Investigations Report 2007–5237
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5237
Evaluation of Approaches for Managing Nitrate Loading from On-Site Wastewater Systems near La Pine, Oregon
Prepared in cooperation with the Oregon Department of Environmental Quality and Deschutes County
By David S. Morgan, Stephen R. Hinkle, U.S. Geological Survey, and
Rodney J. Weick, Oregon Department of Environmental Quality
Table of Contents
Conversion Factors, Datums, and Abbreviations and Acronyms
Abstract
Introduction
Conceptual Model of Ground-Water System
Nitrate Fate and Transport Simulation Models
Nitrate Loading Management Model
Limitations and Appropriate Use of Models
Summary and Conclusions
Acknowledgments
References Cited
Appendix A. Vertical Hydraulic Head Gradient Data from Measurements Made on the Deschutes and Little Deschutes Rivers, in the La Pine, Oregon, Study Area, October 23– November 4, 2000.
Figures
Figure 1. Location of La Pine study area, Oregon, and extent of the nitrate fate and transport model.
Figure 2. Generalized geology and hydrogeologic units of the La Pine region, Oregon.
Figure 3. Three dimensional hydrogeologic model of the La Pine, Oregon, study area.
Figure 4. Distributions of estimated hydraulic conductivity values from slug tests and well-yield data.
Figure 5. Distribution of mean annual recharge, water-table elevation contours (June 2000), and locations of monitoring wells in the La Pine, Oregon, study area.
Figure 6. Water levels in selected wells in the La Pine, Oregon, study area.
Figure 7. Gaining and losing reaches of the Deschutes and Little Deschutes Rivers and locations of measurement sites for gain-loss surveys between October 1995 and October 2000 in the La Pine, Oregon, study area.
Figure 8. Estimated thickness of oxic ground-water layer in the shallow aquifer in the La Pine, Oregon, study area.
Figure 9. Annual and cumulative estimated nitrate loading from on-site wastewater systems in the La Pine, Oregon study area, 1960–2005.
Figure 10. Spatial relations between the upper Deschutes Basin regional ground-water model, the La Pine study area model, and the transect model.
Figure 11. Plan and section views of the transect model showing simulated water-levels, ground-water travel time, and particle paths in the La Pine, Oregon, study area.
Figure 12. Contours of simulated and observed heads (June 2000) for the La Pine, Oregon, study area.
Figure 13. Simulated head residuals and observed heads (June 2000) from the La Pine, Oregon, study area.
Figure 14. Measured and simulated nitrate concentrations in the La Pine, Oregon, study area, 1999.
Figure 15. Simulated nitrate concentrations near the water table in the La Pine, Oregon, study area, 1999.
Figure 16. Historical nitrate loading from on-site wastewater systems and eight nitrate loading scenarios tested with the study-area model.
Figure 17. Simulated equilibrium ground-water nitrate concentrations near the water table for the base scenario in the La Pine, Oregon, study area.
Figure 18. Simulated equilibrium ground-water nitrate concentrations near the water table for 20 milligrams N per liter advanced treatment on-site wastewater systems in the La Pine, Oregon, study area.
Figure 19. Locations of management areas and ground-water nitrate concentration constraint locations in the Nitrate Loading Management Model for the La Pine, Oregon, study area.
Figure 20. Locations of management areas near Burgess Road and management area 31 in the La Pine, Oregon, study area.
Figure 21. Sensitivity of optimal loading solutions to ground-water nitrate concentration constraints in the La Pine, Oregon, study area.
Figure 22. Sensitivity of optimal loading solutions to constraints on the minimum reduction in ground-water discharge loading to streams in the La Pine, Oregon, study area.
Figure 23. Sensitivity of optimal solution to minimum decentralized wastewater treatment performance standards for future homes in the La Pine, Oregon, study area.
Figure 24. Sensitivity of optimal solutions to relative cost difference of nitrate loading reduction for existing and future homes in the La Pine, Oregon, study area.
Figure 25. Optimal reduction in nitrate loading from existing homes in the La Pine, Oregon, study area.
Figure 26. Optimal reduction in nitrate loading from future homes in the La Pine, Oregon, study area.
Figure 27. Comparison of loading and water quality between optimal and nonoptimal management scenarios for the La Pine, Oregon, study area.
Tables
Table 1. Markov chain model parameters and transition probabilities in the final hydrofacies model.
Table 2. Hydraulic conductivity estimates from slug test data from wells near LaPine, Oregon.
Table 3. Basin information for water-level monitoring wells in the La Pine, Oregon, study area.
Table 4. Summary of data from stream gain-loss surveys on the Deschutes and Little Deschutes Rivers in the La Pine, Oregon, study area, 1995–2000.
Table 5. Values of horizontal and vertical hydraulic conductivity for hydrofacies based on field data and model calibration in the La Pine, Oregon, study area.
Table 6. Summary of eight on-site wastewater management scenarios tested with the study-area model in the La Pine, Oregon, study area.
Table 7. Summary of model simulation results for eight on-site wastewater management scenarios tested with the study-area model in the La Pine, Oregon, study area.
Table 8. Response coefficients relating the effects of loading in nearby areas to the nitrate concentration at a constraint location in management area 31 in the La Pine, Oregon, study area.
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Send questions or comments about this report to the author, D.S. Morgan, (503) 251-3263.
For more information about USGS activities in Oregon, visit the USGS Oregon Water Science Center home page.
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