CITY OF SEQUIM 2008 HYDROLOGIC MONITORING REPORT DECEMBER 2009 CITY OF SEQUIIM 2008 HYDROGEOLOGIC MONITORING REPORT Prepared for: City of Sequim Department of Public Works 152 W. Cedar St. Sequim, Washington 98382 Prepared by: Pacific Groundwater Group 2377 Eastlake Avenue East, Suite 200 Seattle, Washington 98102 206.329.0141 www.pgwg.com December 2009 JZ0803 2008SequimMonitoringStudy-final.doc TABLE OF CONTENTS 1.0 INTRODUCTION ........................................................................................................................... 1 2.0 SUMMARY OF FINDINGS AND RECOMMENDATIONS...................................................... 2 3.0 HYDROLOGIC SYSTEM ............................................................................................................. 7 3.1 SURFACE WATER HYDROLOGY ..................................................................................................... 7 3.2 GROUNDWATER HYDROLOGY ....................................................................................................... 7 4.0 CLIMATE TRENDS ..................................................................................................................... 10 4.1 DATA SOURCES ............................................................................................................................ 10 4.2 PRECIPITATION ............................................................................................................................ 11 4.2.1 Rain ........................................................................................................................................ 11 4.2.2 Snow ....................................................................................................................................... 11 4.3 TEMPERATURE ............................................................................................................................. 12 4.4 CLIMATE CHANGE PREDICTIONS ................................................................................................. 12 4.4.1 Predicted Temperature Increases ........................................................................................... 12 4.4.2 Predicted Changes in Precipitation and Snowpack ................................................................ 13 4.4.3 Sea Level Rise ......................................................................................................................... 13 5.0 STREAMFLOW TRENDS........................................................................................................... 14 5.1 DATA SOURCES ........................................................................................................................... 14 5.2 DUNGENESS RIVER .................................................................................................................... 14 5.2.1 Dungeness River Flow Regime ............................................................................................... 14 5.2.2 Changes in Dungeness River Flow ......................................................................................... 14 5.2.3 Future Dungeness River Flows (Climate Predictions) ........................................................... 15 5.3 SMALL STREAMS ON THE SEQUIM-DUNGENESS PENINSULA ........................................................ 15 6.0 WATER USE TRENDS ................................................................................................................ 17 6.1 DATA SOURCES ........................................................................................................................... 17 6.2 GROUNDWATER USE .................................................................................................................... 17 6.2.1 Public Water Systems ............................................................................................................. 18 6.2.2 Domestic Well Withdrawals ................................................................................................... 21 6.2.3 Non-Residential Water Uses ................................................................................................... 22 6.3 CONSUMPTIVE WATER USE ......................................................................................................... 22 6.4 IRRIGATION TRENDS .................................................................................................................... 24 7.0 RECHARGE TRENDS ................................................................................................................. 26 7.1 PRECIPITATION RECHARGE .......................................................................................................... 26 7.2 IRRIGATION RECHARGE ............................................................................................................... 28 7.3 IMPACTS OF CLIMATE CHANGE ................................................................................................... 29 8.0 GROUNDWATER LEVEL TRENDS ......................................................................................... 30 8.1 DATA SOURCES AND MONITORING PRACTICES ........................................................................... 30 8.2 WATER LEVEL TRENDS ............................................................................................................... 31 8.2.1 Shallow Aquifer ...................................................................................................................... 32 8.2.2 Middle Aquifer ........................................................................................................................ 32 8.2.3 Lower Aquifer ......................................................................................................................... 33 8.2.4 City of Sequim Wellfields ........................................................................................................ 33 8.3 INTERPRETATION OF WATER LEVEL TRENDS .............................................................................. 35 8.3.1 Relative Changes in Key Hydrologic Factors ........................................................................ 35 8.3.2 Interpretation of Trends by Area ............................................................................................ 38 SEQUIM 2008 MONITORING REPORT iii DECEMBER 2009 8.3.3 Factors Influencing Future Hydrologic Changes ................................................................... 43 9.0 WATER QUALITY ...................................................................................................................... 45 9.1 DATA SOURCES ........................................................................................................................... 45 9.2 GROUNDWATER ........................................................................................................................... 45 9.2.1 Nitrate ..................................................................................................................................... 46 9.2.2 Conductivity ............................................................................................................................ 46 9.2.3 MCL Exceedances .................................................................................................................. 47 9.3 GROUNDWATER AGE DATING ..................................................................................................... 48 9.4 SURFACE WATER ......................................................................................................................... 49 9.4.1 Fecal Coliform ........................................................................................................................ 49 9.4.2 Nitrate ..................................................................................................................................... 50 9.4.3 Temperature ........................................................................................................................... 50 9.4.4 Dissolved Oxygen ................................................................................................................... 50 9.4.5 Conductivity ............................................................................................................................ 51 9.4.6 Turbidity and Fine Sediment .................................................................................................. 51 10.0 RECOMMENDATIONS .............................................................................................................. 52 11.0 REFERENCES .............................................................................................................................. 54 SEQUIM 2008 MONITORING REPORT iv DECEMBER 2009 TABLES Table 6‐1 Estimated Group A Water System Withdrawals Table 6‐2 Water Use Assumptions Table 8‐1 Monitoring Well Summary Table 9‐1 Summary of Surface Water Quality Evaluations FIGURES Figure 1-1 Study Area Map Figure 1-2 History of Irrigation Ditch Piping Figure 3-1 Conceptual Diagram of Groundwater Flow System Figure 4-1 Climate Gages and Precipitation Distribution Figure 4-2 Annual and Monthly Precipitation at Sequim Figure 4-3 Trends in Sequim Precipitation and Dungeness Watershed Snowpack Figure 4-4 Sequim Annual Temperature Trends Figure 5-1 Dungeness River Streamflow Trends and Irrigation Withdrawals Figure 5-2 Historic Average Irrigation-Season Diversions from Dungeness River Figure 6-1 City of Sequim