Sun Prairie Village County Water and Sewer District Public Water System PWSID # MT0000521 SOURCE WATER DELINEATION AND ASSESSMENT REPORT Date of Report: 06/03/2005 Contact Person: Bobby Broadway Sun Prairie Village County Water and Sewer District Post Office Box 1127 Great Falls, MT 59403 Phone: (406) 965-3944 Table of Contents EXECUTIVE SUMMARY .......................................................................................................................................................8 INTRODUCTION ...................................................................................................................................................................10 PURPOSE..............................................................................................................................................................................10 LIMITATIONS .....................................................................................................................................................................10 BACKGROUND......................................................................................................................................................................11 THE COMMUNITY .............................................................................................................................................................11 GEOGRAPHIC SETTING....................................................................................................................................................11 GEOLOGY............................................................................................................................................................................12 THE PUBLIC WATER SUPPLY .........................................................................................................................................13 WATER QUALITY ..............................................................................................................................................................14 SUN PRAIRIE VILLAGE WATER QUALITY...................................................................................................................14 DELINEATION.......................................................................................................................................................................15 HYDROGEOLOGIC CONDITIONS ...................................................................................................................................15 AQUIFER GEOMETRY AND HYDRAULIC CHARACTERISTICS ...............................................................................16 POTENTIOMETRIC SURFACE..........................................................................................................................................17 CONCEPTUAL MODEL AND ASSUMPTIONS ...............................................................................................................18 WELL INFORMATION .......................................................................................................................................................18 METHODS AND CRITERIA...............................................................................................................................................19 DELINEATION RESULTS ..................................................................................................................................................19 LIMITING FACTORS ..........................................................................................................................................................19 INVENTORY...........................................................................................................................................................................20 INVENTORY RESULTS/RECHARGE REGION ...............................................................................................................22 INVENTORY UPDATE .......................................................................................................................................................22 INVENTORY LIMITATIONS .............................................................................................................................................22 SUSCEPTIBILITY ASSESSMENT ......................................................................................................................................23 MANAGEMENT RECOMMENDATIONS.........................................................................................................................25 MONITORING WAIVERS....................................................................................................................................................27 MONITORING WAIVER REQUIREMENTS.....................................................................................................................27 USE WAIVERS ....................................................................................................................................................................27 WAIVER RECOMMENDATION........................................................................................................................................27 REFERENCES ........................................................................................................................................................................28 GLOSSARY* ...........................................................................................................................................................................30 APPENDICES..........................................................................................................................................................................34 APPENDIX A: SITE LAYOUT............................................................................................................................................35 APPENDIX B: WELL LOGS ...............................................................................................................................................37 APPENDIX C: WATER USE STATISTICS........................................................................................................................43 APPENDIX D: CONCURRENCE LETTER........................................................................................................................45 FIGURES FIGURE 1. SUN PRAIRIE VILLAGE COUNTY VICINITY MAP FIGURE 2. SUN PRAIRIE VILLAGE COUNTY PWS WELL LOCATIONS FIGURE 2A. AERIAL MAP OF THE SUN PRAIRIE VILLAGE PWS VICINITY i FIGURE 3. SUN PRAIRIE VILLAGE AREA GEOLOGY FIGURE 3A. SUN PRAIRIE VILLAGE GEOLOGY (CONTINUED) FIGURE 4. POTENTIOMETRIC SURFACE NEAR SUN PRAIRIE VILLAGE SUPPLY WELLS FIGURE 5. SUNPRAIRIE VILLAGE INVENTORY REGION FIGURE 6. SUN PRAIRIE VILLAGE RECHARGE REGION FIGURE 7. LAND COVER IN THE SUN PRAIRIE VILLAGE INVENTORY REGION FIGURE 8. SEPTIC DENSITY WITHIN THE SUN PRAIRIE VILLAGE INVENTORY REGION FIGURE 9. LAND COVER IN THE SUN PRAIRIE VILLAGE RECHARGE REGION FIGURE 10. SEPTIC DENSITY WITHIN THE SUN PRAIRIE VILLAGE RECHARGE REGION Tables TABLE 1. CLIMATIC SUMMARY FOR GREAT FALLS, MONTANA (243749) .........................................................12 TABLE 2. WELL CONSTRUCTION AND PUMPING RATES FOR SUN PRAIRIE VILLAGE SUPPLY WELLS......14 TABLE 3. SOURCE WATER SENSITIVITY CRITERIA..................................................................................................15 TABLE 4. POROSITY VALUES FOR VARIOUS GEOLOGIC MATERIALS (EPA 1993). ...........................................16 TABLE 5. SOURCE WELL INFORMATION FOR THE SUN PRAIRIE VILLAGE PWS .............................................18 TABLE 6. SIGNIFICANT POTENTIAL CONTAMINANT SOURCES IN THE SUN PRAIRIE VILLAGE PWS INVENTORY REGION........................................................................................................................................................21 TABLE 7. DETERMINATION OF HAZARD OF POTENTIAL CONTAMINANT SOURCES FOR UNCONFINED WELLS..................................................................................................................................................................................23 TABLE 8. RELATIVE SUSCEPTIBILITY TO SPECIFIC CONTAMINANT SOURCES AS DETERMINED BY HAZARD AND THE PRESENCE OF BARRIERS.............................................................................................................24 TABLE 9. HAZARD OF SIGNIFICANT POTENTIAL CONTAMINANT SOURCES FOR THE SUN PRAIRIE VILLAGE PWS INVENTORY REGION AND RECHARGE REGION ............................................................................24 TABLE 10. SUSCEPTIBILITY ASSESSMENT FOR SIGNIFICANT POTENTIAL CONTAMINANT SOURCES IN THE SUN PRAIRIE VILLAGE INVENTORY REGION AND RECHARGE REGION. ..................................................24 ii EXECUTIVE SUMMARY Sun Prairie Village is located in north-central Montana about 10-miles west of the City of Great Falls, and about 1-mile north of the Sun River in Cascade County. Drinking water for the Sun Prairie Village County Water and Sewer District (Sun Prairie Village) Public Water System (PWS) is supplied by four wells located in Section 34, Township 21 North, Range 2 East. This Source Water Delineation and Assessment Report was prepared under the requirements and guidance of the Federal Safe Drinking Water Act and the US Environmental Protection Agency, as well as a detailed Source Water Assessment