Gilpin County Ground Water Level Review

1. Gilpin CountyGround Water Level Review Nov. 16, 2006

2. Background Information • 2 wells supply Justice Center and County facilities • County became aware of concerns about dropping water levels in nearby wells • County asked BBA to study water levels in nearby wells to determine if: • The County’s wells are causing the water level decline in neighboring wells • If data indicate any potential long-term problems with wells

3. Summary of Local Geology and Hydrology • Bedrock in Gilpin County is igneous and metamorphic rocks of Precambrian age (hard rock), which contains numerous fractures near the surface • Ground water flows through fractures in rock • Geologic faulting locally controls ground water flow • Aquifer is recharged by snowmelt and precipitation • Aquifer is renewable and sustainable but can be stressed from pumping

5. Summary of Water Level Data and North Clear Creek Streamflow

6. Drought Conditions • Statewide drought since roughly 2002 • North Clear Creek Streamflow: • Average Discharge 1995 to 2005: 12,920 af/yr • Average Discharge 2000 to 2005: 8,387 af/yr • Less precipitation and runoff is recharging the aquifer • Conditions have improved since 2002 / 2003

8. Geology / Hydrology – cont. • Water level drawdown always greatest at pumping well • Pumping well can not cause more drawdown in other wells than in pumping well itself Static Water Level Pumping Water Level

9. Water Level Data • Shows seasonal fluctuations in County wells • Shows declines in the County wells and neighboring wells • Declines are greater in Adsel, Brown and Peters wells than in County wells • Data from neighboring wells is very limited, which is not adequate to determine conclusive results • Decline rates: • Justice Center Wells: 1.7 ft/yr (1996 – 2006), 2.6 (2002 – 2006) • Peters, Adsel and Brown: 5.2 ft/yr (2002 – 2006)

10. Findings • Water levels have fluctuated in County’s wells, which is expected and natural – seasonal fluctuations greater than 40 feet • Water levels are declining • Declines are less in County wells than in the Brown, Adsel and Peters wells • Indicates that other factors contribute to declines • Drought conditions contribute to declines • Declines in wells south of Justice Center probably result from factors other than County pumping

11. Factors Contributing to Water Level Changes • Well pumping by entities including: • Numerous Homeowners • The County • Black Hawk • Others • Drought Conditions • Land use and hydrologic changes

12. What do Water Level Changes Mean? • Most wells can continue to operate without any problem (wells can tolerate water level changes) • Some wells may require lowering of well pumps. In rare cases, wells may need to be drilled deeper • Future conditions will depend on whether or not water levels continue to decline • The aquifer, or zones within the aquifer, are limited in the amounts of ground water that can be produced. These limits are difficult to quantify

13. Recommendations • Continue to monitor and periodically review groundwater levels • Encourage neighboring well owners to maintain regular water level measurements to develop additional data points • Compare water levels to local hydrologic conditions as drought eases

14. - Questions - Chris Sanchez csanchez@bbawater.com Jeff Clark jclark@bbawater.com 303 806-8952