Possible Effects of Geothermal Waters on Nevada Drinking Water Supplies Local View

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Possible Effects of Geothermal Waters on Nevada
Drinking Water Supplies Local View

• Lisa Shevenell Richard Zehner

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Geothermal Interaction with Groundwaters

• Natural mixing of thermal and non-thermal waters
• May vary with time due to natural (drought) or
  human induced (pumping, irrigation) variations
• Production induced mixing
• Temporal changes may be observed

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Issues Related to Interaction Between Water
Supplies Geothermal Waters

• Changes (T conc.) in waters can be a function
  of several variables
• Geothermal production
• Injection increased geothermal
• Production decreased geothermal, drying of
  springs
• Drought
• Changes in municipal production
• Changes in irrigation

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Reservoir Interference, Pagosa Springs, CO

• Small users complain about temperature declines
  and reduced flow rates when TW5 pumps from Sept
  through May
• Data show temperature rebound in summer months

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Steamboat Hills, Nevada
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Geothermal Waters

• Geothermal waters contain As, B, Cl, SiO2, etc.
• Injected into reservoir to maintain volume and
  pressure for economic reasons
• Dumped on ground or into streams/ocean in some
  countries

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Brine Chemistry (mg/kg)
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Steamboat Hills in the distance from Geiger
Grade, looking west toward Mt. Rose Photo by
Mark Coolbaugh. 5/17/2003
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SBG - 1986, 1992, 2005 CPI - 1988
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Conceptual Model
Upper SB
Lower SB
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Geothermal End Member
Cold End Member
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Increased mixing of geothermal waters with non
geothermal waters with time-Two examples of
differences as a function of distance from faults
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Prior to Production
Close to Fault
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Farther from Fault
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Aquifer WL recovery
Drought 1986-94
50 m from Sage Hill Road Fault
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250 m away from two faults
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Mixing Varies Seasonally
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lower thermal water in fall (gtrecharge from
summer irrigation), greater thermal water in
spring
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Mechanisms for increases in the of thermal
versus non-thermal waters

• (1) Increased groundwater extraction from
  alluvial aquifers for municipal water supply,
  reducing available non-thermal component (e.g.,
  HD and PTR-1)
• (2) Decreased recharge (reduced irrigation and
  below normal precip.) reduces the available
  non-thermal component (e.g., HD and PTR-1)
• (3) Injection of thermal waters near faults
  increase thermal water component (e.g., CD and
  Flame) higher concentrations closer to faults

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Non-thermal fluids showing no change in chemistry
with time Isolated from thermal waters
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PD Conductively heated, isolated from geothermal
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Decreasing geothermal component with time
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Explanation for decreasing geothermal component

• ST in area of historical (dry) hot springs
• Decreasing thermal flow with time due to
  production
• Decreased production from nearby Washoe County
  municipal wells results in increase in available
  non-thermal water
• Systems can self-seal

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Some geothermal wells show no change with
time(Curti Barn and Herz Geothermal Wells)
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Summary

• Changes (and static conditions) in waters can be
  a function of interplay of several variables
• Geothermal production
• Injection increased geothermal
• Production decreased geothermal, drying of
  springs
• Drought
• Changes in municipal production
• Changes in irrigation
• Geologic isolation of different waters

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Summary

• This study demonstrates changing interaction of
  thermal and non-thermal waters in a producing
  system using B and Cl between well connected
  geothermal and alluvial aquifers
• Other chemical constituents found in geothermal
  waters (e.g., As, F, etc.) will also impact the
  nearby water supply

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Brine Chemistry (mg/kg)
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Steamboat Hills in the distance from Geiger
Grade, looking west toward Mt. Rose Photo by
Mark Coolbaugh. 5/17/2003
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These wells show that B and Cl decrease away from
faults
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Reservoir Interference, Pagosa Springs, CO
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