GROUNDWATER AVAILABILITY
IN NORTHWEST GEORGIA
Topic 31
6th Annual Georgia Environmental Conference
Savannah, Georgia
August 25, 2011
Moderator / Speaker
Nils Thompson, P.G.
GEORGIA PROVINCES & AQUIFERS
USGS Fact Sheet 2006-3077
GEORGIA GEOLOGY
Valley and Ridge &
Appalachian Plateau
•
Sedimentary Bedrock
Piedmont & Blue Ridge
•
Crystalline Bedrock
Costal Plain
• Sedimentary Deposits
USGS / GA Dept. of Natural Resources
PALEOZOIC-ROCK
AQUIFERS
• Types of bedrock:
 Sandstone
 Limestone
 Dolostone
Carbonates
•
•
•
•
Unconfined to confined.
Not laterally extensive.
Depths: 15 - 2,100 ft.
Sustainable well yields: 1 - 50
gpm (up to 3,500 gpm).
• Levels affected by
precipitation & local pumping.
USGS Scientific Investigations Report 2009-5070
CARBONATES
Limestone & Dolostone
• Most productive aquifers.
• Groundwater is stored in:
 Overlying soil “sponge”
 Secondary dissolution along
fractures, bedding planes &
conduits in the rock.
• Springs may discharge at rates
up to 5,000 gpm.
USGS Scientific Investigations Report 2009-5070
PALEOZOIC BEDROCK
PALEOZOIC BEDROCK
PALEOZOIC BEDROCK
Characterized by Occurrence of Springs Discharging Groundwater in
some areas via Conduit Flow and Exhibit Diffuse Flow in Other Areas.
GROUNDWATER FLOW TO A WELL
LIMIT OF ZONE OF
CONTRIBUTION
ZONE OF
INFLUENCE
CONE OF
DEPRESSION
TYPICAL BEDROCK WELL
PUMP
GROUT
WATER
TABLE
CASING
OPEN BOREHOLE
BEDROCK
AQUIFER
WELL DEPTHS
15 - 150 ft.
150 - 210 ft.
210 - 260 ft.
260 - 2,100 ft.
• Catoosa
Data from UGA Ag & Environ. Services Labs, October 2003
USGS Scientific Investigations Report 2009-5070
GROUNDWATER
WITHDRAWALS - 2005
0 - 5 MGD
> 5 - 10 MGD
(≈ 3,475 - 6,950 gpm)
•
•
•
•
•
Catoosa
Walker
Chattooga
Bartow
Polk
Data from Fanning, J.L. and V.P Trent, USGS SIR 2009-5002
GROUNDWATER USE
>50% TOT. WATER USE
>50% used for irrigation
>50% used for public supply &
domestic or commercial use
>25% used for industry & mining,
but <50% used for public supply &
domestic or commercial uses, or for
irrigation
>25% used for industry & mining, but
>50% used for public supply &
domestic or commercial uses, or for
irrigation
Groundwater <50% of tot. water used
Georgia’s Water Resources: A Blueprint for the Future, 2007
SUSTAINABLE YIELD FROM A WELL
• Sustainable yield is the amount of groundwater that can be withdrawn
without causing unwanted results.
• Some unwanted results include:
 Water table lowered >30 ft. between pumping wells - Cavities & pipes could form in the soil where groundwater support is lost
- Ground surface could subside above the cavities
- Collapse sinkholes could form after soil falls into an underlying cavity
 Groundwater levels lowered below the top of a confined aquifer –
- Decreases transmissivity of an aquifer
- Decreases well yields from the aquifer
 Spring flow & stream baseflow reduced by >10% of mean annual baseflow.
• Sustainable yields are different for different aquifers.
Georgia Dept. of Natural Resources, Review Draft Synopsis
Report - Groundwater Availability Assessment, March 2010
EPD STATE-WIDE
WATER PLAN MODEL
• Model domain
• The numerical groundwater flow
model simulated sustainable
yields for the entire model
domain:
 27 MGD for a dry year
 70 MGD for an avg. year
Georgia Dept. of Natural Resources, Review Draft Synopsis
Report - Groundwater Availability Assessment, March 2010
USGS GROUNDWATER
MONITORING WELLS
USGS Well
USGS Scientific Investigations Report 2009-5070
AVERAGE pH
6.2 - 6.7
6.7 - 7
7 - 7.4
7.4 - 8
• Gordon
High alkalinity (pH > 7) groundwater
due to carbonate aquifer source.
Data from UGA Ag & Environ. Services Labs, October 2003
HARDNESS
53 - 78 Mg (CaCO3) / L
78 - 115 Mg (CaCO3) / L
115 - 204 Mg (CaCO3) / L
• Gordon
Hard groundwater due to carbonate
aquifer source.
Data from UGA Ag & Environ. Services Labs, October 2003
COPPER
0.004 - 0.015 mg/L
0.015 - 0.029 mg/L
0.029 - 0.048 mg/L
0.048 - 0.074 mg/L
• Chattooga
Data from UGA Ag & Environ. Services Labs, October 2003
IRON
0.003 - 0.023 mg/L
0.023 - 0.049 mg/L
0.049 - 0.111 mg/L
• Chattooga
Data from UGA Ag & Environ. Services Labs, October 2003
CONCLUSIONS
• Carbonate aquifers typically exhibit groundwater flow that ranges
between:
 Quick flow through solution conduits and solution-enlarged fractures.
 Slow flow through fine fractures and intergranular pores.
• Hydraulic properties often change at different locations in carbonate
aquifers depending on the degree of solutional (karst) modification.
• Carbonate groundwater quality leads to:
 Hard water.
 Higher than neutral pH.
QUESTIONS?