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James Kennedy, Ph.D., P.G.

State Geologist

Georgia Environmental Protection Division

Georgia ComprehensiveState-Wide

Water Management PlanAssessment of

Groundwater Availability

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Surface Water Quantity: Assess the quantity of water that is naturally provided and the sustainable quantities of water that meet both off-stream and in-stream needs (Dr. Wei Zeng)

Surface Water Quality: Determine assimilative capacities (the ability of a waterbody to naturally absorb a discharged substance without water quality becoming impaired or aquatic life being harmed) of streams and determine the amount of pollutants that can be discharged to a specific waterbody without exceeding water quality standards (Dr. Elizabeth Booth, P.E.)

Groundwater Availibility: Determine sustainable yields of prioritized aquifers (Dr. Jim Kennedy, P.G.)

State Water Plan Assessments

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Georgia’s Aquifers

USGS Fact Sheet 2006-3077

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2005 Groundwater Use by Aquifer

Data from Fanning, J.L. and V.P Trent, USGS SIR 2009-5002

55.4%

17.5%

7.6%6.0%

9.2%

4.3%

0

100

200

300

400

500

600

700

Aquifer

Wit

hd

raw

al (

mg

d)

0%

10%

20%

30%

40%

50%

60%

Per

cen

t o

f W

ith

dra

wal

Withdrawal (mgd) % of Withdrawal

• 86.5% of groundwater was withdrawn from Coastal Plain aquifers in southern Georgia (Floridan, Cretaceous, Claiborne, Clayton)

• 13.5% of groundwater was withdrawn from crystalline rock and Paleozoic rock aquifers in northern Georgia

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A comprehensive accounting of the sustainable yields of all aquifers in Georgia would be extraordinarily expensive and time consuming

Aquifer assessments of sustainable yield are prioritized

Bases for aquifer prioritization– Functional characteristics of the aquifer (extent and

thickness, recharge to the aquifer, well yield)– Existing evidence of adverse effects due to

withdrawals– Forecasts suggesting significant increases in

demands– Aquifers where it will not be possible to determine

sustainable yield within a reasonable time period

Prioritization of Aquifers and Aquifer Units for Assessment of Sustainable Yield

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Numerical (MODFLOW) computer models of Coastal Plain aquifers where most groundwater is withdrawn, groundwater withdrawals have caused some unacceptable impacts, and forecasts suggest increases in future withdrawals– Upper Floridan aquifer in the Dougherty Plain– Upper Floridan aquifer in Tift County area– Cretaceous aquifer between Macon and Augusta– Claiborne aquifer in southwestern Georgia– Upper Floridan aquifer in the eastern Coastal Plain

Water balance models in the north Georgia crystalline and Paleozoic rock aquifers where less groundwater is withdrawn

Prioritization of Aquifers for Determination of Sustainable Yield

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Prioritized Aquifers in the Lower Flint – Ochlockonee Water Planning Region

Upper Floridan Aquifer

Claiborne Aquifer

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Areas of the Upper Floridan Aquifer Monitored by the USGS

USGS SIR 2009-5070

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Dougherty Plain of Southwestern Georgia

USGS SIR 2006-5070

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Interaction of Groundwater and Surface Water in the Dougherty Plain

USGS SIR 2006-5070

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Highly productive aquifer

Aquifer currently heavily used for public water supply and irrigation

Aquifer interconnected with streams in Lower Flint River Basin

Irrigation pumping affects flows in streams with listed species and streams tributary to the Apalachicola River

Prioritization of the Upper Floridan Aquifer in the Dougherty Plain

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Determine Sustainable Yield from the Existing USGS Model of the Dougherty Plain Upper Floridan Aquifer

USGS SIR 2006-5234

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2007 Groundwater Levels in the Upper Floridan Aquifer of South-Central Georgia

USGS SIR 2009-5070

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Highly productive aquifer

Aquifer currently heavily used for public water supply and irrigation

Dropping water levels during the 2007 irrigation season caused domestic wells to go dry

Increased groundwater use expected due to increasing population and changes in crops to those requiring more irrigation

Prioritization of the Upper Floridan Aquifer in the Tift County area

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Aquifers in Southwestern Georgia

GGS Bulletin 118

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Claiborne Aquifer

GGS HA 21

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2007 Groundwater Levels in the Claiborne Aquifer

USGS SIR 2009-5070

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Highly productive aquifer

Aquifer currently heavily used for public water supply and irrigation

Groundwater levels are dropping at a majority of wells in the aquifer

Aquifer is an alternate source of water to the Clayton aquifer, which currently has use restrictions, and the Upper Floridan aquifer in the Dougherty Plain

Prioritization of the Claiborne Aquifer

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Prioritized Coastal Plain Aquifers Are Within the Regional Aquifer Model in USGS Professional Paper 1410-F (1997)

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Calibrate Regional Coastal Plain Model and Telescope to Prioritized Aquifers to Determine Sustainable Yield

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The Model Incorporates Multiple Aquifer Layers

USGS Circular 1139

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Sustainable yields of the Upper Floridan and Claiborne aquifers will be quantified as million gallons per day for the extents of the modeled aquifers

Sustainable yields will recognize the seasonal variability of groundwater use

Management practices can be used to maximize groundwater withdrawals to the sustainable yield of the aquifer

The Flint River Basin Regional Water Development and Conservation Plan provides information that could be used to identify and implement management practices

Result of Sustainable Yield Determinations

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The Plan was initiated in October 1999 in response to a prolonged drought and evaluated impacts of agricultural water use on the interconnected system of streams and the Upper Floridan aquifer in the lower Flint River Basin

The State water plan assessment of groundwater availability will determine the sustainable yield of the aquifer for agricultural, municipal, and industrial uses and will expand the range of questions answered by the Flint River Basin Plan

The State water plan assessment of groundwater availability will use tools similar to those used to develop the Flint River Basin Plan and will be consistent with technical findings of the Flint River Basin Plan

Flint River Basin Regional Water Development and Conservation Plan

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Sustainable yield is the amount of groundwater that can be withdrawn from an aquifer without causing an unacceptable impact

Unacceptable impacts (i.e., benchmarks) to determine sustainable yield of the Upper Floridan aquifer in the Dougherty Plain:

– Reduction of stream base flows using 25% of annual average discharge as an initial benchmark

– Dropping water levels of more than 30 feet during drought that could impact nearby wells or create sinkholes

Sustainable Yield Benchmarks

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Benchmarks to determine sustainable yield of the Upper Floridan aquifer in the Tift County area and in the Claiborne aquifer:– Dropping water levels of more than 30 feet during

drought– Potentiometric surface drops so far that the aquifer

becomes unconfined– Dropping water levels do not recover by 90% within

90 days of stopping groundwater withdrawals (i.e., recharge to aquifer has been exceeded)

Viabilities of benchmarks will be tested during modeling and may be changed

Sustainable Yield Benchmarks