Water Supply in Coastal Georgia Meeting Water Demand Using Alternative Water Sources to the Upper Floridan Aquifer

Transcription

1 Water Supply in Coastal Georgia Meeting Water Demand Using Alternative Water Sources to the Upper Floridan Aquifer John Clarke U.S. Geological Survey Georgia Water Science Center U.S. Department of the Interior U.S. Geological Survey

2 Ground-Water Issues in Coastal Georgia Saltwater contamination Hilton Head Island Brunswick Competition for available supply Interstate issue Projected growth in region EPD restrictions on usage Need for supplemental/alternative water sources

3 Saltwater Contamination at Hilton Head Island Hilton Head Island Savannah

4 Management of Upper Floridan Aquifer in 24-County Coastal Area (GaEPD, 2006) Areas of saltwater contamination No Additional Withdrawal Incremental Increases No Restriction

5 Red Zone Reduce withdrawals from Upper Floridan Aquifer Water conservation and reuse measures Requested permits must be justifiable Encourage use of alternate water supply sources GW monitoring

6 Yellow Zone Allow step increases in UFA pumping, Monitor impact on aquifer Require implementation of water conservation and reuse measures Ensure water needs are justifiable GW monitoring

7 GaEPD Guidance Document Alternate Water Sources (August 2007) For most groundwater withdrawal permittees in the coastal counties of Georgia, a special condition of all new or modified withdrawal permits will be an evaluation of long-term alternate water sources as a substitute for, or supplement to, the water withdrawn from the Upper Floridan aquifer. You must submit a detailed Alternate Water Source Evaluation report along with the completed form and table to EPD within 24 months of your permit issuance date.

8 Potential Alternative Water Sources Surface water: Streams Ponds Seawater Groundwater: Brunswick-Surficial aquifer system Lower Floridan aquifer

9 Hydrogeologic Units Brunswick aquifer system Floridan aquifer system

10 Coastal Area Water Use 2000 (MGD) Upper Floridan Lower Floridan Surficial and Brunswick Savannah River Source: Payne and others (2005)

11 Streams Potential Sources: Savannah River Ogeechee River Savannah River currently being used City of Savannah s I&D Plant operated since 1940s Water-quality considerations Availability is seasonally variable Higher construction and operating costs than groundwater

12 Savannah River Water Use 2000 (MGD)* 14 Industrial/mining Public Supply Agricultural *excluding thermoelectric Source: Fanning (2003)

13 Ponds May provide water for irrigation supply Requires development of water budget and determination of pond volume (storage) USGS studies at HAAF and Brunswick

14 Brunswick-Surficial Aquifer System Sand aquifers Possible source of drinking and irrigation water Less permit requirements than Lower Floridan Low cost drilling (shallow depth) Typical well depths ft Well yields: gpm Variable thickness Wells at Berwick Plantation (Chatham Co) have been providing an average of 0.29 MGD since 2004, with no long-term wl decline

15 Lower Floridan aquifer 2 nd most productive aquifer Yields exceeding 700 gpm have been obtained More expensive drilling (deeper depths) Possible water quality limitations (TDS, sulfate, chloride) Requires detailed (expensive) assessment to meet GaEPD permit requirements Field testing Groundwater modeling Recently remapped by USGS

16 USGS Studies in Coastal Area Coastal Sound Science Initiative Fort Stewart-Hunter Army Airfield alternative water sources Ponds Surficial aquifer system Lower Floridan aquifer Geology of the Savannah River Basin Revised hydrogeologic framework for the Floridan aquifer system in the Southeastern USA Long-term groundwater and surface-water monitoring programs

17 Lower Floridan Aquifer Studies USGS in coop with US Army Determine the hydrogeology and water quality of the Floridan aquifer system Provide data and model simulations needed to assess the effect of Lower Floridan pumping on the Upper Floridan (GaEPD permit requirement)

18 GaEPD requirements for evaluation of Upper Floridan pumping offsets Steady-state model simulations used to determine amount of Upper Floridan pumping reductions required to Offset maximum simulated drawdown Offset simulated leakage These two requirements can result in widely varying offsets UFA dd LFA dd

19 Controls on Interaquifer Leakage Governed by Darcy s Law: Q = K dh/b * A Leakage highest where: Vertical hydraulic conductivity (K ) is highest; Confining unit is thinnest (b); and Vertical head difference (dh) is greatest K dh Confining Unit Upper Floridan Confining Unit Lower Floridan b Fractures can have significant effect

20 Scope of Field Work Well Construction Geophysical Logging Flowmeter Testing Hydraulic testing Core samples Packer/Slug Tests 24- and 72-hour aquifer tests Water-Quality Analysis Specific conductance during drilling Borehole grab samples Whole well sample

21 Groundwater Model Enables 3-dimensional simulation of future (long-term) conditions using field data Revised MODFLOW model of Payne and others (2005) Variable grid spacing 10ft x 10 ft cells near pumped well Added field data (Kv, Kh) based on field investigations

22 Simulated long-term drawdown response in Upper Floridan near Lower Floridan well Days hours (test period) 1 1-yr 2-yrs >2 years to reach steady state that s where a model helps!

23 Lower Floridan Aquifer Hunter Army Airfield 703-1,080 ft Test yield: 748 gpm Maximum drawdown UFA: 0.76 ft LFA: 36 ft Good water quality Fort Stewart 912-1,250 ft Test yield: 740 gpm Maximum drawdown UFA: 0.4 ft LFA: 39 ft Water is high in dissolved solids (sulfate)

24 Lower Floridan Aquifer Simulated Steady-State Conditions UFA Drawdown (ft) Leakage % Simulated drawdown Hunter Fort Stewart Leakage percent Hunter Fort Stewart

25 Lower Floridan Aquifer Simulated UFA Pumping Offsets (MGD) Hunter Army Airfield Fort Stewart Drawdown Enacted Leakage Drawdown Enacted Leakage Pumping Offset 0 Pumping offset

26 Lower Floridan Aquifer Gain in Withdrawal (MGD) Hunter Army Airfield Original permit Modified permit LFA UFA Fort Stewart 0.5 Original permit Modified permit LFA UFA

27 Water Availability at Ponds

28 HAAF Pond Evaluation USGS in cooperation with U.S. Army Four ponds evaluated for irrigation supply; Descriptions of local site setting and pond bathymetry; Estimates of the pond volume over a range of stages; Development of water budget; Estimated flow rates downstream from golf course pond; and Suitability of pond water quality for irrigation purposes.

29 Golf Course Pond Irrigation previously provided by potable water from Upper Floridan Assessment based on streamflow discharge downstream of dam USGS monitored stormwater site during New gage installed during February 2009

30 Golf Pond Streamflow MGD /1/2009 2/1/2009 3/1/2009 4/1/2009 5/1/2009 6/1/2009 7/1/2009 8/1/2009 9/1/ /1/ /1/ /1/2009 1/1/2010 2/1/2010 3/1/2010 4/1/2010 5/1/2010 6/1/2010 7/1/2010 8/1/2010 9/1/ /1/ /1/ /1/2010

31 Golf Pond Streamflow and Water Use Avg of periodic streamflow Min daily streamflow Avg daily streamflow MGD 0.10 Avg daily water use

32 Percent of Golf Course demand met by minimum flow ( ) Percent of demand met by min flow

33 Gain in Withdrawal Capacity GW and Golf Pond (monthly) MGD Golf Pond LFA UFA Original Permit Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Multiple of Original Permit Gain from original permit (multiple) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

34 Water Level Effect of Red Zone Pumping Reductions on Water Levels at Savannah MGD

35 Acknowledgments USGS Project team: Lester Williams, Greg Cherry, Gary Holloway, Michael Hamrick, Jaime Painter, Welby Stayton, Harold Gill (USGS retired) U.S. Army Environmental Protection and Compliance Branch: Stanley Thomas, Tressa Rutland, Brent Rabon, Nate Williams, Eric Stulpin For more information see: