1. Monitoring Potential Saltwater Intrusion Related to Deepening of Savannah River Channel
Jeff Schwindaman, P.G.
May 31, 2018
US Army Corps of Engineers
BUILDING STRONG®

2. Overview
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3. Conceptual Model – pre-development
(USGS, 2006)

4. Conceptual Model – present day
(USGS, 2006)

5. Groundwater Management Plan (2006 – present)
(GAEPD, 2006)

6. Savannah Harbor Expansion Project (SHEP)

7. Timeline of SHEP GW Monitoring Program
1998 – Initial Aquifer Study
2007 – Supplemental Aquifer Study
2011 – 401 Certification
2013 – Groundwater Monitoring Plan
2013 to 2017 – Annual Groundwater Monitoring Reports
2017 – Background Groundwater Monitoring Report

8. Hydro-stratigraphic Cross Section
“Tybee High”

9. Supplemental Aquifer Study

10. Thickness of Confining Unit

11. SHEP Groundwater Model Results

12. SHEP Groundwater Model Results

13. Monitoring Requirements
Construct a network of groundwater monitoring wells.
Collect background (pre-dredging) groundwater samples.
Establish benchmark Cl- concentrations for each sentry well.
401 Certification, section 4

14. 1. Construct Groundwater Monitoring Network (2009-2013)
Upgradient
GW FLOW
Downgradient

15. 1. Construct Groundwater Monitoring Network (2009-2013)
MW-2R, MW-3, MW-6, MW-7
MW-1, MW-4, MW-5, MW-8
Surficial Aquifer
Miocene Confining Unit
Upper Floridan Aquifer

16. 2. Collect Background (pre-dredging) Cl- Samples (2013-2017)

17. 3. Establish Benchmark Cl- Concentrations (2017)
CDM Smith updated groundwater model in 2015.
Created statistical tool for establishing benchmarks.
95% Upper Prediction Limits (UPLs) and Model-based benchmarks.
MW-4
MW-4

18. 3. Establish Benchmark Cl- Concentrations
Background data
95% UPL benchmark
95% UPL benchmark (projected)
Model based benchmark

19. Conclusions Robust GW monitoring network.
Groundwater head gradient is driving saltwater intrusion.
Dredging anticipated to have negligible effect.
Monitor for upward trends that exceed predictions.
Processes in place in case of exceedance.

20. References
CDM Smith, Savannah Harbor Expansion Project Updated Saltwater Intrusion Modeling to Support the Groundwater Monitoring Program. Technical Memorandum. January 29, 2016.
CDM Smith, Savannah Harbor Expansion Three-Dimensional Salt Water Intrusion Modeling. Technical Memorandum. September 27, 2005.
EPA, Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities, Unified Guidance. EPA 530 R/ U.S. Environmental Protection Agency. March 2009.
GAEPD, Coastal Georgia Water and Wastewater Permitting Plan for Managing Salt Water Intrusion. Georgia Environmental Protection Division. June, 2006.
USACE, Savannah Harbor Expansion Project: Groundwater Monitoring Plan. U.S. Army Corps of Engineers Savannah District. March 2013.
USACE, Background Groundwater Monitoring Report. Savannah Harbor Expansion Project. U.S. Army Corps of Engineers Savannah District. December 2017.
USGS, Simulation of Saltwater Movement in the Upper Floridan Aquifer in the Savannah, Gerogia – Hilton Head Island, South Carolina, Area, Predevelopment – 2004, and Projected Movement for 2000 Pumping Conditions. Provost, A.M., Payne, D.F., Voss, C.I. United States Geological Survey

21. Questions?