In addition to complete or seasonal inundation, these systems will no longer be removed from the water table in the way in which they were designed in even the more conservative models. Loss of the required drainage space in the vadose zone and the aerobic conditions that exist therein will disable the system’s ability to break down fecal coliform and other wastes
25
associated with septic systems. The pathogens released in sewage waste will not only produce a disease pathway but can quickly affect nearby streams and/or shallow wells used for irrigation.
Considering that the average storage capacity of a fine sand, as was noted in the research area, is 6.95 x 10-3 cubic meters (0.21 ft3) of water (Fetter, 2001), the impending loss of up to 1.5m of groundwater storage capacity will have massive effects on the built infrastructure of the coast and how its drainage is engineered. Retention ponds, drainage basins, and other hydraulic systems need to be engineered with long term goals in mind. Stream flashiness and mitigation of flooding under current groundwater storage conditions will be greatly affected by the loss of the storage in groundwater.
These levels of seasonal inundation combined with reduced storage in the surficial aquifer could lead to severe groundwater quality issues. Additionally, the backflows of sewage and wastewater could pose a danger to commercial and residential structures throughout the Georgia Coast. The average water level depth in Upper and Lower Bryan County was 1.4m (4.6ft) and 1.5m (5ft) from ground surface, respectively. Ground water level rise of any significance will have major impacts on life in the Lower Coastal Plain of Georgia.
In Lower Bryan County alone, UGA mapped 4,114 sites of known onsite wastewater treatment systems. Often these systems are tightly clustered into communities. (Figure 11) Unfortunately, these communities are often built very near streams or tidal areas due to commercial fishing or for the attraction of their natural beauty. This tendency toward tight grouping, and their proximity to freshwater resources present special dangers. As dry areas and vadose zone capable of aerobic degradation decrease, concentrations of hazardous chemicals near sensitive receptors will increase. Also, the dilution that might occur if these conditions were isolated will not be possible due to the density of septic fields in relatively small areas. A
26
negative feedback model is created. This could have catastrophic effects on human health and the environment.
27
Due the property values of these areas, and in some cases, economic inability to rebuild elsewhere, these communities are unlike to relocate based on groundwater inundation. Defense of shorelines is expensive and may not be viable at all as groundwater inundation occurs. Thankfully, this density also provides opportunities for development of small to mid-size public treatment systems. These systems will face a similar challenge that electrical and other
underground utilities will face in the future. The gravity fed drainage systems and lift stations will likely need to be installed and designed based on projections. Dewatering and other
engineering difficulties that would be faced under future conditions would make these solutions economically impossible. However, pump design and improvement can be done incrementally as water levels rise. This will only be a first step in an organized retreat.
In many cases, rural areas and isolated properties may never be viable options for addition to public utilities. Our research suggests that regulations should be put into place that require all future installations of septic systems in the lower coastal plain of Georgia to be built above grade. This is the required practice in many states, including nearby Florida, where groundwater resources are vital to the state economy. These regulations generally require septic tanks and drainage fields to be installed above current ground level and then bermed with soils appropriate for proper drainage. This design allows for the necessary drainage required for effective aerobic biodegradation of wastewater prior to reaching groundwater, or limits concentrations of hazardous compounds in wastes to a manageable limit.
There are numerous projection models for sea level rise in the next century. Our models are based on fairly conservative versions of these, and many show greater than 1m of sea level rise by 2100. Similar projections show regional sea level rise will likely be even more prolific than the global average. The rate at which sea level rises, and accordingly groundwater levels
28
rise, will be the determining factor in how our coastal areas will manage future development, infrastructure, and emergency management. Our research shows that sea level rise alone will not be the only threat to these areas, and that the inland coastal plain will likely be as much affected as near coastal zones.
29
5 CONCLUSIONS
In discussion of future sea level rise, options for future land use are often limited to three choices, adapt, defend, and retreat. Due the slow-moving nature of sea level rise, combined with population increase and high property values for coastal real estate, these options are sure to be contentious. Government planning does not typically work on these time scales. However, as flood insurance rates and mortgage banks begin to react to continuing research these will have impacts on the built environment in the Georgia Coastal Plain. This creates a scenario where an “organized retreat” will be necessary. Private citizens, local, state, and federal governments will need to be planning in the time range of 30-50 years. These decisions need to be made with an awareness that these impacts will not be limited to surficial inundation and that rising
30
REFERENCES
Bush, Chelsea E., Farley, Lori A., Meyer, Brian K., Vance, R. Kelly and Reichard, James S., 2016. Investigation of the Shallow Groundwater System: Wormsloe State Historic Site, Chatham County, Georgia. Southeastern Section Geological Society of America, 65th Annual Meeting, Columbia, SC.
Cai, Lin and Zhang, Tong, 2013. Detecting Human Bacterial Pathogens in Wastewater Treatment Plants by a High-Throughput Shotgun Sequencing Technique. Environmental Science and Technology, 47, 5433-5441
Clarke JS, Hacke CM, Peck MF. 1999. Geology and Ground-Water Resources of the Coastal Area of Georgia. Bulletin 113, Georgia Geological Survey, Department of Natural Resources.
Conn, Kathleen E., Barber, Larry B., Brown, Gregory K., and Siegrist, Robert L., 2006. Occurrence and Fate of Organic Contaminants During Onsite Wastewater Treatment. Environmental Science and Technology, 40, 7358-7366.
Cooper HM, Fletcher CH, Chen Q, Barbee MM. 2013. Sea level rise vulnerability mapping for adaptation decisions using LiDAR DEMs. Progress in Physical Geography 37: 745–766. Hails, J.R. and J.H. Hoyt, 1969. An Appraisal of the Evolution of the Lower Atlantic Coastal
Plain of Georgia, U. S. A. Transactions of the Institute of British Geographers, No. 46: 53- 68.
Horton BP, Rahmstorf S, Engelhart SE, Kemp AC. 2014. Expert assessment of sea-level rise by AD 2100 and AD 2300. Quaternary Science Reviews 84: 1–6.
Hoyt, J.H., and J.R. Hails. 1967. Pleistocene shoreline sediments in coastal Georgia: depositional and modification. Science 155: 1541–1543.
31
http://bryancountyga.org/about-us/living-here/statistics-demographics (Accessed 18th January, 2019)
Jevrejeva S, Moore JC, Grinsted A. 2012. Sea level projections to AD2500 with a new generation of climate change scenarios. Global and Planetary Change 80–81: 14–20.
LaForge, L., and Cooke, C.W., 1925. Physical Geology of Georgia, Georgia Geological Survey Bulletin 42, 189 pp.
Levy, Karen, Woster, Andrew P., Goldstein, Rebecca S., and Carlton, Elizabeth J., 2016.
Untangling the Impacts of Climate Change on Waterborne Diseases: a Systematic Review of Relationships Between Diarrheal Diseases and Temperature, Rainfall, Flooding, and
Drought. Environmental Science and Technology, 50, 10, 4905-4922.
Manda AK, Sisco MS, Mallinson DJ, Griffin MT. 2015. Relative role and extent of marine and groundwater inundation on a dune-dominated barrier island under sea-level rise scenarios. Hydrological Processes 29: 1894-1904.
MacNeil, F.S., 1950. Pleistocene Shore Lines in Florida and Georgia. United States Geological Survey Professional Paper No 221-F, 107 p.
Minnesota Pollution Control Agency, 2009. Low Dissolved Oxygen in Water: Causes, Impact on Aquatic Life., Water Quality/Impaired Waters, 3.24, February 2009.
Nicholls, Robert J. and Cazenave, Anny, 2010. Sea Level Rise and Its Impact on Coastal Zones. Science, Vol. 328, Issue 5985, pp. 1517-1520. January 2017.
Nicholls, Robert J., 1995. Coastal Megacities and Climate Change. Geojournal, 37, 3, 369-379. NOAA Technical Report NOS CO-OPS 083. Global and Regional Sea Level Rise Scenarios for the United States.
32
Ogeechee River at US 17, near Richmond Hill, GA
https://nwis.waterdata.usgs.gov/nwis/inventory/?site_no=02203536&agency_cd=USGS&am p; (Accessed: 19th December, 2018)
Provost, Alden M., Payne, Dorothy F., and Voss, Clifford I. Simulation of Saltwater Movement in the Upper Floridian Aquifer in Savannah, Georgia-Hilton Head Island, South Carolina Area, Predevelopment-2004, and Projected Movement for 2000 Pumping Conditions. United States Geologic Study, Scientific Investigations Report 2006-5058.
Rotzoll K, Fletcher CH. 2013. Assessment of groundwater inundation as a consequence of sea- level rise. Nature Climate 3: 477–481.
State of Florida, Department of Health, Chapter 64E-6, Florida Administrative Code, Standards for Onsite Sewage Treatment and Disposal Systems, cited January 27, 2019.
State of Georgia, Department of Public Health, Environmental Health Section, Manual for On- Site Sewage Management Systems
US Census Bureau. Census.gov at: https://www.census.gov/. (Accessed: 18th January, 2019) "US Gazetteer files: 2010, 2000, and 1990". United States Census Bureau at
https://www.census.gov/, 2011-02-12. (Accessed: 18th January, 2019)
Wilson, Steven G. and Fischetti, Thomas R., 2010. Coastline Population Trends in the United States:1960 to 2008. U.S. Census Bureau, PS 25-1139.
33
APPENDICES