Impact of sea-level rise on saltwater intrusion and formation of brominated disinfection byproducts during chlorination Treavor Boyer, Evan Ged, Louis Motz, Paul Chadik, Kathryn Frank, Jonathan Martin 11 February 2014 4 th UF Water Institute Symposium Gainesville Florida
Acknowledgements Research Opportunity Seed Fund: Florida as a laboratory for global urbanization, sea level rise, and future health risks of drinking water sources (PI Boyer, ESSIE) Paul Chadik, ESSIE Lou Motz, ESSIE Kathryn Frank, Urban and Regional Planning Jon Martin, Geological Sciences Evan Ged, M.E. 2013, Florida Sea Grant Scholarship
IPCC AR5 Sea-level rise: Global
NOAA Sea-level rise: Local
Werner et al., 2013 Saltwater intrusion
Werner et al., 2013 Saltwater intrusion
Saltwater intrusion Monitoring well, Broward County USGS
Seawater composition o Chloride: 19,320 mg/l o Bromide: 69 mg/l Stumm and Morgan, 1996
Seawater composition o Chloride: 19,320 mg/l o Bromide: 69 mg/l o Conservative mixing of freshwater and seawater o 0.1% seawater: 19.3 mg/l Cl, 0.069 mg/l Br
Seawater composition o Chloride: 19,320 mg/l o Bromide: 69 mg/l o Conservative mixing of freshwater and seawater o 0.1% seawater: 19.3 mg/l Cl, 0.069 mg/l Br o 1% seawater: 193 mg/l Cl, 0.69 mg/l Br
Seawater composition o Chloride: 19,320 mg/l o Bromide: 69 mg/l o Conservative mixing of freshwater and seawater o 0.1% seawater: 19.3 mg/l Cl, 0.069 mg/l Br o 1% seawater: 193 mg/l Cl, 0.69 mg/l Br
Disinfection byproducts (DBPs) Chlorine + Natural organic material + Bromide Halogenated organic DBPs Trihalomethane (THM4) Cl 3 CH, chloroform BrCl 2 CH, bromodichloromethane Br 2 ClCH, dibromochloromethane Br 3 CH, bromoform
Working hypothesis i. Sea-level rise will increase saltwater intrusion in coastal aquifers ii. Saltwater intrusion will increase the concentration of bromide, as well as chloride, in fresh groundwater iii. Elevated bromide will increase the formation of brominated disinfection byproducts (DBPs) during chlorination iv. DBPs will exceed primary maximum contaminant level (MCL) at earlier time than chloride will exceed secondary MCL
Research objectives 1. Model saltwater intrusion in a coastal aquifer 2. Assess the variability in the bromide-to-chloride ratio 3. Investigate the formation of bromine-containing DBPs for varying degrees of saltwater intrusion 4. Develop an applied science adaptation framework
Research objectives 1. Model saltwater intrusion in a coastal aquifer 2. Assess the variability in the bromide-to-chloride ratio 3. Investigate the formation of bromine-containing DBPs for varying degrees of saltwater intrusion 4. Develop an applied science adaptation framework Wednesday, 8:30 10:00 am: Kathryn Frank: Adapting to Climate, Sea Level, and Other Changes: A Survey of Florida s Coastal Public Water Supply Utilities
Approach Sea-level rise Literature DBP models Groundwater model TDS, Cl Br DBP formation Field data Lab experiments Adaptation, planning
Sea-level rise extrapolated 0.91 0.49 0.11
Dausman and Langevin, 2004 Study area
Groundwater model Freshwater Seawater
Groundwater model
Boundary conditions Boundary Coastal Head = 0 to 0.908 m, TDS = 35 ppt Intracoastal Head = 0 to 0.908 m, TDS = 23 ppt Canal (downstream of salinity barrier) Canal (upstream of salinity barrier) Water Conservation Area (eastern edge of Everglades) Head = 0 to 0.908 m, TDS = 12 ppt Head = 1.37 m, TDS = 0 Head = 1.37 m, TDS = 0
Saltwater intrusion
Chloride intrusion
Chloride intrusion 1.3% seawater
Bromide intrusion? o Standard seawater o Bromide-to-chloride mass ratio: 0.0034730 Millero et al., 2008
Bromide intrusion?
Bromide intrusion? o Standard seawater o Bromide-to-chloride mass ratio: 0.0034730 o Bromide-to-TDS mass ratio: 0.0019134 Millero et al., 2008
Bromide intrusion
Bromide intrusion 0.85 mg/l Br 250 mg/l Cl
Brominated DBPs?
DBP models THM4 = a(toc) b (UVA 254 ) c (Br ) d (Cl 2 ) e (ph) f (T) g (t) h
DBP models
DBP model trends
SLR and DBP formation SLR = 95% Confidence Level (High Scenario) DOC: 1.4 mg/l, UV 254 : 0.037 1/cm, ph 8, 20 C, 2.7 mg/l Cl 2, 24 h
Simulated saltwater intrusion Gulf of Mexico seawater Fresh groundwater 0.1% 0.2% 0.4% 1% 2%
Experimental design Uniform formation conditions: ph 8, 20 C, 2.7 mg/l Cl 2, 24 h
THM4 formation and speciation
SLR and DBP formation SLR = 95% Confidence Level (High Scenario) DOC: 1.4 mg/l, UV 254 : 0.037 1/cm, ph 8, 20 C, 2.7 mg/l Cl 2, 24 h
SLR and DBP formation SLR = 95% Confidence Level (High Scenario) 503 mg/l Br 974 mg/l Br 106 mg/l Br 197 mg/l Br DOC: 1.4 mg/l, UV 254 : 0.037 1/cm, ph 8, 20 C, 2.7 mg/l Cl 2, 24 h
SLR and DBP formation SLR = 95% Confidence Level (High Scenario) DOC: 1.4 mg/l, UV 254 : 0.037 1/cm, ph 8, 20 C, 2.7 mg/l Cl 2, 24 h
Conclusions o Sea-level rise and subsequent saltwater intrusion into coastal aquifers will o Increase bromide o Increase formation of Br-DBPs during chlorination o Create treatment and compliance challenges for THM4 at earlier time than TDS or chloride
Future work o Develop generalized seawater intrusion model o Assess spatial and temporal variability of bromideto-chloride ratio o Investigate and model DBP formation freshwater seawater mixtures
Treavor Boyer Assistant Professor thboyer@ufl.edu Thank you
Broward County Dausman and Langevin, 2004
Parameters Parameter Value Rows, Columns, Layers 16 X 90 X 45 Horizontal Discretization Vertical Discretization Dimensions (x, y, and z) Hydraulic Conductivities: Biscayne Aquifer (K x, K y, and K z ) Lower Surficial Aquifer (K x, K y, and K z ) Dispersivities ( α x, α y, and α z ) Total Cells Active Cells 250 m x 250 m 2.50 m 22,500 m x 4,000 m x 112.5 m 1150, 1150, and 150 m/day 150, 150, and 1.5 m/day 100, 10, and 1 m 64,800 49,728
Parameters Recharge Parameter Value 0.002575 m/day (0.94 m/yr) Maximum Evapotranspiration 0.001948 m/day (0.71 m/yr) Specific Storage (S S ) 1 x 10-5 m -1 Specific Yield (S y ) 0.25 Porosity (η) 0.1 Well Field 10 wells in layers 2-9 Pumping Rate (Q/2) 80,000 m 3 /day
Parameters Solution Extrapolated Sea Level Rise 2015-2115 29 Base Case 30 No Sea-Level Rise 31 0.114 m/100 yrs 32 0.486 m/100 yrs 33 0.908 m/100 yrs Method of Solution Total-Variation-Diminishing (TVD) Method
Dausman and Langevin, 2004 Groundwater model
DBP models
DBP models
DBP formation