impact of sea-level rise on saltwater intrusion and...
TRANSCRIPT
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
4th 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
Sea-level rise: Global
IPCC AR5
Sea-level rise: Local
NOAA
Saltwater intrusion
Werner et al., 2013
Saltwater intrusion
Werner et al., 2013
Saltwater intrusion
USGS
Monitoring well,
Broward County
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)
• Cl3CH, chloroform
• BrCl2CH, bromodichloromethane
• Br2ClCH , dibromochloromethane
• Br3CH, 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
Groundwater
model
Sea-level rise
TDS, Cl–
Literature
Field
data
Br–
DBP
models
Lab
experiments
DBP
formation
Adaptation,
planning
Sea-level rise extrapolated
0.91
0.49
0.11
Study area
Dausman and Langevin, 2004
Groundwater model
Seawater Freshwater
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)
Head = 0 to 0.908 m,
TDS = 12 ppt
Canal (upstream of salinity
barrier)
Head = 1.37 m,
TDS = 0
Water Conservation Area
(eastern edge of Everglades)
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
250 mg/L Cl–
0.85 mg/L Br–
Brominated DBPs
?
DBP models
THM4 = a(TOC)b(UVA254)c(Br–)d(Cl2)
e(pH)f(T)g(t)h
DBP models
DBP model trends
SLR and DBP formation
DOC: 1.4 mg/L, UV254: 0.037 1/cm, pH 8, 20 °C, 2.7 mg/L Cl2, 24 h
SLR = 95% Confidence Level (High Scenario)
Simulated saltwater intrusion
Fresh
ground-
water
0.1% 0.4% 1% 2% 0.2%
Gulf of Mexico seawater
Experimental design
Uniform formation conditions: pH 8, 20 °C, 2.7 mg/L Cl2, 24 h
THM4 formation and speciation
SLR and DBP formation
DOC: 1.4 mg/L, UV254: 0.037 1/cm, pH 8, 20 °C, 2.7 mg/L Cl2, 24 h
SLR = 95% Confidence Level (High Scenario)
SLR and DBP formation
DOC: 1.4 mg/L, UV254: 0.037 1/cm, pH 8, 20 °C, 2.7 mg/L Cl2, 24 h
SLR = 95% Confidence Level (High Scenario)
974 mg/L Br–
106 mg/L Br–
197 mg/L Br–
503 mg/L Br–
SLR and DBP formation
DOC: 1.4 mg/L, UV254: 0.037 1/cm, pH 8, 20 °C, 2.7 mg/L Cl2, 24 h
SLR = 95% Confidence Level (High Scenario)
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
Conclusions
o Develop generalized seawater intrusion model
o Assess spatial and temporal variability of bromide-
to-chloride ratio
o Investigate and model DBP formation freshwater–
seawater mixtures
Future work
Broward County
Dausman and Langevin, 2004
Parameters
Parameter Value
Rows, Columns, Layers 16 X 90 X 45
Horizontal Discretization 250 m x 250 m
Vertical Discretization 2.50 m
Dimensions (x, y, and z) 22,500 m x 4,000 m x 112.5 m
Hydraulic Conductivities:
Biscayne Aquifer (Kx, Ky, and Kz)
Lower Surficial Aquifer (Kx, Ky, and Kz)
1150, 1150, and 150 m/day
150, 150, and 1.5 m/day
Dispersivities ( αx, αy, and αz) 100, 10, and 1 m
Total Cells
Active Cells
64,800
49,728
Parameters
Parameter Value
Recharge 0.002575 m/day (0.94 m/yr)
Maximum Evapotranspiration 0.001948 m/day (0.71 m/yr)
Specific Storage (SS) 1 x 10-5 m-1
Specific Yield (Sy) 0.25
Porosity (η) 0.1
Well Field 10 wells in layers 2 - 9
Pumping Rate (Q/2) 80,000 m3/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
Groundwater model
Dausman and Langevin, 2004
DBP models
DBP models
DBP formation