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

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 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