Impact of sea-level rise on saltwater intrusion and formation of brominated disinfection byproducts during chlorination

Transcription

1 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 th UF Water Institute Symposium Gainesville Florida

2 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

3 IPCC AR5 Sea-level rise: Global

4 NOAA Sea-level rise: Local

5 Werner et al., 2013 Saltwater intrusion

6 Werner et al., 2013 Saltwater intrusion

7 Saltwater intrusion Monitoring well, Broward County USGS

8 Seawater composition o Chloride: 19,320 mg/l o Bromide: 69 mg/l Stumm and Morgan, 1996

9 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, mg/l Br

10 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, mg/l Br o 1% seawater: 193 mg/l Cl, 0.69 mg/l Br

11 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, mg/l Br o 1% seawater: 193 mg/l Cl, 0.69 mg/l Br

12 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

13 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

14 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

15 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

16 Approach Sea-level rise Literature DBP models Groundwater model TDS, Cl Br DBP formation Field data Lab experiments Adaptation, planning

17 Sea-level rise extrapolated

18 Dausman and Langevin, 2004 Study area

19 Groundwater model Freshwater Seawater

20 Groundwater model

21 Boundary conditions Boundary Coastal Head = 0 to m, TDS = 35 ppt Intracoastal Head = 0 to m, TDS = 23 ppt Canal (downstream of salinity barrier) Canal (upstream of salinity barrier) Water Conservation Area (eastern edge of Everglades) Head = 0 to m, TDS = 12 ppt Head = 1.37 m, TDS = 0 Head = 1.37 m, TDS = 0

22 Saltwater intrusion

23 Chloride intrusion

24 Chloride intrusion 1.3% seawater

25 Bromide intrusion? o Standard seawater o Bromide-to-chloride mass ratio: Millero et al., 2008

26 Bromide intrusion?

27 Bromide intrusion? o Standard seawater o Bromide-to-chloride mass ratio: o Bromide-to-TDS mass ratio: Millero et al., 2008

28 Bromide intrusion

29 Bromide intrusion 0.85 mg/l Br 250 mg/l Cl

30 Brominated DBPs?

31 DBP models THM4 = a(toc) b (UVA 254 ) c (Br ) d (Cl 2 ) e (ph) f (T) g (t) h

32 DBP models

33 DBP model trends

34 SLR and DBP formation SLR = 95% Confidence Level (High Scenario) DOC: 1.4 mg/l, UV 254 : /cm, ph 8, 20 C, 2.7 mg/l Cl 2, 24 h

35 Simulated saltwater intrusion Gulf of Mexico seawater Fresh groundwater 0.1% 0.2% 0.4% 1% 2%

36 Experimental design Uniform formation conditions: ph 8, 20 C, 2.7 mg/l Cl 2, 24 h

37 THM4 formation and speciation

38 SLR and DBP formation SLR = 95% Confidence Level (High Scenario) DOC: 1.4 mg/l, UV 254 : /cm, ph 8, 20 C, 2.7 mg/l Cl 2, 24 h

39 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 : /cm, ph 8, 20 C, 2.7 mg/l Cl 2, 24 h

40 SLR and DBP formation SLR = 95% Confidence Level (High Scenario) DOC: 1.4 mg/l, UV 254 : /cm, ph 8, 20 C, 2.7 mg/l Cl 2, 24 h

41 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

42 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

43 Treavor Boyer Assistant Professor Thank you

44 Broward County Dausman and Langevin, 2004

45 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 m 1150, 1150, and 150 m/day 150, 150, and 1.5 m/day 100, 10, and 1 m 64,800 49,728

46 Parameters Recharge Parameter Value m/day (0.94 m/yr) Maximum Evapotranspiration 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

47 Parameters Solution Extrapolated Sea Level Rise Base Case 30 No Sea-Level Rise m/100 yrs m/100 yrs m/100 yrs Method of Solution Total-Variation-Diminishing (TVD) Method

48 Dausman and Langevin, 2004 Groundwater model

49 DBP models

50 DBP models

51 DBP formation