Surface Water and Seawater Interactions in the Coastal Environment of Biscayne Bay, Southeast Florida

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1 Surface Water and Seawater Interactions in the Coastal Environment of Biscayne Bay, Southeast Florida William C. Hutchings, MS, PG Nicholas Albergo, PE, DEE Paper No Salt Lake City Annual Meeting (October 16 19, 19, 2005)

2 Groundwater flow in a coastal environment generally consists of the seaward flow of freshwater overlying the landward flow of seawater with dispersion across the t interface resulting in a transition zone. Tidal fluctuations can result in significant changes to the e flow system, especially in the vicinity of the discharge zone. If the coastal environment includes surface water bodies, interactions between the surface water and fresh-to to-saline groundwater result in complex daily and seasonal effects. These interactions were investigated at a site located within the City of North Miami, Florida as part of the development of a former landfill into a high end residential/commercial mercial development. The site includes several freshwater lakes adjacent to a mangrove e system consisting of both fresh and saline surface water and groundwater ultimately discharging to Biscayne B Bay. Hydraulic characteristics were obtained from a variety of aquifer tests and natural gradient tracer tests that were primarily conducted with rhodamine dye. Qtracer and SEAWAT 2000 were used to analyze the tracer tests. SEAWAT was also used to model groundwater flow under various seasonal sonal periods including the five- year and 25-year storm events, which results in the injection of surplus storm water into the Biscayne Aquifer. The model demonstrated that the groundwater flow system is significantly altered by the presence of, and the associated water level fluctuations in the lakes, especially during the storm events. Vertical flow and mass transport is significantly increased as a result of the lakes and associated seasonal fluctuations. The density of brackish water in the mangroves would be expected to result in vertical flow. However, the mangrove system appears to limit vertical discharge due to the low permeability sediments deposited in this environment. Organic decomposition of the landfill material has generated an ammonia plume whose treatment was evaluated with an experimental prototype permeable reactive barrier. Various models of this environment have also been used to simulate full-scale remedial combinations of slurry walls and reactive barriers with a SEAWAT 2000 three-dimensional model.

3 1 Biscayne Landing, North Miami

4 2 Site Location Map Southeast Lake Altered Mangrove Preserve (AMP) Prototype Treatment Zone Trace of Cross- Section Model

5 3 Concerns The effects of lake level rise,, due to storm water input, on contaminant migration and treatment The down-gradient discharge of ammonia-impacted impacted groundwater into the altered mangrove, Mangrove Preserve, and Biscayne Bay The potential for ammonia migration to the north and the necessity to consider construction of the reactive wall along the northern border The down-gradient discharge of ammonia-impacted impacted groundwater into the altered mangrove, Mangrove Preserve, and Biscayne Bay Stormwater management alternatives and groundwater treatment requirements

6 4 Surface Water Setting The site is located near the west coast of Biscayne Bay, which is in direct connection with the Atlantic Ocean through Haulover Inlet The site is bound to the east by altered mangroves and a Mangrove Preserve exists east of the altered mangroves along the southern half of the site The southern and northern portions of the site lie approximately 2,250-feet and 3,500-feet from Biscayne Bay, respectively Arch Creek lies south of the site and flows into Biscayne Bay The Snake Creek Canal and the Oleta River lie northwest and north-northeast northeast of the site, respectively The Oleta River discharges into Biscayne Bay

7 5 Biscayne Landing, North Miami Snake Creek Canal Oleta River Mangrove Preserve Biscayne Bay Arch Creek Haulover Inlet

8 6 General Characteristics of Biscayne Bay Generally a saline water body receives discharge of freshwater from the Biscayne Aquifer West part of Biscayne Bay exhibits less salinity than seawater due to the discharge of freshwater from Biscayne Aquifer

9 7 Site Hydrogeology The site is underlain by the following formations in ascending order: Pamlico Sand Miami Limestone Key Largo Limestone Anastasia Formation Tamiami Formation

10 8 Model Selection The USGS groundwater flow and mass transport model SEAWAT (Version 2.12) was used to evaluate the above site characteristics. Additional SEAWAT characteristics and capabilities: 1. Three-dimensional finite difference model couples MODFLOW (1988, groundwater flow) and MT3DMS (1998, solute transport, 2. Based on the principle of equivalent freshwater heads,, a function of salinity and density, 3. Capable of modeling variable-density environments (e.g., seawater-freshwater), 4. Groundwater flow directions and relative velocities are inferred from vectors, 5. Since ammonia is a dissolved constituent, model vectors describe potential migration paths and velocities, 6. Additional species (e.g., ammonia), can be modeled with SEAWAT 2000, a recent version that uses MODFLOW 2000.

11 Model Selection (continued) Model Dimentions: 6300 meters (E-W) x 3200 meters (N-S) 43 rows and 51 columns Cells range from 50 to 200 meters 14 layer model Hydrogeologic Boundaries Simulated: Biscayne Bay constant head Mangrove Preserve constant head Arch Creek constant head with gradient Oleta River constant head with gradient Snake Creek Canal constant head with gradient General eastward groundwater flow specified head and general head boundary Site Lakes constant head and High K Method Base of the Biscayne Aquifer no flow

12 9 Model Input Parameters Site lithologies to approximately 75-ft ft-bls were obtained from previous site investigations The lower Biscayne Aquifer was inferred from Fish & Stewart, 1991 The hydraulic conductivities were obtained from a variety of sources including site slug and pumping tests; ; published historical data obtained from the vicinity of the site, and model calibration Model calibration took into consideration current inland extent of seawater intrusion and distribution of salinities in Biscayne Aquifer in vicinity of the site

13 10 Cross-Section Along Row 32

14 11 Cross-Section Along Row 21

15 12 Cross-Section Along Row 23

16 13 0 Cross-Section Along Row 33

17 14 Cross-Section Along Row 24

18 15 Cross-Section Along Row 33

19 16 Additional Simulations Various scenarios were simulated consistent with PBS&J s ICPR model results including: Post-development steady state conditions with NHW (natural high water) elevation of 2.0 ft. Pre- and Post-development conditions after 5-5 year, 24-hour storm events

20 17 Results Concern 1: The effects of lake level rise,, due to storm water input, on contaminant migration and treatment

21 18 Cross-Section Along Row 22

22 19 Conclusions Under NHW conditions, lake levels of 0.61m are approximately 0.1m greater than annual average elevations NHW elevations are consistent with average annual conditions Ammonia plume migration is not significantly affected compared to average historical annual conditions

23 20 Cross-Section Along Row 22

24 Cross-Section Along Row 22

25 22 Cross-Section Along Row 22

26 23 Cross-Section Along Row 22

27 24 Cross-Section Along Row 22

28 25 Cross-Section Along Row 22

29 26 Conclusion Under the 5-year, 5 24-hour event, the lakes exhibit moderate mounding (approximately 1.25 m, annual average elevation is 0.5 m); however, the event is short-lived and the lakes levels quickly decrease to NHW (or lower) elevations within a few days.

30 27 Results Concern 2: The down-gradient discharge of ammonia- impacted groundwater into the altered mangrove, Mangrove Reserve, and Biscayne Bay

31 28 Cross-Section Along Row 22

32 29 Cross-Section Along Row 22

33 300 Cross-Section Along Row 31

34 31 Cross-Section Along Row 31

35 32 Conclusions The Biscayne Aquifer discharges into the altered mangroves and the Mangrove Preserve Due to the volume of water associated with the Biscayne Aquifer, all of the discharge does not occur at the mangroves The ammonia plume extends to approximately 60-ft ft-bls and, as a result, part of this plume migrates towards Biscayne Bay Biological and physical aspects of natural attenuation, biodegradation, chemical reactions, dilution, and dispersion, etc., decrease concentrations (<action levels) as evidenced by the absence of ammonia in samples collected from Biscayne Bay Due to high hydraulic conductivity of the aquifer and rapid mixing, the injected storm water does not rise due to buoyancy Vertical effects of injected storm water in lower Biscayne Aquifer are evident at an elevation of approximately -25 m, NGVD

36 33 Results Concern 3: Storm water management alternatives and groundwater treatment requirements

37 34 Conclusions Under NHW conditions, the ammonia plume is not significantly affected (0.1m) and therefore, discharge to the lakes is encouraged Under conditions of the 5-year/245 year/24-hour storm event, injection of all storm water is to the lakes and to a network of drainage wells resulting in moderate mounding Discharge of storm water associated with 5-year/245 year/24-hour event will result in: General radial flow in vicinity of lakes Increased horizontal and vertical hydraulic gradients in vicinity y of lakes Vertical hydraulic gradients dampened by drainage wells

38 Conclusions (continued) Offside migration may occur in all directions, depending on duration of storm events Groundwater treatment temporarily minimized due to increased flux of water High hydraulic conductivity of aquifer results in rapid dissipation of effects Effects of 5-year/245 year/24-hour storm dissipate within approximately 1 week and offsite migration is minor Majority of the transport of ammonia is in response to local and regional boundaries; not temporary storms Historical and Post-development flow systems are similar, therefore ammonia migration patterns will not be significantly altered

39 35 Simulations Using SEAWAT 2000 Cross-Section Model Tracer Test TT-1 Rhodamine Concentrations in Interval 2 Approximately 571 Hours Following Injection at MW-D2

40 36 Tracer Test TT-2 Rhodamine Concentrations in Interval 3 Approximately 306 Hours Following Injection at MW-B3

41 37 Tracer Test TT-3 Rhodamine Concentrations in Interval 4 Approximately 1284 Hours Following Injection at MW-D4

42 38 Tracer Test TT-4 Rhodamine Concentrations in Interval 1 Approximately 161 Hours Following Injection at MW-W1

43 39 Steady State Salinity Distribution with Constant Boundaries

44 40 Salinity Distribution Approximately 565 Hours (High Tide) after Tracer Injection in Interval-2 (with transient boundaries)

45 41 Salinity Distribution Approximately 571 Hours (Low Tide) after Tracer Injection in Interval-2 (with transient boundaries)

46 42 Salinity Distribution Approximately 155 Hours (High Tide) after Tracer Injection in Interval-1 (with transient boundaries)

47 43 Salinity Distribution Approximately 161 Hours (Low Tide) after Tracer Injection in Interval-1 (with transient boundaries)

48 44 Summary of the Hydraulic Parameters Calculated with QTRACER Analysis by Silvana M.S. Ghiu, PhD Tracer Test ID Date Injection Well Depth Interval Zone ID Tracer Sampling Well Distance from Source Peak Time (Since Injection) Peak Conc Velocity Average Velocity TT1 TT2 29-Mar-04 D Apr-04 TT4 15-Jul-04 MW-W1 B TT3 6-May-04 D ft bls ft h g/l ft/day ft/day I P II III IV 3-15 I Rhodamine WT Rhodamine WT Rhodamine WT Rhodamine WT O M L K T S G G L L K F F I P C WTW

49 Summary of the Hydraulic Parameters Calculated with QTRACER Analysis by Silvana M.S. Ghiu, PhD (continued) Tracer Test ID Dispersion Coefficient Longitudinal Dispersivity Average Dispersion Coefficient Longitudinal Dispersivity Average Longitudinal Dispersivity Porosity K/n Hydraulic Conductivity TT1 TT2 TT3 TT4 ft 2 /s m ft 2 /s ft ft ft/day ft/day 9.3E E , E E , E E , E E E , E E , E E , E E , E E E , E E E E E E E E E E E , E E E , E E , E E E E E E E E E E

45 SEAWAT 2000 3-D Model Simulation Steady State Ammonia Distribution North Part

50 45 SEAWAT D Model Simulation Steady State Ammonia Distribution North Part of the Site Cross-Section Along Row 17 Potential Groundwater Treatment Alternative

51 46 Simulation of Funnel-Gate System After 1.0 Year Cross-Section Along Row 17

52 47 Simulation of Funnel-Gate System After 5.0 Years Cross-Section Along Row 17

Numerical Groundwater Flow Model Report. Caloosa Materials, LLC 3323 Gulf City Road Ruskin, Florida 33570

Numerical Groundwater Flow Model Report Caloosa Materials, LLC 3323 Gulf City Road Ruskin, Florida 33570 GHD 2675 Winkler Ave Suite 180 Fort Myers, FL 33901 11138224 Report July 27, 2017 Table of Contents