The Floridan Aquifer/Chipola River System Study

1
The Floridan Aquifer/Chipola River System Study
Funded by U.S. Geological Survey National Water
Quality Assessment Program (NAWQA) and Florida
Department of Environmental Protection (FDEP)

• Christy Crandall
• U.S. Geological Survey
• Tallahassee, Florida
• 850 942-9500 ext. 3030
• crandall_at_usgs.gov

2
STUDY OBJECTIVES

• Identify significant sources of nutrients to the
  Floridan aquifer system in the lower ACF basin
  and in the Chipola River basin.
• Characterize hydrologic and transport processes
  occurring along flowpaths from areas contributing
  recharge to discharge points of interest using a
  ground-water flow and particle tracking model.
• Use flow and tracking model to match nitrate
  concentrations in ground water from areas
  contributing recharge to 6 NAWQA trend wells,
  Jackson Blue Spring, Baltzell spring group, and
  Sandbag Springsprings that flow into the
  Chipola River.
• Use the ground-water flow and tracking model to
  test hypothetical scenarios changing management
  practices in using the flow and tracking model.

3
Contaminant occurrence in the Upper Floridan
aquifer and recharging Rivers

• Purpose of study is to determine
• Factors affecting nitrate occurrence and
  distribution in the Upper Floridan aquifer in the
  Dougherty Karst Plain
• Distribution of travel times from recharge to
  discharge
• Land use effects on nitrate concentrations
• Transport processes in ground water
• Effects of Withdrawals on flowpaths and travel
  times

4
Background and Study Area
5
Floridan Aquifer System

• Vertically contiguous sequence of limestone and
  dolostone of late Paleocene to early Miocene age
  ranging from 0 to 1250 feet thick in the study
  area
• Sand overlying clay and limestone
• Clay lenses in places between the sand and
  Limestone
• Highly potable
• Contains numerous springs, sinks and other karst
  featureshighly vulnerable.

6
Extent of Floridan
Topography of the Dougherty Karst Plain
7
Floridan Aquifer System in the Dougherty Karst
Plain

• High rates of direct recharge through sinkholes
  and indirect recharge through overburdenmostly
  sand and silty sand
• High rates of discharge to large incised streams
  through springs.

8
(No Transcript)
9
Flow system Conceptualization
10
Northern Extent of Floridan Aquifer System

• Confinement--Recharge occurs mainly in unconfined
  and semi-confined areas
• Potentiometric surfaceflows southward to rivers
  from northern extent

11

• Ground water makes up the majority of discharge
  during low-flow conditions in the Dougherty Karst
  Plain.
• For example at least 63 springs identified and
  sampled along the Chipola River.
• (Barrios and Chellette, 2004)

12
Existing Models 2006

• Models from Elliott Jones and Lynn Torak 1996
  and 2006
• MODFE Finite element transient 2-D model
  developed to simulate the effects of 4000
  irrigation wells on baseflow conditiotns in the
  Flint river.

13
Current MODFLOW Active Model-Grid Boundary
Tallahassee
Jones and Torak MODFE Model Boundaries
14
Comparison of Model Features

• MODFE Developed to simulate the effects of
  irrigation on the Flint/Apalachicola Rivers
  baseflow

• MODFLOW Developed to simulate nitrate tracking
  and concentrations recharging rivers

• Steady State (Torak and others, 1996) and then
  1-year transient (1999-2000) (Jones and Torak,
  2006)
• Variable Element Size
• 1 layer 2-D model
• 4000 Wells simulated

• Steady State
• Uniform cell-size (1000 m)
• 2 layer surficial/residuum, UFA fully 3-D model
• Over 4000 Wells simulated

15

• MODLFOW model derived the following starting
  parameters where available
• from Torak and Jones
• Hydraulic parameters
• Aquifer tops and bottoms
• Pumping data
• Recharge
• Boundary conditions
• River and drain stage and conductance
• Starting heads

16
Boundary Conditions in the MODFLOW Model
17
Simulated Withdrawals in the Upper Floridan
aquifer
18
Model Calibration Data

• 329 head observations in the Floridan aquifer
• 65 flow observations including perennial and
  non-perennial streams

19
MODFLOW Budget Components  Flow in CFS

• CONSTANT HEAD 3,397
• WELLS 0.00
• NONPERENNIALS 0.00
• PERENNIALS 253
• HEAD DEP 5332
• RECHARGE 1,909      
• TOTAL IN 10,890      

• CONSTANT HEAD 2,772
• WELLS 810
• NONPERENNIALS 188
• PERENNIALS 3124
• HEAD DEP 3,996
• RECHARGE 0.00      
• TOTAL OUT 10,890

20
Simulated UFA Heads
21
Observed v. Simulated Head
22
Simulated v. Observed flows
23
Additional Modeling to define Areas Contributing
Recharge
24
Regional Model

• UFA broken into 3 layers
• Local Grid Refinement in areas of interest
• Karst Features added throughout
• Sinkhole
• Conduit layer

25
(No Transcript)
26
(No Transcript)
27
Local Grid Refinement
28
Local Grid Refinement

• 12 layers
• 3 in the surficial
• 9 in the Floridan
• Improves flow path accuracy and travel time
  estimates
• Better areas contributing recharge definition

29
Flow Paths
30
Areas Contributing Recharge and Age of Water
31
Summary

• Add local grids at Balztell and Sandbag Spring
  Group as well
• Finalize nitrate travel time estimates and area
  contributing recharge with these models
• Finish report