The Floridan Aquifer/Chipola River The Floridan Aquifer/Chipola River System StudySystem Study

Christy Crandall

U.S. Geological Survey

Tallahassee, Florida

850 942-9500 ext. 3030

crandall@usgs.gov

Funded by: U.S. Geological Survey National Water Quality Assessment Program (NAWQA)

and Florida Department of Environmental Protection (FDEP)

STUDY OBJECTIVESSTUDY OBJECTIVES• Identify significant sources of nutrients to the Floridan aquifer system in the Identify significant sources of nutrients to the Floridan aquifer system in the

lower ACF basin and in the Chipola River basin.lower ACF basin and in the Chipola River basin.

• Characterize hydrologic and transport processes occurring along flowpaths Characterize hydrologic and transport processes occurring along flowpaths from areas contributing recharge to discharge points of interest using a ground-from areas contributing recharge to discharge points of interest using a ground-water flow and particle tracking model. water flow and particle tracking model.

• Use flow and tracking model to match nitrate concentrations in ground water Use flow and tracking model to match nitrate concentrations in ground water from areas contributing recharge to 6 NAWQA trend wells, Jackson Blue from areas contributing recharge to 6 NAWQA trend wells, Jackson Blue Spring, Baltzell spring group, and Sandbag Spring—springs that flow into the Spring, Baltzell spring group, and Sandbag Spring—springs that flow into the Chipola River. Chipola River.

• Use the ground-water flow and tracking model to test hypothetical scenarios Use the ground-water flow and tracking model to test hypothetical scenarios changing management practices in using the flow and tracking modelchanging management practices in using the flow and tracking model..

Contaminant occurrence in the Upper Contaminant occurrence in the Upper Floridan aquifer and recharging RiversFloridan aquifer and recharging Rivers

Purpose of study is to determine:Purpose of study is to determine: Factors affecting nitrate occurrence and distribution in the Upper Factors affecting nitrate occurrence and distribution in the Upper

Floridan aquifer in the Dougherty Karst PlainFloridan aquifer in the Dougherty Karst Plain

• Distribution of travel times from recharge to dischargeDistribution of travel times from recharge to discharge• Land use effects on nitrate concentrations Land use effects on nitrate concentrations • Transport processes in ground water Transport processes in ground water • Effects of Withdrawals on flowpaths and travel timesEffects of Withdrawals on flowpaths and travel times

Background and Study AreaBackground and Study Area

• Vertically contiguous sequence of limestone and Vertically contiguous sequence of limestone and dolostone of late Paleocene to early Miocene age dolostone of late Paleocene to early Miocene age ranging from 0 to 1250 feet thick in the study arearanging from 0 to 1250 feet thick in the study area

• Sand overlying clay and limestone Sand overlying clay and limestone

• Clay lenses in places between the sand and Clay lenses in places between the sand and LimestoneLimestone

• Highly potableHighly potable

• Contains numerous springs, sinks and other karst Contains numerous springs, sinks and other karst features—highly vulnerable. features—highly vulnerable.

Floridan Aquifer System

TopographyTopography of the of the Dougherty Dougherty Karst PlainKarst Plain

Extent of Floridan

Floridan Aquifer System in the Floridan Aquifer System in the Dougherty Karst PlainDougherty Karst Plain

• High rates of direct recharge through sinkholes and High rates of direct recharge through sinkholes and indirect recharge through overburden—mostly sand and indirect recharge through overburden—mostly sand and silty sandsilty sand

• High rates of discharge to large incised streams through High rates of discharge to large incised streams through springs.springs.

Flow system ConceptualizationFlow system Conceptualization

Northern Extent of Floridan Aquifer System

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

• 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)

Existing Models 2006Existing Models 2006

Models from Elliott Jones and Lynn Models from Elliott Jones and Lynn Torak 1996 and 2006Torak 1996 and 2006

• MODFE Finite element transient MODFE Finite element transient 2-D model developed to simulate 2-D model developed to simulate the effects of 4000 irrigation wells the effects of 4000 irrigation wells on baseflow conditiotns in the Flint on baseflow conditiotns in the Flint river.river.

Tallahassee

Current Current MODFLOW MODFLOW Active Active Model-Grid Model-Grid BoundaryBoundary

Jones and Torak Jones and Torak MODFE Model MODFE Model Boundaries Boundaries

Comparison of Model FeaturesComparison of Model Features

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

• Steady State Steady State (Torak and (Torak and

others, 1996) others, 1996) and then 1-and then 1-year transient (1999-year transient (1999-2000) 2000) (Jones and Torak, (Jones and Torak, 2006) 2006)

• Variable Element SizeVariable Element Size• 1 layer 2-D model 1 layer 2-D model • 4000 Wells simulated4000 Wells simulated

MODFLOWMODFLOW Developed to simulate nitrate Developed to simulate nitrate tracking and concentrations recharging riverstracking and concentrations recharging rivers

• Steady StateSteady State• Uniform cell-size (1000 m)Uniform cell-size (1000 m)• 2 layer surficial/residuum, 2 layer surficial/residuum,

UFA fully 3-D modelUFA fully 3-D model• Over 4000 Wells simulatedOver 4000 Wells simulated

•

MODLFOW model derived the following MODLFOW model derived the following starting parameters where availablestarting parameters where available

from Torak and Jonesfrom Torak and Jones

• Hydraulic parametersHydraulic parameters• Aquifer tops and bottomsAquifer tops and bottoms• Pumping dataPumping data• RechargeRecharge• Boundary conditionsBoundary conditions• River and drain stage and conductanceRiver and drain stage and conductance• Starting headsStarting heads

Boundary Conditions in the MODFLOW Model

Simulated Withdrawals in the Upper Floridan aquiferSimulated Withdrawals in the Upper Floridan aquifer

Model Calibration DataModel Calibration Data

• 329 head observations in the Floridan 329 head observations in the Floridan aquiferaquifer

• 65 flow observations including perennial 65 flow observations including perennial and non-perennial streamsand non-perennial streams

MODFLOW Budget MODFLOW Budget Components  Flow in CFS Components  Flow in CFS

• CONSTANT HEAD 3,397 CONSTANT HEAD 3,397

• WELLS = 0.00 WELLS = 0.00

• NONPERENNIALS = 0.00 NONPERENNIALS = 0.00

• PERENNIALS = 253 PERENNIALS = 253

• HEAD DEP 5332 HEAD DEP 5332

• RECHARGE = 1,909       RECHARGE = 1,909      

• TOTAL IN 10,890       TOTAL IN 10,890      

•CONSTANTCONSTANT HEADHEAD 2,7722,772 •WELLSWELLS == 810810•NONPERENNIALSNONPERENNIALS == 188188 •PERENNIALS = 3124PERENNIALS = 3124 •HEADHEAD DEPDEP 3,9963,996 •RECHARGERECHARGE == 0.000.00         

•TOTALTOTAL OUTOUT 10,89010,890

Simulated Simulated UFA UFA

HeadsHeads

Observed v. Simulated HeadObserved v. Simulated Head

Simulated v. Observed flowsSimulated v. Observed flows

Additional Modeling to define Additional Modeling to define Areas Contributing RechargeAreas Contributing Recharge

Regional ModelRegional Model

• UFA broken into 3 layersUFA broken into 3 layers

• Local Grid Refinement in areas of interestLocal Grid Refinement in areas of interest

• Karst Features added throughout—Karst Features added throughout—– SinkholeSinkhole– Conduit layerConduit layer

Local Grid RefinementLocal Grid Refinement

Local Grid RefinementLocal Grid Refinement

• 12 layers—12 layers—– 3 in the surficial3 in the surficial– 9 in the Floridan9 in the Floridan

Improves flow path accuracy and travel time Improves flow path accuracy and travel time estimatesestimates

Better areas contributing recharge definitionBetter areas contributing recharge definition

Flow PathsFlow Paths

Areas Contributing Recharge Areas Contributing Recharge and Age of Waterand Age of Water

SummarySummary

• Add local grids at Balztell and Sandbag Add local grids at Balztell and Sandbag Spring Group as wellSpring Group as well

• Finalize nitrate travel time estimates and Finalize nitrate travel time estimates and area contributing recharge with these area contributing recharge with these modelsmodels

• Finish reportFinish report