A Saltwater Upconing Model to Evaluate Wellfield Feasibility

Gregory W. CouncilChristopher J. Richards

June 2008Salt Water Intrusion Meeting (SWIM)

Naples, Florida, USA

Location &Purpose

• Franklin Co., FL• Tate’s Hell

• Proposed Wellfield

• Drawdown?• Upconing?

A

A A

A

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%

A

A

G U L F O FM E X I C O

B

C

D

A

F R A N K L I NC O U N T Y

W A K U L L AC O U N T Y

L I B E R T YC O U N T Y

F3

A1 A2

C1

F2

New River

Sop

chop

py R

iv

er

Ochlockonee River

Cow

Cre

ek

Syfrett Creek

Crooked R iver

Ga t

or C

reek

Trou

t Cr e

e k

Tom Hahn Creek

Roberts Creek

Pine

Log

Cre

ek

Ochlockonee Ri ve

r

Ochlock onee River

Carrabelle

Sopchoppy

Tate's Hell #4

Tate's Hell #3Tate's Hell #2

Tate's Hell #1

8427

9005

15,000 0 15,000 30,0007,500

Feet

³

Legend

% Base-Case Supply Wells

% Other Candidate Well Locations

A Aquifer Performance Test Locations

A Deep Oil Exploration Well

Model Grid Frame

Streams

Primary Roads

Secondary Roads

Trails

County Line

Model Column 153

Model Column 220

Apalachicola National Forest

Tate's Hell State Forest

Coun

ty H

wy

67

Hydro-geology

-2800

-2400

-2000

-1600

-1200

-800

-400

0

Ele

vatio

n (ft

)

-2800

-2400

-2000

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-800

-400

0

0 ft 12000 ft 24000 ft

W ellsG ulf ofM exico

N orthw est

23

4

5

6

7

8

9

10

11

12

13

14

15

16

1

In term ediate S ystem

Floridan

Aquifer

System

Interm ediate/F loridan Transition Layer

Surfic ia l A qu ifer S ystem

Field Data

• Slug Tests– Surficial Aquifer

• Aquifer Performance Tests– Floridan Aquifer– Intermediate Confining Unit

• Borehole Geophysical Logs

APT Calibration

0

0.5

1

1.5

2

2.5

3

3.5

4

0.1 1 10 100 1000 10000

Time (min)

Dra

wdo

wn

(ft)

60N-Measured 60N Modeled-Layer 5 60N Modeled-Layer 4

255N-Measured 255N Modeled-Layer 5 255N Modeled-Layer 4

62D-Measured 62D Modeled-Layer 7

Lateral Boundary Conditions

-2800

-2400

-2000

-1600

-1200

-800

-400

0

Ele

vatio

n (ft

)

-2800

-2400

-2000

-1600

-1200

-800

-400

0

0 ft 21000 ft 42000 ft

-30

-25

-20

-15

-10

-5

0

5

10

15

20E

leva

tion

(ft)

-30

-25

-20

-15

-10

-5

0

5

10

15

20

Saltw ater InterfaceSpecified Freshw ater H ead (above In te rface)Specified Sa ltw ater Head (below In terface)

C o lum n 1Gulf o f M exico

A B C D ARow 328 C olum n 263 Row 1

41025.1sf zh

h

fs hz

Fresh: c = 0Saline: c = 35 g/L fhh

Simulation Method

• Top Boundary– Recharge: 500 mm/yr (20 in/yr)– ET: 330 mm/yr (13 in/yr) max

• Pre-pumping equilibrium– Reasonable initial head, concentration– 1000 yr simulation (10 d – 10 yr step)– Solute mass stable; head & conc. stable

• Simulate Pumping– 7,600 m3/d (2 mgd)

Drawdown

• Floridan Aquifer

&%

&%

Crooked River

Tom H ahn Creek

O

ch lockonee River

Pin

e Lo

g C

r eek

Roberts Creek

Oc hlockonee River

1

0.25

0.5

0.7 51.

5

1.25

1.75

1.755,000 0 5,000 10,0002,500

Feet

³

Legend

&% Production Wells

Drawdown (0.25 ft)

Upconing

• Surficial Aquifer

-900

-800

-700

-600

-500

-400

-300

-200

-100

0E

leva

tion

(m)

-900

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-600

-500

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-200

-100

0

0 m 2,000 m 4,000 m

G ulf ofM exico N orthw estW ells

C rookedR iver

250 m g/L and 15,000 m g/L Chloride Concentration Surface (m g/L) Prio r to Pum ping250 m g/L and 15,000 m g/L Chloride Concentration Surface (m g/L) after 50 Years of Pum ping250 m g/L and 15,000 m g/L Chloride Concentration Surface (m g/L) after 1,000 Years of Pum ping

Legend

15,000 m g/L

250 m g/L

Model Sensitivity: Upconing

• Initial Depth of the Brackish Zone– Lateral Boundary Conditions– Dispersivity

• Vertical Hydraulic Conductivity

• Effective Porosity

• Well Location

Conclusions

• Upconing of 250 mg/L chloride:

~35 m in 50 yr

~85 m equilibrium

• Need to identify current position of brackish zone

• Top boundary important for Surficial Aquifer drawdown

• Well placement

• Simple, general method for impact assessment