Conductivity and Suspended Sediments in Karst and Fractured Springs in PennsylvaniaCecilia Mejias and Laura Toran

Department of Geology, Temple University

The properties of groundwater depend on the geology through which the groundwater travels

Three springs in southeastern Pennsylvania were compared: two karst springs and a spring discharging from sandstone

Conductivity, discharge, and suspended sediment were contrasted

Problem Statement

What’s going on?

In Karst Systems:Water seeps into the soil where it will react with the bedrock, (usually limestone or dolomite) exploit the weaknesses in the rock, and cause voids and fissures to form.

Water can easily pass through the fissures that will gradually become conduits which can lead to caves. If the overburden collapses it can make a sinkhole, which will make it easier for water to travel faster directly through the system.

When the water is dissolving the rock it will have a higher ionic content; when it travels fast through conduits it has a lower ionic content.

Water traveling through the karst will have higher sediment amounts since it can travel through the system faster. The water will respond to storms faster.

In Nonkarst systems:

Water percolates through the soil where it may seep through a series of fractures.

The fractures are caused by stress or over burden.

Resistant bedrock such as sandstone does not easily react with water.

The water takes a long time to find its way through the network of fractures.

Therefore storm response will be slowed. The sediment and ion concentrations are also lower

NolteStockton

Bushkill

Spring Locations

Acknowledgements

A special thanks to National Science Foundation Hydrologic Sciences Program for their support to make this project possible. Thank you to all the Temple student workers, especially Jen Tancredi whose work on the Nolte Spring and helpful input has proven invaluable.

Conclusions

SEDIMENT TRANSPORT

Higher at karst springs, Nolte and Bushkill (up to 50 mg/L)

Seemed to be season dependent: higher in fall than in the winter (some exceptions at Bushkill)

Stockton showed little or no variation (0 to 5mg/L) regardless of the season

VARIATIONS IN Ca2+

Nolte ranged from 95 to 115 mg/L

Bushkill ranged from 35 to 65 mg/L

Stockton less than 20 mg/L and little response to storms

CONDUCITIVITY

Lowest in the fractured rock spring (Stockton)

Differences in response indicate that continuous monitoring is especially important in karst springs to predict contaminant transport

Suspended Sediment

Dissolved Ca2+

0

20

40

60

80

100

120

9/1/2003 10/2/2003 11/2/2003 12/3/2003 1/3/2004 2/3/2004

Ca

(2+

), m

g/L

Bushkill Stockton Nolte

www.watersheds.org/blue/earth/karst4.htm

www.h2oguy.com/hydrology/ wellxsec.jpg

Stockton Spring Site

Bushkill Spring Site

Nolte Spring Site

Continuous Monitoring

Biweekly Sampling

Sample Analysis

Stockton Spring (non-karst)

Conductivity

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700

9/1/03 10/2/03 11/2/03 12/3/03 1/3/04 2/3/04

Con

duct

ivity

, uS

/cm

0

1

2

3

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6

7

8

9

10

Dai

ly R

ain,

cm

Conductivity, uS

rainfall, cm

Bushkill Spring (karst)

0

100

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500

600

700

9/1/03 10/2/03 11/2/03 12/3/03 1/3/04 2/3/04

Con

duct

ivity

, uS

/cm

0

1

2

3

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9

10

Dai

ly R

ain,

cm

Conductivity, uS

rainfall, cm

Nolte Spring (karst)

0

100

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600

700

9/1/03 10/2/03 11/2/03 12/3/03 1/3/04 2/3/04

Con

duct

ivity

, uS

/cm

0

1

2

3

4

5

6

7

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9

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Dai

ly R

ain,

cm

Conductivity, uS

Rain fall, cm

Located in Buckingham Township

Spring comes from a fracture in the sandstone in the Stockton formation

Stockton formation contains shale and sandstone

Discharges about 10 L/s at baseflow

Located in Lehigh Valley

This karst is composed of limestone and dolomite

Located in the Ordovian Epler formation

Discharges 3 L/s at baseflow

Bushkill SpringSite

Located in Lancaster County

This karst is composed of limestone and dolomite

Occurs in the Ordovician Epler formation

Discharges 25 L/s at baseflow

Global Water GL400 Datalogger

Conductivity and water level recorded at 20-minute intervals

HOBO temperature logger

Data downloaded every two to four weeks

Measured unstable parameters (pH, T) in the field

Collected samples for sediment, alkalinity, and ions

Duplicates

pH, Temperature

Water level and flow measurements

Dionex ion chromatograph for dissolved ion concentrations

Sediment filtering

Alkalinity Titrations with H2SO4

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50

9/1/2003 10/2/2003 11/2/2003 12/3/2003 1/3/2004 2/3/2004

Tot

al S

edim

ent

Con

cent

ratio

n, m

g/L

Bushkill Stockton Nolte

Bushkill 12/13/03 offscale 226 mg/L

Stockton Spring house, built circa 1700

Methods Bimonthly samples