ORIGINAL ARTICLE

Geochemistry of a spring-dense karst watershed locatedin a complex structural setting, Appalachian Great Valley,West Virginia, USA

Dorothy J. Vesper Æ Rachel V. Grand ÆKristen Ward Æ Joseph J. Donovan

Received: 11 December 2007 / Accepted: 2 September 2008 / Published online: 14 October 2008

� Springer-Verlag 2008

Abstract The distribution and chemistry of the springs in

the Tuscarora Creek watershed is controlled by both geo-

logic structure and karst dissolution. The watershed is

located in eastern West Virginia in the structurally complex

Great Valley of the Appalachian Valley and Ridge province.

The upper portion of the stream parallels strike along a

mapped fault zone and is bordered by clastic rocks that

comprise North Mountain. The lower reaches of the stream

flow cross-strike through Cambro-Ordovician carbonates.

The controlling chemical signature in the spring water is

carbonate dissolution. Little evidence was seen for the

recharge from adjacent clastic rocks although differences in

the Ca/Mg molar ratio between springs indicated the pres-

ence of localized spring basins in headwater reaches. Na, Cl

and Ca generally increased from upstream to downstream in

the cross-strike reaches. Comparison of stream and cumu-

lative spring discharge was consistent with significant

groundwater base-flow contribution directly to the creek,

particularly in the strike-parallel region. The largest spring

in the watershed ([162 L/s) was sampled during and after a

large storm event along with the adjacent creek. The creek

displayed a typical dilution response with each flood pulse,

whereas the spring had only a limited or delayed response.

The overall chemical and thermal stability of the spring,

relative to the creek, indicated the lack of significant direct

hydraulic connection between the two. The conceptual

model for the area includes localized flowpaths in the

headwater region where the stream flow is parallel to strike

and a thrust fault. In addition to the shallow localized

flowpaths, a deeper, more regional flowpath likely exists for

a large spring further downstream.

Keywords Karst � Hydrogeology � Carbonate hydrology �Springs

Introduction

The Appalachian Valley and Ridge province is a highly

complex geologic region in which stratigraphy and struc-

ture play important roles in determining groundwater

movement. In areas underlain by carbonate rocks, such as

the Great Valley, rock dissolution and karst development

further complicate flow patterns for both groundwater and

surface water. A significant body of research has been

conducted related to the geochemistry and hydrogeology of

karst springs and aquifers. Understanding the karst system

in the Great Valley, particularly spring-creek interactions

on the scale of watersheds, requires incorporation of the

stratigraphic and structural framework.

Burton et al. (2002) studied the relationship between

structure and groundwater flow in the Valley and Ridge of

Pennsylvania. They found that bedding-plane partings

contributed significantly to the overall flowpaths and that

the dominant flow occurred parallel to dip direction.

Apparent groundwater ages, based on chlorofluorocarbons

(CFCs) and tritium/helium-3 (3H/3He) data, indicated that

water traveling down dip traveled more quickly than water

traveling updip or via cleavage fractures. By utilizing the

relative ages of groundwater along the two flowpaths, they

were able to identify the anisotropy and incorporate it into

the groundwater flow model. Similar results have been

D. J. Vesper (&) � K. Ward � J. J. Donovan

Department of Geology and Geography,

West Virginia University, Brooks Hall,

Morgantown, WV 26506-6300, USA

e-mail: djvesper@mail.wvu.edu

R. V. Grand

CH2M-HILL, St Louis, MO 63102, USA

123

Environ Geol (2009) 58:667–678

DOI 10.1007/s00254-008-1541-4

found in slightly dipping clastic sedimentary rocks in the

Newark Basin, New Jersey using well testing, chemical,

and geophysical data (Mishalski and Britton 1997; Morin

et al. 1997).

The importance of folds to karst drainage has been

studied in the Alps and Jura Mountains (Goldscheider

2005; Perrin and Luetscher 2007). The Hochifen-Gotte-

sacker karst system, located along the German–Austrian

border, is folded but has only limited cross-strata faulting

(Goldscheider 2005). Where the limestone is not exposed it

is confined above and below by less-permeable units.

Tracer tests indicated that the synclinal axes and troughs

act as the main flow pathways in the system. In contrast,

folded limestones in the Aubonne catchment in the Jura

Mountains are cross-cut by strike-slip faults (Perrin and

Luetscher 2007). This system can be accessed via the

Longirod cave which provides empirical data of the

drainage system. Tracer tests and cave passage orientations

indicated that groundwater drainage is either parallel to

fold axes or approximately perpendicular to the folds but

trending with the strike-slip faults.

The purpose of this study was to evaluate the variability

of multiple springs in a small watershed and the degree to

which structure and stratigraphy control hydrology and

water chemistry. The overall goal was to refine a better

conceptual model for karst-water flow in the Great Valley

in West Virginia. Although recent work has linked struc-

ture and transmissivity for this area (McCoy and Kozar

2007), we need to better understand how springs and water

quality fit into the conceptual model. This is particularly

true given the importance of springs for water supply in the

region. Specific aims for this project included evaluating

(1) trends in spring water chemistry and spring-stream

interactions between the cross-strike and strike-parallel

stream sections, (2) the importance of deep flow to a large

water-supply spring, and (3) the relationship between

geologic structure, spring type and flowpath.

Regional setting and site description

Tuscarora Creek watershed is located in the eastern pan-

handle of West Virginia, USA (Fig. 1). It is part of the

Opequon Creek Watershed which flows northward into the

Potomac River and eventually into the Chesapeake Bay

(Fig. 1ii). The Opequon Creek watershed lies within the

Appalachian Great Valley (Fig. 1iii) which is bounded the

mountains of the Ridge and Valley to the west and the Blue

Ridge to the east (Fig. 1iii, iv). The Valley and Ridge

region is subdivided into two hydrogeomorphic units

(Fig. 1iv): siliciclastic (VRS) and carbonate (VRC). The

studied region of the Great Valley is within the VRC unit

with a central band of VRC shale (Fig. 1iv).

The valley is underlain primarily by Cambo-Ordovician

carbonate rocks extending from the Cambrian Elbrook Fm.

to the Ordovician Trenton Fm. (Fig. 2). The carbonates are

a mixture of interbedded limestones and dolomites with

silty, sandy or cherty layers in some formations. The

Cambrian Elbrook and Conococheague formations under-

line most of the Tuscarora Creek Watershed west of the

City of Martinsburg (Fig. 2). The western boundary of the

valley is defined by North Mountain which is capped by the

Silurian Tuscarora Fm. (Fig. 2). The dominant structure in

western Berkeley County is the Massanutten Synclinorium,

with folded and faulted bedrock trending 020� (Kulander

and Dean 1986; Shultz et al. 1995; Zewe and Rauch 1991).

The core of the synclinorium is located within the outcrop

of the Martinsburg shale. The general dip of the rocks

underlying Tuscarora Creek is to the east (Fig. 2).

Faults, joints, and fractures are also present. The por-

tions of Berkeley County underlain by carbonates are more

faulted than the non-carbonate area (Shultz et al. 1995).

There are several mapped faults within the Tuscarora

Creek watershed (Fig. 2) including the North Mountain

thrust fault along the watershed’s western boundary. Along

the North Mountain fault, the dip is near vertical and may

have enhanced permeabilities owing to pressure-release

mechanisms (Grimsley 1916). Overturned folds and areas

of secondary folding are present, particularly near the core

of the synclinorium (Kulander and Dean 1986).

The upper portion of the Tuscarora Creek flows parallel

to the base of North Mountain (Fig. 2). This orientation is

approximately parallel to strike and the North Mountain

thrust fault. The downstream portion of the creek flows

cross strike, across the carbonate valley in an eastward

direction (Fig. 2).

Although the bulk of the watershed is underlain by

carbonate rocks, karst features are generally subdued

(Jones 1991). Recharge is primarily autogenic and dis-

persed (Jones 1991), although the clastic sequence at North

Mountain may provide a local source of allogenic recharge

to the aquifer in the upstream portions of the watershed.

Limited tracer testing has been conduced in the area

because of slow travel times and low dye recoveries (Jones

1991, 1997). Dye injected into a sink in Dry Run was

recovered in Kilmer Spring, one of the water supplies for

the City of Martinsburg. Dry Run is a northern tributary to

Tuscarora Creek.

A recent study of specific yields in wells in this region

of the Great Valley (McCoy and Kozar 2007) indicated

four factors linked to high yield values: valley topographic

settings, carbonate rocks, overturned anticlines and cross-

strike orientations. Although a large dataset (350 well

tests) allowed these factors to be identified statistically,

there was a wide range of values for specific yield (0.12–

4,220 L/min m) and all categories had overlapping ranges.

668 Environ Geol (2009) 58:667–678

123

Their conceptual model for the region incorporated dis-

persed recharge along near-vertical bedding planes and

subsequent flow along bedding planes.

The 13 springs in this study are located along approxi-

mately 12 km of Tuscarora Creek (Fig. 2; Table 1). Nearly

all of the springs are small and have spring houses. The one

notable exception is Kilmer Spring (12-KMR), which is the

largest spring in the study and part of the water supply for

the City of Martinsburg. It discharges from three spring

houses; the flow is combined in an underground piping

system and fed by gravity to the city water-treatment plant.

In addition to the City of Martinsburg, the Berkeley County

Public Service District and many local landowners rely on

carbonate spring water sources for a large portion of their

water supplies.

This region is undergoing rapid development, particu-

larly in the Great Valley. In West Virginia’s Berkeley

County, the setting of Tuscarora Creek, the population

increased 28% between 1990 and 2000 (US Census Bureau

2006). The upstream part of the watershed is still rural

but downstream the watershed is becoming increasing

developed.

Fig. 1 The location of the study

site relative to (i) regional state

setting—with the Potomac

River Basin (shaded) (ii) the

Tuscarora Creek watershed

(black) within the Opequon

watershed (stippled); (iii)

physiographic regions, APMN

Appalachian Mountains, BR

Blue Ridge, PDUP Piedmont

Uplands, and MELO

Mesozoic Lowlands; (iv)

hydrogeomorphic units, VRSValley and Ridge Siliciclastic,

VRC Valley and Ridge

carbonate, BR Blue Ridge, and

PCR Piedmont crystalline.

Geospatial data modified from

files provided by the

Chesapeake Bay Program

(2008)

Environ Geol (2009) 58:667–678 669

123

Materials and methods

Discharge was measured for the springs and in Tuscarora

Creek using the sum of measured flows over a cross-sec-

tional profile (Buchanan and Somers 1969). Velocity was

measured at 60% of depth using a propeller meter on a

transect with 10–20 intervals across the stream, depending

on stream width. Depth was measured with a wading rod.

Replicate discharge measurements were made at least once

per location. These agreed within 10% with the exception

of Water Street Spring (13-WAT, up to 36% difference);

this spring run lacks straight reaches necessary for high-

quality discharge measurements. For all springs, the dis-

charge was measured during different hydraulic conditions

to provide a range of values. A datum was selected for each

spring for consistent measurement of stage and the depth to

water from the datum was determined during each spring

visit.

Seepage runs were conducted along the upper 5 km of

Tuscarora Creek in October and November 2004 (Fig. 3).

The intent was to compare gaining and losing reaches in

the upper strike-parallel and the lower cross-strike reaches.

During November, the measurements were made by two

teams. Both teams began and ended at the same location;

the four discharges measured at that location were within

8%. Not only does this reflect there was little change in the

stream over the course of the day, but it also provides a

level of accuracy for discharge determinations.

For a limited number of springs, continuous monitoring

was conducted using pressure transducers and data loggers.

The instruments were programmed to collect and save data

on frequent (10 min to 1 h) intervals. Some of the data

loggers also measured electrical conductivity (EC) and

temperature of the water. The pressure transducers were

calibrated using either air pressure or a hydraulic column in

the laboratory prior to installation in the springs and creeks.

The EC and temperature loggers were calibrated or

checked prior to use and periodically in the field.

Grab samples were collected from springs during the

interval from November 2003 and January 2005 on an

Fig. 2 Detailed geology of

watershed with spring locations,

generalized cross-section and

stratigraphic column. Springs

numbered accordingly to

Table 1. Data compiled and

modified from sources in Jones

(1991), Kulander and Dean

(1986), West Virginia

Geological and Economic

Survey (1968), and the West

Virginia GIS Data

Clearinghouse (2008)

670 Environ Geol (2009) 58:667–678

123

approximately monthly basis. The number of sampled

springs increased over that time as more springs were

identified and landowner access was obtained. Owing to

this enhanced later data set, the last four sampling events

were used to illustrate water chemistry so as to maximize

comparability between the locations.

Synoptic stream water samples were collected during

some sampling periods (Table 2). Springs with long spring

runs and no adjacent stream (springs 4, 6, 8 and 13) or

springs located in swampy areas with numerous small

resurgences (springs 2, 3, 7 and 10), were not included in

this comparison.

Additionally, storm-water samples were collected from

Kilmer Spring and adjacent in Tuscarora Creek between 22

June and 9 July 2006. These samples were collected using

automated water samplers on time intervals ranging from

1 h during the storm to as much as 6-h several days after

the storm peak. Rainfall data were collected using a tip-

ping-bucket rain gage at Kilmer Spring and measured a

total 11.6 cm of precipitation over this period. On-site field

data were collected for all monthly grab samples and most

storm samples. Calibrated hand meters were used to obtain

temperature (±0.04�), pH (±0.01) and EC (±1%) data.

Alkalinity was measured in the field using a two-point

titration method (American Public Health Association

2000) and reported as milligram per liter as HCO3-. The

alkalinity data were collected so that charge balance errors

could be calculated and the derived parameters (saturation

indices and CO2 partial pressures) could be estimated.

Water samples were field filtered using a tortuous-path

0.45-lm filter. Samples for cation analysis were preserved

using nitric or hydrochloric acid. The samples were kept

cold until transported to the analytical laboratory at the

National Center for Coal and Energy at West Virginia

University. The samples where held in the laboratory

refrigerator at 4C until analysis. Analysis was completed

for Ca, Mg, Na, K, Fe, and Mn using inductivity cou-

pled plasma—optical emission spectroscopy (ICP-OES)

according to EPA method 200.7. Iron and manganese

concentrations were nearly always below their 0.1 mg/L

detection limits. For most of the study, the anions (Cl, NO3,

and SO4) were measured using an Lachet 8000 colorimetric

autoanalyzer following EPA Methods 325.2, 353.3 and

375.2, respectively. The samples from the final three

sampling periods were analyzed for anions using ion

chromatography (IC) following EPA Method 300.0.

Although the change in method may have created some

bias in the data, the overall trends, as discussed below,

were not dependent on that change. Equipment blanks,

duplicates, and blind standards were analyzed with the

samples and indicated that major element chemistry was

acceptable.

Saturation indices for calcite (SIC) and dolomite (SID)

and the associated hypothetical carbon dioxide partial

pressures (PCO2) were calculated for the monthly samples

using Visual MINTEQ (Gustafsson 2005; USEPA 2000).

The mean charge balance error for major constituents was

less than six percent.

Table 1 Spring location and discharge data

ID on Fig. 2 ID Water supply UTM Coordinates Discharge (L/s)

n Range Mean

1 NWM No 753972–4370527 6 4.2–9.4 7.1

2–3 WG1 & WG2

(combined flow)

WG1-Private;

WG2-No

754259–4371064

754266–4371085

3 5.7–21 14.7

4 JSF No 754171–4371817 1 14.4 –

5 PHS No 754770–4372140 Unable to measure discharge—piped

from springhouse to fishing pond.

No flow during summer

6 DBR No 755197–4373129 2 2.8–3.4 –

7 BRK No 755347–4373119 2 1.2–3.4 –

8 DOD Private 755565–4373213 1 8.8 –

9 BEL Private 755913–4372843 7 23–38 32.2

10 TFS No 756884–4372591 Seep—too small to measure

11 OLN No 757377–4372473 6 3.7–9.3 6.2

12 KMR (Kilmer) Public 243691–4373141 15 Unknown [162

13 WAT (water street spring) No 245122–431249 12 15.7–33 23.6

UTM coordinates based on NAD_83 Datum. All springs are in zone 17S except for Water Street Spring (18S). Discharges measured between

November 03 and March 05—frequency dependent on identification and access. Water Street Spring is also known as the Martinsburg Water

Supply Spring (but is not currently used as a water supply). Discharge data for Kilmer Spring is based on water treated at plant—a minimum

value

Environ Geol (2009) 58:667–678 671

123

Results

Spring and stream discharge

The springs in the study, with the exception of Kilmer

Spring, were small with discharges less than 30 L/s

(Table 1). The exact discharge of Kilmer Spring was

unknown, but a minimum discharge was known from

water treatment operations. The entire spring output is

gravity fed to the Martinsburg treatment plant. Based on

plant records for 15 random dates between April 2004 and

August 2006, an average discharge of 162 L/s was treated

(Stephen Knipe, City of Martinsburg Director of Public

Utilities, personal communication 2006). However, the

total spring volume was greater than this; the excess

overflow water was not quantified by the plant. Given the

configuration of the spring and collection system, it was

not feasible to measure spring discharge for Kilmer at the

source area.

A seepage run was conducted on Tuscarora Creek in

November 2004; its purpose was to compare discharge in

creek sections which are parallel-strike and cross-strike.

Therefore, the study was conducted in the upper 5 km of

the creek (Fig. 3). Flow was measured in the creek and in

the springs flowing into the creek. The cumulative dis-

charge of the springs was not sufficient to account for the

stream flow, indicating the stream was gaining over the

distance measured (Fig. 3). Similar data collected during

October 2004 had comparable results.

The percent of baseflow contribution to the stream was

approximated by fitting an exponential equation to the

stream discharge data, a linear equation to the cumulative

spring flow data, and subtracting the difference (Fig. 3).

Using this approach for the November data, the baseflow

was calculated to contribute between 40 and 60% of the

flow to the stream. This likely overestimated baseflow

contribution inasmuch as it assumed that all of the springs

were identified and quantified. Whereas additional small

springs were likely to be present, they were unlikely to

change the general conclusion that a significant portion of

the water in Tuscarora Creek was acquired through base-

flow, not spring flow. Springs provided the greatest fraction

of input to stream discharge in the strike-parallel creek

reaches, whereas baseflow provided the greatest fraction of

flow in the cross-strike reaches.

Seasonal and spatial variation in carbonate chemistry

The spring water chemistry was classified as a calcium-

bicarbonate water type throughout the watershed. Chemical

changes in spring water from upstream to downstream were

generally subtle although some trends were observed. In

the upper sections of the watershed, where the stream flows

parallel to strike and a thrust fault, the carbonate constit-

uents (e.g., Ca, Mg, Ca/Mg molar ratios) were more

variable between springs than in the lower cross-strike

stream reaches (Fig. 4). Average concentrations from the

final four periods were used to best illustrate the trends

(Fig. 4), but individual sampling periods had similar

results.

Vertical bars, based on the standard deviation of four

sample periods, illustrate the temporal chemical variability

for each spring location (Fig. 4). Spring chemistry along

the strike-parallel reaches was variable both temporally

(indicated by the vertical bars) and spatially (comparing

between springs). The temporal variability in the chemistry

of the cross-strike springs was generally low. Chemical

concentrations in the cross-strike springs were generally

either consistent (Mg) or increasing with distance down-

stream (Ca, Na).

The concentrations of the carbonate-sourced constituents,

as demonstrated by Ca, typically increased downstream in

Fig. 3 (i) Discharge measurement locations in the upper Tuscarora

Creek Watershed. (ii) Results of seepage run, November 2004 for

Tuscarora Creek (stream) and cumulative spring discharge (spring).

Shaded areas illustrate calculated spring and direct input based on an

exponential fit to the stream data (R2 = 0.91) and a linear fit for the

spring input (R2 = 0.91). (iii) Fractional contribution of spring and

baseflow input to Tuscarora Creek. Distances on (ii) and (iii)

measured beginning with the most upstream perennial spring at 0

672 Environ Geol (2009) 58:667–678

123

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Environ Geol (2009) 58:667–678 673

123

the cross-strike stream-reach springs (Fig. 5i). Although

adjacent springs switched concentration order during occa-

sional months (e.g., March 2005), the trend was generally

consistent even through seasonal change. The Ca/Mg molar

ratio was typically less than three, but spring 1-NWM had a

ratio between 3 and 4, indicating slightly different source

waters (Fig. 4). Spring 1-NWM is the most upstream

perennial spring.

Na and Cl were found in their highest concentrations in

the furthest downstream spring (13-WAT) through all

sampling periods (Figs. 4, 5ii, iii); and Cl molar concen-

trations were present in excess of the Na molar

concentrations (Fig. 5iv). Both of these trends were

consistent for each period of data regardless of anion

analytical method. All IC-measured Cl concentrations fall

within the range measured calorimetrically. WAT spring is

located in an urban area that has been intensively modified,

and is not in its original natural setting. Ostracod data

indicated that the water being discharged is from a

groundwater source modified to discharge from a pipe

(Smith et al. 2004). This spring was historically used as a

water supply for Martinsburg (McColloch 1986).

The influence of urbanization may be seen in the City of

Martinsburg. Spring 13-WAT, located in downtown Mar-

tinsburg, had the highest measured concentrations of Na

and Cl (Fig. 5), common indicators of anthropogenic

sources (Panno et al. 2006). This spring has been altered

from its natural setting; it currently discharges from a metal

pipe but historical evidence (McColloch 1986), ostracod

data (Smith et al. 2004), and consistent chemistry (Fig. 4)

support that it is discharging groundwater. The presence of

elevated Na and Cl indicates that this spring may also be

influenced by contaminant sources.

Storm responses at Kilmer Spring and Tuscarora Creek

A total of 77 Kilmer Spring water and 88 Tuscarora Creek

water samples were collected during the June 2006 storm

event, of which 57 were analyzed for major cations. The

storm surge was recorded as two distinct stage peaks in the

creek (Fig. 6) but only a smaller, later surge was observed

in the spring. Although the magnitude of the peaks cannot

be compared given the different setting geometries, the

timing indicated that the spring was slower to respond and

returned to baseline more slowly. The EC in the creek

decreased during the storm pulses owing to dilution, but

was comparatively constant in Kilmer Spring.

For Ca, Mg, and SO4, the pre-storm concentrations were

similar; these diverged during the storm (Fig. 6). K was

significantly higher in the creek water throughout the

sampled period. In all cases, the chemical concentrations at

Kilmer Spring showed relatively little variation, whereas

the stream-water chemistry was diluted during the storm

(Fig. 6). The difference in the responses indicates that

rainfall input to Kilmer Spring is not rapidly transferred to

the spring.

Variation in Ca/Mg molar ratios

The molar relationship between Ca and Mg in the spring

waters illustrated the changes in water chemistry, and

possibly flowpaths, over a 12-km reach of Tuscarora Creek.

The most upstream springs (Fig. 7) had distinctly different

Ca/Mg ratios from each other indicating that these small

springs were being drawn from different and probably

nearby sources. The temporal and spatial variability in their

Fig. 4 Changes in spring water chemistry from upstream to down-

stream. Graphed values are averages for the last four sampling

periods; error bars indicate one standard deviation above and one

below. Geologic formations legend on Fig. 2

674 Environ Geol (2009) 58:667–678

123

water chemistry (Fig. 4) further supported the presence of

short, localized flowpaths to the springs in this area.

Longer, less discrete flowpaths could be expected to create

a more integrative chemistry at these springs. That is,

instead of the springs having distinct Ca/Mg ratios, the

chemistry would be more uniform spatially.

The next downstream group of springs (Fig. 7ii) are

located in a spring-dense area where Tuscarora Creek turns

from being a strike-parallel stream to a cross-strike stream.

The Ca/Mg ratios measured in these springs have over-

lapping ranges, suggesting that the flowpaths in this area

are less localized that further upstream or that the springs

are sourced from similar rocks. Springs in the cross-strike

reach (Fig. 7iii) are similar to the previous group.

Downstream springs Kilmer and WAT (Fig. 7iv, vi)

were similar to each other and have slightly higher Ca/Mg

ratios than the springs located upstream. The Ca–Mg

relationship at Kilmer spring was consistent across sea-

sonal and storm samples (Fig. 7iv, v). The Ca/Mg values in

Tuscarora Creek (Fig. 7vii) fell within the overall range

reported for the springs.

Variation in PCO2–SIc relationships

A total of 22 spring and stream-water sample pairs were

collected over the course of the study (Table 2). Samples

were collected upstream from the confluence of the stream

and spring flows. Comparison of all data indicated that

spring water samples had generally higher PCO2 and lower

SIC values than the surface water samples (Fig. 8i). As

spring water resurges, carbon dioxide degasses, resulting in

an increase in SIC. The reaction progress for the degassing

is illustrated by the sloped lines in Fig. 8. The relative

distribution of the spring and stream water samples is

consistent with the emergence of groundwater and its

subsequent degassing in the surface setting.

Some of the stream water samples had SIC values higher

than might be predicted by the degassing of the sampled

springs, suggesting that there may have been another water

source with a PCO2 similar to the springs but a higher SIC..

Baseflow contribution to the creek, as indicated by the

stream flow data (Fig. 3), could account for this contribu-

tion. However, there were no discernable patterns in the

PCO2 and SIc data spatially for the creek samples, and no

sample was obtained from the groundwater underneath the

creek.

The difference in PCO2 and SIC between spring waters

was not as great as the difference between springs and

stream water, but there some general changes based on the

average measured values (Fig. 8ii). Spring waters in the

upstream reaches (1–3), which had distinctively different

Ca/Mg molar ratios, had similar PCO2 and SIC values,

plotting near the average of the other spring data. Spring 4-

JSF, the flashiest of the springs, had the lowest SIC in water

and is the most likely spring to be fed by allogenic

recharge. Water from springs located near where the stream

turns direction (7–9) generally have low PCO2 and SIC

values than the downstream spring waters. Waters from the

Fig. 5 Concentrations of (i) Ca

(ii) Na, and (iii) Cl in

cross-strike springs (7 and

downstream). iv) Comparison

of molar concentrations of Cl

and Na. The line on (iv) has a

slope of 1

Environ Geol (2009) 58:667–678 675

123

furthest downstream springs (10–13) had the highest PCO2

and SIC values, possibly indicating longer flowpaths or

travel times.

Discussion

A conceptual model for groundwater flow in the Tuscarora

Creek watershed is a combination of localized and longer

flowpaths controlled primarily by stratigraphy and struc-

ture. In the headwater stream reaches, along the North

Mountain Fault and parallel to strike, there are numerous,

chemically variable springs and creek water is a mixture of

point-source contribution from springs and more diffuse

baseflow. The variability of the upstream reaches may be

controlled by stratigraphy, permeability along faults, or the

proximity to allogenic recharge from North Mountain.

Most of these springs (numbers 1 through 6) are mapped in

the Rockdale Run member of the Beekmantown Group.

This formation appears as a band between two mapped

thrust faults which place the Rockdale Run between the

Cambrian Elbook and Ordovician Martinsburg formations.

The only spring in the study that regularly turns turbid

(4-JSF, Personal Communication, Jim Smith spring owner

2004) is located in this reach and is the only spring that

identifiably flows directly from rock. The greater vari-

ability of these springs is supported by well and stream data

from other studies (Shultz et al. 1995), indicating greater

groundwater transmissivity along the fault. Alternatively, it

is possible that in the upstream areas the faults or lower

permeability zones in the Elbrook Fm. act as barriers to

flow, creating localized flowpaths through isolation. It has

been reported that many of the fault zones are cemented

and more likely to act as barriers than flowpaths (Jones

1991). However, transmissivity data collected by Shultz

et al. (1995) were higher in the upstream sections parallel

to strike and the thrust faults.

In the middle-watershed cross-strike reaches, there are

fewer springs and they have less chemical variability either

from each other or through time. However, the computed

fraction of the creek water that comes directly from base-

flow is more than 50%. The greater contribution of

baseflow in the cross-strike (approximately dip-parallel)

direction may be related to the relative scarcity of springs.

Kilmer Spring, a public water-supply source, is consid-

erably larger and more consistent in chemistry than all other

springs in the watershed. It is mapped on a thrust fault that

brings the Rockdale Run Fm. in contact with the Conoco-

cheague Fm. Its limited and delayed response to a major

rain event, while the adjacent Tuscarora Creek was highly

variable, indicated that the surface water is largely inde-

pendent of the water source for Kilmer. The source of water

at Kilmer Spring has been the focus of research and spec-

ulation in the past. High concentrations of bacteria have

been measured in spring water in the past (Hobba 1976) and

dye tracing from shallow injections (Hobba 1976; Jones

1991) indicate at least a partial component of shallow water

input. Apparent age dating of Kilmer Spring water has been

conducted by the US Geological Survey: estimated—ages

of atmospheric isolation of this water were determined to

fall between 4 and 8 years (Busenberg and Plummer 2008).

The authors also report that the tritium concentrations

suggest that the recharge for the 2004 water occurred in the

late 1990s, consistent with the 4–8 year age range.

A possible flowpath for the spring water at Kilmer Spring

would be along the synclinal bedding planes with upward

flow along fractures. Although stacked groundwater basins

have been identified in flat-lying carbonate rocks such as the

Fig. 6 Comparison of storm response in Kilmer Spring (black linesand symbols) and adjacent in Tuscarora Creek (gray lines and

symbols). Data from 2006

676 Environ Geol (2009) 58:667–678

123

Mammoth Cave region (Palmer 1981), the Valley and Ridge

province has more complex geologic structures and dip-

controlled flow parallel to bedding planes may be important.

Although the down-dip flowpath is only speculative based

on the data presented herein, studies in similar terrains

indicate that is a possible explanation for character of Kil-

mer Spring. In the Shenandoah Valley, the USGS found that

younger-age waters are found in the core of the synclinori-

um and older water along the limbs (Yager 2006). This

pattern could be modeled based on anisotropy that accounts

for flow both along bedding planes and cross-fractures

(Yager 2006). Age data from nested wells in folded and

fractured clastic rocks in Pennsylvania had similar patterns

with the dip direction along bedding-planes being an

important location for groundwater flow (Burton et al.

2002). Data from the Alps and the Jura Mountains

(Goldscheider 2005; Perrin and Luetscher 2007) also sup-

ports the importance of karstic flow along folds and cross-

cutting fractures. Underlying drains, that cross-cut fold

structures have been observed in the Jura Mountains (Perrin

and Luetscher 2007) and may also contribute to the larger

springs.

The chemical evolution of spring water in the water-

shed, as defined by PCO2 and SIC, is not a simple function

from upstream to downstream. However, localized

upstream flowpaths with more integrative downstream

flowpaths could account for this distribution. The largest

and least-variable spring has minimal local surface input as

evidenced by its delayed and attenuated response to a

major storm event.

Fig. 7 Comparison of Ca–Mg

molar ratios for different springs

in the watershed and for all

creek data (lower right). Solidlines for slopes of 1, 1.7, 2.5 and

5. X- and Y-axes consistent on

all graphs

Fig. 8 (i) SIC and PCO2 data for

both spring and stream waters.

(ii) For mean spring values

based on sampling periods 6–9.

Sloped lines for equilibrium

degassing calculated assuming

three Ca activities (aCa2?),

0.002, 0.001 and 0.005 (lowest)

Environ Geol (2009) 58:667–678 677

123

The exact ground-water flowpaths for the springs in

Tuscarora Creek Watershed cannot be determined. How-

ever, the presence of localized upstream spring basins plus

a more regional flow system are supported by changes in

geochemistry of the spring waters both temporally and

spatially.

Acknowledgments This project was funded by WV Water

Research Institute and the US Department of Agriculture, National

Research Initiative, grant number 2003-35102-13537. We would also

like to thank the City of Martinsburg and the spring owners for

property access; the Chesapeake Bay Program for providing regional

geospatial data that crosses state lines, and Dr. Jaime Toro for help

with the geologic cross-section.

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