investigating landfill-impacted groundwater seepage into headwater streams using stable carbon...

HYDROLOGICAL PROCESSESHydrol. Process. 18, 1915–1926 (2004)Published online 12 May 2004 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/hyp.1457

Investigating landfill-impacted groundwater seepage intoheadwater streams using stable carbon isotopes

E. A. Atekwana1* and R. V. Krishnamurthy2

1 Department of Geology and Center for Earth and Environmental Science, Indiana University, Purdue University Indianapolis,Indianapolis, Indiana, 46202, USA

2 Department of Geosciences, Western Michigan University, Kalamazoo, Michigan, 49008, USA

Abstract:

The impact of landfill contaminated groundwater along a reach of a small stream adjacent to a municipal landfill wasinvestigated using stable carbon isotopes as a tracer. Groundwater below the stream channel, groundwater seeping intothe stream, groundwater from the stream banks and stream water were sampled and analysed for dissolved inorganiccarbon (DIC) and the isotope ratio of DIC (υ13CDIC). Representative samples of groundwater seeping into the streamwere collected using a device (a ‘seepage well’) specifically designed for collecting samples of groundwater seepinginto shallow streams with soft sediments. The DIC and υ13CDIC of water samples ranged from 52 to 205 mg C/Land �16Ð9 to C5Ð7‰ relative to VPDB standard, respectively. Groundwater from the stream bank adjacent to thelandfill and some samples of groundwater below the stream channel and seepage into the stream showed evidence ofυ13C enriched DIC (υ13CDIC D �2Ð3 to C5Ð7‰), which we attribute to landfill impact. Stream water and groundwaterfrom the stream bank opposite the landfill did not show evidence of landfill carbon (υ13CDIC D �10Ð0 to �16Ð9‰).A simple mixing model using DIC and υ13CDIC showed that groundwater below the stream and groundwater seepinginto the stream could be described as a mixture of groundwater with a landfill carbon signature and uncontaminatedgroundwater. This study suggests that the hyporheic zone at the stream–groundwater interface probably was impactedby landfill contaminated groundwater and may have significant ecological implications for this ecotone. Copyright 2004 John Wiley & Sons, Ltd.

KEY WORDS carbon isotopes; dissolved inorganic carbon; streams; seepage; tracers; landfill; groundwater

INTRODUCTION

The discharge of contaminated groundwater to surface water bodies constitutes a significant portion ofcontaminant loading, which impairs surface water quality (e.g. Blevins, 1989; US EPA, 1991; Modica et al.,1998; van Lanen and Dijksma, 1999; Fryar et al., 2000; Schilling and Wolter, 2001; Neumann et al., 2002;Hancock, 2002; Hayashi and Rosenberry, 2002). In addition to impairing surface water quality, contaminatedgroundwater discharged to surface waters also affects the structure and functioning of aquatic ecosystems(e.g. Gregory et al., 1991; Malard et al., 1996; Brunke and Gonser, 1997; Meyer, 1997; Hancock, 2002;Hayashi and Rosenberry, 2002). Stream-water quality impairment from polluted groundwater discharge inmany heavily urbanized and industrialized watersheds occurs as point sources from facilities (e.g. industrial,commercial and waste disposal facilities) located near streams. Consequently, impacts to stream water fromcontaminated groundwater associated with these facilities are usually localized, occurring only along limitedstream reaches.

A straightforward and simple approach to investigating the impacts of point source contamination ofstreams by groundwater is to compare the geochemical properties of stream water with near-channel

* Correspondence to: E. A. Atekwana, Department of Geology and Geophysics, University of Missouri–Rolla, 1870 Miner Circle, Rolla,MO 65409, USA. E-mail: [email protected]

Received 11 November 2002Copyright 2004 John Wiley & Sons, Ltd. Accepted 9 June 2003

1916 E. A. ATEKWANA AND R. V. KRISHNAMURTHY

groundwater, below-channel groundwater and groundwater seeping into the stream (e.g. Rutherford andHynes, 1987; DeWalle and Pionke, 1989; Benner et al., 1995). However, groundwater pollution of streamsystems is difficult to study because instream water quality and ecological disturbance resulting from suchpollution may occur at variable scales; from the microhabitat to the watershed scale (Woessner, 2000;Sophocleous, 2002). Additionally, investigating zones of groundwater pollution of streams is especiallydifficult because the effects of pollution may be limited to the interface between groundwater and streamwater.

In this study, the impact of landfill contaminated groundwater was investigated along a stream reachadjacent to a municipal landfill in a small headwater catchment in Michigan, USA. Previous investigationsof benthic macro-invertebrates and stream-water quality impairment in the lower catchment, which includedthe stream reach adjacent to the landfill, were conducted as part of an ecological assessment by the MichiganDepartment of Natural Resources (MDNR) in 1979 and 1986. The Michigan Department of Natural Resources(1979, 1986) studies documented low abundance and diversity of macro-invertebrates, and those observedwere tolerant of stressful conditions indicative of poor stream water quality. Visual observations of streamconditions and measurements of dissolved oxygen and temperature were used to assess water quality in thestream. The MDNR investigations concluded that although stream quality was judged to be poor, impactsto stream water from landfill contaminated groundwater could not be readily detected in the stream water(Michigan Department of Natural Resources, 1979, 1986). Further investigations of possible landfill impactsto stream water and streambed sediments were conducted by Canonie Environmental (1989). In the CanonieEnvironmental (1989) study, semi-volatile organic compounds, organochlorine pesticides and polychorinatedbiphenyls observed in contaminated groundwater at the landfill site were not detected in the stream water.Streambed sediments showed higher As, Ba, Cd, Co, Pb, Mn and Zn in upstream locations compared withlocations adjacent to the landfill and downstream of the landfill, and sediments from the stream reach adjacentto the landfill and downgradient of the landfill had higher Al, Cu, Fe and Va relative to upstream locations(Canonie Environmental, 1989). The Canonie Environmental (1989) report also concluded that definitive proofof impact to the stream by landfill contaminated groundwater was not readily discernable in stream water orsediments. Although the Michigan Department of Natural Resources (1976, 1986) and Canonie Environmental(1989) reached similar conclusions, there was still reasonable suspicion that landfill contaminated groundwaterwas having an impact on the stream reach. There are two main reasons why the Michigan Department ofNatural Resources (1976, 1986) and Canonie Environmental (1989) studies may not have detected the impactof the landfill contaminated groundwater in the stream reach. Firstly, a tracer suitable for tracking of landfillcontamination in groundwater was not used in these studies and secondly, greater volume of stream dischargerelative to seepage flux to the reach may have been sufficient to mask the effects of landfill contaminatedgroundwater.

In this study, we conducted sampling and analyses for evidence of landfill impact in stream water,groundwater below the stream channel, groundwater seeping into the stream and groundwater in the streambank sediments. We used stable carbon isotopes as a tracer to track landfill contaminated groundwater. Heavycarbon isotope ratios (υ13C) of dissolved inorganic carbon (DIC) in groundwater in the vicinity of landfillshave been used as diagnostic of landfill contamination (Games and Hayes, 1977; Walsh et al., 1993; Baedekerand Back, 1979; Rank et al., 1996; Hackley et al., 1996). In a conceptual model of groundwater–stream-waterinteraction in gaining stream reaches, groundwater seeping into streams may have sources that are both nearand far from the stream, with the age of groundwater seepage increasing from the stream banks towardsthe centre of the stream channel (Modica et al., 1998). Thus in this study, groundwater sampled from thestream banks may represent local sources, whereas groundwater sampled from below the streambed mayrepresent sources from more distant locations or a mixture of both. In addition to using heavy carbonas diagnostic of landfill carbon pollution, we use DIC and υ13CDIC to model mixing between landfillimpacted groundwater and stream water, near-channel and below-channel groundwater for the stream reachinvestigated.

Copyright 2004 John Wiley & Sons, Ltd. Hydrol. Process. 18, 1915–1926 (2004)

LANDFILL-IMPACTED GROUNDWATER SEEPAGE 1917

STUDY SITE

The stream reach investigated in this study is located on a small stream (Davis Creek) adjacent to amunicipal landfill in Kalamazoo, Michigan, USA (Figure 1). The landfill is unlined and located in glacialdrift approximately 46 m thick (Schmaltz, 1978). The glacial drift consists of fine sands, gravels and cobbles,

Monitoring Well

Piezometer

Seepage Well

Stream Water

0 20 m

SW4

SW3

SW1

SW2

W-MW1

DC3

DC1

0

MICHIGAN

LANDFILL

500 m

Sampling Locations

Stream

flow

StudyArea

Railroad

Davis Creek

E-MW1

W-MW2

W-PZ2

E-MW2

E-PZ2

W-MW3

W-PZ3

E-MW3

E-

Davis Creek Streambed Well

DCSW

DC2

0

E-PZ3

Figure 1. Map showing the stream segment adjacent to a municipal landfill investigated in this study. Insert shows the approximate locationin Kalamazoo, Michigan, USA (landfill map modified from Canonie Environmental, 1989)



Tabl

eI.

Sam

plin

glo

catio

n,de

pth

tobo

ttom

ofsc

reen

edin

terv

al,

spec

ific

cond

ucta

nce

(SpC

),di

ssol

ved

inor

gani

cca

rbon

(DIC

)an

dυ13

CD

ICof

seep

age

into

Dav

isC

reek

,gr

ound

wat

erbe

low

Dav

isC

reek

and

grou

ndw

ater

from

stre

amba

nkse

dim

ents

adja

cent

toD

avis

Cre

ek.

See

Figu

re1

for

sam

plin

glo

catio

ns

Sam

ple

Dep

thto

Scre

enSp

C(µ

S/cm

)D

IC(m

gC

/L)

υ13C

DIC

�‰�

Bot

tom

(cm

)25

/9/9

51/

10/9

514

/11/

954/

12/9

514

/12/

9522

/1/9

6M

inim

umM

axim

umM

EA

NSD

26/6

/96

26/6

/96

SW1

N/A

—45

447

848

947

747

745

448

947

513

57�1

1Ð3W

-MW

123

2Ð5—

——

1303

1279

1137

1137

1303

1240

9015

6�1

1Ð9D

C1

69Ð9

——

—48

047

048

747

048

747

99

54�1

1Ð5E

-MW

111

8Ð1—

——

784

774

763

763

784

774

1155

�10Ð0

SW2

N/A

633

648

701

650

709

693

633

709

672

3262

�8Ð8

W-M

W2

235Ð3

1050

1005

896

916

908

903

896

1050

946

6510

9�0

Ð1W

-PZ

225

4Ð1—

——

——

—11

0�1

Ð6E

-MW

220

1Ð493

889

189

189

788

489

088

493

889

920

102

�14Ð0

E-P

Z2

279Ð0

——

——

——

86�1

3Ð2SW

3N

/A15

1114

3013

8113

0613

7813

4513

0615

5113

9985

185

C3Ð2

W-M

W3

210Ð9

1640

1596

1668

1603

1639

1581

1581

1668

1621

3320

5C5

Ð3W

-PZ

325

8Ð5—

——

——

—21

1C5

Ð7D

C2

120Ð7

1320

1303

1250

1231

1276

1234

906

1101

1006

7210

1�2

Ð3D

C3

63Ð2

906

1101

1063

1028

980

959

1231

1320

1269

3710

6�1

Ð7E

-MW

3N

/A93

810

3987

888

487

673

273

210

3989

110

011

8�1

6Ð9E

-PZ

311

7Ð8—

——

——

—89

�14Ð4

SW4

248Ð4

772

752

876

874

878

875

752

878

838

5912

4C1

Ð0D

CSW

N/A

665

643

702

739

1747

1279

643

1747

963

453

52�1

1Ð0

SW,

seep

age

wel

l;M

W,

Mon

itori

ngw

ell;

PZ,

Piez

omet

er;

N/A

,no

tan

alys

ed;

—,

not

inst

alle

dat

sam

plin

gtim

e.



interbedded with discontinuous clay/till layers of varying thickness (Geological Services, Inc., 1981; Leja,1983). The glacial drift is underlain by the Mississippian Coldwater Shale that varies in thickness between274 and 305 m and consists of gray shales that contain abundant ironstone concretions (Straw, 1978). TheColdwater Shale bedrock is essentially impermeable, thus the groundwater aquifer in the area is located withinthe glacial drift, which is unconfined and considered as a single unit owing to the discontinuous nature of theclay/till layers (Allen et al., 1972; Straw, 1978). Local groundwater flows towards the northeast west of DavisCreek and to the northwest east of Davis Creek (Geological Services Inc., 1981; Canonie Environmental,1989). Thus Davis Creek represents a local groundwater discharge zone for shallow groundwater flow at thestudy site. The area between the landfill and Davis Creek has been altered previously. Results of a geophysicalsurvey and soil borings showed that some portions of the area had been used for disposal activities (Atekwana,1996). The disposed materials, which included trash and soil, occur in discontinuous irregular cells, some ofwhich extend close to the stream bank (Atekwana, 1996).

METHODS

Stream water and groundwater sampling

To evaluate possible impacts of landfill polluted groundwater discharged to the stream reach, we sampledstream water, groundwater from the stream banks adjacent to (west bank) and opposite (east bank) the landfill,and groundwater below the stream channel. Stream water from Davis Creek (DCSW) was sampled by thegrab method at the most downstream location in the study site (Figure 1). Groundwater from the stream bankswas sampled using monitoring wells and piezometers. Monitoring wells and piezometers were constructedof 5Ð1 cm diameter PVC pipes and fitted with 76 cm and 6Ð3 cm screens, respectively. Monitoring wellsand piezometers installed west of Davis Creek (W-MW1, W-MW2, W-MW3 and W-PZ1, W-PZ2, W-PZ3)and to the east of the creek (E-MW1, E-MW2, E-MW3 and E-PZ1, E-PZ2, E-PZ3) are shown in Figure 1.Groundwater below Davis Creek stream channel was sampled using wells installed at two locations representedby DC1 and DC2 and DC3 (Figure 1). The streambed wells were constructed of 5Ð1 cm diameter PVC pipes.Wells DC1 and DC2 were fitted with 6Ð3 cm screens, whereas DC3 was fitted with a 76 cm screen. Depth tothe bottom of the screened intervals for stream bank monitoring wells and piezometers and streambed wellsare shown in Table I.

Sampling groundwater seepage into Davis Creek

Traditionally, the direction of movement of water across the groundwater–stream interface can bedetermined and sampled for water quality analyses using seepage meters (Lee, 1977; Lee and Cherry, 1978).One important requirement for the successful application of seepage meters is that the device be completelysubmersed in the water column (Lee 1977; Lee and Cherry, 1978). The seepage meter installation anddeployment requirements make it difficult to use in small low-discharge streams, which are often shallow.Davis Creek is a small stream and during periods of baseflow, water depths are less than 10 cm deep. Althoughwe could sample groundwater below the streambed using wells, in the absence of knowing the sedimentcharacteristics below the streambed, we could not be certain that the groundwater sampled below the streamwas actually seeping into the stream in the reach being investigated. Hence, a device was constructed andused to sample seepage into Davis Creek.

The device constructed for sampling groundwater seepage into streams is called a ‘seepage well’ (Atekwana,1996). The seepage well was constructed from two main components, a 5Ð1 cm PVC pipe and a ‘five-gallon’plastic container (Figure 2a). The plastic container was cut approximately 20 cm from the base. A threadedPVC flange was inserted from the inside through a circular hole cut in the base of the container and securedwith a threaded coupling on the outside. A rubber gasket was fitted on the flange inside the base of thecontainer prior to assembly to prevent leakage or exchange of seepage and stream water. The length of the



20 cm

5.1cm PVC Pipe

threaded coupling

rubber gasket

PVC flange

Cut-off “5 gallon”plastic container

100 cm

stream

groundwater

(a)

(b)

Figure 2. (a) Components utilized for the construction of seepage well and (b) schematic diagram showing an installed seepage well instreambed sediments. The arrows show the direction of groundwater flow into the stream and seepage well in a groundwater fed stream

PVC pipe used in this experiment was about 1 m. A major limitation of the seepage well (and seepage meters)is that it is difficult to deploy or hard to use in streambeds with non-soft substrates (e.g. stones, cobbles andgravels).

The seepage well was installed by pushing the base of the device 20 cm into the streambed sediments andensuring that the device was level (Figure 2b). The device can be purged of water trapped during installationby pumping using a submersible, peristaltic or other suitable pump. The seepage well works on the sameprinciple as a seepage meter (Lee, 1977). If groundwater seeps into the stream at the location where thedevice is installed, it flows into the device and a rise in the water level is observed in the pipe. Conversely,if the stream is losing water to the groundwater system, a rise in the water level will also be observed in thedevice. In the case of a losing stream, the chemistry of the water in the device will be identical to that ofstream water after installation and purging (e.g. Clark and Fritz, 1997).

Testing the seepage well. To test the operation of the seepage well, a simple experiment was conducted.We hypothesized that similarity in water chemistry for seepage into Davis Creek compared with groundwaterbelow the streambed would confirm suitability of the seepage wells as a device for sampling groundwaterseepage into the stream. Four seepage wells (SW1, SW2, SW3 and SW4) were deployed at selected locationsin Davis Creek along the stream segment being investigated (Figure 1). In addition to sampling groundwaterbelow the stream channel at DC1, DC2 and DC3, groundwater was also sampled from monitoring wells inthe stream bank west (W-MW1, W-MW2, W-MW3) and east (E-MW1, E-MW2, E-MW3) of Davis Creek



(Figure 1). Sampling for verification of the operation of the seepage wells was conducted between October1995 and January 1996 and consisted of measuring the specific conductance of water. During each samplingevent, the specific conductance was measured for stream water and water in the seepage wells, streambed wellsand monitoring wells in the stream banks using a YSI specific conductance probe. The specific conductanceof water in the seepage wells was measured after slow purging of more than 10 L of water from the device,and the streambed wells and stream bank monitoring wells after purging of three or more well bore volumes.

Stable carbon isotopes analyses

Water for stable carbon isotope analyses was collected in June 1996. Water was sampled from Davis Creek(DCSW) by the grab technique. Water was also collected from the seepage wells (SW1, SW2, SW3, SW4),from below the stream channel (DC1, DC2, DC3) and stream bank monitoring wells and piezometers west(W-MW1, W-MW2, W-MW3, W-PZ1, W-PZ2, W-PZ3) and east (E-MW1, E-MW2, E-MW3, E-PZ1, E-PZ2,E-PZ3) of Davis Creek (Figure 1). Prior to water sampling, water was purged from seepage wells, monitoringwells and piezometers as previously described. Water collected and analysed for DIC and carbon isotopes wastreated following the method described by Atekwana and Krishnamurthy (1998). The DIC concentrations arereported in mg C/L with a precision of 1%. The υ13C of DIC was measured using a Micromass isotope ratiomass spectrometer and reported in the υ notation

υ�‰� D ��Rsample/Rstandard� � 1� ð 103

Where R is 13C/12C. The υ values are reported relative to VPDB Standard for carbon. Routine υ13Cmeasurements have an overall precision of better than 0Ð1‰.

RESULTS AND DISCUSSIONS

Verification of seepage into Davis Creek using seepage wells

The results of the specific conductance measured during seven sampling events to verify the performanceof the seepage wells are presented in Table I and plotted in Figure 3. Summary statistics of the specificconductance measurements are also shown in Table I. The specific conductance of Davis Creek stream water(DCSW) increased from less than 750 µS/cm between September and early December 1995 to more than1200 µS/cm in mid-December and January 1996. The increase in specific conductance for Davis Creekstream water in December and January was related to runoff of winter precipitation contaminated with saltfrom road de-icing. Interestingly, groundwater sampled below Davis Creek streambed (DC1, DC2, and DC3)and water from the seepage wells (SW1, SW2, SW3 and SW4) and groundwater from the stream bankswest (W-MW1, W-MW2, W-MW3) and east (E-MW1, E-MW2, E-MW3) of Davis Creek did not mimicthe temporal trends observed for stream water, but rather remained relatively constant (Figure 3a–d). Thespecific conductance of groundwater from the west stream bank of Davis Creek was generally higher comparedwith values for groundwater in the east stream bank (W-MW1 versus E-MW1, W-MW2 versus E-MW2and W-MW3 versus E-MW3). Groundwater below the streambed and seepage into the stream had specificconductance values that were generally higher than values for groundwater in the east stream bank andlower than values for groundwater in the west stream bank. This suggests that the source of the high specificconductance groundwater below the creek was similar to groundwater in the west stream bank near the landfill.Groundwater below Davis Creek and seepage into Davis Creek showed an increase in specific conductance ina downstream direction, although the values for SW4 were lower compared with SW3 (Figure 1 and Table I).This observation will be explored later along with the carbon data. The important observation from watersampled by the seepage wells and the streambed wells is that values for specific conductance for groundwaterseeping into the stream were closer to values for groundwater below the streambed compared with stream



0

200

400

600

800

1000

1200

1400

1600

1800DC1SW1W-MW1E-MW1DCSW

(a)

(d)

SW2W-MW2E-MW2DCSW

(c)

DC3DC2SW3W-MW3E-MW3DCSW

9/24/95 10/24/95 11/23/95 12/23/95 1/22/96

DCSW

Spe

cific

Con

duct

ance

(µS

/cm

) 2000

0

200

400

600

800

1000

1200

1400

1600

1800

Spe

cific

Con

duct

ance

(µS

/cm

) 2000

0

200

400

600

800

1000

1200

1400

1600

1800

Spe

cific

Con

duct

ance

(µS

/cm

) 2000

0

200

400

600

800

1000

1200

1400

1600

1800

Spe

cific

Con

duct

ance

(µS

/cm

) 2000

(b)

SW4

Date of Observation

9/24/95 10/24/95 11/23/95 12/23/95 1/22/96

Date of Observation

9/24/95 10/24/95 11/23/95 12/23/95 1/22/96

Date of Observation9/24/95 10/24/95 11/23/95 12/23/95 1/22/96

Date of Observation

Figure 3. Temporal variation of specific conductance for Davis Creek stream water, groundwater below Davis creek, groundwater seepinginto Davis Creek, and groundwater from stream bank sediments (see Figure 1 for sample locations)

water (e.g. SW1 and DC1, SW3 and DC2 versus-Davis Creek stream water (DCSW)). These results suggestthat the seepage wells were functioning properly.

Stable carbon isotopes

Concentrations and the υ13CDIC of water samples are also presented in Table I. Groundwater sampled fromthe west stream bank had DIC between 109 to 211 mg C/L and υ13CDIC in the range of �11Ð9 to C5Ð7‰.Groundwater from the east stream bank had DIC between 55 and 118 mg C/L and υ13CDIC between �16Ð9and �10Ð0‰. Samples of groundwater below the creek and seepage into the creek had DIC ranging from 54to 185 mg C/L and υ13CDIC in the range between �11Ð5 to C3Ð2‰. Davis Creek stream water had DIC of52 mg C/L and υ13CDIC of �11Ð0‰.

The υ13CDIC of groundwater collected from the west stream bank was relatively high, except for groundwaterfrom W-MW1 (Table I). The high υ13C of DIC in these water samples indicates a source of heavy carbonmost likely from landfill impact (Games and Hayes, 1977; Baedecker and Back, 1979; Walsh et al., 1993;Hackley et al., 1996; Rank et al., 1996). Groundwater from the east stream bank, which ranged between�16Ð9 and �10Ð0‰, is not consistent with groundwater impacted with landfill carbon. The DIC and υ13CDIC

for groundwater below Davis Creek and seepage into the stream increased in a downstream direction tomaximum values at SW3, then decreased further downstream to SW4 (Figure 1). Also, where DIC andυ13CDIC in groundwater in the west stream bank was high, groundwater below the streambed and groundwater



SW MW PZMWPZWest Bank East Bank

Landfill

Landfill Leachate Plume

MW = Monitoring well PZ = Piezometer SW = Seepage well Groundwater flow line

Figure 4. Schematic cross-section showing groundwater flow across the site, and landfill–groundwater and groundwater–stream interaction

seeping into the stream was high in DIC and υ13CDIC. A similar relationship was observed for specificconductance for groundwater from the west stream bank, groundwater below the streambed and seepage intothe stream, which suggests that the higher specific conductance of groundwater below the streambed andseepage samples is indicative of landfill impact.

A conceptual model of groundwater flow at the study site is shown in Figure 4. In this model, regionalgroundwater flowing towards Davis Creek below the landfill mixes with landfill contaminated water beforedischarging into Davis Creek. Based on this model, we expect that all groundwater sampled below DavisCreek and seepage into the creek would show evidence of heavy carbon from landfill contamination. We notethat groundwater from the west stream bank and below the streambed and seepage into the stream at the mostupstream station (W-MW1, DC1, SW1) show no evidence of landfill carbon (υ13CDIC D �11Ð3 to �11Ð9‰;Table I). Lack of evidence of landfill carbon in the most upstream stations and the longitudinal variabilityof specific conductance and carbon in the seepage samples may be the result of preferential discharge oflandfill impacted groundwater into different stream segments along the stream reach. Preferential discharge oflandfill contaminated groundwater to different segments of the stream reach could be due to alteration of thelocal hydrogeology west of the creek by previous disposal activities (Atekwana, 1996). Alternatively, localheterogeneity in the glacial drift below the landfill could cause preferential groundwater flow leading to thesame observations.

To assess mixing of groundwater below Davis Creek and to identify the υ13CDIC of the source carbon,υ13CDIC is plotted against 1/DIC (Figure 5). A regression line through data points that include only samplesof seepage into Davis Creek (SW1, SW2, SW3 and SW4) and groundwater below Davis Creek (DC1, DC2and DC3) is described by the following least-squares regression equation: υ13CDIC D �1157Ð5�1/DIC� C 9Ð6;R2 D 0Ð99; p < 0Ð001; n D 7. The υ13CDIC of groundwater contaminated with landfill carbon mixing withunimpacted groundwater below the streambed can be determined from the y intercept of the regression line(Grossman et al., 1989). The y intercept of this line gives a υ13CDIC value of C9Ð6‰ for the landfill impactedgroundwater component. υ13CDIC value as high as C10 to C20‰ has been reported for groundwater impactedby landfills (Games and Hayes, 1977; Baedecker and Back, 1979; Hackley et al., 1996). Thus, the υ13CDIC

of the heavy carbon end-member from the regression model is consistent with landfill carbon contamination.It is interesting to note that groundwater values from the west stream bank (except for W-MW1) lie

close to and on the upper end of the trend of the mixing line, indicating impact from landfill carbon ingroundwater from these locations (Figure 5). We also observe that at the most upstream sampling location,groundwater from the east stream bank (E-MW1), groundwater below the stream bed (DC1) and groundwater



SW1

E-MW1

0

5

10

SW2

DC1

DCSW

W-MW3

W-PZ3

SW3 SW4

W-MW2W-PZ2

DC2

W-MW1

E-MW2E-PZ2

E-PZ3

E-MW3

DC3

-200 0.005 0.01 0.015 0.02 0.025

-15

-10

-5

y = -1157.5x + 9.6R2 = 0.99; p<<0.001; n=7

1/DIC (mg C/I)

δ13C

DIC

(0/ 0

0)

Monitoring Wells - West Bank

Monitoring Wells - East BankPiezometers - West Bank

Piezometers - East Bank

Seepage into Davis CreekDavis Creek Stream Water

Groundwater Below Davis Creek Channel

Figure 5. Cross-plot of υ13CDIC versus 1/DIC for groundwater from Davis Creek stream banks, groundwater below Davis Creek, seepageinto Davis Creek and Davis Creek stream water sampled on 26 June 1996. The regression line shows the mixing between landfill-impacted

and unimpacted groundwater below Davis Creek streambed

seeping into the creek (SW1), as well as Davis Creek stream water (DCSW) cluster at the lower end of themixing line (Figure 5). We believe that the groundwater samples located on the lower end of the mixingline represent uncontaminated water. As Davis Creek stream water was collected at the most downstreamlocation, significant input of heavy carbon from landfill-contaminated groundwater should have resulted inan increase in the DIC and υ13CDIC, causing stream water to lie between uncontaminated groundwater andlandfill-contaminated groundwater from the west stream bank (Figure 5). Thus we suggest that the samplesat the lower end of the mixing line that includes Davis Creek stream water (DCSW), groundwater (DC1)and seepage (SW1) have a carbon signature of groundwater typically discharged into the stream from thewatershed, whereas groundwater sampled at DC2 and DC3 and seepage sampled at SW2, SW3 and SW4represent a mixture of this water and landfill contaminated water (Figure 5). The isotopic values of watersamples at the lower end of the mixing line are consistent with groundwater undergoing carbon evolutioninitiated by CO2 from C3 vegetation �υ13C D ¾�25‰� and aquifer carbonates with υ13C values of ¾C1Ð5‰(Nascimento et al., 1997) measured in the Kalamazoo area (e.g. Clark and Fritz, 1997). This observation isalso consistent with the υ13CDIC and DIC measured in small streams in the Kalamazoo area unimpacted bylandfill carbon and uncontaminated groundwater with υ13CDIC and DIC of �10 š 2‰ and 60 š 10 mg C/L,respectively (Atekwana and Krishnamurthy, 1998; Nascimento et al., 1997). Additional support for the aboveconclusions comes from the fact that υ13CDIC reported for groundwater in glacial drift aquifers of south-westernMichigan range between �12Ð9 and �10Ð8‰ (Dannemiller and Baltusis, 1990).

Groundwater samples that do not fall on the mixing line are from W-MW1 on the west stream bank and E-MW2, E-PZ2, E-MW3 and E-PZ3 from the east stream bank (Figure 5). These water samples generally havelower υ13CDIC and higher DIC (Table I) compared with uncontaminated groundwater below Davis Creek.The lower υ13CDIC of these samples suggest that they are not impacted by landfill carbon. Additionally,groundwater samples from the monitoring well and piezometer cluster at these locations show that groundwaterfrom shallower depths from monitoring wells had higher DIC and more negative υ13CDIC compared withgroundwater from deeper depths from piezometers (E-MW2 versus E-PZ2; E-MW3 versus E-PZ3; Table I).



The higher DIC for water from the monitoring wells in the monitoring well and piezometer cluster can beexplained by input of lighter inorganic carbon into groundwater as it flows to shallower depths at theselocations. Higher DIC and lower υ13CDIC have been observed for stream segments draining CO2-rich peats(Palmer et al., 2001). We speculate that the higher DIC and lower υ13CDIC in groundwater at W-MW1, E-MW2, E-PZ2, E-MW3 and E-PZ3 may come from oxidation of organic matter at shallower depths in thestream bank sediments.

Stream water sampled from Davis Creek showed no evidence of heavy carbon. In fact, the DIC andυ13CDIC measured for Davis Creek stream water was in the range measured for Davis Creek at the mouth ofthe catchment, as well as other streams in the Kalamazoo area (Atekwana and Krishnamurthy, 1998). Althoughevidence of landfill impact to groundwater below the stream and seepage into the stream was observed, thelack of evidence of landfill impact to stream water may simply be related to the relative flux of seepagecompared with stream water discharged along the stream reach. It is important to note that although we couldconclude that there was no evidence of landfill contamination in Davis Creek stream water, similar to theMichigan Department of Natural Resources (1979, 1986) and Cannonie Environment ed (1989) studies, resultsfrom groundwater below the stream and seepage into the stream suggest significant impact to the hyporheiczone at the stream–groundwater interface. This impact is consistent with the aquatic communities that suggestpollution related stress in the stream segment investigated in the study area (Michigan Department of NaturalResources, 1979, 1986).

CONCLUSIONS

The results of this study suggest that it would not be possible to detect the impact from landfill contaminatedgroundwater to a localized stream reach by analysing stream water for landfill carbon sampled by the grabtechnique. However, groundwater below the stream and groundwater seeping into the stream showed evidenceof landfill impact. This water is a mixture of landfill polluted groundwater and uncontaminated groundwaterlocally discharged into the stream.

The absence of measurable landfill-polluted groundwater impact to stream water may be the result ofhigher volume of stream flow relative to groundwater seeping into the stream for the reach investigated.Our results also show that the mixing dynamics below the streambed may have an impact on the actualconcentration of the tracer investigated in the groundwater below the stream or in stream water. Althoughassessing stream water quality on a watershed scale in heavily urbanized and highly industrialized headwaterwatersheds may require identifying the cumulative impacts of localized sources of groundwater pollution tostreams, the ecological impacts of groundwater pollution may be localized and limited to the hyporheic zone.

REFERENCES

Allen WB, Miller VB, Wood MW. 1972. Availability of water in Kalamazoo County, Southwestern Michigan. U.S. Geological Survey WaterSupply Paper .

Atekwana EA. 1996. Hydrogeology and stable isotope investigations of a landfill impacted site in southwest Michigan. PhD thesis, WesternMichigan University, Kalamazoo, MI.

Atekwana EA, Krishnamurthy RV. 1998. Investigations of seasonal variations in dissolved inorganic carbon and υ13C of surface watersusing a modified gas evolution technique. Journal of Hydrology 205: 265–278.

Baedecker MJ, Back W. 1979. Hydrological processes and chemical reactions at a landfill. Ground Water 17: 429–437.Blevins DW. 1989. Sources of coal-mine drainage and their effects on surface-water chemistry in the Claybank Creek basin and vicinity,

north-central Missouri, 1983–84. U.S. Geological Survey Water Supply Paper .Benner SG, Smart EW, Moore JN. 1995. Metal behavior during surface groundwater interaction, silver-bow creek, Montana. Environmental

Science and Technology 29: 1789–1795.Brunke M, Gonser T. 1997. The ecological significance of exchange processes between rivers and groundwater. Freshwater Biology 37:

1–33.Canonie Environmental. 1989. Phase I Remedial Investigation, Cork Street Landfill Site, Vol. 1. Kalamazoo, MI.Clark ID, Fritz P. 1997. Environmental Isotopes in Hydrogeology . Lewis Publishers: Boca Raton, FL.



Dannemiller GT, Baltusis MA. 1990. Physical and chemical data for ground water in the Michigan basin, 1886–89. U.S. Geological SurveyOpen-File Report .

DeWalle DR, Pionke HB. 1986. Tracing stormflow sources in seepage zones using oxygen-18. In Headwaters Hydrology , Woessner WW,Potts DF (eds). American Water Resources Association: Bethesda MD, USA; 511–516.

Fryar AE, Wallin EJ, Brown DL. 2000. Spatial and temporal variability in seepage between a contaminated aquifer and tributaries to theOhio River. Ground Water Monitoring and Remediation 20: 129–146.

Games LM, Hayes JM. 1977. Carbon isotopic study of the fate of landfill leachate in groundwater. Journal of the Water Pollution ControlFederation 49: 668–677.

Geological Services Inc. 1981. Hydrogeological Study for the Cork Street Landfill, Kalamazoo, Michigan. Report prepared for Dispose-O-Waste Co: Kalamazoo, MI, USA.

Gregory SV, Swanson FJ, McKee WA, Cummins KW. 1991. An ecosystem perspective of riparian zones. Bioscience 41: 540–551.Grossman EL, Coffman BK, Fritz SJ, Wada H. 1989. Bacterial production of methane and its influence on ground-water chemistry in

east-central Texas aquifers. Geology 17: 495–499.Hackley KC, Liu CL, Coleman DD. 1996. Environmental isotope characteristics of landfill leachates and gases. Ground Water 34: 827–836.Hancock PJ. 2002. Human impacts on the stream–groundwater exchange zone. Environmental Management 29: 763–781.Hayashi M, Rosenberry DO. 2002. Effects of ground water exchange on the hydrology and ecology of surface water. Ground Water 40:

309–316.Lee DR. 1977. A device for measuring seepage flux in lakes and estuaries. Limnology and Oceanography 22: 140–147.Lee DR, Cherry JA. 1978. A field exercise on groundwater flow using seepage meters and mini-piezometers. Journal of Geological Education

27: 6–10.Leja SL. 1983. A magnetic and resistivity survey of Cork Street landfill, Kalamazoo, Michigan. MS Thesis, Western Michigan University,

Kalamazoo, MI.Malard F, Plenet S, Gibert J. 1996. The use of invertebrates in ground water monitoring: a rising research field. Ground Water Monitoring

and Remediation 16: 103–113.Meyer JL. 1997. Stream health: incorporating the human dimension to advance stream ecology. Journal of the North American Benthological

Society 16: 439–447.Michigan Department of Natural Resources. 1979. Stream Assessment of Davis Creek, Kalamazoo County, Michigan. Report, Water Quality

Division, MDNR: Lansing, MI, USA.Michigan Department of Natural Resources. 1986. Stream Assessment of Davis Creek, Kalamazoo County, Michigan. Report, Water Quality

Division, MDNR: Lansing, MI, USA.Modica E, Burton HT, Plummer LN. 1998. Evaluating the source and residence times of groundwater seepage to streams, New Jersey

Coastal Plain. Water Resources Research 34: 2797–2810.Nascimento C, Atekwana EA, Krishnamurthy RV. 1997. Concentrations and isotope ratios of dissolved inorganic carbon in groundwaters

of denitrifying environments. Geophysical Research Letters 24: 1511–1514.Neumann M, Schutz R, Schafer K, Muller W, Mannheller W, Liess M. 2002. The significance of entry routes as point and non-point sources

of pesticides in small streams. Water Research 36: 835–842.Palmer SM, Hope D, Billett MF, Dawson JJC, Bryant CL. 2001. Sources of organic and inorganic carbon in a headwater stream: evidence

from carbon isotope studies. Biogeochemistry 52: 321–338.Rank D, Papessch W, Rajner V. 1996. Environmental Isotopes Study at a Research Landfill (Breitenau, Lower Austria). IAEA-SM-336/111P,

International Atomic Energy Agency: Vienna; 379–381.Rutherford JE, Hynes HBN. 1987. Dissolved organic carbon in streams and groundwater. Hydrobiologia 154: 33–48.Schilling KE, Wolter CF. 2001. Contribution of base flow to nonpoint source pollution loads in an agricultural watershed. Ground Water

39: 49–58.Schmaltz LJ. 1978. Surficial geology. In Kalamazoo County. Geology and the Environment , Passero RN, Chase KM, Chase RB, Schmaltz LJ,

Straw WT (eds). Western Michigan University: Kalamazoo, MI; 17–23.Sophocleous M. 2002. Interactions between groundwater and surface water: the state of the science. Hydrogeology Journal 10: 52–67.Straw WT. 1978. Bedrock geology. In Kalamazoo County. Geology and the Environment , Passero RN, Chase KM, Chase RB, Schmaltz LJ,

Straw WT (eds). Western Michigan University: Kalamazoo, MI; 25–34.USEPA. 1991. A review of methods for assessing nonpoint source contaminated ground-water discharge to surface water. EPA 570/9-91-010,

U.S. Environmental Protection Agency: Washington DC, USA.Van Lanen HAJ, Dijksma R. 1999. Water flow and nitrate transport to a groundwater-fed stream in the Belgian–Dutch chalk region.

Hydrological Processes 13: 295–307.Woessner WW. 2000. Stream and fluvial plain ground water interactions: rescaling hydrologic thought. Ground Water 28: 423–429.Walsh DC, LaFleur RG, Bopp RF. 1993. Stable carbon isotopes in dissolved inorganic carbon of landfill leachate. Ground Water Management

16: 153–167.


investigating landfill-impacted groundwater seepage into headwater streams using stable carbon...

Documents