UNIVERSITY OF WISCONSIN

by

John D. Dadisman

A Thesis

submitted in partial fulfillment of the requirements for the degree

MASTER OF SCIENCE

College of Natural Resources

UNIVERSITY OF WISCONSIN Stevens Point, Wisconsin

May 1990

APPROVED BY THE GRADUATE COMMITTEE OF:

Dr. Byron rman

Professor of Soil Science

Dr. Ronald Henser Professor of Soil Science

• Jack Heaton Professor of Fisheries

Jeffery Andrews 1ronmental Task Force

central Wisconsin trout stream where decreased fish and invertebrate populations had been noted. A

network of groundwater monitoring wells were installed and inorganic parameters monitored over a 5 year

period. The compiled data indicated a close

relationship between groundwater and surface water quality. Results for most chemical constituents

indicated good water quality, however some impacts due to irrigated agriculture, residential septic systems and road salt were apparent. Concentrations of most inorganic parameters tended to increase with depth, reaching maximum concentrations at mid-aquifer. This may be the result of groundwater recirculation during

irrigation. Nitrification of ammonia fertilizers appears to result in the reduction of carbonate alkalinity in the shallow aquifer. Nitrate

concentration in groundwater samples averaged 11.7 mg/L, which exceeds the EPA Maximum Contaminant Level for drinking water supplies. Chloride concentrations in groundwater were elevated adjacent to roadways possibly due to road salt. Groundwater, surface water and sediment samples from the river were analyzed for pesticide residues. While parent forms of the

pesticides or herbicides recommended for area

agriculture were not detected, numerous unidentified compounds were noted. One unidentified compound was detected in groundwater and sediments between the stream and a potato field treated with the pesticide VAPAM. This compound appeared to be a component or breakdown product of the pesticide. Confirmed

identification of the compound was attempted using gas chromatography - mass spectrometry, however the

results were inconclusive.

iii

ACKNOWLEDGEMENTS

I would like to extend my sincere thanks to Dr.

Byron Shaw, my advisor, for kindling my interest in this project, and to my graduate committee members and Dr. Shaw for providing the encouragement and support to bring it to completion.

Special thanks are extended to Dick Stevens, Jeffery Andrews and the staff of the UWSP

Environmental Task Force for technical and analytical support that is the foundation of this thesis.

And I must thank my wife and best friend Sara, and my family for the patience, underst"anding and inspiration that has finally driven me to complete this project.

iv

Acknowledgements Table of Contents List of Tables List of Figures List of Appendices Introduction

Study Area

Groundwater Monitoring Wells Methods

Pesticide Well Construction Sampling

Extraction and Analysis Instrumentation

Data Analysis Results and Discussion

Surface and Groundwater Chemistry Introduction

Conductivity Total Hardness Alkalinity Nitrate Chloride Sulfate

Surface Water Grab Samples Organics Residue Monitoring

Method Performance - Waters Sample Results

Method Performance - Sediments Sample Results

Vapam Residue

Conclusions and Recommendations Inorganics

Organics References

V

iv

V

vi

vii

ix 1 3 7 11 11 13 13 15 15 16 16 18 24 26 29

37 39

41 41 41 49 50 50 51 55 55 56 58

LIST OF TABLES

1. Mean Concentrations of Water Quality Parameters in Deep, Shallow and All Nested Groundwater

Monitoring Well, and Surface Water, and In-stream

Monitoring Well Samples. 17

2. Chloride/Nitrate Ratio in Groundwater Samples. 40 3. Results of Grab Samples Collected Every 140

Meters, Hoover Road to Kennedy Road, Little Plover

River. 43

4. Instrument Detection Limit and Calculated Method Detection Limit for Selected Pesticides. 45 5. Instrument Detection Limit and Calculated Method

Detection Limit for Selected Herbicides and

Fungicides. 46

6. Spike Recovery Data for Selected Pesticides in Laboratory Water, Methylene Chloride Liquid

Extraction Screen. 47

7. Spike Recovery Data for Selected Pesticides in Laboratory Water, Sep Pak Solid Phase Extraction

Screen. 48

8. Unknown Contaminant Concentration in Groundwater Samples Relative to Metham Sodium (VAPAM). 54

vi

2. Regional Land Use Map Showing Topographic and Groundwater Divide for the Little

Plover River Watershed. 5

3. Land Use and Sampling Zones for the Little

Plover River. 6

4. Environmental Task Force Groundwater Monitoring Wells and Surface Water Sampling Sites for the

Little Plover River Basin. 8

5. Pesticide Monitoring Well Locations, Little

Plover River. 10

6. Sampling Device for Monitoring Wells. 12 7. Specific Conductance, Surface Water vs.

Groundwater Samples, Little Plover River Basin. 19 8. Mean Specific Conductance Values in the Little

Plover River Basin Groundwater and Surface Water

Sampling Network. 20

9. Mean Conductivity Values (umhos/cm2), Listed With Increasing Depth, Groundwater Samples,

little Plover River Basin. 22

10. Map Showing Depth of Unconsolidated Aquifer and

Groundwater Divide, Little Plover River Basin. 23 11. Total Hardness, Surface Water vs. Groundwater

Samples, Little Plover River. 25

12. Mean Hardness Values (mg/L), listed with Increasing Depth, Groundwater Samples, Little

Plover River Basin. 27

13. Mean Alkalinity Values in the Little Plover River Basin Groundwater and Surface Water

Sampling Network. 28

14. Non-Carbonate Hardness vs. Nitrate Concentration In Groundwater Monitoring Well Samples. 30 15a. Nitrate Concentrations Over Time, Groundwater

Samples from Shallow Monitoring Wells, Little

Plover River Basin. 32

vii

15b. Nitrate Concentrations Over Time, Groundwater Samples From Deep Monitoring Wells, Little

Plover River Basin. 33

16. Nitrate Concentration vs. Depth in Monitoring

Well Nests, Little Plover River Basin. 34 17. Nitrate Concentrations in Pesticide Monitoring

Wells, Little Plover River. 36

18. Chloride Concentrations in Deep and Shallow

Wells, Little Plover River Basin. 38 19. Sulfate Concentrations, Deep Monitoring Wells,

Little Plover River Basin. 42

20. Chloride, Nitrate and Sulfate Concentrations in Surface Water Samples, Compared to Seepage Data

Collected by Weeks (1965), Little Plover River. 44

viii

A. Groundwater Monitoring Well Logs, Little Plover

River Basin. 61

B. Recommended Pesticides and Possible Breakdown

Products. (UWEX) 83

C. Water Quality Indicator Parameters, Groundwater

Monitoring Wells, Little Plover River Basin. 85 D. Water Quality Indicator Parameters, Little

Plover River Pesticide Monitoring Wells. 103 E. Results and Relative Retention Times (To

Aldrin) of Selected Little Plover River

Samples. 109

F. GC/MS Results for the Analysis of Little Plover

River Pesticide Monitoring Well C Samples. 115

ix

INTRODUCTION

The study of pesticide residues in aquatic systems has steadily grown with the increased awareness of detrimental effects to aquatic life.

An excellent review of the literature dealing with the transport and effects of trace contaminants on freshwater fish and

invertebrates may by found in Buikema et al (1982), and Spehar et al

(1982).

The principal objective of this investigation was to locate and identify sources and transport routes of pesticide residues in the Little Plover River.

The Wisconsin Department of Natural Resources has noted a

significant decline in brook trout (Salvelinus fontinalis) population in the Little Plover in recent years (WDNR 1984). Gammarus sp. a common invertebrate in cold water streams and formerly abundant' in the Little Plover (Scullin 1977), is now absent from certain sections of the stream. Both events parallel the dramatic increase in

intensively irrigated agriculture in the Little Plover watershed (Butler 1978).

The transport into the stream of agricultural chemicals is by three possible routes:

1. Drift from aerial application over adjacent fields. Haines et al (1981) noted depressed cholinesterase activity in brook trout (Salvelinus fontinalis) after aerial application of carbaryl to nearby forests.

2. Direct runoff or erosion during periods of heavy rainfall or irrigation. Significant changes in invertebrate diversity and community structure due

1

to pesticide runoff has been noted in several case studies (Heckman 1982).

3. Groundwater transport due to the highly permeable nature of the Central sands geology. At least seven organic compounds of agricultural origin have been detected in central Wisconsin groundwater (WDNR

1982).

STUDY AREA

The Little Plover River is a small trout stream located in the sand plains region of central Wisconsin (Fig. 1).

The stream is approximately 6.6 kilometers long. It originates in the Arnott moraine (Sec.18-19, R.9E., T.23N.) and discharges into the Wisconsin River (Sec.16, R.8E., T.23N.) 0.5 kilometers below Springville Pond which is a small impoundment 3 kilometers below the study area. The topographic watershed of the Little Plover (Fig. 2) extends from the second moraine in the east to the gauging station on Hoover Avenue in the west (USGS 1979). Groundwater contributes

approximately 95% of the streamflow in the Little Plover (Weeks et al 1965).

Soils in the vicinity of the Little Plover River are formed mainly in outwash sand and gravel and are of the Richford - Rosholt - Billet association, and Plainfield - Friendship association. These soils are excessively to moderately well drained, have slopes of 0- 2%, and rapid permeability often in the range of 6-20 inches per hour. Most of the acreage of these associations adjacent to the stream is in irrigated cropland (Lesczynski 1974). Soils of the Arnott moraine to the east are of the Point - Dancey - Mosinee association. The alluvial lands adjacent to the stream include wet alluvial land and Marckey Muck (SCS 1979). Both moraine and alluvial land areas are primarily wooded.

Groundwater and stream sampling for pesticide residue analysis was from four general zones along the Little Plover River. Figure 3 shows the zone delineation and current land use during this

3

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FIGURE 1.-Index map of \Visconsin.

(from Weeks et al, 1965)

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Figure 2. Regional Land Use Map Shm~ing· Topographic and Groundwater Divide for the Little Plover River Watershed, Porta~e County, Wisconsin.

LEGEND

Topographic divide Groundwater divide

t1~ Mixed forest 1•1m•ii Residential

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7

investigation. Characteristics of the four study zones are as follows:

I. Arnott Moraine and Headwaters.

Extending east from Kennedy Rd. and branching into the Arnott moraine are the original headwaters of the Little Plover. This area is primarily wooded with some pastureland, and appears isolated at least from direct runoff or aerial drift of pesticides.

II. Kennedy Rd. to Treatment Zone.

This section is characterized by large areas of upwelling. The stream is poorly defined in many areas, and branches into several channels broken by beds of Veronica sp., Trout redds are located in this area and Gammarus sp. are numerous. At least 3 drainage ditches entering this area are directly from irrigated fields.

III. Treatment Zone to Eisenhower Rd.

This section of the stream consists of alder (Alnus spp.) and an area referred to as the "treatment zone". The "treatment zone" was cleared of brush and most tree cover in 1973 as a trout habitat

improvement project (Scullin 1977). At least 1 drainage ditch, open to runoff or aerial drift and directly connecting irrigated cropland, enters this area. Gammarus sp. are absent from this section and trout populations appear reduced.

IV. Eisenhower Rd. to Hoover Rd.

This area is primarily wooded and lightly to moderately populated, and appears free of direct pesticide runoff or aerial drift. The stream channel is well defined with at least one area of significant groundwater discharge east of State Highway 51. Gammarus sp. are present although numbers appear reduced.

Groundwater Mon1tor1ng Wells

A system of 20 groundwater monitoring wells at six locations (Fig. 4) were installed by the University of Wisconsin - Stevens Point Environmental Task Force during 1980. Copies of drilling logs, and well depths can be found in Appendix A. The purpose of these wells and seven surface water collection sites (Fig. 4) is to monitor

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background and trends in the water quality of the Little Plover River Basin.

Eight pesticide monitoring wells were installed in or adjacent to the stream bed for the purpose of this investigation (Fig. 5).

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METHODS

The sampling techniques and analytical methods employed to collect the data utilized in this investigation can be segregated into two separate groups: the inorganic analyses or water quality indicators, and the organics or pesticide residue analyses. The inorganic analysis data generated by the Environmental Task Force at the University of Wisconsin - Stevens Point followed the sampling and analytical methodologies stated in Standard Methods (APHA 1980).

The collection, storage, and analysis of environmental samples for organic compounds is more complex and differs substantially from methods used for inorganic analysis. The techniques described below were designed for a broad spectrum analysis and identification of pesticide residues in water and sediment.

Pesticide Well Construction

The pesticide monitoring wells were constructed of 1.5-inch schedule 80 PVC with a 1 ft section of 0.01 in slotted sand point, and a screw cap. Wells were manually driven with a large wooden mallet into the sand bed of the stream to a depth of 4 to 8 feet.

Streambed wells were not sealed.

To determine if contamination by the PVC of water samples was occurring, a 3 foot section of the PVC pipe was filled with organic free laboratory water, capped and allowed to stand for 3 months as a pipe blank. The water was then analyzed by the methods described below. No interfering contamination was noted in the results.

11

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13

Sampling

Water samples were collected in acetone rinsed solvent bottles supplied with Teflon lined plastic screw caps. Samples from wells were drawn through Teflon tubing directly into the sample bottle to prevent contact with plastic or rubber pump parts or stoppers

(Pettyjohn et al 1981). Electric or hand operated peristaltic pumps were used to create a vacuum to draw water from the well, to the sample bottle (Fig. 6). Wells were pumped for at least 10 min. to assure evacuation of 3 well volumes.

Surface samples were collected manually. The bottle was rinsed 3 times with sample water before filling. Samples were brought back to the lab and stored at

3°c

Sediment samples were manually collected in 192 cc soil tins.

Tins were prepared by washing and soaking in hot soapy water, hot water rinsed, distilled water rinsed, dried, and acetone rinsed.

Sediments were brought back to the lab, placed on acetone rinsed household grade aluminum foil, and allowed to air dry overnight.

Extraction and Analysis

Water samples were extracted for broad spectrum scans using two methods: reversed phase cl8 solid phase extraction, and methylene chloride liquid/liquid extraction.

Extraction by cl8 Sep Pak consisted of drawing 1000 ml of sample through a solid phase Sep Pak extraction column and eluting with 3 ml of methanol. The extract was then ready for analysis by High

Pressure Liquid Chromatography (HPLC).

Water samples were solvent extracted with methylene chloride using a modification of EPA method 608. The method modification

consisted of extracting an 800 ml sample with 60 ml of methylene chloride twice. The extract is passed through a bed of anhydrous sodium sulfate and into a 250ml boiling flask. The boiling flask is connected to a rotary evaporator and the extract brought to near dryness at 35°c at a vacuum pressure of ca 125mm of Hg. in a N2 atmosphere. The flask is removed from the evaporator. The extract is transferred to a graduated centrifuge tube which is placed in a 3S°C water bath and the volume adjusted to exactly 2 ml. under a gentle stream of N2. The extract was then ready for analysis by gas chromatography (GC).

Sediment samples were analyzed for organochlorine compounds using an extraction technique described by Hammarstrund (1976). This method consisted of extracting 25g of air dried, sieved sediment

sample in a soxhlet extractor. Glasswool instead of extraction thimbles were used in order to avoid contamination.

The sediments were extracted with 100ml of hexane:acetone (50:50 v/v) for 12 hours. After 12 hours the extracts were washed with 500ml of water and 10ml saturated sodium chloride solution. The aqueous phase was re-extracted with 25ml hexane and discarded. The hexane extracts were combined and washed 2 times with 100ml water and 5ml of saturated sodium chloride solution. The hexane phase was passed through a bed of anhydrous sodium sulfate and concentrated under a gentle stream of N2 at 35°c. and rediluted to 25ml with hexane for GC analysis.

Spikes and reagent blanks were run through all procedures both for the water and sediment extractions. All reagents were pesticide grade and glassware was prepared according to procedures described in Section 3a. (EPA 1980).

15

Instrumentation

• Varian 3700 gas chromatograph, equipped with a ECD-63Ni detector, FPO-sulfur, phosphorus detector, Varian CDS lllC integrator, Varian Model 8000 autosampler, and a Corning model 845 strip chart recorder.

• Tracor 560 gas chromatograph, equipped with a Hall 700A - halogen, sulfur, nitrogen specific modes, FID, FPD-

sulfur, phosphorus modes, and a Corning Model 840 strip chart recorder.

• Waters Model 441 HPLC absorbance detector at 229nm, ISCO Model V4 variable wavelength absorbance detector at 190nm, Waters Model 710B WISP autosampler, Waters Model 45 solvent delivery system, and a Waters Model RCM-100 radial compression module.

Data Analysis

This investigation was primarily limited to those compounds listed in Appendix Band compounds available from the Environmental Protection Agency {EPA) analytical reference standards collection

(EPA 1981). Appendix Bis a listing of pesticides recommended by the Portage County UW-Extension for corn and potato production (Doersch et al 1984. and Binning et al 1983). In addition, possible breakdown products, and acute toxicity information (Johnson 1980) are shown.

Introduction

The chemistry and hydrogeology of the Little Plover River Basin is representative of the Central Sand Plain Region of Wisconsin in the following ways: 1.) surface and groundwater systems are closely related in both mineral and hydraulic characteristics (Holt 1965, Weeks et al 1965), 2.) concentrations of chemical constituents tend to increase with depth and decrease with distance from the moraines

(Karnuskas 1977), 3.) the geologic system contains carbonate minerals and water quality is characterized as hard to moderately hard and alkaline, and generally is considered good for most domestic, commercial and recreational uses.

To establish background surface and groundwater quality of the little Plover River Basin, the UW - Stevens Point Environmental Task Force (ETF) began, in 1980, to periodically collect water samples from monitoring wells and surface sites along the river (Figure 5) for general water quality indicator testing. Results of the first five years of this monitoring can be found in Appendix C. Aliquots of the pesticide monitoring samples taken from the wells located in the little Plover River bed (Figure 5) were also analyzed for general water quality indicator parameters. These results can be found in Appendix D.

Mean values for water quality indicator parameter results in deep, shallow and all ETF nested groundwater monitoring wells, Little Plover River surface water samples, and in-stream pesticide

monitoring wells are shown in Table 1. Mean values for the deep

16

Table 1. Mean Concentration of Water Quality Parameters in Deep, Shallow and All Nested Groundwater Monitoring Well, and Surface Water, and In-stream Monitoring Well Samples. Little Plover River Basin, Portage County, Wisconsin. (Values in mg/L unless otherwise indicated)

Nested Wells Surface Instream Monitoring Wells

Deep Shallow All Water Well A Well B Well D Well 1 Well E Well F

pH (units) 7.3 6.9 7.2 7.6 7.6 7.3 7.5 7.1 7.4

Conductance (unhos) 456 281 363 373 404 353 315 331 366 368

Alkalinity 111 79 93 152 110 154 152 162 170 176

Total Hardness 209 124 163 187 200 187 175 180 203 225

Ca Hardness 138 77 104 121 124 120 118 109 141 184

Reactive P 0.013 0.018 0.016 0.015 0.027 0.032 0.039 0.023 0.062 0.007

Total P 0.045 0.038 0.057 0.054 0.035 0.074 0.024

Ammonia N 0.03 0.038 0.042 0.063 0.06 0.12 0.08 0.05 0.11 0.07

Nitrate 15.4 7.2 11.4 4.4 15.4 4.5 0.8 3.7 2.8 0.5

TKN 0.054 0.08 0.24 0.55 0.09 0.49 1.88

Chloride 31.6 12.2 22 8.9 28.9 11.3 5.6 2.9 12. 1 4.3

Sulfate 16.3 17.6 16.2 11. 7 11. 7 9.8 12.4 4.9 14.9 23.1

Note: Wells A, B, D and 1 shown in downstream to upstream order, wells E, F and C in Zone III drainage ditch. See Figure 5.

Well C 7.2 378 192 206 0.36 133 0.474 0.77

o.

1.18 12.2 7.6

Leonard Band Worzalla A. The shallow well results were based on Norway A, Barnsdale A, Pavelski D, Leonard C and Worzalla C. The Airline well nest results were not included in the deep or shallow mean calculations due to the local influence of the buried sandstone

ridge on groundwater quality, in this well nest.

Conductivity

Specific conductance is an indication of the ion content of a water sample and, therefore directly correlates to the total dissolved solids. The conductivity of potable waters in the United States generally ranges from 50 to 1500 umhos/cm (APHA 1980).

Specific conductance for surface and groundwater samples from the Little Plover River basin averaged 373 umhos/cm and 366 umhos/cm, respectively, during the study period (Table 1). Generally, little or no trend or seasonal variation in groundwater or surface water conductance was apparent (Figure 7). There was a notable increase in conductivity for samples collected in August of 1983; however, it was determined that this was a laboratory anomaly for this parameter.

Figure 8 shows a graphical presentation of the mean conductivity data contained in Table 1. This Figure illustrates the relationship between the nested groundwater wells, the instream wells and surface water samples from the river.

Mean specific conductance for the deep nested wells was 456 umhos/cm compared to 281 umhos/cm for the shallow wells. This

appears to indicate an increase in specific conductance with depth in the aquifer. However, mean specific conductance for instream wells and surface water samples, which represent the discharge of

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510 500 490 460 470 460 450 440 430 420 410 400 390 380 370 360 350 340 330 .320 310 300

8/80

Groundwater Samples, Little Plover River, Portage County, Wisconsin.

Specific Conductance

Surface vs Groundwater

+ I-' ~

9/80 10/80 11/80 1/81 9/81 11/82 3/83 8/83 10/83 1/84 6/84 6/85 Sanplc Dote

0 G.W. Wells + LP. Surface

Figure 8. Mean Specific Conductance Values in the Little Plover River Basin Groundwater and Surface Water Sampling Network.

Specific Conductance

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wb - in-stream well B.

wd - in-stream well D.

wl - in-stream well 1.

we - in-stream well K.

wf - in-stream well F.

wc - in-stream well C.

wf WC

21

groundwater from deep in the aquifer, ranged from 315 umhos/cm to 404 umhos/cm, indicating a subsequent decrease in specific conductance with depth. This apparent inconsistency can be explained by the relative penetration of the deep nested monitoring wells in the unconsolidated aquifer deposits. The depth of the unconsolidated aquifer deposits in the Little Plover Basin extend at least 90 ft below the water table (Figure 9). The deep nested monitoring wells extend approximately 30 ft below the water table. The deep nested wells, therefore, better represent the water quality conditions at a mid-aqui~er depth.

The apparent increase in specific conductance to a mid-aquifer depth may be related to irrigated agriculture in the area. Weeks and Strangland (1971) attributed the buildup of dissolved solids at an aquifer depth of 30 ft to 35 ft, to the recirculation of groundwater during pumping.

Conductivity values for the groundwater monitoring wells also varied areally and with depth in the study area. The deepest wells of the Pavelski, Leonard, and Airline well nests to the north of the stream decreased in conductivity with distance from the Arnott

moraine with mean values of 513, 478, and 329 umhos/cm, respectively (Figure 10). The inverse was true in the deepest wells of the

Worzalla, Barnsdale, and Norway well nests located south of the stream, here mean conductivity values were 340, 460, and 491 umhos/cm, respectively.

As shown in Figure 2 the Little Plover River Basin groundwater recharge area extends considerably further to the northeast of the stream than to the south. The higher specific conductance values

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measured 1n the Pavelsk1, Leanard and A1rl1ne well nests north of the stream likely reflect the higher dissolved solids associated with

"older" regional groundwater and irrigated agricultural practices.

The "older" regional groundwater would have been in contact w1th aquifer materials longer resulting in higher dissolved solids

content. Irrigation would tend to further increase dissolved solids through the increased leaching of soils and the input of fertilizers and liming materials.

The lower specific conductance values measured in the Worzalla, Barnsdale and Norway well nests south of the river reflect a smaller area of groundwater recharge (Figure 2). Here the groundwater is relatively "young" and naturally lower in dissolved solids. The slight increase in specific conductance values for the deep nested wells south of the stream likely reflect the impact of upgradient irrigated fields (Figure 3).

Total Hardness

Total hardness is a measure of calcium and magnesium ions.

Sources are dolomite ([Ca,Mg], C03) and limestone (CaC03) rock

fragments common 1n the glacial till and ice-contact deposits of this area (Holt 1965). Since calcium and magnesium are the predominant cations in solution, the general trends seen in the conductivity of surface and groundwater samples would be similar for hardness. Mean hardness for the deep nested groundwater monitoring wells was 209 mg/L compared to 124 mg/L for the shallow nested wells, and there appeared to be good correlation between fluctuations in groundwater and surface water mean hardness values (Figure 11). This indicates that dilution due to surface runoff into the stream was

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Figure 11. Total Hardness, Surface Water vs.

Groundwater Samples, Little Plover River, Portage County, Wisconsin.

Total Hardness

Surface vs Groundwater

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190 +

180

170

160

150

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D G.W. Wells + LP. Surface

insignificant. The relationship between in-stream wells (A, B, D and 1) and the shallow vs deep nested wells (Table 1.) was generally the same as that observed for specific conductance.

Slightly higher hardness values observed at Wells C, E and F may be the local results of liming activities in the adjacent field.

Figure 12 shows hardness values were highest in the Pavelski well nest, closest to the Arnott moraine and generally decreased toward the west with movement through the less calcium and magnesium rich outwash deposits. Hardness increased with depth in all nests with the exception of the airline nest where local effects of the sandstone ridge forces deeper groundwater toward the surface (Figure 10).

Alkalinity

Alkalinity primarily consists of carbonate, bicarbonate and hydroxide ions and is indicative of the buffering capacity of a water. Precipitation moving through the soil is charged with CO2 forming carbonic acid which facilitates the dissolution of soil and aquifer materials leading to increased alkalinity and, in calcic and dolomitic terrain increased hardness. Alkalinity may also be a factor in the breakdown of certain pesticides including aldicarb

(Harkin et al, 1982).

Mean alkalinity values for the shallow vs. deep nested wells were 79 mg/Land 111 mg/L, respectively, showing the same

relationship with depth as did hardness and conductivity (Table 1).

However mean alkalinity values in surface water and instream well samples were consistently higher than that of the groundwater (Figure 13). Mean surface water alkalinity for the study period was 152

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Mean Haraness Values (mg/1) Listed with Increasing Depth, Groundwater Samples, Little Plover River Basin, Porta~e County, Wisconsin,

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Figure 13. Mean Alkalinity Values in the Little Plover River Basin Groundwater and Surface Water Sampling Network.

Alkaiinity

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d - deep nested wells.

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29

mg/L. These results indicate a consistent increase in alkalinity with depth in the aquifer, as opposed to hardness and specific conductance which apparently reached a maximum groundwater concentration at mid-aquifer.

The apparent trend toward increased alkalinity with depth in the aquifer appears to be related to the elevated nitrate concentrations detected in the shallow and mid-aquifer samples (see next section).

As described above the relationship between total hardness and alkalinity in the carbonate aquifer should be relatively constant.

However, this was not the case in all monitoring well samples. As shown in Figure 14, there is a strong positive relationship between non-carbonate hardness (total hardness - carbonate alkalinity) and nitrate levels in the groundwater. The cause of this relationship appears to be the reduction of carbonate (C03) as a result of the nitrification of ammonia fertilizers. Anhydrous ammonia when applied to soil is rapidly oxidized to nitrate through soil microorganisms

(nitrification). Nitrification is a hydrogen ion producing process, thus resulting in the reduction in carbonate alkalinity, as seen in in samples from nitrate contaminated groundwater (Figure 14).

Nitrate

The predominant form of nitrogen in groundwater is nitrate, especially in the highly permeable soils of the Central Sand Region, where the rate of nitrification is high and denitrification is practically non-existent (Saffiga and Keeney, 1977). Total nitrate levels in the Central Sand Plains are about four times the Wisconsin state average (Hindall 1977).

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Figure 14. Non-Carbonate Hardness vs. Nitrate Concentration in Groundwater Monitoring Well Samples. Little Plover River Basin, Portage County, Wisconsin.

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Nitrate contamination of potable groundwater is of special concern due to the potential human health effects. Infants and unborn fetus' are at risk of methemoglobinemia when elevated nitrate levels are present in drinking water. The USEPA drinking water standard for nitrate-nitrogen is 10 mg/L.

Sources of nitrate in groundwater include septic systems, livestock operations, barnyards, and agricultural fertilizers. All of these are present in the Little Plover River Basin.

The average nitrate-nitrogen concentration in the groundwater of the study area was 11.4 mg/L with 46% of the monitoring well samples exceeding the 10 mg/L standard. No general trend in nitrate

concentration was observed over the study period. However while the deep monitoring well samples showed little fluctuation (Figure 15a), the shallow wells of the Airline and Pavelski well nests varied by as much as 60% between sample collection dates (Figure 15b).

Fluctuation in nitrate concentrations of the shallow nested well samples may reflect the leaching of nitrate during precipitation and/or irrigation.

There was a distinct change in groundwater quality with depth (Figure 16). Nitrate concentrations in the Norway, Barnsdale, and Leanard well nests increased with depth, while the inverse was true in the Worzella and Airline well nests. The Worzella nest is located at the upgradient edge of an irrigated field and nitrate

contamination may have been moving laterally with the westward groundwater flow rather than downward. The Airline well nest is located in a predominantly residential area, and septic systems may be a substantial source of the nitrate contamination seen in the

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Nitrate Concentrations Over Time, Groundwater Samples from Shallow

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fiqure 15b. ,Nitrate Concentrations Over Time, Groundwater Samples from Deep Ne_sted _Monitoring Wells, Little Plover River Basin, Portage County, Wisconsin.

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shallow well here. In addition the sandstone ridge in close

proximity of this well nest may complicate the groundwater flow paths of this area. The highest single nitrate - nitrogen concentration

(47.9 mg/L) was observed in the shallow well of the Airline nest on August 1980.

The Pavelski well nest is located adjacent to several irrigated fields. Here the groundwater nitrate - nitrogen concentrations were consistently the highest averaging between 15.7 and 28.9 mg/L.

Figure 16 shows the highest mean nitrate concentration in the Pavelski well nest at a depth below surface of 40 feet. As with specific conductance and hardness the buildup of nitrate levels at mid-depth beneath irrigated fields may be attributed to the

recirculation of groundwater during pumping (Weeks and Strangland, 1971).

Figure 17 shows changes in nitrate concentrations at in-stream wells during the study period. Nitrate levels in Well A steadily increased from 11.5 mg/Lin August, 1984 to 19 mg/Lin August, 1985, and declined to 16.0 mg/L by November, 1985. Well A is located in the groundwater upwelling area caused by a sandstone ridge forcing groundwater to the surface. Since the sampling period for this well represented only fifteen months, a relatively short period for

groundwater flow, the observed increase in nitrate concentrations may represent only a fluctuation rather than a long term trend.

The mean nitrate concentration in Well A was 15.4 mg/L while the mean nitrate concentration of the remaining streambed wells was

generally less than 4.0 mg/L. Samples collected from Well Bon January, 1985 and April, 1985 were 15 mg/Land 7.5 mg/L,

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respectively. This possibly indicates that the hydraulic influence of the sandstone ridge extends at times at least to the location of Well B (Figure 5).

Nitrate concentrations in the Little Plover River surface water samples averaged 4.4 mg/L compared to 11.4 mg/L for the monitoring wells (Table 1). As with specific conductance and hardness,

concentrations of nitrates in the deep groundwater discharging to the river are lower than at mid-aquifer.

Nitrate concentrations at in-stream well D (0.8 mg/L), well F (0.5 mg/L) and well C (0.1 mg/L) were considerably lower than the average for surface water or groundwater. Slightly reducing conditions may be the cause of lower nitrates at these locations.

Chloride

Chloride ion concentration in surface and groundwater of the the study area, while not significantly affecting water quality can be an indicator of anthropic related activities within the recharge basin.

Sources of chloride include road salt, septic systems, animal wastes, and agricultural fertilizers.

No discernible seasonal or general trend in chloride

concentration was evident in the surface or groundwater during the study period. Some well samples did however show substantial

fluctuations in chloride concentrations between sample dates (Figure 18). This may be the result of the pumping and recirculation of groundwater during irrigation.

Table 1 shows mean chloride concentrations of groundwater to be approximately 2.5 times the mean surface water value (22 mg/Land 8.9 mg/L respectively), and with the exception of Well A, all in-stream