HYDROGEOLOGY, SIMULATED GROUND-WATER 

FLOW, AND GROUND-WATER QUALITY AT TWO 

LANDFILLS IN BRISTOL, VERMONT

By Thomas J. Mack

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 94-4108

Prepared in cooperation with the

VERMONT DEPARTMENT OF ENVIRONMENTAL CONSERVATION,

AGENCY OF NATURAL RESOURCES,

SOLID WASTE DIVISION

Bow, New Hampshire 

1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

For additional information write to:

Chief, New HampshireVermont District 

U.S. Geological Survey 

Water Resources Division 

525 Clinton Street 

Bow, NH 03304

Copies of this report can be purchased from:

U.S. Geological Survey

Earth Science Information Center

Open-File Reports Section

Box25286, MS 517

Denver Federal Center

Denver, CO 80225
CONTENTS

Abstract.............................................................................................................................................................................. 1

Introduction........................................................................................................................................................................ 2

Purpose and Scope.................................................................................................................................................. 4

Previous Investigations........................................................................................................................................... 4

Acknowledgments.................................................................................................................................................. 4

Methods of Study............................................................................................................................................................... 4

Data Compilation.................................................................................................................................................... 5

Surficial Geologic Mapping.................................................................................................................................... 5

Surface Geophysical Surveys................................................................................................................................. 5

Seismic Refraction...................................................................................................................................... 5

Electromagnetic Survey Methods and Application..................................................................................... 5

Very Low Frequency Terrain Resistivity........................................................................................ 7

Electromagnetic Terrain Conductivity............................................................................................ 9

Observation-Well Placement................................................................................................................................. 10

Borehole Geophysical Methods............................................................................................................................. 12

Electromagnetic Logs................................................................................................................................. 12

Natural-Gamma-Radiation Logs................................................................................................................ 14

Aquifer Tests.......................................................................................................................................................... 14

Streamflow Measurement...................................................................................................................................... 15

Ground-Water-Flow Modeling.............................................................................................................................. 17

Ground-Water-Quality Sampling........................................................................................................................... 18

Hydrogeology..................................................................................................................................................................... 18

Geology................................................................................................................................................................... 19

Bedrock....................................................................................................................................................... 19

Unconsolidated Deposits............................................................................................................................. 19

Glacial Aquifers..................................................................................................................................................... 23

Aquifer Characteristics............................................................................................................................... 24

Ground-Water-Flow System....................................................................................................................... 25

Ground-Water Levels and Flow Directions.................................................................................... 25

Recharge and Discharge................................................................................................................. 29

Simulation of Ground-Water Flow..................................................................................................................................... 31

Description of Conceptual and Numerical Models ............................................................................................... 31

Model Grid and Boundary Conditions .................................................................................................................. 31

Selection of Input Parameters................................................................................................................................ 34

Calibration............................................................................................................................................................. 34

Sensitivity Analysis............................................................................................................................................... 35

Ground-Water Flow............................................................................................................................................... 38

Regional Flow............................................................................................................................................ 38

Flow at the Landfills................................................................................................................................... 40

Private Landfill............................................................................................................................... 40

Municipal Landfill.......................................................................................................................... 40

Model Appraisal.................................................................................................................................................... 44

Ground-Water Quality........................................................................................................................................................ 44

Quality of Native Water......................................................................................................................................... 47

Extent of Contaminated Ground Water ................................................................................................................. 48

Private Landfill........................................................................................................................................... 50

Municipal Landfill...................................................................................................................................... 50

Characteristics of Contaminated Ground Water..................................................................................................... 52

Physical Properties and Major Constituents........................................................................................................... 52

Trace Elements............................................................................................................................................ 54

Organic Compounds.................................................................................................................................... 58

Relation of Water Quality to Geohydrologic Characteristics................................................................................ 58

Summary and Conclusions.................................................................................................................................................. 60

Selected References............................................................................................................................................................ 62

Contents iii
CONTENTS" Continued

Appendixes

1. Seismic-refraction profiles in Bristol, Vermont........................................................................................................ 67

2. Well-depth and screened-interval data for the study area in Bristol, Vermont......................................................... 75

3. Lithologic logs of wells in Bristol, Vermont............................................................................................................ 79

4. Borehole geophysical logs of wells in Bristol, Vermont.......................................................................................... 87

5. Hydraulic conductivity and lithologic descriptions of wells in Bristol, Vermont.................................................... 95

6. Measured and calculated heads in Bristol, Vermont, April 1991............................................................................. 99

7. Summary of water-quality analyses in Bristol, Vermont.......................................................................................... 103

FIGURES

1-5. Maps showing:

1. Locations of landfills and extent of study area, Bristol, Vermont............................................................. 3

2. Locations of seismic profiles, Bristol, Vermont........................................................................................ 6

3. Locations of measurement sites for very low frequency terrain resistivity .............................................. 8

4. Locations of measurement sites for electromagnetic terrain conductivity................................................ 11

5. Locations of observation wells.................................................................................................................. 13

6, 7. Graphs showing:

6. Typical slug-test response curve................................................................................................................ 14

7. Typical dimensionless head-change curve................................................................................................ 15

8-10. Maps showing:

8. Locations of streamflow-measurement sites and gaining and losing stream reaches............................... 16

9. Generalized surficial geology in the study area......................................................................................... 20

10. Altitude of the bedrock surface in the study area...................................................................................... 21

11. Hydrogeologic sections A-A' and B-B'................................................................................................................ 22

12. Hydrogeologic section C-C................................................................................................................................ 23

13. Hydrographs showing monthly water level in well MGW-11 at Middlebury and precipitation

at Burlington, Vermont................................................................................................................................. 26

14. Water-level hydrographs for selected wells in Bristol, Vermont........................................................................ 27

15-18. Maps showing:

15. Altitude of water table in Bristol, Vermont, April 18, 1991...................................................................... 28

16. Location of model grid and cell types for the aquifer system in Bristol, Vermont................................... 32

17. Simulated water-table configuration of the upper aquifer (model layer 1)............................................... 36

18. Simulated potentiometric surface of the lower aquifer (model layer 2).................................................... 37

19. Graph showing statistical distribution of the differences between measured and simulated heads

for sensitivity tests for the ground-water-flow model of Bristol, Vermont................................................... 39

20,21. Maps showing:

20. Simulated ground-water flow paths for water in the upper aquifer (model layer 1) beneath

the landfills........................................................................................................................................... 41

21. Simulated ground-water flow paths for water in the lower aquifer (model layer 2) beneath

the landfills........................................................................................................................................... 42

22-24. Sections showing:

22. Ground-water flow path along model row 34 at the private landfill in

Bristol, Vermont................................................................................................................................... 43

23. Ground-water flow path along model row 26 at the municipal landfill in

Bristol, Vermont................................................................................................................................... 45

24. Ground-water flow path along model column 32 at the municipal landfill

in Bristol, Vermont............................................................................................................................... 46

25. Map showing specific conductance of ground water in Bristol, Vermont, September, 1990............................. 49

26. Hydrogeologic section B-B' showing specific conductance of ground water at the private landfill................... 51

27. Distribution of concentrations of selected dissolved chemical constituents in native ground water and

in samples from near landfills in Bristol, Vermont....................................................................................... 53

28. Graph showing chloride concentrations at wells W-511, MW-102s, and MW-102d......................................... 55

iv Contents
CONTE NTS- - Continued

TABLES

1. Effective exploration depths for given terrain resistivities at operating frequencies of 15

to 25 kilohertz............................................................................................................................................... 7

2. Inductive electromagnetic exploration depths at three intercoil spacings and low-transmission

frequency...................................................................................................................................................... 9

3. Streamflow measured from January-July 1991, Bristol, Vermont...................................................................... 17

4. Estimated horizontal hydraulic conductivity of aquifer materials determined from slug and specific

capacity tests, predominant material type, and mean grain size in Bristol, Vermont................................... 24

5. Water budget for the study area for April and May 1991 for Bristol, Vermont.................................................. 31

6. Estimated and simulated ground-water budget for the study area in Bristol, Vermont...................................... 38

7. Observation wells, springs, and surface-water sites sampled, by location relative to landfill

and by water category, Bristol, Vermont...................................................................................................... 47

8. Regulatory limits and summary statistics for physical properties and chemical constituents in native

water from wells and springs in Bristol, Vermont, 1990-91......................................................................... 48

9. Summary statistics for physical properties and chemical constituents in water from wells and

springs near the private landfill, Bristol, Vermont, 1990-91 ........................................................................ 56

10. Summary statistics for physical properties and chemical constituents in water from wells and

springs near the municipal landfill, Bristol, Vermont, 1990-91.................................................................... 57

11. Volatile organic compounds for which water samples were analyzed, Bristol, Vermont................................... 59

12. Volatile organic compounds detected in observation wells, grouped by landfill, Bristol, Vermont,

September 1990 to October 1991................................................................................................................. 60

Contents v
CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATED WATER-QUALITY AND GEOPHYSICAL UNITS

Multiply By To Obtain

acre 4,047 square meter

cubic foot per second (ft3/s) 0.02832 cubic meter per second

foot (ft) 0.3048 meter

foot per day (ft/d) 0.3048 meter per day

gallon (gal) 3.785 liter

inch (in.) 25.4 millimeter

inch per year (in/yr) 25.4 millimeter per year

mile (mi) 1.609 kilometer

million gallons (Mgal) 3,785 cubic meter

million gallons per day (Mgal/d) 0.04381 cubic meter per second

square foot (ft2) 929.0 square centimeter

square foot per day (ft2/d) 0.09290 square meter per day

square mile (mi2) 2.590 square kilometer

Water temperature is given in degrees Celsius (°C), which can be converted to degrees Fahrenheit (° F) 

by use of the following equation: °F = 1.8 (°C) + 32

Sea Level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)-a geodetic datum derived from 

a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929.

ABBREVIATED WATER-QUALITY AND GEOPHYSICAL UNITS USED IN REPORT

In this report, the concentration of a chemical in water is expressed in milligrams per liter (mg/L) or micrograms per liter Qig/L). 

Milligrams per liter is a unit expressing the concentration of chemical constituents in solution as weight (milligrams) of solute per unit 

volume (liter) of water; 1,000 Hg/L is equivalent to 1 mg/L.

Specific conductance of water is expressed in microsiemens per centimeter at 25 degrees Celsius (^S/cm). This unit is equivalent to 

micromhos per centimeter at 25 degrees Celsius (^mho/cm), formerly used by the U.S. Geological Survey.

In this report, the electrical conductivity of Earth materials is expressed in millisiemens per meter (mS/m); 10 nS/cm is equivalent to 

1 mS/m. This unit (mS/m) is equivalent to millimhos per meter, formerly used by the U.S. Geological Survey. The electrical resistivity of 

Earth materials is expressed in ohm-meters (ohm-m); 1 ohm-m is equivalent to the inverse of 1 siemen per meter. The frequency of radio 

transmissions, in thousands of cycles per second, is expressed in kilohertz (kHz).

vi Conversion Factors, Vertical Datum, and Abbreviated Water-Quality and Geophysical Units
HYDROGEOLOGY, SIMULATED GROUND-WATER 

FLOW, AND GROUND-WATER QUALITY AT TWO 

LANDFILLS IN BRISTOL, VERMONT

By Thomas J. Mack

Abstract

A study was done by the U.S. Geological 

Survey, in cooperation with the Vermont Agency of 

Natural Resources, to describe the hydrogeology of 

unconsolidated deposits, simulate ground-water 

flow, and to describe ground-water quality at two 

landfills in Bristol, Vermont. The study area is characterized by a glacial delta more than 200 feet thick, 

having an exposed face about 150 feet high, on the 

west flank of the Green Mountains. A municipal 

landfill, more than 20 years old, is atop the delta in 

a coarse-grained deposit, where depths to water 

range from 30 to 130 feet below land surface. A private landfill, also more than 20 years old, is at a 

lower altitude next to the delta in medium- to finegrained sediments as much as 100 feet thick, where 

the depth to water is from 10 to 50 feet. A sand, silt 

and clay lens next to the delta possibly extends into 

the delta and acts as a confining unit, separating an 

upper unconfined aquifer and a lower confined 

aquifer. The horizontal hydraulic conductivity of 

the coarse-grained deltaic sands and gravels was 

estimated, by slug and specific-capacity tests, to 

range from 120 to more than 250 feet per day. The 

horizontal hydraulic conductivity of fine- to 

medium-grained sands was estimated to range from 

10 to 30 feet per day and that of till to be about 1 

foot per day.

Recharge to the glacial aquifers is predominantly from ground-water leakage from the underlying bedrock aquifer and accounts for about 80 

percent of the total recharge. Infiltration of precipitation, approximately 14 inches per year, accounts 

for about 10 percent of total recharge, and inflow

from adjacent unconsolidated aquifers accounts for 

the remaining 10 percent. High upward gradients of 

0.03 to 0.3 are evidence that most recharge is as 

upward ground-water leakage from bedrock.

Surface electromagnetic geophysical terrain 

surveys, electromagnetic induction and very low 

frequency methods were used to identify areas 

underlain by electrically conductive landfillleachate plumes. Natural-gamma radiation and 

electromagnetic borehole geophysical logs were 

used to identify and vertically delineate landfillleachate plumes in the aquifers. Leachate plumes 

were near the water table and ranged in thickness 

from less than 5 to nearly 20 feet.

A two-layer ground-water-flow model of the 

upper and lower glacial aquifers was developed and 

calibrated under steady-state conditions, approximated by the conditions observed during April and 

May 1991. Advective ground-water-flow paths 

were calculated by a particle-tracking analysis. 

Simulated paths of landfill leachate are generally 

concentrated in the upper aquifer, or upper part of 

an aquifer, at the private and municipal landfills. 

Ground water from beneath the private landfill discharges as ground-water outflow to the aquifer by 

way of a gap in the bedrock ridge west of that landfill. Some ground water beneath the private landfill 

discharges to a brook west of the private landfill. 

Most ground water beneath the municipal landfill 

discharges as ground-water outflow to the southwest at a gap in the bedrock ridge west of the private landfill. This ground water follows a longer 

path before discharging at the gap in the ridge than 

does ground water from beneath the private landfill.

Abstract 1
Ground water beneath the east end of the municipal 

landfill possibly flows southward to eventually discharge at the southern model boundary in the 

Bristol Flats area. Flow paths in the upper aquifer 

beneath both landfills remained in the upper layer, 

and paths in the lower aquifer generally flow into 

the upper aquifer.

Water samples degraded by landfill leachate 

generally had a specific conductance greater than 

400 LiS/cm (microsiemens per centimeter at 25 

degrees Celsius); the median was about 700 LiS/cm. 

The maximum specific conductances were 

2,920 LiS/cm at the municipal landfill and 

1,980 LlS/cm at the private landfill. Native ground 

water had a median specific conductance of 

355 LiS/cm, and ranged from about 200 to 

400 LiS/cm.

Leachate degraded water from the landfills 

contained mean concentrations of common constituents and trace elements that were 1.5 to 10 times 

the background concentrations. Trace elements 

detected in leachate from the landfills included 

copper, nickel, zinc, cobalt, lead, and arsenic. 

Nickel was the most commonly detected trace element (19 detections), followed by zinc (8 detections). Some chemical constituents in water 

samples appear to be present in lower 

concentrations than were found during earlier 

investigations.

Ten volatile organic compounds were detected 

at four observation wells associated with the municipal landfill, and three volatile organic compounds 

were detected at two observation wells associated 

with the private landfill. No one volatile organic 

compound was consistently detected, and concentrations generally were at or near detection limits. 

Volatile organic compounds were detected fewer 

times and at lower concentrations than in previous 

investigations. Volatile organic compounds were 

not detected in samples of native water.

INTRODUCTION

Two solid-waste landfills, one privately owned and 

one municipally owned, have been used in Bristol, 

Vermont (fig. 1) for more than 20 years. Most of the

solid wastes generated by domestic and industrial activities throughout Vermont have been disposed of in 

unlined landfills, which can affect the quality of water in 

underlying aquifers. Other investigations have demonstrated that landfills can degrade local ground-water 

quality (Kimmel and Braids, 1980; Wexler, 1988a). The 

demand on Vermont's ground-water resources is continually increasing. To plan for future ground-water use, 

water managers and planners will need to obtain data on 

ground-water-flow systems and the effects of landfills 

on ground-water quality as efficiently and effectively as 

possible.

The Vermont Agency of Natural Resources, Solid 

Waste Division (VANR) and the U.S. Geological Survey 

(USGS) began a cooperative study to examine the 

hydrogeology and ground-water quality at the two landfills in Bristol. The study, which was done from April 

1990 to September 1992, demonstrates the application 

and analysis of geophysical, hydrogeologic, and 

numerical ground-water-flow simulation techniques at 

the landfills.

The study area consists of the two landfills (fig. 1) 

and a surrounding 2-mi area. The study area is on the 

west flank of Hogback and South Mountains, which are 

part of the Green Mountains (fig. 1). The village of Bristol is on a prominent glacial delta; an exposed face of the 

delta rises more than 150 ft above the New Haven River 

Valley bottom. The delta was formed by glacial meltwater that once flowed between Hogback and South Mountains into glacial Lake Fort Anne. The private landfill, at 

the southwestern edge of the delta, is at the base of the 

deltaic sequence just north of a cemetery in an area 

marked by sand and gravel excavations. The municipal 

landfill is within the deltaic sequence at the northwestern 

edge of the delta.

The private landfill (fig. 1), formerly a sand and 

gravel excavation pit, has been operated by several 

owners since it opened in 1968; in 1992 it was approximately 10 acres in area. The landfill received not only 

municipal wastes from 10 surrounding towns but also 

industrial wastes from local manufacturing companies. 

Landfilling proceeded eastward and westward from the 

center of the former excavation site. During this study, a 

1-acre scrap-metal pile, located in a gravel excavation 

pit a few hundred feet north of the landfill, was considerably reduced in size by trucking offsite. When the 

study began, the private landfill was inactive but filling 

resumed in 1991 and the landfill is scheduled to be 

capped within a few years.

2 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
44"08'30

44"07'30

Base from U.S. Geological Survey rj 

Bristol, Vt., 1963; South Mountain, Vt., 1963; |-

1:24,000 0 200 400 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 1 . Locations of landfills and extent of study area, Bristol, Vermont.

Introduction 3
The municipal landfill (fig. 1) has been owned and 

operated by the town of Bristol since 1968 and may have 

informally received solid waste before 1968. This 8-acre 

landfill was also a former sand and gravel excavation pit 

and received only municipal wastes since its operation 

by the town. Filling began at the western end of the landfill, and as of 1992, the surface was nearly completed to 

the natural grade. The eastern end of the excavation pit 

occupied by the landfill has been used primarily for temporary storage of scrap metals, and in the past, was used 

as a brush and wood-burning area. A recycling program, 

begun in 1990, has reduced the rate of refuse brought to 

the landfill.

Purpose and Scope

This report describes the hydrogeology, simulation 

of ground-water flow, and water quality of the glacial 

aquifers that underlie two landfills in Bristol. Specifically, this report (1) describes the use of various hydrogeologic methods for studies of landfills in glaciated 

terrain, and (2) describes the ground-water-flow patterns 

and ground-water quality beneath the landfills. The 

study is limited to the unconsolidated glacial deposits of 

this area and does not include the underlying bedrock 

aquifer.

Previous Investigations

Previous investigations of the study area included a 

study of the private landfill for the VANR (Marshfield 

Engineering Services, 1979) that was primarily concerned with the design and operation of the landfill but 

it did address some aspects of hydrogeology and water 

quality. The investigation included installation of seven 

monitoring wells, measurements of ground-water levels, 

and water-quality sampling. Three of the wells installed 

were downgradient from the landfill, and two were 

downgradient from the scrap-metal piles north of the 

landfill. The remaining wells were destroyed before the 

USGS investigation began.

Investigations of the municipal landfill by the 

VANR (Hackbarth, 1980) and by a consultant to the 

town of Bristol (Johnson Company, 1989) also were 

done. These two studies resulted in design and operation 

reports that included some hydrogeologic data. The first 

investigation (Hackbarth, 1980) resulted in the installation of three observation wells at the landfill site. Wells 

were not installed downgradient from the landfill 

because drilling is difficult in this area. During the

second investigation (Johnson Company, 1989), three 

wells were installed downgradient from the municipal 

landfill in the glacial delta deposits. A terrainconductivity survey was used to determine observationwell placement, and slug tests were done to estimate 

aquifer characteristics. Both investigations included 

water-level measurements and water-quality sampling 

as part of the data collection.

A geologic report on the Burlington-Middlebury 

region (Stewart, 1973) describes the bedrock geologic 

setting and surficial geology and gives appraisals of 

ground-water availability. A ground-water favorability 

map of the Otter Creek Basin, which includes the study 

area, was produced by Hodges (1967) and includes 

Stewart's work (1973). The Bristol delta and surrounding area is less than 15 mi from Middlebury College, in 

Middlebury, Vt., and has been the subject of senior thesis's by students of the geology department (Brewster 

Baldwin and John Schmidt, Middlebury College, oral 

commun., 1991).

Acknowledgments

The author thanks James Surwilo of the VANR for 

his support and assistance, particularly with waterquality sampling and analysis. The author thanks 

officials of the town of Bristol and numerous 

landowners for their cooperation and for granting access 

to their properties.

METHODS OF STUDY

Methods of study described in the following sections include compilation and analysis of available data 

and collection and analysis of hydrogeologic data. Data 

collected includes surficial geologic mapping, surface 

geophysical surveys, lithologic logs of USGS test holes, 

borehole geophysical logs, water-level measurements, 

aquifer tests (slug tests), and streamflow measurements. 

Water-quality samples were collected and analyzed by 

the VANR.

The order that the methods of study are discussed 

in this report are generally the most useful order of 

application to hydrogeologic contaminant studies in glaciated areas. Each method provides a more focused location of further data-collection activities and more 

specific or detailed information. Data compilation consolidates available data to locate initial study efforts and 

avoid redundant efforts. Surficial geologic mapping

4 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
provides an initial view and insight into the deposits 

present. Surface geophysical surveys provide insight 

into aquifer properties or geometry.

Data Compilation

Subsurface data on ground-water levels, stratigraphy, and depth to bedrock (James Ashley, Vermont 

Department of Environmental Conservation, Water 

Supply Division, written commun., 1991) were 

extracted from more than 230 drillers' logs of domestic 

wells in Bristol reported to the State since 1974. The 

locations of domestic wells used in this study were 

checked for accuracy. Other subsurface data included 

test wells at the Bristol municipal landfill (Hackbarth, 

1980; Johnson Company, 1989), test wells at the private 

landfill (Marshfield Engineering Services, 1979), and 

test wells for a proposed leachfield (Brent Whitney, 

Thermo Engineering, written commun., 1991).

Surficial Geologic Mapping

The areal extent of unconsolidated deposits was 

mapped and described at vertical faces of gravel pits and 

at hand-dug excavations. Contacts between sedimentary 

units were traced between pits by projection and interpolation. This information is used in construction of 

geologic sections and development of conceptual 

models of the ground-water system underlying the study 

area.

Surface Geophysical Surveys

Surface geophysical surveys consisted of seismicrefraction profiles and electromagnetic terrain surveys. 

Seismic-refraction surveys were used to determine the 

depth to water table and bedrock surfaces. Electromagnetic terrain surveys consisted of electromagnetic terrain 

conductivity (EM) surveys and very low frequency terrain resistivity (VLF) surveys. Both were used to measure contrasts in electrical properties of aquifer 

materials and ground water. Interpretation of EM 

surveys generally requires additional subsurface data.

Seismic Refraction

Seismic-refraction surveys were done at 19 sites 

(fig. 2) to determine depth to water table and bedrock 

surfaces. The interpreted seismic-refraction profiles of 

15 of those 19 sites (appendix 1) provided information 

for water-table and bedrock-surface maps and were used

to help determine placement of test wells and aid in the 

interpretations of other geophysical surveys. Interpreted 

seismic-refraction profiles were not completed at four of 

the survey sites (d-d', e-e',j-j', and <?-<?'; fig. 2) because 

the hydrogeologic conditions at these sites did not meet 

the requirements necessary for data interpretation. Two 

physical requirements are fundamental to a successful 

seismic survey. The first is that layer velocities increase 

with depth; the second is that individual layers are thick 

enough (which generally means that layer thicknesses 

must increase with depth) for the refracted energy 

wave to be detected by surface geophones. At sites j-f 

and q-q', the saturated zone was too thin less than the 

thickness of the unsaturated zone to be detected (such 

a zone is called a blind zone). At sites d-d' and e-e\ a 

high-velocity saturated zone overlies a low-velocity 

unsaturated zone (this is called a velocity inversion).

The results of seismic-refraction profiles were 

interpreted by use of the methods described by Haeni 

(1988). A 12-channel, signal-enhancement seismograph 

was used to measure the time required for a sound wave 

to travel from a shot point, usually an explosive charge, 

to each of the 12 geophones in a geophone spread. Most 

surveys were done with 50-foot spacing between geophones and with three to five shotpoints per geophone 

spread. Geophone spacing is critical and must be 

designed with the depths of interest in mind; however, 

the number and spacing of shotpoints is also important 

to the integrity of the seismic data collected. Shotpoint 

and geophone setups will differ throughout an 

investigation because depths to water table and bedrock 

surfaces are rarely uniform.

Data were interpreted by use of a seismic-refraction 

inverse computer modeling program (SIPT) developed 

by Scott (1977) and based on a delay-time and iterative 

ray-tracing technique. Haeni (1988) provides a description and guidelines for use of this program. SIPT is 

designed to handle complex field setups and to develop 

interpretations for multilayer, dipping-bed geologic 

settings.

Electromagnetic Survey Methods 

and Application

EM surveys measure the combined conductivity, or 

resistivity, of the earth materials and any water or other 

fluid present. In general, dry sand and gravel is resistant, 

whereas silt and clay is conductive. Any given earth 

material is more conductive when saturated. The 

specific conductance of distilled water, 1 (iS/crn (Hem,

Methods of Study 5
73°06' 73'04'30"

44°08'30" "5T

44"07'30'

a' SEISMIC-REFRACTION 

LINES

Base from U.S. Geological Survey 0 

Bristol. VI.. 1963. 1:24.000 (.

400 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 2. Locations of seismic profiles, Bristol, Vermont.

1989, p. 68), is indicative of a resistant substance; 

specific conductance increases with the addition of ions. 

Ambient uncontaminated or native ground water underlying the Bristol area has a specific conductance of about 

200 to 400 LiS/cm. New Haven River water generally 

has a specific conductance of 100 to 200 u,S/cm. Water 

flowing through a landfill or other contaminant source, 

typically dissolves and incorporates more ions. Leachate 

contaminated ground water from landfills may have a 

specific conductance greater than 1,000 LlS/cm (Kimmel 

and Braids, 1980; Wexler, 1988a). Therefore, because of 

the contrast between the specific conductance of 

leachate and native ground water, EM techniques can be 

used in the detection of contaminant plumes. In the

optimal EM survey, measurement points would be 

arranged in a regular grid pattern; however, this ideal 

arrangement is not always possible because of cultural 

interferences (metal fences, buried or overhead cables, 

pipelines, vehicles, and buildings), limited access, or 

large topographic relief.

Cultural interferences can hamper an investigation 

by obliterating the measurements at a specific site. 

Power transmission lines can strongly affect a survey 

because they produce interfering magnetic fields. 

Above-ground structures affect the EM survey because 

magnetic fields extend in a spherical pattern above and 

below the ground.

6 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
When the stratigraphy of the area surveyed is 

highly variable, the data interpretation becomes complex and may require modeling to interpret the results. 

Forward and inverse computer-modeling programs are 

available for EM terrain conductivity data (Granthem 

and others, 1987); a forward computer model is available for VLF interpretations (Granthem and others, 

1986). Forward models simulate the response of the EM 

survey equipment to thickness and electrical conductivity of a layered earth model (which may approximate the 

hydrologic model of the system). In practice, the number 

of earth layers, layer thickness, and electrical conductivity is adjusted until the simulated instrument response 

approximates the observed instrument response. In 

some cases, several combinations of earth layers and 

electrical conductivities can reproduce the observed 

instrument response. Forward modeling can produce a 

unique solution however, at least one variable (such as 

layer thicknesses or other hydrogeologic information) 

must be known. Inverse modeling can optimize the 

interpretation and produce a better simulation with less 

trial and error. If some hydrogeologic information is 

known, the model results can be used to determine 

whether the instrument response at a particular site is 

affected by the hydrogeology of the area or by a 

conductive zone of contaminated ground water.

Very Low Frequency Terrain Resistivity

Very low frequency (VLF) radio signals are transmitted from naval communications stations for use in 

submarine navigation systems. Previously, these signals 

were used in geophysical surveys for locating ore deposits. VLF resistivity surveys have been used to locate 

fracture zones in dolomite (Yager and Kappel, 1987) and 

to detect ground-water contamination at a landfill in 

Connecticut (Grady, 1989). The VLF equipment used in 

this investigation consists of a lightweight handheld 

receiver and two probes that function as receiver coils 

(Geonics, 1979a, b).

A VLF terrain-resistivity survey uses a 15 to 

25 kHz (kilohertz) VLF signal. The transmitting stations 

used in this study were Cutler, Maine (24.0 kHz), Seattle, Wash. (24.8 kHz), and Annapolis, Md. (21.4 kHz). 

The VLF signal consists of a horizontal radial electromagnetic field at the Earth's surface: and two components that penetrate the Earth's surface; a vertical 

electrical field and a horizontal magnetic field. As the 

terrain resistivity increases, the horizontal electric field 

increases. VLF equipment measures the ratio of and the

phase angle between the horizontal electric field and the 

horizontal magnetic field and is calibrated to read 

apparent terrain resistivity in ohm-meters.

The effective depth of exploration depends mostly 

on terrain resistivity and only slightly on operating frequency. The expected exploration depths for a given 

terrain resistivity at operating frequencies of 15 to 25 

kHz are listed in table 1.

Where the terrain resistivity is high, such as in a 

thick unsaturated sand and gravel unit, the VLF exploration is effective to considerable depths. The effectiveness of the VLF survey decreases in an electrically 

conductive zone at the ground surface, such as a surficial 

clay layer. The VLF survey effectively penetrates the 

materials present until a conductive zone is reached. 

Any material beyond that conductive zone is virtually 

undetected.

The phase angle between horizontal electric and 

magnetic fields indicates the type of material stratification. A phase angle less than 45° indicates that conductive materials overlie more resistive materials, a phase 

angle greater than 45° indicates that resistive materials 

overlie more conductive materials, and a phase angle of 

45° indicates that the material within the exploration 

depth is electrically homogenous.

VLF terrain-resistivity measurements were made at 

sites near the two landfills, subject to accessibility and 

nearby cultural interferences. Measurement sites were 

generally 50 to 100 ft apart. Apparent VLF terrain resistivities are shown in figure 3. VLF terrain-resistivity 

measurements were made at other sites throughout the 

study area to assist in geologic interpretations of the 

subsurface materials.

Table 1 . Effective exploration depths for given terrain 

resistivities at operating frequencies of 15 to 25 

kilohertz

[Data from Geonics, 1979b]

Terrain resistivity 

(ohm-meters)

10,000

1,000

500

100

50

10

Exploration depth 

(feet)

1,150

330

260

115

80

33

Methods of Study 7
73W 73'05'

44'08'30"

44'08'

.800 APPARENT TERRAIN RESISTIVITY, 

IN OHM-METERS, AT OBSERVATION POINT

Base from U.S. Geological Survey 

Bristol, Vt., 1963, 1:24,000

500

I

1,000 FEET

100 200 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 3. Locations of measurement sites for very low frequency terrain resistivity.

8 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills In Bristol, Vermont
VLF survey results of an area can be interpreted 

qualitatively without modeling where the geology is 

uniform. This was the case on the delta at Bristol, 

where VLF measurements can be compared for a qualitative interpretation of changes in the subsurface resistivity. Terrain-resistivity measurements greater than 

500 ohm-m at this site are generally characteristic of an 

unsaturated sand and gravel unit that is more than 100 ft 

thick (fig. 3). Measurements near the southern boundary 

of the municipal landfill are less than 500 ohm-m. Near 

the face of the delta, an area of low resistivity (200 to 

300 ohm-m) extends southward from the west end of the 

landfill for a few hundred feet (fig. 3) and probably indicates an area of electrically conductive ground water. 

Phase angles were generally greater than 45° on the delta 

deposits; thus, resistive material probably overlies 

conductive material.

Clay layers (which limit VLF exploration depth) 

are present to the south and west of the private landfill 

and pinch out to the north and east. VLF measurements 

made on the valley floor adjacent to the delta and southwest of the private landfill were limited because of the 

presence of clay at the land surface. Because of complex 

geology, widely varying topography, and cultural interferences on Burpee Road (fig. 3), few measurements 

were made west of the private landfill. Estimates of 

equipment response, based on forward modeling, indicate that low-conductivity leachate (less than 

1,000 (iS/cm) may not be distinguishable from clay at 

the private landfill.

Terrain resistivities on the valley floor adjacent 

to the delta primarily reflect variations in the local 

stratigraphy of glacial materials and not changes in 

ground-water quality. A comparison of adjacent measurements is adequate to assess lateral changes in 

ground-water quality; therefore, measurements were not 

contoured in figure 3. Contoured measurements emphasize regional geologic trends. For example, changes in 

terrain resistivity from west to east along a line immediately south of the private landfill (fig. 3) reflect the resistivity (greater than 1,000 ohm-m) of a dolomite ridge 

west of Burpee Road (phase angle near 45°), a low resistivity sequence of sand and clay (less than 100 ohm-m) 

at Burpee Road, a moderately resistive sand and diminishing amounts of clay (greater than 100 ohm-m) to the 

east near the cemetery, and a resistive largely 

unsaturated sand and gravel (greater than 1,000 ohm-m).

Terrain resistivities west of the private landfill, 

were low and could indicate that a clay layer is present 

or that ground water is conductive in that area. Phase

angles were less than 45° adjacent to the delta, an indication that conductive material overlies resistive material. Resistive bedrock is near land surface in this area 

and accounts for phase angles of less than 45°. Phase 

angles on the dolomite ridge west of the landfills were 

all about 45°, an indication of uniformly resistive 

material with depth.

Electromagnetic Terrain Conductivity

Inductive EM techniques have been widely used 

for mineral exploration for many years and are now used 

to detect contaminant plumes (McNeill, 1980a; Mack 

and Maus, 1987; Grady, 1989). The equipment used 

consists of a transmitter and transmitter coil and a 

receiver and receiver coil. The two components are separated by a 33-, 66-, or 131 -foot cable during the survey. 

Physical contact with the ground is not necessary; each 

coil is simply held upright or set on the ground when a 

reading is taken.

In inductive EM, an alternating current is passed 

through a coil to induce a magnetic field that penetrates 

the ground. This magnetic field induces a current in the 

ground that generates a secondary magnetic field out of 

phase with the first. The receiver coil is placed a 

specified distance from the transmitter coil and receives 

the secondary magnetic field. At low transmission 

frequencies, the ratio of the secondary to primary 

magnetic field is linearly proportional to the 

conductivity of the terrain (McNeill, 1980a).

Exploration depth depends on intercoil spacing, 

coil orientation, and transmission frequency (table 2). 

The two coil orientations are described as vertical dipole 

or horizontal dipole; in the vertical dipole orientation, 

the two coils are flat on the ground and in the horizontal 

dipole orientation, the two coils are upright. 

Measurements made when the intercoil spacing is 131 ft

Table 2. Inductive electromagnetic exploration 

depths at three intercoil spacings and lowtransmission 'frequency

[Data from McNeill, 1980a]

Intercoil spacing

Feet

33 

66 

131

Meters

10 

20 

40

Exploration depth (feet) for given 

coil orientation

Horizontal 

dipoles

25 

49 

98

Vertical 

dipoles

49 

98 

197

Methods of Study 9
are often difficult to obtain because equipment operation 

with a large exploration depth becomes increasingly 

sensitive to cultural interferences. As the survey area 

increases, the interaction between equipment and 

cultural interferences increases.

An EM survey done at the municipal landfill by a 

previous investigation (Johnson, 1989) indicated high 

terrain conductivity immediately south of the landfill. 

The largest EM anomalies were found by use of the EM 

equipment at 131 ft intercoil spacing, vertical dipole orientation. No additional EM measurements were made in 

this area because the considerable depth to water (130 ft) 

made the utility of the measurements questionable.

EM measurements of terrain conductivity were 

made at low areas on the delta, on the valley floor downgradient from the municipal landfill, at selected sites 

near the private landfill, and at sites throughout the study 

area for geologic control. EM measurements were not 

made in a grid pattern in this investigation because of the 

variable topography in many areas, the considerable 

depth to water (130 ft) in elevated areas of the delta, and 

the cultural interferences along Burpee Road. Similar to 

the VLF survey, the EM survey reflects the different 

lithologies in the study area. For this reason, analysis of 

the EM survey was limited to a qualitative comparison 

of EM measurements in figure 4.

Terrain-conductivity measurements made on the 

dolomite ridge west of the landfills indicate EM 

conductivities of 0.3 to 0.9 mS/m (millisiemens per 

meter). Measurements made on exposed Green Mountain quartzite, about 1 mi east of the study area, were 0.4 

to 1.3 mS/m. These measurements enhance EM data 

interpretations by providing the EM conductivity of 

only the dolomite and quartzite bedrock because the 

measurements do not integrate other materials.

Immediately southwest of the municipal landfill 

terrain conductivities are high (9 and 12 mS/m) for an 

area characterized by predominantly thin sand and 

gravel. Farther west of the landfill, terrain conductivities 

are moderate (5 to 8 ms/m). The high conductivities 

immediately west of the municipal landfill indicate the 

presence of conductive ground water near the land surface, whereas the low conductivity measured with the 

66-foot vertical dipole indicates near-surface bedrock.

Terrain-conductivity measurements made near the 

private landfill (fig. 4) are difficult to interpret because 

of variations in depth to water (from 0 to greater than 

50 ft) and the presence of clay layers. Measurements

made west of the landfill along Burpee Road reveal high 

apparent terrain conductivities. Farther west, measurements were made in a depression containing a small 

pond when the water surface was frozen. The topographical low area containing the pond is beneath the surficial 

clay layer, yet high terrain conductivities were measured 

near the land surface from Burpee Road westward to a 

brook by use of a horizontal dipole orientation at an 

intercoil spacing of 33 ft. Estimates of instrument 

response based on forward modeling indicate that the 

high apparent terrain conductivities can be the result of 

clay units in this area. Measurements made immediately 

south of the private landfill at a cemetery indicate that 

the surficial and lower clays thin from west to east (similar to the VLF survey results) from Burpee Road to the 

base of the delta. Results from the VLF and EM surveys 

indicate that conductive ground water is probably not 

present southeast of this landfill. However, because of 

the presence and complexity of conductive clay south 

and west of the landfill, it is not possible to determine 

without additional data whether conductive ground 

water is present south and west of the landfill.

Observation-Well Siting

Observation wells were sited to provide information on the glacial-aquifer lithology, hydraulic characteristics, and horizontal and vertical ground-water-flow 

directions, and for collection of water-quality samples of 

native ground water and landfill leachate. Some wells 

were installed upgradient from the landfills to allow for 

sampling of ambient, uncontaminated water (native 

water); the rest of the observation wells were installed 

downgradient from the landfills to collect data in areas 

where possible landfill-leachate contamination was indicated by surficial geophysical surveys. Where possible, 

additional observation wells were installed to supplement available hydrogeologic data and to help 

determine the lateral extent of leachate contamination.

Observation wells were initially installed as deeply 

as equipment would allow in the unconsolidated glacial 

sediments to permit borehole geophysical logging of as 

much of the aquifer as possible. Wells were then 

installed adjacent to the first group of wells at predetermined intermediate depths based on results of borehole 

geophysical logs (described in the section 'Borehole 

Geophysical Methods'). Vertical hydraulic gradients 

were determined by installing multiple wells at selected 

sites and setting well screens at different depths in the 

aquifer.

10 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
73°06' 73°05'

44°08'30"

44°08'

.12 APPARENT TERRAIN CONDUCTIVITY, IN MILLISIEMENS 

2 PER METER-Top number is conductivity for the

horizontal dipole orientation, 33-foot intercoil spacing; 

bottom number is conductivity for the vertical dipole

/-\ric»rito*i/-\ri CC_f/"U"\t iritarr^nil oi"iar*ii"i«

J I - -2 Municipal 

Landfill

Private RM , ,,.,, DlVI Landfill 577

Base from U.S. Geological Survey 

Bristol, Vt., 1963, 1:24,000

500 1,000 FEET

100

I

200 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 4. Locations of measurement sites for electromagnetic terrain conductivity.

Methods of Study 11
A total of 48 observation wells were installed for 

this study. All were constructed of flush-threaded 

polyvinyl chloride (PVC) casing and slotted PVC 

screens sized according to the aquifer material at the 

screen zone. Wells were grouted with bentonite seals 

either along the entire casing length or above the screen 

and at a few feet below land surface to prevent flow in 

the borehole. After completion, wells were developed 

by evacuating the well several times to remove water 

and any other material introduced during drilling and to 

improve the hydraulic connection with the aquifer. Well 

locations are shown in figure 5, well data are listed in 

appendix 2, and lithologic logs are given in appendix 3.

A 4-inch-diameter hollow-stem auger drill was 

used to install 30 wells with 2-inch-diameter1 slotted 

screens and 6 wells with 1-inch-diameter slotted 

screens. The hollow-stem auger rig allowed split-spoon 

samples of relatively undisturbed aquifer materials to be 

collected ahead of the drill stem for lithologic identification and grain-size analysis. A 6-inch-diameter mudrotary drill was used to install six 2-inch-diameter PVC 

wells in the glacial delta where drilling with the auger 

rig was not possible because of cobbles and large boulders. A small 2-inch-diameter drill was used to install 

six shallow 2-inch-diameter wells to a depth of 14 to 20 

ft.

Borehole Geophysical Methods

Two borehole geophysical methods were used in 

this study EM induction and natural-gamma radiation 

(gamma) logging. The two logging techniques were 

used comparatively (Mack, 1993) to determine whether 

electrically conductive zones were indicative of clay or 

of conductive ground water. The borehole geophysical 

logs also were used to improve interpretation of lithologic logs. Borehole geophysical logs obtained during 

this study are shown in appendix 4.

Borehole gamma logging generally is used to delineate silt or clay layers, or lenses, in unconsolidated 

deposits in a borehole. The EM-induction log technique, 

referred to as "the EM log," measures the electrical conductance of the formation outside the borehole. The conductivity discussed throughout this report section refers 

to the electrical conductivity of the formation or specific 

conductance of water, not the hydraulic conductivity of 

aquifer materials. The EM log operates on the same 

principles as the surface EM survey discussed

'in this report, well diameter is the nominal inside diameter.

previously and also produces an integrated measure of 

the effects of the materials present. The total integrated 

conductance is controlled primarily by the amount of 

clay minerals relative to coarse-grained materials and 

the presence and concentration of the dissolved solids in 

ground water.

Electromagnetic Logs

The EM log was originally designed for use in the 

oil industry to measure formation resistivity through oilbased drilling mud, where no conductive medium is 

present between the probe and the formation (Keys, 

1988). The principles of the EM log are similar to those 

of the EM terrain-conductivity equipment; results differ 

in that EM logging provides detailed information on vertical changes in formation conductivity. The EM probe 

contains three coils; one for transmitting an electromagnetic field and two for receiving an induced, or secondary, magnetic field (McNeill, 1986). The transmitted 

electromagnetic field, or primary field, induces a flow of 

eddy currents in the material in and around the borehole. 

These currents induce a secondary magnetic field that is 

received by and causes an induced voltage in the 

receiver coil. The electrical conductivity of the rock and 

water outside the borehole is proportional to the magnitude of the secondary magnetic field received. The 

second receiver coil in the probe is used to negate the 

effect of the borehole and borehole fluids on instrument 

response.

The transmitter coil for the equipment used in this 

investigation transmits at about 39 kHz and has two 

receiver coils spaced 14 and 20 in. from the transmitter 

(McNeill, 1986). This coil configuration gives a maximum instrument response from material about 1 ft from 

the probe and ensures that the instrument responds to 

material beyond the area disturbed by drilling processes 

or borehole fluids in a 4- to 6-inch-diameter borehole 

(McNeill, 1986). A thickness of about 13 ft is required 

to produce a full instrument response so that the conductivity of the unit can be accurately determined (Taylor 

and others, 1989). A layer less than 1.6 ft thick can be 

detected if the conductivity contrast between it and the 

adjacent units is large; however, determination of layer 

thickness and conductivity is not possible (Taylor and 

others, 1989).

An induction log can be used in an uncased borehole or in wells with nonmetallic casing, such as PVC, 

2-inch diameter or greater. The induction log is ineffective in a metal-cased well. Metal in or near the borehole,

12 Hydrogeoiogy, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills In Bristol, Vermont
73'06' 73'04'30"

44'08'30'

44-07'30"

__»v / ' i /,, s* . -~ / v . ~^s ^

« :*//- W\319 "lAt2'BR-1^= r.^ v_ o i - ^^>~BR-2v\ ee-e / i-^--~~=r>"^

^RHmJ Va^^'BplVfe \.4=i^>309 X r^

Base from U.S. Geological Survey

Bristol, Vt.. 1963; South Mountain, Vt., 1963;

1:24,000

Figure 5. Locations of observation wells.

400 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Methods of Study 13
such as a steel well protector used at the surface or metal 

fragments from a drill bit, will show distinctly on the 

induction log as a sharply spiked positive or negative 

response trace that may go beyond normal scale.

Natural-Gamma-Radiation Logs

Gamma logs are used in ground-water studies for 

identification and correlation of lithology. The gamma 

log measures the total gamma radiation, measured in 

counts per second, detected in a borehole within a 

selected energy range. Gamma-emitting radioisotopes 

are natural products of uranium- and thorium-decay 

series and potassium-40. Uranium and thorium are concentrated in most clays by the processes of adsorption 

and ion exchange (Keys, 1988). Potassium is abundant 

in some feldspar and mica that decompose to clay (Keys, 

1988). Therefore, fine-grained detrital sediments that are 

rich in clay are generally more radioactive than quartz 

sand or carbonate rocks and can be readily distinguished 

from quartz sand or carbonate rocks by use of a gamma 

log.

A gamma log can be used in uncased boreholes and 

in PVC or steel-cased wells because gamma radiation 

will penetrate most casings. A steel casing, however, 

will attenuate gamma penetration slightly.

Aquifer Tests

Two aquifer tests, slug and specific capacity, were 

used in the study to determine aquifer characteristics. 

During a slug test, the water level in a well is raised or 

lowered rapidly and the water-level response is measured. During a specific-capacity test, water is withdrawn at a constant rate from a well and the response of 

the water level is measured. Slug tests were done at 28 

observation wells and specific-capacity tests were done 

at 5 wells, results are given in appendix 5.

The slug-test method used in this study is described 

by Prosser (1981). In practice, the well casing is sealed 

and pressurized with air to displace the water column. 

Once the aquifer has stabilized to the increased pressure, 

the pressure is released instantly by a ball valve and the 

water-level change to initial conditions is digitally 

recorded with an electronic pressure transducer. A 

digital-data recorder collects data at intervals of less 

than 1 second. Slug-test data that form smooth response 

curves can be obtained in less than 1 minute from aquifer materials where the hydraulic conductivity is high. 

An example curve showing a rapid slug-test response 

obtained by this method is shown in figure 6.

At some wells, it was difficult to adequately pressurize the casing to use the slug-test method described 

by Prosser (1981) because the well screens extended

1

Q 

I

5

5

LU_l

CC

1

uj 4

2

W-339

50 100 

TIME, IN SECONDS

150 200 250

Figure 6. Typical slug-test response curve.

14 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills In Bristol, Vermont
above the water table and or the depth to water was too 

great. If the depth to water is great, there are more PVC 

joints from which air can escape than if water is nearer 

to land surface. Under such circumstances, a weight was 

used to displace the water level. In this type of slug test, 

the change in water level is measured when the weight 

is dropped into the well and the level has stabilized, and 

then again after the weight was removed from the well. 

Use of a weight (or, similarly, a slug of water) may not 

produce accurate results because the initiation of the 

slug test is not instantaneous, the test response may 

occur as the weight is dropped or withdrawn, or the 

weight or slug of water may be too small to create an 

adequate water-level change.

Slug-test data were analyzed according to the 

method presented by Cooper and others (1967). Type 

curves for instantaneous head change in a well of finite 

diameter (Cooper and others, 1967) can be used to calculate transmissivity at a well screen. According to the 

method of Cooper and others (1967), dimensionless 

head (instantaneous head change divided by the maximum head change) is plotted with log time from the first 

head change. An example of a dimensionless headchange curve for a typical slug test (fig. 6) is shown in 

figure 7. Calculation of an aquifer storage coefficient by 

this method is possible, but the resulting value is 

probably not accurate (Cooper and others, 1967).

However, storage coefficient can be estimated to an 

order of magnitude from grain-size data. This estimate 

subsequently allows the use of the appropriate type 

curve from Cooper and others (1967) to calculate the 

transmissivity of the screen zone.

Where slug tests could not be used, the transmissivity of selected wells was estimated from specific-capacity tests by use of the method of Theis and others (1963). 

Estimates of transmissivity by this method are only 

approximate but are considered to be reasonable for a 

sufficiently long test (at least a few hours). However, 

specific capacity (discharge divided by drawdown) is 

affected by well construction, well performance, and 

pump capacity; deficiencies in any of these can reduce 

the estimated transmissivity.

Streamflow Measurement

Streamflow was measured at nine stations on the 

New Haven River and at all the tributary streams that 

enter and leave the study area. Measurement stations are 

shown on figure 8 with the exception of site 0 (0.5 mi 

east of the study area on State Route 17 on the New 

Haven River) and sites 20 through 22, which drain 

directly off South Mountain (1 mi south of the study 

area). Streamflow was measured by use of standard or 

pygmy current-flow meters on the New Haven River and

Q LU LU 3

§ Q

LU S

I ^

o CD

o S

LU I

1.0

0.8

0.6

5 0.4

0.2

W-339

0.1 10 

TIME, IN SECONDS

100 1,000

Figure 7. Typical dimensionless head-change curve.

Methods of Study 15
73'06' 73'04'30"

44'08'30"

44'07'30"

GAINING STREAM REACH 

iiiiiiiiiiiiiin LOSING STREAM REACH

STREAM REACH WITH LESS 

THAN 10 PERCENT CHANGE 

IN FLOW

AS-8 STREAMFLOW-MEASUREMENT 

SITE AND NUMBER

Base from U.S. Geological Survey

Bristol, Vt., 1963; South Mountain, Vt., 1963

1,000 i

2,000 FEET

200 400 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 8. Locations of streamflow-measurement sites and gaining and losing stream 

reaches.

16 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
on tributaries according to the methods described by 

Rantz and others (1982a). Tributaries with small streamflows (less than 1 ftVs) were measured by use of v-notch 

weirs and Parshall flumes as described by Rantz and 

others (1982b). At measurement stations 20 through 22, 

flow from South Mountain was measured by use of a 

calibrated bucket and stopwatch.

The flow measurements are summarized in table 3. 

Measurement sites listed in table 3 are designated as 

having either streamflow into (in), or out of (out) the 

study area, or as a site where flow was within (») the 

stream-aquifer system. The net streamflow gain, shown 

in table 3, is calculated by adding all streamflow into the

study area (in) and subtracting all streamflow out of the 

study area (out). Sites 0, 20, 21, and 22 are outside the 

study area but were measured to help quantify and 

analyze runoff from the Green Mountains.

Ground-Water-Flow Modeling

A numerical ground-water-flow model can be used 

to simulate the flow of water in an aquifer under steadystate or transient conditions. Development of a groundwater-flow model requires that all fluxes into and out of 

the system and all aquifer characteristics be quantified. 

Many solutions to modeled flow systems are not unique; 

that is, various combinations of input parameters can fit

Table 3. Streamflow measured from January-July 1991 in Bristol, Vermont

[All data measured in cubic feet per second; in, out, and » designates streamflow into, out of, or within the stream-aquifer system at the 

study area. <, actual value is less than value shown; , no measurements]

Site 

No. 

(fig- 8)

0

1

2

3

4a

4b

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

Instantaneous streamflow for selected

01/15 03/27 05/21

149 74.8

95.4

79.6

146 84.4

83.4

<01

2.98

0

0

<01

.08

.05

2.15

.26

..

(11.5)

0.09 - 3 .12

.08 -- 3 .04

3 .08

sampling dates

07/03

18.9

21.6

20.9

24.8

23.9

21.1

26.5

26.1

0

2.31

0

0

0

.08

.07

.01

.11

.05

0

(6.9)

0

0

.02

07/11

31.4

29.2

26.9

34.2

0

0

0

0

-

Relation of 

stream-aquifer 

system

(')

In

»

»

»

»

»

»

Out

In

Out

»

»

»

»

»

»

»

Out

In

In

(Net out of the

study area)

( \

( \

(4)

Upstream from study area.

2 Estimated flow.

3 5/02/91 measurement date.

4 Not in study-area drainage.

Methods of Study 17
together reasonably and produce acceptable results. 

During the development of a model, a hypothesis 

describing the conceptual flow system is tested and 

refined to improve understanding of the flow system. 

Reilly and others (1987) discuss the use of simulation to 

aid solute-transport studies and present a framework for 

a study of physical mechanisms of transport. The 

ground-water-flow model consists of the numerical data 

sets that represent the conceptual model of the groundwater aquifer system. These data sets become input to 

the computer program known as the numerical model.

The finite-difference numerical model developed 

by McDonald and Harbaugh (1988), MODFLOW, was 

used to simulate ground-water flow in the aquifer. 

Results of simulated water levels are given in appendix 

6. MODFLOW consists of a main program and a set of 

independent subroutines or "packages." Each package 

handles a specific feature of the hydrologic system, such 

as wells, recharge, or rivers. This program can be used 

to simulate three-dimensional flow and to estimate flow 

at all six faces of rectangular cells that represent parts of 

the modeled system.

A stream-routing subroutine (Prudic, 1989) was 

used to simulate stream-aquifer interactions. This subroutine can account for streamflow volume in the simulated stream and allows a stream to dry up if the water 

level in the aquifer declines below the streambed.

A particle-tracking program developed by Pollock 

(1989), MODPATH, was used to compute pathlines of 

ground-water flow. MODPATH is designed as a postprocessor to MODFLOW; MODFLOW output files are 

used directly in computational schemes. MODPATH 

uses a semianalytical particle-tracking scheme to compute the path of a particle through the simulated aquifer 

from any given starting point in a model cell to its point 

of discharge.

Ground-Water-Quality Sampling

Ground-water samples were collected semiannually from autumn 1990 through autumn 1991 by VANR 

from as many monitoring wells as possible after development. A few samples were collected at dates between 

the semiannual samples. Additional monitoring wells 

were added throughout the study; therefore, the number 

of wells sampled increased continuously to the end of 

the study. Although investigation of the bedrock aquifer 

was outside the scope of this study, the VANR routinely 

collected water-quality samples from at least five

bedrock domestic wells near the landfills when the semiannual samples were collected. Results of laboratory 

and field analysis are given in appendix 7. Before samples were collected, three or more casing volumes were 

removed from each well, if possible, to introduce representative formation water into the casing. Because some 

wells were screened in low-yield till or very fine-grained 

sediments, it was not always possible to remove three 

casing volumes of water; however at least one casing 

volume was removed before any sampling.

Most of the wells were installed with dedicated 

polyethylene-bailer or polyethylene-tubing samplers to 

minimize the potential of cross contamination or contamination by cleaning agents used on a nondedicated 

sampler. The polyethylene-tubing sampler was equipped 

with a one-way valve at the base of the tubing; water was 

displaced upward by moving the tubing up and down. 

This tubing was used for collecting samples from wells 

where a large amount of water was in the well or the 

depth to water was great. Polyethylene-tubing samplers 

were most efficient where the amount of water in the 

well was greater than a few feet and when recovery was 

rapid. In wells containing only a few feet of water or 

less, samples were collected with dedicated bailers. 

When necessary, wells were purged by use of a bailer or 

submersible pump, and samples were subsequently 

collected with a bailer.

Samples were analyzed at the Vermont Department 

of Environmental Conservation (VDEC) Laboratory 

in Waterbury, Vt. Analyses included pH, specific conductance, sulfate (804), arsenic, barium, cadmium, calcium, chloride, chromium, copper, iron, lead, 

magnesium, manganese, nickel, potassium, selenium, 

silver, sodium, zinc, and 36 volatile organic compounds 

(VOC's). The VDEC Laboratory participated 

in the Standard Reference Water Sample Program, a 

quality-assurance program administered by the USGS 

(Long and Farrar, 1992).

HYDROGEOLOGY

The hydrogeologic setting of Bristol, Vt., is characterized by unconsolidated glacial deposits in contact 

with the Green Mountains. The geology of the bedrock 

and unconsolidated deposits are briefly described in the 

following report sections. Aquifer characteristics and 

ground-water flow in the glacial aquifers are described 

in detail in the report section "Glacial Aquifers."

18 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
Geology Unconsolidated Deposits

The prominent geologic features in the study area 

(fig. 9) are the west face of the Green Mountains (Hogback and South Mountains), which form a north-south 

boundary rising more than 1,500 ft above the study area, 

and a gently sloping terrace of unconsolidated material. 

This unconsolidated material is believed to be the surface of a glacial delta that formed by glacial meltwater 

flowing westward from the Green Mountains. The upper 

surface of the delta is more than 150 ft above the valley 

floor (fig. 9).

Bedrock

The bedrock geology of the study area (fig. 9) is 

characterized by the Cheshire Quartzite of Cambrian 

age of Hogback and South Mountains to the east and 

the Cambrian Dunham Dolomite to the west (Doll and 

others, 1961; Stewart, 1973). Bedrock bedding and 

cleavage strike north-south and dip vertically or 

steeply westward. The contact between these units is 

probably beneath the western edge of the delta. Cheshire 

Quartzite crops out west of Burpee Road and north of 

Pank Road just outside the study area. Quartzite and 

dolomite may interfinger by folding and faulting 

beneath the study area (Stewart Clark, U.S. Geological 

Survey, oral commun., 1991). Quartzite is locally massive and resistant to physical and chemical weathering 

and erosion. Dolomite is more susceptible to weathering 

and erosion than the quartzite. The dolomite, a carbonate 

rock, is dissolved by acidic water and contains fractures 

enlarged by solution weathering.

A map of the bedrock surface (fig. 10) shows considerable relief. The bedrock-surface altitude ranges 

from slightly higher than 300 ft above sea level at the 

southern landfill to higher than 400 ft at the northern 

landfill. A substantial depression or trough in the bedrock surface underlies the Bristol Flats area (fig. 10). A 

bedrock ridge trending north-south (fig. 9) is roughly 

parallel to Vermont route 116 near Bristol Flats, and 

crosses Burpee Road and extends to the north near a 

cemetery. The ridge generally consists of dolomite and 

possibly a quartzite at its base south of Plank Road. The 

ridge forms a westward boundary for the study area but 

is eroded near the pond adjacent to Burpee Road. The 

break in the ridge is most likely an area of predominantly dolomite and is referred to as the "dolomite gap" 

throughout this report. The bedrock surface dips sharply 

west of the ridge to less than 200 ft above sea level 

(fig. 10).

The unconsolidated deposits throughout most of 

the study area consist of coarse-grained deltaic sands 

and gravels (fig. 9). The deltaic deposits are bounded by 

fine- to coarse-grained glaciolacustrine deposits and till 

(fig. 9). Representative geologic sections (A-A', B-B", 

and C-C') showing the stratigraphy of glacial deposits 

are in figures 11 and 12. A sequence of glaciofluvial 

sand, gravel, and boulders more than 200 ft thick 

(figs. 11 and 12) represent a delta built into proglacial 

Lake Vermont, which formed as retreating continental 

ice blocked the northward drainage of the Champlain 

Valley (Chapman, 1937; Stewart and MacLintock, 1969; 

Wagner, 1972). Bedding structures typical of deltaic 

sequences can be seen in the exposed west flank of the 

delta. Discontinuous silt and clay lenses are present 

locally in the deltaic sequence (W-337, appendix 4). 

Glaciolacustrine deposits consisting of an alternating 

sequence of silt, clay, sand, and gravel are between the 

delta and the ridge along Burpee Road (sections A-A 

andB-B", fig. 11) and in the Bristol Flats area. Throughout the valley floor, a clay layer is found at the land surface above the water table. Below the surficial clay, a 

medium- to coarse-grained sand unit is found in the 

gravel pits along the west face of the delta. This sand 

forms part of the upper glacial aquifer (discussed later).

A saturated silt, sand, and clay layer, ranging in 

thickness from about 5 ft (W-324, appendix 4) to greater 

than 15 ft (W-322, appendix 4), lies below the upper 

sand unit (section C-C', fig. 12). The clay in this unit is 

present as lenses, a few inches thick, between lenses of 

fine to medium sand with some silt. In lithologic logs, 

the thickness of this silt, sand, and clay unit is not readily 

distinguished from the unit below without the aid of the 

borehole geophysical logs shown in appendix 4. This 

silt, sand, and clay constitutes a confining unit and 

appears to be continuous west and south of the private 

landfill (section B-B" , fig. 11) from approximately the 

middle of the study area south into Bristol Rats. The unit 

was not found immediately north of the private landfill 

(well W-304) but it was found farther to the north in the 

logs of wells MW-101, MW-102d, W-309, and W-310. 

The easternmost observations of this unit (at the 

private landfill) are in the logs of wells W-308 and 

W -504 (MW-4; Marshfield Engineering Services, 

1979). The unit is either discontinuous near the eastern 

side of the landfill or may have been excavated before 

the landfill was created. Drill cuttings from well W-332, 

installed east of the landfill, did not appear to contain the

Hydrogeology 19
73'06' 73"04'30"

44"08'30"

44°07'30"

Base from U.S. Geological Survey 0

Bristol, Vt., 1963; South Mountain, Vt., 1963: \-

1:24,000 0

1,000

i

2,000 FEET

200 400 METERS

EXPLANATION

DURHAM DOLOMITE 

CHESHIRE QUARTZITE 

TILL-COVERED BEDROCK 

DELTAIC DEPOSITS 

GLACIOLACUSTRINE DEPOSITS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 9. Generalized surficial geology in the study area.

20 Hydrogedogy, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
73°06' 73"04'30"

44-08'30'

44'07'30"

Buntee 

i-Rbad 400 BEDROCK-SURFACE CONTOURShows altitude of bedrock surface. 

Dashed where inferred. Interval is 

50 feet. Datum is sea level. -^\^ V ItiiiiilflROii. M tttittmt «« - llin-.' * it.

f/W V?x® /' I ' \~'~2&£,

Base from U.S. Geological Survey 0

Bristol, Vt., 1963; South Mountain, Vt., 1963; U

1:24,000 A

1,000

i

2,000 FEET

200 400 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 10. Altitude of the bedrock surface in the study area.

Hydrogeology 21
e

FEET 

600-i

550- 

500- 

450- 

400- 

350- 

300- 

250-

B' B"

Landfill

gio §:°

in 

o

CO

 Clay, silt, 

>gj and sand,

250

, i

500 FEET

i ' r

0 50 100 150 METERS

VERTICAL EXAGGERATION X 2.6 

DATUM IS SEA LEVEL

300-

200

500 1,000 FEET

0 100 200 300 METERS

VERTICAL EXAGGERATION X 5 

DATUM IS SEA LEVEL

EXPLANATION

 CONTACT-Approximately located. Dashed where inferred 

W"|18 WELL AND IDENTIFICATION NUMBER

Figure 11. Hydrogeologic sections A-A' and B-B. (Lines of section shown In fig. 5)"

22 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
FEET 

500 1 Railroad

400-

300-

200-

100

- . - » ';-Sand and ". --'. .' .* "»'* gravel ' .'

- ' -o - t ' « ' * ' '

500

100 200

1,000 FEET

_I 

T

300 METERS

VERTICAL EXAGGERATION X 5 

DATUM IS SEA LEVEL

EXPLANATION

CONTACT-Approximately located. 

Dashed where inferred

W-330 WELL AND IDENTIFICATION 

NUMBER

Figure 12. Hydrogeologic section C-C. (Line of section shown in figure 5)

silt, sand, and clay unit; however, a geophysical log of 

well W-332 would be necessary for positive 

identification of clay at this location.

Below the sand, silt, and clay confining unit is a 

fine- to medium-grained sand unit, with some silt that 

extends from the private landfill southward into Bristol 

Flats (section C-C', fig. 12). The materials composing 

this unit are very similar to the sand and silt in the confining unit but without the clay lenses. Drillers' logs 

indicate that this lower unit becomes coarser and the 

amount of gravel increases towards the Bristol Flats 

area. Glacial till, a dense mixture of silt, clay, sand, and

angular to subrounded pebbles, directly overlies bedrock throughout most of the study area. Till crops out at 

the surface, north of the delta, near Plank Road. Till is 

not present in all areas and can range in composition 

from predominantly clay to predominantly coarse sand.

Glacial Aquifers

The upper and lower sand units, previously 

described, constitute an upper glacial aquifer under 

water-table conditions and a lower glacial, generally 

confined aquifer (figs. 11 and 12). The upper glacial

Hydrogeology 23
water-table aquifer herein referred to as the upper 

aquifer is extensive and generally consists of mediumto coarse-grained sands and gravel. The lower glacial 

aquifer herein referred to as the lower aquifer is 

found predominantly west and south of the delta and 

generally consists of fine-grained sands. The confining 

unit that separates the two aquifers pinches out in the 

delta in an eastward direction, and is herein considered 

part of the lower aquifer. The lower aquifer extends into 

the delta where it grades into coarse material and is not 

distinguishable from the upper aquifer. Domestic well 

logs from the Bristol Flats area indicate that the lower 

aquifer consists of medium- to coarse-grained sand and 

gravel.

Aquifer Characteristics

Aquifer characteristics were determined by interpretation of drillers' logs, grain-size analyses, borehole 

geophysical logs, and aquifer tests at observation wells. 

Borehole geophysical logs were used to enhance the 

interpretation of drillers' logs and to aid in the delineation of upper and lower aquifers. Grain-size analysis of 

split-spoon samples from borings drilled during this 

investigation were used to characterize material types 

and the degree of sorting. Results from aquifer tests 

were compared to lithologic material types obtained at 

the same screen zones so that estimated hydraulic 

conductivities could be extrapolated and applied to other 

areas of similar lithology.

Estimated hydraulic conductivities and lithologic 

descriptions of material at well screens where aquifer 

tests were conducted are listed in appendix 5. The correlation of estimated hydraulic conductivities and associated material type depends not only on the formation at 

the screen zone but also on the response-test method and 

material description. For example, results from a slug 

test are representative of a small volume of aquifer material, whereas a specific-capacity test yields hydraulic 

conductivities that are representative of a larger aquifer 

volume.

Estimated horizontal hydraulic conductivity and 

mean grain size of aquifer materials are summarized in 

table 4. Similar hydraulic conductivities have been estimated for sand and gravel aquifers in southern New 

Hampshire by use of an empirical grain-size relation 

developed by Olney (1983) and supported by aquifertest data (Harte and Mack, 1992). The horizontal 

hydraulic conductivities in table 4 are generalized

Table 4. Estimated horizontal hydraulic 

conductivity of aquifer materials determined from 

slug and specific capacity tests, predominant 

material type, and mean grain size in 

Bristol, Vermont

[mm, millimeter; ft/d, foot per day; <, actual value is less than value 

shown; >, actual value is greater than value shown]

Material 

type

Till ........................

Sand, fine. .............

Sand, coarse..........

Mean 

grain 

size 

(mm)

.... <0.01-0.5

.1

.3

.7

2.0-4.0

Estimated horizontal 

hydraulic conductivity 

(ft/d)

Median

1 

10 

30 

120 

250

Range

<l-4 

1-30 

10-60 

60-200 

150->250

estimates grouped by material types. The range in 

hydraulic conductivity for glacial sand and gravel is 

considerable and varies with the degree of sorting.

The sand and gravel of the upper aquifer and the 

delta is highly permeable. Median horizontal hydraulic 

conductivities were about 100 ft/d and ranged from 10 to 

greater than 200 ft/d (table 4). Interpretation of an aquifer test of a well screened in a similar sand and gravel 

aquifer, 8 mi south of the study area on the west flank of 

the Green Mountains, resulted in a hydraulic conductivity of 95 ft/d (D.L. Maher Co., 1985). The fine to 

medium sands of the lower aquifer have a hydraulic conductivity that ranges from 1 to 30 ft/d. Glacial till generally has a hydraulic conductivity of less than 4 ft/d; the 

median is about 1 ft/d. Till that has a predominantly 

coarse sandy matrix has a hydraulic conductivity of 3 to 

4 ft/d. Silt and clay can be expected to have an hydraulic 

conductivity less than 0.1 ft/d. At a well (W-323) 

screened in the lower confining unit (sand, silt, and 

clay), the hydraulic conductivity was 30 ft/d as estimated from results of the slug-test method. The relatively high hydraulic conductivity is a result of 

preferential flow through sand lenses, which function as 

horizontal pathways within the confining unit, and is 

the basis for inclusion of this unit as part of the lower 

aquifer.

No data were available to estimate the vertical 

hydraulic conductivities of both aquifers; however, 

values of one-tenth the horizontal hydraulic conductivity are assumed to be reasonable. Other investigators 

who have studied glacial sand and gravel aquifers in the 

Northeast have found vertical hydraulic conductivity to

24 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
be approximately one-tenth (Childress and others, 1991; 

Harte and Mack, 1992), one-tenth to one sixtieth 

(Getzen, 1977) and one-fifth (de Lima and Olimpio, 

1989) of the horizontal hydraulic conductivity. 

The hydraulic conductivity of the confining unit is 

vertically anisotropic; the horizontal hydraulic conductivity is probably 100 to 1,000 times greater than the 

vertical hydraulic conductivity. The effective horizontal 

hydraulic conductivity of the confining unit is strongly 

affected by sand and pebble lenses. The vertical 

hydraulic conductivity of the confining unit is affected 

by the hydraulic conductivity of the clay. Clay has an 

hydraulic conductivity of about IxlO'5 to IxlO'7 ft/d 

(Freeze and Cherry, 1979). Wexler (1988b) summarized 

vertical hydraulic conductivities reported for a clay and 

sand confining unit on Long Island as ranging from 

7.0 x 10'2 to 2.2 x 10-5 ft/d. Childress and others (1991) 

used 5 x 10'3 ft/d as the vertical hydraulic conductivity 

for a clay unit in Ohio.

Ground-Water-Flow System

Water levels were measured monthly in the observation-well network and at a USGS observation well 8 

mi south of the study area. Water-level measurements 

were used to determine fluctuations in ground-water 

levels and general directions of ground-water flow. An 

estimation of the long-term average ground-water level 

is necessary for use in ground-water-flow simulation. 

Discharge measurements along the New Haven River 

and on tributary streams in the area were used to identify 

gaining and losing stream reaches and to estimate 

recharge.

Ground-Water Levels and Flow Directions

Fluctuations in ground-water levels are caused 

principally by variations in recharge to and discharge 

from the aquifer and by variations in evapotranspiration. 

Water levels from an observation well (MOW-11) open 

to the bedrock and in a similar physiographic area 8 mi 

south of the study area were used to identify long-term 

and seasonal trends in water levels in the bedrock and 

glacial aquifers in the region (fig. 13) (David Butterfield, 

Vermont Agency of Natural Resources, written 

commun., 1992). Average monthly water levels, 

monthly precipitation, and long-term average monthly 

precipitation for August 1990 through November 1991 

are included in figure 13.

A slight rise in the water table from snowmelt 

recharge and increased precipitation was observed in 

March 1991. Recharge is reduced by the onset of evapotranspiration during the growing season; however, water 

levels decline as aquifer drainage exceeds recharge 

rates. The average annual range in water level at this 

well is 4 ft; from November 1990 through May 1991, the 

water level was the most stable and only slightly above 

the long-term average annual level. In April 1991, the 

water level was about 1 foot above the long-term average (1981-91) but below the monthly average water 

level (fig. 13); therefore, the April 1991 water level is 

similar to a long-term average water level. Water levels 

in May 1991 matched the long-term average level; however, water levels in wells in Bristol were generally 

highest for the year in May. Average precipitation in 

April approximates the long-term average precipitation 

(fig. 13).

The annual range in ground-water-level 

fluctuations in the aquifers in Bristol was from less than 

2 ft to nearly 5 ft and was generally 2 to 3 ft throughout 

the year. Smaller fluctuations were observed at wells in 

coarse-grained sediments where water was far 

below land surface, such as in the delta. For example, 

well W-318 (fig. 14), which had a water-level range of 

only 1.2 ft, is set in coarse-grained sand, and depth to 

water was 100 ft. Under such conditions, precipitation 

filters slowly through the thick unsaturated zone, thus 

smoothing out pulses of recharge. Ground-water-level 

fluctuations were greater at wells screened in finegrained materials, such as at wells W-305 and W-306 

(fig. 14). High water levels were observed in late autumn

1990. when evapotranspiration was reduced and 

recharge increased because of increased precipitation, 

and generally were the highest in May 1991 because of 

increased precipitation and snowmelt. Low water levels 

were observed during summer 1991 when precipitation 

was below normal. The ground-water-flow system is 

probably never in steady-state condition (no change 

in storage); however, the period of least change and 

close-to-average water levels during the study was April

1991.

A water-table map for April 18, 1991, a period of 

approximately average water levels, is shown in 

figure 15. The potentiometric surface of the lower aquifer is similar to but higher than the water-table surface. 

Ground-water flow throughout the study area is predominantly from northeast to southwest. At the delta face 

southwest of the municipal landfill, a steep head gradient

Hydrogeology 25
I

o

EXPLANATION

MONTHLY PRECIPITATION

MONTHLY AVERAGE PRECIPITATION

MONTHLY AVERAGE WATER LEVEL

MONTHLY WATER LEVEL

AVERAGE WATER LEVEL FOR THE YEARS 1981-1991

AVERAGE MONTHLY PRECIPITATION

Figure 13. Hydrographs showing monthly water level in well MGW-11 at Middlebury 

and precipitation at Burlington, Vermont.

results from a reduction in transmissivity caused by a 

facies change to finer grained sediments and by a reduction in aquifer thickness. At the private landfill, a 

ground-water-flow divide at the south side of the landfill 

results in a somewhat radial ground-water-flow pattern. 

Ground water flows westward, discharging to a small 

brook and through the dolomite gap a few hundred feet 

west of the landfill; ground water also flows southward 

to the aquifers at Bristol Flats.

Ground water in the upper aquifer is unconfined. 

Depth to the water table ranges from 10 to 55 ft at the 

private landfill and from 25 to 75 ft at the municipal 

landfill. Whereas the depth to the water table from the 

delta surface is as much as 130 ft, elsewhere, the water 

table near the two landfills emerges as springs at the land 

surface.

Ground water in the lower aquifer is confined; the 

head in this aquifer is generally 2 ft above the watertable surface but has been measured at some wells as 

much as 12 ft above the water-table surface. The saturated thickness of the lower aquifer ranged from 0 to the 

north, where the aquifer pinches out or grades into till, 

to greater than 100 ft in the Bristol Flats area. In the 

delta, no lithologic distinction can be made between the 

upper and lower aquifers. Although the confining unit is 

not continuous, the aquifer in the delta is distinguished 

as an upper and a lower aquifer in this report because of 

the large head differences between these aquifers in 

most locations.

At one well cluster east of the private landfill 

(W-332 and W-333), the head in the lower aquifer was 

12 ft below that of the upper aquifer. It is possible that

26 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
WATER LEVEL IN FEET ABOVE SEA LEVEL

(Q

(D

C 

O

cc

Q

<L

a 

a

o 

CD

Ol

o

CO 

O

w

Z

o

(D 

O

w 

o

Z

Ol 

01

o 

ro 

a.

\* 

\ o>

't c

01 

O

01 05 

Ol O

CO

00

\s

I

D

, , 1 , , i ,

01

o

Ol 

Ol

c

T3 

T3 

CD

o>

o

c? 1

o

Ol

.^ 

o 

o

00

I

JD

C

i
73'06' 73"04'30"

44W30"

44'07'30'

-380- WATER-TABLE CONTOUR- 

 /// / Shows altitude of water

table, April 18,1991. Dashed 

. ,. where inferred. Contour 

<!:/'/, interval is 20 feet. Datum is 

sea level.

"/ -'-^ T^'

Base from U.S. Geological Survey

Bristol, Vt., 1963; South Mountain, Vt., 1963;

1:24,000

1,000

i

2,000 FEET

200 400 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 15. Altitude of water table in Bristol, Vermont, April 18,1991.

26 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
the shallow well (W-333) is either screened in a locally 

perched aquifer or poorly connected to the upper aquifer. 

After well W-333 was pumped, recovery took more than 

8 hours; such a slow recovery was atypical of other wells 

in the area. Wells W-332 and W-333 were installed near 

the end of the study and, because the validity of waterlevel measurements at well W-333 could not be 

confirmed, water levels from this well were not used in 

the study.

Recharge and Discharge

Recharge to the upper aquifer is derived from three 

main sources: infiltration of precipitation directly on the 

aquifer, inflow from upland till or bedrock, and leakage 

from streams that cross the aquifer. Under steady-state 

conditions, recharge by infiltration of precipitation, 

called direct recharge in this report, is equal to the precipitation minus evapotranspiration and surface runoff. 

Surface runoff is usually negligible in areas underlain by 

sand and gravel. Direct recharge, therefore, can be 

approximated as precipitation minus evapotranspiration 

(Lyford and Cohen, 1988). Precipitation measured at a 

gage in Burlington, Vt., 22 mi to the north, was 38.0 in. 

during water year 1991; the long-term annual average is 

33.7 in. The precipitation gage in Burlington, at an altitude of 332 ft, is closer to the altitude of the study area 

(380 to 580 ft) than to the altitude of a gage in Lincoln 

(2,020 ft), about 10 mi southeast of the study area. Longterm average-annual precipitation at the Lincoln gage is 

about 54 in.

In the Northeast, precipitation varies from year to 

year, but annual evapotranspiration remains nearly constant (Lyford and Cohen, 1988). Therefore, if the longterm annual evapotranspiration equals long-term rainfall 

minus long-term streamflow, then long-term annual 

potential recharge should equal long-term annual 

streamflow. On the basis of this method, Lyford and 

Cohen estimated a long-term annual streamflow of 

about 20 in/yr for west-central Vermont. The mean 

streamflow measured in the New Haven River at New 

Haven, 6 mi southwest of the study area, was 220 ftVs, 

or 25 in., in water year 1991 (Kenneth Toppin, U.S. Geological Survey, written commun., 1992). Precipitation in 

water year 1991 was 27 percent above the long-term 

average; therefore, the long-term maximum potential 

recharge probably is about 20 in/yr.

Direct recharge to a stratified-drift aquifer can be 

estimated by the method of Rasmussen and Andreasen 

(1959), where the sum of the water-level rises in a watertable well is multiplied by the specific yield. By this 

method, ongoing recession, or drainage, from the aquifer is accounted for by extending the recession limb 

before recharge and adding the total rise from the 

extended recession. Specific yield of the glacial-aquifer 

sediments in Bristol was assumed to average about 0.30. 

Analysis of hydrographs of water-table wells near the 

landfills (fig. 14) yield estimates of recharge ranging 

from about 12 to 15 in/yr. The lower estimates were 

from hydrographs of wells at sites with a thick unsaturated overburden, such as W-308 and W-318 (fig. 14). At 

such wells, water-table rises and recession limbs in the 

hydrograph could not easily be distinguished. A 

representative recharge for this area during 1991 is 

about 14 in/yr (3.7 x 10'8 ft/s).

Ground-water discharge from the upper and lower 

aquifers occurs as seepage to streams, ground-water 

outflow to adjacent aquifers, and leakage to the underlying bedrock aquifer. Recharge to the upper aquifer 

occurs as leakage from tributary streams that cross the 

aquifer and from overland flow from adjacent bedrock 

and till-covered mountains to the east. Additional 

recharge occurs as upward ground-water flow from the 

bedrock to the lower aquifer. To estimate these fluxes 

and to assess stream-aquifer interactions, streamflow 

was measured during extended periods of little or no 

rainfall in the New Haven River and the tributaries 

entering or leaving the aquifer.

The net streamflow gain in the part of the New 

Haven River that crossed the study area was about 

11.5 ft3 /s in May 1991 and 6.9 ft3 /s in July 1991 

(table 3). A streamflow gain of 20 ft3/s (a 26-percent 

increase) in May and 4 ft3/s (a 20-percent increase) in 

July was measured at site S-3 at the face of Hogback and 

South Mountains. Most of the gain was then lost to the 

aquifer (table 3) further downstream. Gains also were 

measured between sites S-5 and S-6 during May and 

July. Streamflow-measurement error was estimated to 

be no more than 5 percent of the measurement. The magnitude of the gains observed, 20 and 26 percent of 

streamflow, are not likely to be accounted for by measurement error or to have been repeatable under different conditions if measurement error was significant. 

Springs with a constant temperature of 8 to 9°C were 

observed in this area of the New Haven River and were 

distinguishable from the river, which had a temperature

Hydrogeology 29
of 21°C in July. The springs were observed throughout 

the year and caused sections of the New Haven River to 

remain uncharacteristically free of ice during winter. 

The glacial aquifer upgradient from this measurement 

site is no more than half a square mile in area and is 

highly unlikely to contribute this amount of water to the 

river. The source of the large gain between S-2 and S-3 

is believed to be ground-water discharge from bedrock, 

in the Hogback and South Mountain upland areas to the 

east (fig. 1), flowing through the glacial aquifer. Precipitation on the mountains is more than 60 percent greater 

than precipitation in the valley that includes the study 

area. Ground-water-flow simulations, discussed in 

"Simulation of Ground-Water-Flow," also indicate that 

recharge other than direct recharge is necessary to cause 

the hydrologic conditions observed.

Because of the steepness of the west flank of the 

Green Mountains in Bristol (fig. 1), very few streams 

flow westward off the mountains to recharge the aquifers 

in and around the study area. These streams in the study 

area, sites S-18 and S-19 (fig. 8) on Hogback Mountain, 

contributed less than 3 percent of the total streamflow 

gains measured in the New Haven River (about 0.4 ftVs 

in May and 0.05 ftVs in July; table 3). Similar streams 

flowing off the west flank of South Mountain immediately south of the study area, S-20, 21, and 22 (fig. 8), 

were measured for comparison. Streamflow in these 

streams generally was less than 1 ftVs at different times 

of the year and virtually zero during low-flow periods 

(table 3).

The small brook upgradient from the municipal 

landfill (fig. 8) flows when the water table is high enough 

to intercept the base of the brook. At its outlet from 

the study area, streamflow in this brook is less than 

1 ftVs most of the year. Most of this brook is usually dry 

during summer when its start-of-flow is generally near 

site S-15.

The tributary flowing south off Bristol Flats (S-9, 

fig. 8) is sustained by the ground-water discharge from 

the aquifer at Bristol Flats, and streamflow is fairly constant throughout the year. In 1991, streamflow was 

3.0 ft3/s in the spring and 2.3 ft3/s during the summer 

(table 3).

Ground water also discharges as ground-water outflow to adjacent aquifers. Ground-water outflow is 

primarily at two locations: at the gap in the dolomite

ridge west of the private landfill and through the sand 

and gravel aquifer at Bristol Rats. Ground-water inflows 

and outflows were calculated from Darcy's law:

= KiA, (1)

where

Q is discharge,

K is hydraulic conductivity,

i is hydraulic gradient, and

A is area through which discharge occurs.

Ground-water outflow at the gap in the dolomite 

ridge was calculated to be 1.3 tf/s. The mean hydraulic 

conductivity of the glacial sediments was about 80 ft/d, 

the average hydraulic gradient was 0.015, and the crosssectional area was about 95,000 ft2 . Ground-water 

outflow at the study area boundary at Bristol Rats was 

estimated to be 5 ft3/s. The hydraulic conductivity of the 

glacial sediments (estimated from drillers' logs) was 

100 ft/d, the average hydraulic gradient was 0.008, and 

the cross-sectional area was about 500,000 ft2 .

At the east boundary of the aquifer, ground water 

enters where the New Haven River flows between Hogback and South Mountains. The hydraulic gradient was 

estimated to be similar to the gradient of the river surface at this location (0.011), the horizontal hydraulic 

conductivity was estimated to be 175 ft/d, and the crosssectional saturated area was about 75,000 ft2 . Groundwater inflow at the east boundary of the aquifer is about 

1.7 ftVs.

The total water budget for spring 1991 is summarized in table 5. The remainder of all inflow minus outflow is assumed to be equal to upward leakage from 

bedrock to the overlying glacial aquifer. Some ground 

water probably discharges to the underlying bedrock; 

however, because hydraulic gradients are mostly 

upward throughout the study area, this discharge is 

likely to be small. About 0.27 Mgal/d (0.4 ftVs) of 

recharge from domestic leach field systems enters the 

aquifer at the delta (Scott Powell, Bristol Water Department, oral commun., 1991). This water is added to the 

budget because this water originates from outside the 

study area. Most of the ground water ultimately 

discharges as streamflow (table 5).

30 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
Table 5. Water budget for the study area for April 

and May 1991 for Bristol, Vermont

[ft3/s, cubic foot per second; Mgal/d, million gallons per day; in/yr, 

inch per year]

Water-budget component

Inflows: 

Infiltration of precipitation 

(14 in/yr). 

Ground-water flow..........................

Leach field.......................................

Outflows: 

Net streamflow................................

Ground-water flow..........................

Net difference 

(bedrock leakage inflow).

ftVs

1.8 

1.7

.4

11.5

6.3

13.9

Rate

Mgal/d

1.2 

1.1

.3

7.4

4.1

8.9

SIMULATION OF GROUND-WATER FLOW

Ground-water flow was simulated in the study area 

to further the understanding of the local and regional 

ground-water-flow system. A particle-tracking simulation provided detailed analysis and understanding of the 

local ground-water-flow system underlying the two 

landfills.

Simulation of ground-water flow at the two landfills is presented by descriptions of the conceptual model 

and development of the ground-water-flow model, the 

model grid and boundary conditions, and selection of 

model-input parameters. Accuracy and use of the model 

is described by a calibration and sensitivity analysis, 

ground-water-flow simulation, and model appraisal.

Description of Conceptual and 

Numerical Models

The conceptual model of the ground-water-flow 

system, for the purposes of the numerical model, is 

a simplified representation that integrates all known features of the system and characterizes the aquifer into 

similar hydrogeologic units by means of assigned representative parameters. The conceptual model represents 

the complex hydrologic and geologic environments in 

nature. In a conceptual model, the appropriate level of 

hydrologic detail depends on the purpose and scope of 

the investigation, the amount and quality of the data, and 

the sensitivity of the numerical model to increases in the 

level of detail. A two-layer conceptual model of the 

aquifer system requires boundary conditions that are

simplifications of the hydrogeologic system. The effects 

of simplifying assumptions on the ground-water-flow 

model differ with numerical model complexity and 

application. Useful discussions of simplifying 

assumptions are provided by Morrissey (1983), deLima 

and Olimpio (1989), and Mack (1991). The boundaries 

in the aquifer system at Bristol and the effects of the 

simplifications applied to the model developed are 

discussed in the following paragraphs.

The glacial delta and outlying areas are described 

by a two-aquifer system: an upper coarse-grained aquifer under unconfined conditions and a lower, fine- to 

coarse-grained aquifer under confined conditions, which 

are separated in places by a sand, silt, and clay confining 

unit. The conceptual model of this system is based on the 

geologic sections shown in figures 11 and 12. The dominant ground-water-flow paths are in the upper and 

lower aquifers, although horizontal flow occurs in the 

sand, silt, and clay confining unit. The low vertical 

hydraulic conductivity of the confining unit, although 

not quantitatively measured, is evident by the large vertical gradient between the upper and lower aquifers. The 

primary effect of the confining unit is the restriction of 

vertical flow. Because the confining unit contains significant thicknesses of sand, which have hydraulic characteristics similar to those of the lower aquifer; flow in the 

confining unit was simulated as part of the lower aquifer; 

that is, the confining unit itself was not modeled as a separate layer. The thickness of the confining unit was 

incorporated into the lower aquifer model layer, and the 

confining effects of this unit were simulated by a low 

vertical hydraulic conductivity to restrict upward flow.

Model Grid and Boundary Conditions

A rectangular finite-difference model grid was 

superimposed over a map of the study area to discretize 

the conceptual model into individual model cells. The 

outline of the active area for the upper model layer is 

shown in figure 16. The model grid is divided into cells 

that range in size from 50 by 50 ft to 400 by 500 ft 

(fig. 16). Because of the steep valley walls throughout 

most of the study area, the lower model layer represents 

nearly the same area as the upper layer. The north and 

southwest model boundaries for the lower layer consist 

of a few less rows and columns of cells. Fine discretization was used for the ground-water-flow simulation of 

the two landfills not only because these are areas of 

interest but also because the density of data is greater for 

the landfills than for the surrounding areas. The finest

Simulation of Ground-Water Flow 31
73'06' 73W30"

44'08'30"

Private 

La

44°07'30"

SIMULATED GROUND-WATER 

FLUX FROM BEDROCK 

AQUIFER

SIMULATED GENERAL HEAD 

SIMULATED STREAM

Base from U.S. Geological Survey

Bristol, Vt., 1963; South Mountain, Vt.. 1963:

1:24,000 scale

1,000

i

2,000 FEET

I i I ' I

0 200 400 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 16. Location of model grid and cell types for the aquifer system in Bristol, 

Vermont.

32 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
discretization (50 by 50 ft) was used southwest of the 

municipal landfill because of the high hydraulic 

gradients near the face of the delta (fig. 16). Coarse 

discretization was used in the eastern and southern 

model areas (fig. 16), where the objective of the model 

is to simulate regional boundary fluxes to the glacial 

aquifers and where the hydraulic gradient is the lowest.

The upper boundary of the model is the unconfined 

calculated head surface (water table), which is simulated 

as a specified-flux (recharge) boundary. The New Haven 

River and small streams in the model are simulated as 

head-dependent-flux boundaries.

The lower boundary of the model is the bedrock 

surface (fig. 10) and is simulated as a specified-flux and 

a no-flow boundary. In some ground-water-flow 

simulations in the Northeast, it is assumed that little or 

no ground water flows from the bedrock that underlies 

the glacial aquifer because the permeability of bedrock 

is generally orders of magnitude lower than that of the 

glacial aquifer; however, as described in the "Recharge 

and Discharge" section, the water budget (table 5) shows 

a net gain of 14 ft3/s that can be explained only as 

upward leakage from the bedrock aquifer. Because this 

flow forms a significant amount of the overall aquifer 

budget, leakage from bedrock was incorporated into the 

model by simulating a specified flux at the lowest activecell boundaries in the northern and eastern parts of the 

modeled area (fig. 16). Initial hypothesis-testing 

simulations indicated that a uniform flux from the bedrock aquifer could not approximate the observed 

ground-water-flow system. The flux was distributed in 

the areas shown in figure 16 because streamflow data 

indicate that a large amount of the flux from the bedrock 

aquifer originates near the west face of the Green Mountains. Additional hypothesis testing indicated that a flux 

from the bedrock aquifer in the northern part of the modeled area, near the municipal landfill, was necessary to 

maintain the heads measured in the lower part of the glacial aquifer. Stewart (1973) noted solution-weathered 

enlargements of fractures in dolomite in the Bristol area 

that probably function as conduits for leakage from the 

bedrock aquifer to the glacial aquifers. Springs flow 

from the solution-weathered fractures in the dolomite 

outcrops (fig. 9) north of Plank Road (Brewster Baldwin, Middlebury College, written commun., 1990). 

Solution-enlarged fractures could be related to 

northeast-southwest trending fracture traces in the Bristol area (Johnson Company, 1989). Although cells 

representing recharge fluxes are somewhat arbitrarily

located, measured vertical gradients and potential solution-enlarged fractures provide support for placement of 

the fluxes shown in figure 16. No data are available to 

proportion flux from the bedrock aquifer in the 

remainder of the model area; therefore, a no-flow 

boundary was used.

Evidence for a large flux from the bedrock aquifer 

includes the following observations: (1) heads in the 

bedrock aquifer at wells along Burpee Road were above 

those in the glacial aquifers (appendix 2); (2) the head at 

bedrock well W-233 (fig. 5) was a few feet above the 

land surface; (3) a large upward vertical gradient, 

0.3 ft/ft (a 12-foot head difference over an aquifer thickness of 40 ft), was observed at clustered wells BR-6 and 

W-316 screened in the glacial delta at the north end of 

the modeled area, where no confining unit is present;

(4) streamflows off the west flank of the Green Mountains in the study area were negligible (table 3); and

(5) large streamflow gains from the aquifer system 

(table 3) were repeatedly measured in the New Haven 

River.

Lateral model boundaries are simulated as shown 

in figure 16. The Green Mountains to the east are treated 

as a specified-flux boundary, as described above, and 

form the east model boundary. Near the intermittent 

stream south of Plank Road, thin till and bedrock (fig. 9) 

forms the northern model boundary and is treated as a 

specified-flux boundary. Initially, model simulations 

included the till-covered hillside at Plank Road; however, high hydraulic gradients in the till require the use 

of a finer model grid than was warranted for the scope of 

this study. This area, therefore, was not simulated 

explicitly. The bedrock ridge west of Burpee Road 

(fig. 9) forms the west model boundary and is treated as 

a no-flow boundary (fig. 16), although some ground 

water probably leaks to or from the bedrock. The gap in 

the dolomite ridge directly west of the private landfill 

(fig. 9), along the western model boundary, is simulated 

as a general-head boundary.

The valley-fill aquifer beneath Bristol Flats, south 

of the landfills, extends beyond the study area. A south 

model boundary was selectively placed far enough from 

the landfills to have little effect on simulation of flow 

in those areas and at a point in the aquifer where hydraulic gradients could be reasonably estimated and streamflows measured. This boundary is simulated as a 

general-head boundary to provide for flow out of the 

aquifer (fig. 16).

Simulation of Ground-Water Flow 33
Selection of Input Parameters

The parameters assigned to each cell are assumed 

to be constant and represent an average value within 

each cell. Parameters that must be assigned to cells 

include hydraulic conductivity, cell bottom, cell top for 

the lower cells, recharge, discharge, and stream characteristics. Parameters are assigned initial input values that 

are based on estimated or known data. Initial-input 

values are modified or accepted during calibration to 

become the final model-input values.

Horizontal hydraulic conductivity was estimated 

from grain-size distributions and from slug and specificcapacity tests; initial input values are listed in table 4. 

Vertical hydraulic conductivity was assumed to be a 

fraction of the horizontal hydraulic conductivity; 0.1 for 

the coarse materials and 0.001 for the confining unit. 

Vertical hydraulic conductivity generally is less significant than horizontal hydraulic conductivity in models 

simulating nonstressed flow systems (Harte and Mack, 

1992).

The depth and width of streams were measured at 

streamflow-measurement sites and at other locations. 

The altitude of streams were either measured at streamflow-measurement sites or estimated from topographicmap contours. The hydraulic conductivity of streambeds, based on examination of the streambed materials, 

was estimated to be 5 ft/d for the New Haven River 

bottom and 1 to 3 ft/d for tributaries and the pond west 

of Burpee Road. Childress and others (1991) measured 

similar values at streams in a glaciated area of Ohio. 

Streambed thickness used was 2 ft for the New Haven 

River bottom and 1 ft for all other streams. Recharge 

from infiltration of precipitation to the aquifer was set at 

3.7 x 10-8 ft3/s (14 in/yr), as discussed in the section 

"Recharge and Discharge."

Calibration

Calibration is the process of adjusting initial-input 

values until the difference between measured heads and 

flows and simulated heads and flows is within acceptable limits. Model-input values generally were changed 

for a group of cells, or zones, rather than on a cell-bycell basis to keep the conceptual representation of 

the aquifer system intact and to avoid adjusting input 

values at individual cells until simulated heads or 

ground-water flows matched measured values.

In general, model-input values were similar to initial-input values based on data for April and May 1991. 

A large part of calibration consisted of adjustments of 

initial-input values between data points and the 

distribution of allocations of fluxes at the appropriate 

model boundaries. Calibrated vertical and horizontal 

hydraulic conductivities were similar to the initial-input 

values and the conductivities listed in appendix 4 and 

discussed in "Aquifer Characteristics." Model-input, 

streambed hydraulic conductivities were the same as the 

initial-input values.

The flow model was calibrated by observing the 

difference between simulated and measured water levels 

(appendix 6) at model cells and estimated and measuredhead data. Heads were estimated at new wells that had 

been installed after April 1991 by comparing water 

levels at nearby sites and estimating head fluctuations in 

the new wells on the basis of fluctuations measured in 

nearby wells. Ground-water levels for April were estimated at well sites where wells had not yet been 

installed by adding 2.2 ft to the November 1991 head for 

the same well site.

The standard mean difference between calculated 

and estimated or measured heads (appendix 6) compares 

favorably for simulation of an aquifer system with high 

hydraulic and vertical gradients and complex fluxes. The 

mean head difference, simulated head minus measured 

and estimated heads, was 0.6. The absolute mean head 

difference of 2.5 ft is an accurate measure of total error 

and indicates a favorable comparison between simulated 

and measured heads overall. Most of the simulation 

error is produced at the delta face and at the eastern 

model boundary. Simulated vertical gradients (the 

vertical-flow component) compared favorably with 

measured or estimated vertical gradients (appendix 6). 

The absolute error between measured- and simulatedhead gradients was small (2.0 ft). The high upward vertical gradient (11.2 ft) measured at the municipal landfill 

(between wells W-316 and BR-6) was reproduced 

(11.9 ft) by a simulated flux from the bedrock aquifer. 

The downward vertical gradient measured between 

wells MW-101 and W-337 (indicated by a negative-head 

difference in appendix 6) was not reproduced by the 

simulation because of the complex hydrogeology at 

this location. The simulated head at W-337 also is the 

largest error in calculated head (-9.5 ft, appendix 6). 

Well W-337 is at the delta face, where the measured 

hydraulic gradient is very high: more than 30 ft of head 

change in a distance of 300 ft. Simulation of this high

34 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
hydraulic gradient at the delta face was improved (initial 

head errors were greater than 20 ft) by reducing the cell 

discretization to 50 by 50 ft. Finer discretization allows 

model nodes to be centered closer to observation wells 

and allows for better representation of heads by 

representing smaller aquifer areas.

The simulated water table is shown in figure 17, 

and the simulated, potentiometric surface in the lower 

aquifer (layer 2) is shown in figure 18. Although comparisons between simulated and measured head surfaces 

are difficult to make because of the 20-foot-contour 

interval of the measured water-table surface (fig. 15) and 

the large hydraulic gradient across the model area, the 

simulated water table (fig. 17) compares favorably to the 

measured water table (fig. 15). Important features of the 

water table and potentiometric surface are reproduced 

by the ground-water-flow simulation; ground-waterflow directions throughout the model are correct, vertical gradients are similar to measured values, and simulated water-table contours appropriately indicate gaining 

and losing reaches of the New Haven River.

The simulated hydraulic gradient at the delta face 

(fig. 17) is slightly offset and not as large as the measured gradient. A better match of simulated to measured 

heads near the delta face and at the eastern model boundary could be achieved by use of an even finer discretization and by adjustments to recharge and hydraulic 

conductivity of the current model. However, because 

acceptable simulations of hydrologic conditions are produced and model parameters are within realistic ranges, 

for the purpose of this study, further refinements to the 

model are not warranted.

A relatively large head-difference error of 9.4 ft 

was measured near the east model boundary at well W554. This error is not considered significant because (1) 

this is not an area of emphasis in the simulation, and (2) 

the match of measured to simulated heads at nearby 

wells (W-12, W-551, W- 552, W-553, W-555, W-556) 

was favorable. A much better match at well W-554 

could be obtained by use of finer discretization in this 

area and by adjustments to or a redistribution of 

boundary fluxes; however, these improvements are not 

necessary for the purpose of this study.

Simulation errors greater than 3 ft at the two landfills are of a greater concern than simulation errors 

greater than 5 ft elsewhere in the model. Areas of significant errors between measured and simulated heads 

include the north model boundary, the till-stratified-drift

interface, and along the face of the delta. The errors 

resulted for various reasons. Along the north model 

boundary, simulated heads were dependent on the simulated flux from bedrock to reproduce the measured heads 

and large upward vertical gradient. Without knowledge 

of bedrock-fracture locations and hydraulics, the estimated flux from the bedrock aquifer cannot be distributed accurately. Along the delta face, errors are 

inherently the result of significant lithology contrasts 

and large head changes (laterally and vertically).

An estimated and simulated water budget for the 

study area is shown in table 6. Parameters such as direct 

recharge and leakage from bedrock were set at or near 

the estimated rates. Model fluxes such as streamflow 

leakage and ground-water inflow and outflow are 

simulated by head-dependent boundaries and not at a 

rate specified in a given model input-data set.

The calibrated model reproduces the estimated 

total water flux (18 ft3/s) adequately. The major difference between the model and estimated budgets is that 

the model simulates less streamflow and more groundwater flow out of the aquifer system than is estimated. 

Most of the differences in flux are associated with the 

streamflow of the New Haven River and ground-water 

outflow from the aquifers at Bristol Flats (table 6). The 

simulation differences are not critical to the overall flow 

simulation or to flow at or near the landfills because the 

simulated total discharge at the south model boundary 

(14 ft3/s) and the simulated total budget amount (17 fWs) 

are plausible. The simulated ground-water seepage to 

the New Haven River (3.8 ft3/s) is low because of the 

difficulties in reproducing the extreme gain (20 ft3/s) 

between measurement sites 1 and 3 (table 3) and 

difficulties in proportioning the large upward discharge 

from the bedrock aquifer that produces the streamflow 

gain.

Specified fluxes are adequately simulated at the gap 

in the dolomite ridge at the west model boundary. Fluxes 

at this boundary affect flow at the private landfill and the 

municipal landfill. Simulated streamflow is slightly 

greater than estimated amounts.

Sensitivity Analysis

The sensitivity of the model was analyzed to assess 

the relative effects of model-input parameters and 

boundary conditions on results of the simulations. 

The principal model parameters direct recharge, 

streambed hydraulic conductivity, horizontal hydraulic

Simulation of Ground-Water Flow 35
73"06' 73°04'30"

44W30"

44-07'30"

Private 

Landfill

ACTIVE MODEL BOUNDARY

-H400 SIMULATED WATER-TABLE

CONTOUR-Shows altitude of i 

water table. Contour interval ? 

is 10 feet. Datum is sea level. '

> GENERAL DIRECTION OF

GROUND-WATER FLOW :>

_ i I t" I ' MIH!«BIB«.«*I|, -<

Base from U.S. Geological Survey 0

Bristol, Vt., 1963; South Mountain, Vt, 1963; U

1:24,000 n

1,000i

2,000 FEET

200 400 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 17. Simulated water-table configuration of the upper aquifer (model layer 1).

36 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
73'06' 73'04'30"

44W30'

44C 07'30"

ACTIVE MODEL BOUNDARY

i -^400- SIMULATED POTENTIOMETRIC CONTOUR-Shows altitude 

of potentiometric curface. 

Contour interval is 10 feet. 

Datum is sea level.

-+ GENERAL DIRECTION OF 

GROUND-WATER FLOW

^ l 

Base from U.S. Geological Survey 0 

Bristol. Vt., 1963; South Mountain, Vt., 1963; |-

1,000 2,000 FEET

1:24,000 0 200 400 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 18. Simulated potentiometric surface of the lower aquifer (model layer 2).

Simulation of Ground-Water Flow 37
Table 6. Estimated and simulated ground-water 

budget for the study area in Bristol, Vermont

[Rates are in cubic feet per second. , not simulated]

Water-budget component Estimated or 

measured rate

Simulated 

rate

Recharge to aquifer: 

Direct recharge (precipitation)....... 1.8 1.7

Streamflow leakage........................ .3

Leach fields..................................... .4

Ground-water inflows:

Eastern boundary at New Haven 1.7 1.7 

River. 

Leakage from bedrock.............. 13.9 13.7

Total................................................... 18.1 17.1

Discharge from aquifer:

Discharge to streams: 

Northwest Brook.......................... .2 1.3

Bristol Flats Brook....................... 3.0 2.3

New Haven River........................ 8.6 3.8

Subtotal........................................... 11.8 7.4

Ground-water discharge 

Western boundary at 1.3 1.8

dolomite gap. 

Southern boundary at 5.0 7.9

Bristol Flats. 

Subtotal........................................... 6.3 9.7

Total................................................... 18.1_____17.1

conductivity, flux to the glacial aquifer from the bedrock 

aquifer, and general-head-boundary hydraulic conductivity were changed by 50 percent above and below 

the model input or calibrated values. Vertical hydraulic 

conductivity was changed by factors of 0.1 and 10 times 

the calibrated values. Results of the sensitivity analysis 

are summarized in figure 19. Simulation results are 

shown as boxplots of water-level residuals (simulated 

head minus measured head) for the 58 wells and checkpoints listed in appendix 6, and as simulated discharge to 

streams and from ground-water discharge at the west 

model boundary for each of 13 model simulations.

The model is most sensitive to changes in horizontal hydraulic conductivity and recharge from bedrock 

(fig. 19). Investigators (de Lima and Olimpio, 1989; and 

Harte and Mack, 1992) have shown that ground-waterflow models are most sensitive to reductions in horizontal hydraulic conductivity. The model is least sensitive to 

adjustments of vertical hydraulic conductivity and the 

general-head-boundary hydraulic conductivity. The

model was also minimally sensitive to changes in areal 

recharge and streambed hydraulic conductivity. None of 

the sensitivity simulations indicate that changes to any 

one parameter could produce an overall improved simulation. Recharge, streambed conductivity, and generalhead-boundary conductivity values increased by 50 percent and produced head distributions similar to the calibrated simulation but with larger overall error. A 

reduction in streamflow at the west model boundary, 

which compares favorably with estimated streamflow, 

can be produced by a reduction of the flux from bedrock; 

however, this is not a viable simulation because the 

resultant simulated heads are too low.

Ground-Water Flow

Analysis of the ground-water flow in the upper and 

lower aquifers is based on calibrated-model simulations 

of head (appendix 6) (figs. 17 and 18), the water budget 

(table 6), and flow-path projections based on results 

from a particle-tracking analysis. Ground-water-flow 

paths at the two landfills were calculated by placing 

particles at various locations in the upper and lower 

aquifers beneath the landfills.

Regional Flow

The regional ground-water flow in the study area is 

unusual because it is largely controlled by flow from the 

underlying and adjacent bedrock aquifer, which is the 

dominant recharge component to the aquifer system. 

Recharge from bedrock leakage accounts for about 80 

percent of the total simulated recharge, whereas 

recharge from precipitation accounts for only about 10 

percent of the total recharge. This large flux from bedrock leakage is indicated by large upward head gradients 

throughout the aquifer system and relatively high heads 

in the northern part of the glacial aquifer (figs. 17 and 18, 

appendix 6).

The New Haven River is a major feature in the 

Bristol aquifer system, and, although large gains and 

losses are noted in the measured streamflow, the river 

generally is a ground-water drain (table 3). A river entering a coarse-grained glacial aquifer and having a head 

higher than that in the aquifer loses water to the glacial 

aquifer (Harte and Mack, 1992). At Bristol, however, 

large streamflow gains were measured as the river 

crossed the aquifer because of the ground-water leakage 

from bedrock. Small streams flowing off the flank of the 

mountains commonly lose water to the aquifer;

38 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills In Bristol, Vermont
C/D

20

15

10

tD

9

LU

X

Q 

LU

CE

I

LU

C/D

0 -5

I

-10

-15

-20

1.85 1 71 1

1.37 1.49 1

X

X

1

X

1

83 1

59 1

1

X

1

X

.81

29

X

I

1

1

X 

X

|

74 1.23 2.14 1

67 1.96 1.23 1

X

1

X

1

75 1.82 1.40 2.00 1.13 1.84

.61 1-48 0.60 2.47 1.66 1-49

\- -\

Outside value 37 

Whisker 32 L

X

1

1

X

X

1 1 1

i i 

Outside value 23

X

1

" X

Whisker -24

Orr1.

O

X

O 

LU

CE

X

O 

LU

CE

in 

x

m

C/D

in 

x

CD 

C/D

in 

x

X

in 

x

X

X

o 

X X

o

X

O

in 

o 

x

in 

x

GROUND-WATER OUTFLOW 

(CUBIC FEET PER SECON

NET STREAM DISCHARGE 

(CUBIC FEET PER SECOND

EXPLA

Outside value: plotted i

plus 1.5 to 3.0 times t

Upper adjacent value is 

or equal to upper qua

Whisker 

75th percentile 

Upper quartile

50th percentile

Lower quartile 

25th percentile 

Whisker

Lower adjacent value is 

than or equal to lowe

x Outside value: plotted 

minus 1.5 to 3.0 time

RECH Precipitation recharge

SBK Streambed hydraulic c

HK Horizontal hydraulic co

VK Vertical hydraulic cond

Q Recharge from bedroc

GK General-head bounda

Figure 19. Statistical distribution of the differences between measured and simulated heads for sensitiv

water-flow model of Bristol, Vermont.
however, the stream at Bristol Flats and the northwestern stream are gaining streams and thus drain the glacial 

aquifer. Simulated ground water discharged to streams 

accounts for about 43 percent of the total aquifer discharge (table 6). Measured discharges to streams 

account for about 65 percent of the total discharge.

Ground water in the simulated glacial-aquifer 

system discharges primarily through the south model 

boundary at Bristol Flats, which represents 80 percent of 

the total ground-water discharge. Ground-water discharge at the south boundary accounts for 45 percent of 

the total simulated aquifer system (combined stream 

water and ground water) discharge. The remaining 

20 percent of the total ground-water discharge is at the 

gap in the dolomite ridge along the west model 

boundary.

Flow at the Landfills

The simulated path of ground-water flow in the 

aquifers beneath and near the landfills are shown in figures 20 and 21. Flow lines represent the simulated path 

of a particle placed at specific locations in a model cell 

(25 and 75 percent of the cells thickness) and tracked 

forward (in the direction of flow) from the landfills. 

Flow paths do not represent the concentration of a chemical constituent but simply the average path that water 

from a specific location can be expected to take through 

the aquifers.

Private Landfill

Particle-tracking analysis indicates a ground-water 

divide immediately south of the private landfill in the 

upper aquifer, where flow is either west to the gap in the 

dolomite ridge (figs. 20 and 21) or south towards Bristol 

Flats. The analysis indicates that ground water at the 

southeast edge of the private landfill may eventually 

flow southward. Ground water beneath the remainder of 

the landfill discharges to the dolomite gap area, although 

the ground-water flow in the lower aquifer beneath the 

south boundary of the private landfill apparently flows 

southward before discharging to the west.

A sectional view of the flow path of ground water 

in the aquifers beneath the private landfill is shown in 

figure 22. The section shown is a MODPATH approximation of a dipping, variable-thickness aquifer section, 

represented here by horizontal rectangular cells and 

local coordinates as a nonsloping uniform aquifer. The 

line of cross section (row 34, fig. 22) was selected where

the direction of ground-water flow is predominantly parallel to the row direction. Pathlines are constructed by 

placing a few particles at selected starting locations in 

the upper and lower aquifer along model row 34 and initiating a forward pathline analysis. Most of the resultant 

pathlines are not parallel to the model grid; that is, there 

is a horizontal component of flow into or out of the page. 

As a result, those flow paths are projected through the 

aquifer onto the model row shown to illustrate the general flow paths along this section of the aquifer. Particle 

paths that leave a row and travel in an adjacent row 

cannot be shown without such projection. Because of 

this path deviation, only a few particle paths are shown 

to reduce overlapping pathlines and to avoid obscuring 

the figure.

Water that enters the aquifer at the surface of layer 

1 at the private landfill follows a relatively short flow 

path and discharges to the aquifer and stream at the dolomite gap (fig. 22). Distinctions should not be made in the 

upper aquifer (model layer 1) between flow-path discharges to the stream and ground-water flow past the 

stream through the dolomite gap. MODPATH cannot 

accurately partition flow paths to the sinks in a cell (in 

this case the stream and the aquifer) because all sinks are 

uniformly distributed within the cells (Pollock, 1989). 

Although the total flow budget is acceptable, model 

layer discretization is probably not fine enough to accurately represent vertical partitioning of flow at the 

stream cells in layer 1. Ground water near the top of the 

lower layer flows into the upper layer as it moves westward towards the dolomite gap (fig. 22). Ground water 

deepest in the lower aquifer apparently flows westward 

to the general-head-discharge boundary at the dolomite 

gap with less upward movement.

Municipal Landfill

The particle-tracking analysis shows that ground 

water from the municipal landfill flows southward and 

westward (figs. 18 and 19). The flow paths from this 

landfill cover a greater amount of the study area than the 

simulated flow paths for the private landfill. Ground 

water from the west end of the municipal landfill follows 

a relatively short flow path to discharge at the north end 

of the dolomite gap. Ground water from the middle to 

the eastern parts of the municipal landfill follows a much 

longer flow path beneath the private landfill and 

discharges at the south end of the dolomite gap. Ground

40 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
73'06' 73'04'30

44W30'

44C 07'30"

ACTIVE MODEL BOUNDARY

TTI I I CELL WITH SIMULATED : 

'(ft STREAM j

//// /" SIMULATED GROUND-WATER- := 

///// ^ FLOW PATH

Base from U.S. Geological Survey 0

Bristol, Vt., 1963; South Mountain, Vt., 1963; U

1:24,000 0 200 400 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 20. Simulated ground-water flow paths for water in the upper aquifer (model 

layer 1) beneath the landfills.

Simulation of Ground-Water Flow 41
73W 73'04'30"

44'08'SO"

44'07'SO"

ACTIVE MODEL BOUNDARY

CELL WITH SIMULATED 

STREAM

/ / / I* SIMULATED GROUND-WATER-

'//// / FLOW PATH-Solid where flow

S / / f / ic in i mr\ar ^ant iifc^r /I^a\/Ckr 1\ is in upper aquifer (jayer 1), 

dashed where flow is in lower 

aquifer (layer 2)

Base from U.S. Geological Survey

Bristol, Vt,, 1963; South Mountain. Vt, 1963:

1:24,000

1.000 i

2,000 FEET

200 400 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 21. Simulated ground-water flow paths for water in the lower aquifer (model 

layer 2) beneath the landfills.

42 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills In Bristol, Vermont
WEST

Private la

(/>

I

i 

§o

«?

!

i

DC 

LLJ

LLJ 

Q 

O

Z d3A

3QO

El

-B=

10

EXPLANATION

HORIZONTAL RECTANGULAR MODEL CELL 

REPRESENTED IN LOCAL COORDINATES

PATH LINE AND DIRECTION OF FLOW 

D PARTICLE STARTING LOCATION

MODEL COLUMN

h

100

i

0 20 40 

VERTICAL EX

Figure 22. Section showing ground-water flow path along model row 34 at the private landfill in Bristol, V

shown in fig. 16)
water beneath the easternmost part of the municipal 

landfill flows just east of the private landfill and then 

discharges southward through Bristol Flats (fig. 18).

Sectional views of the ground-water-flow paths 

from the municipal landfill are shown in figure 23 along 

model row 26 and in figure 24 along column 32. Row 26 

and column 32 were selected to examine vertical and 

horizontal flow because lateral flow was closely aligned 

in the row and column directions. A few particles were 

placed selectively in model cells to reduce overlapping 

pathlines, and flow paths were projected onto row 26 or 

column 32 to produce readable figures.

The flow paths projected along column 32 (fig. 24) 

indicate an upward gradient beneath the landfill and 

show that most of the simulated ground water flows into 

the upper aquifer (layer 1) and discharges at the dolomite gap (rows 23-36). Ground-water flow near the top 

of the upper aquifer (layer 1) remains at the water-table 

surface. Ground water beneath the eastern part of the 

landfill follows a simulated flow path to Bristol Flats 

(fig. 17). Ground water flowing westward from the 

municipal landfill along row 26 (fig. 23) follows a similar vertical flow pattern. Most ground water at this site 

flows to the upper aquifer and discharges to either the 

stream or the boundary at the dolomite gap. Few flow 

paths remain in layer 2. Some flow paths originating at 

column 32 (fig. 24) and ending in rows 34 and 35 layer 

1, appear to stop in the middle of the figure, but they 

actually follow a westerly path perpendicular to the 

figure.

Model Appraisal

An important consideration of a numerical groundwater-flow simulation is the uniqueness of the solution. 

Various combinations of reasonable model input parameters and boundary conditions can produce similar or 

improved simulations of ground-water flow. This is particularly applicable for a complex-flow simulation such 

as the one presented in this report. The number of nonunique solutions can be reduced if estimates of input 

parameters and fluxes are as accurate as possible and if 

proposed and known hydrologic concepts of the flow 

field are tested in preliminary simulations in order to 

refine the conceptual model.

A comparison of measured and estimated heads to 

simulated heads ("Calibration" Section) indicates that 

the simulation of ground-water heads in the upper and 

lower aquifers is acceptable. The simulation error 

absolute mean-head difference of 2.5 ft and standard 

mean-head difference of 0.6 ft is acceptable for a complex aquifer system such as that underlying Bristol with 

steep head gradients. Large residuals are noted at an 

observation well near the delta face; however, this error 

may not be significant because of the steep head gradients (fig. 17) at this location. Simulated differences in 

head between the upper and lower aquifer ranged from 

1 to 11 ft and compared favorably to measured head differences. A comparison of the estimated and simulated 

ground-water budget for the model (table 6) indicates 

that the simulation reproduces the estimated budget 

closely. The primary error in the simulation is that more 

ground water and less surface water discharges from the 

aquifer at the southern model boundary than was estimated. However, the simulated combined ground- and 

surface-water discharge closely approximates the combined estimated discharge. Because the southern model 

boundary is not the primary area of interest in this study, 

the effect of this discrepancy is considered negligible.

GROUND-WATER QUALITY

Ground-water samples from 53 observation wells 

and 7 springs and surface-water sites were collected 

from September 1990 to October 1991 for analysis of 

common inorganic and organic constituents. All water 

samples were collected and analyzed by the VANR in 

accordance with USEPA sampling guidelines, and 

results were compared to State and Federal primary 

drinking-water regulations established for chemical 

constituents that can produce adverse health effects 

(Vermont Agency of Natural Resources, 1988; U.S. 

Environmental Protection Agency, 1991). Analytical 

results are presented in appendix 7.

Chemical properties of the ground- and surfacewater samples varied greatly. On the basis of the analytical results, ground water in the Bristol area can be 

divided into two categories: (1) native ground water, or 

water that has been little affected by human activities or 

landfill processes and (2) water that can be associated 

with landfill processes, such as landfill leachate and 

leachate-degraded water. Landfill leachate has high concentrations of chemical constituents resulting from the 

percolation of water through landfilled materials and 

(or) the ongoing chemical reactions between leachate 

and aquifer materials. Leachate-degraded water could 

have concentrations of chemical constituents that 

exceed background concentrations but are less than

44 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
WEST

LUcC

QLU

LUQ; 

QLU

a

i

Mu

10

EXPLANATION

HORIZONTAL RECTANGULAR MODEL CELL 

REPRESENTED IN LOCAL COORDINATES

PATH UNE AND DIRECTION OF FLOW 

D PARTICLE STARTING LOCATION

15 20 

MODEL COLUMN

25

20040

100 

VERTICAL EXAG

Figure 23. Section showing ground-water fiow path along model row 26 at the municipal landfill in Bristol, 

shown in fig. 16.)
I 

<g

Mu

lated Ground-Water

Q

a 

a

I

O 

g

o

i

i

M

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o>-

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lilcc

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, ^

40

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r

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V-

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 - 

35 30 25 20 15 

MODEL ROW

EXPLANATION

HORIZONTAL RECTANGULAR MODEL CELL 

REPRESENTED IN LOCAL COORDINATES

PATH UNE AND DIRECTION OF FLOW 

PARTICLE STARTING LOCATION 

LOCATION AT WHICH PARTICLE LEAVES

<

-~,

-^.

-

-~ 

X,

"-^.

X,

\

X

-<-

 

'~-~ 

 - 

-Q

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10 

0 200 

i i i

0 10

VERTICAL EXA

MODEL ORTHOGONAL TO SECTION 

(in row direction)

Figure 24. Section showing ground-water flow path along model column 32 at the municipal landfill in Br

shown in fig. 16.)
those measured for landfill leachate. This water is 

probably the result of diffusion and mixing of leachate 

with native ground water. Wells, springs, and surfacewater sites sampled are listed in table 7; sites are 

grouped into native or landfill-degraded categories. 

Samples from some sites had an unusual detection of 

chemical constituents above background concentrations 

and were identified as possibly affected by landfill 

leachate (table 7).

Quality of Native Water

Water in wells not degraded by landfill leachate 

(table 7) was sampled to obtain information on background concentrations of chemical constituents in native 

ground water. Ranges and median concentrations of 

those chemical constituents found in native water from 

wells and springs are listed in table 8. Native water in the 

glacial aquifers is generally soft (low calcium and

Table 7. Observation wells, springs, and surfacewater sites sampled, by location relative to landfill 

and by water category, Bristol, Vermont

[Well locations: See figure 5. Spring locations: See figure 8. 

Prefixes W-, BR-, MW- indicate wells; prefix S- indicates spring or 

surface-water site]

Native water

Municipal landfill

W-303 S-10 

W-309 S-ll 

1 W-310 S-13 

'W-311 

W-318 

3W-319

Private landfill

W-304 W-321 

W-305 'W-322 

W-306 W-323 

'W-307 'W-324 

'W-308 W-329 

'W-320

Uncategorized

W-12 

2W-312 

W-315

Leachate-degraded water

Municipal landfill

W-301 W-2 

W-302 W-4 

W-316 BR-2 

W-317 BR-6 

W-327 MW-101 

W-328 MW-102s 

W-330 MW-102 

W-331 W-334 

W-335 3W-336 

W-337 S-14

Private landfill

W-507 W-338 

W-508 W-339 

W-509 W-340 

W-510 W-341 

W-511 W-342 

W-325 W-343 

W-326 Pond 

3W-332 S-15 

3W-333 S-16

1 Possible landfill-leachate effects.

2 Possible road-salt contamination.

3 Sampling was insufficient or not possible; additional sampling is necessary to accurately characterize water from this well.

magnesium concentrations) and moderately low in 

dissolved solids, as indicated by a median specific 

conductance of 354 |iS/cm.

The primary cations in native water are calcium, 

magnesium, sodium, and sulfate (table 8). Other ions 

commonly found at small concentrations include iron, 

manganese, and barium. Concentrations of iron ranged 

from less than 10 to 2,890 |lg/L, the median 

concentration was 42 |lg/L.

In general, the metals that were analyzed for were 

at concentrations less than detection limits (table 8). Fifteen of 41 samples (appendix 7) had concentrations of 

dissolved copper that exceeded the detection limit (10 

|lg/L); however, the estimated 75th percentile (12 |lg/L) 

only slightly exceeded the detection limit. Concentrations of lead, nickel, and zinc exceeded the detection 

limits in a few samples (appendix 7). Concentrations of 

cadmium were found at or near the detection limit 

(4, 2, and 2 |lg/L) in three native-water samples (W-310, 

W-322, and W-307) on separate occasions. Concentrations of chromium, cobalt, arsenic, selenium, and silver 

did not exceed the detection limit in native-water 

samples.

Water from some wells had low concentrations of 

many constituents; yet, these results may not completely 

represent native water. For example, two water samples 

from well W-334, which is screened in the lower aquifer 

downgradient from the municipal landfill, had significant concentrations of nickel (23 and 13 jig/L) and elevated concentrations of sodium (48.2 mg/L) and 

copper (76 |lg/L). Similarly, water from well W-308. 

which is adjacent to the private landfill but not directly 

downgradient from it, had significant concentrations of 

copper (21 and 17 |lg/L) in two samples and elevated 

concentrations of zinc (112 and 72 |lg/L), and lead 

(73 |ig/L) in three samples. Water from well W-324, 

screened in the lower aquifer adjacent to the private 

landfill, had low concentrations of all constituents analyzed for, with the exception of two volatile organic 

compounds (VOC's) that were slightly above detection 

limits (53 |lg/L of acetone and 56 |lg/L of 2-butanone). 

Well W-324 was installed later in the investigation, and 

only one sample was collected and analyzed; therefore, 

it is uncertain if this one detection is an anomaly. Further 

sampling would be necessary at these wells to determine 

if the water sampled is affected by landfill leachate.

2In this report, the term "elevated concentration" refers to a 

concentration above regulatory limits or median concentrations.

Ground-Water Quality 47
Table 8. Regulatory limits and summary statistics for physical properties and chemical constituents in 

native water from wells and springs in Bristol, Vermont, 1990-91

[SMCL, Secondary maximum contaminant level set by the U.S. Environmental Protection Agency (1988c). MCL, Maximum contaminant 

level set by the U.S. Environmental Protection Agency (1988a). Enforcement standard that requires notification of the \fermont Agency of 

Natural Resources (1988) and written communication, 1994. Statistics for mean, standard deviation, 25th percentile and 75th percentile are 

calculated by methods described by Helsel and Cohn (1988). |iS/cm, microsiemen per centimeter at 25 degrees Celsius; mg/L, milligram per 

liter; |ig/L, microgram per liter. <, actual value is less than value shown; - not applicable or too few to calculate statistics]

_, . . Number Physical property or _.

chemical constituent , samples

Physical properties

Specific conductance 

(liS/cm)

pH (units)

Major constituents (mg/L)

Calcium, dissolved

Magnesium, dissolved

Sodium, dissolved

Potassium, dissolved

Sulfate, dissolved

Chloride, dissolved

Trace constituents (Mg/L)

Arsenic, dissolved

Barium, dissolved

Cadmium, dissolved

Chromium, dissolved

Cobalt, dissolved

Copper, dissolved

Iron, dissolved

Lead, dissolved

Manganese, dissolved

Nickel, dissolved

Selenium, dissolved

Silver, dissolved

Zinc, dissolved

52

10

36

37

48

36

53

52

38

38

53

47

24

41

54

53

52

38

38

38

53

Number 

less than 

detection 

limit

-

0

0

0

0

0

0

38

0

50

47

24

26

10

38

6

35

38

38

46

SMCL

None

6.5-8.5

None

None

None

None

250

250

None

1,000

None

50

None

1,000

300

None

50

None

None

100

5

MCL

None

None

None

None

None

None

400

None

50

2,000

5

100

None

1,300

None

'5

None

100

50

50

None

_ , Stan- Enforce- , , 

. dard 

ment Mean , . 

4. j j devia- standards tion

100

None

-

None

10

-

250

250

50

2,000

5

100

None

1,300

300

15

50

100

50

50

5,000

347 62

7.15

42.4 16.1

20.4 6.1

1.56 8.10

.34 .55

17.84 7.88

9.9 9.8

-

56 44

..

..

12 27

227 465

..

196 228

..

-

25th percentile

307

7.52

36.3

16.8

4.88

1.11

13.05

2.5

-

24

-

-

--

1

14

-

47

-

--

-

-

Median

354

7.60

39.6

20.8

9.02

1.30

16.54

6.7

-

38

-

-

4

42

-

114

-

--

~

-

75th percentile

384

-

44.4

22.1

13.05

1.46

20.35

15.0

-

75

-

-

12

254

--

242

-

-

-

--

Maximum 

detection

465

--

118

43.8

48.2

3.80

43.0

40.9

<5

203

4

<10

<10

178

2,890

73

1,100

23

<5

<5

308

MCL under review (U.S. Environmental Protection Agency, 1991)

Extent of Contaminated Ground Water

Leachate contaminated ground water is produced 

by the percolation of recharged water through landfilied 

waste. Water in the waste is displaced by additional 

recharge to the landfill. Chemical processes involved in 

the production of leachate include oxidation, reduction, 

dissolution, precipitation, ion exchange, and sorption 

(Baedecker and Back, 1979). Solids, liquids, and gases 

from the waste are incorporated into (or) suspended in

the leachate. Bacterial action produces metabolic carbon 

dioxide that dissolves in water and decreases pH. 

Leachate-solvent capability increases by addition of 

bacterially generated organic acids. The resulting acidic 

condition favors increased hardness and increased concentrations of solids and metals particularly iron and 

manganese compared to background concentrations. 

Chloride and sulfate salts of sodium, potassium, calcium, and magnesium are highly soluble and are 

generally leached directly from wastes (Nicholson and

48 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
others, 1983). Leachate generation is a complex process 

that varies with waste composition, hydrogeology, and 

landfill age and design. Elevated concentrations of constituents are expected only in new unlined landfills that 

have a rapid rate of early-stage biodegradation (Myers 

andBigsby, 1990).

Specific-conductance data have commonly been 

used to map the extent of landfill-leachate contamination plumes (Kimmel and Braids, 1980; Wexler, 1988a). 

In the Bristol area, ground water contaminated by

leachate is readily distinguishable from native ground 

water, which generally has a specific conductance less 

than 400 (j,S/cm. The extent of leachate contamination 

near the landfills is indicated in figure 25 by lines of 

equal specific conductance in ground water. Surface and 

borehole geophysical data were used to infer contours of 

specific conductance where water samples were not 

available. Leachate contamination was detected with 

application of borehole geophysical logging (Mack, 

1993).

73'06' 73°04'30"

44°08'30"

44'07'30"

BRISTOL^

.JUL

Private 

Landfill

LINE OF EQUAL SPECIFIC 

CONDUCTANCE, 9/90-Dashed l

where approximately located.

Interval 500 microsiemens

per centimeter at 25 degrees

Celsius.

SURFACE-WATER STATIONNumber is station identifier.

Base from U.S. Geological Survey 0 

Bristol, Vt., 1963, 1:24,000 \

0 200 400 METERS

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 25. Specific conductance of ground water in Bristol, Vermont, September, 

1990.

Ground-Water Quality 49
Private Landfill

The leachate plume, an area of ground water 

degraded by leachate, emanating from the private landfill (fig. 25) does not extend downgradient as far as the 

plume from the municipal landfill and appears to be 

wide for the size of the private landfill. Factors such as 

the contour of the water table, horizontal hydraulic conductivity, and permeability and surface-water runoff of 

the landfill probably contribute to a laterally dispersed 

plume at the private landfill. The water table at the private landfill has a radial-flow component. The groundwater-flow simulation, and the particle-tracking analysis 

(figs. 18 and 19) indicate that ground water in the upper 

aquifer (model layer 1) flows southwestward before 

flowing westward to the dolomite gap. The borehole 

geophysical logs of wells W- 320, W-322, and W-307 

(appendix 4) indicate such a flow pattern from the area 

of the landfill by the presence of a thin zone of conductive ground water at the water-table surface at wells W320 and W-322 but not farther southwest at well W-307. 

Additionally, horizontal hydraulic conductivity was 

lower at the private landfill than at the municipal landfill 

site. Low hydraulic conductivity can increase seasonal 

water-level fluctuations, which then affects groundwater flow and increase lateral dispersion of chemical 

constituents. Surface runoff could disperse the leachate 

plume from the private landfill because surface runoff is 

channeled and directed by a culvert to an area across the 

ground-water-flow gradient near observation well W510 (northwest of the landfill). After significant rainfall, 

runoff having a specific conductance that exceeds 2,000 

LiS/cm is ponded in an area adjacent to well W-510. The 

ponding of the runoff probably altered the original 

extent of the leachate plume produced from this landfill.

Water samples collected from observation wells 

W-332 and W-333 had elevated specific conductances 

and elevated concentrations of sodium. Samples from 

well W-333 may not be representative of native ground 

water because the well may not have been fully developed and the local ground water might still contain drilling mud. This well cluster is less than 150 ft upgradient 

from the landfill; it is uncertain whether leachate could 

be moving with radial flow or whether leachate reached 

this location by lateral movement through the 80 ft thick 

unsaturated zone. Further sampling would be necessary 

for adequate characterization of the area upgradient 

from the private landfill.

Figure 26 shows the vertical extent of the plume in 

the downgradient direction along section B-B' near the 

private landfill. This geologic section is constructed 

from an analysis of borehole geophysical and lithologic 

logs of wells along this line of section (Mack, 1993). 

The EM logging was more sensitive than the surface EM 

techniques to elevated specific conductances associated 

with leachate contamination (Mack, 1993). For example, the elevated specific conductance at well W-339 was 

not distinguishable from the aquifer materials by surface 

EM methods. The leachate plume is concentrated near 

the water-table surface near the landfill and is deeper in 

the upper aquifer as the distance downgradient from the 

landfill increases. The leading edge of the plume is near 

observation well W- 339, in a zone less than a few feet 

thick about 17 ft below the water-table surface. The particle-tracking analysis shows that ground water in the 

upper aquifer (model layer 1) remains in the upper 

aquifer downgradient from the landfill (fig. 22).

Municipal Landfill

The leachate plume at the municipal landfill is 

indicated in figure 25. The size and location of the plume 

is a result of the size of the landfill and the directions of 

ground-water flow beneath the landfill (figs. 17, 18, 20, 

and 21). The leachate plume is only slightly wider than 

the width of the landfill and extends about 500 to 700 ft 

from the landfill in the direction of ground-water flow. 

As a result, the longitudinal dispersion of the plume is 

greater than the lateral dispersion, a finding that is consistent with those of Kimmel and Braids (1980) for two 

landfills in New York. The most concentrated leachate 

contamination, as indicated by the specific conductance 

of the ground water (well W-335, fig. 25), is directly 

downgradient (southwest) from the western half of the 

landfill and is concentrated in the upper aquifer, as 

indicated by the simulated ground-water-flow paths 

(figs. 23 and 24).

Surface-geophysical measurements from the area 

near well W-335 indicate that leachate contamination 

decreases in the direction of ground-water flow; however, further testing in this area was not possible. The 

ground-water-flow simulation indicates that ground 

water from beneath the eastern part of the municipal 

landfill remains in the upper aquifer and flows past the 

north side of the private landfill. Ground water beneath 

the gravel pits immediately west of the landfill is slightly 

affected by landfill leachate. Borehole geophysical logs 

indicate that well W-301 is the only well adjacent to the

50 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
 ££:?;Water table SgS;

feAVai-U :.->:<: A:~- s-jf *'f'**:.-.r7 '£

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& iwsli^^i^i^gvioi^til^

320

I 

10

100

I

200 FEET

20

I 

30 40 50 METERS

W321 

370

EXPLANATION

WELL SCREEN INTERVAL-Upper number is well number. 

Lower number is specific conductance, in microsiemens 

per centimeter at 25 degrees Celsius

VERTICAL EXAGGERATION X 5 

DATUM IS SEA LEVEL -500 LINE OF EQUAL SPECIFIC CONDUCTANCE, 9/90-lnteryal 

500 microsiemens per centimeter at 25 degrees Celsius

Figure 26. Hydrogeologic section B-Ef showing specific conductance of ground water at the 

private landfill. (Line of section shown in figure 5)

delta that is affected by leachate from the municipal 

landfill. Borehole geophysical logs of wells W-310 and 

W-303 do not indicate leachate contamination northwest 

of the landfill (appendix 4).

Surface-geophysical measurements indicate that 

leachate contamination probably disperses immediately

west of wells W-301, W-331, W-327, and W-304. Surface-geophysical measurements near W-304 and borehole-geophysical measurements of W-304 did not 

indicate the presence of leachate contamination from the 

municipal landfill immediately north of the private landfill. Contaminants that typically make up leachate are 

either dilute (less than background concentrations) or

Ground-Water Quality 51
not present in ground water north of the private landfill. 

Ground water from the east end of the municipal landfill 

follows a long flow path (fig. 18) east of the private landfill. As a result, any elevated concentrations of chemical 

constituents that can be attributed to the landfill leachate 

have probably been reduced to background 

concentrations by the time this water reaches Bristol 

Flats.

Characteristics of Contaminated Ground 

Water

Physical Properties and Major Constituents

Analyses of ground-water samples collected from 

wells screened near the water-table surface at the two 

landfills were examined for evidence of contamination 

by leachate (appendix 7). Samples from a spring at the 

face of the delta in a gravel pit directly west of the 

municipal landfill were included in the analyses for the 

municipal landfill. Samples from a spring at the bank of 

a small stream about 800 ft west of the private landfill 

were included in the analysis for the private landfill. 

Springs were included with the ground-water analyses 

because they could be sampled at the source where water 

emerged from the ground. Other surface-water samples 

were not included in this analysis. Summary statistics of 

chemical analyses of ground water at or near the municipal and private landfills are presented in tables 9 and 10. 

The results indicate elevated concentrations of several 

chemical constituents.

Concentrations of physical properties and major 

constituents in ground water at the landfills were compared to those in native water (fig. 27). Specific conductance, an indicator of dissolved-solids concentration, 

exceeded background levels for ground water underlying both landfills. The median specific conductance (fig. 

27) was greater at the private landfill (655 LiS/cm) than 

at the municipal landfill (491 LiS/cm); however, more 

wells were installed and sampled in the leachate plume 

at the private landfill than at the municipal landfill. The 

highest specific conductance (2,920 LiS/cm) and concentration of sodium (432 mg/L) were at a well downgradient from the municipal landfill (W-335). Medians for 

these constituents, however, were higher for the private 

landfill (tables 9 and 10) than for the municipal landfill.

Median concentrations of dissolved calcium were 

greater in water associated with leachate contamination 

from the private landfill than in water associated with

leachate contamination from the municipal landfill. 

Median calcium concentrations from samples at the private landfill were about twice the background concentrations (fig. 27); however, the 75th percentiles of all 

sample concentrations were approximately the same for 

both landfills and were more than twice the 75th percentile for native water samples. At wells near the landfills, 

samples with elevated concentrations of calcium were 

similar in concentration, but samples having elevated 

calcium concentrations were more numerous at the private landfill than at the municipal landfill. Median concentrations of potassium at both landfills (fig. 27) were 

only slightly higher than background concentrations (1 

mg/L); however, analysis of samples degraded by landfill leachate reveal a range of potassium concentrations 

from 0.84 to 23.9 mg/L. The potassium concentrations 

in leachate degraded water from the two landfills were 

similar.

Median concentrations of sulfate in ground water 

contaminated by leachate were similar to background 

concentrations (16 mg/L, fig. 27); however, samples 

from wells W-332, MW-101, W-316, and W-317 had 

higher sulfate concentrations (50 to 100 mg/L) than 

samples from other wells. Water from well W-333 had a 

sulfate concentration of 248 mg/L (appendix 7). 

Because only one sample was collected from this well, 

additional sampling would be required to determine if 

this sample is representative of ground water at this site. 

The origin of the sulfate in ground-water samples is difficult to determine, because atmospheric deposition of 

sulfate through precipitation can constitute a significant 

loading to ground water. (Atmospheric sulfate originates 

primarily from stack emissions of fossil-fueled 

industrial facilities.)

Examination of chloride data from wells at the two 

landfills, collected before and during this investigation, 

revealed some trends. Water from wells BR-2, W-2, and 

W-4 at the municipal landfill and M-507, W-508, and W510 at the private landfill had concentrations of chloride 

that ranged from 4.3 to 43.4 mg/L, which were similar to 

concentrations found in previous investigations; however, chloride concentrations in water samples from 

wells MW-101, MW-102s, and MW-102d at the municipal landfill and well W-511 at the private landfill 

decreased. This trend is shown in figure 28 for wells 

MW-102s, MW-102d, and W-511. Concentrations of 

chloride measured in water samples from wells installed 

for this study, wells W-338 and W-325 at the private 

landfill and well W-335 at the municipal landfill, were

52 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
tJUU

jjj 450

c 400

ffi

w 350

0 300

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SODIUM

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.

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l.UUU

ffi 900

c 800

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CHLORIDE

-

-

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-

-

-

-

^

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b.UUU

| 5,500

| 5,000

^ 4,500

^5

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LU

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MANGANESE

MAX1 = 10,100 

MAX2 = 9,320

.

-

-

-

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_

. .

- -

B

r fl - :

Background Landfills u Background Landfills u Background Landfills 

N^46 Municipal Private N=52 Municipal Private N=52 Municipal Private 

M=46 N=31 N=51 N=31 N=44 N=23 

200

[E 180

£ 160

en 

1 140

5

3 120

2

2 100

g

| 80

I 60

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CALCIUM

-

-

_

.

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.

. _ . ' '

- e -

1U.UUU

^ 9,000

ffi 8,000

| 7,000

« 6,000

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§ 5,000

z

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O

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IRON MAX = 22,600

-

-

-

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-

- -

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i i 1 1 1 1

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^ 90

rr 80

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-

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Background Landfills u Background Landfills Background Landfills 

<D N*36 Municipal Private N=54 Municipal Private N=37 Municipal Private 

3 N=23 N=25 N=52 N-32 N=29 N=24 

| EXPLANATION

^ J3>fz l~t 75th percentile -

U C Q|

jjj g-"aT median - -

c a> & 

E ^ to ^ 25th oercentile LJ

N NUMBER OF SAMPLES

 OUTLIERS BEYOND 

3 TIMES THE IQR

en

CJ

Figure 27. Distribution of concentrations of selected dissolved chemical constituents in native ground wat

near landfills in Bristol, Vermont.
higher than concentrations of water samples from wells 

MW-101, MW-102s, MW-102d, and W-511. Given a 

trend of decreasing chloride concentration (fig. 28), concentrations in the area of wells W-338 and W-325 may 

have been higher before 1991 than those measured in 

this study.

Chloride is a common constituent in wells near 

roads subjected to deicing salt (Hall, 1975). Groundwater samples from wells screened in the upper aquifer 

and downgradient (west) from Burpee Road had sodium 

and chloride concentrations greater than those in native 

water; however, water samples from wells immediately 

upgradient from Burpee Road also had elevated sodium 

and chloride concentrations. Median concentrations of 

chloride and sodium in native water were 9 and 7 mg/L, 

respectively. Samples collected from well W-508 had 

chloride concentrations that ranged from 24 to 34 mg/L, 

and samples collected from well W-325 had chloride 

concentrations of 104 and 111 mg/L. The pond 

immediately west of Burpee Road, which receives 

runoff from Burpee Road, had chloride concentrations 

that ranged from 19 to 33 mg/L and sodium concentrations of about 17 mg/L. Water from wells screened 

about 17 ft below the water table west of Burpee Road 

(W-338, W-340, W-341, and W-342) had chloride and 

sodium concentrations from 25 mg/L to greater than 200 

mg/L. Landfill leachate probably contributes most of the 

sodium and chloride in shallow ground water in the 

upper aquifer west of Burpee Road. Water from well W312, adjacent to State Routes 17 and 116 (fig. 1), had 

concentrations of chloride and sodium of 26 and 41 

mg/L (appendix 7); this road receives more deicing salt 

than Burpee Road.

Trace Elements

Trace elements commonly found in landfill 

leachate include arsenic, cadmium, chromium, cobalt, 

copper, iron, lead, magnesium, manganese, mercury, 

nickel, selenium, strontium, and zinc. With the exception of lead, all are either in insoluble, elemental form or 

are in complex form as specific industrial wastes.

Many samples collected during this investigation 

did not contain trace elements in detectable concentrations at the detection limits (tables 9 and 10). Iron is 

commonly present in higher concentrations than other 

metals. In the Bristol area, the median background iron 

concentration was 42 Lig/L (table 8).

Concentrations of iron in ground water degraded by 

landfill leachate generally are higher than the background concentration. At the municipal landfill, the 

median concentration of iron in ground water was 97 

Lig/L (table 10) and at the private landfill was 114 Lig/L 

(table 9). Samples collected near the two landfills had 

iron concentrations greater than 1,000 Lig/L and three 

samples collected near the private landfill had iron concentrations of about 20,000 Lig/L (appendix 7). Median 

concentrations of magnesium at the landfills were 1.5 to 

2 times greater than the median background concentration of 21 mg/L (table 8). Median concentrations of 

manganese in ground water contaminated by leachate 

were about 2 times the median background concentration of 114 Lig/L (table 8). Ground-water concentrations 

of manganese and iron vary considerably between locations and with time (appendix 7), as indicated by the 

high standard deviations of concentrations in native 

water samples. In general, samples with high manganese 

concentrations also had high iron concentrations. Concentrations in most samples, including native water, 

exceeded State and Federal drinking-water limits (Vermont Agency of Natural Resources, 1988; U.S. 

Environmental Protection Agency, 1988a).

Iron and manganese are common in water from 

sand and gravel aquifers and indicate geochemical reactions with aquifer materials. These metals have been 

found naturally in high concentrations in sand and 

gravel aquifers in New Hampshire (Mack and Lawlor, 

1992). For example, two of three water samples from W312 (appendix 7), which is far removed from the effects 

of either landfill, had elevated concentrations of iron and 

manganese. The origin of naturally occurring iron and 

manganese in ground water is difficult to determine 

without further water-quality information.

The metals most commonly detected in ground 

water near both landfills were copper, nickel, and zinc. 

Copper, a common metal, is readily dissolved by acidic 

water. Copper was detected in 22 of 35 water samples 

from wells at and near the municipal landfill and in 6 of 

25 samples for the private landfill. Median concentrations of copper were less than 10 Lig/L in ground water 

from both landfills. Nickel was detected in 10 of 34 samples from the municipal landfill (table 9), at a maximum 

concentration of 29 Lig/L (wells W-317, and MW-102s) 

and in 10 of 25 samples at the private landfill (table 10) 

at a maximum concentration of 51 Lig/L (well W-507). 

Nickel was detected in samples from two wells screened

54 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
200

180

160 -

cc 140 

ffi

O 120

I 

z

100

I

I 80

LU 

O

I 

O

60

40

20

A--A

W-102d

i

1982 1983 1984 1985 1986 1987

YEAR

1988 

Figure 28. Chloride concentrations at wells W-511, MW-102s, and MW-102d. (Locations of wells shown 
Table 9. Summary statistics for physical properties and chemical constituents in water from wells and 

springs near the private landfill Bristol, Vermont, 1990-91

[Statistics for mean, standard deviation, 25th percentile, median, and 75th percentile are calculated by methods described by Helsel and Cohn 

(1988). uS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, milligrams per liter; Ug/L, micrograms per liter. <, actual value is 

less than value shown; --, not applicable or too few to calculate statistics]

Number 

Property or constituent of 

samples

Physical properties

Specific conductance 

(^S/cm at 25°C)

pH (units)

Major constituents (mg/L)

Calcium, dissolved

Magnesium, dissolved

Sodium, dissolved

Potassium, dissolved

Sulfate, dissolved

Chloride, dissolved

Trace constituents (Mg/L)

Arsenic, dissolved

Barium, dissolved

Cadmium, dissolved

Chromium, dissolved

Cobalt, dissolved

Copper, dissolved

Iron, dissolved

Lead, dissolved

Manganese, dissolved

Nickel, dissolved

Selenium, dissolved

Silver, dissolved

Zinc, dissolved

41

8

25

24

31

25

31

31

24

25

30

38

19

25

32

30

23

26

24

24

32

Number 

less than 

detection 

limit

-

0

0

0

0

1

0

24

0

30

37

18

19

1

30

3

16

24

24

27

Detection .. 

,. . Mean limit

-

--

-

-

-

0.20

-

5

-

2

10

10

10

10

10

10

10

5

1

40

738

-

79.3

30.7

48.06

5.42

24.29

60.4

-

88

--

-

-

8

2,758

-

1,041

10

-

-

26

Standard 

deviation

351

~

37.1

13.8

43.68

6.09

45.16

54.8

-

84

-

-

-

9

6,223

-

1,955

11

-

11

25th r ercentile

439

6.62

57.4

19.2

17.30

1.55

9.50

20.3

-

34

-

--

--

2

33

--

40

3

-

-

19

Median

655

6.80

80.2

32.7

36.00

2.18

14.90

27.9

-

58

-

--

--

4

114

201

6

-

33

75th percentile

944.07

7.07

99.2

38.5

67.40

7.75

20.20

104.0

120

--

--

--

10

1,520

-

1,710 .

12

-

-

81

Maximum 

detected

1,980

--

156

66.0

213

23.9

248

228

<5

310

<2

103

24

38

22,600

<10

10,100

51

<5

<1

87

in the lower aquifer (table 10), in one sample downgradient from the private landfill (W-321), and in two samples downgradient from the municipal landfill (W-334). 

The presence of nickel in these samples is probably 

related to landfill leachate. Nickel is used extensively in 

stainless steel and other alloys and can be found in many 

waste materials. Concentrations of nickel in native water 

is generally less than a few micrograms per liter (Hem, 

1989). Zinc was detected in three ground-water samples 

from wells near the municipal landfill and in five

ground-water samples from wells near the private landfill. Zinc is used in brass and bronze, in galvanized 

metals, and as a white pigment in paint (Hem, 1989). 

Concentrations of copper, nickel, and zinc were detected 

in native water samples from wells considered as background near both landfills (appendix 7). Some of these 

wells (W-310 and W-311 near the municipal landfill and 

W-307, W-308, W-320, and W-322 near the private 

landfill) possibly are affected by landfill leachate 

(table 7).

56 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
Table 10. Summary statistics for physical properties and chemical constituents in water from wells and 

springs near the municipal landfill, Bristol, Vermont, 1990-91

[Statistics for mean, standard deviation, 25th percentile, median, and 75th percentile are calculated by methods described by Helsel and 

Cohn (1988). jiS/cm, microsiemen per centimeter at 25 degrees Celsius; mg/L, milligram per liter; Ug/L, microgram per liter. <, actual value 

is less than value shown; , not applicable or too few to calculate statistics]

Number 

Property or constituent of 

samples

Physical properties

Specific conductance 

(US/cm)

pH (units)

Major constituents (mg/L)

Calcium, dissolved

Magnesium, dissolved

Sodium, dissolved

Potassium, dissolved

Sulfate, dissolved

Chloride, dissolved

Trace constituents (Mg/L)

Arsenic, dissolved

Barium, dissolved

Cadmium, dissolved

Chromium, dissolved

Cobalt, dissolved

Copper, dissolved

Iron, dissolved

Lead, dissolved

Manganese, dissolved

Nickel, dissolved

Selenium, dissolved

Silver, dissolved

Zinc, dissolved

50

16

23

29

46

23

51

51

34

37

47

47

24

35

52

44

44

34

34

34

46

Number 

less than 

detection 

limit

--

0

0

0

0

0

0

33

0

47

47

23

13

5

42

5

24

34

33

43

Detection 

limit

-

-

--

-

0.20

--

5

-

2

10

10

10

10

10

10

10

5

1

40

Mean

648

-

67.8

32.1

32.1

4.64

32.11

53.5

-

85

-

11

616

-

824

--

~

--

Standard 

deviation

455

~

34.4

12

72.5

5.77

31.25

132

--

50

-

-

10

1,163

-

1,173

-

-

--

25th percentile

367

6.72

38.6

22.8

6.17

.97

15.90

13.3

--

40

-

-

5

24

-

82

-

-

-

Median

491

7.12

54.6

32.8

13.9

1.62

22.20

27.2

-

89

-

-

9

97

-

251

-

-

75th percentile

814

7.40

95.5

41.3

26.3

6.31

34.10

41.5

-

119

-

-

15

838

-

908

-

-

-

-

Maximum 

detected

2,920

-

107

59

432

19.9

71.8

820

5

190

<2

<10

15

32

5,350

16

4,790

29

<5

6.0

198

Concentrations of cadmium ranging from 5 to 7 

exceeded the U.S. Environmental Protection 

Agency (1988a) and Vermont Agency of Natural 

Resources (1988) enforcement standard in water samples from wells MW-101, MW-102s, W-4, and W-2 at 

the municipal landfill (Johnson Company, 1989). Cadmium is used in electroplating and in manufacturing batteries, pigments, ink, plastics, and fluorescent and video 

tubes. Cadmium was not detected in water samples from 

wells where it had been detected during previous studies. Cadmium was detected at low concentrations in only 

three water samples (appendix 7) from wells that may be

affected by landfill leachate. Water from wells W-307 

and W-322, near the private landfill, had cadmium concentrations at the detection limit (2 (ig/L). Water from 

one well (W-310) near the municipal landfill had a cadmium concentration of 4 |ig/L. When concentrations are 

near the detection limit, it is difficult to determine 

whether the concentration is the result of contamination 

or the result of sampling or analytical error. Cadmium is 

probably not a dominant constituent in the leachate; it 

has perhaps been leached out of landfilled wastes and is 

presently in ground water in low concentrations.

Ground-Water Quality 57
Arsenic, used in some pesticides (Hem, 1989), was 

found in one water sample from well BR-2 at the detection limit of 5 Lig/L. Cobalt was found at a concentration 

of 19 Lig/L in water from well BR-2 near the municipal 

landfill and 24 Lig/L in water from well W-325 near the 

private landfill. Silver, commonly used in photographic 

materials and present in some industrial wastes (Hem, 

1989), was detected at a concentration of 6.0 Lig/L in 

water from well W-2. Selenium is present in leachate 

from disposal of waste ink and rubber. Selenium was not 

detected above the detection limit in any water samples.

Organic Compounds

Water samples were analyzed for the 36 volatile 

organic compounds (VOC's) listed in table 11. During 

the study, a few VOC's were detected at observation 

wells associated with the two landfills, but no VOC's 

were detected in native water, surface water, or springs. 

VOC's detected in water samples collected during this 

study, sample concentrations, and sampling dates are 

grouped by wells associated with the two landfills and 

are listed in table 12. VOC's were detected 10 times in 

water samples from four observation wells near the 

municipal landfill and 3 times at two observation wells 

near the private landfill. The VOC's detected were at 

concentrations at or near detection limits. As with 

metals, concentrations of VOC's detected at or near the 

detection limit could be a result of sampling or analytical 

error.

Water from observation well W-324, at the private 

landfill, had the highest VOC concentrations: 53 Lig/L of 

acetone and 56 Lig/L of 2-butanone. These concentrations, however, are just above the detection limit for 

these constituents of 50 Lig/L. Only one sample was collected from this well, which was installed late in the 

investigation, and it is not known if the sample is representative of water in the aquifer. VOC's were not 

detected in other nearby observation wells (W-320 and 

W-321) in the lower aquifer at the private landfill. Toluene was detected at a concentration of 2 Lig/L (detection 

limit of 2 Lig/L) in water from well W-507 screened in 

the base of the upper aquifer at the private landfill. Previous detections of VOC's at the private landfill were for 

water samples from wells W-508, W-510, and W-511 

(all screened in the upper aquifer) and for surface-water 

samples (in 1984) from the drainage culvert at the landfill and at the pond west of the landfill across Burpee 

Road (James Surwilo, Vermont Agency of Natural 

Resources, written commun., 1992). The drainage

culvert at the private landfill originally directed runoff 

from the landfill to the pond west of the landfill; however, runoff has been diverted for some time to an area 

north of the landfill near observation well W-510 (fig. 5).

More VOC's were found in water samples from 

observation wells at the municipal landfill than in samples from wells at the private landfill (table 12). The 

greatest number of VOC detections in ground water 

(five during this study) was from well MW-102d; the 

most prevalent compound found was 1,2-dichloroethene 

(two detections). Well MW-102d is screened near the 

base of the aquifer at the west boundary of the municipal 

landfill (fig. 5). Three VOC's were detected at W-317 

(table 12), which is at the same location as MW-102d but 

screened at the water table. Water from well MW-102s, 

at the same location but screened at an intermediate 

depth in the aquifer, did not contain detectable concentrations of VOC's during this study. No patterns of the 

compounds detected were indicated at the well clusters 

(table 12).

Relation of Water Quality to Geohydrologic 

Characteristics

Leachate contamination has been detected in 

ground water at or near both landfills. Borehole geophysical logs and ground-water samples indicate that the 

leachate contamination is concentrated near the water 

table within the upper aquifer downgradient from both 

landfills. Concentrations of common inorganic constituents in water samples degraded by landfill leachate are 

higher than those in native water in the upper aquifer 

underlying both landfills. Common inorganic constituent concentrations are generally at or near background 

concentrations in the lower aquifer near the two landfills. Background concentrations of common constituents and trace metals are generally less than detection 

limits; this finding indicates that lower detection limits 

may be needed for accurate quantification of constituent 

concentrations. Concentrations of some trace metals in 

the upper aquifer near the landfills are greater than their 

detection limits; however, concentrations in the lower 

aquifer are generally lower than their detection limits. 

The most common trace metals in water associated with 

landfill leachate were copper, nickel, and zinc. VOC's 

were detected in the upper and lower aquifers at the 

western end of the municipal landfill. The VOC detections in water from well MW-102d indicate that some 

contaminants migrate to the lower aquifer despite a large 

upward vertical gradient; however, the confining unit is

56 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
Table 11. Volatile organic compounds for which water samples were analyzed, Bristol, Vermont

[|ig/L, microgram per liter]

Compound

Vinyl chloride

Chloromethane

Bromomethane

Chloroethane

Trichloroflouromethane

Acetone

1 , 1 -Dichloroethene

Carbon disulfide

Methylene chloride

Methyl-t-butylether (MTBE)

1 ,2-Dichloroethane

1 , 1 -Dichloroethane

Vinyl acetate

2-Butanone

Chloroform

1,1,1 -Trichloroethane

Carbon tetrachloride

Benzene

Detection limit 

(ug/L)

10

10

10

10

10

50

2

2

2

10

2

2

50

50

2

2

2

2

Compound

Trichloroethene

1 , 1 ,2,2,-Tetrachloroethane

1 ,2-Dichloropropane

Bromodichloromethane

4-Methyl-2-pentanone

cis- 1 ,3-Dichloropropane

Toluene

trans- 1 ,3-Trichloropropene

1 , 1 ,2-Trichloroethane

2-Hexanone

Tetrachloroethane

Dibromochloromethane

Chlorobenzene

Ethylbenzene

Xylenes

Styrene

Bromoform

Detection limit 

(Ug/L)

2

2

2

2

20

2

2

2

2

20

2

2

2

2

2

2

2

not continuous at the municipal landfill. At the private 

landfill, VOC's may be limited to the upper aquifer as a 

result of the upward head gradient and the confining 

unit. Although VOC's were detected in the lower aquifer 

at the private landfill, the reliability of the data was questionable because the VOC's were near the detection 

limits and no other constituents were elevated.

Some constituents were found immediately upgradient from the landfills in previous investigations and 

during this investigation. Analytical results for water 

samples from observation wells W-332 and W-333 (less 

than 150 ft from the private landfill) were of questionable quality but could be affected by lateral contaminant 

migration through unsaturated sediments as much as 80 

ft thick. Contaminants also were detected in water samples from observation wells MW-2 and BR-2, which are 

less than 25 ft upgradient from the municipal landfill.

For example, previous investigators (Johnson Company, 

1989) found VOC's and trace metals at well BR-2. 

During this study, however, trace metals were detected, 

but VOC's were not (appendix 7). Detections of contamination at well BR-2 may have been caused by drainage 

from the landfill surface or lateral contaminant migration through unsaturated sediments towards this well, 

particularly during wet seasons. Previous contaminant 

detections at wells BR-2 and MW-2 could also be the 

result of a more highly concentrated leachate in the landfill than was present during this study. A stream less than 

150 ft to the north drains the area during wet seasons. 

Well W-319 was installed upgradient from well BR-2, 

midway to the stream, to provide additional data on the 

hydrogeology and water quality in this area; however, 

well W-319 did not yield enough water for adequate 

samples to be taken.

Ground-Water Quality 59
Table 12. Volatile organic compounds detected in observation wells, grouped by landfill, Bristol, Vermont, 

September 1990-October 1991

[Maximum contaminant level (MCL) set by the U.S. Environmental Protection Agency (1988a). Vermont Agency of Natural Resources 

(1988) and written communication (1994). ng/L, microgram per liter, none, a standard has not been established]

Well

MW-102d

MW-102d

MW-102d

MW-102d

MW-102d

MW-101

MW-101

W-317

W-317

W-337

Compound

1 ,2-Dichloroethene

1 ,2-Dichloropropane

Methylene chloride

1,2-Dichloroethene

1 ,2-Dichloroethene

Benzene

Toluene

1,1-Dichloroethane

1,1,1-Trichloroethane

Benzene

Sample date

MUNICIPAL

Sept. 1990

Sept. 1990

May 1991

May 1991

Oct. 1991

Oct. 1991

Oct. 1991

Feb. 1991

Oct. 1991

Aug. 1991

Concentration

LANDFILL

3

2

2

4

3

2

5

2

3

3

Maximum 

contaminant 

level

none

5.0

none

none

none

5.0

1,000

5.0

200

5.0

Enforcement 

standard

(ug/L)

70

0.50

5.0

70

70

1.0

2,420

5.0

200.0

1.0

PRIVATE LANDFILL

MW-507

W-324

W-324

Toluene

Acetone

2-Butanone

Oct. 1991

Oct. 1991

Oct. 1991

2

53

56

1,000

none

none

2,420

700

none

The concentrations of some water-quality constituents in ground water at both landfills appear to have 

decreased since earlier investigations. Some chemical 

constituents may have been leached from the landfilled 

waste, thereby resulting in a less concentrated leachate. 

For example, concentrations of cadmium and sodium at 

the municipal landfill and sodium at the private landfill 

are generally less than concentrations previously 

detected. Although trends indicate decreases in chemical constituents in leachate from both landfills, solidwaste disposal was resumed in 1991 at the private landfill after a period of inactivity. Waste disposal is still 

underway at the municipal landfill. These water-quality 

trends could possibly represent the effects of recycling 

and waste screening to reduce the influx and types of 

solid waste to municipal landfill. These trends could represent short-term processes that could change if the 

characteristics of the emplaced waste change with time.

SUMMARY AND CONCLUSIONS

The Bristol, Vermont area is characterized by a glacial delta more than 200 ft thick, having an exposed face 

about 150 ft high, which was deposited on the west flank 

of the Green Mountains. A municipal landfill, more than 

20 years old, overlies this coarse-grained deltaic deposit; 

depths to water range from 30 to 130 ft below land surface. A private landfill, also more than 20 years old, is at 

a lower altitude adjacent to the delta in medium- to finegrained glaciolacustrine sediments up to 100 ft thick; 

depths to water range from 10 to 50 ft. A sand, silt, and 

clay unit, found throughout most of the study area adjacent to the delta and possibly extending into the delta in 

places, functions as a confining unit separating the glacial aquifer into an upper unconfined and a lower confined aquifer. The estimated horizontal hydraulic 

conductivity of the coarse-grained deltaic sands and 

gravels, determined by slug and specific-capacity

60 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
response tests, ranged from 60 to greater than 250 ft/d. 

The horizontal hydraulic conductivity was estimated to 

be 1 to 60 ft/d for fine- to medium-grained sands and 

about 1 to 4 ft/d for till.

Recharge to the glacial aquifers is predominantly 

from upward ground-water leakage from the underlying 

bedrock aquifer and accounts for about 80 percent of the 

total recharge. Infiltration of precipitation (about 14 

in/yr) accounts for about 10 percent of total recharge, 

and inflow from adjacent glacial aquifers accounts for 

the remaining 10 percent. Large upward hydraulic gradients, ranging from 0.03 to 0.3, between the upper and 

lower glacial aquifers, and within aquifers, are evidence 

that most recharge is as upward ground-water leakage 

from bedrock.

Surface electromagnetic geophysical terrain surveys were used to identify areas underlain by electrically 

conductive ground water and (or) earth materials and to 

place observation wells. Natural-gamma radiation and 

electromagnetic borehole geophysical logs were used to 

identify and vertically delineate landfill-leachate plumes 

within aquifer materials and to place well-screen settings. Leachate plumes were found near the water table 

and in thickness that range from less than 5 to nearly 

20ft.

A three-dimensional numerical ground-water-flow 

model of the glacial aquifer was developed by use of a 

fine grid at or near the landfills and a coarse grid to 

extend to significant hydrogeologic boundaries. The 

model was constructed as two layers to simulate the 

upper and lower glacial aquifers. To simulate the confining unit, its thickness was incorporated into the thickness of the lower layer and an appropriate vertical 

hydraulic conductivity was assigned between the two 

layers.

The model was calibrated under steady-state conditions, approximated by the conditions observed during 

April and May of 1991. Measured and estimated hydraulic-head data from 58 observation wells were compared 

with simulated heads. Simulated heads matched measured and estimated heads with a standard mean difference of 0.6 ft and an absolute mean difference of 2.5 ft. 

Large head-difference errors (greater than 5 ft) were 

noted at one location near the model boundary, where a

coarse grid spacing was used, and at some locations at 

the delta face, where high hydraulic gradients were 

observed. The total ground-water budget simulated by 

the model (17 ft3/s) reproduced the total estimated 

ground-water budget (18 ft /s) and specific streamflows 

and ground-water outflows reasonably closely.

Advective ground-water-flow paths frohi beneath 

the landfills to discharge locations at the model boundaries were simulated by use of a particle-tracking analysis. Ground water from beneath the private landfill 

leaves the study area as ground-water outflow through a 

gap in the bedrock ridge west of the landfill. Some 

ground water beneath the private landfill discharges to a 

brook west of the private landfill. Most ground water 

beneath the municipal landfill also discharges as groundwater outflow to the southwest at the gap in the bedrock 

ridge. Ground water follows a much longer path from 

beneath the municipal landfill than the private landfill 

and ultimately discharges at the gap in the ridge. Ground 

water beneath the east end of the municipal landfill possibly flows southerly to eventually discharge at the south 

model boundary in the Bristol Rats area. Upward vertical gradients were simulated throughout the landfill 

areas. Simulated flow paths in the upper aquifer beneath 

both landfills remained in the upper aquifer throughout 

the area. Simulated flow paths in the lower aquifer 

beneath both landfills generally moved to the upper 

aquifer.

Water samples from 54 wells and 7 surface-water 

and spring sites were collected and analyzed by the Vermont Agency of Natural Resources. Results were 

grouped into native and landfill-degraded water. Native 

water had a median specific conductance of 354 |iS/cm, 

and ranged from approximately 200 to 465 nS/cm. The 

primary cations in native water are calcium, magnesium, 

sodium, and sulfate. Other cations commonly found at 

low concentrations include iron, manganese, and 

barium. Concentrations of most trace elements, such as 

chromium, cobalt, selenium, and silver, were below 

detection limits in native water samples. Copper, lead, 

nickel, and zinc were detected near detection limits at 

some observation wells.

Summary and Conclusions 61
Water samples degraded by landfill leachate generally had a specific conductance greater than 400 uS/cm; 

the median was about 700 uS/cm. The maximum 

specific conductances were 2,920 uS/cm at the 

municipal landfill and 1,980 (iS/cm at the private 

landfill.

Leachate from the landfills contained mean concentrations of many common constituents and metals 

that were 1.5 to 10 times the mean background concentrations. The elevated constituents included calcium, 

potassium, sodium, chloride, iron, magnesium, and 

manganese. Trace metals detected in leachate from the 

landfills included copper, nickel, zinc, cobalt, and lead. 

Nickel was the most commonly detected trace element 

(20 detections) followed by zinc (8 detections).

Water samples were analyzed for 36 volatile 

organic compounds (VOC's) during the study. Seven 

VOC's were detected at four observation wells associated with the municipal landfill and three VOC's were 

detected at two observation wells associated with the 

private landfill. No single VOC was consistently 

detected, and concentrations were generally at or near 

detection limits. VOC's were not detected in background samples. One sample, from a well adjacent to the 

private landfill, had concentrations of acetone and 2- 

butanone near the detection limits. It is uncertain 

whether the water was contaminated during sampling 

(no other chemical constituent in this sample indicate 

the presence of leachate) or if the sample was degraded 

by landfill leachate.

Some chemical constituents in water samples seem 

to be present in lower concentrations than those 

observed in previous investigations. For example, concentrations of chloride appeared to be decreasing at both 

landfills, and cadmium (which was detected at the 

municipal landfill in a previous investigation) was not 

detected during this investigation. VOC's were detected 

fewer times and at lower concentrations in this investigation than in previous investigations. Operations are 

changing at both landfills. Without additional sampling 

it is not possible to determine if the water-quality trends 

observed in this investigation are short term or if the 

concentration of leachate constituents will continue to 

diminish. What effect changes in the operation of both 

landfills will have on the concentration of leachate 

constituents is unknown.

Ground water contaminated by landfill leachate 

was concentrated in the upper glacial aquifer. Hydraulic 

gradients between and within the glacial aquifers 

are upward throughout most of the study area and 

were duplicated in the numerical flow simulations. Measured heads in the bedrock aquifer at domestic wells 

along Burpee Road also indicate an upward vertical gradient to the glacial aquifers. Examination of specific 

ground-water fluxes between the bedrock and glacial 

aquifers at domestic well sites was beyond the scope of 

this investigation.

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62 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
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64 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
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41 p.

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Selected References 65
APPENDIX 1

61
0 10 20 30 METERS

VERTICAL EXAGGERATION X 1.4 

DATUM IS SEA LEVEL

400

C

FEET 

450-

425

400- 

375- 

350

30 METERS

VERTICAL EXAGGERATION X 1.0 

DATUM IS SEA LEVEL

Land surface

Water table'

Bedrock surface.

25 50 FEET

0 5 10 15 METERS

VERTICAL EXAGGERATION X 0.9 

DATUM IS SEA LEVEL

Figure 1-1. Seismic-refraction profiles for a-a', b-b', and c-c' (locations shown in 

fig. 2).

Appendix 1 69
f

FEET 

450-

400-

350-

300

f

Land surface

Water table'

Bedrock surface

0 25 50 FEET

0 5 10 15 METERS 

VERTICAL EXAGGERATION X 0.5 

DATUM IS SEA LEVEL

9

FEET

500-1

450-

400--- Water table

50 100 FEET

0 10 20 30 METERS

VERTICAL EXAGGERATION X 0.7 

DATUM IS SEA LEVEL

9'

h

FEET

450 n

400-

50 100 FEET

0 10 20 30 METERS

VERTICAL EXAGGERATION X 0.7 

DATUM IS SEA LEVEL

Figure 1-2. Seismic-refraction profiles for f-f, g-g', and h-h' (locations shown in 

fig. 2).

70 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
50 100 FEET

0 10 20 30 METERS

VERTICAL EXAGGERATION X 0.7 

DATUM IS SEA LEVEL

k

FEET 

550 -|

k'

Land surface

500 -

450 -

400

Water table

50 100 FEET

0 10 20 30 METERS

VERTICAL EXAGGERATION X 1.0 

DATUM IS SEA LEVEL

FEET 

500 -

Land surface

400 -

300 -

200

Water table'

,Bedrock surface

50 100 FEET

0 10 20 30 METERS

VERTICAL EXAGGERATION X 0.5 

DATUM IS SEA LEVEL

Figure \-3. Seismic-refraction profiles for i-i', k-k', and l-l' (locations shown in fig. 2).

Appendix } 7}
m

FEET

500 -i

400 -

300 -

200

Water table

Land surface

m'

50 100 FEET

0 10 20 30 METERS 

VERTICAL EXAGGERATION X 0.5 

DATUM IS SEA LEVEL

n

FEET

450 -i

400 -

350 -

300

50 100 FEET

0 10 20 30 METERS

VERTICAL EXAGGERATION X 1.0 

DATUM IS SEA LEVEL

O

FEET

450 -

400

350 -

300

Land surface

'----____ Water table, _________--------

Bedrock surface

50 100 FEET

0 10 20 30 METERS

VERTICAL EXAGGERATION X 1.0 

DATUM IS SEA LEVEL

O'

Figure 1-4. Seismic-refraction profiles for m-m', n-n', and o-o' (locations shown in 

fig. 2).

72 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
p

FEET

500 n

Land surface

400-

300-

Water table

200

Bedrock surface^

50 100 FEET

0 10 20 30 METERS 

VERTICAL EXAGGERATION X 0.5 

DATUM IS SEA LEVEL

r

FEET 

550 -i

500 -

450 -

400

Water table.

, Bedrock surface

r'

Land surface

50 100 FEET

0 10 20 30 METERS

VERTICAL EXAGGERATION X 1.0 

DATUM IS SEA LEVEL

50 100 FEET

0 10 20 30 METERS

VERTICAL EXAGGERATION X 0.7 

DATUM IS SEA LEVEL

Figure 1-5. Seismic-refraction profiles for p-p', r-r', and s-s' (locationsshown in

Appendix 1 73
APPENDIX 2
Appendix 2. Well-depth and screened-interval data for the study area in Bristol, Vermont

[All depths in feet from measurement point. Altitudes in feet above sea level or land surface, ft, foot; , not applicable]

Well Other Latitude 

No. identifier

B2W-301

B2W-302

B2W-303

B2W-304

B2W-305

B2W-306

B2W-306b -

B2W-307

B2W-308

B2W-309

B2W-309b -

B2W-310

B2W-311

B2W-312

B2W-315

B2W-316

B2W-317

B2W-318

B2W-319

B2W-320

B2W-321

B2W-321b -

B2W-322

B2W-322b -

B2W-323

B2W-324

B2W-325

B2W-326

B2W-327

B2W-328

B2W-329

B2W-330

B2W-331

B2W-332

B2W-333

B2W-334

B2W-335

B2W-336

B2W-337

B2W-338

44 08 15

44 08 15

44 08 17

44 08 06

44 08 00

44 08 00

44 08 00

44 07 53

44 07 55

44 08 24

44 08 24

44 08 20

44 08 20

44 07 49

44 08 05

440821

440818

44 08 18

44 08 24

440756

44 08 00

440800

44 07 56

44 07 56

44 08 00

44 08 00

44 08 00

44 08 01

44 08 09

44 08 09

44 08 02

4408 11

44 08 1 1

44 07 59

44 07 59

44 08 15

44 08 15

44 08 16

44 08 14

44 08 00

Longitude

o / /'

073 05 46

073 05 46

073 05 46

073 05 48

073 05 58

073 05 58

073 05 58

073 05 52

073 05 38

073 05 20

073 05 20

073 05 43

073 05 43

073 05 29

073 06 00

073 05 27

073 05 40

073 05 29

073 05 39

073 05 44

073 05 56

073 05 56

073 05 52

073 05 52

073 05 59

073 05 53

073 05 53

073 05 54

073 05 43

073 05 43

073 05 54

073 05 47

073 05 47

073 05 39

073 05 39

073 05 36

073 05 36

073 05 40

073 05 42

073 0556

Water-level Depth to Depth to 

altitude, screened end of well 

April 18, 1991 interval creasing 

(ft) (ft) (ft)

1 435.0

428.9

444.4

406.5

401.0

399.3

399.3

405.1

407.5

488.4

484.1

458.0

455.8

408.0

! 398.4

!470.9

453.0

453.1

484.1

406.1

404.8

402.3

404.1

404.1

! 399.8

!404.8

!403.2

!404.9

Ull.9

'408.6

!402.9

!415.3

!413.7

!414.1

1 416.

1 455.

1 447.

!446

1 446.9

! 399.

35-37

8-9

28-30

35-37

65-69

31-33

9-11

78-80

66-68

93-99

69-70

66-68

37-39

42-44

70-72

40-42

77-82

115-117

10-16

88-92

77-79

40-42

78-80

40-42

35-37

89-91

21-25

17-19

53-55

33-35

68-72

30-32

10-12

126-130

76-80

178-182

141-145

121-125

137-143

18-20

37

9

31

37

69

33

11

100

84

99

70

68

39

44

100

42

82

117

16

92

80

42

100

42

37

91

25

19

55

35

72

32

12

135

80

187

145

135

143

20

Height of 

measurement point 

above land 

surface 

(ft)

2

2

3

3

2

2

2

0

2

2.5

2.5

2.5

2.5

2

2

2.5

3

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

1.5

0

0

0

0

1

Altitude of 

measurement point 

(ft)

430.84

430.88

448.79

410.27

404.47

405.00

405.06

438.40

460.83

525.48

525.34

487.65

487.65

444.41

442.30

506.54

527.57

552.83

497.56

450.50

411.31

411.28

431.21

431.28

404.97

424.50

423.55

420.21

442.05

442.50

413.53

424.20

424.27

487.36

487.10

574.

574.

574.09

574.38

409.8

Appendix 2 77
Appendix 2. Well-depth and screened-interval data for the study area in Bristol, Vermont-Conf/nued

Well

No.

B2W-339

B2W-340

B2W-341

B2W-343

B2W-351

B2W-352

B2W-353

B2W-354

B2W-355

B2W-356

B2W-507

B2W-508

B2W-509

B2W-510

B2W-511

BR-2

MW-2

MW-4

BR-6

MW-102s

MW-102d

MW-101

Other 

identifier

2W-1

2W-2

2W-3

2W-4

2W-5

2W-6

3MW-7

3MW-8

3MW-9

3MW-10

3MW-11

4BR-2

4MW-2

4MW-4

4BR-6

5MW-102s

5MW-102d

5MW-101

Latitude

o ' "

44 08 00

440801

44 07 59

44 08 03

440751

44 07 52

44 07 54

44 07 55

44 07 55

44 07 53

44 08 01

44 08 09

4408 18

4408 13

44 08 02

44 08 22

44 08 22

44 08 20

440821

4408 18

4408 18

44 08 14

Longitude

o / //

073 05 59

073 05 56

073 05 56

073 05 54

073 04 44

073 04 39

073 04 40

073 04 40

073 04 39

073 04 50

073 05 48

073 05 53

073 05 53

073 05 53

073 05 58

073 05 39

073 05 27

073 05 38

073 05 27

073 05 40

073 05 40

073 05 42

Water-level Depth to Depth to 

altitude, screened end of well 

April 18, 1991 interval creasing 

(ft) (ft) (ft)

r398.

r 399.

! 396.

r402.

!483.9

!485.3

!470.2

!465.5

J472.5

!463.9

404.8

402.7

403.1

1.8

401.7

480.8

486.4

461.5

482.1

452.9

455.4

445.4

18-20

18-20

19-21

13-14

14-24

15-25

31-41

31-41

31-41

40-50

_

68-76

81-96

119-124

167 -177

20

20

21

14

24

25

41

41

41

50

53

30

25

27

16

38

51

67

76

96

124

177

Height of 

measure- Altitude of 

ment point measureabove land ment point 

surface (ft) 

(ft)

1

1

1

0

2

2

2

2

2

2

1

0

2

2

1

2

2

3

3

2

2

0

403.0

405.1

410.0

415.0

500.82

503.07

505.96

506.69

510.60

498.04

435.96

416.37

412.15

404.13

411.81

509.00

522.66

514.95

505.15

527.99

528.13

574.19

1 Estimated water-level altitude.

2 Bristol leachfield well (Thermo Engineering, written commun., 1991).

3 Bristol Waste Management Landfill (Marshfield Engineering Services, 1979).

4 Bristol Municipal landfill (Hackbarth, 1980).

5 Bristol Municipal landfill (Johnson Company, 1989).

78 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
APPENDIX 3
Appendix 3. Lithologic logs of wells in Bristol, Vermont

[Altitudes are given in feet above sea level. Well number shown in bold, ft, foot; , no data]

Description of material

Top of unit

or sample

(ft)

W-l, Altitude 370 ft

Boulders and hardpan ..................

Silt................................................

Bedrock........................................

W-4, Altitude 420 ft

Boulders and gravel.....................

Sand, coarse; cobbles...................

Sand, fine; silt ..............................

Clay; end of hole 70 ft .................

W-5, Altitude 420 ft

Gravel; end of hole 68 .................

W-12, Altitude 590 ft

Gravel; end of hole 150ft............

W-28, Altitude 535 ft 

Sand.............................................

Bedrock........................................

W-37, Altitude 400 ft

Gravel; end of hole 40 ft..............

W-38, Altitude 436 ft

Clay; sand ....................................

Bedrock........................................

W-42, Altitude 435 ft

Sand and boulders........................

Boulders.......................................

W-43, Altitude 440 ft

Sand and boulders........................

Sand and gravel............................

W-45, Altitude 420 ft 

Clay..............................................

Sand and gravel............................

Bedrock; end of hole 200 ft .........

W-47, Altitude 370 ft 

Gravel...........................................

Hardpan (till)............... .................

Bedrock, end of hole 298 ft .........

W-54, Altitude 435 ft

Boulders and gravel .....................

Sand and gravel; end of hole 

37ft..........................................

W-60, Altitude 400 ft

Clay, hardpan (till?) .....................

Bedrock (limestone); end of hole 

249ft........................................

W-62, Altitude 590 ft

Clay and sand...............................

Limestone; end of hole 225 ft......

0

100

261

0

26

50

69

0

0

0

6

0

92

0

12

0

12

0

50

100

0

7

22

0

_ /S

0

20

Bottom of

unit 

or sample

(ft)

100

261

26

50

69

92

12

12

50

100

7

22

23

78

20

Description of material

W-76, Altitude 420 ft

Boulders.....................................

Sand, silt....................................

Boulders.....................................

Gravel; end of hole 60 ft............

W-77, Altitude 445 ft

Clay...........................................

Sand and gravel .........................

Bedrock; end of hole 173 ft.......

W-81, Altitude 430 ft

Gravel; end of hole 41 ft............

W-82, Altitude 400 ft

Boulders.....................................

Sand...........................................

Sand, clay ..................................

Gravel, packed, (till?);

end of hole 198 ft...................

W-86, Altitude 460 ft

Sand and gravel .........................

Bedrock.....................................

W-87, Altitude 45 1ft

Sand and gravel .........................

Bedrock.....................................

W-92

Clay...........................................

Sand...........................................

Clay...........................................

Bedrock; end of hole 200 ft. ......

W-93, Altitude 446 ft

Clay...........................................

Sand...........................................

Clay; sand, coarse......................

Bedrock; end of hole 350 ft. ......

W-98, Altitude 570 ft

Boulders and hardpan................

Bedrock; end of hole 248 ft.......

W-102, Altitude 415 ft

Unconsolidated deposits,

undifferentiated.. ....................

Bedrock; end of hole 175 ft.......

W-106, Altitude 445 ft

Boulders.....................................

Gravel; end of hole 62 ft............

W-115, Altitude 430 ft

Boulders.....................................

Bedrock; end of hole 123 ft.......

Top of unit

or sample 

(ft)

0

12

30

50

0

15

87

0

0

25

90

148

0

95

0

34

0

43

55

95

0

40

55

70

0

44

0

105

0

15

0

39

Bottom of 

unit

or sample 

(ft)

12

30

50

15

87

--

25

90

148

95

-

34

43

55

95

-

40

55

70

--

44

--

105

-

15

--

39

Appendix 3 81
Appendix 3. Lithologic logs of wells in Bristol, Vermont-ConWnued

Description of material

W-127, Altitude 375 ft

Gravel, coarse ..............................

Clay..............................................

Till................................................

Bedrock; end of hole 450 ft .........

W-143, Altitude 440 ft

Sand and gravel............................

Bedrock, limestone; end of hole

205ft........................................

W-147, Altitude 575 ft

Unconsolidated deposits, undifferentiated ................................

Bedrock........................................

W-152, Altitude 460 ft

Hardpan (till?) and boulders ........

Gravel; end of hole 145 ft............

W-167, Altitude 520 ft

Gravel...........................................

Bedrock; end of hole 77 ft ...........

W-169, Altitude 550 ft

Sand .............................................

Bedrock; end of hole 270 ft .........

W-170, Altitude 505 ft

Sand.............................................

Bedrock; end of hole 160 ft .........

W-173, Altitude 370 ft

Clay, gravel, cobbles....................

Bedrock; end of hole 280 ft .........

W-174, Altitude 370 ft

Clay, gray, and sand.....................

Bedrock; end of hole 180 ft .........

W-193, Altitude 525 ft

Sand and gravel............................

Bedrock; quartzite; end of hole

200 ft ........................................

W-199, Altitude 560 ft

Clay and stones ............................

Bedrock; end of hole 520 ft .........

W-200, Altitude 570 ft

Boulders .......................................

Sand.............................................

Bedrock; end of hole 180 ft .........

W-205, Altitude 405 ft

Gravel...........................................

Sand.............................................

Sand, silty; clay............................

Gravel, coarse ..............................

Sand .............................................

Hardpan (till)...............................

Top of unit

or sample 

(ft)

0

17

46

66

0

55

0

10

0

110

0

14

0

38

0

32

0

160

0

140

0

34

0

20

0

15

55

0

18

26

46

72

174

Bottom of 

unit

or sample

(ft)

17

46

66

55

10

110

14

38

32

~

160

-

140

--

34

--

20

-

15

55

18

26

46

72

174

230

Description of material

W-205 Continued

Bedrock; end of hole 274 ft.........

W-206, Altitude 41 Oft

Boulders......................................

Clay, blue, solid...........................

Sand.............................................

Sand, coarse; gravel;

end of hole 46 ft ......................

W-209, Altitude 405 ft

Gravel and boulders ....................

Clay .............................................

Sand.............................................

Gravel..........................................

Gravel, sandy (till?).... ........ .........

Bedrock; end of hole 324 ft.........

W-211, Altitude 405 ft

Sand and boulders .......................

Sand, with clay layers .................

Gravel; end of hole 100 ft .... .......

W-219, Altitude 570 ft

Gravel (till?).. ...... ....................... .

Bedrock.......................................

W-230, Altitude 470 ft

Fill...............................................

Gravel and boulders ....................

Gravel; end of hole 64 ft .............

W-233, Altitude 400 ft

Gravel..........................................

Sand.............................................

Clay .............................................

Sand.............................................

Gravel; end of hole 220 ft ...........

W-235, Altitude 410 ft

Gravel..........................................

Gravel; clay .................................

Gravel; end of hole 223 ft ...........

W-301, Altitude 430.84 ft

Sand, medium, some coarse........

Clay, dark gray; some silt............

Silt; clay ......................................

Sand, fine.....................................

Silt, fine sand, clay, pebbles

(till);coarse sand and gravel

below.......................................

Silt and clay; fine sand and

pebbles below..........................

Till, coarse pebbles; fine to

coarse sand; refusal 35 ft. ........

Top of unit

or sample 

(ft)

230

0

22

38

44

0

18

85

140

195

209

0

12

82

0

40

0

16

28

0

45

50

160

210

0

60

180

0

12

17

19

22

27

32

Bottom of 

unit

or sample

(ft)

22

38

44

-

18

42

140

195

209

-

12

82

-

40

16

28

45

50

160

210

-

60

180

-

9

14

19

22

24

29

82 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
Appendix 3. Lithologic logs of wells in Bristol, Vermont-Conf/nued

Description of material

Top of unit 

or sample 

(ft)

Bottom of 

unit 

or sample 

(ft)

Description of material

Top of unit

or sample

(ft)

W-303, Altitude 448.7 ft

Sand and pebbles......................... 0 22

Sand, clayey; pebbles; possibly 

till; refusal 28.5 ft..................... 22

W-304, Altitude 410.27 ft

Gravel, cobbles, and boulders 0 17

Sand, coarse; some pebbles......... 17 19

Sand, coarse; some pebbles......... 22 24

Sand, coarse, pebbles (till); 

refusal 35 ft.............................. 27

W-305, Altitude 404.4 ft

Sand, fine..................................... 7 9

Sand, medium.............................. 12 14

Sand, fine..................................... 17 19

Sand, fine; silt.............................. 22 24

Sand, very fine, gray.................... 27 29

Silt; clay, laminated...................... 32 34

Sand, fine, and pebble lenses; silt; 

clay........................................... 37 39

Sand, fine; pebbles....................... 42 44

Sand, very fine; some pebbles 47 49 

Sand, fine; pebbles....................... 52 54

Till; sand, fine gray; pebbles; silt. 57 59 

Till; sand, medium to coarse, 

gray; pebbles refusal 67.5 ft..... 62

W-307, Altitude 438.40 ft

Clay; silt and fine sand................. 0 16

Sand, fine; silt.............................. 21 34

Sand, fine to medium................... 34 67

Clay; silt; sand fine,..................... 67 80

Sand, fine; silt; clay...................... 80 100

Till; end of hole 100 ft................. 100

W-308, Altitude 460.83 ft

Sand, fine, yellow; some silt 0 17

Clay, sandy, gray-brown.............. 17 22

Sand, coarse; pebbles................... 22 27

Pebbles; sand, fine to medium 27 32 

Sand, very coarse; pebbles;

gravel, fine................................ 37 52

Gravel, fine, and pebbles; clay ,_ , .

lens...........................................

Sand, coarse 57 59 

Sand, medium to very coarse 62 74

Clay, dark gray; silt, gray-green; 

refusal 85.5 ft........................... 77

W-309, Altitude 525.48 ft 

Sand, medium to coarse; 

pebbles..................................... 0 43

Sand, coarse; pebbles................... 43 45

Sand, fine, brown......................... 48 55

Bottom of

unit 

or sample

(ft)

W-309 Continued 

Sand, very fine; silt and clay layers, gray ................................... 58 60

Sand, medium.............................. 63 65

Sand, fine, brown; some silt and 

clay layers................................ 68 75

Clay, gray; some silt.................... 78 80

Sand, very fine, gray; clay, gray.. 83 85

Till, sand, clay, pebbles; refusal

100ft........................................ 93

W-310, Altitude 487.65 ft

Sand, fine; some silt stringers 0 24 

Sand, very coarse; gravel, coarse 37 39 

Sand, medium; some pebbles 42 44 

Sand, fine to medium................... 47 49

Clay, gray; some silt; at base tillsand, clay, pebbles................... 52 54

Till-sand, pebbles, gray clay........ 57 59

Sand, coarse, gray, some fine;

some rounded pebbles............. 62 64

Till-sand, coarse, gray; pebbles;

clay; refusal 70ft..................... 67

W-312, Altitude 444.41 ft

Sand, fine; pebbles....................... 0 37

Sand, fine to coarse; refusal -

43ft.......................................... J/

W-313, Altitude 504.92 ft 

Cobbles, gravel, boulders; end of

hole 52 ft.................................. 0

W-314, Altitude 574.69 ft 

Cobbles, coarse sand; end of hole

59ft.......................................... 7

W-315, Altitude 442.30 ft

Sand, fine; silt; clay, gray ............ 0 14

Sand, very fine to medium; some

silt............................................ 17 29

Clay, gray; sand, fine................... 32 37

Sand, coarse to very coarse; some 

pebbles..................................... 37 69

Till-sand, coarse, gray; pebbles; 

clay; refusal 100ft................... 77

W-316, Altitude 506.54 ft

Gravel and landfill material......... 0 13

Pebbles and sand......................... 13 25

Sand, fine, uniform; end of hole 

39ft.......................................... 25

W-317, Altitude 527.57 ft

Sand, fine; pebbles....................... 0 48

Cobbles........................................ 48 50

Sand............................................. 50 77

Appendix 3 83
Appendix 3. Lithologic logs of wells in Bristol, Vermont-Conftnued

Description of material

Top of unit

or sample

(ft)

Bottom of

unit 

or sample

(ft)

W-317 Continued

Sand, medium; end of hole

79ft..........................................

W-318, Altitude 552.34 ft 

Sand, medium; pebbles;

end of hole 112 ft.....................

W-319, Altitude 497.46 ft

Silt and fine sand,,,,,,,,,,,,.

Sand, silt, and cobbles; refusal

15 ft ..........................................

W-320, Altitude 450.50 ft 

Clay and silt; some sand, fine 

Silt, clay, and fine sand ................

Sand, fine,,,,,,,,,,,,,,..,,,. 

Sand, medium ..............................

Clay, silt, and sand,,,,,,,.,,,. 

Till, gray, sandy, angular

pebbles; end of hole 90 ft.........

W-321, Altitude 411.31ft 

Sand, fine; silt; clay,,,,,,,,,,. 

Sand, fine to medium; some silt... 

Sand, fine to medium...................

Sand, silt, clay .............................

Till; refusal 80 ft ..........................

W-322, Altitude 431.21ft 

Sand, silt, clay .............................

Sand, medium..............................

Silt and clay,,.,,,,,,,,,,.,,,. 

Sand, silt, clay,,,,,,,,,,,,,,. 

Till, silty, sandy, angular pebbles;

end of hole 100 ft .....................

W-324, Altitude 424.50 ft 

Sand, very fine; silt......................

Sand, coarse.................................

Sand, fine to medium...................

Sand, medium ..............................

Sand, fine; silt, clay,,,,,,,,,,. 

Sand, medium ..............................

Sand, fine; silt; some clay ............

Till; end of hole 90 ft...................

W-326, Altitude 420.21ft

Fill cobbles, trash.......................

Sand, coarse; pebbles; silt; end of 

hole 17ft..................................

W-327, Altitude 442.05 ft 

Sand, medium to very coarse; 

cobbles .....................................

Silt; clay, solid.............................

Sand, fine; pebbles; refusal

77

58.5 ft.

0

10

0

12

25

45

70

81

0

15

22

45

77

0

25

60

75

83

0

15

25

39

53

55

77

90

0

15

0

37

39

10

12

25

45

70

81

15

22

45

77

25

60

75

83

15

25

39

53

55

77

90

15

37

39

Description of material

W-329, Altitude 413.53 ft

Sand, gravel, and cobbles.............

Sand, silt, clay ..............................

Sand..............................................

Clay.............................................

Sand, fine, uniform.......................

Sand, very fine; clay.....................

Sand, fine; refusal 70 ft ................

W-330, Altitude 424.20 ft

Sand, medium to coarse ...............

Silt and clay..................................

Till, coarse; end of hole 30 ft

W-332, Altitude 495. 15 ft

Gravel, sand and cobbles..............

Cobbles and gravel.......................

Sand, possibly fine with clay. .......

Sand, medium.. ...... .......................

Gravel and cobbles; sand,

medium to fine..........................

Till................................................

Bedrock, dolomite; end of hole

135ft.......................................

W-334, Altitude 574 ft

Fill-trash; sand, fine; cobbles......

Sand, gravel, cobbles....................

Boulders, cobbles .........................

Sand, possibly medium................

Sand, medium; cobbles;

boulders...................................

Clay, possibly ...............................

Till, sand, clay, boulders;

end of hole 200 ft .....................

W-336, Altitude 574 ft

Fill-trash.....................................

Sand, coarse; gravel; boulders

Sand, fine...,.....,.....,.,,.,.....,.,.

Sand, fine; pebbles; some clay;

end of hole 168 ft .....................

W-337, Altitude 500.82 ft

Fill-trash,.,,,,.,,.,,.,,,,,.,.,

Gravel, cobbles, boulders, fine

sand; end of hole 150ft............

W-338, Altitude 41 1ft

Sand, medium; silt;

end of hole 20 ft .......................

W-339, Altitude 405 ft

Sand, fine; end of hole 20 ft

W-340, Altitude 407 ft

Sand, fine to medium;

end of hole 20 ft .......................

Top of unit

or sample

(ft)

0

10

13

17

19

50

65

0

22

25

0

56

83

95

105

127

131

0

10

70

85

127

180

185

0

5

83

130

0

4

0

0

0

Bottom of 

unit

or sample

(ft)

10

13

17

19

50

65

-

22

25

-

56

83

95

105

127

131

-

10

70

85

127

180

185

-

5

83

130

-

4

-

84 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
Appendix 3. Lithologic logs of wells in Bristol, Vermont-Conf/nued

Description of material

W-351, Altitude 574.38 ft

Gravel and sand; end of hole

24ft..........................................

W-352, Altitude 503.07 ft

Cobbles and sand; end of hole

25ft

W-353, Altitude 505.96 ft

Coarse sand, gravel, cobbles; 

end of hole 41 ft.......................

W-354, Altitude 506.69 ft

Sand and gravel; end of hole

43ft..........................................

W-355, Altitude 5 10.60 ft

Sand and gravel; end of hole 

41ft..........................................

W-356, Altitude 498.04 ft

Sand and gravel; end of hole 

57ft..........................................

W-504, Altitude 424.49 ft

Sand, medium ..............................

Sand, fine to medium ...................

Clay, blue; end of hole 44 ft.........

W-505, Altitude 420. 10 ft

Silty sand, trace clay ....................

Sand, coarse .................................

Gravel, medium; sand, fine; trace

silt.............................................

Sand, very fine to coarse,

predominantly medium;

end of hole 38 ft.......................

W-507, Altitude 443.73 ft

Silt, clay, sand..............................

Gravel, medium; sand, silty .........

Sand, fine, trace silt; end of hole

58ft..........................................

W-508, Altitude 417.48 ft

Silty sand, trace clay ....................

Clay, some silt, little sand............

Sand, little silt; end of hole

28ft..........................................

W-509, Altitude 412. 15 ft

Gravel, little silt...........................

Gravel, coarse, much silt..............

Till................................................

W-510, Altitude 404. 13 ft

Gravel; end of hole 30 ft..............

Top of unit

or sample 

(ft)

0

0

0

0

0

0

0

24

37

0

13

20

24

0

35

48

0

8

17

0

15

20

0

Bottom of 

unit

or sample

(ft)

--

24

37

13

20

24

--

35

48

--

8

17

--

15

20

_

..

Description of material

W-903, Altitude 5 10 ft

Sand, silty ....................................

Silt, sandy ....................................

Sand, fine.....................................

Silt, sandy; end of hole 20 ft........

W-904, Altitude 5 10 ft

Sand, fine to silty.........................

Sand, fine; silt..............................

Silt, fine sand; gravel at 34 ft

Bedrock, weathered, soft; refusal 

/i/l ft

W-905, Altitude 5 10 ft

Landfilled material ...................... 

Gravel, small stones;

refusal 33 ft..............................

BR-2, Altitude 505.56 ft 

Sand, silty ....................................

Silt...............................................

Silt, clayey...................................

Silt; refusal 40 ft ..........................

BR-6, Altitude 503.05 ft

Sand and gravel; garbage ............

Sand and gravel ...........................

Sand, medium..............................

Sand; silt layers ...........................

Till or gravel ................................

MW-101, Altitude 574.19 ft

Sand, medium; gravel;

some boulders..........................

Gravel, medium, gray;

boulders ...................................

Gravel, small; sand......................

Silt, sandy, gray ...........................

Sand, fine to medium, brown

Clay, silty, gray; end of hole

178ft........................................

MW-102d, Altitude 528.13 ft

Sand, medium, brown;

some gravel...... ........................

Sand, medium, gravelly...............

Sand, fine; some silt;

little gravel...............................

Silt, sandy, gray ...........................

Sand; gravel.................................

Till, silty, gravelly, gray; end of

hole 127 ft................................

Top of unit

or sample 

(ft)

0

5

10

15

0

20

30

39

0

5

0

20

25

35

0

5

30

60

70

0

40

81

130

135

178

0

27

70

107

110

125

Bottom of 

unit

or sample

(ft)

5

10

15

20

30

39

5

20

25

35

--

5

30

60

70

78

40

0 1

130

135

178

27

70

107

110

125

Appendix 3 85
APPENDIX 4
WELL W301 WELL W308

ELECTROMAGNETIC

CONDUCTIVITY, IN

MILUSIEMENS PER METER

-10 0 10 20 30 40 EC 60

GAMMA, IN COUNTS 

PER SECOND

80 100 120 VA

Uajer livel ' JL I

WELL W303

ELECTROMAGNETIC

CONDUCTIVITY, IN

MILUSIEMENS PER METER

10 20 30 « 50 60

GAMMA IN COUNTS 

PER SECOND

0 20 « 60 60 100 CO V

t

sand and 

pebbles .

__ __.

Till 

Refusal

(-^*> e- K S5E SEALEVEL,

Qi 

425 mt- *fs c;ALTITUDE

ELECTROMAGNETIC

CONDUCTIVITY, IN

MILUSIEMENS PER METER

-10 0 10 20 30 40 50 60

Interference

Interference

Water level

GAMMA, IN COUNTS 

PER SECOND

0 20 40 60 BO 100 120 140

Refusal

460

455

450

445

440

435

430

425

y<

01(/>

410 ^>

405 g>

400 g

395 § 

K 

390 5^

385 

380 

375 

370

WELL W307

ELECTROMAGNETIC

CONDUCTIVITY, IN

MILUSIEMENS PER METER

GAMMA, IN COUNTS 

PER SECOND

W301 

346

S13 A 

460

EXPLANATION

SCREENED INTERVAL OF OBSERVATION 

WELL Top number is well number. 

Bottom number is specific conductance 

of water samples from the screened 

interval, in microsiemens per centimeter 

at 25 degrees Celsius

SPRING Top number is spring 

number. Bottom number is 

specific conductance

Figure 4-1. Borehole geophysical logs showing geologic section, screened interval, and associated specific 

conductance of ground water for observation wells W301, W303, W 307, and W308, and for spring S14, Bristol, 

Vermont (locations shown in figs. 5 and 8)

Appendix 4 89
WELL W309 WELL W315

ELECTROMAGNETIC

CONDUCTIVITY. IN

MIULISIEMENS PER METER

-10 0 TO 20 30 40 50 60

GAMMA, IN COUNTS 

PER SECOND

20 40 SO 80 100 t2C HO

UJ 70

a

85

90

95

100

105

Interference

Water level

Clay, silt

and fine

sand

Refusal

0

5

10

15

20

I- 25

UJ

£30

 35 UJ* 

O 40

D

en so 

D

Z 55

9a: l

UJ

CD 70

ELECTROMAGNETIC

CONDUCTIVITY. IN

MILLISIEMENS PER METER

-10 0 10 20 30 40 5C 60

UJ 

Q 8C

90

95

100

105

Water level

W315E 

420 E

Interference

GAMMA, IN COUNTS 

PER SECOND

4C 80 80 100 120 140

WELL W310

ELECTROMAGNETIC

CONDUCTIVITY, IN GAMMA, IN COUNTS 

MILUSIEMENS PER METER PER SECOND

-10 0 W 20 30 +0 50 (0 0 20 4C CO 80 100 120

UJ 15

Z 20

fe 30 

W 35

UJ 

CD 55

UJ 

Q 65

W309 

315

Interference

EXPLANATION

SCREENED INTERVAL OF OBSERVATION 

WELL Top number is well number. 

Bottom number Is specific conductance 

of water samples from the screened 

Interval, in microsiemens per centimeter 

at 25 degrees Celsius.

WELL W320

ELECTROMAGNETIC

CONDUCTIVITY. IN

MILLISIEMENS PER METER

-10 0 10 20 30 40 50 80 0 20 40 60 60 100 CO 140

450

UJ

a

Figure 4-2. Borehole geophysical logs showing geologic section, screened interval, and associated specific 

conductance of ground water for observation wells W309, W310, W315, and W320, Bristol, Vermont (locations 

shown in fig. 5).

90 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
WELL W324

ELECTROMAGNETIC

CONDUCTIVITY, IN

MILUSIEMENS PER METER

GAMMA, IN COUNTS 

PER SECOND

20 40 so ao 100 no wo

WELL W329

ELECTROMAGNETIC 

CONDUCTIVITY, IN GAMMA, 

MILUSIEMENS PER METER PER

-10 0 10 20 30 40 50 GO

IN COUNTS 

SECOND 

ao too co MO

413

"FlneTsand, 

silt, and clay 

Vefy"fine

sand 

and thin 

clay lenses

WELL W321

WELL W322

ELECTROMAGNETIC

CONDUCTIVITY, IN

MILUSIEMENS PER METER

-10 0 » 20 30 40 50 SO

GAMMA, IN COUNTS 

PER SECOND

0 20 40 80 00 100 GO HO

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

-InterferenceWELL W305

ELECTROMAGNETIC

CONDUCTIVITY, IN 

MILLISIEMENTS PER METER

 10 0 10 20 ;io *O SO 80 Oi < i r-S

GAMMA, IN COUNTS 

PER SECOND

20 40 80 80 100 CO WO

403 

398 fc 

393 £ 

388 z 

383 _; 

378 S 

373^ 

368 £

CO 

363m

358o

CD 353 < 

348 S 

343? 

-338 5 

333

ELECTROMAGNETIC

CONDUCTIVITY, IN

MILUSIEMENS PER METER

-10 0 10 20 30 40 50 50

GAMMA, IN COUNTS 

PER SECOND

20 40 «0 80 100 (20

10

15

t 2°

LU OC u. £0

z 30

ul 35

< 40

U_

Sj 45 

"> 50 

i 55 

3 60

S 65

uj 70

x^5

t 80

g 85

90

95

100

EXPLANATION

SCREENED INTERVAL OF OBSERVATION 

WELL Top number is well number. 

Bottom number is specific conductance 

of water samples from the screened 

interval, in microsiemens per centimeter 

at 25 degrees Celsius.

Figure 4-3. Borehole geophysical logs showing geologic section, screened interval, and associated 

specific conductance of ground water for observation wells W324, W321, W305, W329, and W322, Bristol, 

Vermont (locations shown in fig. 5).

Appendix 4 91
WELL W6 WELL W334

ELECTROMAGNETIC

CONDUCTIVITY. IN

MILUSIEMENS PER METER

-10 0 10 20 30 40 50 50

GAMMA. IN COUNTS 

PER SECOND

10 60 80 100 120

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

Interference

 Water

 level

|W316 

6 1.170

j W6 

i420

CUJ

u_

2

0

10

20

30

40

50

LLJ

£ 60

LL.

§ 70

en

Q 80

3 90 

I 100

_1

oo 110 

I 120

UJ

Q 130 

140 

150 

160 

170 

180 

190

ELECTROMAGNETIC

CONDUCTIVITY. IN

MILUSIEMENS PER METER

-to 0 10 20 30 40 SO 80 70 60 90 100

GAMMA, IN COUNTS 

PER SECOND

20 4O 80 80 100 CO

Interference

W334 _ 

390 1

WELL W102d

ELECTROMAGNETIC 

CONDUCTIVITY. IN 

MILUSIEMENS PER METER 

-10 o ra zo so « so 10 o

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

125

T Water level

g W317 

gl 1.620

I W102S 

I 810

Interference -4

W102d 

i 400

EXPLANATION

SCREENED INTERVAL OF OBSERVATION 

WELL Top number is well number. 

Bottom number is specific conductance 

of water samples from the screened 

interval, in microsiemens per centimeter 

at 25 degrees Celsius.

Figure 4-4. Borehole geophysical logs showing geologic section, screened interval, and associated specific 

conductance of ground water for observation wells W6, W102d, and W334, Bristol, Vermont (locations shown 

in fig. 5).

92 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
WELL W327 WELL MW101

CONDUCTIVITY, IN GAMMA, IN COUNTS 

MILLISIEMENS PER METER PER SECOND

-10 0 10 20 30 0) 50 60 70 60 80 100 0 20 W 60 10 100 OO «0

K

LU

if

z

LU

LL 

IT

D 

CO

Q

i

LU 

CD

LU

Q

5

10

15

20

25

30

.

" I

- J

. \ Water level i

\ g W328 35 r v- 355

40

45

50 

55

60

65

J

- I

B W327 

M 345

 3£

.

-n

Sill and~ciay

-

F r35

 >_ Medium 10 i 43°

5" coarse sand ...

lr and cobbles"

^^*

_^^-

^S425

420

415

410

t _--

^^-

^;

 *~ Rnesand 

and some pebbles .

Refusal

400

395

390 

385

380

 575

K

LU

LU 

LL

Z

_r

$

a

<LU

CO

0

9

LU

Q

1

IT 

D 

CO

QL.

LU 

Q

WELL W330

ELECTROMAGNETIC

CONDUCTIVITY, IN

MILLISIEMENS PER METER

-10 0 10 20 30 W 50 CO 70 80 90 100

GAMMA, IN COUNTS 

PER SECOND

20 « 80 «0 100 CO HO

y

5

10

15

20

25

30

-i^

, _ .

V^ j. Water level

 j W331 g

_ ) 690 H

'I

^4-

W330 H

350 e

1

-

'

-

-

.

._Clay_

a 

2

CO K

LULU 

LL

LU 

O

ELECTROMAGNETIC

CONDUCTIVITY, IN

MILLISIEMENS PER METER

GAMMA, IN COUNTS 

PER SECOND

-10 0 10 20 30 W 50 60 0 20 W GO 10 100 CO

LL

Z

LL 

IT 

D 

CO 

Q

Interference 

(steel casing)

Sand and 

gravel

Silt and

Silt and clay

, Till,

-claySand

Sand

LL

Z

W331 

690

EXPLANATION

SCREENED INTERVAL OF OBSERVATION 

WELL Top number is well number. 

Bottom number is specific conductance 

of water samples from the screened 

interval, in microsiemens per centimeter 

at 25 degrees Celsius

Figure 4-5. Borehole geophysical logs showing geologic section, screened interval, and associated 

specific conductance of ground water for observation wells W327, W330, and W101, Bristol, Vermont 

(locations shown in fig. 5)

Appendix 4 93
APPENDIX 5
Appendix 5. Hydraulic conductivity and lithologic descriptions of wells in Bristol, Vermont

[Type of aquifer test: Specific-capacity tests were limited by the capacity of the pump used, ft/d, foot per day. >, actual value is greater than 

value shown; <, actual value is less than value shown]

Well No.

W-303

W-304

W-305

W-306

W-308

W-309

W-310

W-311

W-312

W-315

W-320

W-321

W-323

W-325

W-327

W-329

W-330

W-331

W-335

W-337

W-338

W-339

W-341

W-356

BR-2

MW-4

W-507

W-509

W-508

W-510

W-511

Hydraulic conductivity 

(ft/d)

0.7

2

3

10

60

>150

4

45

30

55

>150

>150

10

5

30

12

5

27

3

200

>150

>150

30

27

60

250

<1

30

100

120

>150

180

15

Description of material 

near well screen

Till, clayey sandy

Sand, fine

Sand, poorly sorted (till)

Sand, very fine; silt

Sand, coarse; gravel

Till, sand, clay pebbles

Sand, coarse; pebbles; clay

Sand, medium

Sand, fine to coarse

Sand, fine to coarse

Sand, fine

Sand; silt; clay

Silt; clay; fine sand and pebble lenses

Sand, fine to medium

Sand, fine

Sand, fine

Till, sand, silt

Sand, medium to coarse

Sand and gravel

Sand and gravel

Sand, fine to medium

Sand, fine

Sand, medium

Sand and gravel

Sand, fine

Sand

Sand, coarse

Sand

Sand

Sand and gravel

Sand

Type of aquifer test

Slug

Slug

Slug

Slug

Slug

Specific capacity

Slug

Slug

Slug

Slug

Slug

Specific capacity

Slug

Slug

Slug

Slug

Slug

Slug

Slug

Slug

Specific capacity

Specific capacity

Slug

Slug

Slug

Slug

Slug

Slug

Slug

Slug

Specific capacity

Slug

Slug

Appendix 5 97
APPENDIX 6
Appendix 6. Measured and calculated heads in Bristol, Vermont, April 1991

[--, no data]

Well

No.

W-12

W-318

W-302

W-301

W-303

W-311

W-310

BR-2

W-319

MW-2

W-309b

W-309

W-316

BR-6

MW-4

W-317

MW-102s

MW-102d

W-328

W-327

W-331

W-330

W-335

W-334

W-337

MW-101

W-315

W-304

W-509

W-510

W-306

W-305

W-323

W-340

W-321b

W-321

W-307

W-308

W-320

W-507

W-322

W-325

Layer

2

1

1

2

2

1

2

1

1

1

1

2

1

2

1

1

1

2

1

2

1

2

1

2

1

2

1

1

1

1

1

2

2

1

1

2

2

1

2

1

2

1

Model

Row

8

14

18

18

14

11

11

8

7

7

6

6

9

9

11

12

13

13

26

26

23

23

14

14

19

19

27

30

28

31

36

36

36

35

36

36

43

40

40

40

40

38

Column

45

32

15

15

14

15

15

25

25

31

38

38

31

31

27

23

23

23

13

13

13

13

25

26

21

20

3

13

9

9

5

5

5

6

7

7

10

25

19

13

10

10

Measured 

(ft)

'480.0

453.1

428.9

'435.0

444.4

455.8

458.0

480.8

484.1

486.4

484.1

488.4

470.9

482.1

461.5

453.0

452.9

455.4

'408.6

'411.9

'413.7

'415.3

'447.3

'455.5

'446.9

445.4

'400.4

406.5

403.1

401.8

399.3

401.0

'399.8

'401.2

402.3

404.8

405.1

407.5

406.1

404.8

404.1

'403.2

Head

Calculated 

(ft)

479.6

454.1

423.3

433.7

443.9

454.9

461.7

479.7

485.5

487.4

483.2

488.3

471.2

483.1

461.1

449.9

446.8

453.4

412.5

425.5

415.2

419.0

447.8

453.4

437.4

439.1

399.1

409.8

408.0

406.3

398.5

398.8

398.8

400.5

402.2

404.3

407.5

412.9

410.2

408.5

407.8

406.2

Hydraulic gradient

Difference 

(ft)

-0.4

1.0

-5.6

-1.3

-.5

-.9

3.7

-1.1

1.4

1.0

-.9

-.1

.3

1.0

-.4

-3.1

-6.1

-2.0

3.9

3.6

1.5

3.7

.5

-2.1

-9.5

-6.3

-1.3

3.3

4.9

4.5

-.8

-2.2

-1.0

-.7

-.1

-.5

2.4

5.4

4.1

3.7

3.7

3.0

Measured 

(ft)

_

6.0

2.2

4.3

11.2

2.5

_

3.3

__

1.6

8.2

-1.5

1.7

_

-_

2.5

_

_

Calculated 

(ft)

~

10.4

-

6.8

5.1

11.9

6.6

_

3.0

._

3.7

5.6

1.7

.3

_

. 

2.1

__

_

Difference 

(ft)

_

4.4

4.4

.8

.7

4.1

_

-.3

_

2.1

-2.6

-3.2

1.4

_

~

-.4

_

_

Appendix 6 101
Appendix 6. Measured and calculated heads in Bristol, Vermont, April 1991-Conftnued

Well

No.

W-324

W-341

W-508

W-326

W-511

W-329

W-332

W-312

W-233

W-551

W-552

W-553

W-554

W-555

W-556

W-82

Standard mean

Absolute mean

Layer

2

1

1

1

1

2

2

1

2

Model

Row

38

37

37

35

34

34

36

46

56

42

40

37

36

38

38

57

Column

10

7

8

9

8

8

25

32

42

47

47

46

46

46

45

40

Measured 

(ft)

'404.8

'402.7

402.7

'404.9

401.7

402.9

'414.1

408.0

'405.0

'483.9

'485.3

'470.2

'465.5

'472.5

'463.8

'398.0

-

Head

Calculated 

(ft)

408.0

402.1

403.7

405.1

404.3

405.6

416.8

411.2

400.5

483.6

485.3

475.0

474.9

474.9

461.4

396.7

~

Difference 

(ft)

3.1

-0.6

1.0

.2

2.6

2.7

2.7

3.2

-1.5

-.3

0

4.8

9.4

2.4

-2.4

-1.3

+.6

2.5

Hydraulic gradient

Calcu- Differ- Measured , , 

,-,. lated ence

(ft) (ft) (ft)

1.6 1.8 .2

__

__

1.2 2.3 1.1

..

__

__

__

__

_

__

__

..

+1.0

2.0

Estimated head.

102 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
APPENDIX 7
Appendix 7. Summary of water-quality analyses in Bristol, Vermont

[mmddyy, month, day year; nS/cm, microsiemen per centimeter at 25 degress Celsius; mg/L, milligram per liter; ng/L, microgram per

Well 

No.

W-12

W-303

W-304

W-305

W-306

W-309

W-310

W-311

W-312

W-315

W-318

W-307

W-308

W-320

Date H 

(mmddyy) ^

091990 -

090690 7.6

052091 7.45

101091

090590 7.6

050891

052291

100891

090590 7.6

050891

100891

090590 7.6

050891

100891

090590 -

050891

052291

100991

090590 7.4

052091 7.08

101091

090690 -

052091 6.58

101091

091990

050891

052291

101091

091990 -

021391

052091 7.18

101891

090690 -

050891

052291

100891

090690 -

050891

100891

021391

050891

Specific 

conductance 

(US/cm)

298

230

355

357

230

293

302

326

280

-

414

210

-

385

180

303

318

315

260

412

416

330

386

465

376

365

364

-

417

335

458

-

-

320

356

300

-

426

459

291

368

Calcium, 

dissolved 

(mg/L)

~

42.8

39.2

-

65.8

--

28.8

-

42.6

44.7

--

43.0

39.6

-

33.2

--

36.9

-

45.4

43.4

-

-

61.1

-

30.6

-

32.6

-

-

30.5

42.2

-

18.3

28.1

26.8

-

45.4

51.0

-

36.1

Potassium, 

dissolved 

(mg/L)

-

1.48

1.20

-

3.80

-

2.26

-

1.35

1.48

-

1.28

1.18

-

1.11

--

1.11

--

1.20

1.10

-

-

1.30

-

0.76

-

1.48

-

--

1.66

1.02

-

0.23

1.34

1.31

-

1.33

1.30

-

1.41

Chloride, 

dissolved 

(mg/L)

13.0

1.4

1.5

1.7

2.2

1.5

-

3.2

1.3

1.2

2.6

12.4

14.9

16.0

8.0

9.6

-

9.0

4.8

5.0

4.9

32.4

6.7

19.7

29.3

40.9

-

31.0

11.8

27.6

30.5

23.8

5.1

1.3

-

1.9

6.7

16.7

18.0

2.5

1.6

Sodium, 

dissolved 

(mg/L)

5.80

3.24

-

3.12

7.29

6.98

-

4.52

2.91

2.33

3.82

12.3

10.9

11.2

3.79

5.65

-

3.44

4.06

-

4.40

7.35

-

10.1

25.2

25.8

-

23.9

7.12

16.9

__

19.7

9.15

18.3

15.1

17.8

-

9.09

8.96

9.81

9.43

Iron, 

dissolved 

(mg/L)

19

1,020

21

18

20

2,890

--

18

<10

147

14

<10

42

<10

10

147

--

<10

984

117

43

469

54

42

1,030

408

-

244

131

60

14

<10

293

1,030

17

21

438

342

<10

76

252

Manganese, 

dissolved 

(mg/L)

<10

326

87

153

85

583

~

90

80

109

95

245

155

13

215

265

-

127

439

13

149

1,100

26

16

240

171

-

10

62

<10

<10

<10

96

191

96

94

187

94

<10

541

551

Magnesium, 

dissolved 

(mg/L)

~

25.4

23.1

-

34.7

~

21.8

-

21.9

24.5

-

17.5

16.8

-

16.8

-

17.0

-

26.9

26.3

-

-

17.1

--

13.9

-

12.9

-

~

17.5

17.6

-

13.9

13.7

13.1

-

20.8

22.0

-

21.7

Zinc, 

dissolved 

(mg/L)

308

<40

<40

<40

<40

<40

-

<40

<40

<40

<40

<40

<40

<40

<40

<40

-

<40

<40

<40

<40

51

<40

<40

<40

<40

-

<40

<40

<40

<40

<40

<40

<40

<40

<40

112

72

<40

<40

168

Chromium, 

dissolved 

(mg/L)

<10

<10

<10

<10

<10

<10

-

<10

<10

<10

<10

<10

<10

<10

<10

<10

-

<10

<10

<10

<10

<10

<10

<10

<10

<10

--

<10

<10

' <10

<10

<10

<10

<10

<10

<10

<10

<10

<10

<10

<10

104 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
liter; <, actual value is less than value shown. --, no data]

Well 

No.

W-12 

W-303

W-304

W-305

W-306

W-309

W-310

W-311

W-312

W-315

W-318

W-307

W-308

W-320

Date 

(mmddyy)

091990 

090690

052091

101091

090590

050891

052291

100891

090590

050891

100891

090590

050891

100891

090590

050891

052291

100991

090590

052091

101091

090690

052091

101091

091990

050891

052291

101091

091990

021391

052091

101891

090690

050891

052291

100891

090690

050891

100891

021391

050891

Cadmium, Copper, Lead, Cobalt, 

dissolved dissolved dissolved dissolved 

(mg/L) (mg/L) (mg/L) (mg/L)

<2 -- <10 

<2 -- <10

<2 <10 <10 <10

<2 <10 <10

<2 -- <10

<2 <10 <10 <10

-

<2 <10 <10

<2 -- <10

<2 <10 <10 <10

<2 12 <10

<2 -- <10

<2 <10 <10 <10

<2 <10 <10

<2 - <10

<2 <10 <10 <10

-

<2 <10 <10 <10

<2 -- <10

4 <10 <10 <10

<2 <10 <10

<2 -- 15

<2 27 <10 <10

<2 <10 <10

<2 -- <10

<2 <10 10 <10

-

<2 12 <10

<2 - <10

<2 <10 <10

<2 11 <10 <10

<2 13 <10 <10

<2 -- <10

2 158 21 <10

<2 <10 <10 <10

<2 <10 <10

<2 - <10

<2 21 73 <10

<2 17 <10 <10

<2 12 <10

<2 <10 11 <10

Arsenic, 

dissolved 

(mg/L)

;;

<5

<5

--

<5

-

<5

-

<5

<5

--

<5

<5

--

<5

-

<5

<5

<5

--

<5

<5

--

<5

<5

-

--

<5

<5

-

<5

<5

<5

-

<5

<5

<5

Selenium, 

dissolved 

(mg/L)

;;

<5

<5

--

<5

-

<5

-

<5

<5

-

<5

<5

--

<5

-

<5

<5

<5

<5

<5

--

<5

<5

--

-

<5

<5

<5

<5

<5

--

<5

<5

<5

Barium, 

dissolved 

(mg/L)

30

39

--

52

-

Ill

-

38

75

-

27

76

--

36

40

42

21

132

31

-

24

14

--

72

18

24

50

28

-

24

31

38

Nickel, Silver, Sulfate, 

dissolved dissolved dissolved 

(mg/L) (mg/L) (mg/L)

13.2 

19.1

<10 <1 19.6

<10 <1 20.0

17.3

<10 <1 8.6

..

<10 <1 17.0

24.8

<10 <1 22.7

<10 <1 22.9

15.8

<10 <1 16.5

<10 <1 17.3

42.2

<10 <1 43.0

<10 <1 41.2

23.5

<10 <1 23.6

<10 <1 23.4

15.7

<10 <1 11.3

<10 <1 11.2

6.0

<10 <1 5.6

<10 <1 6.9

15.2

18.2

<10 <1 19.6

<10 <1 19.6

8.8

<10 <1 11.9

<10 <1

<10 <1 11.6

11.5

<10 <1 14.2

<10 <1 15.5

14.6

<10 <1 17.9

Appendix? 105
Appendix 7. Summary of water-quality analyses in Bristol, Vermont-ConWnuec/

Well 

No.

W-320

W-321

W-322

W-324

W-323

W-329

W-334

W-509

S-13

S-15

S-12

S-ll

W-301

W-302

S-14

W-317

MW-102s

Date 

(mmddyy)

052291

100891

021391

050891

052291

100891

050891

052291

100891

100891

100891

081491

082291

101791

092090

050891

052291

100891

052091

101091

090590

050991

101091

070690

090590

050991

070690

090590

090690

052091

052091

101091

091990

070690

090590

052091

082291

101091

021391

050991

100991

091990

052091

PH

-

-

-

-

-

-

__

-

-

-

-

8.24

-

-

-

__

-

-

-

7.1

-

6.9

7.3

-

8.0

7.1

7.6

7.28

-

_

7.6

7.1

7.4

6.60

7.12

-

-

-

-

-

5.96

Specific 

conductance 

(US/cm)

365

386

304

372

369

383

340

338

354

359

354

398

390

-

379

318

336

350

-

464

520

367

-

310

340

291

200

190

240

358

-

346

376

470

520 .

810

1,000

952

955

1,618

1,135

1,260

812

Calcium, 

dissolved 

(mg/L)

37.0

36.9

-

41.1

-

39.7

37.6

41.4

37.9

37.3

__

-

37.7

-

118

42.4

50.2

61.0

-

39.4

37.0

-

-

33.4

__

-

37.7

38.8

37.8

-

-

100

__

95.5

-

-

164

-

Potassium, 

dissolved 

(mg/L)

1.44

1.13

-

1.35

-

1.71

1.12

1.47

1.25

1.35

__

-

1.89

1.45

_

.96

.90

.60

-

1.60

3.94

-

1.42

_

.91

1.00

.95

-

-

6.31

_-

19.9

-

-

1.62

-

Chloride, 

dissolved 

(mg/L)

-

0.9

7.2

3.8

-

3.1

1.4

-

3.1

12.0

2.8

__

4.5

3.8

7.6

9.1

__

7.2

15.6

15.1

68.4

22.1

50.1

18.7

22.9

10.2

24.7

24.7

1.5

1.5

-

1.7

2.9

11.7

13.3

31.4

44.2

41.5

23.8

96.8

16.4

26.4

36.6

Sodium, 

dissolved 

(mg/L)

10.0

8.31

13.3

11.0

-

6.03

14.3

8.13

11.3

4.58

__

48.2

15.5

4.63

6.93

_

6.03

-

9.15

34.1

13.8

24.8

8.82

9.47

6.75

14.4

14.8

3.36

-

3.31

3.28

4.88

6.17

6.1

-

37.6

30.5

22.4

88.0

16.1

7.23

Iron, 

dissolved 

(mg/L)

28

<10

26

139

-

<10

261

14

<10

<10

87

29

291

733

_

14

167

16

70

66

144

8,180

98

39

1,150

182

331

40

380

39

591

888

135

<10

53

12

539

167

39

839

<10

Manganese, 

dissolved 

(mg/L)

444

226

535

150

-

18

149

-

117

114

56

_

-

341

386

944

_

39

<10

84

58.0

11.0

83.0

249

49.0

41.0

76.0

135

194

117

151

131

708

108

<10

-

_

16

207

624

924

4,790

137

Magnesium, 

dissolved 

(mg/L)

21.3

22.2

-

20.3

-

21.3

16.6

23.6

16.1

20.8

__

12.2

21.8

-

43.8

__

21,3

19.3

18.5

-

15.7

15.5

-

-

14.2

_

22.8

23.0

22.1

-

-

38.3

44.0

41.3

-

-

55.3

-

Zinc, Chromium, 

dissolved dissolved 

(mg/L) (mg/L)

<40 <10

<40 <10

<40 <10

<40 <10

..

<40 <10

41 <10

<40 <10

<40 <10

<40 <10

__

<40 <10

<40 <10

<40 <10

<40 <10

_

<40 <10

<40 <10

<40 <10

<40 <10

<40 <10

<40 <10

23 <5

<40 <10

<40 <10

<20 <5

<40 <10

<40 <10

<40 <10

<40 <10

<40 <10

<40 <10

<20 <5

<40 <10

<40 <10

<40 <10

<40 <10

<40 <10

<40 <10

<40 <10

<40 <10

<40 <10

106 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
Well 

No.

W-320

W-321

W-322

W-324

W-323

W-329

W-334

W-509

S-13

S-15

S-12

S-ll

W-301

W-302

S-14

W-317

MW-102s

Date 

(mmddyy)

052291 

100891

021391

050891

052291

100891

050891

052291

100891

100891

100891

081491

082291

101791

092090

050891

052291

100891

052091

101091

090590

050991

101091

070690

090590

050991

070690

090590

090690

052091

052091

101091

091990

070690

090590

052091

082291

101091

021391

050991

100991

091990

052091

Cadmium, Copper, Lead, Cobalt, 

dissolved dissolved dissolved dissolved 

(mg/L) (mg/L) (mg/L) (mg/L)

<2 12 <10 

<2 <10 <10

<2 <10 <10

<2 <10 <10 <10

-

<2 <10 <10

2 18 <10 <10

-

<2 <10 <10

<2 12 <10

<2 <10 <10

<2 76 <10 <10

<2 <10 <10 <10

<2 -- <10

<2 10 <10 <10

__

<2 <10 <10

<2 11 <10 <10

<2 <10 <10 <10

<2 -- <10

<2 <10 <10 <10

<2 <10 <10

<1 -- 9

<2 -- <10

<2 13 <10 <10

<1 - <5

<2 - 10

<2

<2 18 <10

<2 <10 <10

<2 <10 <10

<2 -- <10

<1 - <5

<2 -- <5

<2 <10 <10

<2 <10 <10 <10

<2 <10 <10 <10

<2 32 <10

<2 18 <10 <10

<2 <10 <10 <10

<2

<2 14 <10 <10

Arsenic, 

dissolved 

(mg/L)

<5 

<5

-

<5

<5

<5

-

<5

<5

<5

__

<5

<5

-

<5

__

<5

<5

<5

-

<5

<5

-

-

<5

--

-

<5

<5

<5

--

-

<5

<5

<5

-

<5

<5

<5

Selenium, 

dissolved 

(mg/L)

<5 

<5

-

<5

--

<5

<5

-

<5

<5

<5

__

<5

<5

-

<5

__

<5

<5

<5

--

<5

<5

-

-

<5

__

-

-

<5

<5

<5

--

-

<5

<5

<5

-

<5

<5

<5

Barium, 

dissolved 

(mg/L)

50 

98

-

48

59

35

-

203

125

93

__

20

21

-

170

__

99

34

21

--

14

28

--

--

10

_

--

38

20

18

-

-

66

75

98

190

135

112

Nickel, Silver, Sulfate, 

dissolved dissolved dissolved 

(mg/L) (mg/L) (mg/L)

<10 <1 19.0

14.0

<10 <1 17.1

20 <1 19.8

<10 <1 12.8

-

<10 <1 20.7

<10 <1 15.3

<10 <1 14.8

__

23 <1 27.5

13 <1 23.6

13.3

<10 <1 11.6

<10 <1 12.9

<10 <1 13.9

<10 <1 14.2

10.6

<10 <1 6.8

<10 <1 16.7

7.4

7.1

<10 <1 9.5

12.3

9.8

19.7

<10 <1 19.0

<10 <1

<10 <1 19.8

20.3

13.8

15.9

<10 <1 23.8

10 <1 27.4

<10 <1 21.9

64.7

29 <1 42.6

11 <1 30.8

17.0

29 <1 14.4

Appendix? 107
Appendix 7. Summary of water-quality analyses in Bristol, Vermont-Con/y'nued

Well

No.

MW-102s

MW-102d

BR2

BR6

W-316

W2

W4

W-327

W-328

W-330

W-331

MW-101

W-335

W-337

W-337

W-337

W-507

W-507

W-507

W-508

Date 

(mmddyy)

100991

091990 -

052091 7.12

101091

091990 -

050891

052291

101091

091990 -

050991

100991

021391

050991

100991

091990 -

050891

052291

101091

091990 -

050991

101091

081592

100991

081592

082291 7.55

100991

100991

082291 7.25

100991

091990 -

052091 6.33

081591

101791

090591

101791

081491

082291

101791

092090 -

050891

100991

092090 -

Specific 

conductance 

(US/cm)

805

342

401

395

268

230

219

255

433

451

472

819

636

366

490

200

409

492

524

454

368

345

511

444

506

355

354

694

762

1,260

970

820

-

2,920

~

720

421

-

386

323

276

544

Calcium, 

dissolved 

(mg/L)

76.7

-

-

39.0

-

-

27.7

-

-

88.1

-

-

54.6

-

44.1

-

34.7

-

-

47.0

-

34.7

-

--

61.9

38.6

-

51.4

-

__

-

107

-

79.5

__

-

106

-

45.3

40.2

Potassium, 

dissolved 

(mg/L)

7.29

-

.84

~

-

.88

-

-

4.49

-

-

3.32

-

1.25

-

1.02

-

2.26

-

.90

-

-

.97

1.18

-

.97

-

__

-

9.98

-

2.28

-

12.1

-

1.36

1.48

Chloride, 

dissolved 

(mg/L)

39.2

18.7

18.3

19.8

4.3

10.8

-

4.8

22.7

23.6

30.3

44.0

18.2

37.6

26.5

43.4

-

31.6

28.7

19.9

27.2

-

8.9

-

33.0

12.8

1.7

33.2

34.2

86.2

48.8

-

41.2

820

536

__

46.8

65.2

18.4

17.5

18.2

27.9

Sodium, 

dissolved 

(mg/L)

36.5

10.0

-

11.7

3.07

7.02

-

3.64

9.16

8.55

21.0

40.0

13.9

14.0

11.3

19.2

-

16.2

16.6

16.5

14.8

-

4.12

-

11.4

9.33

3.33

20.3

9.50

56.9

__

-

25.4

432

269

__

25.6

28.3

9.12

10.6

10.3

18.2

Iron, 

dissolved 

(mg/L)

26

837

57

<10

5,350

4,070

2,270

3,140

153

15

4,250

1,470

551

1,060

973

-

13

973

132

29

-

24

-

26

35

59

131

64

952

21

-

24

139

11

__

29

<10

1,220

553

19

133

Manganese, 

dissolved 

(mg/L)

3,790

182

70

73

2,770

2,270

2,300

1,980

344

39

3,090

2,340

2,960

862

840

-

<10

561

120

15

-

230

-

-

<10

352

-

<10

1,020

392

548

-

273

__

-

556

536

66.0

93

96.0

Magnesium, 

dissolved 

(mg/L)

37.8

-

-

22.1

~

-

11.2

-

-

32.8

-

-

13.9

-

31.2

-

16.0

-

-

21.3

-

23.5

-

25.0

24.1

22.9

59.0

25.6

-

__

-

36.0

44.0

45.8

__

34.3

34.3

-

66.0

14.9

Zinc, Chromium, 

dissolved dissolved 

(mg/L) (mg/L)

<40 <10

<40 <10

<40 <10

<40 <10

118 <10

<40 <10

<40 <10

198 <10

<40 <10

<40 <10

49 <10

<40 <10

<40 <10

<40 <10

<40 <10

..

<40 <10

<40 <10

<40 <10

<40 <10

..

<40 <10

..

<40 <10

<40 <10

<40 <10

<40 <10

<40 <10

<10

<40 <10

-

<40 <10

<40 <10

<40 <10

__

<40 <10

<40 <10

<40 <10

<40 103

<40 <10

<40 <10

108 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
Well 

No.

MW-102s 

MW-102d

BR2

BR6

W-316

W2

W4

W-327

W-328

W-330

W-331

MW-101

W-335

W-337

W-507

W-508

Date 

(mmddyy)

100991 

091990

052091

101091

091990

050891

052291

101091

091990

050991

100991

021391

050991

100991

091990

050891

052291

101091

091990

050991

101091

081592

100991

081592

082291

100991

100991

082291

100991

091990

052091

081591

101791

090591

101791

081491

082291

101791

092090

050891

100991

092090

Cadmium, Copper, Lead, Cobalt, 

dissolved dissolved dissolved dissolved 

(mg/L) (mg/L) (mg/L) (mg/L)

<2 12 <10

<2

<2 <10 <10

<2 <10 <10

<2 - <10

<2 15 16 19

..

<2 <10 <10 <10

<2 - <10

<2 <10 <10 <10

<2 <10 <10 <10

<2 - <10

<2 <10 <10 <10

<2 30 <10 <10

<2 - 15

<2 25 <10 <10

-

<2 <10 <10

<2 - <10

<2 <10 <10 <10

<2 <10 <10

-

<2 27 <10

-

<2 <10 <10 <10

<2 <10 <10

<2 20 <10

<2 12 <10 <10

<2 12 <10

<2 -- <10

<2 <10 <10 <10

-

<2 <10 <10 <10

<2 <10 <10 <10

<2 <10 <10 <10

__

<2 23 <10 <10

<2 <10 <10 <10

<2 - <10

<2 <10 <10 <10

<2 <10 <10 <10

<2 <10

Arsenic, 

dissolved 

(mg/L)

<5

<5

<5

-

5

<5

-

<5

<5

<5

<5

--

<5

-

<5

<5

<5

<5

--

<5

<5

<5

<5

<5

-

<5

-

<5

<5

<5

_.

<5

<5

-

<5

<5

Selenium, 

dissolved 

(mg/L)

<5

<5

<5

-

<5

<5

-

<5

<5

<5

<5

-

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

-

<5

<5

<5

<5

_

<5

<5

-

<5

<5

Barium, 

dissolved 

(mg/L)

197

11

14

-

16

-

21

-

42

146

--

90

137

-

43

-

26

78

31

-

127

-

58

95

138

102

133

--

168

89

110

103

__

85

91

-

8

22

Nickel, Silver, Sulfate, 

dissolved dissolved dissolved 

(mg/L) (mg/L) (mg/L)

24 <1 13.8 

10.2

<10 <1 11.4

<10 <1 12.2

12.6

nf

18 <1 14.6

20 <1 14.9

22.2

<10 <1 31.0

<10 <1 24.8

102.0

<10 <1 50.0

<10 <1 20.6

26.0

<10 6.0 15.5

<10 <1 22.1

54.6

<10 <1 39.6

11 <1 28.4

..

<10 <1 19.3

-

<10 <1 21.2

<10 <1 17.8

<10 <1 19.9

<10 <1 30.4

<10 <1 27.3

71.8

<10 <1 68.1

~

<10 <1 46.2

15 <1 35.2

<10 <1 31.7

__

12 <1 44.4

<10 <1 34.1

10.0

51 <1 9.9

<10 <1 11.0

12.7

Appendix? 109
Appendix 7. Summary of water-quality analyses in Bristol, Vermont-Conffnued

Well 

No.

W-508

W-510

W-511

W-325

W-326

W-332

W-333

W-339

W-338

W-339

W-340

W-341

W-342

W-343

Pond

S-16

S-17

Date 

(mmddyy)

100891

050891

092090 -

050991

100891

092090 -

092090 -

050991

100891

082291

100891

082291

100891

081591

082291 6.87

081591

082291

081491

082291 6.40

100891

081491

082291 7.24

100891

081491

082291 7.10

100891

081491

082291 7.05

100891

081491

082291 6.86

100891

082291 6.74

070690 7.1

090590 7.8

050891

052291

090590 7.3

101091

050991

090590 6.6

100891

Specific 

conductance 

(|iS/cm)

494

618

807

420

1,052

637

656

770

791

1,097

1,183

-

1,050

570

655

452

860

951

1,250

440

409

425

785

943

900

1,980

1,407

927

870

944

-

1,160

560

540

439

439

270

-

422

560

-

Calcium, 

dissolved 

(mg/L)

57.7

63.2

-

90.7

80.2

__

-

75.1

87.9

130

133

-

120

-

16.8

22.0

11.5

-

69.9

72.3

__

58.4

57.2

-

97.4

95

-

156

-

-

93.8

127

81.7

-

-

46.4

-

-

47.6

47.3

-

101

Potassium, 

dissolved 

(mg/L)

1.32

1.12

-

2.97

4.78

__

-

6.87

7.78

2.07

2.01

-

23.9

-

7.73

5.62

22.9

2.06

2.18

__

1.42

1.04

-

1.64

1.62

1.74

-

-

9.14

7.93

5.80

-

-

7.23

-

-

1.40

1.18

-

8.97

Chloride, 

dissolved 

(mg/L)

24.1

34.5

107

94.8

148

20.3

20.6

24.8

27.9

104

111

-

37.3

-

16.8

6.2

26.9

-

153

228

__

14.0

13.4

-

. 62.0

65.2

-

144

-

-

92.5

25.2

112

33.2

25.0

18.6

--

16.7

27.4

27.0

27.6

50.3

Sodium, 

dissolved 

(mg/L)

15.0

21.8

59.4

18.8

76.8

16.9

17.3

55.6

19.3

63.9

59.0

«

24.8

-

117

86.0

213

-

78.6

104

10.1

10.0

-

42.8

44.1

-

97.7

-

-

40.7

24.4

67.4

18.6

17.2

16.3

-

13.2

17.3

16.7

21.3

36.0

Iron, 

dissolved 

(mg/L)

1,870

38

159

64

11

20,200

19,900

6,490

8,400

69

389

141

1,180

-

31

17

62

-

152

11

__

96

39

-

71

<10

20

-

-

77

17

22,600

1,030

20

286

-

14

96

45

1,620

2,600

Manganese, 

dissolved 

(mg/L)

580

1,880

40

<10

<10

2,020

201

1,640

1,800

~

1,760

10,100

9,320

-

-

15

-

911

__

-

<10

-

-

75

-

-

-

-

__

36

-

1,720

318

16.3

-

45.0

54.0

34.0

1,710

126

Magnesium, 

dissolved 

(mg/L)

32.2

38.8

-

24.9

31.5

__

-

-

24.7

37.0

42.3

-

33.3

-

7.60

15.9

3.59

37.6

45.8

__

15.1

17.4

-

37.3

35.0

45.8

-

-

27.3

27.7

38.9

-

16.3

-

-

19.5

17.8

-

36.8

Zinc, Chromium, 

dissolved dissolved 

(mg/L) (mg/L)

<40 <10

<40 <10

<40 <10

<40 <10

<40 <10

81 <10

58 <10

<40 <10

49 <10

<40 <10

<40 <10

<40 <10

<40 <10

..

<40 <10

<40 <10

<40 <10

..

<40 <10

<40 <10

__

<40 <10

<40 <10

-

<40 <10

50 <10

<40 <10

-

-

<40 <10

<40 <10

<40 <10

<20 <5

<40 <10

71 <10

-

<40 <10

<40 <10

<40 <10

87 <10

<40 <10

110 Hydrogeology, Simulated Ground-Water Flow, and Ground-Water Quality at Two Landfills in Bristol, Vermont
Well 

No.

W-508

W-510

W-511

W-325

W-326

W-332

W-333

W-339

W-338

W-339

W-340

W-341

W-342

W-343

Pond

S-16

S-17

Date 

(mmddyy)

100891 

050891

092090

050991

100891

092090

092090

050991

100891

082291

100891

082291

100891

081591

082291

081591

082291

081491

082291

100891

081491

082291

100891

081491

082291

100891

081491

082291

100891

081491

082291

100891

082291

070690

090590

050891

052291

090590

101091

050991

090590

100891

Cadmium, Copper, Lead, Cobalt, 

dissolved dissolved dissolved dissolved 

(mg/L) (mg/L) (mg/L) (mg/L)

<2 <10 <10

<2 - <10

<2 <10 <10 <10

<2 19 <10

<2 - <10

<2 ~ <10

<2 <10 <10 <10

<2 <10 <10

<2 14 <10 24

<2 11 <10

<2 <10 <10 <10

<2 <10 <10

-

<2 23 <10 <10

<2 <10 <10

<2 38 <10 <10

-

<2 <10 <10 <10

<2 <10 <10 <10

__

<2 17 <10 <10

<2 <10 <10 <10

-

<2 <10 <10 <10

<2 <10 <10 <10

..

<2 <10 <10 <10

-

<2 <10 <10 <10

<2 <10 <10 <10

<2 <10 <10 <10

<1 <5

<2 -- <10

<2 <10 <10 <10

-

<2 -- <10

<2 <10 <10

<2 <10 <10 <10

<2 - <10

<2 <10 <10 <10

Arsenic, 

dissolved 

(mg/L)

<5 

<5

<5

<5

__

<5

<5

<5

<5

--

<5

-

<5

<5

<5

<5

<5

_

<5

<5

<5

<5

-

<5

-

-

<5

<5

<5

~

<5

-

-

<5

<5

-

<5

Selenium, 

dissolved 

(mg/L)

<5 

<5

-

<5

<5

-

<5

<5

<5

<5

-

<5

-

<5

<5

<5

-

<5

<5

__

<5

<5

<5

<5

-

<5

-

-

<5

<5

<5

-

-

<5

-

-

<5

<5

-

<5

Barium, Nickel, Silver, 

dissolved dissolved dissolved 

(mg/L) (mg/L) (mg/L)

22 25 <1 

310 25 <1

33 <10 <1

136 <10 <1

105 <10 <1

164 <10 <1

58 11 <1

58 <10 <1

<10

310 <10 <1

24 <10 <1

49 <10 <1

7 11 <1

45 14 <1

93 21 <1

36 <10 <1

40 11 <1

68 <10 <1

46 <10 <1

46 <10 <1

-

-

58 <10 <1

189 <10 <1

96 26 <1

-

650 <10 <1

..

..

19 <10 <1

11 <10 <1

-

179 10 <1

Sulfate, 

dissolved 

(mg/L)

12.2 

14.9

19.4

24.6

26.8

<.2

1.3

2.7

4.0

20.2

18.5

-

2.9

-

97.7

49.1

248

-

15.8

15.0

_

23.1

12.3

15.7

15.2

-

21.6

-

3.9

18.1

5.8

17.3

18.3

8.0

-

12.5

12.7

12.4

9.8

9.5

Appendix? Ill