HYDROGEOLOGIC STUDY

EAST GRAY, MAINE

for the

Maine Department of Environmental Protection

by

Robert G. Gerber, Inc.

Consulting Civil Engineer & Geologist

South Harpswell, Maine

29 November 1982

N

o

ROBERT G. GERBER, INC.

R. F. O. 1. BOX 483 ' • SOUTH HARPBWELL. MAINE O4O79

2O7-833-6334

29 November 1982

Mr. John Krueger, Director

Div. of Licensing and Enforcement

Bureau of Hazardous Materials Control

State House Station 17

Augusta, Maine 04333

Re: Transmittal of Final Report—Hydrogeologic Study, East Gray

Dear Mr. Krueger:

In accordance with my contract with the Department of

Environmental Protection (DEP), I have completed my study of the

migration of chemical contaminants in the ground water from the

McKin Chemical Company site in East Gray, Maine. The attached

report contains the summary of my findings.

The project team consisted of the following: Robert G.

Gerber who mapped surficial geology, conducted the computer

analyses, and managed the project; John R. Rand who mapped

bedrock, analyzed historical data, assisted in computer data

preparation, and constructed the report figures; Weston

Geophysical Corp., who performed the geophysical investigations;

and Mr. James K. Richard, who did the lineament analysis and

assisted in mapping surficial geology. All members of the

project team are Certified Geologists in Maine. Mr. Gerber is

also a Registered Professional Engineer in Maine.

Through our field mapping, aerial photo interpretation, data

analyses, borings, seismic refraction profiling, water sampling

and analyses by DEP, and computer modelling, we find the following:

1. The McKin Chemical Company processed oily wastes and other industrial wastes at the site in East Gray from at least

1972 to 1977. As early as 1973, local residents began to

complain of odor and peculiar tastes in their well water.

Inilfial tests found organic chemicals such as trichloroethane

(TCÊ ancT'̂ trTchloroethylene (TCEy) present in the domestic

drilled water wells north of the chemical company. Studies took

place during the period 1977 to 1980, which concluded that the

ground water contamination had probably originated at the McKin

Chemical Company site. In 1980 the DEP hired a contractor to

remove 35,000 gallons of chemicals from the site, but more

remain. In August 1982, my consulting firm was retained to do a

more thorough investigation of the hydrogeology of the East Gray

area.

2. The area in which the ground water has been contaminated

lies in the watershed of the Royal River. An important point of

Page 2 of 4, Krueger, 11/29/82

Hydrogeologic Study, East Gray

reference is the area of the "Boiling Springs" and the Maine

Central Railroad bridge which lie about 2000' south of Gray

Station and 4000' east of the McKin site. The drainage area of

the Royal River above this site is 69.8 square miles. All ground

water beneath the McKin site that flows in both the surficial and

bedrock aquifers ultimately discharges into the Royal River. No

surface or ground water moves southwesterly from the site toward

Gray Meadow and the Meadow Brook drainage.

3. There are three major soil units under and near the

McKin site. Stratified sand and gravel covers an area north and

west of the site. Glacial till underlies the sand almost

everywhere throughout the study area and is exposed on upland

areas to the west and south of the site and to the east of the

Royal River. Glaciomarine fine sands, silts, and clay-silts

overlie the sand and till along the steep slopes that lie

adjacent to the Royal River and Collyer Brook. The clayey

glaciomarine deposits have presented a barrier to ground water

flow from the more permeable sand and gravel deposits. Springs

and seeps occur where this ground water flowing from the sand and

gravel escapes to the surface through the clayey deposits.

4. The topography of the bedrock surface in the site area

slopes generally down to the east, toward the Royal River. In

detail, the bedrock surface forms a broad northeast-trending

trough to the west of the site which passes easterly between an

east-west ridge just south of Collyer Brook and the end of a

narrow ridge which projects north-northeasterly from the site.

The bedrock surface rises to the south from the site. This

peculiar topography of the bedrock surface is a significant

factor in controlling the initial movement of ground water toward

the north, away from the site.

5. The bedrock beneath the site is inferred from regional

mapping to be composed of granite, pegmatite, or schistose

migmatite, possibly transected locally by thin, tabular mafic

dikes. Although these bedrock types are in themselves

essentially impervious, they are capable of transmitting ground

water along narrow partings where the rock has been broken by

joints, cut by tabular dike intrusions, or, in the schistose

migmatite, separated along micaceous layers. The preferred

avenues for ground water movement in the bedrock appear to be

toward the northwest along joint openings and toward the

north-northeast along tabular dikes, with a relatively minor

increment of ground water flow toward the east-northeast along

micaceous partings in the migmatite.

6. Ground water leaving the site in the surficial aquifer

flows to the northwest initially, until encountering a coarse

gravel deposit that trends east-west under the intersection of

Depot and Mayall Roads. After merging with flow in this gravel

Page 3 of 4, Krueger, 11/29/82

Hydrogeologic Study, East Gray

deposit, ground water flows eastward and is discharged in springs

and small streams that form part of a local surface drainage

network that enters the Royal River adjacent to the Boiling

Springs. The coarse gravel deposits lie in contact with or lie

just beneath the Royal River between Boiling Springs and the

Maine Central Railroad Bridge. Most of the ground water that

originates at the site is discharged to the Royal River in the

immediate vicinity of the Boiling Springs. The total ground

water discharge rate in this area is about 800 gallons per

minute. There is no evidence that any of the site ground water

continues south of the Maine Central Railroad bridge, along the

trend of the Royal River.

7. Ground water that leaves the site in the bedrock aquifer

flows toward the north initially, then spreads out in a diffuse

manner to turn slowly eastward toward the Royal River. Most of

the bedrock ground water that originates at the site is

discharged to the overlying gravel deposits in the vicinity of

Boiling Springs.

8. Through computerized ground water simulations, we have

been able to identify the approximate path and magnitude of

concentration of the chemical TCE within both the surficial and

bedrock aquifers. Our simulated distributions of the contaminant

concentration are in good agreement with measured concentrations

from water samples taken in the site area. The path of the

contaminant plume within the surficial aquifer is relatively

narrow and well-defined. Contamination entering the site soils

would reach the Boiling Springs after about 5 years. Ten years

after introduction of the contaminant at the site at an assumed

average rate of about 26 gallons per year, the concentration of

TCE would begin to reach a steady state condition at the Boiling

Springs. Although the time history of chemical leakage into the

aquifer beneath the site is not known, it may have been at rates

as high as 125 gallons per year during the initial period of

contamination. The remaining volume of chemicals contained in

the soils under the site cannot be calculated from the available

data.

9. The distribution of contaminants in the bedrock aquifer

is of greater extent than in the surficial aquifer. Contaminant

is transferred to the bedrock aquifer from the surficial aquifer.

The distribution of contaminants in the bedrock aquifer is

controlled largely by the ground water flow pattern in the

bedrock and the locations of the overlying contaminated surficial

ground water. The presence of pumping wells in the bedrock

aquifer will also affect the contaminant distribution and we

infer that the domestic wells that were in use during the 1970's

north of the site caused much higher concentrations of

contaminants to enter the bedrock aquifer in the local area than

would have otherwise been the case.

Page 4 of 4, Krueger, 11/29/82

Hydrogeologic Study, East Gray

10. Although concentrations of TCEy may be increasing in

some wells, we believe this is due to a "retardation" effect

peculiar to that chemical. Concentrations of TCE are generally

stable or beginning to decrease at most sampling locations. We

do not expect much further increase in contaminant levels in the

surficial aquifer. Certain areas of the bedrock aquifer may show

somewhat increased contaminant levels in the future— perhaps on

the order of 10-20%.

11. If the site is isolated in some way so that no

additional chemicals can leak into the aquifer under the site,

concentration levels will begin to decline in both aquifers after

several years. After five years there will be major reductions

in contaminant concentrations in the aquifers. After 10 to 12

years most of both aquifers will have been reduced to less than

30 parts per billion of TCE in most of the surficial aquifer, and

less than 15 parts per billion in the bedrock aquifer. The rate

of aquifer cleansing could be increased by a combination of

ground water withdrawal wells and injection wells in the

surficial aquifer. However, any contaminated ground water that

is pumped from the aquifer in such a scheme would have to undergo

costly treatment. It is our understanding that consultants hired

by the Environmental Protection Agency will evaluate the costs

and benefits of any site clean-up work.

It has been a pleasure to have been of service to the State

of Maine.

Respectfully submitted,

\ \%T.fV̂

Robert G. Gerber ,

HYDROGEOLOGIC STUDY

EAST GRAY, MAINE

for the

Maine Department of Environmental Protection

by

Robert G. Gerber, Inc.

Consulting Civil Engineer & Geologist

South Harpswell, Maine

29 November 1982

TABLE OF CONTENTS

Section Page

INTRODUCTION 1

HISTORICAL BACKGROUND 1

METHODS 2

SITE AREA GEOLOGY 5

PHYSIOGRAPHY AND WATERSHEDS 5

BEDROCK GEOLOGY 6

Introduction . . . . . . . . . . . 6

Bedrock Lithologies 7

Bedrock Structure . . . . . 7

Faults 8

Joints, Dikes, and Foliation . . . . . . 8

Lineament Analysis . . . . . . . . . 9

SURFICIAL GEOLOGY 10

Soil Thickness 11

Soil Types and Distribution 11

Significance of Surficial Geology to Contaminant Spread . 14

HYDROGEOLOGIC ANALYSIS 14

METHODS 15

Delineation of Aquifer Boundaries 16

Bottom of Surficial Aquifer 18

Permeability and Transmissivity . . . . . . . 18

Storativity and Specific Yield . . . . . . . 20

Dispersivity . . . . . 2 0

Pollutant Attenuation by Retardation and other Mechanisms 21

Aquifer Inputs and Withdrawals of Water . . . . . 22

Application of Contaminant to the Aquifer . . . . 23

INTERPRETATION OF COMPUTER SIMULATION RESULTS . . . 25

Ground Water Flow in the Surficial Aquifer . . . . 25

Bedrock Aquifer Flow 26

Contaminant Transport Modelling—Surficial Aquifer . . 27

Contaminant Transport Modelling—Bedrock Aquifer . . . 28

THE FUTURE OF THE CONTAMINANT PLUME 29

MAINTAINING THE STATUS QUO 29

PREVENTING CHEMICALS FROM LEAVING THE SITE . . . . 30

GROUND WATER REMOVAL OR FLUSHING BY PUMPING . . . . 32

SUMMARY AND CONCLUSIONS 32

LIST OF REFERENCES 33

Table 1—1982 Water Sample Locations and Test Results

TABLE-OF CONTENTS (continued)

List of Figures

Figure 1—Site Area Wells, Springs and Seismic Survey Locations

Figure 2—Site Area—Geologic iMap

Figure 3—Site Vicinity—Inferred Bedrock Elevation

Figure 4—Site Vicinity—Inferred Elevation, Surficial Water

Table

Figure 5—Site Area Computer Simulation—Elevation of the

Potentiometric Surface (Bedrock Aquifer)

Figure 6—Site Vicinity—Computer Nets—Surficial

Figure 7—Site Area Computer Nets—Bedrock

Figure 8—Site Area—Historical Test Data: 1,1,1-Trichloroethane

and Trichloroethylene

Figure 9—Computer Simulation—Contaminant Distribution in

Surficial Aquifer

Figure 10—Computer Simulation—Contaminant Distribution in

Bedrock Aquifer

Figure 11—Computer Simulations—Contaminant Distribution in

Surficial Aquifer after Isolating McKin Site:

after 2, 5, and 10 years

Figure 12—Computer Simulations—Contaminant Distributions in

Bedrock Aquifer after Isolating McKin Site:

after 2, 5, and 10 years

List of Appendices

Appendix A—Water Supply Questionnaire

Appendix B—Well Data Summary and Analysis

Appendix C—Weston Geophysical Corp. Seismic Refraction Survey

Appendix D—Borings Logs and Sample Descriptions

-11

HYDROGEOLOGIC STUDY

EAST GRAY, MAINE

INTRODUCTION

Hydrogeology is the study of movement of water through soil

and bedrock. This report contains a summary of the findings of a

study conducted from August through November 1982 by Robert G.

Gerber, Inc., on the hydrogeology of the East Gray area of Maine.

The study was done under contract with the Maine Department of

Environmental Protection (DEP) using funds appropriated by the

Maine Legislature expressly for this purpose. The general objec

tive of this study was to learn more about the extent of ground

water contamination in the East Gray area that has been alleged

to have been caused by chemicals leaking from the McKin Chemical

Company site on Mayall Road.

More specifically, the study objectives as defined in the

contract with the DEP included:

a) to place four new monitoring wells

b) to undertake geophysical investigations to study the

geologic profile in the area around the McKin site

c) to map the bedrock and surficial geology

d) to describe background surface and ground water

quality

e) to model the ground water aquifer using a specific

computer model

f) to meet with the DEP staff and public as the study

progresses to keep them informed

g) to prepare a final report and conclusions concerning

the extent of the ground water contamination.

HISTORICAL BACKGROUND

The McKin Chemical Company processed oily waste and clean-up

debris that was generated from a 100,000-gallon oil spill from

the tanker "Tamano" in Casco Bay in 1972. The East Gray site was

-1

also used for processing other industrial wastes and the McKin

Chemical Company was in operation at the site for several years

prior to 1972 (Gardner Hunt, pers. com.) and operated until 1977.

Although the manner and locations in which chemicals entered the

ground is not completely known, it is apparent that certain

chlorinated hydrocarbons and other chemicals did enter the ground

and pass into the ground water beneath the site.

As early as 1973 local residents began to complain of odor

and peculiar tastes in their well water. Initial tests found

that dimethyl sulfide and chlorinated hydrocarbons such as

trichloroethane (TCE) and trichloroethylene (TCEy) were present

in domestic drilled water wells north of the site. Hart

Associates was retained by the Environmental Protection Agency

(EPA) and DEP to conduct a hydrogeologic study of the area to lo

cate the source and extent of the contamination. Their report

was submitted in November 1977. The DEP installed borings and

monitoring wells on and near the McKin site in 1979 and 1980. A

short interpretative report was prepared for the DEP in 1980 by

BCI Geonetics. About 35,000 gallons of waste that had been

stored at the site was removed by DEP-hired contractors in 1980.

This was not the complete inventory of chemicals that had been de

termined at the site, and some chemicals are still stored there.

In June 1981, another report was prepared by Ecology and

Environment, Inc., under contract to EPA. Except for the BCI

Geonetics report, most of the other work was confined to sampling

of local wells and surface waters and determining the magnitude

and extent of the contamination. No detailed geologic studies

were done in the area until this present study of 1982.

METHODS

Most of the methods that were used in this study were dictat

ed by the DEP contract. The initial part of the study involved

synthesis of the mass of data in the DEP files and collection of

new data. John R. Rand went through the entire DEP file and sum

-2

marized the important data pertaining to the hydrogeology, as

presented on the Tables and Figures of this report. New data

collection on water wells was accomplished by mailing a survey

form (Appendix A) to all property owners of record in the East

Gray area. About 33% of the questionnaires were returned,

although many of the respondents indicated that there were no

wells on their property. The results are tabulated in Appendix

B. Well locations are shown on Figure 1. Local residents were

very cooperative during this study and we are particularly

appreciative for the cooperation of Portland Sand and Gravel,

Blue Rock Industries, Mr. Frederick Farrell, Mr. Emerson

Mitchell, and Ms. Lucymae Bowles.

Geologic data collection included 8800 lineal feet of seis

mic refraction profiling by Weston Geophysical Corp. at the loca

tions shown on Figure 1 and described in Appendix C. During the

geophysical field investigations, James Richard and Melissa

Whitaker assisted Weston Geophysical. Five new borings were made

(two borings made side-by-side at location B101) in which ground

water monitoring wells were installed. The locations of these

borings are shown on Figure 1 and the drillers logs and our inter

pretive logs are given in Appendix D. Carol White provided the

field inspection of the borings done by Henry Michaud & Son.

Robert Gerber described the soil samples. Locations and eleva

tions of all geologic data points were located as accurately as

possible by reference to a photo-enlarged 1980 10-foot contour

map of the area. Limited funds did not permit accurate

surveying.

Bedrock field mapping was conducted by John R. Rand. James

K. Richard analyzed lineaments on topographic maps, aerial

photos, and Landsat imagery. Robert G. Gerber, James K. Richard,

Peter Garrett (DEP), and Carol White mapped the surficial geology

of the area. The bedrock geology, as interpreted by John Rand is

given on Figure 2. The generalized surficial geology, as inter

preted by Robert Gerber is also given on Figure 2. John Rand pre

-3

pared the bedrock contour map on Figure 3. Figure 7 contains a

rose diagram that indicates the proportions of bedrock features

determined from field mapping that trend in various directions.

Robert G. Gerber analyzed the ground water regimes and pre

pared the computer models that simulated the ground water flow

and contaminant spread. The methodology used for the computer

analysis is described in more detail later in the report. The

computer grids are given on Figure 6 (surficial aquifer) and

Figure 7 (bedrock aquifer). John Rand contoured existing data

from the surficial aquifer to produce the water table contour map

in Figure 4. Figure 5 is the map of the potentiometric contours

for the bedrock aquifer as generated by the computer analysis.

Figures 9 and 10 show the computer-simulated distribution of TCE

in the surficial and bedrock aquifers, respectively, for the 1982

condition. Figures 11 and 12 show how the distribution of TCE in

the surficial and bedrock aquifers will change with time if cer

tain actions are taken to remove or isolate the chemicals under

the McKin site.

Water samples were taken for analysis of organic chemicals

by the DEP laboratory and Energy Resources Company of Cambridge,

Massachusetts. Field collection of water samples was done by

Carol White, Peter Garrett (DEP), Edward Logue (DEP), Andrews

Tolman (Maine Geol. Survey), Dorothy Tepper (US Geol. Survey),

and John Williams (DEP). A graphic presentation of historical wa

ter quality results through time at selected locations is present

ed on Figure 8. Table 1 summarizes the results of the fall 1982

water quality sampling. Sampling locations are shown on Figure

1.

Many discussions have been held with the DEP during the

course of this study in order to keep them informed and to ex

change data. The DEP has participated in several parts of the

study and supplied information for this report. Several meetings

were held in Gray to inform the Town of the progress of the

study. After the contract award, an initial meeting was held to

-4

discuss the scope of work, to exchange information, and to solic

it help from the Town's people in the data collection effort.

Richard Day, Gray Town Codes Enforcement Officer, and the Greater

Portland Council of Governments were helpful in this regard and

provided tax maps and local newspaper announcements. At the com

pletion of the geologic field data collection, another meeting

was held with the Town to discuss the interim findings. On 13

December 1982 a final meeting will be held with the public to

present the findings of this study.

All graphics for the report and public presentations were

prepared by John Rand.

SITE AREA GEOLOGY

PHYSIOGRAPHY AND WATERSHEDS

The East Gray area has a very heterogeneous physiography

(land surface form). Within the triangle of Depot Road, Mayall

Road and Route 115 the ground surface is relatively flat or gent

ly undulating on a sandy surface. Between Mayall Road and the

Royal River and between Mayall Road and Collyer Brook, the

gently-sloping sandy surface terrain gives way to closely-spaced

gullies cut into silty and clayey soils. West of the site and

west of Depot Road, the ground surface is deeply pitted with

depressions formed on an irregular sand and gravel surface. Far

to the south and to the west of the site the terrain rises onto

moderately-sloping hillsides developed in a stony soil which has

a moderately dense surface drainage pattern. This latter soil is

known as glacial till and has a moderately low permeability (the

measure of the rate at which water will pass through the soil).

The deeply-pitted sand and gravel terrain is called "ice contact"

terrain and was formed when swiftly-moving rivers flowed over and

through glacial ice-covered terrain about 13,000 years ago. The

flat sandy areas are ice contact deltas or glacial outwash that

was deposited when the glacial meltwaters flowed into the sea

which was about 300 feet higher then than it is now. The clayey,

-5

highly dissected river banks are formed in what are called

glaciomarine deposits. These soils consist of interbedded fine

sands, silts and clay. Because the silts and clays have a

relatively low permeability, most precipitation runs off the

soils instead of infiltrating to become ground water. Therefore,

the drainage network is much more dense in these soils than in

more sandy soils.

Although there is no direct surface runoff at the site, the

site is included within the surface watershed of the Royal River.

The watershed area of the Royal River above Brickyard Station,

several miles southeast of the site, is 73.6 square miles. The

watershed of Royal River at the railroad bridge, east of Boiling

Springs, is 69.8 square miles. The watershed of Collyer Brook

above its confluence with the Royal River, is 18.6 square miles.

Neither surface water nor ground water from the site moves

southwesterly toward Gray Meadow.

BEDROCK GEOLOGY

Introduction

The study of the bedrock (ledge) geology has been made

through a combination of literature search, field mapping, remote

sensing techniques, analysis of water well data and by reference

to analogous studies. The exact nature of the bedrock under the

site is not known since it is covered by 36' to 65' of soil and

no core borings have been made at the site. Conditions at the

site and in other parts of the study area where no bedrock is ex

posed are interpreted using standard geologic techniques of infer

ence and extrapolation. Figure 2 defines the locations of

bedrock outcrop that were examined as part of this study.

Within one mile from the site, only two areas of bedrock out

crop are known: granite and pegmatite are exposed in a stream

bed about 1000' southeast of the site; and pegmatite and migma

tite are exposed 4000 to 5000 feet southwest of the site. In ad

dition, 10' of pegmatite bedrock was cored (see log in Appendix

-6

D) from a depth of 104' to 114' in boring B103, 4000' east of the

site.

In the area from one to two miles from the site, bedrock is

exposed at several widely-scattered locations to the southeast,

east, north and northwest of the site. Rock types at these loca

tions range from migmatite to pegmatite and granite. Thin north-

to northeast-trending mafic dikes transect the country rocks at 5

of the more distant outcrop areas to the east and southeast of

the site. The observed dikes are thin, ranging from a few inches

to a maximum of 30" in thickness.

Bedrock Lithologies

Regional geologic maps (Doyle, 1967; Hussey and Pankiwskyj,

1975) place the site within the area of the Sebago Granite

Pluton, in a location where the outcrop pattern of the pluton is

markedly "necked" by the encroachment—from both the southwest

and northeast—of phyllite and micaceous quartzite of the Eliot

Formation. The indiscriminant occurrences of granite, pegmatite

(coarse-grained granite) and migmatite (feldspar-rich or

granitized schistose rock) that are exposed within two miles of

the site suggest that the site bedrock lies in the roof zone of

the Sebago Granite intrusive and may also consist variably of

granite, pegmatite and foliated migmatite. These bedrock types

inferred for the site may also have been intruded by one or more

nearly-vertical, tabular mafic dikes (iron-rich igneous intru

sives occurring in planar form).

Bedrock Structure

The features of bedrock structure that are particularly im

portant in controlling the direction and rate of ground water

flow within the bedrock include faults, joints (fractures), foli

ation (micaceous layering or schistosity), mafic dikes, and sol

uble lithologies (rocks that dissolve and develop open channels).

-7

Faults

We have found no evidence that suggests the presence of a po

tentially-permeable fault at the site. Where fault zones in the

crystalline rocks of Maine are sufficiently fractured and open to

comprise important bedrock aquifers, they also commonly occur in

troughs or valleys since the broken rock is less resistant to

weathering and erosion than unbroken rock. Since test borings

and water well records indicate that the bedrock surface forms a

distinct ridge beneath and to the north of the site (Figure 3),

there does not appear to be a significant likelihood of a

permeable fault-zone aquifer there.

With reference to Figure 3, the topography of the bedrock

surface inferred from scattered borings, water wells and seismic

refraction data suggests the presence of a distinctive bedrock

trough passing about one-quarter mile northwest of the site.

This trough runs on a trend of N60°E. If a bedrock trough truly

does exist as our data suggest, it may reflect a fault zone, but

seems more likely to us to reflect a band or roof pendant of rel

atively soft, micaceous metamorphic rock. Numerous analyses of

Collyer Brook water taken during the past 5 years have shown that

no contaminant is entering the brook at the northeasterly projec

tion of the zone.

Joints, Dikes, and Foliation

A rose diagram is presented on Figure 7 to summarize the ori

entations of high-angle (steeply-dipping or nearly vertical) bed

rock joints, mafic dikes and migmatitic foliation that were

measured on outcrops throughout the area. While the 52 high-

angle joints that were measured are seen to strike in all direc

tions, a modest preference seems to be toward N50-60°W. The

prominent rose trend toward N20-30°E is due principally to the

strikes of 3 of the 5 mafic dikes measured in the area. These

dikes inherently have higher bulk permeability than their enclos

ing country rock, due to relatively close internal jointing.

-8

Outcrops commonly show the dikes appearing in weathered troughs,

suggesting that they are relatively soluble, and may contain open

passageways at depth.

Planes of potentially important bedrock partings are formed

by foliation in micaceous migmatitic rocks. This foliation is a

layering—like the pages of a book—that forms in certain rocks

that are metamorphosed. As shown by the rose diagram on Figure

7, foliation readings on 21 migmatitic outcrops show a close

clustering of strikes toward the east-northeast. The dip or in

clination of the foliation is commonly very steep. Computer sim

ulations of bedrock ground water flow in steeply-dipping

quartzitic schist at Wiscasset (Gerber and Rand, 1980) found that

the permeability parallel to foliation was about 5 times greater,

on the average, than parallel to the joints that ran perpendic

ular to foliation. We do not believe that this is necessarily

the case in East Gray, however. At none of the 21 observed migma

tite outcrops in the East Gray area did the rock exhibit any nota

ble tendency to weather and part along foliation planes, as it

did in Wiscasset. It is our impression that ground water move

ment in the rock in East Gray is controlled more by the joints

and the mafic dikes than by foliation. The significance of these

features is discussed in more detail later in the report.

Lineament Analysis

A lineament analysis of the study area was conducted using

satellite imagery and standard panchromatic aerial photography at

two scales to identify possible bedrock structural patterns. In

the early phases of the study we had hoped that this would aid in

identifying the preferred directions of bedrock ground water move

ment, since so little outcrop was available for study near the

site. Lineaments are visible as tonal, vegetal, or topographic

alignments and may represent structural elements such as fracture

zones, faults and foliation.

-9

To provide an understanding of the regional setting, linea

ments were first identified on 1:1,000,000 scale Landsat imagery.

Two prominent lineament directions were detected. In the coast

al area, lineaments parallel the regional strike (plane of foli

ation) of the bedrock at approximately N20°E. A second set

strikes northwest, roughly perpendicular to the first set of

lineaments. A third, less prominent set, strikes approximately

east-west and is particularly noticeable in the area surrounding

Sebago Lake. This latter set appears to coincide approximately

with the foliation developed within the Sebago Pluton and adjoin

ing rocks.

To obtain more detailed lineament data for the site area, it

was necessary to use aerial photography capable of clearly depict

ing cultural features without obscuring linear trends. Two

scales were examined: 1:24,000 and 1:12,000. The 1:12,000 (1" =

1000') scale photography was determined to be unsuitable as linea

ments could not be precisely defined. The 1:24,000 (1" = 2000')

scale photography provided an excellent overview of the area and

better conditions for identifying linear features.

Identifications of lineaments was completed using stereoscop

ic and composited methods. Sixty-one lineaments were identified

within the study area. Two general directions predominate. The

strongest direction lies between N70°E and N90°E. The second

direction is less well-defined and trends northwesterly, or ap

proximately perpendicular to the first.

By comparing the results of the lineament analysis and field

mapping of the bedrock, it is apparent that the east-northeast

trending set corresponds geometrically to local bedrock foli

ation. The second set of local lineaments coincides with a minor

orientation of field-mapped fractures.

SURFICIAL GEOLOGY

The surficial geology of the site area has been mapped by

various governmental agencies. The pertinent literature refer

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ences include Prescott (1980), Prescott (1977), Caswell (1979),

Thompson (1976), and Prescott, Smith and Thompson (1976). All of

the these studies were reconnaissance-level in nature and did not

have the advantage of all of the data that were available for our

interpretation. Therefore, the following description is based

solely upon our detailed study of the local surficial geology.

Soil Thickness

A separate map of soil thickness has not been prepared for

this report; however, one can determine the approximate soil

thickness at any point in the study area by subtracting the bed

rock surface elevation on Figure 3 from the surface elevation at

the same point. With the exception of the southern edge of the

area covered by the surficial finite element model and the vicin

ity of node 72 shown on Figure 6, bedrock lies at a relatively

great depth under the remainder of the surficial aquifer finite

element model area. A glance at the seismic refraction profiles

in Appendix C shows that soil averaged about 150' thick along

most of the profiles (locations shown on Figure 1). Bedrock well

#4 (Figure 1) encountered 200 feet of soil. According to the sta

tistical analysis of the bedrock well data in Appendix B, the me

dian soil depth is almost 100'. This large soil thickness caused

great difficulty and expense in the drilling and geophysical

field programs. The areas of greatest soil thickness appear

along the northeasterly trending trough on Figure 3 and along the

Royal River valley. Soil thickness is interpreted to be not near

ly so great (30-50') along Collyer Brook, upstream of the Pumping

Station that serves as the Pineland Center water supply.

Soil Types and Distribution

The surficial geology information shown on Figure 2 was de

veloped from a combination of field mapping, aerial photo inter

pretation, geophysical profile interpretation, and well and

boring data interpretation. Field mapping was very detailed

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around the site 'and the zone between Mayall Road and the Royal

River and Mayall Road and Collyer Brook. The three separate grav

el pit operations west of Depot Road (called "Pownal Road" on the

topographic map) provided many exposures of glacial ice contact

and outwash deposits in those areas.

The Figure 2 depiction of the surficial geology fails to

show the 3-dimensional nature of the deposits, which are very het

erogeneous. Large areas of glacial till are shown to the far

west and south of the site. These stony, silty soils were laid

down under the glacial ice advance between 22,000 and 16,000

years ago. They are compact and have a moderately low permeabil

ity. Although glacial till was found in the bottom of boring

B104, it was not distinguishable as a separate seismic refraction

velocity (Appendix C). Along seismic line 4, however, a typical

till velocity of 6000-6500 feet per second was measured, indicat

ing that the majority of the soil profile in that area was till.

Seismic lines 5 and 7 should have shown saturated till, but this

could not be interpreted from the field data because of the great

thickness of overlying unsaturated sand and gravel. There are

large areas of Figure 2 that are indicated by the widely-spaced

dotted pattern to be sand over till. In these areas, we infer

that there is a significant thickness of glacial till overlying

bedrock, which controls ground water movement in these areas. We

did not find any evidence of any washboard or other moraines

along the west side of the Royal River. Although there seems to

be a parallel alignment of ridges and gullies trending east-

northeast, similar to moraines farther to the south, the topo

graphic pattern appears to be developed solely by erosion in

glaciomarine deposits.

Following the deposition of the glacial till, the continen

tal glacier melted until its leading edge was resting in sea wa

ter that was about 300' higher than present-day sea level about

13,000 years ago. During summer melting periods, large rivers of

glacial meltwaters flowed through the site area. Evidence for

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this is seen in the exposed gravel banks of the Portland Sand and

Gravel operation about one-half mile northwest of the McKin site.

It appears that the major meltwater river entered the area of

Portland Sand and Gravel's operation from the northwest, then bi

furcated at the northwestern edge of the pit. The major branch

flowed east toward the Royal River; the minor branch turned south

and flowed toward Gray Meadow. Deltaic sand and gravel deposits

formed in a large area, including under the McKin site, to the

southeast of this meltwater stream bifurcation. These sediments

spread out to cover areas of glacial till that had been deposited

thousands of years earlier. Along the distinct courses of the

two meltwater channels, the eastward-flowing channel apparently

washed away all till along a narrow path to the Royal River and

we infer it to consist of very coarse gravel and cobbles at the

bottom. The southern meltwater branch appears to be perched on

till or shallow bedrock to the west of sampling point 31 (Figure

1) and there is no evidence to indicate that it now diverts

ground water flow in that area to the south.

The final major surficial unit of interest to the study is

the soil unit identified as "GM" on Figure 2. This unit consists

of a thin-bedded (typical beds are 1/16" to 1" in thickness) se

quence of fine sands, silts and clay-silts. These deposits are

the result of deposition in sea water of the finer particles of

rock that had been pulverized by the continental glaciation.

This deposition occurred concurrent with and immediately follow

ing the deposition of the ice contact deposits. As the meltwater

streams entered the water-filled valley, the coarse sands were de

posited on the face of a delta and the fine sands, silts and

clays settled to the valley bottom. A typical sequence of this

"glaciomarine deposit" in the East Gray area consists of five to

ten feet of fine to medium sand overlain by low permeability

thin-bedded fine sands, silts and clay-silts, finally topped by

none to 20' (locally) of fine sand. In boring B103, this

sequence was found to be 103 feet thick. Although individual

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clayey layers within this sequence are usually saturated below

20" depth, thin beds of fine sand may not be saturated on the

valley walls under the clayey layers. Therefore, seismic

velocities that are typical of saturated glaciomarine

deposits— 5000 feet per second—were not found except at the

western end of line 2 (Appendix C).

Significance of Surficial Geology to Contaminant Spread

The observed spread of chemical contamination in the ground

water appears to be directly related to the thickness, nature and

permeability of the surficial soils. Bedrock and/or till ridges

occur to the far west, far south, and on the north side of Mayall

Road north of the Portland Sand and Gravel pit operations. The

only major outlet for ground water flow from a relatively large

watershed area is through the coarse gravels of the former gla

cial meltwater channel that runs east from the Portland Sand and

Gravel pit toward the Royal River. The low permeability clayey

glaciomarine deposits on the east face of the delta act as a

leaky dam. Ground water from the west leaks through the clay and

erupts in springs in the slope east-northeast of the site as

shown on Figure 2. Boring B102 suggests that the top of the ex

tension of the sand aquifer that runs under the clay is about

equal to the Royal River bottom elevation just east of the

"Boiling Springs". At this major bend in the River there is ap

parently a major discharge of the ground water that originates in

a large area to the west, including the site.

HYDROGEOLOGIC ANALYSIS

Most of the data collection and interpretation until this

time has related to tracking the path of the chemical contamina

tion in the ground water and surface waters. Only W. B. Caswell,

in his short report to DEP (BCI Geonetics, 1980) began any anal

ysis of the ground water regime of the site area. His analysis

was based primarily on bedrock well data, most of which came from

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domestic wells in the triangle between Depot and Mayall Roads,

north of the site. Ground water levels, the contaminant plume,

and the bedrock contours were all sloping downward to the north.

No TCE or TCEy was detected in the Royal River north of Gray

Station, and only a few low and questionable laboratory results

suggested any contamination in Collyer Brook. The Boiling

Springs on the west bank of the Royal River, east of the site

were found to produce a fairly stable level of TCE contamination

and the concentration of TCE in the Royal River at Brickyard

Station has also been fairly constant, but inversely related to

river flow rate. Prior to this study there had been no

evaluation of the surficial aquifer flow nor of the level of con

tamination, nor any evaluation of the mechanism of transfer be

tween the surficial and bedrock aquifers.

METHODS

As required by contract, we have evaluated the ground water

regime in both the surficial and bedrock aquifers through a combi

nation of field investigations, water quality analysis, hand cal

culations and computer simulation modelling.

In order to understand a ground water regime in detail, it

is necessary to be able to reproduce its response to stresses

such as precipitation, pumping wells, and discharge to streams.

The factors that control this response are the 3-dimensional

boundaries of the aquifer, recharge and discharge rates, and the

physical properties of the aquifer such as permeability and stor

ativity. We have evaluated all of these factors to the best of

our ability using the available information, and have developed

simulation flow models that appear to simulate the behavior of

the aquifers with reasonable accuracy.

The methods that we have used to develop this model are de

scribed in this section. One of the fundamental problems is to

determine the general geology of the aquifer. This was done

through a combination of literature search, aerial photo interpre

ts

tation, field mapping, geophysical investigations, borings, anal

ysis of water well data, and back-calculation of information from

observed ground water levels and estimated permeabilities.

Delineation of Aquifer Boundaries

Four models were developed to study this problem: a) a re

gional flow model of the surficial aquifer that either included

natural aquifer boundaries, or extended far enough beyond the

site area to have no effect on the results in the site area; b) a

surficial aquifer model that covered an area near the site that

was sufficient for contaminant transport studies; c) a regional

flow model of the bedrock aquifer; and d) a site area contaminant

transport model for the bedrock aquifer. The site area models

use fixed water tables and water inputs and withdrawals for their

boundary conditions that are established by the regional models.

The transfer of ground water between the bedrock model and surfi

cial model was simulated using water table elevations in the sur

ficial model and leakage coefficients that described the amount

of water transfer between the two aquifers as a function of surfi

cial aquifer thickness, surficial water table position relative

to that in the bedrock aquifer, and surficial aquifer vertical

permeability.

The regional models are the finite element models shown on

Figures 6 and 7, for the surficial and bedrock models, respective

ly. The computer program is a Galerkin-type finite element, 2

dimensional saturated flow model—AQUIFEM—developed by Townley

and Wilson (1980). The northern and eastern boundaries of the re

gional flow models are interpreted to be no-flow boundaries along

Collyer Brook and the Royal River. The western and southern

boundaries of the bedrock regional flow model are also assumed to

be no-flow boundaries (this assumption is probably incorrect at

node 38, but did not appear to affect the model significantly).

Many of the western and southern boundaries of the surficial

regional flow model are treated as constant flux boundaries that

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allow ground water flow either into or out of the aquifer perpen

dicular to these boundaries. Inflow from upland till regions was

estimated from recharge areas and typical recharge-per-unit-area

values, then checked against estimated till transmissivities (per

meabilities times aquifer thickness) and ground water gradients.

Outflow between nodes 179 and 180 was estimated in a similar

manner. Outflow between nodes 1 and 3 was a parameter that was

varied during analysis to study its overall effect on the model.

The many small drainageways within the surficial regional model

were treated as intermittent or partially-penetrating streams.

These streams are not treated as "line sinks" or constant head

boundaries. They are treated in a manner permitted by AQUIFEM to

accept ground water discharge at a rate proportional to the

ground water gradient next to the stream, and a leakage parameter

which is estimated from methods in Townley and Wilson (1980, p.

68-70) and Rushton and Redshaw (1979, 207-209). When ground

water levels are defined below the bed of the stream, no exchange

of water takes place between the aquifer and the stream.

A special condition occurs within the surficial aquifer

along the string of nodes 166, 167, 185, and 168. Ground water

discharge occurs in springs on the first three nodes, then re

enters the ground as recharge at node 168. The springs were han

dled with the standard leakage parameters, and the recharge was

treated as injection at node 168. Several runs were necessary to

simulate a balanced zero net flow.

The areas covered by the solute (contaminant) transport mod

els are shown on Figures 6 and 7, respectively, for the surficial

and bedrock models. They occur in identical locations for both

aquifers to simplify solute transfer calculations between aqui

fers. The computer model is a block-centered, rectangular

finite-difference, saturated flow model developed by Konikow and

Bredehoeft (1978), often called the K&B model, which uses the

"method of characteristics" to solve the solute transport equa

tion. This model, which is referred to hereinafter as the "K&B

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model", uses fixed water table elevations on the outside bound

aries as determined from the regional flow model. Since this mod

el does not have the same sophistication as AQUIFEM in handling

partially-penetrating streams, stream discharge rates that were

determined by AQUIFEM were placed in the same positions and at

the same rates in the K&B model as if they were diffuse

discharge.

Bottom of Surficial Aquifer

Using the AQUIFEM model, we input aquifer permeabilities in

stead of transmissivities in the surficial aquifer, so that the

position of the potentiometric surface would be solved as part of

the model output. This was necessary since it was not known be

forehand how much of the aquifer that lay beneath areas mapped as

glaciomarine clay deposits would actually be artesian. This re

quired that we know the approximate bottom of the aquifer. The

bottom of the surficial aquifer was assumed to be the bedrock sur

face. Using the well data (Appendix B) , the seismic refraction

profile results, and the field mapping interpretation, we con

structed the bedrock contour map of Figure 3.

Aquifer thickness is important to the surficial contaminant

transport model, since dispersion is inversely proportional to

aquifer thickness, all other factors equal. For the bedrock mod

el, thickness is not known since water may flow at depths as

great as 700'. Generally, however, the majority of water flows

within the top 300' of rock in granitic rock. Since no disper

sion coefficients were applied in the bedrock contaminant trans

port model, the thickness did not affect plume dispersion.

Permeability and Transmissivity

Aquifer permeability is a measure of the volumetric rate

that water will flow through an aquifer if it is flowing on a

slope of 1 on 1. Transmissivity is found by multiplying perme

ability by aquifer thickness. There are no test data from either

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aquifer that determined transmissivity, however localized

permeabilities were estimated from borehole tests in B102 and

B103 in the fine sand glaciomarine deposits. Initial permeabil

ities were also estimated from field mapping and from correla

tions of observed grain size distributions with

permeability-versus-grain-size tables. For the bedrock model,

rock transmissivity was initially estimated from the few (14)

wells with reported yields (Appendix B—see statistics), but in

the surficial and bedrock aquifers, permeability and transmissiv

ity, respectively, were the major variables that needed to be de

termined. Permeabilities in the surficial aquifer were assumed

to be isotropic (equal in all directions at any point).

Transmissivities in the bedrock aquifer were also treated isotrop

ically although the model was designed to allow anisotropic treat

ment if it appeared that it would be necessary to calibrate the

model. The rose diagram (Figure 7) of the fracture orientations

shows that the AQUIFEM model axes were aligned with the mafic

dikes and major joint concentrations—the two major inferred av

enues of ground water movement. Calibration of the bedrock flow

model, although corroborating data are sparse, does not seem to

indicate the need for anisotropic treatment.

After many trial combinations of permeabilities and stream

leakage coefficients, an acceptable agreement with field-observed

or interpreted water table elevations was obtained. Since some

deviations between anticipated and model-predicted water table el

evations could not be eliminated with the original grid design,

the final water table contour map presented with this report is

our hand-drawn interpretation that we used to calibrate the surfi

cial flow model (Figure 4). A scan of the final data set for the

AQUIFEM surficial flow model indicates that typical permeabil

ities of the sand and gravel deposits were in the range of 10 to

100 feet per day, as we expected. The coarse-grained glacial ice

contact deposits apparently have a very high (2000 feet per day)

permeability, making them equal to some of the highest measured

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permeabilities in Maine eskers. An inferred permeability for the

lodgment till is as low as 0.01 feet per day (3 x 10~ cm/sec).

The majority of the bedrock aquifer was found to produce a

moderately high transmissivity of 100 square feet per day. The

median yield of the 14 wells with data is 5 gallons per minute,

an average yield for Maine wells. However, the low water level

readings in many of the other wells intuitively suggest

above-average bulk transmissivity for the area as a whole.

The K&B model will only accept input as transmissivities, so

for the long-term steady state simulation of contaminant trans

port, the transmissivities calculated from the AQUIFEM output

were input to the K&B model.

Storativity and Specific Yield

The specific yield of an aquifer is a measure of the amount

of water released per unit of volume of aquifer when water is al

lowed to drain from the aquifer by gravity. For most practical

problems it can be equated with storativity when dealing with "wa

ter table" or "unconf ined" aquifers, such as the case here.

Storativity is the volume of water added to or removed from a

unit surface area of aquifer under a unit change in water table.

The only difficulty comes in the evaluation of rapid changes in

water table in stratified soils where soil strata with relatively

lower permeabilities restrict the rate that water can drain from

coarser strata above them, producing an apparent storativity that

is less than the specific yield.

For this report, a knowledge of specific yield was not impor

tant since only the steady state, average annual condition was

simulated because long-term (10-year) simulations were necessary.

Dispersivity

The USGS solute transport model requires values of lon

gitudinal (along the direction of flow) and transverse (perpendic

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ular to direction of flow) dispersivities as input to the model.

Dispersion is a molecular and physical phenomenon that causes a.

contaminant plume to spread beyond the limits of what one would

delineate by a simple convective, or flownet analysis.

Dispersion is a scale-dependent phenomenon and a measure of the

heterogeneity of an aquifer. For regional models involving sever

al thousand feet of flow in stratified sand and gravel aquifers,

the longitudinal and transverse dispersivities of 50 feet and 15

feet, respectively, are appropriate according to the literature

(e.g., Fried, 1975). Failure to account for dispersion can re

sult in underestimating the apparent transport rate of a contam

inant, and in underestimating the horizontal width of a

contaminant plume.

No dispersivity is assumed for the bedrock aquifer since

this phenomenon is poorly understood in bedrock and there are no

data available here to validate any particular value. Thus, the

contaminant transport simulations done for the bedrock aquifer in

this study assume convective flow without dispersion.

Pollutant Attenuation by Retardation and other Mechanisms

The 2-dimensional solute transport model does not take the

sorptive capacity of the soil into account, nor the evaporative

loss of the volatile chemicals that we deal with here. However,

since these retardation factors are not well known, are different

for each chemical, and greatly complicate modelling beyond the

scope of this study, retardation was not taken into account. At

this time, there are insufficient data to allow any calibration

of retardation coefficients, even if they were incorporated.

Thus it has to be kept in mind when viewing Figures 9 through 12

that these treat the chemicals as "conservative" contaminants

(i.e., contaminants whose concentration is only reduced by mixing

with water) which move as tracers in the ground water.

It is significant to note that TCEy apparently has a greater

retardation coefficient than TCE. Recent test results for TCEy

-21

are showing significantly increased concentrations over those mea

sured at the same points in 1980, for example, whereas there has

been no corresponding significant increase in TCE.

Aquifer Inputs and Withdrawals of Water

The major aquifer water input to the surficial aquifer is

precipitation recharge. Using the results of USGS records and

many other studies of this type that we have performed, we have

assumed that on a yearly average, 60% of the average precipita

tion enters the ground water to become recharge in the sand and

gravel areas, 25% in the till areas, 5% in the glaciomarine clay

ey areas, and intermediate values in the transition areas.

Average annual precipitation was assumed to be 43" although the

monthly and annual deviations from the average can be large (see

precipitation graph on Figure 8). Since the long-term contam

inant transport simulations were for 10 to 11 year periods, the

average annual value is the most appropriate number, however.

For the bedrock aquifer, water transfer to and from the aqui

fer is a function of the water table position in the overlying

surficial aquifer and the vertical permeability and thickness of

the surficial aquifer. The rate of water transfer is proportion

al to the difference between the potentiometric surfaces in the

two aquifers, multiplied by the leakage coefficients. If the po

tentiometric surface in the bedrock aquifer drops below the

bottom of the surficial aquifer, the leakage rate becomes con

stant and proportional to surficial aquifer thickness. The

AQUIFEM bedrock flow model was developed using this principle of

water transfer through leakage. Once the flow model was calibrat

ed, the appropriate calculated leakage rates were input to the

K&B model.

Since water is necessarily added to the surficial model area

by precipitation, it must be taken out at approximately the same

rate, otherwise the water table would not cycle year after year

around the same average position. In the surficial models, this

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water is removed as stream flow or as a constant flux along the

boundaries. The largest area of predicted discharge is the north

ern branch of the major drainage leading west from the Royal

River, just south of the Boiling Springs. In the zone between

nodes 2 on the east and 89 on the west (Figure 6), about 800 gal

lons per minute is discharged from ground water to surface water.

Much of this probably occurs under the Royal River in this vicin

ity. However the local tributary stream discharge is also signif

icant. Field mapping found this area to be the largest

concentration of springs in the entire study area, as suggested

on Figure 2. This should be the case since the surficial model

indicates that a large ground water flow in a high permeability

zone occurs under this area. In the case of the bedrock aquifer,

discharge occurs in a diffuse manner over most of the areas north

and east of Mayall Road. The model also suggests, however, that

there is a localized concentration of discharge to the surficial

aquifer near the Boiling Springs.

Application of Contaminant to the Aquifer

No modelling was done of contaminant transport in the unsat

urated zone of the aquifer. This is a difficult problem at best

and there are no data to calibrate such a model at the site. The

models developed for this study are 2-dimensional, saturated flow

models that are incapable of accounting for fluid density differ

ences or non-homogeneous aquifers. When contaminants are intro

duced into the aquifer, simulations of contaminant concentrations

with time reflect vertically-averaged contaminant concentrations

for the entire grid element, which for this study is 340 feet by

340 feet square.

The time history of application of the organic chemicals at

the site is not known, but since the concentrations of the chem

ical TCE have been relatively constant with time at the Boiling

Springs and in the Royal River at Brickyard Station, it appeared

that the chemical was being added at a relatively constant rate

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for at least several years in time. The probable source of the

contaminant is a. leak or spill of the chemicals onto the ground

at some time in the past. These chemicals are settling slowly

through about 40' of unsaturated soil under the site. Whenever

it rains, a little of the contaminant is transported downward to

the water table. Over several years' time this can result in a

fairly steady application rate of the contaminant to the aquifer.

For the purposes of this study, the chemical was added as a con

stant concentration of ground water recharge which was derived

from precipitation during the time (ten years) of the surficial

aquifer simulation. Starting with an arbitrary percentage input,

simulated concentrations were back-calculated using a factor that

was computed to adjust the predicted Boiling Springs concentra

tion to about 200 parts per billion (ppb) of TCE, which is close

to the historical observed value. TCE was used for modelling pur

poses because there are more data on TCE concentrations around

the area than for any other.

Once the concentration with time was determined for each

grid cell of the model, this was applied to the water that leaked

into the corresponding recharge cells of the bedrock aquifer as a

stepped time input until ten years was also simulated for the bed

rock aquifer.

For simulations of the effects of removing the contaminant

or isolating the site from precipitation recharge, the initial

concentrations of contaminant in each respective aquifer were as

sumed to be the concentrations that developed after ten years of

introduction of the contaminant. An additional ten years was sim

ulated to observe the rate of cleansing of the aquifers. Again,

for the bedrock aquifer, the concentration of contaminant that

leaked into the aquifer from the surficial aquifer had to be in

put in a stepped manner in time.

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INTERPRETATION OF COMPUTER SIMULATION RESULTS

Ground Water Flow in the Surficial Aquifer

Our calibration of the surficial aquifer flow model suggests

that .there is much more glacial till underlying the model area

than we had originally anticipated. Therefore, the area of sat

urated sand and gravel aquifer is much smaller than suggested,

for example, on the map by Caswell (1979). We infer, for exam

ple, that there is a ridge of till underlying the sand and gravel

along Mayall Road, north of the Portland Sand and Gravel pit oper

ation. The area under the Pownal Road, northeast of the intersec

tion with Mayall Road, is also largely underlain by till. As

previously mentioned, the narrow ridge of ice contact sand and

gravel that lies west of node 166 on the surficial AQUIFEM model

appears to be perched on till with very little saturated thick

ness of sand and gravel over the till. The large spring at node

166 is apparently at the contact of the gravel over the till.

The recharge area that lies upgradient (southerly) of the

site that is available for dilution of any contaminants leaving

the site is small. Ground water flows away from the site to the

northwest. Further from the site, the ground water that orig

inates at the' site turns north, then east, and flows to the Royal

River. This explains why no contamination was detected in the

"McKin spring", just east of the site. South of the site, the

ground water divide is in the vicinity of Route 115, with ground

water to the south passing into a surface drainage that passes to

the southeast of the site.

Sensitivity analyses on the rate of constant flow leaving

the aquifer under the Royal River between finite element nodes 1

and 3 indicate that the flow is small there. Back-calculated per

meabilities for this area suggest that any deposits under the

clay in this area are no coarser than fine sand. This explains

why almost all contaminants that originate at the site are dis

charged to the Royal River in the small area between the Boiling

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Springs and the railroad bridge where the sand and gravel aquifer

terminates and is in contact with or close to the bottom of the

River in this area. There is no suggestion that the coarse sand

and gravel continues to the south of the Railroad Bridge. Water

samples from Boring B103, near the Railroad bridge and south of

Boiling Spring No. (Figures 1 and 2), showed no TCE or TCEy con

tamination in surficial or bedrock materials at that location in

October 1982.

Bedrock Aquifer Flow

Figure 5 represents the computer-simulated potentiometric

surface contours in the bedrock aquifer. Bedrock ground water

flow moves to the north from the site, then turns east and final

ly southeast to discharge to the surficial aquifer in the

vicinity of the Boiling Springs. Overall aquifer transmissivity

is interpreted to be somewhat greater than average for Maine bed

rock aquifers. However there are two apparent areas of low trans

missivity: one area is 500 to 1000 feet due east of the site;

the other area is in the vicinity of Philip Humphrey's well, bed

rock well #4 on Figure 1. We interpret an area of relatively

higher bedrock transmissivity to lie to the northwest of the

site, in the vicinity of the bedrock trough shown on Figure 3.

The bedrock aquifer model was simulated assuming that the

Humphrey well, which is still being used, was being pumped at an

average rate of about 50 cubic feet per day. Since the wells in

the triangle between Depot Road and Mayall Road are not now being

pumped, no pumping stress was applied on them in the model. Had

we simulated the pumping of these wells, the potentiometric sur

face would have obviously been lower in that area.

The area of highest discharge rate to the surficial aquifer

is in the area of the Boiling Springs. This would be expected be

cause of the permeable nature of surficial aquifer there and the

fact that the surficial aquifer is discharging to the River

there.

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Contaminant Transport Modelling—Surficial Aquifer

As discussed earlier in this report, there are several diffi

culties involved with simulating contaminant transport in the

East Gray aquifers: the time history and rate of leakage of chem

icals into the aquifer are not known; and the contaminant that

was introduced was not a "conservative" contaminant. Despite the

difficulties posed by these unknown factors, we believe that we

have developed some useful information; however it must be eval

uated with care.

Figure 9 shows the results of 10 years of introduction of a

constant rate of TCE into the surficial aquifer in a 340 foot by

340 foot square area centered on the McKin site. The concentra

tions under the site were back-calculated by applying a ratio

that was necessary to adjust the Boiling Springs grid cell concen

tration to about 200 ppb TCE. Treating the TCE as a conservative

solute, the computer model predicts that about 26 gallons per

year of TCE entered the aquifer at the site. Our hand-calculated

estimates, however, based on our analysis of the concentrations

observed over time at Boiling Springs and Brickyard Station,

could place the amount of TCE discharged into the aquifer under

the site at as high as 125 gallons per year. These discrepancies

could be explained by the non-conservative nature of the TCE, in

ability of sample results to develop correct "average" concentra

tions in the Royal River (particularly at the Railroad Bridge,

where the distribution of contaminant may not be uniform across

the River channel), or by improper simulation of the time history

of the chemical leakage at the site. With respect to the last

point, there is some evidence to suggest, at least in the surfi

cial monitoring wells at the site (e.g., well |8, Figure 8) that

the amount of contaminant leaving the site has decreased with

time since 1980. Since the simulation shows that it took 5 years

for the first contaminant to reach Boiling Springs, then about 4

more years to begin to stabilize near 200 ppb, the actual time

-27

history of chemical leakage at the site could have been as a

large slug initially, followed by lesser amounts decreasing with

time thereafter. In a ten-year simulation this would not affect

the results much at Boiling Springs, but could have resulted in

greatly increased concentrations near the site in the early

years.

There are several other important implications of Figure 9.

Notice that the path of the contaminant plume is first to the

northwest, then turns east to run down the high-permeability zone

to the Royal River. Notice that the plume does not turn to run

to the south at the Royal River. This is in agreement with the

water test results on Monitoring well BIOS, which found no contam

ination in either the soil or bedrock well. Although the verti

cally-averaged concentration of TCE is simulated to be between

200 to 300 ppb between the Boiling Springs and sampling stations

24 and 26 (Figure 1), west of Boiling Springs, only the spring at

station 24 found any TCE contamination (25 ppb, Table 1—ERGO

test results). The models used in this study are not three-

dimensional and would not account for contaminant stratification

within the aquifer. It appears that most of the contaminant is

travelling along the bottom of the surficial aquifer.

Contaminant Transport Modelling—Bedrock Aquifer

Figure 10 shows our simulation of the contaminant distribu

tion in the bedrock aquifer after 10 years of simulation. There

are several interesting aspects of this simulation. First, no

tice that even though no dispersion is accounted for in the mod

el, the contaminant plume covers a much larger area than that of

the surficial aquifer. Although the plume comes very close to

Collyer Brook, there is no indication that it discharges to

Collyer Brook in any significant amount, which is in agreement

with test results on Collyer Brook. Notice that the center of

the plume tracks toward Boiling Springs, although the initial

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track from the site is more toward the north than the surficial

plume.

The simulation indicates that the bedrock plume first

reached Boiling Springs about 2 years after initial contaminant

introduction. However, the increase of concentration with time

was slow and was still increasing at 10 years into the simula

tion. This may explain why the concentration of TCEy at drilled

wells 4 and 15 appear to have increased with time.

While the simulation that is summarized on Figure 10 seems

to agree nicely with recently measured concentrations of TCE in

bedrock wells at sample locations 14 and 17 (Table 1), it does

not explain the low readings at sampling locations 15 and 16.

The well (#9) at sampling location 15 had very high TCE concentra

tions in 1977. In fact the Figure 10 concentrations are about a

factor of 10 lower in the triangle area between Mayall and Depot

Roads than the values observed in the wells there in 1977, at the

time the wells were in use. We have concluded that this is due

to the fact that the wells were inducing a much greater rate of

local recharge of contaminated surficial aquifer water into the

aquifer at that time, than in the present condition with the

wells not being pumped. At sample location 16, drilled well #6

is near the edge of the plume and some adjustments of the bedrock

flow model could move the simulated plume farther to the east,

better to match the October 1982 sample results.

THE FUTURE OF THE CONTAMINANT PLUME

MAINTAINING THE STATUS QUO

The time series of water quality tests for TCE and TCEy on

Figure 8 do not seem to show any major downward trends in concen

tration of the chemicals in most of the water sampling locations.

Indeed, there is some indication that TCEy is increasing with

time at some points. Although some of the surficial monitoring

wells at the site (e.g. wells 8 and 16) may have begun to show a

decline in concentrations, DEP site well #7 contained very high

-29

levels of'TCEy (Table 1) during this fall's sampling. It is not

known whether or not storage tanks are still leaking into the

soil. If all of the chemicals were presumed to have entered the

soil prior to 1977, the mechanics of unsaturated flow would sug

gest that after some point in time, there should be a decrease in

the absolute volume of chemical that would enter the aquifer.

Even if the addition of chemicals to the soil stopped after 1977,

our simulations show that no major change in concentration of the

chemicals would be observed at Boiling Springs for another 5

years. If the addition of chemicals to the soil is still going

on, then the concentrations of the chemicals will likely remain

the same, or even increase slightly throughout much of the bed

rock and surficial aquifers. To the best of our knowledge, there

is only one ground water user, Philip Humphrey, that is presently

affected by the ground water contamination.

PREVENTING CHEMICALS FROM LEAVING THE SITE

There are several ways to prevent any further addition of

chemicals to the ground water: a) creating a barrier around the

site that would prevent further migration of ground water through

or away from the site; b) sealing the top of the site so that no

more precipitation could filter through the unsaturated soils and

wash more chemicals into the ground; or c) removing the contam

inated soils from under the site. This report is not intended to

evaluate the cost effectiveness or feasibility of these alterna

tives. This report was only intended to give a generalized eval

uation of the hydrogeologic aspects of several of the major site

clean-up approaches.

Regardless of the particular method used to isolate the

site, all of the methods can be treated basically the same from a

hydrogeologic standpoint. The approach is to begin a new simula

tion with the aquifer having initial concentrations of the chem

icals as shown in Figures 9 and 10, cut off the addition of

-30

further chemicals to the aquifer, then simulate the process of

the aquifer cleansing itself.

The decreases with time of the TCE contaminant concentra

tions in the aquifers are shown on Figures 11 and 12 for the sur

ficial and bedrock aquifers, respectively. Dealing with the

surficial aquifer first, notice that after two years, little

change takes place in the aquifer, except in the immediate site

area. After 5 years, the western half of the contaminated

surficial aquifer has shown significantly decreased

concentrations, however, the area of the Boiling Springs still

has not changed much. After 10 years the aquifer is much

improved in quality overall, with only the low-permeability soils

northwest of the Boiling Springs still not having changed much.

In the series of Figures 12A, B, and C, the change in concen

tration of the chemical TCE in the bedrock aquifer is shown over

time, after the site is isolated. Notice that after 2 years, the

only area in the bedrock aquifer that has decreased is immediate

ly under the site. All other areas have actually increased be

cause the contaminants are still being added to the bedrock

aquifer from the surficial aquifer and the bedrock aquifer had

not reached chemical equilibrium after the initial 10 years' sim

ulation. After 5 years of site isolation, however, concentra

tions are decreasing throughout the entire aquifer. At ten years

TCE concentrations are even more improved. Although not shown in

this report, the simulation was carried out to 11.4 years, by

which time the western half of the contaminated portion of the

bedrock aquifer had decreased everywhere to 3 ppb or less, but

the area under Boiling Springs was still in the range of 10 to 15

ppb. Because of the mechanisms of contaminant transfer between

the surficial and bedrock aquifers, it is apparent that the rate

of cleanup of the bedrock aquifer would be greatly increased if

the surficial aquifer could be cleansed at a faster rate, partic

ularly north of the site, in the triangular area between Mayall

and Depot Roads.

-31

GROUND WATER REMOVAL OR FLUSHING BY PUMPING

Some ground water contamination in other parts of the coun

try has been handled by pumping the contaminated water out of the

ground and treating the water, then injecting it into the ground

or discharging it to surface waters. Another method is to inject

water to control the direction of flow or the rate of dilution of

the contaminant. For the bedrock aquifer and low permeability

soils within our study area, manipulation of the ground water by

pumping or injection would probably not be effective or feasible.

In the high-permeability surficial zone, these techniques could

be used to accelerate the clean-up of the surficial aquifer,

which would also accelerate the clean-up of the bedrock aquifer.

The optimum location for a withdrawal well in the high-

permeability zone would be about 1000' south of the intersection

of Mayall and Depot Roads. Clean ground water injection wells

could prove useful in moving contaminated water out of the area

under the site, which has a moderately low permeability. We have

not evaluated the technical aspects of these options in detail,

since additional field data are necessary and modifications to

the existing ground water simulation models are necessary before

a meaningful evaluation of these alternatives can be performed.

With a combination of withdrawal and injection wells, the contam

inant distributions as shown for 10 years after site isolation in

Figures 11 and 12C might be achieved in one to three years. This

assumes that the site was isolated at the start of the pumping.

SUMMARY AND CONCLUSIONS

The summary and conclusions of this report are given on the

letter of transmittal at the beginning of this report.

-32

LIST OF REFERENCES

BCI Geonetics, Inc., 1980. A consultant report by W. B. Caswell

to the Maine Dept. of Environmental Protection concerning

the ground water contamination in East Gray, Maine

Caswell, W.B., compiler, 1979, Sand and gravel aquifers, maps 11

and 12, Cumberland and Androscoggin Counties, Maine. Maine

Geological Survey, Dept. of Conservation, Augusta, ME 04333

Caswell, W.B., and E.M. Lanctot, 1976 (rev. 1978), Ground water

resource maps of Cumberland Co. Maine Geological Survey,

Dept. of Conservation, Augusta, ME 04333

Doyle, R.G., 1967, Preliminary geologic map of Maine. Maine

Geological Survey, Dept. of Conservation, Augusta, ME 04333

Ecology and Environment, Inc., 1981, Preliminary site assessment

and emergency action plan, McKin site, Gray, Maine. FIT

project prepared for U.S. EPA, Contract No. 68-01-6056

Fried, J.J., 1975, Groundwater pollution. Elsevier Scientific

Publ. Co., Amsterdam, 330 p.

Gerber, R.G. and J.R. Rand, 1980, Geology and hydrology—Mason

Station ash disposal facility, Wiscasset, Maine. A

consultant report to Central Maine Power Co., Edison Drive,

Augusta, ME 04336

Hart, Fred C. Associates, 1978, Analysis of water contamination

incident in Gray, Maine. Prepared for U.S. EPA, Contract

No. 68-01-3897

Hussey, A.M. II, and K. Pankiwskyj, 1975, Preliminary geologic

map of southwestern Maine. Open-file map 1976-1, Maine

Geological Survey, Dept. of Conservation, Augusta, ME 04333

Konikow, L.F., and J.D. Bredehoeft, 1978, Computer model of

two-dimensional solute transport and dispersion in ground

water: Book 7, Chapter C2, Techniques of Water-Resources

Investigations of the U.S. Geol. Survey, Washington, D.C.

20242, 90 p.

Prescott, G.C., Jr., 1980, Ground water availability and surfi

cial geology of the Royal, Upper Presumpscot, and Upper Saco

-33

River Basins, Maine. Water-Resources Investigations

79-1287, U.S. Geol. Survey, Washington, D.C. 20242

Prescott, G.C., Jr., 1979, Maine hydrologic-data report no. 10,

ground-water series, Royal, Upper Presumpscot, and Upper

Saco River Basins, Maine. U.S. Geol. Survey, Washington,

D.C. 20242

Prescott, G.C., Jr., 1977, Ground water favorability and surfi

cial geology of the Windhara-Freeport area, Maine.

Hydrologic Investigations Atlas HA-564, U.S. Geol. Survey,

Washington, D.C. 20242

Prescott, G.C., Jr., 1976, Maine basic-data report no. 9,

ground-water series, Windham-Freeport-Portland area. U.S.

Geol. Survey, Washington, D.C. 20242

Prescott, G.C., Jr., G.W. Smith, and W. B. Thompson, 1976,

Reconnaissance surficial geology of the Cumberland Center

Quadrangle, Maine. Maine Geological Survey, Dept. of

Conservation, Augusta, ME 04333

Rushton, K.R., and S.C. Redshaw, 1979, Seepage and groundwater

flow. John Wiley & Sons, Chichester, England, 339 p.

Thompson, W.B., 1976, Reconnaissance surficial geology of the

Gray Quadrangle, Maine. Maine Geological Survey, Dept. of

Conservation, Augusta, ME 04333

Townley, L.R., and J.L. Wilson, 1980, Description of and user's

manual for a finite element aquifer flow model, AQUIFEM-1.

Technology Adaptation Program, Mass. Inst. of Technology,

Cambridge, MA 02139, 294 p.

-34

TABLE 1--1982 WATER SAMPLE LOCATIONS AND TEST RESULTS

(Sample locations are shown by numbered arrows on Figure 1)

• No. Map Designation Land Owner Tax Lot Maine Coordinates DEP Sample TCE TCEy Notes/Other

(Fig 1) (Figure 1) Map No. North East Number µg/l µg/l

1 Gerber--BlOlA Blue Rock Indust. 33 30 383,930 465,030 Could not sample well 2 Gerber--Bl02 Lucymae Bowles 39 10 383,610 469, 720 104558 J71 Jl20 Methyl ethyl ket·:me Jl3 ,000 3A Gerber--Bl03 soil Fred. Farrell 38 13 383,080 470,220 105111 Kl Kl 3B Gerber--Bl03 rock Fred. Farrell 38 13 383,080 470,220 105137 Kl Kl 4A Gerber--Bl04 upper Emerson Mitchell 39 8 386,020 467,020 105017 Kl Kl Electron capture detection 4A Gerber--Bl04 upper Emerson Mitchell 39 8 386,020 467,020 KO.l 0.5 ERCO test results 4B Gerber--Bl04 deep Emerson Mitchell 39 8 386,020 467,020 105019 Kl Kl Electron capture detection 5 DEP Well 8 (site) Richard Dingwell 38 20 382,990 466,140 Could not sample 6 DEP Well 13 (site) Richard Dingwell 38 20 382,660 466,370 l05074 Kl Kl 6 DEP Well 13 (site) Richard Dingwell 38 20 382,660 466,370 105073 16 0.7 ERCO test results 7 DEP Well 14 (site) Michael Valente 38 35 382,690 466,070 105076 1(C Kl 8 DEP Well 15 (site) Michael Valente 38 35 382 '890 465 '890 105075 Kl Kl 9 DEP Well 7 (site) Michael Valente 38 35 383,310 466,130 10419 2 53 130,000 Methylene chloride JlOO

10 Test Well 17 Blue Rock Indust. 33 30 382,910 464' 770 L04577 Kl -~Kl

11 Drilled well 1 Ralph Wink 39 20 385,880 470,100 Could not sample