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
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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
Recommended