Good morning, good afternoon or good
evening wherever you are located. The
geology of New England can be very
complex and the overview that I'm going
to give is going to be primarily
concentrated on its relation to
groundwater. About 500 million years ago
the continent of Pangaea was formed and
what is important is that the North
African plate collided with the North
American plate. The first example of that
are the Berkshires and the related
deposits on the borders with New York and
Connecticut and Vermont. What is most
interesting is that we have limestone
and marble deposits which are
unrealistically formed at the latitude
that now exists except that when our
portion of the North American continent
was being formed New England was in fact
below the equator. Next as the continents
started to pull apart and to separate
the Connecticut River was formed and we
have information in the next slide
showing in fact what it looks like today
and where the deep blue is suggesting
the parts of the ocean that may in fact
be deepest. This is an example obviously
of a lava flow. We have no examples that
we can count to in New England. In fact
if there had been much in the way of
volcanic activity, subsequent erosion has
removed it. Another example of what may
or may not have ever taken place in New
England; however, what is most important is
that as the continents pulled away
large fractures were developed at
different parts of New England and they
do play an important part in whether you
are developing a sand and gravel well or
something in the underlying bedrock. Here
we have an example of a fracture that is
moving at a oblique angle. You can see
the darker deposits here which is a dike
and this is an example of what we look
for in New England. Hopefully at the
later time I'll discuss in rock wells.
Okay, we have a lot of granitic materials,
igneous materials in New England. Gabbros,
felsites but granite's are one of
the major components of the underlying
bedrock. Here we're talking about near
the very top of a batholith where in
fact granitic material has intruded into
the overlying bedrock; however, has not
broken out on the surface. Well what is
most important to us in New England
and with regard to the development of
high yielding bedrock wells, about two
and a half million years ago, it started
to freeze. The temperature dropped between
five and ten degrees and in Labrador ice
started to form which did not melt
during the summer. Eventually it's
estimated that a thickness of close to
three miles of ice was developed. With
this amount of weight, the bottom part
had a certain plasticity and it started
to flow southwards. Now we know that
there are definitely five times in the
last two and a half million years that
ice has completely covered New England.
However, I have heard recent estimates it
may be as high as seventeen glacial
events have
taken place; however, each subsequent
event may have destroyed some of the
evidence of what preceded it. Here's an
example of multiple mountain glaciers
flowing into a major one. What is of
interest to us is the dark bands which
is the material that has been ingested
into the ice, bedrock, previous existing
soils, even organic debris. Example again
of a glacier advancing. In this case into
the ocean, and lastly as the glacier
moved forward it pushed debris in
front of it, much like a bulldozer. A
glacier never advances in one
push and does not retreat in a single
push. There are advances, stagnation, more
advance, partial retreat, more advances.
Well here we're looking about something
that is quite interesting is the glacier
widened and deepened the valleys, the
material ingested into the ice was then
deposited during the glacial retreat and
here we have several examples that may
be of interest. You'll notice that we
have blocks of ice right here. As sand
and gravel being released from being
ingested in the ice is swept around
these, that when it later melts it will
be left as a depression forming a
kettlehole, and around kettleholes the
potential for sand and gravel deposition
with what would appear to be water-
developing transmissive sediments may in
fact be possible. An example again of a
glacier in retreat. Please notice on
either side as a glacier retreats it
shrinks in
from the sides and down from the top but
in fact you can get coarse sand and
gravel deposits on the side of the
valley.
All right, this slide is very important
because we are seeing subsequent
deposition at multiple points during
this retreat. Over on the left hand side,
you will notice that a stream is coming
out beneath the ice. This is carrying
very coarse sediments that ultimately
when covered as the glacier retreats
further up the valley may in fact
represent a favorable zone to develop a
public or high yielding well supply. It
continues to pro-grade further on out
with the sediments getting finer until
we have a glacial lake in which clay
deposits are going to be found. This will
account for how we can end up within a
glaciated valley with sediments that are
totally different at different points
within the valley. All right, here we have
what ultimately is going to become an
esker. This particular stream at the
bottom here is a high velocity and is
going to be carrying very coarse
sediments. To get an idea of the size, I
can't see it, up here on the right-hand
side is a person who is about this high
just to give some perspective as to the
size of what will ultimately become an
esker as the ice melts and the coarse
deposits here are left within the valley.
Here we're talking about the characteristic
of a valley that has been glaciated. You
will notice a u-shape. Again we're
talking about what has depositioned. The
valley itself is markedly deeper to the
underlying bedrock. Cartoon here showing
exactly what's going on. If you'll notice
clearly here was a stream beneath the
glacial ice
putting an esker,
drumlins and I will explain this in a
little bit, we have the terminal moraine, I
indicated that we advance forward
pushing material - this would be glacial
till, and here is an outwash plain,
something that again we look forward to
finding because the potential for a high-
yielding well exists in that type of
deposition. Here we have glacial till
which drillers call hard pan. This is
material which was laid down beneath the
ice. It goes anything from clay particles
through silt, sands and in fact boulders.
Now there are two types of till. If the
glacier stagnates and the ice melts down
and the material within is just
deposited beneath the ice, then in fact
it's an ablation till. However, if we are
talking about something that is laid
down as the glacier in fact has
thousands of feet of ice on top, it it is
much denser and this becomes somewhat
important because in the development of
bedrock wells in many case it is
overlain by glacial till. If you have
an ablation till, more water can be
stored within it and it can de-water
into the underlying bedrock fractures
more effectively. Here we have an outwash
plain, and as you can see during the
summer, there is much more melting going
on, and in this particular case it
probably was a warm summer with much
deposition going on, a moderate winter, a
very cold summer followed by an even colder
winter. So that this is the type of
material that in sand and gravel
deposits will in fact be potential for a
high-yielding well.
All right, this particular slide is very
important because if you dig at the
surface you have nothing but coarse
clean sand and gravel. However, please
note that if you put in a test well
right in this location, you are not going
to find anything and yet moving a short
distance away, there are very coarse
sediments that in fact, when saturated,
would yield a whole lot of water.
Something right in here would yield a
lot of water but there and the other
side there will not. That is why you can
never be sure with a singular test well
that in fact you have found something
that could be developed most effectively.
This is the spring runoff in the
Pemigewassett Valley in northern New
Hampshire. This is the type of deposition
that would be quite similar to what in
fact would end up being an outwash plain
but note you have very coarse material
right here, but in this particular area
right there you have the deposition of
fine material all taking place
simultaneously. Here we have what is left
of an esker. Obviously this had been a
tunnel beneath the ice of a glacier, but
even at this distance you can see how
coarse and clean the sand and gravel is.
Eskers are one of the important
features that we look for in the
development of high-yielding wells. This
is an esker that actually was in a
lake. The source of recharge is quite
obvious, but this particular well that
was drilled right there had the
potential to yield 3 million gallons per
day which is a very high-yielding well
in New England, and to get an idea of the
perspective, this is the
Franconia Notch in northern New
Hampshire this is the Pemigewassett River
and you can see the deposition of very
coarse material that if the glacier
was still in the location right here
would cover up this material which in
fact can transport a large amount of
water. Now here we have a drumlin, where
this is composed of basal till. While in
itself, it is not a potential source, it
is used by communities, this site right on
the top for water towers. This is
approximately 3/4 of a mile in length a
quarter of a mile in width and
approximately three to four hundred feet
in elevation. However, on the southwest
and southeast quadrants of drumlins
there in many cases are deposits of
permeable sand and gravel deposits. If
anybody has any questions, we are ready
to answer them. Hi Ted, we actually do
have a couple of questions. One is, can
you talk about the difference between
basal and ablation tills and talk about
how much water each type of those tills
could produce? As a matter of fact, most
tills are only good for old dug wells
for a single family. We're talking one or
two gallons per minute and most of these
in fact go into the very upper regions
of the groundwater table so that the
ablation till is less dense than a basal
till but neither is particularly of any
benefit to develop a high yielding well.
Great. Thanks for that. A follow-on
question to that is why are eskers, kettle-
holes and outwash plains good spots to
look for high-yield wells? The reason
that they are is they're mostly
comprised of well-rounded clean sand and
gravels, in many cases devoid
of finer sediments which would block the
interstices or voids between the individual
particles therefore groundwater can move
through those deposits rapidly, making
them very good sources for potential
high yielding wells. Great. Thanks, and
we've got one other one. How important is
detailed surficial geologic mapping for
siting large yielding water supplies?
Surficial mapping is going to be
beneficial because it is going to help
you in several ways. Number one, it's
going to show you what the potential for
the underlying saturated sediments
will be, but also you should be able on
that mapping to look up gradient to make
a determination
how much watershed is up gradient to
provide recharge. Also if you look
closely at areas up gradient you can
rule out sites where there may be
potential for materials that, dumps
would be example or landfills, any up
gradient farming that may elevate
nitrogen and you can also take a look
and see is there any industrial activity
or roads that could degrade water
quality. Great. Thanks for that. We've got
one other question on one of the images
that you showed. The person is asking how
did you in the second to last slide
determine that there was an esker at the
location? So I think if you back up a
couple slides when you were talking
about eskers... That particular shot was
taken right next to interstate 495 in
Boxborough Massachusetts, which is one of
the major mapped eskers in the
state of Massachusetts so that it's
clearly identified by the contours that
that is an esker. Great. Thank you, and so
that's all we've got for questions right
now so I'm going to
go ahead and pass things back to you.
Thanks. Here we have an indication of
what is typical in New England: water
table, unconfined aquifers are most
prevalent. We do not have much in the
artesian with a confining layer
overlaying it. As a matter of fact, I
would say that of the wells developed by
my company, 95 percent would be in the
unconfined saturated material and less
than five percent would be in the
confined layer and which is true
artesian. We still find that the old
technology of drive and wash is the
least expensive and the most effective
way to determine what the stratigraphy
is within a area that we believe sand
and gravel potential for development of
groundwater exists. Here we're talking
about a bombardier mounted drilling rig
with a hammer being raised and lowered
that will drive a 2 and a half inch
diameter schedule 80 steel pipe into the
ground.
Here's a coupling going on the bottom
the schedule 80 pipe. It has an outside
diameter of 2.75 inches and an inside
diameter of 2.33. Here we're talking
about a 350 pound hammer which is being
raised and lowered approximately 30
inches to drive the 2 and a half inch
casing into the material. Water is now
jetted into the casing which has an open
bottom to flush out the sediments that
in fact will lodge within the casing.
That water
comes out flushed and is dropped
into a bucket where it is captured. It is
graded for color. It is graded for
transmissive capability and the
coarseness and the description of the
sediments which are being flushed out.
Color is important. In New England we
have found that gray sediments have a
tendency to have elevated concentrations
of soluble iron and manganese
whereas brown sediments have a tendency
to be lower concentration to none of
those two metals. This is approaching
what we call refusal. Refusal may be
either the underlying bedrock or dense
glacial till. We have, I have only four
examples where till has ever been underlain
by permeable sediments and in those
cases, it has been a flow till. The till
itself became saturated and flowed over
on top of permeable sediments and then a
re-advance of the glacier overlaid the
till with sand and gravel which is clean.
Here's an example of when we look at the
log of the sediments that have been
penetrated. We will select a test screen.
A screen itself is a series of vertical
rods around which is wrapped trapezoidal
wire and the open area in
thousandths of an inch is the slot size.
Therefore something that, which would be 10
1/10 of an inch would be a 100 slot
screen. The typical screens used in most
test wells are between 40 and 100 slot.
Now this is an example of what the
advantages between a wire wound screen
on the left
and a shutter screen on the right. The
shutter screen has much less open area
and the fact that it is a lip is more
difficult to develop to maximize the
yield of the test well. The well is
developed using a diaphragm mudsucker
pump which has a pump pause. After the
water has been dislodged, a column of
water falls back down the test well
turning over the formation so that more
fine material, finer than the slot size
of the screen, may be brought close to
and dislodged. We are trying to get a
jacket of course clean gravel larger
than the slot size of the screen
adjacent to this test screen itself. Here
we are pumping it with a centrifugal
pump and what we are noting first of all
what is the static water level. How far
beneath the ground is in fact the water
table? That is going to account for what
the inches of vacuum on the very top of
the well - this becomes important. If in
fact this pumps 40 to 50 or 60 gallons
per minute, we will move to linear feet
away and drive an observation well to
the same depth as the test well. Here we
may choose to put a different slot size
screen in, usually coarser of the two
wells. Whichever pumps the higher
capacity, we will then run a pumping test
of two to four hours in duration noting
the GPM of the test well, the inches of
vacuum and what the drawdown is within
whatever has become the observation well.
This will give us a preliminary specific
capacity of
that particular stratum from which we
can project upwards what the ultimate
yield of a permanent well may be capable
of producing. There's a test well log
which in fact is going to describe on
the left hand side the different stratum,
their thickness it also is going to give
an indication of whether wash water was
lost. Good indication if you lose wash
water, it will probably give wash water.
We note the color as indicated before,
which is important because we may give
up some potential yield to put to
develop a shallower stratum which may in
fact have better water chemistry. The
duration of the pumping test would be
noted and what the total drawdown in the
observation well would be. Also, it should
be noted how quickly after the pumping
is curtailed does it recover back to the
original static water level. Well this is
an example of one of the methodologies
used to run and conduct the pumping test
which is usually the second stage after
a favorable test well has been found.
Rather than putting an 8 inch or 12 inch
diameter test well in the center, if it
is particularly shallow, more water can
be pumped by putting in a group, usually
a hexagonal group with one observation
well in the center, to check what the
drawdown is going to be. However, we can
also put in an 8 or a 12 inch well. Now I
had indicated that we usually put in a
test well and 2 foot away an observation
well; however, in Auburn, Massachusetts
we put in the test well. It did 40
gallons per minute. We moved 2 feet away
and put in an observation well that only
pumped 15 gallons per minute. We moved
and put in an observation
well two feet away on the
opposite side that pumped 60 gallons a
minute, and then moved and put in the 8
inch well at this location 2 feet from
here and it pumped 200 gallons per
minute. If in fact, this had been the
original test well, the town of Auburn,
Massachusetts would never have ended up
with a public water supply sited here.
There are different types of drilling
machines that can put in permanent wells
and the test well. This happens to be a
dual rotary barber machine which has the
capability to spin casing and also has a
drill bit in the center. If in fact you
have a cobble complex or encounter a
boulder, this piece of machinery can
drill through it and in fact in North
Kingstown, Rhode Island using this piece
of equipment, we were able to go through
a 10-foot diameter boulder into
permeable sediments beneath it and we
were able to develop a well that pumped
1 million gallons per day. This is the
type of material that we're looking for.
If you look closely, we're talking medium
to coarse sand with fine gravel and
cobbles. You will notice there is no
indication on the person holding any
evidence of fine sand, clay, or silt and
again going back to make an
indication, in New England now, shutter
screens are almost never used. They still
may be utilized for irrigation wells in
the Midwest and out in the mountain
states. The advantage being that the
shutter screen is far less costly than
the wire wound screen. Here we have an
example of a well that would be typical
of a test well in the intermediate
stage. It is not gravel packed. The
natural sediments are coarse enough that
in fact development can pull through.
What is obviously shown here is finer
sediments through ending up with a
jacket of coarser material. This is
called a telescope screen. The OD of the
telescope screen is slightly smaller
than the ID of the well casing above it.
All right, conducting a pumping test - you
have to be able to take the water being
pumped and discharge it far enough away
that in fact it is not going to be able
to come back and provide recharge
overinflated the potential capacity of
the well. Wells can be pumped with a
suction lift pump if they are shallow
but remember, a suction lift centrifugal
pump can only draw water from a depth as
deep as 24 feet beneath the surface, so
in a very shallow aquifer, a pumping test
can be conducted with a suction lift
pump.
However, in deeper wells most are now
conducted with a submersible pump
powered by a generator. Here we have an example
of a shallow aquifer. This is going to be
a tubular well field, 50 feet on center,
a series of small diameter wells are
manifolded. This is the pumping test and to
a suction manifold to a suction pump and
the discharge is being run up and out of
the particular basin. So shallow aquifers
certainly are still potential high
yielding sites. Our company just rebuilt
a well field for the Brunswick Thompson
water district in Brunswick, Maine. There
were more than 50 of these small diameter
wells and the ultimate yield is going to
be 800
gallons per minute. What is important is
when you are conducting a pumping test,
is to accurately measure the flow. Many
times it's done by an orifice weir
right at the point of discharge where
the weir will restrict the flow causing
in a tube on the side an elevation to
come up which is measured. There are
tables that will predict exactly what
the yield will be. Also you want to be
able to take the discharge water onto a
sheet of plywood that we have jokingly
called an energy dissipator and keeping
a Con. Comm. happy surrounding it by sand
and hay bales so that there will be no erosion.
We're back to potential questions.  We do
have a few of those. One is are there
scenarios where a well should not be
installed in a sand and gravel terrain?
The answer being yes. If in fact you know
that the water chemistry is going to be
of such a poor state that in fact it
would cost too much to in fact build a
treatment facility for it. Now this could
be if you are proximal to swamps or now
called wetlands. The closer you are to
those type of surface supplies, the
greater the likelihood that your
groundwater is going to have elevated
iron and manganese. Again I mentioned
before, farms, you have the problem of
animal waste.
You also have the the problem that there
may be a rare and endangered species of
some sort that if in fact you pump that
sand and gravel deposit at the desired
maximum rate, you are going to have an
adverse impact upon those. And lastly,
some pollution can come from from very long
distances. For example, if your sand and
gravel deposit overlies a major fault,
it is possible that pollution can move
as much as a couple of miles away. So
that you have to be very knowledgeable
of what is going on. Most people do not
think that sand and gravel deposits
derive recharge from the underlying
bedrock. That is incorrect.
There is a distinct relationship between
the overburden and the underlying
bedrock. Great. Thanks for that. A couple
other questions we have coming in. One is
has sonic drilling been used
successfully in sand and gravel terrain?
Yes it has. As a matter of fact sonic
drilling, again, if you have reason to
believe you are going to have major
boulders and/or cobble complexes that
the two and a half inch diameter driven
well cannot penetrate, the sonic rig is
certainly something that is excellent.
Also in fact that if your static water
level is going to be below 24 feet, a
sonic rig will allow you to put in a 4
or a 6 inch diameter test well that you
will then be able to put a submersible
pump in and make an accurate evaluation.
Great. One other question that we have is
would you ever put in observation well
closer than two feet to a test well? No.
Okay. What you don't know - you know that
they're 2 feet apart on the surface - what
you don't know is a well that's 80 or
90 feet deep what in fact it is going to
be. The closer it is, the more misleading
the potential specific capacity is going
to shown to be, which in fact is
going to give you incorrect information.
Thank you and that's all the questions
we have for this section.
Until about fifty years ago, in New
England drilling a rock well was pretty
much a hit or miss scenario. The problem
being is that we had no methodology
available to make a determination where
zones of fractured bedrock may be.
Obviously this example if you randomly
sited a well and drilled right here you
had the potential of getting a much
higher well capacity than if you went
either side. The USGS in New England has
stated that if you throw a rock over
your shoulder backwards you have a 98
plus percent chance of getting
sufficient water to take care of a
single home. However, less than 10 percent
of all wells randomly sited will do 10
gallons a minute and less than 1/2 of 1%
will do 50 gallons a minute or greater.
As I indicated that most of the bedrock
in New England is primarily igneous or
metasediments - sedimentary rocks which
have been metamorphosed. We have very few
deposits of sedimentary rocks such as
sandstones or conglomerates and we have
very few deposits of limestones.
Therefore, the crustal fracturing of the
Earth's crust has to prevent fractures
which will allow groundwater to be
stored and to be yield. If in fact you
drill and don't hit any of these
fractures, you are not going to get a
well that is going to produce much water.
Here's an example of what may be a
moderately yielding well. It has
encountered one fracture. Here we have an
example of what we hope to find if we're
looking for a high yielding well within
the underlying
bedrock. This is an example of one of the
type of fractures that we hope to
encounter. This particular one is near
route 128 in Massachusetts and you can
see the number of vertical fractures
that are existing and not only does this
store water but it moves at a potential
to have a high velocity. Well how do we
determine where these are? Dr. Parizek
at Penn State, now 45 to 50 years ago,
started plotting high yielding bedrock
wells and he found out there was a
linear or curvi-linear feature to them
which he was able to associate being
zones of highly fractured bedrock. Now
directly over these zones of highly
fractured bedrock, the flora is going to
be different. If the bedrock table is
close to the surface, you're going to
find that large trees with deep bedroot
are able to be able to intercept the
groundwater table more easily, but this
may be a zone where groundwater is
and surface water is draining into
the fracture matrix and the material
growing here is going to be stunted more
than what is on either side. Well using
aerial photography you can do fracture
trace or lineament mapping and try to identify these feature and
when in fact they are identified, you
look for an area where multiple
fractures converge at a single location.
This is advantageous because your odds
of intercepting fractures that are going
to yield water is increased, but also you
are going to be able to induce recharge
from multiple points of the compass.
And plotting this up, it is obvious that
drilling at this location right here is
going to give a markedly higher
likelihood for a favorable high yielding
bedrock well than if you drill at any of
these points not in any way associated
with the identified linear features. Now
when you are going through this
identification process, you obviously
have to take a look at any anthropogenic
activity that may account for it -
fences, roads, paths, pipelines - anything
like that would have to be dismissed and
what is left has a high degree of
probability of being a zone of fractured
bedrock. If you are doing a town-wide
study, you'd take a look and see where each
of these identified areas might be and
then you'd take a look and say if a high
yielding well is there, where is the
source of recharge going to be? Is it
going to have an adverse impact upon
existing wells or any of the other
activities that in fact are using
groundwater or surface water?
There may be times when you are drilling
a rock well that you encounter fractures
which are unstable. It is rare, but there
are times when a well screen has to be
put in that section of unstability in
order to make sure that a pump is not
locked in by debris falling on top of it
or in fact enough debris falls in that
in fact you reduce the yield. Here's a
typical rock well. In New England, we have
to have a seal of neat cement usually so
that a driller will start off over-sizing
a hole and then will put casing at
least 15 feet into competent bedrock.
When the casing is sealed in place, then
a smaller diameter bit is usually
drilled down to see if in fact
fractures are encountered and what the
preliminary water chemistry may be. If in
fact it then turns out that the yield
may be potentially greater, you have the
opportunity to ream the well out to the
diameter of the steel casing. And the way
that you do a preliminary idea of what
the yield is, because you are pumping
with compressed air, is to set a pipe of
a certain diameter inside a small dam
and from the invert to the elevation of
the water will give you a preliminary
gallons per minute. Time for questions.
We've got a few coming in actually. One
question is what are the advantages or
disadvantages to having a bedrock well
versus a sand and gravel well? Well the
advantages are number one, there may be
no sand and gravel or the sand and
gravel has been maxed out and that you
are not going to be able to develop
anymore. The second is that in cases
where the fractured bedrock is
overlain by glacial till, you might be
able to set up something where during
times of drought, you pump from the
bedrock wells knowing that you are not
in any way going to have an adverse
impact upon surface water bodies, be it
upon the lake or stream. Great. Thanks for that.
We've got a couple other questions. One
is could you discuss the extent to which
glacial sediments cover fracture traces?
Specifically, don't glacial deposits mask
underlying fracture traces? Normally that
would be a very logical interpretation;
however, that has not turned out to be
the case. We are somewhat amazed that you
are able to pick up fractures beneath
some areas of till. Now if you're talking
two or three hundred feet, the likelihood
that it is going to mask it; however, you
may in fact be able to be able to
determine a linear feature and then
nothing is shown and then on the other
side of a valley where there is a
thinner overburden, it picks up again and
you can surmise that those two straight
features are in fact connected beneath
the area where it becomes difficult to
identify a specific linear connection.
Okay and that's all the questions we
have for now.
