RESEARCH· ·1970·

B208. GROUND-WATER CONTAMINATION
facilitated by study of water levels, a largely neglected
technique in southeastern Connecticut.
The sequence in which the wells produced waterborne
styrene indicates how water moves through the bedrock.
Six wells are reported to have produced water
with recognizable styrene odor, in the following order:
Ly 291, Ly 219, Ly 217, Ly 218, Ly 220, and Ly 221.
The early arrival of waterborne styrene in the .fh·st two
wells, Ly 291 and Ly 219, is attributed to their closeness
to the eastern burial site, where bedrock was reportedly
struck at a depth of 6 to 8 feet below the road
surface, and where styrene-contaminated soil and fill
were found to extend down to bedrock. ~1ovement of
waterborne styrene is believed to have been largely
north-northeastward, downdip along north-dipping foliation
joints. Movement dominantly along cross joints
is considered unlikely because they are vertical or near
vertical, and the log for Ly 291 indicates that it penetrated
four water-bearing fractures in an apparent
thickness of only 88 feet of bedrock. Within the foliation
joints, however, movement was undoubtedly more
rapid at their intersections with cross joints; these
larger openings, by their geometry, formed northeastplunging
pipes. Even in the unlikely possibility that
the contaminating slug was confined to these pipes and
did not spread out as it moved downdip about 75 feet
(about 50 feet horizontally), it would have been very
close to the two wells-about 15 feet from Ly 291 and
about 20 feet from Ly 219. Ly 219 responded much
more strongly to local recharge (rainfall) than did
Ly 291, as shown in figure 2. Its greater sensitivity is
presumably due to its larger cone of depression; its
yield is only about a quarter that of Ly 291, and both
supplied about the same amount of water for domestic
needs. ·
The third well, Ly 217, is about halfway between the
two sources of contamination and updip from both, if
movement is thought to have taken place solely along
foliation joints. As ground water presumably moved
westward along foliation joints in the schist toward
the Thames estuary, pumping from Ly 217 would expand
its cone of depression northward along northtrending
cross joints, thereby intercepting the westmoving
slug of contaminated water. It is possible, however,
that another small source of styrene was buried
in the area. Also, it is known that some subsurface
water circulates above the bedrock surface. Omission
of this aspect of the study, owing to incomplete data,
is not believed to affect the validity of the conclusions
developed here.
Well Ly 305 is closer to the eastern source of contamination
than Ly 217 but is farther south. Well Ly
305 never produced waterborne styrene, either because
of its location or because of a difference in the bedrock
joint pattern; it is the only well in the immediate area
known to tap quartzite. That the joints it penetrates
are few and tight is · indicated by its yield of 2112
gallons per minute, the lowest recorded in the area.
Ly 218, the fourth well, is very close to the western
burial site and may have been the only one contarninated
by it. Its delayed response is due in part to the
smaller size of the western contamination source and
to delayed pumping-its users were the last of the six
affected homeowners to take up residence. A puzzling
feature of the western burial site is that contaminated
soil extended to a depth of only 6 feet when it was
excavated in November 1961, although digging continued
to a depth of 10 feet.
The fifth well to be affected, Ly 220, is situated at a
greater distance from the eastern burial site than any
of the previously affected wells. The overall flow -line
distance to this well may be estimated by the algebraic
addition of its three component movements : westward
along foliation joints for a distance of about 110 feet,
northward along vertical joints for about 60 feet, and
diagonally downward for a~out 180 feet. The estimated
total of about 350 feet is only an approximation; it is
greater if flow lines followed a more circuitous route,
and smaller if movement was largely along northplunging
pipes formed by joint intersections, as previously
indicated. Sheeting joints may have shortened
the overall distance to this well, which taps granite
gneiss. Ly 221 was the sixth and last well affected. It
reportedly produced waterborne styrene only twice, in
May 1962. Ly 307 was unused until March 1962 and,
with the exception of Ly 305, was the only well in the
immediate area unaffected by waterborne styrene.
The sequence of decontamination in the wells corroborates
some conclusions based on their contamination.
As previously indicated, the western burial site
was excavated in eady November 1961, and measurable
styrene in water from Ly 218 disappeared after
autumn 1962. The eastern burial site was excavated in
October 1962, and no styrene was detected in water
from Ly 291 after l\1arch 1963 nor from Ly 219 after
September 1963. Ly 217, situated farther down the
hydraulic gradient from the eastern site, yielded water
samples with measurable styrene until autumn 1964.
CONCLUSI·ONS
( 1) Till and bedrock in southeastern Connecticut are
vulnerable to contamination by hydrocarbons. Stratified
drift-the principal aquifer-is believed to be
more vulnerable because it is far more permeable than
till or bedrock, and water is pumped from it at much
higher rates.
(2) Within the bedrock aquifer, waterborne hydrocarbons,
as exemplified by styrene in this investigation,