fect the natural remediation of the WP, four solar-
installed and operating during the dredging op-
powered instrumentation stations were erected
eration, time limitations and equipment problems
(Fig. 26). Each station contains a rechargeable 12-
prevented dredging in the area adjacent to the
V power supply, a Campbell CR-10 datalogger, an
Hydrolab, so it was not directly affected. However,
SM-716 storage module, a four-sensor thermistor
the data collected can be utilized as baseline data
string, and a four-sensor moisture block string.
for comparative purposes for next year's work.
Temperature and moisture content are two factors
In addition to these sensors and the related sam-
that greatly influence the sublimation process of
pling and analysis, several other studies inter-
white phosphorus and thus must be monitored to
leaved with the dredging project to determine
evaluate remediation efficiency.* In addition to the
impact and the efficacy of this remediation strat-
standard sensor suite, one instrumentation station,
egy. Invertebrate sampling in the area to be
located in the center of the basin, has an ultrasonic
dredged was conducted by Carl Bouwkamp of
water level gauge and an air temperature sensor.
AEHA, and a vegetation survey was conducted
The water level sensor is a Campbell Model
in this area by Charles Racine of CRREL. Marianne
UDG01 Ultrasonic Depth Gauge, which incorpo-
Walsh, also of CRREL, obtained and analyzed sur-
rates a Polaroid ultrasonic transducer and model
face sediment samples to indicate the degree of
6500 sonar ranging module. It is mounted on an
contamination of the area to be dredged (Racine
arm located about 2.5 m above the original basin
et al. 1993). Work by Dan Lawson in relation to
bottom. The air temperature sensor is a Campbell
physical systems processes will indicate
Model 701 thermistor sensor mounted in a gilled
redeposition of sediments caused by dredging and
enclosure. Air temperature and spoils level are
natural processes.
monitored as part of the remediation process
A study planned for this season to determine
within the basin.
the effectiveness of the remediation strategy for
Outflow of the supernatant is monitored to en-
the retention basin was not conducted due to the
sure that the Flats are not being recontaminated
small volume of spoils generated during this
by the dredging process. After passing over the
year's abbreviated dredging season. This study
weir and through the filtering fence, the superna-
will be conducted next year in association with
tant is sampled for later analysis for WP contami-
Marianne Walsh's remediation work.
nation. During the 1994 field season, the amount
of spoils pumped into the retention basin was in-
sufficient to accumulate sufficient supernatant to
DREDGING ACTIVITY
pass through the drop inlet structure, and thus no
samples were taken. The standard operation pro-
Prior to commencing active dredging activities,
cedure for this sampling is described in Appen-
a series of pumping tests was conducted to quali-
dix D for further reference for the 1995 field sea-
tatively determine the operating parameters of the
son. The possible availability of a mobile field lab
dredging system. In these tests, we pumped clear
and the use of fiber-optic headspace analysis will
water through the spoils line to the retention ba-
make sample storage and processing much sim-
sin. Due to changes in basin design to address con-
pler and more reliable.
cerns of the RPMs, the vertical head of the system
The last monitoring instrument directly related
is about 3 m greater than the dredge specifications
to the dredging operation is a Hydrolab station
indicated. This greatly affects dredge performance
located at Canoe Point. The Hydrolab is connected
and thus tests were conducted to ensure the sys-
to an instrumentation station similar to those lo-
tem would perform adequately for our needs. The
cated in the basin. The addition of the Hydrolab
pump tests also were used to check the spoils line
enables the measurement of water quality param-
for weak points and to indicate the effect the boom
eters such as dissolved oxygen, pH, conductivity,
box would have on dredge operation. Line pres-
salinity, temperature and depth. This station will
sures and system performance can be indicated
give a good indication of the dredge's effect on
only from pumping water, because when spoils
the surrounding pond. Although this station was
are pumped, the density of the material increases,
thus decreasing flow rate while increasing line
pressure. Fundamental fluid dynamics relation-
ships for dredging illustrate this (Huston 1970):
*M.E. Walsh, Applied Research Division, U.S. Army
Cold Regions Research and Engineering Laboratory,
SG = ρ/1000 (kg/m3)
(11)
Hanover, New Hampshire.
29
Previous Page
