Water surface elevations
Placement of P4 particles
Piezometers were used to measure the water
In mid-May, before the series of flooding tides
surface elevation along the transect. Each pie-
beginning May 23, P4 particles were planted at
each site. Ten >5-cm-deep cores were obtained at
zometer was constructed from 1.9-cm-i.d. CPVC
pipe. Slots were cut at one end of the tube to allow
each site using an Oakfield Model B 2-cm-diame-
water to enter. Slots (1 mm wide) were spaced at
ter soil sampling tube. Cores were obtained within
a 0.25-m2 area and were approximately 20 cm
1-cm intervals on either side of the first 10 cm of
apart. Within the 0.25-m2 area, cores were ob-
each 1.52-m-long pipe. A nylon mesh was pulled
over the slotted end and secured with duct tape.
tained from areas with similar conditions (i.e. sim-
On May 20, piezometers were inserted to a depth
ilar water depth, vegetation cover). A P4 particle
of approximately 80 cm at sites 19. A 2-cm-diam-
produced in the laboratory was placed at a depth
eter placement tool was gently inserted into the
of 35 cm within each core, and each core was
ground to form a pilot hole slightly smaller than
placed within a nylon mesh bag. The bag was tied
the o.d. of the CPVC pipe. The piezometer pipe
off, and survey tape and string were attached.
was then inserted into the hole. The turf at site 10
Each site was surrounded by survey lath, and
(river levee) was too thick to allow gentle inser-
strings from the nylon bags were tied around the
tion of the placement tool, so no piezometer was
lath. The cores were left undisturbed until August.
placed at this site. The water level inside each
pipe was read on a periodic basis using a thin
Retrieval of P4 particles
wooden dowel. Water levels were measured on
In August the nylon bags containing the cores
May 24, June 20 and August 19.
were retrieved. On August 2223 five cores were
recovered for visual examination. These cores
Water level measurements at the
were placed in plastic bags in a cooler, returned to
permanently flooded site
our field lab, and, on the same day as collection
Pond water levels were monitored at the per-
from the field, examined. If a P4 particle was
manently flooded site (site 1) using a Campbell
found, its diameter was measured using a mi-
Scientific UDG01 ultrasonic depth gauge. The
crometer, and the appearance of the particle and
depth gauge was attached to the end of a bracket
the surrounding sediment was noted.
arm, which was in turn attached to the center
The rest of the cores were recovered on August
mast of the tripod. The sensor was suspended on
30 and prepared for analysis of P4 residues by gas
the bracket arm approximately 2.5 m above the
chromatography. The cores were removed from
water surface. The primary components of the
the nylon bags and placed in preweighed jars con-
depth gauge sensor are the Polaroid ultrasonic
taining 10 mL of reagent-grade water. These sam-
ples were cooled to 4C and returned to CRREL,
transducer and the Polaroid 6500 sonar ranging
module (CSI 1993). The sensor measures the dis-
where isooctane was added and the samples were
tance from the bottom of the sensor to a surface
shaken overnight. The residual P4 in the isooctane
by bouncing an ultrasonic pulse off of the surface
extracts was determined by gas chromatography.
and listening for the return echo. The distance to
the surface is determined from the elapsed time.
Analysis of data
The speed of sound in air depends on the air tem-
The mass of P4 remaining for each of five repli-
perature, so that is also measured by the datalog-
cate particles at each location was determined fol-
ger at the same time. The signal from the depth
lowing solvent extraction using the standard labo-
gauge sensor is processed by the datalogger, cor-
ratory method for P4 residue in sediment. Residual
rected for the air temperature, and stored. Read-
particle masses were normalized to the Day 0 mass
ings were taken by the datalogger every ten min-
(M/Mo) and plotted vs. location.
utes and averaged every hour. The accuracy of
the depth gauge sensor for the setup we used is
RESAMPLING OF PREVIOUSLY
1 cm. The elevation for the bottom of the depth
CHARACTERIZED CONTAMINATED SITE
gauge sensor was established by surveying from
a known control point. Water surface elevations
Collection of samples
were determined from the difference between the
Site 883 was relocated based on UTM coordi-
water surface and the elevation of the bottom of
nates and the presence of the stubs of some lath
the sensor.
that had been used to mark the site in 1992. The
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