(18 in.). Only a few areas within the center of the
ing October 1996. Surveying was done using a
dredged area came close to the target depth of 90
Leitz SET4B electronic total station and a triple re-
flective prism mounted on a 1.45-m-tall prism
cm (36 in.). Minimum depth for breaking the con-
rod. For the dredge area survey, we used two
taminant pathway to feeding mallards, the larg-
benchmarks (BMs), Canoe Point BM and Clunie
est of the dabbling ducks, is 40 cm (Low et al.
BM, along the shore near the area dredged that
1970).
had been previously surveyed. For the retention
basin we used two benchmarks (Berm and Crane)
Attenuation study
located on the EOD pad. Universal Transverse
A scaled-down version of the natural attenua-
Mercator (UTM) horizontal coordinates and the
tion project and the ongoing contaminant attenu-
elevation were known for each of the bench-
ation study being conducted in the retention
marks.
basin were carried out in 1996. These studies are
For the dredged area survey, a 20-cm-diam.
extremely important in evaluating the efficacy of
various remediation studies being conducted at
flat plate was attached to the tip of the prism rod.
ERF. Due to restrictions on working in the Flats,
This provided a uniform bearing surface for the
we concentrated on the parameters affecting the
rod tip, keeping it from sinking down into the
pond bottom sediment. The plate was located at
sublimation of white phosphorus in the basin
the flat bottom of the dredged area rather than
sediments.
attempting to locate the tip halfway up the
slumped edge of the dredged channel. A more
Soil moistures
accurate reading of the dredge depth was
In early June, a series of soil moisture measure-
obtained in this manner, and a horizontal offset
ments were made in the sediments of the previ-
factor was added to the area surveyed to compen-
ous years' dredging activities. Soil cores 2 cm in
sate for the displacement of the tip.
diameter were taken down to liner depth at 10
different locations in the basin. Four of these loca-
Dredge area survey
tions corresponded to areas where plugs contain-
Both the perimeter of the area dredged in 1996
ing WP particles had been planted the previous
and spot measurements of dredge depths within
fall when the basin attenuation study was ini-
tialized. The other six locations follow the taper-
the dredged area were surveyed. A map of the
ing sediment delta between the corner of the
dredged area is shown in Figure 14. The total area
dredged in 1996 was approximately 2915 m2, or
fencing around the north spoils splash pad and
Instrument Station 1, both locations of particle
about 0.72 acres. The average dredged depths
plugs (Fig. 15). The other two plug locations are
along the sample transect lines and at additional
at Instrumentation Station 3 and between the
locations within the dredged area are given in
berm and splash pad, adjacent to the spoils inlet
Appendix C. The average depth for the area
pipe.
dredged in 1996 was 63 cm (25 in.). Certain areas,
The data indicate that the sediment in most
such the channel from Canoe Point Pond out to
locations and depths was still nearly saturated
Pond 183 were much shallower, averaging 45 cm
Total Dredged Area = 2915 m2 (0.72 acres)
6,801,250
6,801,200
6,801,150
6,801,100
355,400
355,150
355,200
355,250
355,300
355,350
355,450
Easting
Figure 14. Area dredged in 1996 (x denotes surveyed point).
15
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