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 means. Rates plotted are the means and standard deviation of three replicates
and represent values greater than the controls.
Calculations
The rates in this test are defined as milligrams per square meter per day. The
total tracer concentration is determined by Equation C1:
Pd Vr
Tt
(1)
Then, the rate of release or mass uptake is evaluated using Equation 2,
Tt / Au / day
Ra
(2)
where
Tt = tracer total concentration (mg) in the unit
Pd = tracer dissolved concentration (mg/ml) as determined by chemical
analysis
Vr = volume of water (ml) remaining in the water column after a given
sampling
Ra = rate of release or mass uptake, mg/m2/day
Au = area (m) of the unit
day = number of days of study
The recommended thickness can then be evaluated by comparing the release
rates (Ra) of tracers through the thicknesses tested to the release rates of tracers
from the capping material alone. For a given thickness to be considered effec-
tive, its release rates must equal those from the capping material alone, or there
should be no statistically significant difference.
Figure C2 is an example graph showing oxygen-depletion rates of the Black
Rock Harbor sediment capped with sand plotted against cap thickness (centi-
meters). It is important to note that a series of cap thicknesses ranging from 2 to
26 cm were evaluated. The data points for Figure C2 are means and standard
deviations of three replicates. Results show that a 22-cm cap of sand resulted in
inhibition of oxygen demand equal to that of the sand cap itself, thus indicating a
seal effective in isolating the overlying water column from oxygen demand due
to Black Rock Harbor sediment. In this case, the recommended thickness for
reducing oxygen demand on the overlying water by the contaminated sediment is
22 cm.
C7
Appendix C Capping Effectiveness Tests
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