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Page Title: 5.1.1 Runoff Processes
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5.1.1 Runoff Processes
The runoff pathway is of potential concern as soon as the water ponded
during placement is decanted and the dredged material is exposed to precipitation
and continues as long as the dredged material surface is exposed through the life
of the CDF. A schematic of CDF conditions and fate of runoff water in a CDF is
shown in Figure 5-1. Immediately after disposal and initial decanting processes,
resuspension of newly placed dredged material through the process of
precipitation impact on the dredged material surface will generate runoff water
similar to effluent water produced during filling. Suspended solids in the runoff
can range up to 10 g/L during this stage, and most contaminants will be associated
with these suspended solids. Most heavy metals will be low in the dissolved
phase and high nutrient levels associated with anaerobic conditions in the dredged
material will still be present. If CDF weirs are boarded such that they provide
retention of runoff prior to discharge, TSS in runoff will be reduced.
Transpiration
Runoff
Leaching
Ponded
Discharge
Figure 5-1. Illustration of the CDF surface runoff process
Once the dredged material surface is exposed, the material begins to dry and
oxidize. Runoff quality from dried and oxidized dredged material may differ
significantly from the effluent water quality during dredged material disposal. For
instance, some metals become very soluble once dredged material oxidizes, and
simply controlling suspended solids discharges in runoff will not control the
discharge of metals in runoff released from the CDF. Since effects on runoff
quality, such as ponding and runoff rates, are variable because of site management
and climatic conditions, the runoff evaluation presently only considers direct,
uncontrolled discharge in the testing process.
5-2
Chapter 5
Surface Runoff After Disposal Operations

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