Remediation: Techniques and Cost - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 399

FIGURE 11.24
Example of dredging. (From United States Environmental Protection Agency (USEPA), Hudson River PCBs
Superfund site, http://hunsondredgingdata.com/Monitoring/Water?currentweek=08-16-2002 (accessed June
26, 2010), 2010a.)
11.7.4 Bioremediation
Bioremediation of contaminated sediments involves the same processes as those used for
bioremediating soil and groundwater. However, many contaminants often present in sedi-
ments such as PCBs and mercury are not readily remediated using microbes (USEPA 2005c).
11.7.5 Capping
Sometimes, no active remedial method is available to effectively remove all contaminated
sediment without potentially casing more harm, as occurs with the suspension of sedi-
ments in the water column. In these situations, capping may be preferred. Capping con-
taminated and submerged sediments must be conducted slowly so any disturbance is kept
to a minimum (USEPA 2005c).
11.7.6 Natural Attenuation
Natural attenuation may be an affective remedial option in the following situations: (1) the
source(s) have been eliminated, (2) the contaminated sediments are not heavily impacted,
and (3) other methods will not substantially reduce the risk posed by the presence of the
contaminated sediments (USEPA 2005c).
11.8 Surface Water Remediation
The preferred approach to remediating surface water has been through the enactment
of pollution prevention regulations. Since the National Pollutant Elimination System
(NPDES) was enacted in 1972, significant improvements have been made in improving
the surface waters of the United States (USEPA 2008a, 2010b). The NPDES process requires
municipalities and industry to meet specified standards in order to discharge wastewater
or stormwater to the surface waters of the United States (USEPA 2010b).