Remediation: Techniques and Cost - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 401

O 2 through plants to
root zone

Planting
substrate

Chemical

Physical

Influent

Treated
water

Biological

FIGURE 11.27
Simplified ENS for remediation of surface water. (From Eifert, W.H., Simple, Reliable and Cost-Effective Solutions
for Water Management and Treatment: A Technology Overview with Case Studies , Roux Associates, New York, 2010b,
p. 15. With permission.)

Engineered wetlands or Engineered Natural Systems (ENS) for water treatment is
another effective method for the remediation of surface water under certain conditions.
This process involves a combination of natural biological, chemical, and physical processes
to remediate common surface water contaminants. Constructing an effective ENS requires
matching the available degradation methods with the contaminant properties at the site,
with a typical ENS utilizing several different natural methods to destroy contaminants
including photolysis, bioremediation, phytoremediation, chemical degradation, settling,
and many others. Figure 11.27 shows a simplified schematic of an ENS.

11.8.1 Spills

Remediating impacted surface water from spills is most effective when a quick response
confines the release to as small an area as possible. Releases to surface water are most
often related to petroleum products such as fuels, refined oil, and unrefined or crude
oil. Common techniques for responding and addressing a surface water fuel or oil spill
include (NOAA 2010):

• Doing nothing: If there is no possibility the spill will reach shore or sensitive areas
and natural attenuation will likely remediate the spill through these natural pro-
cesses: photolysis, biodegradation, physical dispersion through wave action and
surface currents, and dilution.
• Containing the spill with booms and collecting the material with skimmer pumps.
As noted in Chapter 7, fuels and oil are LNAPL compounds and therefore float.
Using booms and skimmers can remove significant contaminant mass.
• Using dispersants to break up, spread, and enhance natural degradation.
Dispersants lower the surface tension of LNAPL compounds and can help reduce
the environmental impacts.
• Introducing biological agents: Adding biological agents such as carbohydrates
may hasten degradation of the affected area.

Figures 11.28 and 11.29 show the remedial response activities to a small oil spill on a river.
Here, containment and cleanup of the spill is accomplished with booms and adsorbent pads.