Urbanization and the Geoenvironment - Sustainable Practices in Geoenvironmental Engineering - page 254

TABLE 7.10
Application of Natural Attenuation at Landill Sites

Electron
Donors

Microbial
Process Location Geology Chemicals Studies

Farmington, NH
landill (1995 to
present)

Silty sand (up
to 22 m below
surface)
Bedrock

TCE, DCE,
VC, trace
ethane, DCM,
TEX, ketones

TX, DCM,
ketones

Acetogenesis,
methanogenesis
Cometabolic
oxidation

NA
investigation in
groundwater,
laboratory
studies

Niagara Falls,
NY (1994)

Overburden,
fractured
bedrock

TCE, DCE,
VC, DCA, CA,
CT, CF, DCM,
CM, ethene
ethane

Landill
leachate, other
chemicals

Methanogenesis
Sulfate
reduction

NA
investigation in
groundwater,

Cecil County,
MD
(1995-1996)

Sand and ill
over fractured
saprolitic
bedrock

VC release VC Aerobic

oxidation
Anaerobic
oxidation

NA
investigation in
groundwater

Source: Sharma, H.D. and Reddy, K.R.: Geoenvironmental Engineering . 2004. Copyright Wiley-VCH Verlag GmbH

& Co. KGa. Reproduced with permission.

Water quality in the vicinity must remain acceptable despite contaminant dilution, deg-
radation, and sorption processes. According to the Action Plan for Switzerland Towards a
Sustainable Development (FOEFL, 1997), these controlled leachate landills fall within the
concept of sustainable development since few resources are consumed. Contact with the
waste is not necessary. As with all bioreactor-type landills, a proper monitoring program
is necessary—to ensure that fugitive leachates are captured and treated effectively with
natural attenuation processes. To date, although little hard documentation exists regard-
ing the use of MNA for remediation of fugitive leachates from landill sites, the limited
options available favor its use. Examples of its use are shown in Table 7.10. Christensen et
al. (2000) has suggested that there are ive critical factors:

1. Local hydrogeological conditions

2. Size of the landill and the variable nature of the leachate plume or plumes

3. Complexity of the leachate plumes

4. Long time frame for evaluation of the attenuation capacity of the soil

5. Demonstrating the effectiveness of natural attenuation based on a mass reduction
basis

7.5.2 Remediation of Urban Sites

There are numerous beneits to restoring contaminated urban and brownield sites. They
include reducing sprawl, providing tax revenue, improving land and public health by
improving air quality, removing threats to safety, and reducing greenhouse gas emis-
sions (NRTEE, 1998). The United States and United Kingdom have national efforts in
place for brownield redevelopment. In addition, transportation costs can be reduced
by up to $66,000/ha/year if brownields are redeveloped compared with greenields by
reducing urban sprawl (NRTEE, 2004). Also 4.5 ha of greenland can be preserved for