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Natural Attenuation
Natural Attenuation of both petroleum and halogenated hydrocarbons has received increasing
acceptance at sites where plumes are not adversely affecting off-site receptors. In general,
natural attenuation may be considered as an acceptable alternative for all or part of a
contaminant plume where several criteria are met:
 The site is properly characterized The source of contamination is removed or under control Evidence of natural attenuation is observed at the site No sensitive receptors on or off the site are predicted to be impacted
Natural attenuation includes a variety of physical, chemical, and biological processes that, under
the appropriate conditions, act without intervention to reduce the mass, toxicity, mobility,
volume, or concentration of contaminants in soil or ground water. Most regulatory authorities
accept the use of natural attenuation, but require that it be monitored. Monitoring is ideally
conducted in such a way to maximize the accuracy of determining that natural attenuation is
appropriate and that the process continues as predicted.
ESN is fully equipped to install systems to monitor prior to and during natural attenuation.
Wells are installed to obtain water and vapor samples upgradient plus across and down the
plume, plus downgradient, in three dimensions.
Prior to determining that natural attenuation is the preferred alternative, analysis of ground water
(and to an extent vapors and soils) for some or all of the following analytes is undertaken.
Samples are taken in water at 2-3 levels within the aquifer (plus in vapor at 1-2 depths). The
exact list of analytes is determined on a project specific basis. These are in addition to the
targeted contaminants.
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O2*, CO2*
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Fe*, Mn*
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Methane, Ethane, Ethene
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Nitrate, Sulfate
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Eh*, pH*, Temperature*
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Alkalinity*, Chloride
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Those constituents that are starred (*) should always be done on-site to provide for maximum
quality control. The others generally are the types of analytes reported from ESN mobile labs on
a routine basis, so that an integrated analytical product is convenient and inexpensive on-site,
whether fuels or VOCs.
Because the analytical results are available in real time, a preliminary determination can be made
as to the applicability of natural attenuation on the site. In addition, it is possible to determine
which sampling locations are best for extended monitoring. These can be converted into small
bore, permanent monitoring wells during the testing phase. Doing so, and using Direct Push
obtain two significant advantages:
No additional mobilization costs or time wasted No cuttings or other IDW are generated |
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