Final Natural Attenuation Directive

[Lenny Siegel <lsiegel@cpeo.org>]

U.S. EPA's Final (April 21, 1999) Directive, "Use of Monitored Natural
Attenuation at Superfund, RCRA Corrective Action, and Underground
Storage Tank Sites," (#9200.4-17P) does not differ substantially from
the agency's Interim Final (December 1, 1997) draft. It is designed to
allow, even to encourage the use of monitored natural attenuation as a
remedy - usually as a partial remedy - where it can be shown to
accomplish the permanent destruction of harmful substances in a
reasonable time frame. But it also discourages reliance upon natural
attenuation where it does not adequately protect human health and the
environment. 

To the extent that regulators and/or the public are paying attention and
following the guidance of the Directive, polluters will not be able to
use the concept of natural attenuation simply to walk away from polluted
sites. The Directive uses flexible language, and it relies heavily upon
site-specific analysis. Consequently, it's essential that people who
live near contaminated property get involved early, often, and
comprehensively in both the remedy selection process as well as
long-term monitoring. That's the best way to ensure that the Directive
is properly implemented

There are many editorial changes and minor clarifications in the final
Directive. Below I describe what I consider the most significant
differences between the December, 1997 and April, 1999 versions.

* EPA has added a new section on "Contaminants of Concern," drawing upon
smaller amounts of material from other sections of the 1997 draft. It
says, "In general, since engineering controls are not used to control
plume migration in an MNA [monitored natural attenuation] remedy,
decision makers need to ensure that MNA is appropriate to address ALL
CONTAMINANTS that represent an actual or potential threat to human
health or the environment." The document specifically mentions MTBE,
"tentatively identified compounds," and the transformation products of
naturally occurring minerals such as arsenic and manganese compounds.

* It adds public involvement to the list of principles to be considered
during remedy selection: "Remedial actions in general should include
opportunity(ies) for public involvement that serve to both educate
interested parties and to solicit feedback concerning the decision
making process." The principles merely recap the requirements of
existing programs; still, highlighting public involvement is important,
not just to win acceptance, but to design a satisfactory, comprehensive
remedial strategy.

* The section on site characterization contains a lengthy new paragraph
on the importance of applying a correct site conceptual model. If
long-term secondary sources (such as non-aqueous phase liquids) or
preferential subterranean pathways are not recognized, the entire remedy
selection process is thrown into doubt.

* EPA adds new emphasis to the need to address to the uncertainty
created by the longer timeframes often introduced by the use of
monitored natural attenuation: "Adequate performance monitoring and
contingency remedies... should be utilized because of this higher level
of uncertainty."

* EPA drops it suggestion, in the 1997 draft, that Comprehensive State
Groundwater Protection Programs be consulted.

* The new version offers guidance for analyzing natural attenuation
rates, "a measured decrease in contaminant concentrations of at least
one order of magnitude is necessary to determine the appropriate rate
law to describe the rate of attenuation ... Due to variability resulting
from sampling and analysis, as well as plume variability over time,
smaller apparent reductions are often insufficient to demonstrate (with
95% level of confidence) that attenuation has in fact occurred at all."
This finding is based upon a 1998 personal communication from EPA
scientist John T. Wilson. Wilson is one of the world's leading experts
on natural attenuation, so the reference is credible. Still, one hopes
the supporting research will be published soon.

* Finally, the final Directive suggests that it may be possible to
adjust the frequency of monitoring: "For example, it may be appropriate
to decrease the monitoring frequency at some point in time, once it has
been determined that natural attenuation is progressing as expected and
very little change is observed from one sampling round to the next. In
contrast, the monitoring frequency may need to be increased if
unexpected conditions (e.g. plume migration) are observed."

It summary, EPA's final document supports natural attenuation as a
remedy if it can be shown to protect public health and the environment
about as well as other approaches, but that its selection and continued
use must be carefully justified. To ensure that the details justify
natural attenuation as a remedy, it's critical that public stakeholders,
as well as regulatory agencies, understand the policy, the science, and
the site-specific conditions that underlie decision-making.

The Directive has been posted on EPA's web site at:
http://www.epa.gov/swerust1/directiv/d9200417.htm


Lenny Siegel
-- 


Lenny Siegel
Director, Center for Public Environmental Oversight
c/o PSC, 222B View St., Mountain View, CA 94041
Voice: 650/961-8918 or 650/969-1545
Fax: 650/968-1126
lsiegel@cpeo.org
(PLEASE NOTE THAT WE ARE PHASING OUT
MY OLD E-MAIL ADDRESS: lsiegel@igc.org)
http://www.cpeo.org