THE TIERED APPROACH TO CLEANUP LEVELS
The Site Mitigation Update advisory subcommittee on Land Use and Remedy
Selection, assigned to make recommendations on California's hazardous
waste cleanup laws, spent a good deal of time reviewing what is known as
the "tiered approach." I think that the approach will eventually be
adopted in California, as it has been in several other states.
The tiered approach itself makes sense, but it must be designed
carefully, for it is built on the uncertain building blocks of risk
assessment and land-use based cleanup.
Nationally, while most groundwater cleanup standards are based upon
fixed numbers such as the MCLs (maximum contaminant levels), soil
cleanup is usually governed by site-specific risk assessments.
Toxicologists or other experts consider the extent and concentration of
contamination, as well as the likely pathways through which that
pollution might reach human receptors (people), and come up with
concentration levels that represent a threshold of safety. Those levels
are based upon a cancer risk range - such as one in a million additional
deaths - and a numerical combination of all other human health risks,
such as liver disease, reproductive problems, developmental disorders,
The fundamental aspect of the tiered approach is the creation of look-up
tables, similar to groundwater standards, containing cleanup goals for a
long list of contaminants. If the concentration of pollutants at a site
is lower than the figures in the table, or is brought below those
levels, then no additional cleanup is required. To protect public
health, those levels are set at highly protective concentrations. That
is, the levels are established based upon conservative assumptions of
rapid migration and widespread exposure.
Usually the tiered approach incorporates different levels for each
contaminant, plus formulas for combining risk factors should multiple
contaminants be present. They also include separate columns based upon
the assumed land use. That is, the levels for industrial or recreational
use are less strict than those for residential (unrestricted) use.
Many responsible parties or developers are willing to accept
conservative soil cleanup standards to avoid the expense, hassle, and
particularly the time involved in the traditional risk assessment. That
is, in the real estate business, time is money, and many developers
would rather sweep the place clean than spend a lot of time haggling
with regulators and toxicologists.
Under the tiered approach, there is at least one intermediary level, in
which the responsible party, with regulator approval, can plug in less
conservative assumptions. For example, if the look-up table assumes that
a contaminant will rapidly spread through soil, but the responsible
party can demonstrate that the soil at the site retards migration, then
it can calculate a less stringent cleanup level.
Then, if the responsible party still feels that the cleanup level for
one or more contaminants are too stringent, it still has the option of
going to a full-blown risk assessment, to show that the look-up value or
even the modified values require too much cleanup. That is, the polluter
or developer always has the option of doing things the way it has
traditionally been done.
In addition, other factors, such as ecological risk, agricultural uses
of the property, or a clear pathway to groundwater may trigger a
full-blown risk assessment as well.
Historically, community activists have been suspicious of such risk
assessments because they have been used by polluters to justify
contamination or the failure to clean it up. Technically, we have
criticized risk assessments as:
* based upon incomplete data or uncertain science
* ignoring multiple, cumulative, and synergistic effects
* considering the impact of pollution on healthy, adult, white males
* incorporating land use scenarios (for defining potential pathways)
which allow polluters to promise to restrict access rather than clean up
Good toxicologists are trying to address these problems, but in fact the
shortcomings are independent of the tiered approach. That is, these
problems exist whether the risk assessment is generic - that is, used to
develop the look-up tables - or site specific. It's critical, therefore,
that concerned activists supervise risk assessments in their community
and that they be involved in the development of any look-up tables that
may impact their communities.
The tiered approach should lead to a more rapid response to lingering
Brownfields contamination. It can promote more cleanup, but only if it's
based upon conservative assumptions and, more important, only if
representatives of the affected public are at the table when the
numbers, formulas, and procedures are developed.
Lenny Siegel Director, SFSU CAREER/PRO (and Pacific Studies Center) c/o PSC, 222B View St., Mountain View, CA 94041 Voice: 650/961-8918 or 650/969-1545Fax: 650/968-1126 email@example.com
Effective August 2, 1997, "415" area code numbers for the area south of San Francisco, including Mountain View, have changed to "650." However,"415" may be used until February 1, 1998.