Environmental Engineering Reference
In-Depth Information
the regulatory objectives. To ensure that the ecosurvey is focused on the
relevant points, it must draw on information collected during the desk study,
and be closely linked to the CSM. Furthermore, the ecosurvey must take
account of the results of Tier 1, and not rely solely on the phase 1 survey.
The Environment Agency (
2008b
) provides more information on various
aspects of surveys for assessing ecological impacts on contaminated land, and
methodologies for actually conducting the surveys are generally well-known
and available in the literature (e.g., Hill et al.
2005
). But it is essential to tailor
the ecosurvey to the specific conditions present at the site being investigated so
that the information supplements the other information gained during the
ERA (e.g., chemical analyses at Tier 1, and bioassays if performed at Tier 2).
If the methods used at Tier 2 identify that significant harm or SPOSH is
not occurring, the site can exit the framework, having documented the decision
(probably in agreement with the relevant nature conservation agency). If the
evidence suggests that significant harm or SPOSH is occurring, the site must
progress to Tier 3. As in other tiers, the appropriate person can take voluntary
management action at this stage, without the need to progress to Tier 3 (
Fig. 9.4
).
Tier 3
The objective of Tier 3 is to demonstrate whether the contaminants on site are
responsible for the significant harm or SPOSH identified at Tier 2. Tier 3 aims
to identify cause and effect attribution (
Fig. 9.5
).
By the time a site has progressed to Tier 3, it has been established that
significant harm (or SPOSH) is occurring to a relevant receptor, and it is likely
that the contaminants on site are at toxic concentrations and responsible
for the significant harm (or SPOSH). For Part 2A, a linkage between the con-
taminant and the receptor must be demonstrated, but the current state of
the science does not permit a mechanistic approach, such as that developed
for identifying toxicants responsible for whole effluent toxicity (USEPA 1991,
1993a, b). At present, it is more appropriate to use causal criteria (such as those
developed by Hill
1965
), for assessing the available evidence, identifying key
gaps and informing a decision about whether or not chemical contaminants
can reasonably be held responsible for impacts (Environment Agency
2008d
).
Essentially, a list of criteria (e.g., strength of association, consistency of associ-
ation, specificity, plausibility etc.) is drawn up and weighted according to
perceived relevance. If the assessment demonstrates that the more heavily
weighted criteria are generally satisfied, cause and effect can be attributed to
the contaminant on site with reasonable confidence. Similarly, if very few of
the heavily weighted criteria are satisfied it is likely that the contaminant is
not causing the effects recorded. Where evidence is equivocal, more informa-
tion is required and further investigative work may be necessary (Environment
Agency
2008e
).
