Annexure - Hydrogeology: Objectives, Methods, Applications - page 320

If the environmental goals cannot be reached, or if signifi cant damages
can appear in the ecosystems in relationship with the contaminated
groundwater reservoir, stricter threshold values may be used.
Annex II : Threshold values
The thresholds are fixed so as to take into account the contiguous
ecosystem—groundwater interaction, the impediments to (even future)
use of the reservoir, the reference concentrations (natural background
noise), and the hydrologic budget. In addition, the origin of pollutants,
their toxicology, their dispersion profile, their persistence, and their
bioaccumulation potential will be used.
The fi xing of thresholds should be based on controls of the collected data,
based on the quality of the data, the analytic capabilities, and the level of
background noise.
A minimal initial list of substances needing a defi ned threshold value
includes: arsenic, cadmium, lead, mercury, ammonium, chlorides, sulfates,
trichloroethylene and tetrachlorethylene. Conductivity indicates salt water
intrusions.
Member states must communicate the number of at-risk groundwater
reservoirs, as well as the pollutants and pollution indicators contributing
to this classifi cation, with their concentrations, the size of the reservoirs,
their relationship with surface water, as well as the geochemical background
noise, and the threshold values. The relationship between the threshold
values and the background noise, the environmental quality goals and other
protection standards, toxicologic and ecotoxicologic information, data on
persistence, the potential for bioaccumulation, and the dispersion profi les
of the pollutants must also be detailed.
Annex III: Evaluation of the chemical state of groundwater
For any at-risk reservoir and for each identifi ed pollutant, member states
will use the collected information, comparing the annual arithmetic mean
of the concentration with the threshold value. An estimation of the extent
of the zone above the threshold value or the standard is then desired.
Annex IV: Identifi cation of trend reversals with signifi cant long-term
increases
It is based on the adequate frequency and number of points being
monitored in order to:
• differentiate these trends from natural variations;