France – Greece – Austria – Poland - HPC AG

Laboratory test to
improve microbiological
contaminant
degradation
Result of the electric resistance tomography
hydrocarbons and chrome VI was determined.
Due to the historical background
however the result could have been forecast.
Two contamination sources were determined.
In the course of time, the network
of monitoring wells was expanded
and today there exist about 20 groundwater
monitoring wells with construction
depths between 40 m and 120 m in order
to contain VOCs which possess a tendency
to descent through the aquifer due to
their higher density than water. The
groundwater aquifer extends to depths of
300 - 500 m over several occasionally
highly fissured limestone formations.
A crucial factor for the distribution of the
contaminants dissolved in groundwater is
the existence of two deep wells on site
serving for the recovery of groundwater
for cooling processes. Until 2006, about
300,000 m 3 of groundwater were recovered
per year. The pumping cone produced
helped to fix the contaminant plume
more or less on the site. However, contaminant
concentrations in groundwater
could not be significantly decreased.
By reducing by 80 % the pumped water
quantities collected to about 55,000 m 3 per
year, i.e. from averagely 35 m 3 /h to 7 m 3 /h,
the situation slowly began to change and
concentrations in the area of the contaminant
plume increased in the central areas
of the contamination centers, but the
contaminant plume extended only slightly
because of fracture and Karstzones.
The first phase of the investigation program
recommended by HPC Envirotec
included a Toxicological Exposure Risk
Quantification (TERQ), as already implemented
by us since several years as standardized
service for human-toxicological
12 www.hpc.ag HPC, September 2009
HPC Envirotec France
risk evaluation of environmental contamination
(contaminated sites, etc.). It was
important to obtain a realistic evaluation
of the health risks as impact from the
groundwater contamination to the staff
employed on site and for residents located
in the downgradient area of the site.
Considering the multi-substance aspect
(existing „contaminant cocktail“), acceptable
concentrations for tolerable risks for
human health could be determined for
various, existing and potential exposition
scenarios for the site and its downgradient
area. An additional advantage of TERQ was
that the remediation targets could be
Contaminant plume in limestone aquifer
determined according to the specific site
use, allowing maximum legal and financial
safety for operator, user and authorities.
This approach allows optimum management
of remediation costs with simultaneous
exclusion of non-acceptable, toxic
long-term risks.
The transparency delivered for the health
risks posed by the site (in this case restricted
to the site) enabled us to elaborate a
detailed investigation program in cooperation
with competent authorities and site
operator in order to better evaluate processes
occurring in subsoil and to find alternatives
for the traditional pump & treat
remediation (option considered by the
authorities), which was applied as standard
procedure during the 1980/90ies.
This procedure, however, was in many
cases disappointing (mainly for VOC contamination
by chlorinated solvents) both
from an economic point-of-view and as far
as efficiency was concerned.
Our experience of the last years with innovative
ENA methods has proven that
there exist alternatives to pump & treat.
In October 2008 HPC Envirotec started to
implement a feasibility study for the application
of dynamized natural bioattenuation
(DNBA study) or enhanced natural
attenuation (ENA).
The task schedule elaborated by
HPC Envirotec comprised the
following Methodology:
1. Site investigations to obtain exact
knowledge of the geological, tectonic
and hydrogeological situation in the
limestone aquifer. Prior to the start of
investigations, diametrically opposed
groundwater flow directions had been
assumed as well as the existence of
underground rivers with jointing and
karstification.
2. TERQ (= QHRA)
3. In-situ and laboratory testing in the
course of the Natural Bio-Attenuation
feasibility study in order to determine
the potential application of various
methods for dechlorination of the
VOC (TCE, PCE, etc.) plume and to
convert chrome VI to inoffensive, precipitable
chrome III.
4. Implementation of in-situ pilot tests
with the two most efficient treatment
methods of pre-testing.
In detail, implementation of the four
investigation phases was ensured as
follows: The first in-situ investigation
included implementation of traditional
gamma-ray logs in all boreholes. The
results were correlated with the first
existing boring profiles and indicated that
a tectonic disturbance ran diagonally
across the entire site. The horizontal
stowage amounts to about 20 m. Now it
was possible to interpret more precisely
the slightly irritating map of the groundwater
flow situation dominating the site
and its surroundings.
Understanding by combining. Acting by
purpose.
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