Proposta di ricerca:
Introduction
The successful management of ash arising from the combustion of low-rank coal for electricity
generation presents significant engineering and environmental challenges all over the World. In fact
the ash contains many soluble minerals as well as potentially hazardous elements and species
(PHES) which can be mobilized in the surrounding environment causing the pollution of surface
and ground waters and the reduction of soil quality and productivity through the modification of its
physico-chemical conditions and nutritional properties. In this way PHES can also enter the food
chain introducing serious risks for public health through the human consumption of fresh water,
agricultural products and cattle breeding. The proportion of particular solutes and/or trace elements
is site specific, depending both on the original chemical and mineralogical composition of the coal
impurities and on the physico-chemical interactions between ashes, water, soils, climate regimes
and bacterial activities.
Regional context
India is a country extremely rich of coal deposits whose exploitation for the production of energy is
expected to massively increase in the following years with the consequence of amplifying the
environmental problems linked to the transitory or final disposal of ashes in wide ponds. Some of
these deposits, in the form of ash fly ponds, are nowadays spread all over the country and are often
matter of concern for the local populations. The ash ponds of Koradi and Khaparkheda Thermal
Power Stations near Nagpur, that we selected as a case study, is one typical example. The ash
disposal of the power plants is practiced on sites which are not secured landfill. Besides, the water
table in the region is shallow and it varies from 6m to 15m. Most of the habitations close to the ash
ponds use the ground water as their principal source from drinking. In Italy, where coal ash is often
reused in concrete production plants, serious problems can arise from their temporary storage while
the disposal of residual ashes are a major concern associated with the incineration plants of urban
wastes.
Scientific and technical challenges
Fly ashes are characterized by extremely high concentrations of almost all the heavy metals existing
in nature, including many radioactive isotopes and organic-metallic compounds (even of volatile
nature) that are produced through both chemical reactions and bacterial mediation. This aspect
implies that the correct identification of the disposal sites and of the right technologies to
immobilize the ashes are of key importance to protect natural resources and grant food, water and
health security of the populations. The principal environmental concerns relating to the disposal of
ash are the potential for groundwater contamination from salt fluxes and the transport of trace
elements. Thus long term disposal requires a thorough understanding of both the solute fluxes from
the ash as well as the controls on the transport of these solutes through groundwater. The particular
composition of these wastes can stimulate the massive use of geochemical modeling techniques and
isotopic approaches to study the chemical modification of the ash deposits over time and to
reconstruct the migration path of hazardous metals into the ground and the groundwater. The
application of these techniques to the fly ash pond environment systems are relatively uncommon
while the use of unstable isotopes and of the radioactive disequilibria in the U and Th decay series
to reconstruct the migration path of metals from these basins to the groundwater is a brand new
application of a consolidated methodology.
Methodologies
The quantification of impact on the groundwater will be attempted through Groundwater flow and
Solute transport modeling. Systematic sampling of groundwater, stream water and soils will be
accompanied by the analytical measurement of radioactive disequilibria of metallic isotopes like Po,
Pb, Ra, Ac, Th, and U considering the activities of specific isotope couples. In fact some of these
couples can highlight the element mobility over the time scale of interest, from thousands of years
(e.g. 226Ra/230Th) to one hundred years (210Pb/226Ra) and to the last 10 years (232Th/228Ra).
The study of stable isotopes of oxygen, carbon and nitrogen can also help to highlight the flux
patterns of water from the ponds to the surrounding environment also allowing to better describe the
hydrogeological behavior of the disposal site.
Experimental work will be performed in the lab using sample columns and studying the different
behavior of hazardous elements and isotope fractionation under different leaching condition by
changing the leaching agent, the number of cycles as well as pH and Eh.
The application of geophysical ERT technology will allow the spatial modelling of possible
contaminant plumes. Using the ERT technology, high resolution images of the subsurface
resistivity distribution can be mapped effectively. The case study provides a unique opportunity to
implement the ERT technology in mapping the plumes from the ash ponds.
Collected data will be used in a GIS environment to map the distribution pattern of pollutants, to
display the processes using multivariate statistics and to model the geologic environments.
Expected Outcomes
- Enforcement of scientific collaboration between NEERI and IGAG in the perspective of creating a
joint laboratory to study environmental pollution processes using and integrated geophysical and
geochemical approach.
- Development of new methodologies for the improvement of water and food security in areas
contiguous to fly ash ponds.
- Mutual transfer of knowledge to understand the leaching process from the ponds and reaction
mechanism.
- Data collected during the study will be the subject for discussion in scientific conferences and are
expected to be published in scientific journals at a national and international level.
Obiettivi:
The proposed project aims to study the mechanisms which lead to the transport of solutes from ash
disposal and to develop a methodology to quantify their potential long term impacts on groundwater
in the vicinity of the disposal sites. Side activities will include the identification of some guidelines
for the positioning and monitoring of future disposal sites.
These activities will also lead to an enforcement of the collaboration between CNR-IGAG and
CSIR-NEERI that just started with a joint workshop in 2010 thanks to the financial support of the
Italian Embassy in New Delhi, CSIR-NEERI, DST (GoI), Ministry of Water Resources (GoI) and
the organization work provided by CSIR-NEERI.
The ash ponds of Koradi and Khaparkheda Thermal Power Stations near Nagpur will be used as a
case study. This choice allows to minimize the survey costs and to proceed with the basic
requirements of this study just using the financial resources already available for the participant
Institutes.
This project will foster the setting up of the first Indo-Italian laboratory working on holistic study of
groundwater pollution.
New methodologies for the improvement of water security in polluted areas are expected to be
developed thanks to the mutual transfer of knowledge about the leaching process from the ponds
and reaction mechanism.
Pianificazione del lavoro
Piano di lavoro primo anno:
• Visit of CNR scientists to India.
• Interactive discussions will be held on the field programme and finalization of sampling strategy.
Joint field visit will be made to the study area i.e. Koradi, which is 15 km from Nagpur for an early
sampling
campaign
• The sampling points, namely the key observation wells, the soil sampling locations and the
sampling points in the ash ponds will be delineated in the field
• Visit of CSIR-NEERI scientists (2nos) to Italy. The visit will be utilized for setting up and starting
of the early laboratory experiments with discussion about the correspondence between field and
laboratory data
Piano di lavoro secondo anno:
• Visit of CNR scientists to India for the systematic sampling of groundwater, soil, ashes and pond
waters
• Visit of CSIR-NEERI scientists (2nos) to Italy for the analysis of stable and unstable isotopes and
discussion of the results
• Conceptualization of the flow and solute transport modeling and preparation of articles
Piano di lavoro terzo anno:
• Interpretation of stable and unstable isotope data to understand the tracking of contaminants from
the pond
• Validation of the flow and solute transport model and identification of some relevant guidelines
for selection and monitoring of ash ponds
•
Environmental
mapping
of
pollutants
and
hydrogeological
modelling
• Exchange of visit between CNR and CSIR-NEES scientists to finalize the final reports and the
submission of manuscripts to peer reviewed journals