Valutazione del rischio ambientale e della vulnerabilità degli acquiferi dovuti a depositi di scorie da combustione utilizzando isotopi stabili e instabili

Responsabili di progetto

Mario Voltaggio, Satish Wate

Accordo

INDIA - CSIR-expired - Council of Scientific and Industrial Research

Bando

CNR/CSIR 2012-2014

Dipartimento

Terra e Ambiente

Area tematica

Scienze del sistema Terra e tecnologie per l'ambiente

Stato del progetto

Nuovo

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 della ricerca

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.

Ultimo aggiornamento: 21/05/2024