Theme: 10. Characterization, Fate and Transport

Topic Area: 10a. Advanced Investigation Tools and Techniques

Formatted Title:

Environmental Forensics: Case Studies on the Use of CSIA for Site Characterization and Source Determinations

Background/Objectives:

A Water Safety Plan (WSP) is a comprehensive approach to guaranteeing the safety of drinking water, encompassing sound water supply practices that extend from collecting water in the catchment area to delivering it to consumers. The primary objectives of a WSP are (i) preventing the contamination of source waters, (ii) treating the water to reduce or eliminate contaminants, and (iii) meeting established water quality standards. Isotopic data plays a pivotal role in this process, offering critical insights for hazard identification and risk assessment. It is instrumental in the management and monitoring phases, ensuring a consistently safe and acceptable supply of drinking water. Stable isotope analyses, such as ²H, ¹⁸O, and ³H in H₂O, already play a significant role in robust water resource management plans. Additionally, other analyses, such as compound-specific isotope analysis (CSIA), can make a valuable contribution to characterizing and managing groundwater contaminants.

Approach/Activities:

To investigate the sources and migration routes of commonly found chlorinated groundwater contaminants, such as perchloroethylene (PCE), chloroform (CF), trichloroethylene (TCE), and others, a comprehensive approach was employed. This study, conducted within the framework of the WSPs for two major cities in northern Italy, Milano and Pavia, integrated isotope analysis, groundwater flow and transport modeling, and statistical techniques. The research employed chlorine and carbon CSIA (³⁷Cl & ¹³C-CSIA) and the analysis of isotopes ²H, ³H, ¹⁸O in diverse hydrogeological settings. These methods were instrumental in providing additional insights for the development of a conceptual model for contamination. This model encompassed aspects like identifying the sources of contamination, evaluating the effectiveness of remediation and containment measures, and understanding the overall pathways of these contaminants within the groundwater. Importantly, this knowledge was vital for managing water supply systems in the two cities.

Results/Lessons Learned:

Environmental isotopes, specifically ²H and ¹⁸O in H₂O and 3H in H₂O, played a crucial role in enhancing our comprehension of groundwater flow dynamics, primarily regarding recharge and the interplay among different layers and aquifers. On the other hand, ¹³C-CSIA and ³⁷Cl-CSIA proved valuable tools for assessing pollution, particularly in the case of PCE. These analyses revealed distinct δ¹³C and δ³⁷Cl signatures for PCE in close proximity to various polluted areas, facilitating the attribution of responsibilities (source identification) and distinguishing between plumes and diffuse contaminations (as observed in the City of Milano). In addition, the results of ¹³C-CSIA and ³⁷Cl-CSIA for TCE and dichloroethylene (cis-DCE) provided more precise insights into the role of natural attenuation processes in containing and mitigating contamination.

In summary, the combined results of ¹³C-CSIA and ³⁷Cl-CSIA, along with groundwater flow and contaminant transport modeling and statistical analysis, significantly contributed to the development of a comprehensive conceptual model regarding the sources and pathways of chlorinated solvents in the groundwater of the Milan Metropolitan area and the city of Pavia. This holistic understanding of the origins and the assessment of contaminant fate are essential for water management professionals to successfully manage water resources and implement prevention and mitigation measures to prevent further deterioration. The case studies presented here underscore how integrating isotope applications with hydrogeological investigations serves as a refined and indispensable tool for the management and risk assessment within Water Safety Plans in urban areas.

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Massimo Marchesi