No abstract

Innovative technologies with injection of chemical compounds were applied in order to remediate 28 contaminated sites with petroleum hydrocarbon impacted groundwater spread in the Italian territory. The used reagents can be classified into three main technologies: enhanced bioremediation products with oxygen released, In Situ Chemical Oxidation (ISCO) and surfactants. The analysis of these technologies allowed to better understand how to conduct the design, the execution and monitoring phases of the remediation. For the design phase soil and groundwater samples were collected from each site in order to identify the magnitude of the contamination and different calculation methods were tested to quantify the reagents needed for the remediation. For the execution phase the following application methods were performed and analysed: reagents injection into monitoring wells, injection by direct push into the soil, injection into devoted injection wells, application of the reagents into filter socks, application of the reagents into a dig. Pros and cons of each method were so identified. During the monitoring phase the remediation efficacy was evaluated using, not only chemical concentration of contaminants, but also chemicalphysical parameters spatial distribution as a valid support. In the wide range of remediation technologies, the use of chemical reagents has been progressively more appreciated by the designers and by public authorities and is now extensively applied because it is in some cases more effective, cheaper or quicker. These technologies, in fact, proved to be a solid and sustainable alternative to plant technologies, and they were very effective also in fine aquifers. For 62% of the analysed sites, chemical injections led to a reduction of the contamination within 1 year from the application.

This study aims to analyse the opportunities and critical issues related to the use of amendments as remediation techniques. The performance of amendments (Aerobic Bioremediation, In Situ Chemical Oxidation and Surfactants) was compared with the performance of other groundwater remediation technologies (Air Sparging, Pump&Treat, Multi-Phase Extraction, Pump&Reinjection, Monitoring Natural Attenuation) based on a dataset of 180 contaminated sites. The considered factors are: effectiveness of the remediation; cost to remediate; operational time; environmental sustainability. The occurrence and types of amendment-related issues analyzed were studied on the 40 sites where the amendments had been applied. Issues occurred in 20% of the 40 analyzed cases and consisted of: a) partial or total occlusion of the monitoring wells and by-product formation, for example heavy metals (5%); b) uncontrolled increase in contaminant concentrations and potential downstream migration (8%); c) byproduct formation without well obstruction (7%). For each critical event, a detailed analysis was conducted to understand the processes (pH-Eh equilibria, contaminant desorption, hydraulic conductivity reduction), to highlight the design and procedural gaps (surplus of amendment, injection method selection, contaminant removal by purge). However, it has been observed that the issues can be avoided or mitigated with an accurate design, pilot tests performance, with the application of delivery and monitoring protocols, and at least with a prompt response adopting a corrective action plan, if necessary. The use of amendments turns out to be an effective solution: in 64% of the analyzed sites, it led to a significative reduction of the contamination within one year from the application. The cost is about one third if compared to the average of the other technologies. The operational time is about half the average operational time of the other technologies. Based on the results of sustainability analysis, amendments technologies reduce the production of waste, energy and water consumption, and they minimize air emissions. Considering the sustainability in its broadest sense (environmental, economic, and temporal), it is possible to state that the remediation by amendments is the most sustainable and would meet the interest of all the stakeholders.