On behalf of ENIrewind (then Syndial), Ramboll performed an assessment for the sustainable remediation of contaminated sediments in Pallanza Bay, Lake Maggiore, Italy.
Sediments in Lake Maggiore, a subalpine lake in northern Italy, contain dichlorodiphenyltrichloroethane (DDT) and mercury (Hg) from historical industrial contamination. DDT and Hg were discharged for several years into the Toce river, which flows into Lake Maggiore.
Ramboll undertook an ecological risk assessment (ERA) to support feasible options for environmental management, specifically sustainable remediation, to comply with the Italian Environmental Ministry’s order. There is no specific guidance for ERA of freshwater contaminated sites in Italy, and so a technical board of experts from academia, public environmental agencies, research institutes and industry was established, to develop a shared approach to evaluating site-specific ecological risks.
Risks to aquatic life and to human health from fish consumption were evaluated using multiple lines of evidence, including a comparison of site-specific sediment data to benchmarks derived by Ramboll from a wide literature search to assess causal concentration-response relationships.
Identifying sustainable remediation options
A comparative assessment of sustainable remediation options was made by predicting changes in ecosystem services from baseline conditions, referred to as the Net Environmental Benefit Analysis (NEBA) approach. It provided formal quantification of the change in ecosystem service values (ecological and human use) associated with remedial options and compared to remediation costs and predicted changes in risk.
In addition to the ERA, which focussed on biological effects, an assessment of the physical environment was made. Potential secondary sources of contaminated sediment and uncontaminated sediment for natural deposition were identified by mapping the area historically flooded using numerical hydraulic simulations, evaluating sedimentological modelling results in terms of erosion and deposition trends, and investigating areas of natural storage of fine sediment identified by a geomorphological study.
Based on the results of the comparative analysis and ERA, it was concluded that current conditions do not pose a significant risk to biota, however, disturbance of sediments would mobilise contaminants increasing risks to aquatic life and from fish consumption. Moreover, radio dating of sediment cores and historical fish tissue data offer compelling evidence that conditions in Pallanza Bay are improving naturally through the deposition of cleaner sediments over historical deposits.
Potential remedial options included monitored natural recovery (MNR), MNR combined with riparian enhancement, capping and dredging.
Assessing net environmental benefits
Ramboll assessed the potential effects, in the short- and long term, on ecosystem services following the implementation of each potential intervention, quantifying, in addition to environmental risks and costs, the decline or beneficial change in the value of ecological and anthropogenic services provided by the Bay of Pallanza. The interventions were divided in to four categories: measures to protect water resources, measures to protect the fish fauna and birdlife, measures to increase the natural recreational and social values of the Bay, measures aimed at reducing the risk of flooding.
After identifying the most significant ecosystem services, the impacts and benefits of the interventions were estimated in monetary terms over a 25-year time horizon. From these comparisons the benefit-cost ratios (BCR) were obtained, and the results showed higher benefits than costs for the majority of interventions. In particular, for a specific intervention related to the enhancement of wildlife corridors, a range of BCR between 9.94 and 16.46 was obtained, showing that an action capable of improving the ecological quality of a territory can produce a wide variety of benefits.
Economic benefits up to three times the investment value
In conclusion, the study showed that the net economic benefits were estimated to be between €200 million and €350 million, against an initial investment (remediation costs) of €103 million.
The analysis concluded the most sustainable option to be MNR integrated with compensatory restorative actions to improve riparian habitats, which provide environmental benefits without negative impacts.