Maria Filippini

Toward operational methods for the assessment of intrinsic groundwater vulnerability: A review

ABSTRACT Assessing the vulnerability of groundwater to adverse effects of human impacts is one of the most important problems in applied hydrogeology. At the same time, many of the widespread vulnerability assessment methods do not provide physically meaningful and operational indicators of vulnerability. Therefore, this review summarizes (i) different methods used for intrinsic vulnerability assessment and (ii) methods for different groundwater systems. It particularly focuses on (iii) timescale methods of water flow as an appropriate tool and (iv) provides a discussion on the challenges in applying these methods. The use of such physically meaningful indices based on timescales is indispensable for groundwater resources management.

A global review on ambient Limestone-Precipitating Springs (LPS) : Hydrogeological setting, ecology, and conservation

Springs are biodiversity hotspots and unique habitats that are threatened, especially by water overdraft. Here we review knowledge on ambient-temperature (non-geothermal) freshwater springs that achieve sufficient oversaturation for CaCO3 -by physical CO2 degassing and activity of photoautotrophs- to deposit limestone, locally resulting in scenic carbonate structures: Limestone-Precipitating Springs (LPS). The most characteristic organisms in these springs are those that contribute to carbonate precipitation, e.g.: the mosses Palustriella and Eucladium, the crenophilous desmid Oocardium stratum, and cyanobacteria (e.g., Rivularia). These organisms appear to be sensitive to phosphorus pollution. Invertebrate diversity is modest, and highest in pools with an aquatic-terrestrial interface. Internationally, comprehensive legislation for spring protection is still relatively scarce. Where available, it covers all spring types. The situation in Europe is peculiar: the only widespread spring type included in the EU Habitat Directive is LPS, mainly because of landscape aesthetics. To support LPS inventorying and management to meet conservation-legislation requirements we developed a general conceptual model to predict where LPS are more likely to occur. The model is based on the pre-requisites for LPS: an aquifer lithology that enables build-up of high bicarbonate and Ca(2+) to sustain CaCO3 oversaturation after spring emergence, combined with intense groundwater percolation especially along structural discontinuities (e.g., fault zones, joints, schistosity), and a proper hydrogeological structure of the discharging area. We validated this model by means of the LPS information system for the Emilia-Romagna Region (northern Italy). The main threats to LPS are water diversion, nutrient enrichment, and lack of awareness by non-specialized persons and administrators. We discuss an emblematic case study to provide management suggestions. The present review is devoted to LPS but the output of intense ecological research in Central Europe during the past decades has clearly shown that effective conservation legislation should be urgently extended to comprise all types of spring habitats.

Does groundwater protection in Europe require new EU-wide environmental quality standards?

The European Groundwater Directive could be improved by limiting the scopes of the Annexes I and II to the manmade and natural substances, respectively, and by defining a common monitoring protocol. The changes in the European landuse patterns, in particular the urban sprawl phenomena, obscure the distinction between the point and diffuse sources of contamination. In the future more importance will be given to the household contamination. Moreover, the agricultural environment could be used for developing new conceptual models related to the pharmaceuticals.

A decision tree tool supporting the assessment of groundwater vulnerability

The Water Framework Directive and Groundwater Directive aim at preserving and improving the groundwater status. Groundwater bodies are classified as being or not being at risk of failing to meet these objectives. Those at risk are subject to more precise risk assessment where the concept of vulnerability is considered in the pathway part of the source–pathway–receptor scheme. However, no further details on implementation strategies are provided. In order to support groundwater managers and decision-makers in implementation of programs protecting groundwater, a systematic operational approach based on a decision tree is proposed, which leads the user through the stages of vulnerability assessment. First, a problem has to be formulated related to a threatening of the quantitative and/or qualitative status of a groundwater body. Next, the stated problem needs to be related to the intrinsic or specific vulnerability. Methods used for the intrinsic vulnerability assessment belong to two categories: subjective rating and objective methods. Method selection depends primarily on: data availability, knowledge and available resources. A key issue is the lag time associated with transport between a source/event of contamination and the water body. This lag time is primarily controlled by the temporal scale of water flow. It provides information about flow processes and at the same time also about timescales required for the implementation of strategies. Effects of any measures taken cannot be observed immediately but at the earliest after these estimated lag times emphasizing the need to also proactively safeguard groundwater resources and preserve their good status.

Use of the Conduit Flow Process for the simulation of passive mitigation measures against the piezometric damming effect at the new underground High Speed railway station of Florence

The new High Speed railway station of the city of Florence will be located below ground level inside a huge excavation, 25 m b.g.s deep, 450 m long and 50 m wide; the pit, already built, is surrounded by concrete cut-off walls causing a piezometric damming effect against the main aquifer of the Arno River. As permanent mitigation measure against the piezometric mounding, the design of the station considers a series of drain pipes drilled horizontally on up and down gradient sides of the pit and connected by blind wall tubes. A numerical finite differences model has been implemented with the Modflow code, in order to quantify the expected damming effect and to properly design the drain-based mitigation measures (i.e. frequency and length of the drains). One of the major challenges of the numeric approach was the coupling between the groundwater flow in the porous medium and the water flow towards and through the drains and the blind wall tubes connecting the sides of the excavation. Thus, the drains were simulated using a recently published Modflow Process originally developed for karst conduits (Conduit Flow Process – CFP), which allows combining the groundwater flow in the porous medium with laminar or turbulent flow into pipes. In order to guarantee an acceptable head differential between both sides of the excavation, the results showed that the system should permit a discharge flow rate of about 0.026 m3/s, considering a hydraulic gradient equal to 0.5% (i.e. hydraulic gradient from the averaged piezometric distribution before pit excavation). Conductance turned out to be the most influent parameter towards the effectiveness of the drainage system.