In the densely urbanised Milan Metropolitan area (northern Italy), the long history of anthropogenic activities still exerts a significant pressure on groundwater resource. One of the most serious threats to the water quality of urban aquifers is attributed to diffuse contamination, which is caused by a series of unknown small sources (i.e., multiple point sources) distributed over large areas. In the study area and in many industrialised regions of the world, tetrachloroethylene [PCE], trichloroethylene [TCE] and hexavalent chromium [Cr(VI)] represent the common example of long-standing and persistent pollution in groundwater. In the Milan Metropolitan area, high levels of PCE + TCE and Cr(VI) were detected in the shallow aquifer as well as in the deep aquifer.

To assess and map the shallow and deep aquifers susceptibility to PCE + TCE and Cr(VI) contamination at a regional scale, the Weights of Evidence modelling technique has been applied. This method has been used to objectively evaluate the spatial correlation between the high presence of these pollutants in each aquifer and hydrogeological and land use factors that can potentially influence the contamination. Moreover, the results allowed us to quantify on a large scale the effect that preferential flowpaths, due to both thickness variation in the aquitard and the areal density of multi aquifer wells, have in reducing the protection of the underlying deep aquifer. The end-products of the study constitute a key tool to be used by water-resource managers and decision-makers for the improvement of groundwater management and protection strategies.

在人口稠密的米兰大都市区（意大利北部），人为活动的悠久历史仍然对地下水资源造成巨大压力。对城市含水层水质的最严重威胁之一是由于分散污染，这是由分布在大面积上的一系列未知的小水源（即多点水源）引起的。在研究区域和世界上许多工业化地区，四氯乙烯[PCE]，三氯乙烯[TCE]和六价铬[Cr（VI）]代表了地下水长期持续受到污染的常见例子。在米兰大都市地区，浅层含水层和深层含水层中都检测到高水平的PCE + TCE和Cr（VI）。

为了评估和绘制区域范围内浅层和深层含水层对PCE + TCE和Cr（VI）污染的敏感性，已应用证据权重建模技术。该方法已被用于客观评估每个含水层中这些污染物的高含量与可能潜在影响污染的水文地质和土地利用因素之间的空间相关性。而且，这些结果使我们能够大规模地量化：由于阿奎塔尔的厚度变化和多含水层井的面积密度所导致的优先流动路径在降低对深层含水层的保护方面的作用。该研究的最终产品构成了水资源管理者和决策者用来改善地下水管理和保护策略的关键工具。