A methodology is proposed to define indices for quantifying risks under the threat of reducing in groundwater levels, the existence of saltwater intrusion (SWI), and an increasing nitrate contamination load in submarine groundwater discharge (SGD). The proposed methodology considers coastal regions under geological heterogeneity and it is tested on a groundwater system in Nassau County of Long Island, New York (USA). The numerical model is constructed with the SEAWAT code. The parameter uncertainty of this model is evaluated by coupling the Latin hypercube sampling method (as a sampling algorithm) and Monte Carlo simulation to consider the uncertainty in both hydraulic conductivity and recharge rate. The indices are presented in spatial maps that classify areas of risk to potential threats. The results show that two of the water districts have a high risk under conditions of decreasing groundwater level. Salinity occurs in the southern and southwestern parts of the Nassau County aquifer and a considerable area of high risk of SWI is identified. Furthermore, the average SGD rate with the associated fluxes of nitrate is estimated as 81.4 million m³/year (average 0.8 tons of nitrate through SGD per year), which can adversely affect the quality of life in the local coastal ecosystems. The framework developed in this study could help the water district managers to identify high-risk areas for short-term and long-term planning and is applicable to other coastal settings.

提出了一种方法来定义指标，以量化在地下水位降低，盐水入侵（SWI）的存在以及海底地下水排放（SGD）中硝酸盐污染负荷增加的威胁下的风险。所提出的方法考虑了地质异质性下的沿海地区，并在美国纽约长岛拿骚县的地下水系统上进行了测试。数值模型是使用SEAWAT代码构建的。该模型的参数不确定性通过结合拉丁超立方体采样方法（作为采样算法）和蒙特卡洛模拟来评估，以考虑水力传导率和补给率的不确定性。这些索引显示在空间地图中，该地图对潜在威胁的风险区域进行了分类。结果表明，在地下水位降低的条件下，两个水区风险较高。盐度在拿骚县含水层的南部和西南部发生，并且发现了相当高的SWI风险区域。此外，平均SGD率以及相关的硝酸盐通量估计为8140万米³ /年（平均每年通过SGD收集0.8吨硝酸盐），可能会对当地沿海生态系统的生活质量产生不利影响。本研究中开发的框架可以帮助水区管理者识别高风险区域，以进行短期和长期规划，并适用于其他沿海地区。