This study follows the geochemistry of nitrogen in a Cretaceous and unconfined sedimentary aquifer in the city of Urânia (Brazil) over 20 years. Although the sewer network was built in the 1970s, the nitrate contamination problem (>45 mg/L-NO3−) persists to this day. The oldest urbanization areas located in the north of the city initially used cesspits for wastewater and currently present the highest nitrate concentrations (>120 mg/L-NO3−), with the plume reaching the deeper aquifer portions (up to 100 m). The contamination is not as dramatic in the south part of the city, where urbanization including installation of the sewage network with PVC pipes that are more resistant to leak than the old ceramic networks occurred after 1985. Based on the constructive well profiles, three hydrogeochemical zones were established: shallow ( 60 m), with 17 mg/L-NO3−. The current total nitrate mass in the aquifer exceeds 731 kg-NO3−. Numerical flow (Modflow) and transport (MT3D) model scenarios support the hypothesis that the nitrate contamination is caused by substantial infiltration of nitrogen through the cesspits until the 1970s, but after the 1990s, leaks from the sewer network should be responsible for the maintenance of the recently observed high concentrations of nitrate.

中文翻译：

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巴西城市含水层中的硝酸盐污染：一个顽固的问题

这项研究跟踪了 20 多年来乌拉尼亚市（巴西）白垩纪和非承压沉积含水层中氮的地球化学。尽管下水道网络建于 1970 年代，但硝酸盐污染问题 (>45 mg/L-NO3−) 一直持续到今天。位于城市北部的最古老的城市化地区最初使用粪坑处理废水，目前硝酸盐浓度最高（>120 mg/L-NO3−），羽流到达更深的含水层部分（高达 100 m）。城市南部的污染没有那么严重，在 1985 年之后，城市化进程包括安装带有比旧陶瓷管网更耐渗漏的 PVC 管的污水管网。 根据建设井剖面，三个水文地球化学区建立：浅（60 m），含 17 mg/L-NO3−。目前含水层中硝酸盐的总质量超过 731 kg-NO3−。数值流 (Modflow) 和传输 (MT3D) 模型情景支持这样的假设：直到 1970 年代，硝酸盐污染是由通过污水坑的大量氮渗入引起的，但在 1990 年代之后，下水道网络的泄漏应负责维护最近观察到的高浓度硝酸盐。