Nitrate Contamination in Brazilian Urban Aquifers: A Tenacious Problem

Author(s)

Hirata, Ricardo ^[1] ; Cagnon, Fabiana ^[1] ; Bernice, Aline ^[1] ; Maldaner, Carlos Henrique ^{[1, 2]} ; Galvao, Paulo ^[3] ; Marques, Carlos ^[1] ; Terada, Rafael ^[1] ; Varnier, Claudia ^{[1, 4]} ; Ryan, M. Cathryn ^[5] ; Bertolo, Reginaldo ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Geosci, CEPAS USP Groundwater Res Ctr, BR-05508080 Sao Paulo - Brazil

^[2] Univ Guelph, Inst Groundwater Res G360, Guelph, ON N1G 2W1 - Canada

^[3] Fed Univ Minas Gerais Belo, Dept Geol, Pampulha Campus, BR-31270901 Belo Horizonte, MG - Brazil

^[4] Govt State Sao Paulo, Secretariat Infrastruct & Environm, Inst Geol, BR-0401512 Sao Paulo - Brazil

^[5] Univ Calgary, Geosci Dept, Calgary, AB T2N 1N4 - Canada

• Document type: Journal article
• Source: WATER; v. 12, n. 10 OCT 2020.
• Web of Science Citations: 2

Abstract

This study follows the geochemistry of nitrogen in a Cretaceous and unconfined sedimentary aquifer in the city of Urania (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 (<20 m deep), with average nitrate of 63 mg/L-NO3-; intermediate (20-60 m), with 30 mg/L-NO3-; and deep (>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. (AU)

• FAPESP's process: 15/03806-1 - Water availability and quality threats in a Guarani Aquifer System outcrop zone
• Grantee: Edson Cezar Wendland
• Support Opportunities: Program for Research on Bioenergy (BIOEN) - Thematic Grants
• FAPESP's process: 19/20544-1 - Nature based solutions for the recovery of urban aquifers contaminated by nitrate
• Grantee: Carlos Henrique Gil Marques
• Support Opportunities: Scholarships in Brazil - Master