Urban impact of dissolved metals in the Paso del Norte segment of the Rio Grande

Sumayeh Ahmad Freiwan, University of Texas at El Paso


The Paso del Norte segment of the Rio Grande experiences two seasons per year; the (wet) irrigation season and the (dry) non-irrigation season. The goal of this study was to improve the understanding of occurrence and contribution of dissolved metals in this region during the non-irrigation season. The objectives of this study were to (1) evaluate the impact of anthropogenic sources of metals on the Rio Grande water quality during the non-irrigation season, and (2) estimate the metal loads carried by the flow to the downstream region of El Paso. In order to evaluate the surface water quality of the Paso del Norte region, the sampling points investigated several major water discharges including agricultural drainage, stormwater runoff, and municipal wastewater treatment plants. For two sequential dry seasons of the period from 2011 to 2013, water samples were collected weekly and analyzed by IC and ICP-OES. The detection limits for ICP-OES were less than the EPA drinking water maximum contaminant limits (MCLs), except for Hg, Pb and Se. The mean pH ranged from 7.1 in treated wastewater to 8.4 for the Rio Grande water, and variation between the two sampling dry seasons was insignificant. The stormwater runoff provided the Rio Grande with the lowest mean electrical conductivity (161 µS/cm) and mean alkalinity (44.7 mg/L as CaCO3), and diluted the higher concentrations of major ions within the river system. The agricultural water in Montoya Drain discharged the maximum mean EC (4175 µS/cm) and mean concentrations of Na+ (758 mg/L), Ca2+ (156 mg/L), and Cl − (719 mg/L). The maximum concentrations of Mg2+ (78 mg/L) and SO42− (724 mg/L) were observed in the Rio Grande at the international boundary. The maximum mean concentrations of K+ (17 mg/L) and NO3− (19 mg/L) were observed in treated wastewater effluent. The mean F− concentrations in all samples were all less than 1.35 mg/L. The highest mean concentrations of Cd, Ni, Pb, and W, were 1.1, 11.3, 10.9 and 18.6 µg/L, respectively in the Rio Grande, observed downstream of Sunland Park and upstream of the Montoya Drain. The maximum mean concentration of Li (508µg/L) was observed in the Montoya Drain. The greatest mean concentrations of As, Ba, Mn, Sn and Sr were 47, 62, 229, 209, and 3217 µg/L, respectively observed in the Rio Grande at the international boundary near the ASARCO smelter site. The stormwater runoff was observed with the greatest mean concentrations of Al, Cu, V, and Zn at 48.8, 40.2, 5.9, 48.7 µg/L, respectively. The concentrations of Be, Hg, Sb and Se were mostly less than detection limits. The mass balance approach was applied in order to estimate the mass loads of metals in the Paso del Norte region during the non-irrigation season. The mean daily mass loads in the American Canal downstream of the Robert Bustamante wastewater treatment plant were estimated to be Al (3.54), As (2.4), Ba (10.3), Cd (0.05), Cr (0.2), Cu (2.21), Fe (6.7), Li (35), Mn (4.9), Ni (1.0), Pb (0.43), Sn (20.4), Sr (311), U (7.2), V (1.2), W (1.3), and Zn (10.8), all in kg/day. Through this study, the water quality analysis and the mass balance analysis revealed elevated concentrations of Cd, Ni, Pb, V and W in the stream segment between the Sunland Park and the Montoya Drain, which may be a result of underground discharge or buried waste. With respect to the hypotheses of this research (during the non-irrigation season), the Montoya Drain provides a significant load of salinity to the river, but the wastewater treatment plant effluents and stormwater runoff dilute the salinity. However, stormwater runoff was observed to contain relatively high concentrations of metals. High metals concentrations were also observed at the international boundary near ASARCO, but the flow though this segment during non-irrigation is negligible. It is recommended that point-source control measures be evaluated, such as engineered wetlands, for mitigating metals discharge to the river.

Subject Area

Environmental education|Environmental Health|Environmental engineering

Recommended Citation

Freiwan, Sumayeh Ahmad, "Urban impact of dissolved metals in the Paso del Norte segment of the Rio Grande" (2013). ETD Collection for University of Texas, El Paso. AAI3597958.