Metal Concentration in Agricultural Fields Downstream from the Gold King Mine Spill (2015).

Heightened concern regarding the quality of water used for agriculture and human consumption from Animas and San Juan River sources was in the national spotlight when, on August 2015, 3 million gallons (11.3 million litres) of heavy metal contaminated water spilled into the Animas River from the Gold King Mine (GKM). Immediately after the spill, irrigation ditches within the state of New Mexico and Navajo Nation were closed for weeks, excluding Animas River irrigation water from the agricultural fields. Questions remain as to whether the GKM metals were flushed out of the river or not and if surface water contamination may have spread through the watershed. The goal of this project is to determine the concentration of various metals in agricultural fields across the Animas watershed of New Mexico region. Portable X-ray fluorescence (PXRF) was used to evaluate the total concentration of 9 elements (Al, As, Pb, Ca, Cr, Cu Mn, Fe, Zn) of potential concern metals in fields used to grow alfalfa, vegetables and pasture grass. Representative soil samples were collected from each field for verification of PXRF analysed concentration using inductively coupled plasma-optical emission spectroscopy (ICP-OES) after acid digest in the lab. The analysed results were compared to the US Environmental Protection Agency (EPA) residential screening level (RSL) in soil. The spatial variability of the metal concentrations was also analysed by mapping in ArcGIS by interpolation using Inverse Distance Weighted (IDW) method to compare with future changes in concentrations of metals, both spatially and temporally. The concentrations of As, Mn and Zn were observed to be above the EPA-RSL. However, other elements of concern were below the EPA-RSL. The concentration will be further compared and correlated to metal concentration for post-growing season analysis over two more growing seasons.