This Environmental Assessment evaluates an interim measure to control chromium plume migration and maintain the 50 parts-per-billion (ppb) and greater chromium contamination level with the Los Alamos National Laboratory (LANL) boundary while long-term corrective action remedies are evaluated and implemented. Concentrations of chromium within the groundwater plume beneath Mortadad Canyon exceed the New Mexico groundwater standard of 50 ppb near the property boundary between LANL and the Pueblo de San Ildefonso and are as high as 1,000 ppb in the plume center.