UMTRA Project Water Sampling and Analysis Plan, Mexican Hat, Utah

Jacobs Engineering Group, Inc.

DOE/AL/62350-118 Prepared for U.S. Department of Energy, UMTRA Project Office, Albuquerque, New Mexico


The Mexican Hat, Utah, Uranium Mill Tailings Remedial Action (UMTRA) Project site is a former uranium mill that is undergoing surface remediation in the form of on-site tailings stabilization. Contaminated surface materials from the Monument Valley, Arizona, UMTRA Project site have been transported to the Mexican Hat site and are being consolidated with the Mexican Hat tailings. The scheduled completion of the tailings disposal cell is August 1995.

Water is found in two geologic units at the site: the Halgaito Shale Formation and the Honaker Trail Formation. The tailings rest on the Halgaito Shale, and water contained in that unit is a result of milling activities (from the hydraulic placement of tailings) and, to a lesser extent, water released from the tailings from compaction during remedial action construction of disposal cell. Water in the Halgaito Shale flows through fractures and discharges at seeps along nearby arroyos. Flow from the seeps will diminish as water drains from the unit. Ground water in the lower unit, the Honaker Trail Formation, is protected from contamination by an upward hydraulic gradient. There are no nearby water supply wells because of widespread poor background ground water quality and quantity, and the San Juan River shows no impacts from the site.

This water sampling and analysis plan (WSAP) recommends sampling six seeps and one upgradient monitor well completed in the Honaker Trail Formation. The purposes of sampling are to evaluate changes to water quality and seep flow rate as a result of cell construction, characterize the site, and evaluate risk to human health and the environment. Samples will be taken in April 1994 (representative of high ground water levels) and September 1994 (representative of low ground water levels). Analyses will be performed on filtered samples for plume indicator parameters.