Summary of the Hydrogeologic Workplan

Purpose

Purpose of the Hydrogeologic Workplan

• To characterize the hydrogeologic setting beneath the Laboratory
• To enhance the Laboratory’s groundwater monitoring program

Drivers

Hydrogeologic Workplan Drivers

A major driver for preparation of  the workplan was the New Mexico Environmental Department’s (NMED’s) letter dated August 17, 1995 which raise the following four concerns.

• Individual zones of saturation beneath the Laboratory have not been adequately delineated, and the “hydraulic interconnection” between these is not understood.
• The recharge area(s) for the regional aquifer and intermediate perched zones have not been identified, and the effect of fracture-fault zones on recharge is unknown.
• The ground-water flow direction(s) of the regional aquifer and intermediate perched zones, as influenced by pumping of production wells are unknown.
• Aquifer characteristics cannot be determined without additional monitoring wells installed within specific intervals of the various aquifers beneath the facility. Location of wells designed for aquifer testing cannot be addressed adequately without delineation of individual zones of saturation beneath the Laboratory.

Objectives

Hydrogeologic Workplan Objectives

The workplan is designed to provide answers to these three questions:

• Is characterization of the hydrogeologic system beneath Los Alamos National Laboratory adequate to determine where uppermost subsurface water, alluvial groundwater, intermediate perched zone groundwater, or regional aquifer groundwater exists and whether concentrations of contaminants in alluvial groundwater, intermediate perched zone groundwater or regional aquifer groundwater exceed regulatory limits or risk levels?
• Is the characterization information sufficient either to establish detection monitoring programs pursuant to 40 CFR 264.91-100 for regulated units or to demonstrate that groundwater monitoring requirements could be waived, or to provide appropriate groundwater monitoring as part of corrective actions pursuant to 40 CFR 264.101 for Solid Waste Management Units that have been determined to have had a release that is a threat to human health or the environment?
• Is the characterization information sufficient to satisfy the conditions of the Hazardous and Solid Waste Amendments (HSWA) portion of the Laboratory’s Resource Conservation and Recovery Act (RCIU) operating permit?

Expected Outcomes

Hydrogeologic Workplan Expected Outcomes

The expected outcomes of the activities described in  the workplan are:

• Refined understanding of the hydrogeologic framework at the Laboratory, including recharge areas, hydraulic interconnections, flow paths, and flow rates, synthesized by modeling simulations
• Information sufficient either to design and implement a detection monitoring program that meets applicable requirements and/or to demonstrate that groundwater monitoring requirements can be waived
• Defined areas of existing or potential groundwater contamination, and the potential pathways of contaminant transport from the surface to the regional aquifer, with predictions of directions and rates of movement and risk based on modeling simulations

If it is determined, as a result of this characterization effort, that enhanced groundwater monitoring is necessary, an inter-disciplinary Laboratory group will develop a proposed amendment to the Groundwater Monitoring Plan that will be reviewed and endorsed by the Technical Review Committee (TRC) prior to submittal to the appropriate regulatory agency(ies).