Project Overview
Groundwater - The water that fills the pores or cracks between grains in a layer of sediment or rock.
Aquifer - A geologic layer that allows water to pass through easily, with all its pores saturated with water.
Water Table - The top of the saturated zone.
Vadose Zone - The soil or rock between the ground surface and the water table. It usually contains some water, but also contains air.
The information contained on this website is intended to provide an orientation to the Hanford Site and its groundwater conditions, as observed through work on the Groundwater Performance Assessment Project. If you would like more technical detail than what is presented here, please see the technical reports section of this website.
Groundwater contamination at the Hanford Site is associated with a number of sources within its active and inactive operational areas. Liquid waste, discharged to the ground since the 1940s, percolated through the soil and in many locations reached the water table. Very little liquid waste is currently disposed to the soil, and cleanup of existing groundwater contamination by pump-and-treat systems, for example, is occurring at some sites.
Scientists with the groundwater project study groundwater flow and groundwater contamination in each of the major areas on the Hanford Site. The following factors may affect the distribution, migration, and concentrations of groundwater contaminants:
- Source History - Groundwater contaminants at the Hanford Site originated from hundreds of disposal sites. These sites were used at different periods of time so the plumes were formed and are dissipating in different ways. In addition, plumes originating from many sources are affected by the discharge of uncontaminated or less contaminated water to nearby facilities.
- Stratigraphy - (a) The vadose zone and uppermost aquifer beneath the Hanford Site are made up of layers of different types of sediment. Groundwater tends to flow through sediment with higher permeability rather than less permeable units. (b) In some areas, the shallowest aquifer is connected to deeper aquifers, which could allow contaminants to move into deeper aquifers.
- Declining Water Table - This decline may affect contaminant concentrations, which may vary with depth.
- Well Depth - The depth of the well, the length of the screen, and the depth of the pump intake can affect contaminant concentrations in samples if concentrations vary with depth.
- River Stage - (a) The stage affects distribution and trends of contaminants at sites near the Columbia River by changing direction of flow in the aquifer. (b) High water may remobilize contaminants from the vadose zone or may dilute contaminants when river water flows into the aquifer.
- Groundwater Remediation - (a) Extraction and injection wells affect the direction of groundwater flow locally. This affects contaminant distribution and the ability to monitor other sites (e.g., RCRA units). (b) Treated water is injected back into the aquifer, but may contain residual contaminants or may dilute local groundwater.
An overview of groundwater beneath the Hanford Site and monitoring networks is included on the following pages: