Well Decommissioning

High-Risk Wells Decommissioned Nearly 7,000 wells have been drilled on the Hanford Site. Many of these wells were drilled prior to the institution of well construction requirements to limit the possible migration of water down the well casing to the groundwater. In many cases, these wells were drilled through waste sites or immediately adjacent to waste sites for the purpose of monitoring the releases to the groundwater. These wells provide potential pathways for surface water runoff or artificial recharge from the surface to ingress on waste contained within the vadose zone and drive contaminants in the waste toward the groundwater. Decommissioning of these aging wells represents a sound pollution-prevention measure to protect Hanford groundwater. These actions have not been previously considered as high priority actions and, therefore, have not been funded at levels that would significantly reduce the number of wells requiring decommissioning.

Out of the nearly 7,000 wells located at Hanford, less than half of them are in use. It is estimated that it would take in excess of thirty years to decommission all wells not needed for monitoring or other purposes. A large number of these wells are in areas that will be subject to remedial and closure actions over the next few years. In addition, about 380 of these wells currently are considered high priority due to their proximity to waste sites and their potential to provide pathways for water to leach contaminants from the subsurface.

A survey of the waste site burial grounds and other facilities is needed to identify locations where run on and runoff controls are appropriate. These actions may be more important in areas where final remedies may take many years, such as waste sites immediately adjacent to tank farms.

A two-phase approach will be used to address well decommissioning. The first phase will be to continue to decommission the high-risk wells at a fairly consistent rate. The second phase would emphasize the well decommissioning associated with ongoing and upcoming remedial or closure actions to limit preferential pathways, to remove impediments to surface barrier installation, and to put in place the post-closure monitoring network needed to monitor releases to the groundwater. Ninety-nine wells were decommissioned during fiscal year 2001. Well decommissioning is not currently in the Hanford baseline; however, an accelerated action will decommission high-risk wells by 2006 and the remaining wells by 2018.