Well Workovers – New Direction for Improvement of Groundwater Quality

This presentation is based on the key findings from the Nebraska Grout Study: properly sealed wells will prevent the preferential pathway in the annulus of a well. We will discuss closing the preferential pathway found in existing wells and how to prevent them from occurring in newly constructed wells.

Isolating the primary producing aquifer is crucial. An effective seal above and below the aquifer needs to be established. Neat cement sealing the annulus above the SWL for well workover while a chip bentonite should be used in new well construction for sealing the annulus above/below the SWL.

The key question to ask - what do we do with the 1,000,000+ wells around the country not properly constructed? The answer is either workover or abandonment - one well at a time. A case study will be presented showing the impact of a workover and the improvement of water quality.

Water Quality Isolation depends on; 1) Well Construction; 2) Borehole Geophysics; and 3) Geochemistry. The use of borehole geophysics or elogs is the critical component of the isolation. The elogs are being used to address the issue of inadequate groundwater protection in water wells, especially as it pertains to annular seals and zone separations. The use of borehole geophysics as used for this presentation and the project provides for the:

• conducting of basin and hydrostratigraphic analysis;
• identifying water producing zones along with water quality in well boreholes;
• evaluating the thickness and distribution of transmissive units and aquitards; and
• planning and evaluating well workovers/rehabilitation and abandonment.

The overall objection of each site is to assess water quality in the alluvial sand and gravel; identify production zones in the elogs; and to locate seals and target seal zones for Public Water Supply (PWS).