• a pump test must be perform-
  ed, and the extracted con-
  taminated water must be disposed of as hazardous waste.
• A relatively large number of boreholes (four or more) are required to make one, three-
  dimensional flow velocity vector measurement.
• The velocity determination is an average value character-
  istic of a broad region.

In contrast, in situ permeable flow sen-sors require only crude esti-
mates of the hydraulic conducti-
vity, only a single hole needs to be drilled to measure the full three-dimensional groundwater

flow velocity vector, and the flow velocity that is measured is charac-
teristic of a region with scale lengths on the order of one meter.

Accomplishments

This system has been successfully demonstrated, and the technology has been licensed for use at other sites. Currently, temperature dif-
ferences of about 0.010°C can be measured. At this level, flow velo-
cities as low as a few meters per year can be resolved. The probe design needs to be improved to assure long-term reliability of electronics and sensors in ground-
water conditions. Currently, the lifetime of the sensors is on the order of one year.