Some Observations from Using a Colloidal Borescope in Basalt Aquifers Gerry Winter
What You See in the Field
Objectives Locate flow zone(s) Determine dominant ground water flow direction(s) in each well Estimate ground water flow velocity in the flow zones
Location of Wells near Bliss
Basalts
Bliss Results #1 Well - Best record at depth of ft Flow direction 321º or to the northwest Flow velocity estimated at 16 ft/day Interesting oscillations – pumping well
Bliss #1 - Oscillations
Bliss Results #3 Well - Best records at depths of 80, 86.2, 95, & 99 ft Flow directions 256, 290, 230, & 130 degrees (to the west in shallow zones) Flow velocities estimated at 44 to 97 ft/day
Bliss Results #5 Well - Best records at depths of 84, 84.5, 87, & 87.5 ft Flow directions 133, 90, 94, & 133 degrees (to the southeast or east) Flow velocities estimated at 10 ft/day in shallowest zone and 14 to 18 ft/day other zones
Air Base
Air Base Results Flow velocities estimated at 12 ft/day, 28 ft/day, 10 ft/day, 13 ft/day, & 7 ft/day Flow directions variable, appear to be dependent upon production well pumping even with production wells are off
Air Base
Near Surface Source of TCE Monitoring well almost below source; ground water concentrations near detection limits Ground water flow zone about 32 ft below “water table” If vapor phase partitioning is dominant transport mechanism – concentrations may be low because ground water samples reflect deeper ground water
Observations Ground water flow zones found at contacts between basalt flows Production & irrigation wells can have strong effects on flow directions Irrigation ditches/canals can affect flow directions Monitoring wells typically have 20 slot screen and sand pack but set length may not include basalt flow contact
Observations continued Source of contamination above “water table” may not be detected if flow zone is deeper in well Flow velocities often feet/day Pressure pulses can be observed at distance from pumping well Flow directions can be affected long after pumping stops