Use of tracers to quantify subsurface flow through a mining pit.
Three independent tracer experiments were conducted to quantify the through-flow of water from Herman Pit, an abandoned mercury (Hg) mine pit adjacent to Clear Lake, California, USA. The tracers used were Rhodamine-WT, sulfur hexafluoride, and a mixture of sulfur hexafluoride and neon-22. The tracers were injected into Herman Pit, a generally well-mixed water body of approximately 81,000 m2, and the concentrations were monitored in the mine pit, observation wells, and the lake for 2-3 months following each injection. The results for all three experiments showed that the tracer arrived at certain observation wells within days of injection. Comparing all the well data showed a highly heterogeneous response, with a small number of wells showing this near-instantaneous response and others taking months before the tracer was detectable. Tracer was also found in the lake on four occasions over a one-month period, too few to infer any pattern but sufficient to confirm the connection of the two water bodies. Using a simple mass balance model it was possible to determine the effective loss rate through advection for each of the tracers and with this to estimate the through-flow rate. The through-flow rate for all three experiments was approximately 630 L/s, at least 1-2 orders of magnitude larger than previous estimates, all of which had been based on geochemical inferences or other indirect measures of the pit through-flow.
Schladow
S Geoffrey
SG
Department of Civil and Environmental Engineering, University of California, Davis, California 95616, USA. gschladow@ucdavis.edu
Clark
Jordan F
JF
D002140:California; D017753:Ecosystem; D005618:Fresh Water / Q000737:chemistry*; D008628:Mercury / Q000737:chemistry / Q000378:metabolism*; D008906:Mining; D012235:Rhodamines / Q000737:chemistry; D013459:Sulfur Hexafluoride / Q000737:chemistry; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000378:metabolism*
D012235:Rhodamines; D014874:Water Pollutants, Chemical; D008628:Mercury; D013459:Sulfur Hexafluoride