Water quality was monitored during the LETC TS-1S steamflood experiment conducted in the Northwest Asphalt Ridge tar sand deposit near Vernal, Utah. Ground-water samples were collected by personnel from the Department of Energy's Laramie Energy Technology Center (LETC) and from Western Wyoming College. Samples were analyzed for 41 water quality constituents by Western Wyoming College. TDS and major inorganic ion concentrations peaked early in the experiment and then rapidly declined a couple of weeks later to concentrations approaching those in the injected steam. Saturation of the tar sand deposit by injected steam appeared to bring dissolvable solids into contact with water, to cause dissolution of the solids producing saline water, and to permit the movement of this saline water to the monitoring wells. COD and TOC typically peaked three times during the experiment. The first peak coincided with the inorganic peak; the second peak occurred with the commencement of oil production; and the third peak happened at the end of the experiment. Many of the Utah surface water quality standards and Wyoming ground-water standards were exceeded in samples taken during the tar sand experiment. However, degraded water quality in the tar sand deposit may have little environmental significance since the deposit is not an aquifer and is apparently isolated from underlying aquifers by shale aquitards. (DMC)