Fluid-Entry Temperatures, Depths, and Water Chemistry at Pilgrim Hot Springs, Alaska

Abstract

Repeated static and flowing temperature logs from wells drilled in 1979 and 1982 at Pilgrim Hot Springs indicate that at least a portion of the distal end of the shallow thermal aquifer has cooled by up to 17 oC since 1982. Cooling of the hotter central part of the shallow thermal aquifer has amounted to only 1.5 oC. This is likely a direct result of the drilling activity and subsequent mixing within the open wellbores. Two of these wells at Pilgrim Hot Springs have developed ongoing up or down flows in the wellbore that have changed the chemistry of the fluids sampled at the surface. Since 2010, 13 new complete thermal water chemical analyses have been obtained to augment the 19 pre-existing chemical analyses. The expanded chemistry data set confirms a simple mixing trend between a primitive chloride rich thermal water and a dilute groundwater. This mixing may occur in discrete permeable zones as the available analyses appear to define clusters of different salinity fluids and not a complete continuum between the end members.