CERRO GRANDE FIRE (CGF) IMPACTS ON THE HYDROGEOCHEMISTRY OF CANON DE VALLE (CDV), LOS ALAMOS, NM

The CGF burned through the headwaters and upper reaches of CdV between May 5-12 2000. Springs, surface waters, and alluvial groundwater in CdV have been monitored for a wide-range of hydrogeochemical parameters since 1997, because of the environmental contamination (Ba and high explosives) present in the upper reaches of the canyon. Three springs and five alluvial wells in CdV have: (1) been instrumented for continuous monitoring of T, water level, and specific conductance; (2) been hand sampled weekly for T, pH and water level; and (3) been sampled at least quarterly for a wide suite of chemical constituents including cations, anions, HE, and stable isotopes. In addition, over ten other locations in the CdV hydrologic system, including surface water stations, have been periodically sampled for subsets of these constituents. Although some of these sampling protocols were interrupted by the CGF, the data available for the system from both before and after the CGF enable a detailed empirical investigation of the effects of the CGF on the hydrogeochemistry of a burned canyon system. Little effect was observed on any of the physical parameters of the system (alluvial well water elevations, spring flow rates, water temperature) following post-CGF monsoonal storms. One moderate-sized surface water flood event was observed. This suggests that the physical hydrology of the CDV subsurface system was not strongly impacted by the CGF, although the small magnitude of the monsoonal rains during 2000 make this conclusion subject to further study in 2001. Alluvial wells show a slight increase in specific conductance post-CGF, suggesting an increase in ionic strength in waters within the alluvial system, whereas pH shows no systematic changes due to effects of the CGF. Chemical data from surface waters, alluvial wells and springs will also be presented.