Flow and natural attenuation within a fractured basalt aquifer

The Idaho Water Resources Research Institute conducted an interdisciplinary scientific investigation of a trichloroethylene contaminant plume in a fractured basalt aquifer located in the northern portion of the-Idaho National Engineering and Environmental Laboratory (INEEL). This research was focused on two wells drilled in the fall of 1996 to 126 m below land surface (bls). Core was collected between 60 and 126 m bls in one well. Packer tests revealed stratification of both aquifer properties and contaminants. Ratios of cis- to trans-1,2-dichloroethylene suggest that biodegradation is taking place. Kriged aquifer temperatures imply that the source area is within a thermal high, perhaps a result of microbial respiration. The mole ratio of Cl −/Na+ is elevated down gradient of the injection well, implying that the plume becomes enriched in chloride. The source of chloride may be degradation of the chlorinated ethenes.; After conducting the biodegradation analysis, the intent was to produce a hydraulic tomogram between the two wells. However, regulatory concerns were raised regarding the disposal of investigation-derived waste and all field activities were shut down. In the interim, the planned slug interference test program was evaluated in Columbia River Basalts on the Moscow, Idaho campus. These tests were modeled using parameter estimation software. Although hydraulic tomograms could not be produced, the exercise did allow experimenting with the volume and location of conditioning data and the models ability to improve predictions. Predictive accuracy proved to be more sensitive to the way the model was parameterized than any other factor.; Matrix diffusion was studied because of its potential importance in limiting the movement of the contaminant plume at the INEEL. Matrix diffusion experiments conducted with core collected during drilling were intriguing enough that the decision was made to conduct a push-pull test designed to evaluate in situ matrix diffusion processes. The results suggest that matrix diffusion processes could easily allow contaminants to migrate into the matrix of the Snake River Plain aquifer where it can act as a contaminant source for decades to come.