A Field Test of In-Situ NAPL Removal by Cosolvent Flooding

R. W. Falta, C. M. Lee, J. T. Coates, and S. E. Brame

A pilot scale field test of NAPL removal using miscible cosolvents is being conducted at Operable Unit 1, Hill Air Force Base, Utah. Large amounts of petroleum hydrocarbons and spent solvents were disposed of in chemical disposal pits from 1954 to 1973, and these materials are now present in the subsurface in the form of a nonaqueous phase liquid (NAPL). The field experiment is being performed in a 3m by 5m confined test cell, located in the vicinity of a chemical disposal pit, and it involves the injection and subsequent extraction of several thousand gallons of a mixture of high molecular weigh alcohols. The test cell is confined by interlocking sheet pile walls with grouted joints, driven into an underlying clay. The cell contains four injection wells, three extraction wells, and 60 multilevel sampling probes. A number of complimentary methods are used to evaluate the success of the experiment. Prior to the test, a total of 64 samples from 8 soil cores from the cell are analyzed for several representative compounds. Following the test, a total of 48 samples from 6 soil cores are analyzed for these same compounds. In addition to the direct sampling discussed above, detailed NAPL partitioning tracer tests are performed in the test cell before and after the cosolvent flood. By comparing the breakthrough curves of the different tracers in the multilevel samplers and in the extraction wells, it is possible to estimate the average NAPL phase saturation between sampling locations.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California