[en] Two engineered modifications, trench lining and grouting, have been demonstrated and evaluated. Reinforced chlorosulfonated polyethylene (Hypalon) fabric and a Portland cement-bentonite grout were selected for demonstration within a group of nine 28-m³ experimental trenches containing compacted low-level waste generated at the Oak Ridge National Laboratory. Groundwater monitoring has shown that standing water is present in all nine experimental trenches (both treated and untreated); however, depth of water and water level fluctuation patterns differed according to trench treatment and were minimal in the case of the grouted trenches. Both water pump-in and water pump-out tests conducted on the lined trenches showed that the original goal of watertight liners was not achieved and that water was entering and leaving these trenches with each precipitation event. Water entering into the grouted trenches was inhibited by the cement-bentonite grout backfill, as reflected in the lower values of hydraulic conductivities that were measured in these three trenches compared with those in the three control (untreated) trenches. In examining engineering properties of the grout and liner material, it was found that no significant change in liner tensile strength or liner aging study, indicating that there were no short-term changes in these engineering properties with field weathering. Cover subsidence has not occurred over the grouted or control trenches, while 2 of the lined trenches have settled 7 to 10 cm (2 to 3% of the trench depth) in the first two years. Based on these treatment evaluation tests, the cement-bentonite grouted trenches appear to offer the highest level of water protection compared to the Hypalon lined and the control trenches