When soil and climatic conditions are favorable, alachlor may contaminate drinking water by runoff into surface water or by leaching into ground water. This can occur following normal agricultural use of alachlor or due to contamination such as spills or runoffs. The available data indicates that alachlor residues in ground water attributable to leaching after normal use are rarely higher than 10 ppb and typically fall in the range of 0.2 to 2 ppb (U.S. EPA, 1987a).