ABSTRACTTimber production and wood products industries in the Mid‐Willamette Valley of Oregon annually dispose of about 547,000 tons (500,000 tonnes) of wood and bark wastes. Land storage or disposal of these wastes can result in the generation of significant volumes of leachate.Wood waste leachates are commonly characterized by lignin‐tannin (measured as tannic acid), oxygen demanding materials, color, and odor. In this study, lignin‐tannin concentrations in the ground water ranged as high as 7.5 mg/l; iron and manganese were also shown to increase markedly relative to natural background concentrations, ranging as high as 13 mg/l and 106 mg/l, respectively.In August 1972 the area affected by the contaminated ground water covered about 4 acres (1.6 hectares) and extended nearly 1,000 feet (330 meters) downgradient from the disposal site. By late January 1973 the plume had migrated laterally to affect an area of about 15 acres (6 hectares) while extending over 1,500 feet (460 meters) downgradient. The lateral migration is attributed to a seasonal change in the local flow system. At least eleven existing domestic water‐supply wells have been rendered nonpotable by this po