An evaluation methodology was developed to help transportation agencies make prudent decisions about the reuse of waste materials and by-products in highway construction. The primary objective of this evaluation process was to assess the potential impact on surface water and groundwater of constituents released from these materials. Test materials included coal fly ash, bottom ash, blast furnace slags, scrap tires, foundry sand, and recycled asphalt pavement. Test materials were screened for potential aquatic impact in their raw form. Then they were amended with either asphalt or aggregate for detailed assessment, including leaching (batch and flat plate or column tests) and environmental removal, reduction, and retardation (soil sorption, volatilization, photolysis, and biodegradation) tests. Short-term bioassays were used to measure directly the potential aquatic impact of derived leachates as a supplement to chemical analyses. For most materials, amendment with asphalt or aggregate largely reduced or eliminated any impact on the aquatic organisms. Among environmental factors, soil sorption appeared to be the most effective contaminant-removal mechanism. All waste-amended asphalts and aggregates exhibited no measurable impact on target organisms after soil sorption. However, for materials such as pressure-treated wood and deck sealer (used as is), environmental tests showed little or no effect in reducing their aquatic impact.