Environmental Impact of Construction and Repair Materials on Surface Water and Groundwater: Screening and Evaluation Methodology

Abstract

The 6-year NCHRP Project 25-9, titled Environmental Impact of Construction and Repair Materials on Surface and Ground Waters, concluded in March 2000. The main purpose of the study was to develop and demonstrate a methodology for identification of the possible impact of highway construction and repair (C&R) materials on the quality of surface water and groundwater in the immediate highway environment. The evaluation methodology consisted of an initial screening of a raw (unamended) C&R material leachate for aquatic toxicity by using bioassay tests and of further detailed testing and evaluation of those materials identified as potentially toxic. In the detailed evaluation, leaching source term tests were conducted to determine leachate composition under varying environmental conditions. Environmental tests were then conducted on the leachate to determine the effects of removal, reduction, and retardation (RRR) processes in the highway environment. The environmental processes included photolysis, volatilization, biodegradation, and soil sorption. The leaching and RRR tests identified interactions between specific environmental processes and leachate contaminants and yielded empirically derived functions for each process. The functions were coupled with selected reference environments in a computer model to simulate fate and transport for surface and subsurface pathways. Model results were reported as concentrations, loads, or fluxes of contaminants as a function of time at the highway boundary. Complete evaluation methodology results are presented for a standard asphalt cement concrete developed to serve as a reference asphalt concrete for interlaboratory comparisons.