Washington State Legislature Substitute Senate Bill (SSB) 5787 added new part 90.48.531 to the Revised Code of Washington (RCW) directing the Washing Department of Ecology to submit a report to the legislature by December 31, 2003 to identify leaching tests for evaluating the potential impacts to water quality in situations where fill material is imported. The legislature directed Ecology to assess whether the tests provide appropriate methods for analyzing water quality impacts for all types of projects and in all circumstances where fill material is imported and identify any gaps in leaching test methodology. Ecology retained SAIC to prepare this report in response to the requirements of RCW 90.48.531. A literature search was conducted, and sixteen leaching tests were identified based on their capabilities to evaluate impacts to water quality from fill materials. Detailed descriptions of each test are given including those leaching tests identified in the soil clean-up rules at Chapter 173340 Washington Administrative Code (WAC) Model Toxics Control Act (MTCA) adopted under Chapter 70.105D RCW (i.e., the SPLP and the TCLP). To evaluate the extent to which leaching tests accurately predict leaching, a literature search was conducted to identify studies in which leaching test results were compared to actual field leachates. Relatively few studies were found, most focusing on inorganic constituents rather than organic constituents. The results of these studies were mixed in that some leaching tests over-predicted the field leaching, some under-predicted field leaching, and others provided ambiguous results. An assessment was conducted of techniques used to evaluate leaching test results. Techniques used depend on the testing objectives and end use of the data. In general, leaching test results are compared to regulatory or risk-based levels (e.g., to classify a waste or soil) using direct comparison or statistical methods, or they are used to predict the constituent release under an anticipated field scenario (e.g., by using models that take into account site-specific release mechanisms, pH, and liquid-to-solid ratio over a specified timeframe). An assessment was conducted to identify gaps in leaching test methodologies. The assessment evaluated each of the sixteen leaching tests against criteria such as implementability, accuracy, reproducibility, and ability of the test to address scenario-specific factors. The findings were consistent with the growing consensus among researchers: Evaluating the leaching behavior of a wide variety of materials in a broad range of management scenarios cannot be addressed adequately by one single laboratory leaching test. Existing leaching tests may be adequate where there is a reasonable match between laboratory test and field conditions, or where the test provides conservative results. An alternative to the use of single scenario batch tests is to use a framework to define the question to be answered, specify the disposal or use scenario, identify relevant parameters influencing leaching, perform tests from a suite of leaching tests for those parameters, and model leaching behavior to simulate and forecast release under the specified time and use scenario. This step-wise approach is used in Europe and a similar framework has been proposed in the United States. The study recommends that Ecology consider such an approach using a small number of leaching tests and a hierarchy in which the type and number of tests employed is scaled to the amount of leaching information required by the user.