As stakeholders and project opponents become more sophisticated, and NEPA compliance more complex, the focus of NEPA litigation is narrowing in on the issue of cumulative impact analysis. Courts and stakeholders are intensifying their scrutiny of cumulative impact analysis in many NEPA documents. In many recent decisions, the courts have urged federal agencies to improve the quality of their cumulative impact analyses.

We've gathered some specific tips to help you prepare sound and defensible cumulative analyses:

• Look at the big picture: not just geography, but over time. An example of this is Tetra Tech's recent cumulative impact analysis of a large US Army project in Hawaii. Because of the size of the project we used the entire state as the region of influence. Because of the state's rapid growth, we looked at fifty years of urban development in agricultural and open space areas and whether the proposed actions would accelerate that trend.

• Quantify your data whenever possible. Cumulative impacts are often difficult to quantify, but be creative and look for hard data to support your analysis. For example, in a recent report on a coastal armoring project in California, we used a trends analysis to determine the project's geological and visual impacts. Our staff looked at the percentage of the California coast that had been subject to coastal armoring (10 percent) and compared it to the percentage of the coastline within the region of influence that had been armored (8 percent), as well as the trend of decreasing armoring over the past thirty years. Using this information, we were able to identify no significant adverse effects on geological resources, but we did identify cumulative adverse effects on visual resources from the project.

• Don't rely on data dumps and conclusory statements: do the actual analysis. Trends and ecosystem analysis can make cumulative assessment much more logical. Recent federal court decisions provide some direction for those preparing NEPA cumulative impact studies. The US Forest Service, the defendant in two recent cases, lost one case and won the other. In the first case, the Forest Service had accumulated plenty of data, but the court was concerned with the level of data analysis. However, in the second case, the court was convinced that the Forest Service had done the necessary analysis .

• Look to the future. Don't rely on lists of projects alone-- look at the trends over time in the past, and project those into the future. If there was a three percent growth rate in the population over the last twenty years, don't forget to factor that into your cumulative analysis of land use or traffic impacts.

In sum, the courts want you to include geographically related projects in the cumulative impact analysis, to analyze what effect previous projects have had on the environment and how they would combine with the proposed action, and to evaluate future similar projects, even if they have not been formally proposed.

Keep these tips in mind when you're preparing your cumulative impacts analysis, and your documents will be stronger for it.

Further guidance on preparing cumulative analysis can be found on NEPA Net.