Problems with existing sludge disposal practices, combined with new information about its nutritive and soil-conditioning qualities, have led to accepted practices of land application of sludge. Both the Department of Transportation, as an agency with large land holdings and landscaping needs, and municipalities in Washington State may benefit from land application of sludge on roadsides.
The use of sewage sludge on roadsides can potentially improve the growth of erosion control grasses, shrubs and trees while minimizing the costs for subsequent reseeding, replanting, or refertilization. Proper site selection and management techniques can potentially minimize public health and environmental impacts from heavy metals, nitrates, pathogens and organic toxicants. Steep roadside slopes, where erosion control is most needed, present a challenge to existing sludge application techniques, but one that is not insurmountable.
A review of current national and local research, and a cost comparison analysis, have shown that roadside utilization of sludge may be a feasible practice without infringing on the health, safety and welfare of the public. Tasks are outlined for a demonstration study to investigate application techniques, vegetation types, public health and environmental impacts, and public acceptance and education.