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Nationwide survey of state transportation agencies answers key questions about cost savings, application results and compost specifications.
Part II
THE MAJORITY of state Departments of Transportation (DOTs) involved with compost utilization have either recently completed or are in the process of developing or revising their specifications for one or more types of compost. These findings are based on a nationwide study conducted for the Florida DOT that involved telephone interviews with landscape architects, engineers, and maintenance and environmental planning officials regarding compost utilization by their agencies. Several DOTs made reference to one or both of two recent publications: the Model Procurement Specifications for Source-Separated Compost published in February, 1996 by the Coalition of Northeastern Governors (CONEG) Source Reduction Task Force and the 1995 Suggested Compost Parameters and Compost Use Guidelines developed by the Composting Council, the Florida Department of Agriculture and Consumer Services, and the Clean Washington Center.
While a range of characteristics pertaining to compost quality and safety are addressed in specifications (Table 1), the most commonly cited product quality and safety issues arising during actual field use concern compost maturity and observable contaminants in the compost.
Some states reported receiving occasional shipments of immature compost and, in others, concern was expressed that unstable compost would cause soil nitrogen depletion. Washington State DOT (WSDOT) has closed loopholes that allowed composters to avoid maturity testing and has now built in a maturity requirement; producers must provide maturity testing kits with compost deliveries so that DOT personnel can perform the test in the field if they suspect that a batch of compost is not mature. WSDOT also now requires that as part of the permitting process, compost manufacturers submit lab test results indicating that compost meets the specifications (other than maturity) established by the WSDOT. In the experience of the Massachusetts Highway Department, commercial compost producers - when compared with local municipal yard trimmings compost producers - make a cleaner, more quality controlled but less stable product which continues to decompose after delivery.
HANDLING CONTAMINANTS
While levels for contaminants such as pathogens, weed seeds, heavy metals, salts and inerts can be and are limited by specifications and, in the first two instances, by the composting process itself, some DOTs report receiving shipments of compost with...