To improve the quality of highway runoff and meet the new stormwater management requirements, the New Jersey Department of Transportation (NJDOT) has installed numerous prefabricated stormwater treatment systems throughout the state produced by a range of manufacturers. The use of such systems, known as Manufactured Treatment Devices (MTDs), is expected to continue in the foreseeable future. As the responsible party for the maintenance of these MTDs, NJDOT is interested in determining optimum maintenance intervals and expected maintenance costs for the range of MTDs utilized by the Department.

Twelve stormwater manufactured treatment devices (MTDs) along New Jersey highways were selected for monitoring and analysis. The selected MTDs were cleaned out for subsequent monitoring from a clean state. The water, sediment, oil, and floatable debris pumped out from the MTDs were quantified and analyzed. Analysis of the data shows that sediment, oil, and floatable debris accumulation varies greatly from one site to another. Sediment collected by the devices showed heavy metal below allowable limits in all cases, which indicates the sediment does not need to be treated as hazardous waste and does not need special handling. Combining the sediment depth measurements before and after the clean out yielded a recommended maintenance interval of about four years, but with a shorter maintenance interval of one and half years where severe land surface erosion problems were observed. Types of information necessary for properly inspecting and maintaining stormwater manufactured treatment devices (MTDs) were also identified through this field monitoring and evaluation project.