Dr. Johan Liebens

To reduce the impact of stormwater pollution on water resources, private land owners, FDOT and local governments have constructed stormwater treatment systems, and have implemented street sweeping protocols. To keep these treatment systems functional, sediments have to be removed and disposed of periodically. Street sweepings have to be disposed of on a daily basis. Because the sweepings and sediments can be very voluminous, the question addressed in this study is if these materials are clean enough to be reused, and if so, what reuse options are desirable and acceptable.

A total of 66 samples from ponds, swales and sweepings, and 8 background samples were collected in Escambia County, FL. The samples were analyzed for particle size, 15 heavy metals, and 2 nutrients. Standard EPA and USDA laboratory methods were employed. Potential and preferred reuses for the materials were catalogued by interviewing Public Works Directors in 15 counties in the Florida Panhandle. Applicable federal and state regulations were identified with a literature and Internet search.
Results show that the particle size distribution of the sediments depends on the differential erosion processes and technical limitations of street sweepers. In ponds and swales particle size is related to local land use but in street sweepings it is not. Heavy metal analysis shows that ponds in commercial areas have higher levels of heavy metals than ponds in residential areas. This difference cannot be explained by the age of the ponds or clay content and, consequently, land use can be assumed to be the major cause for the difference. In street sweepings heavy metal levels are lower in commercial areas than residential areas. This difference is related to the higher frequency of sweeping in commercial areas. Swale sediments from commercial areas are more polluted with heavy metals than swale sediments from agricultural areas. Comparison of various types of agricultural land use shows that swales near cotton fields have higher levels of heavy metals than swales near other crops and pastures. These higher levels for swales near cotton are probably related to more intense use of pesticides, herbicides, defoliants, and fertilizers.

Street sweepings have lower concentrations of heavy metals than sediments from ponds or swales. These lower concentrations are related to the inability of street sweepers to collect the finest particles in street dust, to which heavy metals are known to be adsorbed. The fine particles are therefore washed into retention ponds and contribute to the higher heavy metal concentrations in ponds.

A variety of potential reuses for the sediments and sweepings was identified. The most frequently mentioned reuses were general fill, parks, and road shoulders. Various federal and state regulations that directly or indirectly may apply to the reuses were identified. Although antimony, arsenic, cadmium, lead, and thallium levels in a small number of samples exceed some of the regulatory criteria in these regulations most of the samples analyzed in the present study do not exceed the criteria. Consequently, there seems to be a very good potential for the reuse of sediments from the three stormwater management systems, and for street sweepings in particular. The most appropriate reuse, according to the results of the present study, is in the construction of parks.
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