Physical and chemical data on sediments deposited in the Missouri and the Mississippi River flood plains during the July through August 1993 flood

In July and August 1993, Missouri and Mississippi River floodwaters overtopped or breached levees and inundated agricultural and urban areas in the flood plains. To assess the regional variability of quality of silt and clay sediments transported and deposited during inundation, sediment samples were collected in September 1993 at 25 sites in the Missouri and the Mississippi River flood plains. The samples were analyzed for physical properties and chemical constituents that included particle-size distribution, water content, volatile solids, nutrients, carbon, selected trace elements, pesticides, and semi volatile organic compounds for post flood sediment samples, and particle-size distribution for preflood soil samples. Pesticides were detected in samples from many of the sites, with alachlor detected in one sample at a concentration of 54 micrograms per kilogram. Many semi volatile organic compounds were detected in samples at several sites, with the concentration of fluoranthene in one sample at 270 milligrams per kilogram. Procedures for selecting sites, techniques developed for sampling, laboratory analytical methods, and quality-assurance sampling methods also are described.