It has been established that energy dispersive x-ray fluorescence can provide in situ sediment analysis detectabilities that approach those attainable in the laboratory and that can be used to map the concentration of many heavy element pollutants in lakes, rivers, and estuaries. The method involves excitation with a 109Cd radioisotopic source and analysis of the x rays with an Si(Li) detector housed in a solid-cryogen cryostat with α 0.005-in.-thick Be window. This system, with available technology, would be capable of providing analyses for about 13 elements (Cr, Mn, Fe, Ni, Cu, Zn, As, Br, Rb, Sr, Y, Zr, and Pb) at their typical concentration levels and could provide lower limit values in the 5- to 20-ppm range for Au, Eg, Se, Ge, and Ga in analysis times of about 4 min. A system using advanced excitation techniques should be capable of providing low ppm detectabilities in analysis times of 2 to 3 min. The concentration of Cd could be determined at levels of about 20 ppm but would require a special excitation source. Various experimental arrangements were considered and experimental results for simulated in situ analysis were obtained.