ABSTRACT

All too often, data collected as part of environmental monitoring programs are subjected to interpretation by those unqualified to do so, frequently with results that require extensive litigation. A recent example involved a study carried out in Mobile Bay where geochemical data were used by certain individuals to "identify" bottom sediments contaminated by the drilling of an exploratory well. Elevated barium contents of up to several hundred PPM near the mouth of the Bay were attributed to the spillage of drilling mud, although all drill cuttings, mud, and effluent from the rig had been pumped directly onto barges for disposal at sites onshore. Unfortunately, those making the allegations failed to carry out two analyses on the sediments that would have identified the true source of the barium. First, the sediments should have been X-rayed to determine if the barium was, in fact, the result of barite (subsequent diffractograms were all negative for barite). Second, the actual source of the barium could have been determined. Chemical "stripping" techniques now allow the elements in an analysis to be partitioned into: (1) a pore water fraction, (2) an exchangeable ion phase, (3) ions associated with disseminated carbonate minerals, (4) ions associated with iron and manganese oxide phases, (5) ions attached to clays as organo-metallically chelated compounds, and (6) ions held in structural sites in the clay mineral lattices.

Partitioning of the barium in the Mobile Bay sediments disclosed that most was associated with the various clay mineral phases and substitutional impurities in shell material. Thus, the barium observed was not the direct result of the drilling operation but rather reflected its common association with disseminated oxides in the bottom muds, as a chelated form adhering to the clay platelets and as replacement ions in the lattice of carbonate minerals. Samples obtained from near the mouth of the Bay contained a greater amount of shell material and, therefore, the barium contents were expectedly higher.