AN INITIAL LOOK AT AQUIFER SOLID PHASE GEOCHEMISTRY AND MINERALOGY - CONTRIBUTIONS TO THE FATE OF CONSTITUENTS AT A LARGE MANUFACTURING SITE IN NEW JERSEY

The fate and transport of constituents of potential concern (COPCs) in the subsurface are influenced by physical, chemical, and biological processes. Biogeochemical and solid surface processes have not been previously investigated. COPC fate is to some extent hypothesized to be mediated by surface- associated reduced iron or sulfide minerals in addition to direct microbial degradation on solid surfaces. The objectives of this initial geochemical solid phase study was to increase our understanding of the biotic and abiotic reactions by better understanding the mineral types and geochemical solid phase speciation currently existing at the site. Geochemical solid phase study focused on the aquifer samples collected from a shallow unconfined water table aquifer located in the New Jersey coastal plain. The solid aquifer materials were collected and analyzed under nitrogen to maintain the natural redox state of the aquifer materials. Sampling sites were selected to span a range of redox conditions. Materials analyzed emphasized on collecting samples from visually identified oxide (red-orange color) layers. Samples were submitted for solid phase speciation (e.g. exchangeable, oxide, carbonate) analysis using advanced speciation extraction procedures (EP) and crystal mineralogy analysis.

The characterization and mineralogy of the aquifer material were fairly similar among sites. Mineralogy identified mainly quartz and clay as illite. Crystalline iron was detected in all samples as (FeOOH) and was determined to be oxyhydroxide (y-FeOOH) as lepidocrocite. Iron speciation results identified significant variability in the distributions of Fe(II) and Fe(III) fractions among sites and with depth within the cores. Results of the Fe(II) and Fe(III) species distribution indicated that iron reduction is an important biological process operating at the site. The fraction of Fe(III) oxide that is still available for bioreduction is variable, and further iron reduction may be influenced by the sorbed and precipitated Fe(II) forms or limited by appropriate electron donors. In addition, the presence of biogenic minerals (FeS and FeS₂) in all samples suggest that abiotic degradation of COPCs is feasible and that the microbial iron and sulfate reduction processes may be contributing to abiotic degradation of COPCs.