Fundamental understanding of dominant controls and interlinked processes that affect the cycling of organic carbon and contaminants is essential to better characterize contaminant movement in the subsurface. However, predictions can be challenging as fate and transport of contaminants is strongly dependent on spatio-temporal variability of soil hydraulic and geochemical properties. The objective of this study is to evaluate the effect of temporal variability at seasonal (2-4 months) and annual (yearly) time scales on major redox and acid-base elements at different locations within the Norman landfill site. Norman Landfill is a closed municipal landfill site with prevalent organic contamination. The vadose zone, phreatic zone, slough, and Canadian river within the landfill site provide locations with different spatial characteristics at which dominant biogeochemical processes need to be resolved. Data at the landfill site was sampled approximately once per month from 1998-2006, and samples were analyzed for specific conductance, δ¹⁸O, δ²H, dissolved organic carbon (DOC) and anions (Cl^-, SO₄²⁻, NO₃⁻). Results indicate that spatial variability of processes at slough and aquifer scales is significantly different from each other, and increased biogeochemical activity occurs at capillary fringe and layered interfaces. In particular, HP1 modeling results indicate that coarse soils with no layering had lowest biogeochemical activity, and fine soils with high water retention increased microbial activity and induced reducing conditions. Findings also suggest that time variability controls the progression of reactions affecting biodegradation of contaminants. Wavelet analysis suggests that iron-sulfide reduction reactions had high seasonal variability at the site, while fermentation processes dominated at the annual time scale.