Effluents from wastewater treatment facilities are reclaimed for environmental and landscaping use, resulting in infiltration to groundwater. Trace organic contaminants in these effluents have raised concerns, including the antibiotic resistance contributor sulfamethoxazole (SMX) detected frequently at concentrations exceeding 0.01 μg/L. A push-pull study to evaluate in situ degradation of SMX was undertaken in a shallow alluvial aquifer at the Tongzhou groundwater experimental site in southeast suburban Beijing. Ambient groundwater (1000 L) extracted from an experimental well at a depth of 10 m was spiked with SMX and NaBr, and then injected back into the same well. SMX and Br were "stored" over 15 days and monitored in the experimental well and 4 multilevel (depth: 10, 15, 17.5, 20, 25, and 30 m) observation wells located within 2-3 m distance. The concentration of SMX decreased faster than that of Br in the experimental and one observation well at 10 m depth; samples from all other depths contained little Br and SMX. The half-life of SMX degradation is estimated to be 3.1 ± 0.2 and 6.5 ± 0.6 days in the experimental well and observation well, respectively, under suboxic/anoxic conditions.