A conceptual diagram of the setup of the subsurface tracer test

A conceptual diagram of the setup of the subsurface tracer test. A solution of bromide (conservative tracer), 17ß-estradiol (natural female sex hormone), 4-nonylphenol (detergent degradation product), and sulfamethoxazole (an antibiotic commonly used for treating bacterial infections in humans and animals) was injected into the subsurface. A series of corresponding water samples were collected from the multilevel sampler downgradient of the injection well.