Fig. 4. Nitrate–N/halide ratios for Experimental Array Wells 1 through 3 during (a) Injection 1, January 1998, and (b) Injection 2, January 1998. (c) Dissolved oxygen (DO) concentration during Injection 2, January 1998. Injection 1 consisted of bromide and nitrate (NO3–). Injection 2 consisted of chloride, NO3–, glucose, and acetylene.