You wish to consider the addition of methanol to groundwater for anaerobic microbial removal of nitrate by reduction to N₂ (denitrification). If the nitrate as nitrogen (NO_3- as N) concentration is 84 mg/L, what minimum concentration of methanol should be added to achieve complete nitrate reduction to N₂? Assume no ammonium is present and that f_s = 0.3 for the reaction.