<p>Secondary evaporative mineral precipitates (EMPs) form in underground mines where the nexus between sulfides in country rock, oxygen, and moisture from fracture seepage facilitate their precipitation. Their dissolution rates are rapid, and typically, under conditions with no buffering capacity (e.g. in deionized water) result in acid generation. Twenty EMP samples from the Leeville underground mine (LUG) tested in this way generated acid and high metal concentrations. However, when these materials were dissolved in groundwater at the appropriate ratio for their occurrence in the workings, the acidity generated was neutralized by the groundwater alkalinity. Another source of LUG alkalinity is shotcrete (a cement-based coating on the ribs and back of the 64 km long workings which comprises 68% of the LUG surface area). Addition of the empirical shotcrete ratio with the EMPs in groundwater generally resulted in a further increase in pH and accordingly lower metal concentrations. The reaction between EMPs, shotcrete, and groundwater resulted in precipitation of amorphous ferric hydroxide (AFH), which remained stable in the anoxic environment characteristic of the flooded workings. Geochemical modeling reproduced the dominant mineral phases and pH conditions observed in the laboratory tests, supporting the interpretation of AFH stability under anoxic conditions. In addition, the potential for bacterially mediated sulfide oxidation in the post-closure underground following inundation is unlikely to contribute to acid generation due to the anoxic conditions. These data demonstrate that when the workings are inundated, there will be no adverse environmental consequences to adjacent groundwater when throughflow conditions are reestablished.</p>