Concentrations of arsenic, averaging 17 ppm, are present in groundwater below a tailings disposal area, down gradient from an arsenopyrite residue stockpile (ARS) containing pore water concentrations of 100 ppm arsenic at New Britannia Mine (NBM), Snow Lake, Manitoba. Hydrogeological modeling illustrates arsenic contaminated groundwater will continue to percolate through the base of the ARS and into the local aquifer so long as there is a source concentration. Geochemical distribution of arsenic in surface and pore water (< 8.7 and 9.0 ppm), solids (< 17800 ppm), and plants (< 13600 ppm) along a flow path from the mine to Snow Lake are above Canadian guidelines. Safe levels of arsenic were measured in Snow Lake. Mineralogical investigations of solids by SEM, EMPA, and u-XRD show arsenic bound to secondary hydrous ferric oxides. Both dissolved and solid phase arsenic are mobile. Arsenic reducing bacteria thrive, thereby enhancing the conversion of arsenic to its more mobile and toxic form. Future monitoring and remediation recommendations for NBM are provided.