Results of the studies of ²³⁸U, ²³²Th and ²²²Rn distribution in the drainage waters of the Borok granite quarry, the oldest one among those in operation at present in Russia, are described. Water composition was determined to be mainly Cl-SO₄-HCO₃ Na-Mg-Ca and SO₄-HCO₃ Na-Mg-Ca with TDS 572 - 697 mg/dm3, corresponding to the conditions of oxidative geochemical setting. The hydrogeological structure of the quarry is rather complicated, and its development is impossible without permanent exhaustion of incoming waters (2.24-2.35 mln m3 per year); waters are permanently discharged into the Inya river. The concentrations of natural radionuclides are (mg/dm3): ²³⁸U (9.30•10^-3-0.21), ²³²Th (1.00•10^-6-9.62•10^-5). The activity of radon (²²²Rn) varies within the range 1 to 89 Bq/dm3. Expert evaluation of radionuclide distribution in drainage waters provides evidence of the annual outflow of uranium up to 151 kg and thorium up to 61 kg.