Quantitative knowledge concerning the contamination effect by industrial Pb migrating through soils into groundwaters has been delineated in a special study carried out in a remote, high altitude mountain valley. Approximately 0.5 ton of industrial Pb has been added in past decades from the atmosphere via precipitation and dry deposition to the 3 km2 area of lightly forested and open meadow soil lying within the 13 km2 area of the rocky valley. Industrial Pb could be distinguished and its amounts quantitatively determined by use of its unique isotopic composition, which was different from natural Pb in meadow soil. Industrial Pb introduced into the canyon within snow was interacting and exchanging with the larger reservoir of industrial Pb accumulated in canyon soil. Lead in the snow-melt runoff had become attached to soil-derived colloids, and a mixture of industrial and natural particulate Pb was released from the soil to stream water and groundwater. The flux of Pb leached from the accumulated reservoir of industrial Pb in soil could be measured as it flowed through soil pathways into stream runoff waters draining the valley. Such leached industrial Pb comprised about 75% of the total Pb in stream runoff of snow-melt and 20% of the total Pb in stream runoff of groundwater.