 The company had always disposed of the mill tailings (locally called stamp sands) in lakes adjacent to the mills, but about 1900 began investigating methods to recover the copper remaining in the waste tailings.Beginning in 1915, C&H began reprocessing the stamp sands at Lake Linden, using a finer grind and ammonia leaching.Once the process proved profitable, the Tamarack mill also began reprocessing tailings.