This rapid industrial growth in the post-Civil War period was accomplished with almost no concern for the public health consequences of such rapid industrial growth. After 1870 the United States began using coal as its main energy source, thus creating major air pollution problems in all large cities. The nature of the American factory system encouraged centralization of production in or near urban areas creating bad living environments, as workers were crammed into crowded housing near their plants. NYC in 1901 Waterways in or near cities were polluted by industrial waste dumping, while slaughterhouses and packing houses dumped refuse on vacant city blocks, and the tanning industry washed hides in the urban drinking water reservoirs. The new factories created terrible noise pollution for both workers and neighbors, a health hazard not understood until recently.