Why is the Berkeley Lab building a poop library?

In an effort to better identify origins of pollution in water, the scientists from the Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a massive database of microbial communities that are found in different types of fecal matter. Samples from cows, horses, raccoons, humans, different types of birds, pigs, sea lions and other animals, as well as human sewage have been cataloged. 

This method vastly improves the methodology that has been in use since the 1970s, which went into effect with the passage of the Clean Water Act.