NSF Philadelphia operates a consecutive public drinking water system which requires bi-monthly sampling. From 2013 to 2018, Bluestone has performed coliform and residual chlorine sampling twice per month in accordance with the Revised Total Coliform Rule. Bluestone also conducts quarterly trihalomethane drinking water sampling. Samples are rotated throughout the site to ensure that all sections of the system are adequately monitored. Bluestone is also contracted to perform repeat and additional routine sampling in accordance with the Revised Total Coliform Rule to try to isolate the source of the positive coliform sample.