An interaction of two or more chemicals that results in an effect greater than the sum of their separate effects. Synthetic Organic Chemicals (SOCs): Man-made (anthropogenic) organic chemicals. Some SOCs are volatile; others tend to stay dissolved in water instead of evaporating. System With a Single Service Connection: A system that supplies drinking water to consumers via a single service line. Systemic Pesticide: A chemical absorbed by an organism that interacts with the organism and makes the organism toxic to pests.