Intuitively, contamination reduces the value of property. But intuition does not count as evidence. The issues of how one proves that one ought to take a discount from a property's "clean" value for tax, eminent domain, or other valuation purposes, how big that discount ought to be, and how long it ought to last remain vexing. Last month the Commonwealth Court offered some guidance in Tank Car Corporation of America v. Springfield Township, No. 143 C.D. 2021 (Pa. Commw. Ct. Oct. 19, 2023).