Four specimens of lead service lines removed from the Cincinnati distribution system between approximately 1990 and 2000 were analyzed by optical microscopy, X-ray diffraction, and Energy-dispersive spectrometry on a scanning electron microscope. The analysis revealed a very unique passivating film consisting almost entirely of one or two polymorphs of PbO2, a tetravalent lead mineral. Solubility modeling shows this solid to be orders of magnitude less soluble than the typical divalent lead solids upon which contemporary plumbosolvency treatment guidance is based. The significance of this scale, implications for treatment guidance, and research needs are discussed. Includes 22 references, tables, figures.