Use of ozonation for water treatment leads to the formation of a wide variety of byproducts due to the reaction of ozone with constituents of water, such as bromide and natural organic matter. Identification and quantification of these byproducts are important for several reasons that include: the byproducts readily serve as a source of nourishment for biological regrowth in the distribution system; the byproducts may pose a health concern for consumers; and, the byproducts can serve as precursors to other byproducts through reactions with water constituents or water treatment chemicals. The Philadelphia Water Department (PWD) has made use of EPA Method 556 since 1999 to identify and quantify aldehyde ozonation byproducts formed at PWD's two ozone pilot plants. The use of Method 556 has led to various discoveries that will prove useful to laboratories that analyze drinking water. Examples of discoveries are the insolubility of analytes in method solvents, sources of contamination, and method calibration challenges. In order for the method to be used to analyze large sample batches, this required modifying the method beyond its original stated capabilities. In addition, the ozone pilot plant water matrix posed unique challenges that required extra work such as preservative modification. This paper discusses how PWD overcame method problems, utilized large sample volumes, and assayed complex water matrices. Information on the long-term performance of the method is also given. Includes 11 references, tables, figures.