The pulping processes discussed in this paper, thermomechanical pulping (TMP) and chemithermomechanical pulping (CTMP), are high yield processes, typically 90% or more based on the amount of fiber produced per unit of wood. Less lignin is dissolved in these processes, and thus pulp yields are higher. The TMP process involves steaming the wood chips before mechanical refining, while the CTMP process includes a chemical impregnation step before steaming and mechanical refining. Losses in wood yield and increased wood solutes, which include lignin, in process water are related to the severity of pulping (temperature and chemical charge) and bleaching conditions. Less water is used in the TMP and CTMP processes per ton of pulp produced than in the kraft process and the effluents are more concentrated. Biologically treated effluents entering surface waters have high levels of dissolved organic carbon (DOC) and chemical oxygen demand (COD) due to organic compounds such as lignin which are recalcitrant to biological treatment processes. These organic compounds may still have considerable reactivity to chemical oxidants such as aqueous chlorine. The objectives for the work reported here include: determining the effect of drinking water treatment conditions on producing specific chlorination byproducts using ferulic acid as a lignin model compound; and identifying and quantifying these target chlorination byproducts resulting from the chlorination of TMP and CTMP mill effluents diluted in natural waters.