Allochthonous Contributions of THM Precursors to a Eutrophic Reservoir

Temporal patterns in trihalomethane (THM) precursor concentrations (measured as THM formation potential, THMFP) and loads are documented for West Branch Delaware River (WBDR), the primary tributary for Cannonsville Reservoir, NY, and a secondary tributary, for a 12-month period. The analysis was supported by routine and runoff event-based (11 events) sampling at the mouth of WBDR, and 3 synoptic surveys along its length. Ninety-eight percent of the precursors from WBDR formed chloroform, and 94% were in a dissolved form (DTHMFP). Temporal variations on a seasonal scale, as well as during runoff events, are reported. The range in DTHMFP was 151 to 325μg · L−1. Increases in precursor concentration observed (from 140 to 240 μg · L−1) moving from upstream toward the mouth of WBDR may reflect anthropogenic contributions. A time series of daily loads of DTHMFP from WBDR to die reservoir is presented for the April-December interval of 1995. The volume-weighted concentration for this period was 228 μg · L−1. Dissolved organic carbon had only limited value as a surrogate measure of THM precursor concentration.