SODIUM, CALCIUM, AND RESIN ACID LEVELS IN-GROUND WATER AND SEDIMENTS FROM 2 SITES ADJACENT TO THE TARAWERA RIVER, NEW-ZEALAND

We have previously reported the levels of sodium and a variety of pulp mill sourced organic compounds in water samples from the Tarawera Riv er (Wilkins et al. 1996). This river, which receives effluents from tw o pulp mills, is located in the Bay of Plenty region of the North Isla nd of New Zealand. During the two synoptic surveys, conducted in Decem ber 1991 and January-February 1992, the mean levels of sodium and tota l resin acids detected in downstream water samples were 65 and 74 ppm and, 34 and 121 ppb, respectively (Wilkins et al. 1996). An unusual as pect of this investigation was the detection of an appreciable level o f abietan-18-oic acid. At several points during its passage across the Western Rangitaiki Plains the Tarawera River is constrained behind a stop bank and perched 1-2 m above surrounding farmland, A series of dr ains and canals collect water from the surrounding farmland and discha rge it to the Tarawera River 200 m prior to its entry into the sea, ne ar the township of Matata, At two points the Western Drain traverses f armland in close proximity to the Tarawera River. Water samples from o ne of these sites (Otakiri Road) are typically characterised by an ele vated sodium level (McIntosh, 1995). Leakage of river water, via groun d water seepage has been hypothesised as the source of the additional sodium burden. Other than for the observation that seepage is periodic ally visible on adjacent farmland, much of which is drained by shallow surface drains linked to the Western Drain, little is known about the ground water hydrology and aquifer characteristics, or the sites at w hich seepage occurs and the conditions under which it is significant. A better understanding of the conditions and processes involved would assist in identifying attenuation and other effects experienced by ino rganic and organic species in ground water and aquifers systems adjace nt to the Tarawera River.