Cases and solutions Environmental Geology 36 (1–2) November 1998 7 Q Springer-Verlag 159 Received: 28 August 1997 7 Accepted: 15 December 1997 P. J. Pilotto 7 J. R. Goff 7 D. C. Weatherburn Department of Chemistry, Victoria University of Wellington, PO Box 600, New Zealand J. R. Goff (Y) The Institute of Geological and Nuclear Sciences Ltd., PO Box 30368, Lower Hutt, New Zealand Fax: 64 4 570 1440 7 e-mail: j.goff@gns.cri.nz A contemporary contamination record of stormdrain and harbour sediments, Wellington, New Zealand P. J. Pilotto 7 J. R. Goff 7 D. C. Weatherburn Abstract Sediments from stormdrain catchments and outlets in Wellington city and sediment traps from Wellington Harbour were sampled for trace metal content. Samples were analysed for total me- tal content using XRF and ICP-MS. High values of Pb and Zn were found in stormdrain catchments and outlets, decreasing to elevated background rock levels in the harbour. Maximum values were re- corded in an inner city stormdrain catchment, with levels of Pb (4605 ppm), Cu (2981 ppm) and Zn (3572 ppm) all higher than the biological probable effects levels (PEL). Concentrations of As, Cr, Cu, Pb, Ni and Zn concentrations in all harbour sedi- ment trap samples were below the PEL. The mean values for each harbour sediment trap sample can be used as an accurate historical baseline in future studies. Stormdrain samples with high trace metal levels were close to industrial and construction sites. The proximity of these outlets to recreational areas should be of concern to local authorities. Key words Stormdrains 7 Sediment traps 7 Trace metals 7 Wellington 7 PEL Introduction The study of heavy metal distributions in near-shore se- diments is a particularly useful way of assessing levels of contamination (e.g. Buckley and Winters 1992; Stoffers and others 1986). In the Wellington region, rapid indus- trial and urban development between about 1910 and 1970 led to increased discharges of contaminants into the harbour, although more recently, concentrations appear to have declined (Butterworth 1988; Dickinson and others 1996). During the past decade there have been three studies of contamination in the Wellington region (Stoffers and others 1986; Deely and others 1992; Dickinson and others 1996). Stoffers and others (1986) analysed core and sedi- ment samples from Wellington Harbour. The ~20-mm grainsize fraction was analysed by digestion with an HCl/ HNO 3 (1/1) acid mixture. In general, levels of contamina- tion increased towards the periphery of the harbour. Dee- ly and others (1992) analysed surface samples from Wai- whetu Stream (Fig. 1) by leaching of mud (~60 mm) and sand (60 mm to 2 mm) fractions in 0.5 mol L –1 HCl acid. Lower reaches of the stream were found to be highly con- taminated with zinc and lead. Dickinson and others (1996) on the other hand analysed sediment cores from Wellington Harbour comparing total (~20-mm fraction determined by XRF) and “bioavailable” [using the meth- od of Deely and others (1992) on the ~60-mm fraction] metal concentrations. Copper, zinc and lead were found to be the most anthropogenically enriched metals. This paper reports on complementary research involving the study of elemental concentrations and bioavailable analysis in contemporary sediments from a 15-month se- diment trap and stormdrain survey (Pilotto 1996). Study area Wellington Harbour (Lat 41 16 S ; Long 174 51 E) is an 85-km 2 semi-enclosed embayment located at the southern end of the North Island, New Zealand (Fig. 1). The maxi- mum water depth of the harbour is 32 m (southeast of Somes Island) with an average depth of 14 m (Heath 1977). Basement rock in the Wellington area is late Trias- sic greywacke which consists of unfossiliferous, low-grade metamorphosed sandstones and argillites. Quaternary al- luvial deposits in the Hutt Valley comprise well-rounded greywacke pebbles in a fine sand-silt matrix. These de- posits are mineralogically identical to the basement rock (Roser 1983).