Source:Auckland Regional Council
Extract from the Introduction
Contaminants such as heavy metals, hydrocarbons and toxic exhaust emissions are washed off industrial sites, roads, roofs, and other surfaces whenever it rains. Blocked, leaking, and illegally connected wastewater (sewage) pipes, together with inadequate sewer capacity and pump failures add wastewater contaminants to the mix. Polluted stormwater running off the land enters the drainage system and is eventually discharged into the sea or, in some cases, to groundwater. Toxic contaminants discharged into the marine environment may be dispersed widely, either in solution or bound to very fine particles that remain suspended in the water column. Conversely, contaminants bound to coarse sediments and large organic particles tend to settle out relatively quickly, and accumulate in sheltered near-shore zones. Auckland’s sheltered harbours and estuaries are particularly vulnerable to contamination because waves and currents are not strong enough to keep particles in suspension, so they rapidly sink and become incorporated in sand and mudflat sediments.
Auckland Regional Council technical publication TP168
Revised edition August 2004