Over the past few months there has been robust commentary from diverse sources regarding the discharges of untreated sewage to residents’ properties and to our rivers and the coastal environment.
Late in 2013, on behalf of the wastewater technical advisory group, we undertook a survey of recreational water users to gain an understanding of their experiences relating to water quality in the bay. Our survey unexpectedly coincided with discharges of raw sewage on August 11th and 12th that were implicated in an extensive beach-cast of shellfish, many of which were consumed. Not surprisingly, there was unanimous opposition to the discharge of raw sewage to the rivers or coastal environment from all 250 river and coastal water users who participated in our survey, and a desire to see this stopped as soon as possible. Participants also articulated an understanding of the wider catchment impacts on water quality, including diffuse agricultural discharges, and urban stormwater and port activities, and the need to also address these as part of an overall improvement in water quality. One waka representative stated: “Yea the water quality of the river is a huge concern to us as waka ama paddlers and it’s something that raises its head as a topic both in our clubs and as club members . . . We’re one of the top voluntary organisations around and we’re doing this for our people and we’ve got this barrier of the water quality.” Significantly, all recent commentators have also drawn attention to the impact these sewage discharges are having on our communities.
While direct inflow via illegal connections and damaged or flood-susceptible gully traps may provide the major “flush” of stormwater into the sewerage system while the rain continues, and damaged piping and leaky joints a secondary, subsequent inflow, the city’s sewerage system as a whole contains a series of critical areas where problems can occur. These include: inadequate pipe size for the particular sewerage catchment and/or lack of maintenance; inadequate holding and pumping stations; and possibly illegal connections of sewerage piping to the public stormwater system. While rainfall events can overload the current system and lead to discharges to properties and the rivers, high flows above 450 litres per second will also bypass the wastewater treatment plant and allow untreated sewage to be discharged into the bay.
It has been argued that there is so much sediment and non-human faecal material in the water during such events that the effects of the sewage is minimal. Nevertheless, the addition of raw human waste to this unfortunate broth adds what I believe is a significant threat to environmental and human health. This is particularly so given the constrained hydrology of our urban rivers and inshore coastal system.
In November 2010 we gathered bivalve shellfish from six sites throughout the bay, the Turanganui River, and Te Wherowhero Lagoon, prior to the establishment of the new wastewater treatment plant. Despite there being little rainfall prior to our harvest, all shellfish in the bay and river contained norovirus specifically associated with human gastroenteritis, with extremely high levels at the port, and fair and very high levels at Midway Beach — where adenovirus was also found. No norovirus or adenovirus of the strains sampled for were present in cockles from Te Wherowhero Lagoon. Importantly, recent research has identified the ability of human-derived bacteria and other potentially pathogenic materials such as viruses to persist in the environment for much longer periods than previously believed.
