The proposal originally arose out of the Council's concern that the current septic tank system at Mahia Beach was performing ineffectively (particularly during the influx of holiday makers in the summer months) and the future development meant that a long-term solution to sewage disposal was necessary in the area. The Council proposed to first pump effluent from existing septic tanks into a common pressurised reticulation system. From this system, the effluent would then be pumped to three containment ponds located on the hills behind of the Mahia Beach settlement for further treatment. Once the effluent was treated, it would then be spray irrigated into areas of production forestry.
The Mahia Isthmus Residents and Ratepayers Association Inc ("Residents") opposed the proposal for a number of reasons: the cost involved to individual home owners (around $15,000); the current arrangements were not inadequate; and the high risk of contamination to the Whangawehi stream and surrounding wetlands and headwaters. Local maori also opposed the proposal on the basis that it would destroy the ancestral connection with the land to which the effluent would be sprayed.
The Court refused to make a ruling on whether the Council had sufficiently consulted, reiterating that consultation was not an end in itself and under section 36 of the RMA no applicant or local authority has a duty to consult any person about the application. The important issue to the Court was that the decision-maker had sufficient material to make an informed decision regarding Part 2 issues. In this case, the Court was satisfied that they had "the full spectrum of opinion, clearly and powerfully expressed". The Court concluded that as the proposal would not generate significant adverse effects, alternative sites had little relevance. Regardless of this, in the process of selecting the proposal the Council had considered and discounted five other possible methods to dispose of the sewerage.
The Court considered expert opinion regarding the possible effects of the discharge on the physical receiving environment. The Court held that there had been sufficient investigation into the suitability of the site for irrigation of effluent at the very low weekly and annual amounts specified in the conditions of consent. However, although the conditions required a deficit irrigation regime (that is the amount of effluent sprayed would always be less than the land could absorb), the Court was not convinced that this would eliminate the possibility of overland flows or seepages or the complete failure of the ponds following an extreme event (such as an earthquake). To deal with these possibilities, the Court required that conditions were broadened to "fine-tune" the irrigation regime to avoid such events. In relation to potential contamination of the stream caused by sediment and pathogens, the Court held that the proposed conditions of consent, which required the exclusion of stock (that currently had full access to the stream) and the planting of riparian vegetation, would lead to a considerable improvement compared to the existing environment. In addition to the benefits to the stream quality, the important positive effects of the proposal was that the public health risks of an inadequate sewerage system would be eliminated.
Reflecting on the current reality of the site, the Court noted that the land had been in private ownership since 1864 and since then, had not been subject to any disputes concerning the acquisition of the land nor any attempts to protect areas of archaeological, historical or cultural significance. The Court considered that the conditions of consent as currently proposed "not only recognise and provide for the relationship for maori with the site but will also improve upon the current reality". In granting the consents and designation, the Court considered that the proposal broadly promoted the sustainable management of natural and physical resources and the factors in favour of the proposal outweighed the factors against. It was suggested that the Council could adopt a payment scheme to alleviate the Residents of the burden of having to pay the costs of the scheme up front.