A much awaited review of the Ruataniwha Water Storage Scheme was presented at a Hawke's Bay Regional Council meeting this afternoon.

The engineering section of the review raised concerns for chair Rex Graham as the figure of $1.45 per cubic metre for the RWSS compared with $5 per cubic metre for on farm storage was found to be misleading.

The total didn't include the water from the dam getting to the farms front gate and with this in mind the total was raised to $3.10 per cubic metre for the RWSS.

Mr Graham said this meant the dam was about the same cost as building one privately.

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Council Group Manager Strategic Development James Palmer said the benefits of RWSS was that the water would arrive at the farm gate with significant pressure and no further infrastructure would be required unlike those who have private on farm storage which requires things like pumps.

The council commissioned a review of the scheme back in November after progress on the controversial RWSS stalled with more regional councillors who questioned the dam elected at last year's local body elections.

The review identified the key legal, financial, economic, environment and engineering elements of the scheme and the risk the RWSS scheme would pose to each of these if it proceeded or didn't proceed.

The biggest concern was over its environmental impact.

The review found the greatest risk and uncertainty around the challenges for water quality and out of land use in the Tukituki Catchment with or without the scheme.

The review highlights that meeting the Nitrogen (Dissolved Inorganic Nitrogen or DIN) limits in all Tukituki sub-catchments by 2030 (as required by the Tukituki Plan) is highly improbable and may even be physically impossible.

The Review has identified that the current Tukituki plan has a number of serious deficiencies which means that the Plan will struggle to deliver lower nitrogen levels with or without the scheme.

The Environmental Defence Society and Fish and Game have jointly offered to co-operate with the council in getting an Environment Court ruling on ambiguities in the consent condition for the RWSS.

Environmental Defence Society CEO Gary Taylor said the ambiguities concern the Nitrogen limits in the consent conditions that were set by the Board of Inquiry.

In a letter to council chair Rex Graham, HBRIC recommended that a better way to approach the Plan Change 6 DIN limits might be to require both the RWSS farmers and non-RWSS farmers by the years of 2030 to be achieving sustained reductions in nitrogen losses and be operating in a manner consistent with achieving the 0.8DIN overtime.

Hawke's Bay Today understands councillors will be discussing this at today's meeting.

The review also identifies, and draws conclusions on the other key issues associated with the scheme including council being able to withdraw from further development of the RWSS, and that HBRIC has no contractual obligations which would create liabilities if this occurred.

However, this would cost a write down of about $19.5m already invested, and there was a risk the Crown could seek a refund of its $7m investment to date.

Financially, the critical driver of revenue and risk was water uptake - based on the contracted level of the initial uptake the scheme was expected to break even in its first year. Risks of low uptake would rest with HBRIC, and the council.

At full uptake it would increase the regional GDP by up to $380m and create up to 3580 jobs.

It also concluded that changing the dam to avoid "inundating the DoC land" could make it uneconomic to build - council is awaiting a Supreme Court judgment on land needed for the scheme to go ahead.

It is now up to council to decide if they are comfortable with the overall level of risk in either direction.

A final decision will be made on whether the scheme should proceed, be abandoned or shelved on May 31.