40 The Department of Natural Resources prepared a spreadsheet of converted entitlements for the purposes of cl 25C of the plan. The calculation in that spreadsheet was in accordance with the method identified in (4) above (that is, resulting in a share component of 439 units). On 2 February 2007 the Department received a letter from the applicants disputing their share component of 439 units. The next day the applicants forwarded a further letter noting that their share component should be based on a history of extraction of 267ML (not 115ML, with the difference from 284.5ML explained by the applicants using a different figure for metered extraction in one of the two earlier years). The applicants said the years 2000/01, 2001/02 and 2002/03 were zero or low extraction years and should be excluded from the averaging process. The Director-General of the Department responded on 17 July 2007 to the effect that their share component was based on a history of extraction of 115ML and that while they had "correctly identified an error in the drafting" of cl 25C(4) of the plan, their entitlement had been determined correctly in accordance with the recommendations of the Central West Catchment Management Authority as approved by the NSW and Commonwealth governments. Further, that the error "is being corrected". Mr Coady, an officer within the Department and author of the draft of the letter signed by the Director-General, said that the error to which the letter referred was that the word "since" in cl 25C(4) should be "prior to".
C. Submissions
41 The applicants submitted that:
(1) The so-called explanatory material relied on by the respondent (including Mr Coady's explanation of the asserted error in the plan) is irrelevant to the task of construction of cl 25C(4). The plan is not a statutory rule and ss 33 and 34 of the Interpretation Act 1987 do not apply. The common law is more restrictive. In any event, legislative intention is not discernible from the opinions of Departmental officers. No weight may be placed on information disseminated by the Department before the plan was made, as the plan was the result of a process of consultation incomplete at that time. In particular, the document "Key amendments to Water Sharing Plan for the Lower Macquarie Groundwater Sources 2003" concerned proposed changes subject to comments as the first page discloses. Further, the respondent's reliance on the history of extraction provisions in the other plans that were amended on or after 1 October 2006 (Water Sharing Plan for the Lower Gwydir Groundwater Source 2003, Water Sharing Plan for the Lower Murrumbidgee Groundwater Sources 2003, and Water Sharing Plan for the Upper and Lower Namoi Groundwater Sources) so as to exclude zero and low extraction years "prior to" activation is misplaced. Those plans have no bearing on the construction of the plan in the present case. They involve different water sources, management regimes, and formulae for calculating the history of extraction.
(2) The respondent's approach to the purposive construction of cl 25C(4) involves an illegitimate assumption, namely, that construing "since" as "prior to" would better accord with the purpose the plan was intended to achieve. However, there is no evidence supporting that assumption. In the applicants' case, giving "since" its ordinary (and only) meaning would result in a greater share component due to the applicants' date of activation and history of extraction. If the correct approach were adopted for all converted entitlements the consequence for the water source overall remains unknown. Further, the respondent's approach would involve a policy of punishing those who have been frugal with water after activation. There is no basis for discerning any such legislative intention.