70. Rules about discharges---(1) Before a regional council includes in
 a regional plan a rule that allows as a permitted activity---
   (a) A discharge of a contaminant or water into water; or
   (b) A discharge of a contaminant onto or into land in circumstances
         which may result in that contaminant (or any other contaminant
         emanating as a result of natural processes from that
         contaminant) entering water,---

 the regional council shall be satisfied that none of the following
 effects are likely to arise in the receiving waters, after reasonable
 mixing, as a result of the discharge of the contaminant (either by
 itself or in combination with the same, similar, or other contaminants):
   (c) The production of conspicuous oil or grease films, scums or foams,
         or floatable or suspended materials:
   (d) Any conspicuous change in the colour or visual clarity:
   (e) Any emission of objectionable odour:
   (f) The rendering of fresh water unsuitable for consumption by farm
         animals:
   (g) Any significant adverse effects on aquatic life.

   (2) Before a regional council includes in a regional plan a rule
 requiring the adoption of the best practicable option to prevent or
 minimise any actual or likely adverse effect on the environment of any
 discharge of a contaminant, the regional council shall be satisfied
 that, having regard to---
   (a) The nature of the discharge and the receiving environment; and
   (b) Other alternatives, including a rule requiring the observance of
         minimum standards of quality of the environment,---

 the inclusion of that rule in the plan is the most efficient and
 effective means of preventing or minimising those adverse effects on the
 environment.