138 21.0 Treated water pipeline and outfall (Diffuser) 21.1 Introduction As a result of the increased volume of discharge from the WTP it is necessary to provide appropriate outfall infrastructure. The proposed works are effectively a duplication of the existing pump station, pipeline alignments and outlet diffusers. The two new proposed 250 mm diameter pipelines will extend from the water treatment plant ponds to Ohinemuri River outfall locations #1 and #2 as shown in Figure 31. 21.2 Pipeline installation The installation procedure for the pipeline is set out in Beca (2022) as follows: • The proposed discharge pipes are proposed to be installed via open trench construction at a 2 m offset (typical) from the existing discharge pipes (subject to existing site features and sensitive areas) as shown on the drawings. • The pipes are delivered to site by truck and stockpiled in a dedicated laydown area. Sections of pipes are transported to the work front/s. • Pipes are installed within an excavated trench. Soil removed would be and will be re-used as trench backfill after pipe laying. • The length of open trenching shall be minimised by staging concurrent trenching, pipe laying, backfilling and stabilisation works to reduce exposed areas. • The existing pipeline that runs beneath the future Gladstone pit stockpile is proposed to be relocated as shown on the drawings. • Spoil-material would be temporarily stockpiled adjacent to the trench and re-utilised in backfilling of the trench. Excess material will be removed from the excavation site as soon as practical and stockpiled on OGNZL property. • Reinstatement at ground level will match existing. Features removed to enable construction, such as fences, will be reinstated with temporary fencing installed during construction as required. 21.3 Effects of pipeline construction on aquatic ecological values The new pipeline runs alongside the existing pipeline. The installation procedure is minimised through its staging, local temporary stockpiling and the limited open trenching. The pipeline route does not pass through any significant ecological areas, but it runs close to the Gladstone Wetland, and cuts through the riparian margin of the Ohinemuri River.
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