Stage 2 - Strathalbyn Waste Water Storage and Treatment Process Expansion

⁠⁠⁠5.21.021 - Alexandrina Council of 11 Cadell St, Goolwa, SA, 5214 (the Council) invites tenders from Tenderers for the provision of Stage 2: WWTP and Irrigation Pump Station Package (the Services). The Council will enter into a Contract for Services with the successful Tenderer.

The township of Strathalbyn is serviced by a Community Wastewater Management System (CWMS), which involves wastewater collection, treatment and reuse/disposal. The scheme is primarily a Septic Tank Effluent Disposal Scheme (STEDS), meaning most connections have a septic tank for primary treatment. The township also has a number of full sewer connections. The CWMS is owned and operated by Alexandrina Council (Council).

Effluent generated within the township gravitates through a network of gravity drains into pump stations within the township, and is pumped through a network of rising mains to a sequence batch reactor (SBR) wastewater treatment plant (WWTP) near the intersection of Michelmore Road and Greenway Road. The SBR plant currently operates at 500 – 700 kL/day, and has a capacity of 1,500 kL/day. Based on field observations and a water balance assessment, the existing 120 ML polyethylene-lined storage lagoon at the plant has been found to have inadequate capacity to balance the scheme’s annual water storage variation.

This project involves the construction of a new 110 ML storage lagoon at the plant to provide additional balancing storage. In addition to the new lagoon, the project involves a range of other upgrades to address some deficiencies with the existing plant and improve operation.

The Works for the project have been split into two separate contracts:
* Stage 1: Lagoon Civil Works Package (Currently under Construction)
* Stage 2: WWTP and Irrigation Pump Station Package.
* The Scope of Works for Stage 2 WWTP and Irrigation Pump Station shall include the following:

* Preliminaries
* Location of existing services.
* Modifications to 110 ML storage lagoon batters to accommodate new pump station.
* Construction of new irrigation pump station upon the batter of the 110 ML storage lagoon.
* Construction of 100 kL chlorine contact tank between the SBR plant decant line and the outlet drains to the storage lagoons.
* Modifications to the transfer mains from the balance tank
* Modifications to the WWTP’s gaseous chlorination dosing system.
* Construction of a platform and a wastewater screen on the inlet to the WWTP’s balance tank, including installation of a wash pump.
* Realignment of various pipework in the WWTP.
* Construction of an offtake line to the existing chlorine dosing water storage tank, containing a filter, actuated isolation valve and a pressure sustaining valve.
* Installation of actuated gate valve on the existing rising main to the Ness irrigation site.
* Construction of an inlet manifold on the existing low level outlet pipes from the existing 120 ML, including a new floating suction inlet.
* Decommissioning of the existing irrigation pump station and modifications to internal pipework at the invert of the pit to connect in to the new irrigation pump station inlet pipework.
* Location of existing conduit housing chlorination pipes between chlorination shed and existing irrigation pumping station. Removal of existing pipes and installation of a drawrope to allow for future communication cables.
* Installation of hydrostatic level sensors on existing 120 ML lagoon and new 110 ML lagoon (refer to drawings for detail).
* Removal and relocation of actuated valves in concrete chambers on the 110 ML storage lagoon to the new pump station.
* Construct outlet section of lagoon circulation pressure main into the existing 120 ML lagoon (to connect to stub from Stage 1 works).
* Supply and install of 150mm thick compacted quarry rubble over the WWTP area to be confirmed with the Superintendent.
* Testing and commissioning.