Civil Engineering December 2021 | Vol 29 No 11

Civil Engineering December 2021 31 T he Spring Grove Water Treatment Works (WTW) is situated in Rosetta in the uMgungundlovu District Municipality, serving water to the Mpofana and uMngeni Local Municipalities. The construction of the 20 Mℓ/day plant forms Phase 1 of the three-phase Greater Mpofana Bulk Water Supply Scheme. The WTW sources its water from the Spring Grove Dam and was successfully designed by Umgeni Water’s Engineering Services Department and constructed by Basil Read. The construction of the Spring Grove WTW entailed the following components: Q Q 800 mm diameter raw water pipeline from the existing raw water pump sta- tion to the head of works Q Q Head of works Q Q Dry chemical building Q Q Splitter box Q Q Pulsator clarifiers Q Q Compressed air building Q Q Sand filters Q Q Backwash recovery tanks Q Q Sand degritter Q Q Thin sludge holding tanks Q Q Gravity thickener Q Q Centrifuge building Q Q 5 Mℓ reservoir Q Q Potable water pump station Q Q Ammonia, polyelectrolyte, chlorine buildings and office block Q Q Eskom intake substation. NO WATER PROOFING ON ROOF SLABS A waterproofing membrane is generally applied to flat roof slabs. This is a specialist application, costly, requires periodic replacing, and does not always work. On the reinforced concrete roof slabs for the chlorine and pump house, no waterproofing membranes were applied. Instead, to ensure a waterproof slab, a suf- ficient fall was specified for the rainwater not to pond, no gaps in the shuttering were allowed (so that the fines in the wet concrete do not leak out), 35 MPa concrete was used and proper vibration of the placed concrete was done throughout. After three rainy seasons, no leaks have occurred in the roof slabs. SODIMATE LIME DOSING SYSTEM This was the first complete installation of its kind for Umgeni Water. The lime solution is dosed by means of a 20 m long, 32 mm PVC pipe instead of the usual HPDE pipe which sags and gets blocked. To date this system has proved itself and is performing as intended without any blockages. Benefits of the Sodimate Lime Dosing System include: Q Q Arch breaker system prevents rat holing of lime Q Q Screw feeder and injector systems prevent blockages Q Q Automated slurry mixing system al- lows for a homogenous slurry Q Q Pumping system allows dosing over longer distances. DEWATERING OF SLUDGE During the early stages of the project, there was a request from the Umgeni Water operations team to implement a new type of dewatering equipment that had not previ- ously been used in any of the utility’s plants. The team had been experiencing problems with the usual Alfa Laval system and instead opted for an Andritz dewatering unit. This required a great deal of co-opera- tion between the many role players involved to produce detailed planning, design and drawings to the client’s specifications. Thanks to the teamwork efforts, spanning across three continents, this was a success. IN-HOUSE SUCCESS Undertaking a project of this magnitude and complexity in-house as a State- Owned Entity is not common practice. Doing so has not only resulted in ca- pacitating in-house engineers, it has also resulted in substantial savings of fees (ap- proximately 15% of the total project costs) which would have been payable to the external service providers. The in-house design and construction monitoring fees totalled approximately R17.7 million.  SANRAL SA I CE 2021 Nat i onal Awards Category: Techn i cal Excellence FINALIST Technical Excellence category (Sponsored by Maccaferri SA) KEY PLAYERS Client: Umgeni Water Consultant: Umgeni Water: Infrastructure Development Division – Engineering Services Department Contractor: Basil Read Spring Grove Water Treatment Works Construction underway