Upgrade of estate water supply network
The Waitrose Farm, Leckford Estate, Hampshire
Project challenges
Unstable water quality
The whole estate water infrastructure was installed in 1939 when the estate was acquired by John Spedan Lewis. The pipework would have been laid as steel water pipes and the reservoir built in situ. The main source of abstraction for the drinking water system was a shallow river abstraction, from a tributary of the River Test.
Before electric pumps were installed by MJ Abbott in the early 2000s, diesel pumps were still in use to abstract the shallow waters and pump to the estate reservoirs for treating prior to consumption. Over a period of 3 years all pumps were replaced by electric pumps and automatic dosing of chlorine to the system at source was undertaken.
The quality of the estate drinking water was being monitored by a professional water hygiene company with weekly testing and sampling being stringently undertaken. Over time, it was noted that the water quality was not stable, so MJ Abbott were asked to investigate to help find a solution.
Our approach
Bespoke water system design
To address the water quality consistency, we looked to change the abstraction location away from a shallow water source to the deeper water source from a new borehole. MJ Abbott commissioned a hydrogeological borehole feasibility survey to investigate the potential for a suitable abstraction point away from the river and away from influences associated with shallow water abstractions. The geological report identified a new potential location to drill a new 70m deep borehole deep into the chalk strata and into a saturated chalk layer below the site. Test pumping and water sampling proved that the new borehole was suitable in terms of water quality and water yield. A full application to transfer the abstraction to the new location was applied for and working the Environment Agency, permission was granted for the new abstraction.
Once the new abstraction was proved, consideration was given to redesigning the new water distribution network to replace the aged and failing pipework to overcome leakage and reduce abstraction. MJ Abbott designed a new piped network which allowed pump rates of 30,000 litres/hour to be abstracted and pumped to a new 32,000 litre reservoir which supplied water to the village of Leckford. New 110mm HPPE pipelines were laid across the estate from the new abstraction point, passing several commercial businesses to the highest estate reservoir. New pipelines (of varying sizes) were laid and connected to the various commercial outlets.
To address redundancy in the system and to allow for an alternative supply in the event of borehole pump failure, MJ Abbott designed into the system a link between estate supplies that allowed simple flushing and switch over should the borehole fail, to bring an alternative supply into the whole system. A 90mm link pipe between the two supplies was installed, tested and left operational for 30 days to prove.
The final solution
An upgraded water supply network to serve the estate for years to come
The project took around 5 months to complete from breaking ground to final commissioning and was a complete success.
The new system comprised of:
- 70m deep x 300mm diameter abstraction borehole with Grundfos SP30 submersible pump abstracting approximately 30m³/hour
- Pump control house located over the borehole consisting of a 2m x 2m GRP cabinet with roof hatch to enable removal of the pump
- New pump control system with pump protection and SMS message alert for system failure
- Automatic chlorine dosing station to add sodium hypochlorite to the water to safeguard against potential bacterial contamination
- Installation of 36,000m³ divisional reservoir to supply the village
- Installation of 2,000m of 110mm HPPE distribution mains to estate reservoir
- Installation of 1,200m of 90mm HPPE link pipe between two supplies for redundancy
- Replacement of water service pipes to various outlets
- Demolition of redundant reservoir and pipelines
- Decommissioning of old abstraction point
- Full as built mapping using GPS technology and schematic plans on completion.
