Schachen groundwater pumping station in Weinfelden

Gruner assumed the lead management role in an innovative project: the Schachen groundwater pumping station with horizontal screened well. The design of the groundwater collection system  made special allowance for the flood-prone Thur valley site.

Built between 2010-2012, the horizontal screened well ranks as one of the most modern well installations in Switzerland, perhaps even in Europe. The Schachen groundwater pumping station will ensure the water supply for the Weinfelden region of the Canton of Thurgau in the coming decades. Following an assessment of the site in Weinfelden and the strong groundwater currents in the Thur valley, preference was given to a large horizontal screened well solution as opposed to a series of vertical screened wells. Apart from their lower sinking depths, horizontal screened wells also allow the collection of much larger water quantities at a single location. 

In assessing the options for the well shaft construction, the pros and cons of in-situ concrete solutions (4 m internal diameter) and precast assemblies (2.8 m internal diameter) were examined. Key advantages of the precast-concrete shaft included the shorter construction time and substantially lower cost. The well screens were laid in four horizons, with the top horizon, at a depth of 17 m, designed as a protective horizon with selective extraction. Some of the screens, which incorporated slotted pipes with an internal diameter of 300 mm, were rammed up to 40 m into the ground.

Innovative desanding process

Given the high proportion of sand and heterogeneity of the aquifer at the Schachen site in Weinfelden, a symmetrical double-packer chamber system with impulse generator (high-performance desanding, SDKK) was used for the first time in Switzerland to desand the individual well screens. Thanks to the dedication of the entire project team, the innovative procedure achieved outstanding results with extremely low residual sand contents.

Safety from flooding and impact on outfall

The wellhead lies with an 80 cm freeboard above the highest flood level of 421.20 m above sea level. Gruner engineers designed the overall structure as a watertight trough with adequate resistance to uplift. The nearby Ölibach stream, which previously served as an outfall for the local sewage treatment works, was closely monitored during the interim and acceptance tests. There was no evidence of any impact on the stream throughout the pumping tests, which indicated a theoretical well capacity of around 30,000 ltr/min. Various parameters are being monitored by the Canton of Thurgau Office for the Environment for a two-year period after commissioning, which took place in April 2012. It will be possible to seal off the relevant stream section should any changes unexpectedly occur.

Timeline

1992–2000 Site assessment / 00: Establishment of protection zone / 01: Land acquisition
2005–2008 Detailed investigations at well location
2008–2009 Design, building application for GWPS, building permit, bidding
Aug.–Sep. 2009 Construction of well shaft
Oct. 09–Sep. 10 Construction of horizontal well screens
Mar. 10–Mar. 11 Interim pumping test, desanding of well screens, acceptance pumping test
Apr. 11–Mar. 12 Construction of well building, incl. outfitting and well equipment
Apr. 2012 Commissioning, establishment of protection zone, inauguration with open day

Technical data

Extraction rate: Design rate for low water 15,000 ltr/ min / peak extraction 18,000 ltr/min (3 redundant submersible pumps, each with 6,000 ltr/min capacity)
Well shaft: ID 2.80 m, ED 3.40 m, depth 30 m
Horizontal well screens: 15 units on 4 horizons at depths of 17, 21, 25 and 29 m, total length 414 m (stainless-steel screen pipes with slot perforation, DN 300 mm with 0.8-2.5 mm slot widths) In-situ concrete building 19 x 15 x 6 m, incl. transformer station

Key facts and figures at a glance

Client: Technische Betriebe Weinfelden AG (TBW)
Location: Schachen, Thurtal, Weinfelden, Canton of Thurgau
Total costs: Approx. CHF 6 m
Construction period: Aug. 2009–Apr. 2012
Project period: 2008–2012

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