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Dewatering and groundwater control | Stuart Well Services Ltd

Case Study

Saint Gobain Glass Factory

Client: Saint Gobain Glass UK
Location: Eggborough, Yorkshire
Duration: June 2020 – February 2021

Project Overview

Saint Gobain Glass (SGGUK) first approached Stuart Wells looking for a permanent solution to rising groundwater issues they were having at their floating glass manufacturing facility in Eggborough. As the site was located within a Groundwater Protection Zone, the project involved working closely with the local Environmental Agency (EA) at all stages in the submission and granting of initial GIC and later groundwater transfer licence.

Project Overview

A conceptual model was developed followed by an application to the EA to undertake a pumping test, under an EA GIC (Groundwater Investigation Consent). The pumping test data was used to finalise the design of the permanent dewatering system, obtain hydrogeological information, abstraction and recharge potential, together with assessment of any environmental impact.

The pumping test involved reinjecting all abstracted groundwater back into the aquifer using recharge wells. The test highlighted issues with recharging and the conceptual model was altered to accommodate more recharge wells than initial envisaged. The final design for a permanent dewatering system and basis for an application of an EA groundwater transfer licence consisted of permanent abstraction wells, with all groundwater being recharged back to the aquifer. This consisted of a series of abstraction boreholes around the perimeter of target area to control groundwater level in the Sherwood Sandstone. With all abstracted groundwater transferred via a pipeline to a series of recharge wells located on the site boundary and injected back into the Sherwood Sandstone aquifer.

Between October and Christmas 2020, a total of 6no x 50m deep abstraction wells and 31no recharge wells were drilled, installed, and developed. With approval and granting of the EA transfer licence received before the end of the year, full commissioning and testing of the system including the placement and insulation of the PE recharge pipeline was successfully completed early 2021.

Pumping Test

Ahead of the application to investigate a groundwater source was submitted. A Water Features Survey to evaluate the impact of the proposed abstraction (dewatering) on the surrounding water environment; sensitive water receptors and abstractions was undertaken by Stuart Wells. The pumping test was undertaken to GIC conditions and involved the installed of 2no abstraction well and 8no recharge wells, all located and designed to enable reuse in any subsequent permanent dewatering system. Groundwater levels were observed in existing site monitoring wells, together with all identified environmental assists; prior and during the pump test phase. Pump Testing consisted of the following scope:

Activity Duration Programme
Pre-test monitoring 3 Days Day 1 to Day 3
Equipment Installation and individual operation test 2 Days Day 4 and Day 5
Recovery period 1 Day Day 6
Pumping Test of Abstraction Well No. 1 to Recharge Wells 3 Days Day 7 to Day 9
Pumping Test of Abstraction Well No. 1 and No. 2 to Recharge Wells 4 Days Day 10 to Day 13
Recovery monitoring 1 Day Day 14

Permanent Dewatering Design & EA Groundwater Transfer Licence Application

Data and information generated from the pumping test was used to model a permanent dewatering and recharge design to comply with both groundwater engineering requirements, in terms of required drawdown, contingency wells to allow for long-term maintenance and environmental objectives and constraints.

The achievable recharge flow rates observed during the pumping test and subsequent modelling identified the need for more recharge wells than initially envisaged, together with additional ongoing monitoring requirements. In October 2020, Stuart Wells mobilised 2no rotary drilling rigs to site and drilled, installed and developed installed all remaining abstraction and recharge wells over a 6-week period.

Abstraction Well Detail
No. 8no
Drilling Bore size Rotary Water Flush
nominal 300 mm dia. to approximately 50 m depth.
Well Installation 200mm x 182mm uPVC Screen (1mm slot) – base to 38m BGL
200mm x 182mm uPVC Casing 38m to 1m above GL
1mm-2mm clean, washed silica filter medium base to 5m BGL
Cement/Bentonite Grout 5m to GL
Development Borehole flushed clean prior to install. Airlift development of installation & yield testing

Recharge Well Detail
No. 39no
Drilling Bore size Rotary Water Flush
nominal 300 mm dia. to approximately 50 m depth.
Well Installation 324mm OD Steel Casing grouted to 4.5m BGL
165mm x 155mm uPVC Screen (1mm slot) – base to 11m BGL
165mm x 155mm uPVC Casing 11m to 1m above GL
1mm-2mm clean, washed silica filter medium base to 5.5m BGL
Cement/Bentonite Grout 5.5m to GL
Development Borehole flushed clean prior to install. Airlift development of installation & yield testing

415V Caprari submersible borehole pumps c/w level probes were installed within each abstraction well on 2.1/2” steel riser. In turn these connected to a 110mm PE collection main that linked to a 225mm PE recharge main with individual take-offs at recharge well locations.

All wells were housed within manhole chambers with cablings buried and contained within ducting. The pumps were controlled by 2no 4-way variable speed drive pump control panels, that in turn where connected to site mains power supply.

Groundwater levels were monitored using pressure transducer dataloggers and abstraction flow rates recorded by MAG flowmeters. All monitoring data was managed to enable remote monitoring, establishment of an alarm arrangement, all powered by solar panel set up at individual location.

Accreditations and Associations

ISO-9001 ISO-14001
ISO-22301 ISO-45001
The Temporary Works Forum (TWf)