Pumping Tests: HS2 Ventilation Shaft Case Study

Case Study

Pumping Tests: HS2 Ventilation Shaft

Client: ALIGN JV
Location: HS2 C1Section - Bucks
Duration: Feb 2019 – Aug 2020

Project Overview

As part of the site investigation phase of HS2. Stuart Wells undertook large scale abstraction and recharge Pumping Tests on HS2 for ALIGN JV. The pumping tests were undertaken at four vent shaft locations on the C1 section in the Chiltern Hills, Chalfont St Peter, Chalfont St Giles, Amersham and Little Missenden.

The Objectives of the Pumping Tests

• 1. Provide additional information to determine the hydraulic properties of the subsurface chalk bedrock.
• 2. These parameters are then used to aid design of the proposed ventilation shafts and any temporary groundwater control measures during shaft construction.
• 3. The testing also provided the necessary hydrogeological data required to support applications for the necessary Environmental Permits for groundwater abstraction and discharge.

Services Provided by Stuart Wells

• All temporary works requirements including welfare and track matting
• Drilling and installation and development of all chalk abstraction, recharge and monitoring wells
• Hydraulic Testing included slug, falling and rising head tests, with data interpretion and permeability values generated.
• Geophysical testing included, CCTV survey, verticality and calliper logging
• Provision and installation of pump testing equipment (including generator power supply), data logger monitoring of observational wells, water sampling and analysis, as well as factual reporting of the results obtained.
• Each pumping test comprised of pre-test monitoring, an equipment test, a step test, a constant rate test (7 days), and recovery monitoring.
• Downhole level loggers were utilised to measure groundwater levels throughtout the testing period.
• MAG flowmeters with dataloggers recorded abstraction flow.
• We undertook groundwater sampling and analysis together with field parameter water quality data throughout the test period.