NMA Nomenca Case Study

Case Study

NMA Nomenca

Client: NMA Nomenca
Location: Epworth STW, Lincolnshire
Duration: NA
Excavation Depth: Up to 4.7m
Temporary Works: Open Cut
Dimensions: Within Single 65m x 45m
Structures: 2 Oxidation Tanks & 2 FST Tanks
Ground Conditions: Top Soil, Silty Sand, Firm Clay
Groundwater Level: 1.3m BEGL

Dewatering Proposal:
Concerns where raised over excessive groundwater level reduction beneath existing structures within the works. An estimated distance/drawdown profile was established based on design bulk permeability of k = 5.6 x 10-5 m/sec.Temporary Vacuum wellpoint system installed at nominal 2.0m centres around the perimeter of the works to top of Clay using conventional water jetting installation method. Provision for 6no access points into the works area. Once bulk dewatering achieved, dewatering changed to conventional sump pumping within perimeter slip trench at toe of batter.

1. • A total of 135no wellpoints where installed and the system commissioned in 7 days.


2. • Start up pumping flow was 6 lts/sec with steady state conditions reached after 5 days and a flow maintained at ~ 2-3 lts/sec.


3. • Monitoring points where installed externally to record draw down profile.


4. • Works completed within 6 weeks to programme and budget, with subsequent transfer to sump pump system.