Effective groundwater control during construction is critical to all underground elements of projects, from both geotechnical and environmental viewpoints. Issues regarding dewatering include: 

• Settlement of adjacent structures where such structures may be founded over organic compressible soils.
• Loss of ground.
• Unstable bottom condition if groundwater control measures are not properly identified and implemented.
• Disposal of pumped water that may contain contaminants. 

Where organic soils are present, lowering of groundwater levels outside the excavation could cause consolidation of adjacent soils and potential deterioration of wood piles. This is a common problem for structures located in the Back Bay section of Boston. For deep excavations, the earth
support walls may have to be designed to extend deeper into the less permeable material in order to serve as an effective cutoff. This could result in significant costs. Alternatively, grouting below the bottom of the wall could be used.


GZA was instrumental in incorporating the latter approach on the Central Artery/Tunnel and the Fleet Center in Boston, resulting in considerable cost savings compared to extending the bottom of slurry walls deeper than that required for stability.
GZA has extensive experience with the design of typical groundwater control systems that involve relief wells, sump pumping, and well points. GZA has the capability to develop groundwater seepage models as needed to evaluate both temporary and permanent groundwater control methods, i.e. cut-off, partial cut-off or complete dewatering. The models provide a means for predicting effects of groundwater control in areas adjacent to the construction and for the development of mitigation measures if required. These analyses also aid in predicting the quantity of flow the construction contractor(s) can expect to pump.