Stormwater Pond Outlet Structure Grouting

Washington TWP, NJ


This stormwater pond outlet structure grouting project is located in Washington Township, New Jersey. The stormwater pond in a neighborhood was not holding water. Geotechnical investigations of the lining material showed that it was adequate. The developer determined that outlet structure grouting may be required to address water loss around the buried structures.

Due to a very tight site, the pond design releases water through two structures feeding manifolds. The pond has a well and pump to make up for water loss. However, the pond would still not stay at the level. The inlet and two outlet structures were identified as potential flow paths for water exiting the pond, causing the level to drop.

The township engineer told the developer that if they could not get the pond to hold water, they were going to have to install a liner system, which was very expensive.


Any repair could not impact:

  • water quality,
  • well operations, or
  • the residents.

The repair had to address water flows through various seepage paths around the structures. Due to the open graded stone pipe bedding for the manifold outlet system, there were countless potential flowpaths.


CJGeo successfully performed chemical grouting for the outlet structure grouting. This stopped water migration through the stone beds on two outlet structures and an inlet structure. During the grouting work, significant amounts of grout came into the manifold distribution boxes. This indicated that they were not watertight, and allowing water to seep into them at lower elevation than their design inlet elevations. The work took one day to make the structures watertight.

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