Photos courtesy of Ann McLeod
From an email by the Department of General Services:
It’s our, the Department of General Services’ (DGS), understanding that the sinkholes on the Garrison Elementary School field site are located in the area of the old Garrison School, and we believe that they are caused by the settling of sub grade material due to the improper compaction/excavation during the razing of the old Garrison School approximately 50 years ago.
In order to determine the exact cause of the sinkholes and develop a remediation plan, we are procuring a geotechnical engineer to study the site, identify the extent of the issue and provide recommendations on a remediation solution. The geotechnical investigation will include ground penetrating radar [GPR] or a similar surveying technique combined with soil borings.
We expect the geotechnical investigation to start by the end of this month (March 2013). Our current expectation, based on our understanding of the issue, is that the initial geotechnical work will take approximately 4 weeks (end of April 2013). After we receive the results of the geotechnical work we can develop a preliminary action plan. This plan may directly involve remediation or, depending on the initial geotechnical results, may include additional investigation.
We will report back to stakeholders in early May and update our plan based on the initial geotechnical results.
In the meantime, a construction fence will be installed around the area where the sinkholes have occurred and we will monitor the remainder of the site for any unusual conditions.