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Measuring Contractor Performance Case Study

A dredging contractor was hired to remove sludge in a holding pond.

Customer: Pulp & Paper Company

Problem: Confirm the sludge removal amount claimed by the dredging contractor.

Solution: Sludge Mapper conducted both pre-dredging and post-dredging surveys of the pond. These surveys allow a delta of the sludge volumes in the pond to be compared to the contractor’s claim.

Client Introduction:

A leading Canadian Pulp & Paper company with a North American footprint.


A dredging contractor was hired to remove sludge from a holding pond at the client’s plant. The client sought to validate the accuracy of the sludge removal claim by the contractor.. 


Sludge Mapper conducted an initial sludge survey to measure the existing volume in the pond. This survey was completed 9 months before the commencement of dredging. The initial survey involved collecting pond data to construct a Digital Elevation Model (DEM) of the pond,  acquiring sonar data of the sludge surface, and recording GPS coordinates.  Subsequently, a second sludge survey was carried out after the contractor had completed their work. The two sets of sonar data were meticulously compared using professional-grade dredging software, leading to the computation of a volume delta. This calculation yielded a “wet” sludge volume. A laboratory test was performed on the sludge to determine the dry tonnage. This dry tonnage was then cross-referenced with the contractor’s sludge removal logs for a comprehensive validation process.

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Sludge Mapper’s before and after sludge surveys calculated a dry sludge delta of 352 tonnes removed in contrast to the contractor's claim of 435 tonnes removed. The relatively minor difference in mass could potentially be explained by additional sludge being introduced to the pond over a 9-month period between surveys. Considering this extended duration between assessments, the client expressed confidence in the contractor's performance, leading them to justify the payment. 

Despite the relatively small fraction of the cost of the dredging that the two surveys represent, they serve as a valuable confirmation of the contractor's performance. The thoroughness of these surveys enhances the client's assurance in the accuracy of the sludge removal and justifies the corresponding payment.

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