Warren Mill Dam Sediment Investigation

Under a multi-year renewal contract with the New Jersey Division of Property Management, Princeton Hydro provided sediment, quantification, sampling and analysis services for the Warren Mill Dam impoundment. The project was initiated to understand the amount of sediment behind the dam that would require management or release to create a stable fluvial river channel pending dam removal; understand the geotechnical qualities of the sediment, and; determine the contaminant (HTRW) concentrations within the sediment in relation to ecological screening and human health criteria.

The initial fieldwork encompassed a bathymetric/hydrographic survey utilizing a combination of a Knudsen dual frequency sounder and survey measurements, both tied to a real time kinematic (RTK) survey grade global positioning system (GPS). Following the completion of the field survey, the top of sediment topography was generated and used to develop initial volume estimates. Utilizing this data, a sediment sampling and analysis plan (SSAP) was developed with NJDEP, and NJDEP Land Use Permits and landowner permissions were acquired (right of entry). Once the SSAP was approved, the environmental/geotechnical borings were conducted.

A total of 15 borings were completed from a bargemounted tripod SPT rig by Princeton Hydro and Unitech Drilling. All borings were progressed to refusal on bedrock, and the stratigraphy and lithology of the sediment and soils were logged, including standard penetration tests. Additionally, samples were collected for chemical analysis, including river water samples, to complete elutriate testing to assess the mobility of contaminants during the dam removal process.

Princeton Hydro collected split samples for both HTRW analysis performed by an independent analytical laboratory, and grain size analysis, moisture content, organic content, and Atterberg limits performed by Princeton Hydro’s in-house AASHTO and USACE certified geotechnical laboratory. Field logs were finalized, and a report was prepared describing the field operations, observations, conclusions and recommendations. The report also included a hydrographic map of the impoundment, boring locations, boring logs, analytical results, an interpretive fence diagram of the sediment stratigraphy between borings, and volume calculations.