State of the Art Technology for Plume Mapping and Water Quality Monitoring
Demolition of the largest support structure (Pier E3) of the old Bay Bridge was carried out by imploding the hollow structure into itself. In response to the concern of potential exceedance of water quality standards, a water quality study was conducted to model the potential impacts from turbidity and pH due to the broken down and pulverized concrete. The results of the prediction model were corroborated through a comprehensive monitoring program implemented immediately after the implosion. State-of-the-art instrumentation was developed to track water quality in tidal waters following the Pier E3 implosion. The instrumentation included current drogues that could be remotely located during the study and that also recorded their tracks. Drogues were followed by a vessel equipped with sondes to measure key water quality parameters throughout the water column. The plume mapping technology allowed the sondes to collect critical water quality data at the exact location of impact and be able to compare with prediction models. Thereby demonstrating that the implosion technique with the associated BMP did not cause a detrimental water quality impact. Results of post-implosion water quality were compared to the prediction model as well as applicable water quality standards. The tidally dispersed plume was tracked for over 4 hours after the implosion collecting over 20,000 data points for turbidity, pH and other field parameters. In addition, stationary equipment was positioned to measure direct impact on bay resources and environmentally sensitive areas containing Eel Grass. In addition grab samples were collected throughout the plum, within the water column to be analyzed for metals.
In addition to the concerns for exceedance of water quality standards, there was a concern for potential toxicity to the bay benthic community due to metals. Bay sediment was collected around Pier E3 prior to and following the implosion to evaluate changes in metals and other potentially toxic substances. The sediment monitoring included the collection of intact core samples of the sediment water interface for toxicity analysis. This presentation will address the magnitude and duration of water quality changes following the implosion and will discuss the findings relative to Basin Plan objectives and potential impacts to fisheries in the Bay. Sediment characterizations will also be discussed in relation to toxicity of the benthic community.
The technology utilized in this study is applicable to any surface water body where plume mapping is needed. It can also be used to evaluate any major discharges, or effects of in-water work within any water body.
This presentation will include slides with photograph of the implosion, the monitoring equipment, graphs showing data analysis, and text explaining the process. It will also include a short video clip of the implosion itself.