A construction company was in the construction phase of installing cement pipe sections that will become an underground conduit carrying stormwater away from a stretch of I-75. This conduit will discharge into a 4-acre stormwater detention pond that is 12’ in depth. During excavation, water was continually pumped away from well points to allow equipment and materials access.
A 3,000 gallon weir tank reduced sediment loads in pumped stormwater before discharging into a lake during the dewatering operations. NTU levels collected at various collection points showed an average level of 192 NTUs. Discharge threshold was 29 above background. Background sample collected produced an NTU level of approximately 7 NTU, requiring the contractor to discharge no more than 36 NTUs during the dewatering operations. The use of the weir tank is not able to reduce the NTU levels to levels that are acceptable for discharge into a nearby protected wetland located immediately adjacent to the jobsite.
HaloKlear GelFloc was employed with dewatering bags in a semi-passive system. Influent water read 1241 NTU, while HaloKlear-treated effluent water was tested at 1.82 NTU, well under the guidelines set for recycled water.