Aquatech Dewatering Company, Inc (Aquatech) was called upon to join an assembled project team on an ongoing construction contract in the Greater Toronto Area (GTA) to facilitate a means of addressing an urgent requirement to intercept, bypass and filter exceedingly turbid surface and storm water entering an environmentally sensitive creek.
The surface and storm water from a large drainage area was traveling through an area under construction, then being directed to a large drainage ditch, which ultimately discharged to a natural water course designated as ‘Clinostomus elongatus (Redside Dace) Fisheries Habitat,’ enhancing the systems’ sensitivity to the degradation of water quality.The project’s owner and engineer employed the services of a specialized environmental consultant, Groundwater Environmental Management Services Inc. (GEMS), to assess the site’s requirements for enhanced erosion and sedimentation controls to contain the turbid water on site.
The contractors, now including Aquatech, worked closely with GEMS, who made specific erosion control enhancement recommendations including erosion control matting placed on exposed banks, slopes and stock piles. Sedimentation control enhancements within the drainage ditch were also recommended. The last component was for Aquatech to divert water flows around the area under construction and filter the water to acceptable quality levels. Water quality sampling was completed by monitoring turbidity in Nephelometric Turbidity Units (NTU) and ranged in the watercourse from <12 NTU representative of ‘normal’ dry weather conditions to 243 NTU during significant precipitation events and spring freshet. Water quality entering the water bypass and filtration system ranged from 133 to >1,000 NTU. Due to the sensitivity of the watercourse, the project team consultants preferred to have project discharge waters meeting a target of <12 NTU to ensure that the project would not have a negative impact on the stream and its sensitive fisheries populations.
There were many challenges to address the targets of this site water bypass and filtration, which included the need to design, install and commission a system that would automatically cater to flows that range from as low as 0.0013 m3/second (76 litres/minute) to as much as 0.12 m3/second (7600 litres/minute) depending on weather conditions. In
addition, the filtration system needed to cater to varying water quality (sand size particles as well as silt and clay size particles under two microns) that would significantly change dependent on flow volumes. To ensure that the flow was always being discharged in a manner that would meet acceptable water quality objectives, suitable for a natural creek deemed as ‘Coldwater and Redside Dace Fisheries Habitat’ by regulatory agencies, the bypass pumping and filtration system required an ability to address the broad range of flow volumes and varying water quality. After the system was designed, another major challenge was encountered to install this large bypass and filtration system (large footprint) on a site with a very limited amount of real estate available. This coupled with a timeline of a few days to commission the system necessitated additional space and permission from private land owners adjacent the project location.
The private land owner, Metrus Land Developments (Metrus), was contacted by Aquatech’s staff, who explained the situation and timelines. Metrus recognized the environmental needs of the project and expedited the access permission to Aquatech to enable the response initiative to protect the environment. With permission granted by Metrus, the general contractor was able to construct an access road and staging area for Aquatech and the filtration and bypass pumping equipment. Aquatech started installing the pumping and filtration equipment, working 24 hours a day, and within a few days was able to initiate the pumping and treatment systems. The set-up was performed in a manner that allowed for a staged activation, lower flows were directly bypassed and filtered, and then the high flow rate systems were systematically added to the operating low flow system. Numerous adjustments and modifications were made in the following days to accommodate increased precipitation event induced flows. Once commissioning of the systems was complete, the full range of flows and water quality was able to be transported entirely through the bypass pumping and filtration system to ultimately achieve the desired water quality results. Adjustments to the filtration system continued to significantly improve the water quality results to figures that now exceed expectations and the desired discharge quality released into the receiving natural water course. This bypass and filtration system employs a wide array of automated equipment and piping which allows the system to cater to the varying flow rates that respond directly to weather events. The fully-automated equipment includes several electric and diesel powered pumps, generators, light towers, an integral organic flocculent additive, weir tanks (Aquatech Enviro-Tanks) and micron filtration (sand media and pressurized micron filtration filters). The system has been very successful and effective, with water quality readings as low as <2 NTU exiting the filtration system. These results were previously thought by many as unattainable on this project site without the use of nonorganic treatment methods.