Quarry dewatering compliance

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Courtesy of Greyline Instruments Inc.

Louis W. Bray Construction installed a Greyline Area-Velocity Flow Meter in 2009 to meet Ministry of Environment regulations. Their permit stipulated effluent limits plus monitoring, sampling and flow measurement of wastewater discharged from the site to the South Raisin river. The Ontario Water Resources Act requires flow monitoring for any quarry dewatering greater than 50,000 liters per day.

Quarries operating below the water table dewater by pumping from the quarry pit. Some sites are able to reuse water in washing processes or spray operations but most discharge to a nearby waterway. Since a quarry operation involves only crushing, screening and mixing aggregates, chemical or biological water treatment is not required. Treatment before discharge normally requires a series of settling ponds to drop suspended solids and test wells for water quality assessment.

Filtration after dewatering in the Bray Quarry uses a system of three settling ponds. Water is pumped from the quarry into the first settling pond and then flows by gravity through each pond in succession via connecting culverts. Final discharge flows through a 36' diameter culvert and finally to the South Raisin river. Consulting engineers Genivar proposed an AVFM Area-Velocity Flow Meter from Greyline Instruments as a suitable technology to monitor and data log flow in the partially filled culvert.

The Greyline Area-Velocity Flow Meter sensor was installed at the bottom of the culvert about 1 m from the open discharge. The submerged ultrasonic sensor measures water level, velocity and temperature. Calibrated for a 36' diameter pipe, the instrument converts these readings to a flow rate. During pumping periods water in the horizontal culvert rises to about 300 mm level with velocity of 0.3 m/sec. The AVFM Area-Velocity Flow Meter reads, totalizes and data logs flow rates up to 70 l/sec during pump cycles.

The instrument electronics are installed in an insulated shed 25 m from the sensor location. Cable from the sensor to the electronics is watertight and run underground in PVC conduit. The AVFM Area-Velocity Flow Meter includes a thermostatically controlled enclosure heater, flow rate display, totalizer, programmable control relays, three 4-20mA outputs and a data logger.

Bray Quarry personnel Kevin Jans (Quality Control) and Stuart Thomson (Quarry Manager) periodically download log files from the Greyline AVFM to their laptop computer. Using Greyline Logger software they can generate one-click flow reports including daily total, minimum, average and maximum flow with times of occurrence. Greyline’s software program exports to Microsoft Excel for these reports.

The Quarry permit allows Bray to operate 244 days per year and they are required to submit flow reports twice annually to the Ministry of Environment. With the Greyline AVFM 5.0 Area-Velocity Flow Meter they are able to comply with environmental regulations and easily produce dewatering flow reports.

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