Patriot’s Cincinnati Environmental department recently got to test out their new low-flow groundwater sampling equipment in this abnormally beautiful winter weather! Did you know – Low-flow sampling is a type of groundwater sampling in which the groundwater in the monitoring well is disturbed as little as possible. Water is extracted from the well using a pump (in this case, a new Spectra-Scientific Bladder Pump) at a rate equal to or less than the rate water infiltrates the well from the aquifer. This method allows for a fresh groundwater sample to be collected from the aquifer without purging excess water, and without disturbing the water in the well to collect a fresh groundwater sample representative of the water coming from the aquifer.
Bladder Pumps are much less restricted by groundwater depth than a Peristaltic Pump (another type of Low-Flow pump) which can only pump water from a maximum depth of approximately 25 feet by using a negative pressure (suction) generated at ground level. Some agencies, including the EPA do not recommend the use of peristaltic pumps because the negative pressure applied by the pump risks extracting volatile chemicals and giving negatively biased results which are not representative of the aquifer.
A bladder pump is a submersible pump which utilizes a positive pressure system to pump water out of the well. Pressure is applied to the bladder pump from an external source (compressor or nitrogen tanks) via tubing. The increased pressure inside the pump collapses the bladder, forcing water up the tubing. When the pressure is released, the bladder refills with water from the well. Ball check valves prevent water from flowing out of the tubing during the recharge, and out of the pump during discharge. The Spectra Controller/Compressor allows for the technician to regulate the pressure, discharge time, and recharge time with great precision to obtain the ideal flow rate. A water level meter is used to measure the draw-down in the well, so that the technician knows when the flow rate is lower than the recharge rate of the well.
By utilizing the newly purchased Hanna HI98194 Multiparameter Water Quality Meter and Flow Through Cell, our technicians are able to collect continuous groundwater readings (pH, Temperature, Conductivity, Oxygen Reduction Potential (ORP), Dissolved Oxygen (DO), and Total Dissolved Solids (TDS)) during the purging of the well. Stable groundwater readings indicate that the pump is collecting fresh water from the aquifer and that a sample can be collected. Once samples are collected, the technician can remove the pump from the well, decontaminate the pump, then replace the disposable bladder and tubing to collect samples from the next well without causing cross-contamination.
Low-Flow groundwater sampling is just one of many sampling techniques Patriot utilizes to keep our environment safe and service our clients.