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SOP-009 Standard Operating Procedure Low-Flow Groundwater Quality and Sample Collection Page 7 of 9 Revision No. 1 April 2019 Sharpe Army Depot • Start the digital controller to begin cycling. This initiates the purge sequence. Water will start to flow from the pump discharge line as the well begins to purge. At this point, test the discharge rate before purging the minimum volume by measuring the rate with a graduated cylinder. The psi or the discharge rate may need to be adjusted to obtain a good flow rate. • Once the flow rate is adjusted, check the water level to be sure there is less than 0.3 foot of drawdown observed. If the drawdown exceeds 0.3 foot, reduce the flow rate to no less than • 100 mL/min. If the minimal drawdown that can be achieved exceeds 0.3 foot but remains stable, document and continue purging. If excessive drawdown continues, contact the Field Task Leader for further instruction. • Once the discharge and psi produce a flow rate that obtains the desired purge rate, record the pump controller settings and purge rate on the well sampling data sheet. • Allow the digital controller to cycle at this rate for as long as necessary to discharge the minimum required purge volume. For example, for a well with a minimum required purge volume of 1,600 mL, purge at 400 mL/min for 4 minutes. • Once the required purge volume is removed, start the hand-held water quality meter to begin collection of parameter readings; monitor readings until stabilization is reached. • Stabilization of each of the low-flow parameters can be monitored as the change in values between the maximum and minimum over the last three readings or can be calculated as the percent difference between the current reading and the third reading back. Purging is considered complete when the pH, temperature, conductivity, ORP, DO, and turbidity have stabilized. The parameters are considered stable when the variation in three successive readings does not exceed: pH: ± 0.1 pH unit Temperature: ± 1 degree Celsius (˚C) Conductivity: ± 3% µmhos/cm ORP: ± 10 Mv DO: ± 0.20 mg/L or ±10% (whichever is greater) Turbidity: ±10% NTU or < 10 NTU • When adequate purging (minimum of pump, tubing, and flow cell volume) has been completed and stabilization (minimum of three readings after minimum purge volume has been removed) has been achieved, press <Accept> on the flow cell/analyzer to stop storing. • If parameter stabilization has not occurred after four minutes, continue purging and collecting readings and contact the Field Task Leader for further instruction. Samples may be collected after a total of 6 readings have been recorded. Record final water quality parameters from