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PROCEDURE • Upon arrival at the well site,visually inspect integrity of wells including condition of well casing,well vaults,grout pad and grout seal.Set up and organize the purging and sampling equipment. • Don appropriate PPE.Open well. Measure the depth-to water using an electronic probe. Record any obstructions encountered on the Groundwater Sampling Form. Equipment Calibration Prior to monitoring well purging,the monitoring equipment used to measure pH,DO,turbidity, ORP, and specific conductance should be calibrated or checked according to manufacturer's directions. The pH meter calibration should bracket the pH range of the wells to be sampled (acidic to neutral pH range {4.00 to 7.001 or neutral to basic pH range {7.00 to 10.00}. The DO meter should be calibrated to one point air saturated water. ORP should be calibrated against a known standard,such as a Zobell solution. The instrument should display a millivolt(mv)value that falls within the range set by the manufacturer. The SC meter is calibrated with a known standard,typical standards are 1.0, 10.0,and 50.0 millimhos per centimeter at 25° Celsius. Conventional/Modified Well Purging It is necessary to purge a sufficient volume of the stagnant water from the well casing to ensure that a representative sample of formation water is obtained. The volume of water to be purged is typically 3 well volumes. Monitoring of water quality parameters of the purge water b used to determine when a representative sample can be collected. During purging,the parameters, tem?erature,pH, and specific conductance,are measured every 3-5 minutes. The groundwater sample is collected when these ground-water quality parameters have stabilized. Parameter stabilization is defined as three successive readings with units of: Temperature:. +\-0.5° Celcius PH: +1-0.2 Specific Conductance: +1- 10% If groundwater hasn't stabilized,to the above criteria, after 3 well volumes,2 additional well volumes shall be purged from the well,prior to sample collection. Monitoring well purging will be considered complete after 5 well volumes have been removed from the well. All purge volumes and final water quality parameter readings should be recorded on Groundwater Sampling Logs. Monitoring wells with a designated"Modified"well sampling technique are generally screened within fine-grained units and are low yielding wells. These select wells should be purged accordingly: gw sampling.SOP Page 2 of 5 February 2005