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r BCR & Associates. Ltd. Rev 01 12183 r Standard Procedure 5 Purging and Sampling Groundwater Monitoring Wells r See Site Health and Safety and Equipment Decontamination )&gll Purging The purpose of well purging is to remove stagnant water from the well casing and to provide representative formation water for laboratory analysis. In theory, one WELL BORE volume should suffice for this purpose. In practice, it is difficult to instantaneously evacuate one such volume and replace it completely with formation water without mixing stagnant and fresh formation water. Since well water is removed during purging gradually over time, the measurement of CASING r volummes and specific parameters has become the "industry" standard for determining valid purging. Typically, the well is purged until temperature, specific conductance and pH have "stabilized." The well will be purged with a decontaminated bailer. Purge water will be temporarily lawfully stored in accordance with specific site procedures; typically 55-gallon DOT-17H drums are used for this purpose. The purge water is monitored for specific conductance, temperature and pH. The unit will be calibrated on site for pH, and temperature, and will be adjusted on site to match well water temperature. Typical units are factory conductance calibrated. Where temperature fluctuates rapidly due to the differential between formation water temperature and ambient atmospheric, this condition will be recorded. Initial cloudy water will be monitored and recorded once each casing volume. Purging will continue until the water clears and three successive bailers indicate pH units within one standard unit (i.e. 1110) and specific conductance is within 1 %. r Temperature stabilization often cannot be determined accurately, as noted above. The readings are measured and recorded in the Monitoring Well Purge and Sample Field Form, and samples collected. Law-Yield Formations r Where formation yield is low, the well may be bailed dry. The duration of bailing, and the quantity of water removed is recorded. The well may be sampled when the water level in the well has recovered to 85% of the static level. r�