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<br />Field equipment are calibrated prior to use in the field as appropriate. The calibration procedures <br />follow standard manufacturers' instructions to ensure that the equipment is functioning within <br />established tolerances and as required by the project. A record of field calibration of analytical <br />instruments is maintained in the calibration logbook by field personnel. Copies of the instrument <br />manuals and other equipment calibration records (e.g., thermometers, sounders) are maintained. <br />Any notes on unusual results, changing of standards, battery charging, and operation and <br />maintenance of the field equipment are included in the calibration logbook. <br />All instruments are stored, transported, and handled with care to preserve equipment accuracy. <br />Damaged instruments will be taken out of service immediately and not used again until a <br />qualified technician repairs and recalibrates the instruments. <br />Calibration Procedures <br />Equipment calibration is performed in accordance with the manufacturer's instructions, and <br />calibration checks are performed each day prior to the start of work. Calibration of rental <br />equipment will be performed by a qualified technician prior to shipment of the equipment. <br />Calibration standards are used once. Spent calibration liquids are placed in plastic bottles and <br />transported off-site for disposal. A brief summary of the calibration procedures for field <br />measurement equipment is provided below: <br />• pH: Calibration for pH is performed prior to commencement of sampling activities, using <br />standard buffer solutions having pH values of 4, 7, and 10. Calibration checks for pH values <br />using buffer solutions of 4, 7, and 10 is performed daily. If the reading varies more than 0.10 <br />of a unit between calibration checks, the meter will be recalibrated. <br />• Conductivity: Calibration for conductivity is performed prior to commencement of sampling <br />activities, using potassium chloride (KCl) standard solutions with conductivity values of 1,000 <br />and 10,000 microsiemens/cm. The meter must read within one percent of full-scale to be <br />considered calibrated. A calibration check for conductivity is performed daily. <br />• Turbidity Meter: Turbidity range calibration is performed prior to initiation of sampling <br />activities, using turbidity gel standards of 0, 4.4, 45, and 483 NTUs. The meter is also <br />checked daily during the sampling period with the standard most representative of the <br />anticipated turbidity of the purged groundwater (typically 0 NTUs to 10 NTUs). If the <br />reading varies by more than one unit between calibration checks, the meter will be <br />recalibrated. Multiple physical conditions can cause variations in readings, including <br />bubbles in the sampled water, wet or dirty sample containers, a wet or dirty lens, a wet <br />or dirty optical sensor, or leakage of incidental light into the sample chamber. <br />• Multiple Sensor Meter (pH, Dissolved Oxygen, Conductivity, Temperature, Turbidity): A <br />multiple sensor meter may be used for multiple parameter measurements during sampling. <br />Calibration is performed prior to initiation of sampling activities, using manufacturer auto- <br />calibration solution. If any of the readings are outside of the manufacturers specifications, <br />the meter will be recalibrated for the parameter outside of the calibration range. Calibration <br />checks are performed daily. <br />Equipment not listed herein will be calibrated according to manufacturers' recommendations <br />and/or generally accepted practice. Calibration procedures will be documented for the project