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04ARCADIS Field equipment are calibrated prior to use in the field as appropriate. The calibration procedures follow standard manufacturers' instructions to ensure that the equipment is functioning within established tolerances and as required by the project. A record of field calibration of analytical instruments is maintained in the calibration logbook by field personnel. Copies of the instrument manuals and other equipment calibration records (e.g., thermometers, sounders) are maintained. Any notes on unusual results, changing of standards, battery charging, and operation and maintenance of the field equipment are included in the calibration logbook. All instruments are stored, transported, and handled with care to preserve equipment accuracy. Damaged instruments will be taken out of service immediately and not used again until a qualified technician repairs and recalibrates the instruments. Calibration Procedures Equipment calibration is performed in accordance with the manufacturer's instructions, and calibration checks are performed each day prior to the start of work. Calibration of rental equipment will be performed by a qualified technician prior to shipment of the equipment. Calibration standards are used once. Spent calibration liquids are placed in plastic bottles and transported off-site for disposal. A brief summary of the calibration procedures for field measurement equipment is provided below: • pH.. Calibration for pH is performed prior to commencement of sampling activities, using standard buffer solutions having pH values of 4, 7, and 10. Calibration checks for pH values using buffer solutions of 4, 7, and 10 is performed daily. If the reading varies more than 0.10 of a unit between calibration checks, the meter will be recalibrated. • Conductivity: Calibration for conductivity is performed prior to commencement of sampling activities, using potassium chloride (KCI) standard solutions with conductivity values of 1,000 and 10,000 microsiemens/cm. The meter must read within one percent of full-scale to be considered calibrated. A calibration check for conductivity is performed daily. • Turbidity Meter: Turbidity range calibration is performed prior to initiation of sampling activities, using turbidity gel standards of 0, 4.4, 45, and 483 NTUs. The meter is also checked daily during the sampling period with the standard most representative of the anticipated turbidity of the purged groundwater (typically 0 NTUs to 10 NTUs). If the reading varies by more than one unit between calibration checks, the meter will be recalibrated. Multiple physical conditions can cause variations in readings, including bubbles in the sampled water, wet or dirty sample containers, a wet or dirty lens, a wet or dirty optical sensor, or leakage of incidental light into the sample chamber. • Multiple Sensor Meter (pH, Dissolved Oxygen, Conductivity, Temperature, Turbidity: A multiple sensor meter may be used for multiple parameter measurements during sampling. Calibration is performed prior to initiation of sampling activities, using manufacturer auto- calibration solution. If any of the readings are outside of the manufacturers specifications, the meter will be recalibrated for the parameter outside of the calibration range. Calibration checks are performed daily. Equipment not listed herein will be calibrated according to manufacturers' recommendations and/or generally accepted practice. Calibration procedures will be documented for the project