Laserfiche WebLink
SOP for Operation and Calibration of Field Water Quality Instruments 4 <br />13. The salinity of the water samples is now on the screen. Depending on the project, adjust the salinity to <br />the correct measurement for the individual station to be monitored. All salinity measurements will be <br />listed in the fieldbook for reference prior to measurement of the station. <br />14. The calibrated % saturation value is now on the screen and the small CAL is no longer visible in the <br />lower left corner. <br />15. Toggle between mg/L and % saturation, by pressing the MODE key, to get the dissolved oxygen value <br />in mg/L. <br />16. Record this value in the calibration log under Post - Calibration DO. <br />17. Press the green button to turn the meter off. The meter must be recalibrated each time it is turned on <br />(i.e., at each station). Alternatively, it is acceptable to calibrate in the morning and leave the meter on <br />until the last reading of the day is completed, then turn the meter off at the end of the day. (Refer to <br />the project QAPP to determine whether the meter must be calibrated once per day, twice per day, or at <br />each sample station.) <br />3.4.2 Maintenance Considerations <br />1. Do not let sponge dry out. Keep sponge moist by re- wetting at least weekly. <br />2. A probe may look intact, however the membrane might still be defective. If the instrument will not <br />calibrate properly, replace the membrane. <br />3. If you need to replace the membrane, ensure that membrane housing has been filled with KCL fluid <br />for at least 12 hours before first use. <br />3.4.3 Field Operation <br />DO meters provide the most representative readings when measurements are collect in -situ (for surface <br />water sampling) or in a flow- through cell (for groundwater sampling). A 5- gallon bucket can approximate <br />a flow- through cell when sampling groundwater if the discharge hose from the sampling pump is placed <br />toward the bottom of the bucket and the DO meter is suspended in the bucket, adjacent to the discharge <br />hose. <br />Prior to field use, examine the probe membrane to make sure it is intact and the probe salts have not leaked. If <br />there are air bubbles or any other obvious defects in the membrane, replace it according to the manufacturer's <br />instructions. <br />3.4.3.1 Measuring Dissolved Oxygen in Groundwater <br />To measure DO in groundwater: <br />1. Calibrate the meter at the sampling station (well site). <br />2. Turn on the meter and allow 15 minutes of warm up time before calibration. <br />3. Ensure that the sponge inside the probe chamber is moist. <br />4. Immerse probe -end of meter into sample. In order to get accurate DO readings, water must flow past <br />the probe (or the probe must be stirred in the water); however, it is critical that the water sample is not <br />effervesced. A 5- gallon bucket can serve as a type of flow - through cell for pumped wells, or small <br />cubitainer with zero headspace works for bailed wells. <br />5. Allow time for meter to stabilize (to t0.1 ppm). <br />6. Record values of DO in ppm, DO in %, and water temperature in the fieldbook. <br />7. Rinse probe with distilled or deionized water after each use, and replace in the probe chamber. <br />3.4.3.2 Measuring Dissolved Oxygen in Sur ace Water <br />To measure DO in a stream: <br />1. Calibrate the meter at the sampling station (surface water station). <br />4153A.140129 Whetstone Associates <br />