Field Maintenance

It is important to collect simultaneous data at swap out. This is also known as adjacent measurements.

Before retrieving one instrument and replacing it with another, you must confirm that the sondes are in agreement. In particular, has the in situ sonde been affected by biofouling?

To check:

• Position the replacement sonde at the same depth in the water as the installed sonde and leave both in place through one reading. Note: With optical DO sensors, you can read the sondes in real-time.
• Check data. Are they out of the ordinary?
• If yes, pull sonde out of installation pipe and place it in a 5-gallon bucket of site water next to the replacement sonde.
• Take another reading; do these agree?
• Data are in agreement if they do not differ by more than:
  

  Temperature	+/-0.3 degrees C
  pH	+/-0.5
  Conductivity	+/-15%
  Dissolved oxygen	+/-0.5 mg/L
  Turbidity	+/-3% or 3 NTU (which ever is greater)
  Chlorophyll	+/- 20%
  Rhodamine WT	20% or 5 ug/L (which ever is greater)

To troubleshoot:

• If readings are not in agreement, pull out sonde and look for biofouling on the sensor guard or wipers or organisms in the conductivity cell.
  Note: We strongly recommended that you take photos of the sensors and guard at the end of each deployment. This data is very valuable when investigating unusual or unexpected data.
• If fouled, clean sensors using site water. Note all visual observations in meta data.
• Put both sondes in bucket and continue readings.
• The data collected before cleaning is called the "fouling drift." Conduct post-calibration in standards to determine what, if any, sensor drift occurred. This should take place in the controlled conditions of the lab.

Check Monitoring Platform

• To check the integrity of the installation pipe, deploy a second sonde outside the tube and at the same depth.
• Compare data from the two sondes. If the pipe is fouled, the data will not agree. The sonde inside will record only the microenvironment of the pipe, not the water itself.

• To clean the pipe, use a chimney brush to scrub the inner and outer surfaces. It may be necessary to find a brush designed for a stove pipe. Or you can trim the diameter of a regular chimney brush to fit in a 4-inch pipe. Allow at least 5 minutes after cleaning for the water in the pipe to fully exchange.