Wisconsin Department of Natural Resources
Waste & Materials Management GEMS on the Web (GOTW) Public Access
Potential limitations of GEMS data you should know about!
Despite the DNR's best efforts to provide accurate data, there may be errors and omissions. There may also be delays in adding new data or correcting older data that is found to be incorrect or incomplete.

Listed below are steps in groundwater monitoring data collection and analysis at which data accuracy could be compromised.

  • Sample collection: groundwater samples may not have been collected and preserved properly in the field according to standard protocols.

  • Sample storage: samples collected in the field may not have been stored properly according to standard protocol prior to and during shipment to laboratories for analysis.

  • Sample analysis: samples may not have been analyzed properly for contaminants in the laboratory according to standard laboratory methodologies.

  • Data transcription and loading: in the course of transmitting data from laboratories and various intermediaries, including consultants and municipal officials, to the DNR, data may be inadvertently lost, omitted, or uploaded to the GEMS database incorrectly (Prior to 1996, many sites submitted data on paper forms with increased risk of transcription error. Therefore, older data is more likely to contain transcription errors).
The facility or lab representative or consultant that submits environmental monitoring data to the DNR must sign a certification form stating that to the best of their knowledge the data is correct. Nevertheless, it is not possible to prevent all errors. It is very important that the user not make conclusions based on limited information, such as one piece of data from one monitoring point. Instead, the data as a whole should be evaluated by a scientist who is experienced with such evaluations and considers changes over time and takes into account the location of each monitoring point as well as the natural variability of water quality. Data that appears to be elevated may be caused by naturally occurring substances or by a contaminant source other than the facility being monitored.