River & stream data quality assurance

Our river and stream scientists follow strict protocols to ensure credible and defensible data is gathered about freshwater quality across the state. We follow the Quality Assurance Monitoring Plan and Standard Operating Procedures for ambient freshwater monitoring. These procedures include frequent calibration of meters and testing duplicate samples to eliminate errors.

The quality of our data is evaluated annually, and data aren't considered final until after this evaluation.

We follow strict data gathering protocols

Collecting samples from a river bank.

Our work relies on sound freshwater data that is used to assess the health of the state's waterbodies. Data help us to identify trends and serve as the foundation for federal water quality 303(d) listings and subsequent water-cleanup investigations. Our Freshwater Quality Monitoring team follow strict protocols for sampling and processing to assure we produce quality data supporting water quality protection and cleanup across the state.

The Quality Assurance Monitoring Plan (QAMP) and Standard Operating Procedures are linked below.

Meters are calibrated frequently

We carefully calibrate the conductivity and pH meters we use in the field. We also check to assure that meter readings are within state standards twice daily. Modified Winkler titrations are used to measure dissolved oxygen.

Quality is assured by duplicate samples

Field laboratory
We always collect duplicate samples during each sampling trip, and duplicates are split in both the field and the lab, as additional quality control.

To take into account total variation, we collect a second set of samples at one randomly-chosen station during each sampling trip. This tests the sum of all variations, or total variability, including short-term instream variability. The second sample set is split in the field to assess variability due to lab and field processing, plus analytical variability. One of these splits is split again at the lab to assess lab and analytical variability.

Some data-quality evaluations occur during data entry, and any anomalies are confirmed with the lab. Preliminary data have undergone this level of review.

Overall data quality is evaluated annually against requirements specified in our Quality Assurance Monitoring Plan. Data are not considered finalized until after this evaluation.