National Water-Quality Assessment (NAWQA) Program - South Platte River Basin

Quality-Control Samples

In order to interpret water-quality data, quality-control (QC) information is required to properly assess sample collection, processing, and analysis bias. The South Platte NAWQA study set aside approximately 15 percent of all samples collected for quality-control samples.

Three types of QC samples were collected: blanks, replicates, and spikes. Blanks were samples of inorganic- or organic-free water that had been processed through field equipment and sent to the laboratory to test for contamination from either field equipment or laboratory equipment. Replicates were multiple environmental samples (usually splits from the same sample) that had been sent to the laboratory in separate bottles to test analytical precision. Spikes were samples that had been "injected" with known concentrations of selected pesticides to test laboratory recovery of these analytes.

The data from blanks are entered in the data base under the sites at which they were processed. The parameters used to indicate the type of QC sample collected are called the "MEDIUM CODE" and the "SAMPLE TYPE." The medium code for surface-water QC is Q for blanks and R for replicates and spikes; the medium code for groundwater QC samples is Q for blanks and S for replicates and spikes; the medium code for sediment QC samples is W for replicates. The sample type is 1 for spikes, 2 for blanks, and 7 for replicates.

Surface-Water Quality-Control Sites

Groundwater Quality-Control Sites

Bed-Sediment Quality-Control Sites

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