QASAC-Americas

GOOD - Green Hexagon

Measurement is within the interquartile range (IQR), defined as the 25th to 75th percentile or middle half (50%) of the measurements. For example: sulfate, ammonium, sodium, and potassium.

SATISFACTORY - Blue Trapezoid

Measurement is outside the IQR but within the range defined by the median + IQR/1.349. The ratio, IQR/1.349, is the non-parametric estimate of the standard deviation, sometimes called the pseudo-standard deviation. For example: nitrate, chloride, and calcium.

UNSATISFACTORY - Red Triangle

Measurement is outside the range defined by the   median + IQR/1.349. For example: pH, conductivity, and magnesium.

DETECTION LIMIT - Open Circle

Measurement is below the detection limit of the laboratory’s analytical method. For example: fluoride.

Notes:

1. An outward pointing trapezoid or triangle indicates the measurement is high. An inward pointing trapezoid or triangle indicates the measurement is low.
2. A hexagon or trapezoid with cross-hatching (e.g., potassium and chloride) indicates a measurement that meets the GOOD or SATISFACTORY definition but fails the measurement Data Quality Objective (DQO), defined in the Manual for the GAW Precipitation Chemistry Programme (See Table 1.1.)
3. A straight line (e.g., acidity) without a symbol indicates no measurement was reported.

Table 1.1. Precipitation Chemistry
Data Quality Objectives