Scope of the SMC’s chemistry laboratory intercalibration study

The SMC’s chemistry laboratory intercalibration exercise, launched in fall 2021, is designed to help laboratories that conduct chemistry analyses of runoff samples improve their ability to collect consistent, high-quality data.

The intercalibration is divided into three rounds; the first round was completed in spring 2022 and the other two rounds are scheduled to begin in fall 2022 and fall 2023, respectively.

During each round, all participating laboratories are sent wet-weather samples, dry-weather samples and reference samples, then asked to measure a range of contaminants that fall into three major chemical classes:

  • General analytes: Total suspended solids, hardness, silica, chloride, sulfate, ammonia, nitrate+nitrite, total nitrogen, ortho-phosphorus, total phosphorus
  • Metals: Arsenic, cadmium, chromium, copper, lead, nickel, selenium, zinc
  • Organics:  DDTs, chlordanes, PCBs, pyrethroids (8 compounds), and the 16 USEPA Priority PAHs (not part of Round 1, but scheduled for Rounds 2 and 3)

Laboratories are not required to measure every contaminant; rather, they are encouraged to measure as many of the contaminants as they subsequently intend to bid on contracts to perform for the SMC and its member agencies. Laboratories also may use whatever analysis methods they typically use.

The SMC’s intercalibrations are a type of intercalibration known as performance-based quality assurance. With performance-based quality assurance, limits are set for sensitivity (i.e., detection limits), accuracy relative to a known concentration (i.e., custom-designed reference materials), and precision (i.e., comparison to other laboratories). Letter grades of A through F are assigned based on combined scores for all three of the performance-based criteria across multiple samples.

The SMC is actively recruiting additional laboratories to join the SMC’s chemistry laboratory intercalibration; laboratories that did not participate in the first round are still eligible and encouraged to join the second and third rounds.