Running Annual Average (RAA)

A Running Annual Average (RAA) is the average of the most recent four consecutive calendar-quarter monitoring results for a given contaminant, used to determine compliance with certain drinking water maximum contaminant levels (MCLs).

Where you'll see it on a CCR

CCRs for systems that monitored under the Stage 1 Disinfectants and Disinfection Byproducts Rule (Stage 1 D/DBPR) report total trihalomethanes (TTHM) and haloacetic acids (HAA5) as system-wide RAA values. You'll typically find these in the detected contaminants table alongside the MCL, the measured level, and the likely source. The MCL for TTHM under Stage 1 D/DBPR is 80 µg/L; for HAA5, it's 60 µg/L. If the system-wide RAA for either contaminant exceeds its MCL, the system is out of compliance and must notify customers.

Note that Stage 2 D/DBPR, which applies to most systems today, replaced the system-wide RAA with the Locational RAA (LRAA) — meaning each individual monitoring location must independently comply, not just the system average. If your CCR was produced under Stage 2, you'll see LRAA values rather than a single system-wide RAA. See the disinfection byproducts page for more on how TTHM and HAA5 are regulated.

How RAA is calculated

Sum the four most recent consecutive calendar-quarter results and divide by four. The rolling nature means the oldest quarter drops off each time a new result is added.

Worked example — TTHM system-wide RAA:

| Quarter | Result (µg/L) | |---------|--------------| | Q1 | 75 | | Q2 | 82 | | Q3 | 78 | | Q4 | 84 |

RAA = (75 + 82 + 78 + 84) / 4 = 79.75 µg/L

That result falls below the Stage 1 D/DBPR TTHM MCL of 80 µg/L, so this system is in compliance for this compliance period — but only by 0.25 µg/L. A utility seeing numbers this close to the MCL would typically investigate distribution system conditions rather than wait for the next quarter.

Related terms

Citations