Locational Running Annual Average (LRAA)

A Locational Running Annual Average is the average of the four most recent consecutive calendar-quarter monitoring results collected at a single, fixed sampling site in your distribution system.

Where you'll see it on a CCR

Systems regulated under the Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 D/DBPR) must report their highest LRAA for total trihalomethanes (TTHMs) and haloacetic acids (HAA5) in the CCR. The reported value represents the worst-performing monitoring location — not a blend of results across the whole system. If your system has six monitoring sites, the CCR shows the site with the highest running average, because that is the site driving compliance.

The MCLs are 80 µg/L for TTHMs and 60 µg/L for HAA5. Each individual location must stay below these limits; exceeding the MCL at even one site constitutes a violation regardless of how well the rest of the system performs.

How LRAA differs from RAA

Before Stage 2 D/DBPR, systems calculated a single system-wide Running Annual Average (RAA) by averaging results across all monitoring locations. A site with elevated TTHM or HAA5 levels could be masked by lower readings elsewhere, so the system-average fell below the MCL even while some customers received water consistently above it.

Stage 2 D/DBPR replaced the system-wide RAA with the LRAA specifically to close that gap. Under the LRAA standard, every monitoring location must individually comply. Published at 71 FR 388 (Jan. 4, 2006) and codified at 40 CFR § 141.620, the rule phased in compliance starting in 2012 for the largest systems.

Related terms

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