Monitoring Requirements for Disinfection Byproduct Precursors

Source

Type

System Type

Filtration

Type

Sampling location at each plant

Routine

Reduced¹

Monitoring requirements

Frequency²

Running annual

average

TOC

results

Frequency

Surface water

and

GWUDI

Community and NTNC

Conventional

Combined

Filter effluent³

TOC⁴

Monthly

<2.0 mg/L for two consecutive years or

<1.0 mg/L for one year

1 TOC

(paired) per plant/quarter

Raw

TOC⁴

Monthly

Alkalinity

Monthly

All other types

Raw

TOC

Monthly

≤4.0 mg/L

1 TOC

quarterly

¹Routine monitoring shall begin in the month following the quarter when the running annual average TOC in treated water is ≥2.0 mg/L for systems using conventional filtration and/or >4.0 mg/L in source water.

² TOC monitoring for disinfection precursors for both treated and source water shall be collected at the same time. These samples (source water and treated water) are referred to as paired samples

³Samples collected for TOC shall be collected no further downstream than point of combined filter effluent turbidity monitoring and representative of treated water.

⁴Systems shall take one paired TOC sample and one source water alkalinity sample per month per plant at a time representative of normal operating conditions and influent water quality. The alkalinity sample shall be collected at the same time as the source water TOC sample.