Figure: 30 TAC §290.115(c)(2)

Routine Stage 2 Monitoring Frequency and Number of Sites
Water Type Retail Population Routine Frequency1 Routine Number of Sites5
Surface Water
(or Groundwater
Under the Direct
Influence of
Surface Water)2		 fewer than 500 annual 1 or 23
500 to 3,300 quarterly 1 or 23
3,301 to 9,999 quarterly4 2
10,000 to 49,999 quarterly4 4
50,000 to 249,999 quarterly4 8
250,000 to 999,999 quarterly4 12
1,000,000 to 4,999,999 quarterly4 16
5,000,000 or more quarterly4 20
Groundwater fewer than 500 annual 1 or 23
500 to 9,999 annual 2
10,000 to 99,999 quarterly4 4
100,000 to 499,999 quarterly4 6
500,000 or more quarterly4 8

1All systems must monitor during month of highest disinfection byproduct concentrations.

2A system that uses any treated surface water or groundwater under the direct influence of surface water shall be considered a surface water system for purposes of this section.

3Systems serving fewer than 500 people and surface water systems serving 500 to 3,300 people must identify two sample sites in accordance with 40 Code of Federal Regulations §141.605(b) and may sample at a single site if the highest total trihalomethanes (TTHM) and haloacetic acids (group of five) (HAA5) concentrations occur at the same time and place. If highest TTHM and HAA5 concentrations occur at the same time and location, one dual sample set must be collected at that location. If highest TTHM and HAA5 concentrations occur at different locations, then a single TTHM sample must be collected at the location with higher historical TTHM, and a single HAA5 sample must be collected at the location with higher historical HAA5.

4Systems on quarterly monitoring must take dual sample sets every 90 days.

5Monitoring locations must be approved by the executive director.