Figure: 30 TAC §290.115(c)(5)(C)(ii)(I)

Number and Type of Initial Distribution System Evaluation (IDSE) Sample Sites¹
Population and water type	Near Entry Points	Average Residence Time	Potential High TTHM Locations	Potential High HAA5 Locations	Total Number of Sites
Population and water type	IDSE Site Type
Systems distributing surface water or groundwater under the direct influence of surface water (GUI)
less than 500 that purchase treated surface water or GUI	1	-	1	-	2
less than 500 with no purchased water source	-	-	1	1	2
500 to 3,300 that purchase treated surface water or GUI	1	-	1	-	2
500 to 3,300 with no purchased water source	-	-	1	1	2
3,301 to 9,999	-	1	2	1	4
10,000 to 49,999	1	2	3	2	8
50,000 to 249,999	3	4	5	4	16
250,000 to 999,999	4	6	8	6	24
1,000,000 to 4,999,999	6	8	10	8	32
5,000,000 or more	8	10	12	10	40
Systems that only use groundwater not under the direct influence of surface water
less than 500 that purchase treated groundwater	1	-	1	-	2
less than 500 with no purchased water source nonconsecutive systems	-	-	1	1	2
500 to 9,999	-	-	1	1	2
10,000 to 99,999	1	1	2	2	6
100,000 to 499,999	1	1	3	3	8
500,000 or more	2	2	4	4	12

¹If the number of entry points to the distribution system is fewer than the specified number of entry point monitoring locations, excess entry point samples must be replaced equally at high TTHM and HAA5 locations. If there is an odd extra location number, the system must take a sample at a high TTHM location. If the number of entry points to the distribution system is more than the specified number of entry point monitoring locations, the system must take samples at entry points to the distribution system having the highest annual water flows.