Fourth Unregulated Contaminant Monitoring Rule

The Safe Drinking Water Act (SDWA) requires that once every five years the EPA issue a list of unregulated contaminants to be monitored by public water systems (PWSs).

The fourth Unregulated Contaminant Monitoring Rule (UCMR 4) was published on December 20, 2016. UCMR 4 required monitoring for 30 chemical contaminants between 2018 and 2020 using analytical methods developed by the EPA and consensus organizations. This monitoring provides a basis for future actions to protect public health.

• Federal Register Notice: Final - Revisions to the Unregulated Contaminant Monitoring Rule (UCMR 4) for Public Water Systems and Announcement of a Public Meeting
• UCMR 4 Basic Information Fact Sheet

UCMR 4 Scope, Analytical Methods, and Contaminants

Assessment Monitoring (AM)

PWSs monitored for 10 cyanotoxins during a 4-consecutive month period from March 2018 through November 2020. PWSs monitored for 20 additional contaminants during a 12-month period from January 2018 through December 2020. The EPA paid all analytical costs associated with monitoring at PWSs serving 10,000 or fewer people. See table below for the monitoring design.

• UCMR 4 Fact Sheet for Assessment Monitoring - Cyanotoxins
• UCMR 4 Fact Sheet for Assessment Monitoring - Haloacetic Acid (HAA)
• UCMR 4 Fact Sheet for Assessment Monitoring - Additional Contaminants

Table 1. Monitoring Design

Table 2. Contaminants, Minimum Reporting Levels, Sampling Locations, and Analytical Methods

Table 3. Indicators

Notes

1. Chemical Abstracts Service Registry Number (CASRN), Not Available (NA)
2. The EPA-established UCMR Minimum Reporting Level (MRL) is the lowest concentration that laboratories may report to the EPA during UCMR monitoring. UCMR MRLs are determined using data from multiple laboratories that participate in the EPA’s MRL-setting studies and are not associated with contaminant health effects information. More specifically, an MRL is the quantitation limit for a contaminant that is considered achievable, with 95% confidence, by at least 75% of laboratories nationwide using a specified analytical method (recognizing that individual laboratories may be able to measure at lower levels).
3. Sample Point Locations
   1. Entry point to the distribution system (EP)
   2. Stage 2 Disinfectants and Disinfection Byproducts Rule Locations (D/DBPR)
      1. Distribution system (DS)
      2. Source water (untreated water) (SR)
4. Regulated HAAs (HAA5) were included in the monitoring program to gain a better understanding of co-occurrence with unregulated disinfection byproducts.
   1. HAA5 includes: dibromoacetic acid, dichloroacetic acid, monobromoacetic acid, monochloroacetic acid, trichloroacetic acid.
   2. HAA6Br includes: bromochloroacetic acid, bromodichloroacetic acid, dibromoacetic acid, dibromochloroacetic acid, monobromoacetic acid, tribromoacetic acid.
   3. HAA9 includes: bromochloroacetic acid, bromodichloroacetic acid, chlorodibromoacetic acid, dibromoacetic acid, dichloroacetic acid, monobromoacetic acid, monochloroacetic acid, tribromoacetic acid, trichloroacetic acid. 
5. TOC and bromide samples were required to be collected at the same time as HAA samples. These “indicator” samples were collected at a single source water intake using methods already approved for compliance monitoring.
6. EPA Analytical Methods
   1. EPA 200.8
   2. EPA 525.3
   3. EPA 530
   4. EPA 541
   5. EPA 544
   6. EPA 545
   7. EPA 546
   8. EPA 552.3
   9. EPA 557
   10. EPA 415.3 (Rev. 1.1 or 1.2)
   11. EPA 300.0 (Rev. 2.1) or EPA 300.1 (Rev. 1.0)

Microcystin Phased Sample Analysis

PWSs that used surface water (SW) or ground water under the direct influence of surface water (GWUDI) collected three samples at the entry point to the distribution system (EP) for cyanotoxins. One sample was collected for total microcystins analysis by EPA Method 546 (Adda ELISA), the second for potential microcystin analysis by EPA Method 544, and the third for cylindrospermopsin and anatoxin-a analysis by EPA Method 545.

• If the Adda ELISA result was less than 0.3 micrograms per liter (µg/L) (i.e., the reporting limit for total microcystins), then the sample collected for Method 544 was not analyzed for that sample event, and only the Adda ELISA result was reported to the EPA.
• If the ELISA result was greater than or equal to 0.3 µg/L, the result was reported to the EPA and the EPA Method 544 sample was analyzed to identify and quantify the six specific microcystin congeners and nodularin-R.
• Cylindrospermopsin and anatoxin-a were analyzed by EPA Method 545 for all sample events.