Fourth Unregulated Contaminant Monitoring Rule

The 1996 Safe Drinking Water Act (SDWA) amendments require that once every five years EPA issue a new list of no more than 30 unregulated contaminants to be monitored by public water systems (PWSs).

The fourth Unregulated Contaminant Monitoring Rule (UCMR 4) was published in the Federal Register on December 20, 2016. UCMR 4 required monitoring for 30 chemical contaminants between 2018 and 2020 using analytical methods developed by 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
• EPA Approved Laboratories for UCMR 4

UCMR 4 scope, analytical methods and contaminants

Assessment Monitoring (List 1 contaminants)

PWSs monitored for 10 List 1 cyanotoxins during a 4-consecutive month period from March 2018 through November 2020. PWSs monitored for 20 List 1 additional contaminants during a 12-month period from January 2018 through December 2020. See table below for the sampling 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 Contaminant

National Sample Assessment Monitoring Design

• EPA paid all analytical costs associated with monitoring at small systems.

Ten Cyanotoxin Chemical Contaminants

Two Metals

Eight Pesticides and One Pesticide Manufacturing Byproduct

Three Brominated Haloacetic Acid (HAA) Groups^3,4

Three Alcohols

Three Other Semivolatile Chemicals

Indicators

Notes

1. Chemical Abstract Service (CAS) Registry Number
2. Sampling Locations
   1. Entry points to the distribution system (EPTDS)
   2. Source Water Intake Locations (SR)
   3. Stage 2 Disinfectants and Disinfection Byproducts Rule Sampling Locations (D/DBPR)
3. 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.
   1. TOC methods included: SM 5310 B, SM 5310 C, SM 5310 D (21st edition), or SM 5310 B-00, SM 5310 C-00, SM 5310 D-00 (SM Online), EPA Method 415.3 (Rev. 1.1 or 1.2).
   2. Bromide methods included: EPA Methods 300.0 (Rev. 2.1), 300.1 (Rev. 1.0), 317.0 (Rev. 2.0), 326.0 (Rev. 1.0) or ASTM D 6581-12.
4. Regulated HAAs (HAA5) were included in the monitoring program to gain a better understanding of co-occurrence with currently 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. 

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 (EPTDS) 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 EPA.
• If the ELISA result was greater than or equal to 0.3 µg/L, the result was reported to EPA and the EPA Method 544 sample was analyzed to identify and quantify the six specific microcystin congeners and nodularin.
• Cylindrospermopsin and anatoxin-a were analyzed by EPA Method 545 for all sample events.