Assessments to Find and Fix Causes of Microbial Contamination in a Public Water System

Public water systems (PWSs) are required under the Revised Total Coliform Rule (RTCR) to perform water quality sampling for bacteria called total coliform. Learn more about the rule and related requirements on the Public Water System Compliance with the Revised Total Coliform Rule page. A PWS that repeatedly receives sample results showing total coliforms are confirmed present or has E. coli maximum contaminant level (MCL) violations is required to complete assessments that will identify pathways of microbial contamination into the water system. The assessments identify causes of contamination and corrective actions to address the causes. Assessments come in two types, Level 1 and Level 2.

Level 1 Assessments

Level 1 assessments (L1As) are triggered for PWSs that are collecting fewer than 40 samples per month when two or more routine and/or repeat sample results show total coliforms are present in the same month. For PWSs collecting 40 or more samples each month, a L1A is triggered when greater than 5% of routine and/or repeat samples show total coliforms are present. L1As are also triggered if a PWS fails to take required repeat sample(s) after any single sample result shows total coliforms are present.

If a L1A is triggered, the PWS must notify RIDOH by the end of the day on which the PWS learns of the L1A trigger. Call the office at 401-222-6867 or email DOH.RIDWQ@health.ri.gov with a subject line including “L1A trigger,” the name of PWS, and the PWS ID number.

RIDOH will prepare a L1A trigger letter with directions for the PWS. L1As must be performed by the PWS or a knowledgeable third party within 10 calendar days of the date on the trigger letter from RIDOH. Free technical assistance is available upon request from RIDOH. RIDOH developed a L1A form workbook to ensure a thorough inspection of the PWS is conducted. The L1A form workbook is available in Microsoft Excel and PDF formats.

Level 2 Assessments

Level 2 Assessments (L2As) must be completed when a second L1A is triggered within a rolling 12-month period or by an E. coli MCL violation. For more information about the conditions that trigger an E. coli MCL violation and a L2A as well as the immediate steps to take, see Required Boil Water Advisory (Confirmed E. coli or E. coli in Non-4-Log Well). If a L2A is triggered, the PWS must notify RIDOH by the end of the day on which the PWS learns of the trigger. Call the office at 401-222-6867 or email DOH.RIDWQ@health.ri.gov with a subject line including “L2A trigger,” name of PWS, and PWS ID number.

L2As are conducted by State-certified Level 2 Assessors or by RIDOH, DWQ personnel within 30 calendar days of the sampling event that triggered the assessment. The L2A form workbook must be completed during the assessment by the personnel conducting the L2A. The L2A form workbook is available to download in Microsoft Excel and PDF versions below.