Total Organic Carbon Monitoring

Overview

Find current TOC monitoring schedules here.

Total organic carbon (TOC) is naturally found in water and can react with disinfectants to produce DBPs. Reduction of TOC limits the formation of DBPs. TOC monitoring applies to community and non-transient non-community systems using surface water or groundwater under the direct influence of surface water that add a chemical disinfectant and use conventional filtration (2.5-log) or softening.

NOTE: If seeking a reduction in DBP monitoring, surface water systems using filtration other than conventional filtration must monitor raw TOC only on the schedule below. For systems to remain on reduced DBP monitoring (in addition to meeting other criteria), the source water TOC running annual average must be ≤ 4.0 mg/L, based on the most recent four quarters of monitoring, on a continuing basis at a location prior to any treatment.

Monitoring Schedule for Surface Systems with
Conventional Treatment Plants (2.5-log) Only

Note: Water systems are eligible for reduced monitoring frequency when the average filtered TOC is < 1.0 mg/l for 1 year or < 2.0 mg/l for 2 years. Sampling for both raw and filtered water TOC should occur on the same day.
Parameter	Routine Monitoring	Reduced Monitoring
Raw water TOC	1 Sample per month	1 Sample per quarter
Filtered water TOC	1 Sample per month	1 Sample per quarter
Raw water alkalinity	1 Sample per month	1 Sample per quarter

Sample Sites
Raw water TOC samples must be collected from the source prior to any chemical addition or filtration. Filtered water TOC samples must be collected from the combined filter effluent prior to chlorination.

Example:

Enhanced Coagulation and Enhanced Softening

Minimum Treatment Technique Required (Equivalent to Maximum Contaminant Level)
The Minimum Treatment Technique Required is based on whether enhanced coagulation is required and on a ratio of the percent of TOC actually removed to the percent of TOC that should have been removed.

The running annual average of ratios must be greater than or equal to 1.00 (i.e. the amount of TOC that was actually removed must be equal to or greater than the TOC that should have been removed). A running annual average is the arithmetic average of a year's worth of monthly TOC results and is calculated at the end of every quarter.

Determining Compliance with the Minimum Treatment Technique Required
Compliance is based upon if you need enhanced coagulation. Answer the following six questions in the order that they are listed to determine if you need enhanced coagulation. (If you answer any of the questions with "Yes", you do not need to answer the rest of the questions).


If you answered "Yes" to any of the previous six questions, you are qualified to opt out of enhanced coagulation and you will not need to comply with the Minimum Treatment Technique Requirements (i.e. you do not need to use the Minimum Treatment Technique Requirement Compliance Calculations described below), however, the monitoring requirements still apply and all results must still be submitted to the Drinking Water Program.

If you did not answer "Yes" to any of the six questions, you cannot opt out of enhanced coagulation and compliance is based on a ratio of the percent of TOC actually removed to the percent of TOC that should have been removed. Use the following compliance calculations to determine compliance with the Minimum Treatment Technique Requirement:

Minimum Treatment Technique Requirement Compliance Calculations
In order to achieve compliance, the running annual average of the ratio of the percent of TOC actually removed to the percent of TOC that should have been removed must be greater than or equal to 1.00 (i.e. the amount of TOC that was actually removed must be equal to or greater than the TOC that should have been removed). A running annual average is the arithmetic average of results and is calculated at the end of every quarter.

Where
TOC Actually Removed = TOC concentration (in mg/L) of raw water before filtration divided by the TOC concentration (in mg/L) of the combined filter effluent water.

TOC that should have been removed is based on the raw water TOC and the raw water alkalinity according to the following:

* Systems using enhanced softening must use the TOC removal percentages in this column.
Source Water TOC (mg/L)	Source Water Alkalinity, mg/L as CaCO3
	0 - 60	61 - 120	> 120*
> 2.0 – 4.0	35.0%	25.0%	15.0%
> 4.0 – 8.0	45.0%	35.0%	25.0%
> 8.0	50.0%	40.0%	30.0%

Example: if the raw water alkalinity = 65 mg/L and the raw water TOC = 9.0 mg/L, then the required removal percentage = 40.0%.

Note: It is important to recognize that this percentage can change from month to month depending on the actual raw water TOC and Alkalinity.

Example:

Calculations to Determine Compliance with the Required Removal Ratio of 1.00

Source of Data	Parameter	Results
Raw Water Sampling Data	Source (Raw) Water Alkalinity	65 mg/L
Raw Water Sampling Data	Raw Water TOC	9.0 mg/L
Table of Required Removal Percentages (shown above)	Required Removal Percentage	40.0%
Treated Water Sampling Data	Treated Water TOC	4.0 mg/L
Calculated as Shown	TOC Removed (Raw Water TOC – Treated Water TOC)	9.0 – 4.0 = 5.0 mg/L
Calculated as Shown	Actual Removal Percentage (TOC Removed/Raw Water TOC)	5.0 / 9.0 = 0.556 (or 55.6%)
Calculated as Shown	Calculation of Removal Ratio (Actual Removal Percentage / Required Removal Percentage)	55.6 / 40.0 = 1.39
Calculated as Shown	Ultimate Removal Ratio	1.39 (which is greater than 1.00 therefore, compliance is achieved)