• What happened? What is Total Organic Carbon or TOC?


TOC is a result of decaying organic matter on the watershed.  High levels of precipitation last year resulted in consistently high water levels at the reservoir which increased the flow of decaying organic matter such as leaves into the Beaver Run Reservoir. Consistent rain caused the reservoir to overflow more often than normal, pulling the decaying organic materials towards the treatment plant’s intake, instead of allowing them to settle as they usually do.

  • Why were customers not told immediately?

             Because there is no health risk involved with TOC, public notification may take up to 30 days from review of lab results with regulators and up to 60 days from that review for our interconnected systems such as Monroeville, Plum, Gilpin and Parks Twp.  This violation is                 considered a Tier 2 violation under the regulation and the number of days MAWC is given for notification is specified in that regulation.  If it had been a Tier 1 violation then you would have been notified within 24 hours.

             MAWC put out our notifications as soon as possible after all required reviews and consultations were completed.

  • What are the health risks associated with TOC? 

There are no health risks associated with Total Organic Carbon (TOC). In a recent news report, Lauren Fraley, spokeswoman for the state’s Department of Environment Protection (PADEP) office in Pittsburgh, confirmed that excess Total Organic Carbon (TOC) levels cause no health effects.

  • If there are no health risks why then does this notice mention contacting my doctor and adverse health effects to liver, kidneys, etc.?

MAWC is required by the regulations to use certain statements.  This notice is reviewed and approved by the PADEP before we may release it and those statements are required to be included.  Those statements are concerning the levels of TTHMs and HAA5s in the water.  These levels are no concern with MAWC water, the water meets all regulations for these compounds.

  • So where is the TOC level in the water now and what are you doing to prevent this from occurring again?

TOC levels have been below 2.0 mg/l since December 2018 and the most recent sample result for TOC was 1.56 mg/l.   2.0 mg/l is the compliance level for TOC in drinking water that MAWC must meet for its annual average.

What remains to reach compliance is meeting the Running Annual Average (RAA), which is how the compliance level is calculated by state regulators.  MAWC must be below 1.95 mg/l with its RAA after the results from the 2nd quarter testing which will be completed in June 2019 in order to meet compliance.  Because the regulations require us to round up, the result must be below 1.95 mg/l to be below the 2.0 mg/l. 

MAWC uses Granular Activated Carbon (GAC) filtration for primary removal of TOC in the water supply.  This is considered one of the best available technologies for TOC removal in the drinking water industry.  GAC must be replaced on a specific schedule based on the incoming water.  For MAWC this historically has been 48 months and has worked very well.  MAWC began the process in June 2018 to replace the GAC in our filters and is expected to done with all the filters in August 2019.  With this new GAC we will continue to monitor it for TOC removal and step up our replacement schedule if necessary.

              You may wish to refer to the Trib story, Carbon issues resolved with Municipal Authority of Westmoreland County drinking water for further information.


  • Please do not hesitate to contact MAWC at 724-755-5800 with any further questions.