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Oregon EPHT Drinking Water Indicators

Drinking Water Indicator:   MCL violations and mean concentration

Measure : Disinfection byproducts MCL violations and mean concentrations in Community Water Systems in Oregon

 

http://staging.health.oregon.gov/Teamsite/epht/PublishingImages/images/dbppic.PNG Public water may contain microorganisms, such as viruses and bacteria that can cause serious illness (i.e., gastrointestinal disorders or diarrhea) and even death. Public water suppliers disinfect their water to kill these microorganisms. Disinfection byproducts (DBPs) are a family of chemicals formed when these disinfectants react with naturally occurring organic matter and other substances in source water.

 

When people are exposed to disinfection byproducts at high levels for many years, they may develop cancer or problems with their liver, kidneys or circulatory system. There also may be a connection with miscarriages, premature births, low birth weight and birth defects.

Disinfectant byproducts include haloacetic acids (HAA) and trihalomethanes (THM). The maximum allowable contaminant levels are 60 mcg/L for  HAA5 and 80 mcg/L for TTHM. These levels are calculated as running annual averages.   A running annual average is the arithmetic average of results calculated at the end of every quarter for the previous consecutive four-quarter period. Compliance is achieved when the running annual averages are below 60 mcg/L and 80 mcg/L for HAA5 and TTHM, respectively.

TTHM and HAA5 measures provide simple estimates of the number of community water supplies with high levels of DBPs that could potentially cause adverse health effects. They also can help estimate the number of people potentially exposed to water that does not meet regulatory limits for DPBs.

For CWSs that sampled DBPs, a missing quarter value was assigned the mean value for the calendar year or, if no data were available for the entire year, the mean of the values for the closest preceding and following years. Concentration values of “0” and “no violation” are reported for CWSs that did not disinfect.

The tables and graphs below show disinfection byproduct violations and concentrations by community water system and by population served. Generally, there were few MCL violations in Oregon.   From 2002 to 2007 between 0.6 percent and 2.1 percent of community water systems had at least one violation of either the HAA5 or the TTHM standard, and between 0.2 percent and 3.5 percent of the population may have received water with DBP levels above either the HAA5 or TTHM MCL during the year.

When examined by quarter, the percentages of DBP violations further decrease. In all but one quarter of the six years examined, violations occurred in less than 1 percent of the community water. Between 2002 and 2007 the percentage served by systems with no DBP violations ranged from 96.3 percent in 2003 to 99.6 percent in 2002.  From 2002 to 2007 between 98.9 percent and 99.7 percent of person-months (a measure of exposure) were free of DBP violations.

Between 2002 and 2007 more than 99.5 percent of water consumers of CWS received water with mean HAA5 and TTHM that did not exceed the MCL. For more than 80 percent of consumers, the average DBP levels were less than half the MCL. The graphs below also show that there are significant variations from year to year between HAA5 and TTHM.

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Table 1:  Annual number and percentage of CWSs with a DBP violation, and number and percentage of people receiving water from a CWS with a DBP violation.    

Table 2:  Quarterly percentage and number of community water systems (CWS), and percentage and number of people receiving water from a CWS with a DBP violation.

Table 3:  Percentage of person-months with no DBP violation by year.    

Table 4:  Number and percentage of CWSs and number and percentage of people receiving water from a CWS with different numbers of DBP violations, by year.  

Table 5:  Concentrations corresponding to the reference levels used in tables 5 and 6 as well as graphs 3 and 4. The reference levels are defined as population-weighted percentiles of the distribution of mean TTHM and HAA5 concentrations in 2005. 

Table 6:  Number and percentage of people receiving water from CWS with maximum HAA5 levels in five reference level categories (see Table 4 for definition).  

 

Table 7:  Number and percentage of people receiving water from CWS with maximum HAA5 levels in five reference level categories (see Table 4 for definition).  

 

Table 8:  Distribution of number of people by mean HAA5 concentrations, by year.  

 

Table 9:  Distribution of number of people by mean TTHM concentrations, by year. 

 

Graph 1:  Percentage and number of CWSs with DBP violations by year.  

 

Graph 2:  Percentage and number of people receiving water from CWSs with DBP violations by year. 

 

Graph 3:  Number of people receiving water from CWS with maximum HAA5 levels in five reference level categories (see Table 4 for definition).  

 

Graph 4:  Number of people receiving water from CWS with maximum TTHM levels in five reference level categories (see Table 4 for definition).  

 

Graph 5:  Distribution of number of people by mean HAA5 concentrations for 2007.  

 

Graph 6:  Distribution of number of people by mean HAA5 concentrations for 2007.

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 Table 1:  Annual number and percentage of CWSs with a DBP violation, and number and percentage of people receiving water from a CWS with a DBP violation.    

 

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Table 2:  Quarterly percentage and number of community water systems (CWS), and percentage and number of people receiving water from a CWS with a DBP violation.   

 

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Table 3: Percentage of person-months with no DBP violation by year. The number of person-months without DBP violations is the sum of the CWS populations multiplied by the number of months in which no DBP violation occured. 

 

Year 

% Person-Months

2002

99.7

2003

98.9

2004

99.5

2005

99.4

2006

99.6

2007

99.6

 
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Table 4: Number and percentage of CWSs and number and percentage of people receiving water from a CWS with different numbers of DBP violations, by year. 

 

http://staging.health.oregon.gov/Teamsite/epht/PublishingImages/images/dbptable3.PNG 

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Table 5: Concentrations corresponding to the reference levels used in tables 5 and 6 as well as graphs 3 and 4. The reference levels are defined as population-weighted percentiles of the distribution of mean TTHM and HAA5 concentrations in 2005.

 

http://staging.health.oregon.gov/Teamsite/epht/PublishingImages/images/dbptable3.PNG

 

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Table 6: Number and percentage of people receiving water from CWS with maximum HAA5 levels in five reference level categories (see Table 4 for definition).

 

http://staging.health.oregon.gov/Teamsite/epht/PublishingImages/images/dbptable3.PNG

 

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Table 7: Number and percentage of people receiving water from CWS with maximum HAA5 levels in five reference level categories (see Table 4 for definition).

 

http://staging.health.oregon.gov/Teamsite/epht/PublishingImages/images/dbptable3.PNG

 

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Table 8: Distribution of number of people by mean HAA5 concentrations, by year.

 

http://staging.health.oregon.gov/Teamsite/epht/PublishingImages/images/dbptable3.PNG

 

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Table 9: Distribution of number of people by mean TTHM concentrations, by year.

 

http://staging.health.oregon.gov/Teamsite/epht/PublishingImages/images/dbptable3.PNG

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Graph 1: Percentage and number of CWSs with DBP violations by year.

 

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Graph 2: Percentage and number of people receiving water from CWSs with DBP violations by year.

 

 

 

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Graph 3: Number of people receiving water from CWS with maximum HAA5 levels in five reference level categories (see Table 4 for definition).

 

 

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Graph 4: Number of people receiving water from CWS with maximum TTHM levels in five reference level categories (see Table 4 for definition).

 

 

 

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Graph 5: Distribution of number of people by mean HAA5 concentrations for 2007.

 

 

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Graph 6: Distribution of number of people by mean HAA5 concentrations for 2007.

 

 

 

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