Preparing Your Drinking Water Annual Water Quality Report: Guidance for Water Suppliers

Appendix B: Interpreting Monitoring Data

The information presented in this appendix provides examples of how to interpret your monitoring data for inclusion in the Table of Detected Contaminants (see Section 5.0, Item 4).

  • 1 Sampling site/1 sampling date:

    March 1999 – 0.003 ug/l

    What should be reported in Table of Detected Contaminants?

    Report the highest level detected 0.003 ug/l. You do not need to report a range.

  • Multiple Sampling sites/1 sampling date:
    Barium February 1999
    Well 1 0.60
    Well 2 0.46
    Well 3 ND

    What should be reported in Table of Detected Contaminants?

    Report the highest level detected 0.60 and the range ND – 0.60.

  • 1 Sampling site/Multiple sampling dates:
    Atrazine 1st Quarter 1999 2nd Quarter 1999 3rd Quarter 1999 4th Quarter 1999
    Well 1 0.80 3.8 2.1 0.9

    What should be reported in Table of Detected Contaminants?

    Report the average = 1.9 and the range 0.8-3.8.

  • Multiple sampling sites/Multiple sampling dates:
    Total Trihalomethanes 2nd Quarter 1998 3rd Quarter 1998 4th Quarter 1998 1st Quarter 1999 2nd Quarter 1999 3rd Quarter 1999 4th Quarter 1999
    Site 1 - - - 45 60 125 70
    Site 2 - - - 40 55 115 60
    Site 3 - - - 45 60 105 70
    Site 4 - - - 50 65 135 80
    Quarterly Average 55 125 65 45 60 120 70
    Rolling Annual Average - - - 73 74 73 74

    What should be reported in Table of Detected Contaminants?

    Report the highest annual average = 74 and the range 40-135.

    Notes: The last 3 quarters of 1998 are shown because you need them to compute the rolling annual average. The range would include only detection data from 1998, unless one of the values from the previous year was so extraordinary that consumers would need it to understand the reported annual average.

    If your rolling annual average exceeds 80 (the revised MCL effective in 2001), your report must include the health effects language for TTHMs, even though your system was not technically in violation.

  • Lead and Copper

    For lead and copper results you report the 90th percentile value from the most recent sampling (if it was detected above the detection limit), the range of detections, and the number of sampling sites that exceeded the action level. The 90th percentile is equal to or greater than 90% of the values detected at your water system.

    Lead Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7 Site 8 Site 9 Site 10
    July 1999 ND ND 8 12 19 3 ND ND 4 22

    In this case, you would list the samples in order of lowest level detected to highest level detected (see below).

    Lead Site 1 Site 2 Site 7 Site 8 Site 6 Site 9 Site 3 Site 4 Site 5 Site 10
    July 1999 ND ND ND ND 3 4 8 12 19 22

    The 90th percentile value would be the 9th highest sample detected – 19.

    What should be reported in Table of Detected Contaminants?

    Report the 90th percentile value = 19, the range of detections – ND-22, and the number of sites above the action level of 15, in this case there were 2 results above the action level (See below).

    Contaminant Violation
    Yes/No
    Date of Sample Level Detected
    (Maximum)
    (Range)
    Unit
    Measurement
    MCLG Regulatory Limit Likely Source of Contamination
    Lead Yes 7/99 191
    ND – 22
    ug/l 0 AL- 15 Corrosion of household plumbing systems; Erosion of natural deposits

    1 The level presented represents the 90th percentile of the 10 sites tested. A percentile is a value on a scale of 100 that indicates the percent of a distribution that is equal to or below it. The 90th percentile is equal to or greater than 90% of the lead values detected at your water system. In this case, ten samples were collected at your water system and the 90th percentile value was the second highest value (19 ug/l). The action level for lead was exceeded at two of the sites tested.

    The table reveals that the water level for lead exceeded the action level of 15 ug/l in more than 10 percent of the homes tested. Infants and children who drink water containing lead in excess of the action level could experience delays in their physical or mental development. Children could show slight deficits in attention span and learning abilities. Adults who drink this water over many years could develop kidney problems or high blood pressure. Infants and young children are typically more vulnerable to lead in drinking water than the general population. It is possible that lead levels at your home may be higher than at other homes in the community as a result of materials used in your home's plumbing. If you are concerned about elevated lead levels in your home's water, you may wish to have your water tested and you should flush your tap for 30 seconds to 2 minutes before using your tap water. Additional information regarding lead in drinking water is available from the Safe Drinking Water Hotline (1-800-426-4791).

    If your system takes less than 10 lead or copper samples you would report the average of the two highest levels detected in your table.

    Lead Site 1 Site 2 Site 3 Site 4 Site 5
    July 1999 ND 8 5 ND 14

    Again, you would list the samples in order of lowest level detected to highest level detected (see below).

    Lead Site 1 Site 4 Site 3 Site 2 Site 5
    July 1999 ND ND 5 8 14

    What should be reported in Table of Detected Contaminants?

    Report the average of the two highest values = 11, the range of detections – ND-14, and the number of sites above the action level of 15, in this case there were no results above the action level (See below).

    Contaminant Violation
    Yes/No
    Date of Sample Level Detected
    (Maximum)
    (Range)
    Unit
    Measurement
    MCLG Regulatory Limit (MCL, TT or AL) Likely Source of Contamination
    Lead No 7/99 111
    ND – 14
    ug/l 0 AL- 15 Corrosion of household plumbing systems; Erosion of natural deposits
    1 During 1999 we collected and analyzed 5 samples for lead. The level included in the table represents the average of the two highest levels detected. The action level for lead was not exceeded at any of the sites tested.

    Note: The following table will help you determine your 90th percentile value.

    Number of Samples How to determine 90th percentile
    2-9 Take the average of the two highest levels detected.
    10 Value of the 9th highest level detected.
    20 Value of the 18th highest level detected.
    30 Value of the 27th highest level detected.
    40 Value of the 36th highest level detected.
    50 Value of the 45th highest level detected.

    A system must provide information on lead in drinking water irrespective of whether the system detected lead in any of its samples. If above 15 ug/l the Action Level (AL) in more than 5%, but fewer than 10%, of the sites sampled [or if your system samples fewer than 20 sites and has even one sample above the Action Level (AL), you will need to include the standard explanation for an AL exceedance.

    Lead. If present, elevated levels of lead can cause serious health problems, especially for pregnant women, infants, and young children. It is possible that lead levels at your home may be higher than at other homes in the community as a result of materials used in your home's plumbing. [ NAME OF UTILITY ] is responsible for providing high quality drinking water, but cannot control the variety of materials used in plumbing components. When your water has been sitting for several hours, you can minimize the potential for lead exposure by flushing your tap for 30 seconds to 2 minutes before using water for drinking or cooking. If you are concerned about lead in your water, you may wish to have your water tested. Information on lead in drinking water, testing methods, and steps you can take to minimize exposure is available from the Safe Drinking Water Hotline (1-800-426-4791) or at http://www.epa.gov/safewater/lead.

  • Turbidity

    Turbidity as an Indicator of Filtration Performance

    When reporting turbidity as an indicator of filtration performance (see Table 4A of Part 5 for performance standards), systems must report the highest single measurement and the lowest monthly percentage of samples meeting the requirements specified for that technology. In this situation (conventional filtration serving less than 10,000 people), you may want to report the data in 2 rows of your table as follows:

    Contaminant Violation
    Yes/No
    Date of Sample Level Detected Unit
    Measurement
    MCLG Regulatory Limit (MCL, TT or AL) Likely Source of Contamination
    Turbidity1 No 11/5/09 0.9 NTU NTU N/A TT= ≤ 1.0 NTU Soil Runoff
    Turbidity1 No 11/09/09 96% ≤ 0.3 NTU N/A TT=95% of samples ≤ 0.3 NTU
    Notes:

    1 – Turbidity is a measure of the cloudiness of the water. We monitor it because it is a good indicator of the effectiveness of our filtration system. Our highest single turbidity measurement for the year occurred on 11/5/09 (0.9 NTU). State regulations require that turbidity must always be less than or equal to 1.0 NTU. The regulations require that 95% of the turbidity samples collected have measurements below 0.3 NTU. Although November 2009 was the month when we had the fewest measurements meeting the treatment technique for turbidity, the levels recorded were within the acceptable range allowed and did not constitute a treatment technique violation.

    Systems that are Required to Install Filtration

    Systems that are required to install filtration, but have not, must report the highest monthly average for turbidity. Additionally, systems falling into this category must also include the following statement:

    "Inadequately treated water may contain disease-causing organisms. These organisms include bacteria, viruses, and parasites, which can cause symptoms such as nausea, cramps, diarrhea, and associated headaches."

    Your average monthly turbidity values are usually included in your monthly operation reports. Calculating the average of the reported daily values for each month (i.e., January 1999 – December 1999), derives this number. In your Annual Water Quality Report you would report the highest monthly average calculated for the 12-month period.

    Turbidity 1/99 2/99 3/99 4/99 5/99 6/99 7/99 8/99 9/99 10/99 11/99 12/99
    Average Monthly Value 1.0 1.2 2.0 2.5 2.7 2.5 1.3 1.1 1.2 2.0 2.3 1.4

    How should this information be reported?

    Contaminant Violation
    Yes/No
    Date of Sample Level Detected Unit
    Measurement
    MCLG Regulatory Limit (MCL, TT or AL) Likely Source of Contamination
    Turbidity1 No 5/99 2.7 NTU NTU N/A TT= ≤1NTU Soil Runoff
    Notes:

    1 –Turbidity is a measure of the cloudiness of the water. We monitor it because it is a good indicator of water quality. High turbidity can hinder the effectiveness of disinfectants. Our highest average monthly turbidity measurement (2.7 NTU) occurred in May 1999 on 5/11/99. This value is above the turbidity standard (1 NTU) assigned to our system.

    The Village of Marcy is in violation of the Surface Water Treatment Rule and is required to install a water filtration plant or develop a new water source by June 2001. Therefore, we are required to include the following statement in this report: "Inadequately treated water may contain disease-causing organisms. These organisms include bacteria, viruses, and parasites, which can cause symptoms such as nausea, cramps, diarrhea, and associated headaches." The Village is in the process of actively seeking funding and has hired design engineers to comply with the Surface Water Treatment Rule.

    Filtration Avoidance Systems

    Systems that have met the State's criteria for avoiding filtration must report the highest single turbidity measurement found in any one month. The report should also include an explanation of the reasons for measuring turbidity. An example of this statement is as follows:

    "Turbidity is a measure of the cloudiness of the water. We monitor it because it is a good indicator of water quality. High turbidity can hinder the effectiveness of disinfectants."

    Your highest single turbidity values are usually included in your monthly operation reports. In your Annual Water Quality Report you would report the highest single turbidity measurement found during the 12-month reporting period.

    Turbidity 1/99 2/99 3/99 4/99 5/99 6/99 7/99 8/99 9/99 10/99 11/99 12/99
    Highest Monthly Value 0.45 0.7 0.8 1.5 6.0 2.0 1.5 1.0 0.90 0.4 0.78 0.6

    How should this information be reported?

    Contaminant Violation
    Yes/No
    Date of Sample Level Detected Unit
    Measurement
    MCLG Regulatory Limit (MCL, TT or AL) Likely Source of Contamination
    Turbidity1 Yes 5/15/99 6 NTU NTU N/A TT= ≤5NTU Soil Runoff
    Notes:

    1 –Turbidity is a measure of the cloudiness of the water. We monitor it because it is a good indicator of water quality. High turbidity can hinder the effectiveness of disinfectants. Our highest single turbidity measurement detected during the year (6 NTU) occurred on May 15, 1999. This value is above the State's treatment technique maximum turbidity performance standard (5 NTU).

    The Village of Colden had a turbidity treatment technique violation in May 1999. On May 15, 1999, the turbidity level was measured at 6 NTU. This elevated turbidity measurement was attributed to heavy rains and flash flooding which occurred on May 14th and 15th. The turbidity level measurements returned to below 5 NTU on May 16th. Turbidity has no health effects. However, turbidity can interfere with disinfection and provide a medium for microbial growth. Turbidity may indicate the presence of disease-causing organisms. These organisms include bacteria, viruses, and parasites that can cause symptoms such as nausea, cramps, diarrhea, and associated headaches. Please pay special attention to the additional statement in this document regarding Cryptosporidium.

    Distribution Turbidity Results

    Surface water systems and ground water under the direct influence of surface water systems must report the highest monthly average for turbidity measured in the distribution system.

    Your average monthly turbidity values are usually included in your monthly operation reports. Calculating the average of the reported daily values for each month (i.e., January 1999 -December 1999), derives this number. In your Annual Water Quality Report you would report the highest monthly average calculated for the 12-month period.

    Turbidity 1/99 2/99 3/99 4/99 5/99 6/99 7/99 8/99 9/99 10/99 11/99 12/99
    Average Monthly Value 1.0 1.2 2.0 2.5 2.7 2.5 1.3 1.1 1.2 2.0 2.3 1.4

    How should this information be reported?

    Contaminant Violation
    Yes/No
    Date of Sample Level Detected Unit
    Measurement
    MCLG Regulatory Limit (MCL, TT or AL) Likely Source of Contamination
    Distribution Turbidity1 No 5/99 2.7 NTU NTU N/A MCL >5NTU Soil Runoff
    Notes:

    1 –Distribution Turbidity is a measure of the cloudiness of the water found in the distribution system. We monitor it because it is a good indicator of water quality. High turbidity can hinder the effectiveness of disinfectants. Our highest average monthly distribution turbidity measurement detected during the year (2.7 NTU) occurred in May 1999. This value is below the State's maximum contaminant level (5 NTU).

    Total Coliform

    Systems that Collect Fewer than 40 Total Coliform Samples per Month

    Systems that collect fewer than 40 total coliform samples per month, must report the highest number of positive samples collected in any one month. If 2 or more samples are positive for total coliforms a MCL violation has occurred.

    Systems are required to collect and analyze a specified number of routine samples. However, the number used to determine compliance and maximum contaminant levels is the total of all routine samples plus all repeat samples plus those directed by the local health department to be taken whenever the local health department believes that a potential exists for an MCL violation, or contamination may present a risk to public health.

    For example, if a system is required to collect 24 routine samples per month and if 2 of the routine samples were positive for total coliforms, 4 repeat samples would have to be taken for each of the positive routine samples within 24 hours of being notified of the positive results. Even if the repeat samples are negative, you would report an MCL violation for your system because you had 2 positive Total Coliform samples during one month.

    How should this information be reported?

    Contaminant Violation
    Yes/No
    Date of Sample Level Detected Unit
    Measurement
    MCLG Regulatory Limit (MCL, TT or AL) Likely Source of Contamination
    Total Coliform Yes 5/15/99 2 positive samples N/A N/A MCL=2 or more positive samples in 1 month Naturally present in the environment

    The table shows that we had an MCL violation for total coliform. On May 15, 1999, two of the 24 monthly samples collected indicated the presence of total coliform. Coliforms are bacteria that are naturally present in the environment and are used as an indicator that other, potentially-harmful bacteria may be present. Coliforms were found in more samples than allowed and this was a warning of potential problems. Eight additional samples were subsequently collected on May 17, 1999, total coliform was not detected in those samples; however, we did violate the MCL since two of our original monthly samples were positive for total coliform. It should be noted that E. Coli, associated with human and animal fecal waste, was not detected in any of the samples collected.

    Systems that Collect 40 or more Total Coliform Samples per Month

    Systems that collect 40 or more total coliform samples per month, must report the highest percentage of positive samples collected in any one month. If more than 5% of the samples are positive for total coliforms, them a MCL violation has occurred.

    Systems are required to collect and analyze a specified number of routine samples. However, the number used to determine compliance and maximum contaminant levels is the total of all routine samples plus all repeat samples plus those directed by the local health department to be taken whenever the local health department believes that a potential exists for an MCL violation, or contamination may present a risk to public health.

    For example, if a system is required to collect 50 routine samples per month and if 3 of the routine samples were positive for total coliforms, 4 repeat samples would have to be taken for each of the positive routine samples within 24 hours of being notified of the positive results. If all repeat samples results were negative the following calculations should be made:

    50 Routine compliance samples
    12 Repeat samples
    62 Total Samples x 0.05 (maximum percent allowed to be positive per month) = 3.1

    According to the calculation above, three routine compliance samples are allowed to be positive per month. Therefore, a MCL violation did not occur; however, since total coliforms were detected they must still be reported in the Annual Water Quality Report.

    How should this information be reported?

    Contaminant Violation
    Yes/No
    Date of Sample Level Detected Unit
    Measurement
    MCLG Regulatory Limit (MCL, TT or AL) Likely Source of Contamination
    Total Coliform No 5/99 3 positive samples N/A N/A MCL=>5% of samples positive Naturally present in the environment

    In May 1999, total coliforms were detected in 3 of the 50 routine monthly compliance samples collected at our system. Coliforms are bacteria that are naturally present in the environment and are used as an indicator that other, potentially-harmful bacteria may be present. Twelve additional samples were subsequently collected and total coliforms were not detected in those samples. Since total coliforms were detected in <5% of the samples collected during the month, the system did not have an MCL violation. It should be noted that E. Coli, associated with human and animal fecal waste, was not detected in any of the samples collected.