The Power of Information

National Drinking Water Database


City of Napa Utilities - Napa, CA


Serves 70,000 people

Total trihalomethanes (TTHMs)

Total trihalomethanes constitute the sum of four disinfection byproducts: chloroform, bromodichloromethane, dibromochloromethane, and bromoform.
 
This Drinking Water System
Test Days Exceeding Health GuidelinesDefinition of what this is
55 days
Test Days Exceeding Legal LimitsNumber of days in which the samples taken in that day exceed the Maximum Contaminant Level (Depending on the contaminant and its MCL, that may or may not trigger an MCL violation. Some MCLs are based on averages spanning several months to a year)
2 days
Test DaysNumber of days in which this chemical has reported results in the data we received from the State
58 days
Tests ConductedNumber of individual tests done for this contaminant
489 tests

Testing Summary

ContaminantAverage/
Maximum
Result
Health Limit
Exceeded
Legal Limit
Exceeded

Testing History

-Tested      -Detected      -Over Health Guidelines      -Over Legal Limit*
Total trihalomethanes (TTHMs)Total trihalomethanes constitute the sum of four disinfection byproducts: chloroform, bromodichloromethane, dibromochloromethane, and bromoform.50.5 ppb
107.25 ppb
Yes
9.8 ppb
Yes
80 ppb
NOTE: Each dot in the above graph represents one month.
* Water utilities are noted as exceeding the legal limit if any test is above the maximum contaminant level (MCL). Most MCLs are based on annual averages so exceeding the MCL for one test does not necessarily indicate that the system is out of compliance.

Health Based and Legal Limits for Total trihalomethanes (TTHMs)

Health Based Limits for Total trihalomethanes (TTHMs)

StandardDescriptionLevel
One in one million (10-6) Cancer RiskThe concentration of a chemical in drinking water corresponding to an excess estimated lifetime cancer risk of 1 in 1,000,000. Source: U.S. Environmental Protection Agency.9.8 ppb
EPA Human Health Water Quality CriteriaWater quality criteria set by the US EPA provide guidance for states and tribes authorized to establish water quality standards under the Clean Water Act (CWA) to protect human health. These are non-enforceable standards based upon exposure by both drinking water and the contribution of water contamination to other consumed foods. Source: U.S. Environmental Protection Agency.11.5 ppb
Maximum Contaminant Limit (MCL)The enforceable standard which defines the highest level of a contaminant that is allowed in drinking water. MCLs are set as close to health-based limits (Maximum Contaminant Level Goals, or MCLGs) as feasible using the best available analytical and treatment technologies and taking cost into consideration. Source: U.S. Environmental Protection Agency.80 ppb
Lifetime health-based limit, non-cancer riskConcentration of a chemical in drinking water that is not expected to cause any adverse, noncarcinogenic health effects for a lifetime of exposure. The Lifetime health-based limit (or Health Advisory, HA) is based on exposure for a a 70-kg adult consuming 2 liters of water per day. Source: U.S. Environmental Protection Agency.130 ppb
One in ten thousand (10-4) Cancer RiskThe concentration of a chemical in drinking water corresponding to an excess estimated lifetime cancer risk of 1 in 10,000. Source: U.S. Environmental Protection Agency.980 ppb
Drinking Water Equivalent LevelA lifetime exposure concentration protective of adverse, noncarcinogenic health effects, that assumes all of the exposure to a contaminant is from drinking water. Source: U.S. Environmental Protection Agency.1835 ppb
Children's health-based limit for 10-day exposureConcentration of a chemical in drinking water that is not expected to cause any adverse, noncarcinogenic effects for up to ten days of exposure. The Ten-Day health-based limit (or Health Advisory, HA) is typically set to protect a 10-kg child consuming 1 liter of water per day. Source: U.S. Environmental Protection Agency.4860 ppb
Children's health-based limit for 1-day exposureConcentration of a chemical in drinking water that is not expected to cause any adverse, noncarcinogenic health effects for up to one day of exposure. The One-Day health-based limit (or Health Advisory, HA) is typically set to protect a 10-kg child consuming 1 liter of water per day. Source: U.S. Environmental Protection Agency.10600 ppb

Testing Results

Testing DateAverage
Result
Samples taken that dayNumber of Non-DetectsRange of Results
2009-03-1750.25 ppb4034 to 58 ppb
2009-03-0418 ppb1018 ppb
2009-02-0454.38 ppb1706.5 to 78 ppb
2009-01-0747.26 ppb506.3 to 61 ppb
2008-12-0335.6 ppb2104.6 to 78 ppb
2008-11-0560.29 ppb1020 to 110 ppb
2008-10-0164.06 ppb3007.3 to 150 ppb
2008-09-0354.4 ppb1703.8 to 110 ppb
2008-08-0670.95 ppb3108.8 to 170 ppb
2008-07-169.1 ppb109.1 ppb
2008-07-0959.2 ppb10012 to 90 ppb
2008-06-0453.24 ppb2610 to 110 ppb
2008-05-0768.13 ppb8042 to 84 ppb
2008-04-0241.31 ppb1610 to 57 ppb
2008-03-05107.25 ppb4099 to 120 ppb
2008-02-0667.25 ppb4058 to 83 ppb
2008-01-0928.94 ppb504.7 to 38 ppb
2007-12-0532.5 ppb4021 to 40 ppb
2007-11-0728.5 ppb8020 to 37 ppb
2007-10-0355.92 ppb12039 to 72 ppb
2007-09-0569.42 ppb12055 to 83 ppb
2007-08-0161.75 ppb12034 to 74 ppb
2007-07-1652.61 ppb1503.7 to 81 ppb
2007-06-0643.07 ppb1008.7 to 61 ppb
2007-05-0259.38 ppb8053 to 68 ppb
2007-04-0436.5 ppb4027 to 49 ppb
2007-03-0755.75 ppb4041 to 64 ppb
2007-02-0752.25 ppb4046 to 58 ppb
2007-01-0335.5 ppb4031 to 44 ppb
2006-12-0648 ppb4026 to 76 ppb
2006-11-0862.5 ppb4036 to 85 ppb
2006-10-0465.25 ppb8036 to 91 ppb
2006-09-0664.33 ppb6052 to 87 ppb
2006-08-233.7 ppb210 to 7.4 ppb
2006-08-0261.75 ppb8038 to 110 ppb
2006-07-0538.1 ppb1010 to 66 ppb
2006-06-0743.63 ppb8022 to 68 ppb
2006-05-0370 ppb4030 to 93 ppb
2006-03-0139 ppb4026 to 46 ppb
2005-12-0735.75 ppb4033 to 38 ppb
2005-11-0961.25 ppb4037 to 72 ppb
2005-10-0555.75 ppb12040 to 77 ppb
2005-07-206.1 ppb106.1 ppb
2005-06-0165.13 ppb8039 to 98 ppb
2005-05-0446 ppb4031 to 59 ppb
2005-04-0667.5 ppb4042 to 90 ppb
2005-03-0270.75 ppb4066 to 80 ppb
2005-02-0284.5 ppb4075 to 92 ppb
2005-01-0550.5 ppb4039 to 57 ppb
2004-12-0838.5 ppb4030 to 48 ppb
2004-11-1048 ppb4038 to 58 ppb
2004-10-0662.25 ppb8047 to 88 ppb
2004-09-0138.5 ppb12032 to 47 ppb
2004-08-0239.31 ppb1310 to 62 ppb
2004-07-1451.62 ppb13033 to 72 ppb
2004-06-0242 ppb9024 to 57 ppb
2004-05-1253.5 ppb8043 to 66 ppb
2004-04-0743.25 ppb4031 to 52 ppb