The Power of Information

National Drinking Water Database

Town of Hempstead Wd Utilities - Great Neck, NY

Serves 110,000 people


Perchlorate is a synthetic oxygen additive in solid fuel propellant for rockets, missiles, and fireworks, and is primarily used by the military and the space industry; it may occur naturally in certain imported agricultural fertilizers.
This Drinking Water System
Test Days Exceeding Health GuidelinesDefinition of what this is
26 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)
0 days
Test DaysNumber of days in which this chemical has reported results in the data we received from the State
67 days
Tests ConductedNumber of individual tests done for this contaminant
256 tests

Testing Summary

Health Limit
Legal Limit

Testing History

-Tested      -Detected      -Over Health Guidelines      -Over Legal Limit*
PerchloratePerchlorate is a synthetic oxygen additive in solid fuel propellant for rockets, missiles, and fireworks, and is primarily used by the military and the space industry; it may occur naturally in certain imported agricultural fertilizers.3.28 ppb
6.2 ppb
5 ppb
Legal at any levelThis is the Federal Limit. State Limits may be lower.
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 Perchlorate

Health Based Limits for Perchlorate

Health-Based Screening LevelA benchmark concentration of contaminants in water that may be of potential concern for human health, if exceeded. For noncarcinogens, the HBSL represents the contaminant concentration in drinking water that is not expected to cause any adverse effects over a lifetime of exposure. For carcinogens, the HBSL range represents the contaminant concentration in drinking water that corresponds to an excess estimated lifetime cancer risk of 1 chance in 1 million to 1 chance in 10 thousand. Source: U.S. Geological Survey.5 ppb
California Public Health GoalsDefined by the State of California Office of Environmental Health Hazard Assessment (OEHHA) as the level of contaminant that is allowed in drinking water. For acutely toxic substances, levels are set at which scientific evidence indicates that no known or anticipated adverse effects on health will occur, plus an adequate margin-of safety. PHGs for carcinogens or other substances which can cause chronic disease shall be based solely on health effects without regard to cost impacts and shall be set at levels which OEHHA has determined do not pose any significant risk to health.6 ppb

Testing Results

Testing DateAverage
Samples taken that dayNumber of Non-DetectsRange of Results
2008-12-014.66 ppb510 to 6.4 ppb
2008-11-015.3 ppb504.4 to 6.1 ppb
2008-10-014.88 ppb504.5 to 5.6 ppb
2008-09-015.2 ppb504.5 to 6.1 ppb
2008-09-010 ppb880 ppb
2008-08-015.78 ppb405 to 6.8 ppb
2008-07-010 ppb110 ppb
2008-07-015.28 ppb404.4 to 6.2 ppb
2008-07-010 ppb770 ppb
2008-07-012.47 ppb302.2 to 2.8 ppb
2008-06-010 ppb880 ppb
2008-06-015.44 ppb504.6 to 6.6 ppb
2008-05-010 ppb880 ppb
2008-05-015.33 ppb404.7 to 6.1 ppb
2008-05-010 ppb110 ppb
2008-05-010 ppb110 ppb
2008-04-010 ppb550 ppb
2008-04-010 ppb220 ppb
2008-04-015.2 ppb205.2 ppb
2008-04-010 ppb990 ppb
2008-03-011.16 ppb1240 to 3.3 ppb
2008-03-010.35 ppb430 to 1.4 ppb
2008-03-015.32 ppb504.8 to 6.5 ppb
2008-02-015.53 ppb404.8 to 6.2 ppb
2008-01-015.6 ppb404.8 to 6.2 ppb
2008-01-010 ppb220 ppb
2008-01-010 ppb440 ppb
2007-12-015.63 ppb404.8 to 6.3 ppb
2007-11-015.63 ppb404.8 to 6.5 ppb
2007-10-015.47 ppb304.8 to 6 ppb
2007-10-015.2 ppb304.7 to 5.9 ppb
2007-09-014.87 ppb304.4 to 5.6 ppb
2007-08-014.9 ppb304.8 to 5 ppb
2007-07-015.13 ppb304.5 to 6 ppb
2007-06-012.45 ppb210 to 4.9 ppb
2007-06-014.8 ppb104.8 ppb
2007-05-011.1 ppb101.1 ppb
2007-05-013.18 ppb410 to 6.9 ppb
2007-05-012.85 ppb210 to 5.7 ppb
2007-05-011.1 ppb101.1 ppb
2007-05-012 ppb102 ppb
2007-04-010.33 ppb640 to 1 ppb
2007-04-012.53 ppb301.4 to 3.4 ppb
2007-04-010 ppb220 ppb
2007-04-011.23 ppb420 to 2.7 ppb
2007-04-010.78 ppb420 to 1.7 ppb
2007-03-014.5 ppb204.5 ppb
2007-02-015.25 ppb404.8 to 6.1 ppb
2007-01-014.6 ppb204.6 ppb
2006-12-014.63 ppb303.9 to 5.5 ppb
2006-11-014.8 ppb204.7 to 4.9 ppb
2006-10-011.8 ppb320 to 5.4 ppb
2006-10-012.33 ppb301 to 4.2 ppb
2006-10-010.96 ppb940 to 2.7 ppb
2006-10-010.49 ppb1290 to 2.8 ppb
2006-09-016.2 ppb304.7 to 7.4 ppb
2006-09-015.8 ppb105.8 ppb
2006-08-015.58 ppb404.6 to 6.3 ppb
2006-07-015.45 ppb404.5 to 6.2 ppb
2006-06-015.83 ppb404.7 to 6.6 ppb
2006-05-015.63 ppb404.5 to 6.3 ppb
2006-04-015.13 ppb304.2 to 5.8 ppb
2006-04-013.4 ppb103.4 ppb
2006-04-016.1 ppb106.1 ppb
2006-03-015.78 ppb504.9 to 6.8 ppb
2006-03-013.6 ppb103.6 ppb
2006-02-015.38 ppb404.1 to 6.9 ppb