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Fact Sheet
November 2007
What You Should Know About Ground Water Sampling, Anytown, USA
WHAT IS GROUND WATER?
Ground water is the water that flows in natural storage areas below the earth's surface. Rain water and surface water soak into the ground surface and build up in the soil and cracked rock providing a source of water for human use. These water-soaked zones are called aquifers.
Ground water in aquifers can resurface as a spring, or it can release into a water body, such as a stream, river, lake, pond or ocean. It can also resurface when it is withdrawn from the ground by way of a well and pump.
When pollutants are leaked, spilled or thrown onto the ground, they, like water, move slowly or quickly through the soil, depending on the soil, the nature of the pollutant, and the amount of extra help it gets from incoming precipitation. If there is a water supply well near a source of contamination, that well runs the risk of becoming contaminated by polluted ground water.
SAMPLING RESIDENTIAL WELLS
Residential wells get water from aquifers. You can't always tell the quality of water by the way it looks or tastes. Chemical testing of water
samples in a laboratory is often the only way to find out detailed information on the quality and safety of the well water.
Hazardous waste sites exist across the country. EPA tests wells near those sites where the ground water is suspected to be contaminated. The testing is offered free of charge to residents with private wells near areas where EPA is concerned about the ground water. EPA needs your permission to collect water samples from your property.
EPA will contact you to set a time that is convenient to obtain the sample. Allowing EPA to test your well does not commit you to taking any action.
SAMPLING RESULTS
Sampling of your private well will normally take a few hours, depending on the testing that is conducted. Samples are collected and transported to a laboratory for examination. The average turn-around time for examination of samples tested, depending on the type of samples and contaminants, ranges from 30 to 60 days.
Once the sample results are received by EPA from the laboratory, they are reviewed for accuracy of data. This review process typically takes one to two weeks.
Then, individual reports with cover letters are prepared and sent to each property owner where samples were collected. The overall time frame from sample collection to the property owner's receipt of results can range from 60 to 90 plus days.
UNDERSTANDING YOUR LAB RESULTS
(Matrix, Units, Dilution factor, Analyte, Letters)
At the top of the results, there are codes used to uniquely identify the particular sample. The name of the laboratory doing the testing might also appear on the page, as well as the time and date the sample was collected from your well. Here are some answers to frequently asked questions about your laboratory results.
What is a matrix? The matrix refers to the type of material that makes up the sample. A matrix might include soil, water, or air. For example, since your residential well was sampled, your matrix entry should read, “Water”.
What are units? Units are the measurement used for your analysis. For example, your height is measured in units of feet and inches. Water samples are measured in units of mass per volume. You may see symbols such as ug/l (micrograms per liter) or ppb (parts per billion). Ug/l is a measure of the mass of the substance per liter of water. To put this in perspective, one part per billion is roughly the same as one drop of chlorine in an Olympic-sized swimming pool.
What is a dilution factor? The dilution factor is the amount a sample may be diluted (watered down) in order to get accurate analytical results. Dilution is often required if there are high levels of chemicals in samples. A dilution factor of 1 indicates that the sample was not diluted. A dilution factor of 2 means the sample was mixed with equal parts of a clean solution. Preparing orange juice from concentrate is an example of a dilution. You would mix 1 can of orange juice concentrate with 3 cans of water.
What is an analyte? The word analyte is a general term for the substance we are looking for in the sample. The laboratory does testing to find specific analytes, or substances in the water sample. For instance the laboratory may be looking for metals, solvents or pesticides. The lab report calls these substances analytes.
The report should list each analyte for which the lab was testing and what amounts were found.
What are all these letters? As part of the quality check, EPA may mark the measurement of certain analytes (the substance in the water) with a flag or qualifier to give readers additional information about the measurement.
The flag is usually in the form of a capital letter appearing next to the numerical result. Examples of Flags:
U - Not detected. The analyte is not present at or above the number next to the U. This number is the amount of analyte that would have to be present to be detected by the lab.
B- To ensure that the laboratory is not adding contamination of its own to the results, the lab always tests a clean water sample with the real samples.
R - Unreliable result. A re-test is needed for an accurate measurement.
J- The analyte was detected, but the value of the result is an estimate.
L - The analyte was detected, but the lab report may show an amount lower than what is actually there. The real result may be higher.
U J - The U before the J means that the analyte was not detected in the sample, but the detection limit (number prior to the U J) is an estimated amount.
K- The analyte was detected, but the level is probably lower.
O - No result was obtained.
ADDITIONAL INFORMATION:
For additional information concerning ground water testing, contact:
Belinda Young
U.S. Environmental Protection Agency Office of Public Affairs
901 N. Fifth St.
Kansas City, KS 66101
(800-223-0425)
young.belinda@epa.gov
