Understand your results

Well-testing results

More than 100 drinking water contaminants are regularly analyzed by the North Carolina State Laboratory of Public Health.  Deciding for which contaminants to test and receiving the results can be overwhelming.  Numerous factors can influence which contaminants might be of concern in your area, including the geology, local land use, and hazardous spills near your well. 

It can also be challenging to interpret all of the numbers, abbreviations, and acronyms that appear on the results forms.  This page contains samples of the well-testing results forms used by the NC State Laboratory of Public Health and explanations of all of the features on the forms. 

View a well-testing results form from the State Laboratory and investigate the analysis report that is sent to all private well owners by the NC Division of Public Health. 

Contaminants

Prior to submitting a well water sample for analysis, private well owners must identify the contaminants of concern on a sample submission form that accompanies the well specimen.  For many of us, it is difficult to determine whether the contaminant we are concerned about is inorganic or organic.  In general, many minerals and naturally-occurring elements and metals are inorganic, whereas synthetic products or products that are man-made are organic. 

Inorganic contaminants

The Environmental Protection Agency (EPA) defines inorganic contaminants as mineral-based compounds such as metals, nitrates, and asbestos.

Inorganic contaminants are naturally-occurring in some water, but can also enter water through farming, chemical manufacturing, and other human activities. The EPA has set legal limits on 15 inorganic contaminants in private drinking water and secondary guidelines for an additional 15 contaminants.  Secondary guidelines are based upon the likelihood of a contaminant to cause aesthetic changes to the quality of your water by affecting the appearance, odor, or taste.

Organic contaminants

Organic contaminants are carbon-based chemicals, such as solvents, petroleum products, and pesticides, which can get into water through runoff from croplands,leaking from underground storage tanks and vehicles, or discharges from factories. There are legal limits on 56 organic contaminants in drinking water. 

Headings that appear on your well-testing results form

View a sample well-testing form.

Analyte:  The substance or contaminant that was tested in your well water sample.

Result:  The concentration of the contaminant that was tested in your well.  In some cases, the amount of the contaminant in the water sample is so small that the analytical devices in the laboratory cannot provide a numerical result.  These values are referred to as “below detect” or “trace”.  If these items appear on your well-testing results, the contaminant is at a very low concentration or even non-existent in your well water sample.

RL (Reporting Limit):  The reporting limit is comparable to the Method Detection Limit (MDL) reported by the EPA.  The reporting limit is the minimum concentration of a substance that can be routinely reported using current laboratory methods.

Unit:  The unit is the standard reporting measure for that contaminant.  Some contaminants are reported in mg/L (milligrams per Liter).  Others are reported as ug/L (micrograms per Liter).  A microgram is 1000 times smaller than a milligram.  It is important to read which units the values are reported in on your results form and online materials.  All units reported on this website are micrograms per Liter. 

    Mg/L can be referred to as Parts Per Million (PPM).  Another way of referring to µg/L is Parts Per Billion (PPB).  

Qualifiers:  Qualifiers are important notes about your well water sample written by the State Laboratory.  Occasionally the qualifier will indicate that the sample was not able to be analyzed, or that there was some other contaminant of concern.  The qualifiers may also mean that you should re-submit a water sample or contact the county Health Department.  Qualifiers are indicated in the right column of the results form and are defined on the last page of all well-testing results.
 
View a sample well-testing report for inorganic contaminants.    

View a sample well-testing report for organic contaminants

Analysis report

View a sample analysis report.

The Analysis Report accompanies all well-testing results sent to well owners in North Carolina.  The North Carolina Division of Public Health evaluates well-testing results and determines whether your well water meets state and federal drinking water standards.  If your well water is contaminated, toxicologists in the Division of Public Health will review the results to determine if your water can continue to be used for other household tasks such as bathing, showering, and washing clothes and dishes.