GLOSSARY

Accuracy is a measurement of how close an analytical result is to the true or known value. Accuracy data are generated by performing laboratory control samples and/or matrix spikes and calculating the percent recovery for the analyte(s) of interest. NCL establishes its own acceptance limits for accuracy by calculating the standard deviation “in-house” spike recovery values. Upper and lower warning limits are set at + 2 standard deviations from the mean, and upper and lower control limits are set at + 3 standard deviations from the mean. Prior to NCL’s calculation and establishment of in-house limits for an analytical method, NCL may elect to establish temporary limits of 70-120% recovery as a guideline. In order to see trends in accuracy, percent recovery values can be graphed on Shewhart type charts with appropriate limits noted.

The level of chemical which, if exceeded, triggers treatment or other requirements that a water system must follow.

An immediate (i.e. within hours or days) effect that may result from exposure to certain contaminants (e.g., pathogens).

An analytical batch is a group of 20 or fewer samples of the same matrix, which are prepared and analyzed together. If there are more than 20 samples to be analyzed, each group of 20 or fewer will be handled as a separate batch.

A natural underground layer, often of sand or gravel, that contains water.

The laboratory’s Quality Assurance Unit prepares fortified samples and submits them to the lab for analysis as client samples. The laboratory is unaware that this is not a “real” sample. When the analysis is completed, the percent recovery is calculated and reported to the laboratory and management.

California Assessment Manual.

California Code of Regulations.

The possible result of exposure over many years to a contaminant.

A group of related bacteria whose presence in drinking water may indicate contamination by disease-causing microorganisms.

A water system which supplies drinking water to 25 or more of the same people year-round in their residences.

Anything found in water, soil, or crops (including microorganisms, minerals, chemicals, radionuclides, etc.) which may be harmful to human health.

A continuing calibration verification standard is a mid-level standard analyzed during and/or at the end of an analytical batch. A continuing calibration verifies that the instrument response has not drifted from the initial calibration response. The continuing calibration standard should be within the method specified ranges to be acceptable.

Cooler blanks are small containers of water that are placed in the coolers with the samples. The temperature of the cooler blank is taken upon receipt at the laboratory to determine the sample temperature.

California Toxics Rule.

A microorganism commonly found in lakes and rivers which is highly resistant to disinfection. Cryptosporidium has caused several large outbreaks of gastrointestinal illness, with symptoms that include diarrhea, nausea, and/or stomach cramps. People with severely weakened immune systems (that is, severely immuno-compromised) are likely to have more severe and more persistent symptoms than healthy individuals.

Deionized water.

A chemical (commonly chlorine, chloramine, or ozone) or physical process (e.g., ultraviolet light) that kills microorganisms such as bacteria, viruses, and protozoa.

US Environmental Protection Agency.

External reference standards are used to validate the accuracy of working standards and second lot standards. These standards are usually obtained from Environmental Resource Associates (ERA), or equivalent. They are prepared twice yearly or more frequently if necessary.

Water that has been treated and is ready to be delivered to customers.

Good Laboratory Practice Standards of the EPA (40 CFR Part 160)

A microorganism frequently found in rivers and lakes, which, if not treated properly, may cause diarrhea, fatigue, and cramps after ingestion.

The water that water systems pump and treat from aquifers (natural reservoirs below the earth's surface).

Primarily used for metals analysis. A blank that is analyzed following the calibration curve to verify that the instrument is “clean.”

Primarily used for metals analysis. A standard that is analyzed following the calibration curve to verify the calibration.Inorganic

Mineral-based compounds such as metals, nitrates, and asbestos. These contaminants are naturally-occurring in some water, but can also get into water through farming, chemical manufacturing, and other human activities. EPA has set legal limits on 15 inorganic contaminants...

Internal standards are added to the samples and their associated QC after extraction and prior to analysis. The same amount of internal standard is added to each standard, QC sample, and client sample. A calibration curve, that incorporates an internal standard, will “correct” the results for changes in instrument response, injection variability, etc.

Laboratory Control Samples are analyzed to verify the acceptable performance of an analytical method. Laboratory control samples are prepared by fortifying a matrix blank with a known amount of analytes(s) using a primary standard, or equivalent. LCS’s are spiked with all the analytes in each method, except for multi-peak analytes. These are prepared and analyzed at a frequency of one per batch. The results are reported as percent recovery, which is used as a measure of the accuracy of the analysis.

The component or substrate (e.g.. surface water, drinking water, soil) that contains the analyte(s) of interest.

A matrix spike is performed on a specific matrix to assess the accuracy of an analytical result. A matrix spike is prepared by fortifying a known amount of analyte(s) on an actual sample. Matrix spikes are fortified with all the analytes in the method, except for the multi-peak analytes. Matrix spikes are prepared using second lot standards, if available. Matrix spikes are analyzed for every 10 drinking water samples, and matrix spikes and matrix spike duplicates are analyzed for every 20 non-drinking water samples, or at least once per quarter, whichever is more frequent.

The highest level of a contaminant that EPA allows in drinking water. MCLs ensure that drinking water does not pose either a short-term or long-term health risk. EPA sets MCLs at levels that are economically and technologically feasible. Some states set MCLs which are more strict than EPA's.

A method blank is a blank matrix (such as de-ionized water or Ottawa sand) to which all reagents are added in the same volumes or proportions as specified in the method processing. A method blank is analyzed with each analytical batch. Method blanks are analyzed to monitor the introduction of contaminants into the analytical process.

The method detection limit, as outlined in 40 CFR Part 136, Appendix B, is the minimum concentration of a substance that can be measured and reported with 99% confidence that the analyte concentration is greater than zero. This limit is determined by analysis of a sample in a given matrix containing the analytes. Seven replicates fortified at one to five times the expected detection limit are analyzed. The standard deviation times the Student’s t value is calculated to determine the MDL.

Organic contaminants are carbon-based chemicals, such as solvents and pesticides.

A disease-causing organism.

Precision is the degree to which analytical results are reproducible. Precision data are generated by analyzing laboratory control sample, matrix spike, or samples in duplicate. Duplicate samples are analyzed every batch or every 20 samples. Duplicate pairs are compared to one another by calculating the relative percent difference (RPD) for each pair. In general, the RPD must be within + 20% (the limit specified by the EPA in its Contract Lab Program). However, NCL establishes its own precision warning and control limits for each method. These limits are determined by calculating the standard deviation for the RPDs on in-house duplicate pairs. The warning limits for a method are set at + 2 standard deviations from the mean and the control limits are set at + 3 standard deviation from the mean. In order to clearly see trends in precision data, RPDs can be graphed on Shewhart type charts with the appropriate limits noted.

The % recovery is a measure of the accuracy of a given analysis. It is the spiked result minus the unspiked result divided by the amount spiked and is expressed as a percent.

Any water system which provides water to at least 25 people for at least 60 days annually. There are more than 170,000 PWSs providing water from wells, rivers and other sources to about 250 million Americans. The others drink water from private wells. There are differing standards for PWSs of different sizes and types.

The Resource Conservation and Recovery Act.

The Relative Percent Difference is a measure of the precision of a given analysis. It is the difference between duplicate results divided by the arithmetic mean of the duplicates.