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Terms Used in this Report
Maximum Contaminant Level Goal (MCLG) and Public
Health Goal (PHG)
The level of a contaminant in drinking water below
which there is no known or expected risk to health. MCLGs are set by the
Federal Environmental Protection Agency and PHGs are set by the
California Environmental Protection Agency.
Maximum Contaminant Level (MCL)
The highest level of a contaminant that is allowed in drinking water. Primary MCLs are set as
close to the PHGs (or MCLGs) as is economically and technologically
feasible. Secondary MCLs are set to protect the odor, taste, and
appearance of drinking water.
Primary Drinking Water Standards (PDWS)
MCLs for contaminants that affect health along with
their monitoring and reporting requirements, and water treatment
requirements.
Secondary Drinking Water Standards (SDWS)
MCLs for contaminants that affect taste, odor, or
appearance of the drinking water. Contaminants with SDWSs do not affect
the health at the MCL levels.
Treatment Technique (TT) — A required process
intended to reduce the level of a contaminant in drinking water.
Regulatory Action Level (AL) — The concentration of
a contaminant which, if exceeded, triggers a treatment or other
requirement which a water system must follow.
No Standard (NS) — Contaminant for which there is
no established MCL.
Not Detected (ND) — Contaminant is not detectable
at testing limit
Not Analyzed (NA) — Contaminant was not analyzed.
pCi/L — picoCuries per liter (a measure of
radiation)
ppm — parts per million, or milligrams per liter
(mg/L)
ppb — parts per billion, or micrograms per liter
(µg/L)
ppt — parts per trillion, or nanograms per liter
NTU — Nephelometric Turbidity Unit
TON — Threshold Odor Number
LI — Langelier Index; Noncorrosive = Any positive
value, Corrosive = Any negative value
Measurements
Water is sampled and tested throughout the year.
Contaminants are measured in parts per million (ppm), parts per billion
(ppb), parts per trillion (ppt), and even parts per quadrillion (ppq).
If this is difficult to imagine, think about these comparisons:
|
Parts per
million: |
Parts per
billion: |
Parts per
trillion: |
Parts per
quadrillion: |
|
3 drops
in 42 gallons |
1
drop in 14,000 gallons |
10 drops
in enough water to fill the Rose Bowl
|
1 drop in
enough water to fill 100 Rose Bowls |
|
1 second
in 12 days |
1
second in 32 years |
1 second
in 32,000 years |
1 second
in 31.7 million years |
|
1 inch in
16 miles |
1
inch in 16,000 miles |
1 inch in
16 million miles |
1 drop in
13.2 billion gallons |
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