Chemical analysis results can, without question, be confusing.
However, understanding the basic components can help make sense of
it. While there are many types of analysis results there are many
components common to all of them.
Dates
Many dates appear on the analysis form, but only one is of real
interest to the water system. This is the date the sample was
collected. On the result form, this date is called the
“Sample Date,” “Collection Date,”
“Source Date,” or “Date Collected.”
Qualifiers
These are characters found before the results number. There are
two common qualifiers, “<” (less than) and
“>” (greater than). When you see a
“<” sign in the result, the amount indicated is the
smallest amount that the analysis method can detect. Therefore,
when a “<” sign is in your results, no detectable
amount of that chemical has been found.
It happens rarely, but you may also see a “>”
sign in the result. This means the amount of chemical found is
above the amount the analysis method can measure accurately. You
have at least the amount indicated and probably more.
Units of Measure
A unit of measure is the amount of chemical found in a specific
volume of water—for example, pounds/gallon or
teaspoons/gallon. It is also called concentration units, or simply
units. The four common units of measure used in drinking water
analysis results are mg/L, µg/L, ppm, and ppb.
Milligrams per liter (mg/L) is equivalent to ppm (parts per
million). To convert mg/L to µg/L simply multiply by 1000
(1 mg/L = 1000 µg/L). One part per million is about
the same as one drop of soda in fifty 32-oz. drinks.
Micrograms per liter (µg/L) is one thousand times less
than mg/L and is equivalent to ppb (parts per billion). To convert
µg/L to mg/L, simply divide by 1000 (1 µg/L =
0.001 mg/L).
Even though these amounts appear very small, amounts of any size
can be very potent and very harmful. For example, trace amounts of
pesticides are known to be very harmful at levels 1000 times less
than 1 µg/L or 1 ppb, and strong evidence exists that
lifetime exposure can result in cancer. Therefore, a very minute
amount of chemical constituent can be of significance and
concern.
Types of Chemicals Sampled
Inorganic chemicals (30 TAC §209.106) do
not contain carbon. They are metals such as iron or arsenic,
minerals such as calcium and fluoride, and salts such as nitrate
and nitrite. Many metals, minerals, and salts simply make the water
unappealing to drink while others, when found in excessive
quantities, have detrimental effects on human health. For example,
nitrates in excess of 10 mg/L can cause “blue baby
syndrome,” which results from interferences in the
blood’s ability to carry oxygen and can be fatal to
infants.
Organic chemicals (30 TAC §209.107)
contain carbon and include synthetic organic compounds (SOCs),
volatile organic compounds (VOCs), and trihalomethanes (THMs). SOCs
are found in insecticides, herbicides, and polychlorinated
biphenyls (PCBs). VOCs are found in gasoline, paints, solvents, and
plastics, and are generally considered petroleum-related
products.
THMs and HAAs (30 TAC §209.113) are
chemical by-products that are formed when water is treated with
chlorine. They are also referred to as disinfection by-products, or
DBPs. Many organic chemicals can cause cancer if consumed at levels
greater than the maximum contaminant level (MCL) for many
years.
Radiochemicals (30 TAC §209.108) are
radioactive materials, which can occur naturally or as a result of
oil and gas production or mining. Alpha particles are positively
charged particles while beta particles are negatively charged
particles. Both types can cause cancer if consumed for many years
at levels above the MCL.
Microbiological contaminants (30 TAC
§209.109) include organisms such as coliform bacteria and
Escherichia coli (E. coli), and protozoans such
as Giardia and Cryptosporidium. Many microbiological contaminants
can cause immediate health problems with symptoms similar to flu or
intestinal distress. These symptoms are temporary for healthy
individuals but can be fatal for infants, the elderly, and
individuals whose immune systems are compromised by illness.
Sampling Frequency
Sampling frequencies are based on several factors, such as:
- Type of water system
- Size of the population served by the system
- Type of water (groundwater or surface water)
- Detections and MCL violations
- How vulnerable the water source is to contaminants
Billing
It is the responsibility of the water system to pay for chemical
analysis. Failure to do so will result in monitoring violations.
The laboratories used by the TCEQ are nonprofit, which means that
they only charge for the actual cost of analysis. These
laboratories are responsible for billing the water systems and
sending you the results. If there are billing questions, please
direct them to the laboratory. You may contact the DSHS at
512/458-7318 or the LCRA at 512/356-6022. If you need assistance
with scheduling or interpretation of the results, please contact
the TCEQ at 512/239-4691.
2005 Schedule of Laboratory Fees (PDF)
Maximum Contaminant Level
(MCL)
The TCEQ reviews all chemical analyses. When an exceedance is
found, several things happen:
- A check sample may be collected to verify the result
- Sampling is increased to monitor the violation
- A notice of violation letter is sent to the water system if a
violation exists
- The water system must notify customers of the violation so
vulnerable populations are protected
- The water system must make changes to curtail or correct the
violation
- Summary
of MCLs
