Annual Drinking Water Quality Report

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Annual Drinking Water Quality Report
July 1, 2011

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Water Quality Data Table

The table below lists all of the drinking water contaminants that were detected during calendar year 2010. The presence of contaminants in the water does not necessarily indicate that the water poses a health risk. Unless otherwise noted, the date presented in this table is from testing done in calendar year 2010. The EPA and MDE allows us to monitor for certain contaminants less than once per year because the concentration of these contaminants do not change frequently.

Contaminants	MCLG or MRDLG	MCL, TT, or MRDL	Test results	Range Low	Range High	Sample Year	Is this a Violation?	Typical Source
CITY OF ROCKVILLE WATER TREATMENT PLANT PERFORMANCE
Turbidity (NTU)¹	N/A	TT=0.3	0.05	0.02	0.29	2010	No	Soil runoff
¹Turbidity is a measure of the cloudiness of the water. We monitor it because it is a good indicator of the effectiveness of our filtration system. Our turbidity results are 100% < 0.3 NTU; a value less than 95% constitutes a turbidity violation.

Residual Chlorine (ppm)	4	TT>0.2	2.2	0.8	3.9	2010	No	Water additive to control microbial contaminants
Inorganic Contaminants
Barium (ppm)	2	2	0.035	NA	NA	2010	No	Erosion of natural deposits; discharge of drilling wastes; discharge from metal refineries

Fluoride (ppm)	4	4	0.9	0.4	1.1	2010	No	Water additive that promotes strong teeth; erosion of natural deposits; discharge from fertilizer and aluminum factories

Nitrate (ppm)	10	10	1.7	N/A	N/A	2010	No	Erosion of natural deposits; runoff from fertilizer use; leaching from septic tanks; sewage
Radionuclides
Gross Beta (pCi/L)	0	50	4	N/A	N/A	2010	No	Decay of natural and man-made deposits
Organic Contaminants
Pentachlorophenol (ppb)	0	1.0	0.15	N/A	N/A	2010	No	Discharge from wood preserving factories
WASHINGTON SUBURBAN SANITARY COMMISSION (POTOMAC FILTER PLANT)^A
Inorganic Contaminants
Barium (ppm)	2	2	0.0369 (average)	0.0306	0.0484	2010	No	Erosion of natural deposits; discharge of drilling wastes; discharge from metal refineries

Fluoride (ppm)	4	4	0.547 (average)	0.135	0.88	2010	No	Water additive that promotes strong teeth; erosion of natural deposits; discharge from fertilizer and aluminum factories

Nitrate (ppm)	10	10	0.357 (average)	0.268	0.714	2010	No	Erosion of natural deposits; runoff from fertilizer use; leaching from septic tanks; sewage
^AWSSC test results for the period July 6 - Oct. 6, 2010. This period corresponds to the time frame when all water supplied to Rockville was purchased from WSSC.
Radionuclides
Radium 226 and Radium 228 (combined) (pCi/L)	0	5	2.1^B	N/A	N/A	2010	No	Erosion of natural deposits
^BWSSC test is for Radium 228 only; There was no test result for Radium 226 from July 6-Oct. 6
Organic Contaminants
Dalapon (ppb)	200	200	1.23	N/A	N/A	2010	No	Runoff from herbicide used on rights of way
CITY OF ROCKVILLE WATER DISTRIBUTION SYSTEM
Total Coliform, % positive samples per month	0	5	1²	0	4	2010	No	Naturally present in the environment
²Seven positive samples out of 688 total samples tested. Minimum sampling frequency is 50 samples per month.
Disinfectants & Disinfectant Byproducts³
Residual Chlorine (ppm), measured as free chlorine	4.0	4.0	1.1⁴	0.04	2.2	2010	No	Water additive to control microbial contaminants
Total Trihalomethanes (ppb)	N/A	80⁵	64.9⁶	3.2	78.2	2010	No	Byproduct of drinking water chlorination
Haloacetic Acids (ppb)	N/A	60⁵	34.1⁶	6.6	64.7	2010	No	Byproduct of drinking water chlorination
³There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants. ⁴Annual average. ⁵Running annual average. ⁶Highest running annual average.
Metals @ Consumer Taps
Copper (ppm)	1.3	1.3 (AL)	0.17	0.032	0.57	2010	No	Corrosion of household plumbing systems; erosion of natural deposits
Lead (ppb)	0	15 (AL)	2.7	<2	12	2010	No	Corrosion of household plumbing systems; erosion of natural deposits

Definitions Used in this Report
Unit Descriptions
Term	Definition
NTU	Nephelometric Turbidity Unit
ppm	Parts per million, or milligrams per liter (mg/L). 1 ppm is the same as one drop in 10 gallons of water.
ppb	Parts per billion, or micrograms per liter (μg/L). 1 ppb is the same as one drop in 10,000 gallons of water.
N/A	Not Applicable
ND	Not Detected (by a test procedure)
Important Drinking Water Definitions:
MCLG	Maximum Contaminant Level Goal: The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs ensure a margin of safety for sensitive individuals.
MRDLG	Maximum Residual Disinfection Level Goal: The level of a drinking water disinfectant below which no health risk is known or expected. MRDLGs do not reflect the benefits of using disinfectants to control microbial contaminants.
MCL	Maximum Contaminant Level: The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to the MCLGs as feasible using the best available treatment technology.
TT	Treatment Technique: A required process intended to reduce the level of a contaminant in drinking water.
MRDL	Maximum Residual Disinfectant Level: The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.
AL	Action Level: The concentration of a contaminant which, if exceeded, triggers treatment or other requirements that a water system must follow.