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Annual Drinking Water Quality Report
July 1, 2011
Water Quality Report (pdf)
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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 | 2.1B | 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. |