Healthy Housing and Environment Team

Web-based Information on MTBE and related topics

Water Sampling Data and Information
September 30, 2002 

Providence, RI

Today, the Rhode Island Department of Health, Office of Drinking Water Quality is releasing the results of recent water quality monitoring for the Pascoag Utility District public water system. Results of water samples collected from the Rock Avenue water tank between June 4, 2002 and September 11, 2002 showed no detectable levels of MTBE. Monitoring of the water supply was initiated by HEALTH in response to the detection of MTBE in a sample collected by a private homeowner in late August 2001. This will be the last web site update for this MTBE contamination event.

Mixing of water from the Harrisville Fire District was initiated on September 28, 2001. After some minor equipment adjustments, the booster pump at the connection began running full time on the evening of October 1. The water supplemented the Pascoag Utility District distribution system 24 hours per day, 7 days per week.

Installation of a carbon filtration system at Pascoag Well Station No. 3 was substantially complete on Saturday, November 17. Minor adjustments to auxiliary equipment (e.g., chlorination, pH adjustment, etc.) were done during the following weeks. Monitoring of the water leaving the carbon filtration system was performed regularly to determine the need to replace the carbon media inside the filters.

The carbon was changed in the three primary filters for the first time on December 3, 2001 and in the three secondary filters for the first time on December 8. The carbon was changed again in the three primary filters on December 12. Carbon was replaced in all six filters on December 17. The carbon was changed in the three primary filters for the fourth time on December 24, 2001 and for the fifth time on January 2, 2002. The carbon was changed in all six filters on January 9, 2002, after water samples were collected.

While monitoring for typical gasoline constituents in the Pascoag water system, samples collected by HEALTH were analyzed for a total of 59 volatile organic compounds (VOCs) by EPA Method 524. Most of the compounds checked are associated with petroleum products. Only the gasoline additive MTBE had been detected in the water supply, until a trace level of benzene was first detected in water samples collected at Well #3 on 11/14/01. Benzene has not been detected in the water in the distribution system to date. The following notes apply to the summary of data shown in the table

* Results of samples collected on 09/12/01 and 09/14/01 are from laboratories other than the State of RI Department of Health.

# In addition to MTBE, the well water samples were found to have benzene levels of 0.5 ug/L (equal to the method detection limit) on 11/14, 12/03, 12/13 and 12/27; 0.6 ug/L on 11/20, 11/27, 12/06, 12/20 and 01/03; and 0.7 ug/L on 01/09. The drinking water standard for benzene is 5.0 ug/L.

The following table shows MTBE concentrations in micrograms per liter (ug/L), which is roughly equivalent to parts per billion (ppb).

On January 11, 2002, the Pascoag Well Station No. 3 was shut down due to a court order. Two interconnections were opened between Harrisville Fire District and Pascoag. Based on the MTBE levels found in Pascoag on January 9 and the shut down of the wellfield, HEALTH lifted the advisory relating to bathing children under the age of 6.

On January 14, 2002, water samples collected in the Pascoag distribution system showed very low levels of MTBE (ND to 40 ppb), and bacterial analyses showed low counts of coliform. The coliform positives were not unusual, considering the changes in the flow of the water in the distribution system. Fecal coliform was not detected.

On January 16, 2002, the results of analyses showed all water samples below 40 ppb MTBE- all but one were below 10 ppb. One of eight water samples collected in Pascoag that day was positive for coliform. Again, fecal coliform was not detected in the distribution system.

On January 17, 2002, water samples were collected at five locations routinely sampled for bacterial compliance in the system. The samples showed no coliform present. The results were received by HEALTH late in the afternoon on Friday, January 18, 2002. Earlier that day, HEALTH sampling personnel noted low pressure in the distribution system. Pascoag Utility District worked into the night to correct the problem.

On Saturday, January 19, 2002, HEALTH received the results of bacterial tests on Friday's samples. They showed no coliform present. Similarly, samples collected on January 19 showed no coliform present. Water pressure in the distribution system had improved to the satisfaction of HEALTH.

Based on the results of analyses that showed coliform was absent in the distribution system on Friday, January 18, and MTBE levels were below the secondary drinking water standard of 40 ug/L on January 16, HEALTH lifted the water use ban at 3:00 PM EST on January 19, 2002. Residents may now drink the water and cook with it.

Since January, the sole source of water for Pascoag Water District has been the connections to Harrisville Fire District. There have been some issues with coliform detections and water main leaks found in both water systems, forcing emergency repairs and installation of chlorination systems. Residuals of chlorination by-products have been detected in trace levels, but well below the acceptable threshold of 100 ug/l total.

HEALTH will continue to work with Pascoag Utility District as needed to resolve issues related to the operation and maintenance of the water system. This is the last update for monitoring the MTBE contamination event we will post in the public health news section of the HEALTH website at www.healthri.org.

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