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The US Environmental Protection Agency (EPA) recommends water quality criteriaunder Section 304(a) of the Clean Water Act. States then use these criteria asguidance in establishing water quality standards. The EPA's recommended criteriafor E. coli are based upon studies conducted from 1979 through 1982 thatestablish an historically acceptable risk of 8 gastrointestinal illnesses per1000 swimmers for full body contact recreation. Vermont's E. coli water qualitystandards are much stricter than the EPA recommendation. E. coli levels are alsoused by water suppliers as an indication of the sanitary quality of their sourcewater. In addition, E. coli water quality standards are used by wastewatertreatment utilities to gauge the performance of their treatment processes and toselect appropriate treatment technology. The Champlain Water District (CWD)intake is positioned 2480 feet offshore at a depth of approximately 75 feet inthe northern channel of Lake Champlain's Shelburne Bay in Northwestern Vermont.There are two wastewater facility outfalls within 10,500 feet of the intake, oneat a depth of approximately 20 feet and the other at a depth of 40 feet. CWD'ssource protection plan was adopted in 1995 and a source water characterizationstudy was conducted during 1997 and 1998 using current and temperature profiles,weekly E. coli sampling, and, source water microbial source tracking. The weeklyE. coli sampling has continued to the present. Average E. coli concentrations atthe CWD intake ranged from 3.6 to 7.6 cfu/100 ml from 1997 through October 2000.The maximums ranged from 28 to 77 cfu/100 ml during the same time period. The E.coli results indicate that levels become relatively higher after the thermoclinedrops below the CWD intake and during winter/spring rain/snowmelt events. For themicrobial source tracking monitoring, 50.9 % of isolated clones had unidentifiedenvironmental sources and 26.3 % of the clones were from sewage or human sources.The Vermont E. coli water quality standard is set at 77 cfu/100 ml single samplemaximum, a nearly four-fold reduction in the EPA Clean Water Act (CWA)recommended level of 235 cfu/100 ml. This stringent requirement has causedconcern that Vermont wastewater treatment plants may be discouraged from usingultraviolet light disinfection technology (UV). Examining the available 1999compliance data for fourteen UV wastewater treatment plants currently operatingin Vermont shows that 12 of the 14 are achieving compliance with the stricterVermont standard. Specific data from a wastewater treatment plant employing UVtechnology within CWD's Shelburne Bay watershed shows excellent water qualitywith an average of

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Edition: Vol. - No. Published: 01/01/2001 Number of Pages: 15File Size: 1 file , 280 KB