Portland's Bull Run source is an unfiltered surface water source. The Bull Run water source is of very high quality. Since 1999, there have been no fecal coliform results over 20/100 mL and only two total coliform results over 100/100 mL in over 1,200 samples.
The Surface Water Treatment Rule, adopted by the Environmental Protection Agency in 1989, is a federal regulation that requires all drinking water systems in the nation drawing from surface water sources to meet specific, measurable water treatment standards. Portland’s main water supply sources, the Bull Run reservoirs, are surface water supplies and are subject to this rule.
Portland was one of six large drinking water systems in the country at the time the rule was adopted that did not filter its water supply. The City was able to meet the requirements by modifying its treatment approach and continuously meeting a set of filtration avoidance criteria.
EPA has granted filtration avoidance waivers to Portland and these other unfiltered water systems, and required these systems to continuously meet the source water protection and water treatment standards of the rule. Should any of these systems fail to meet the filtration avoidance criteria, they will be in jeopardy of losing the waiver and being required by the federal government to filter their drinking water.
Portland has been able to consistently meet these criteria, but it occasionally has to shut down the Bull Run system and operate from its back up groundwater supply when storms and other natural disturbances in the Bull Run reservoirs increase the turbidity-- the amount of suspended sediments-- in the water. The Surface Water Treatment Rule requires that the City not serve drinking water exceeding a turbidity level of 5 Nephelometric Turbidity Units (NTU).
Prior to 1991, the Portland Water Bureau had treated Bull Run water by chlorination (adding chlorine) immediately followed by ammoniation to form chloramines, a long lasting disinfectant. This treatment was done at the system headworks in the Bull Run watershed. After the rule went into effect, chlorine was still added at headworks, but a second facility closer to town was added to help maintain water quality in the distribution system. These treatment adjustments and the City’s ability to switch to its back up water supply from the Columbia South Shore Wellfield during turbidity events have enabled Portland to remain in compliance with the rule to date.
Surface Water Treatment Rule (1990)
Effective December 31, 1990, the Surface Water Treatment Rule (SWTR) applies to all systems that use surface water or groundwater under the direct influence of surface water. The Rule established drinking water treatment techniques in lieu of maximum contaminant levels for Giardia lamblia, viruses, heterotrophic plate count bacteria, Legionella, and turbidity.
The Rule requires 99.9 percent (3-log) removal and/or inactivation of Giardia cysts, and 99.99 percent (4-log) removal and/or inactivation of viruses. To meet these requirements, water systems must disinfect according to strict requirements, filter water unless certain source water-quality and site-specific conditions are met, and be operated by qualified personal.
Portland's Bull Run surface water source is one of the few in the nation that meets criteria for avoiding filtration. To qualify for the exemption,
90 percent of the samples taken from the source water must have fewer than 100 total coliform bacteria per 100 milliliters (mL), and fewer than 20 fecal coliform bacteria per 100 mL.
The turbidity level prior to disinfection must not exceed 5 NTU. A detectable disinfection residual must be maintained throughout the distribution system.
Additional site conditions include having a watershed control program, undergoing annual on-site inspections, meeting Total Coliform Rule requirements in the distribution system, and meeting trihalomethane requirements.
The water system must also be free of waterborne disease outbreaks.
The Portland Water Bureau conducted pilot plant work to evaluate potential treatment process changes. The study included various filtration and enhanced disinfection processes. As a result of the study, Portland modified its disinfection system in 1991. The Portland Water Bureau built a new facility to store and feed ammonia so that existing conduits could be used to provide the required chlorine residual concentration and contact time. Chlorine is added to the water at the Headworks. Ammonia is added three hours after the chlorine, in a process called chloramination.
Interim Enhanced Surface Water Treatment Rule (2002)
Published in December 1998, the Interim Enhanced Surface Water Treatment Rule (IESWTR) applies to surface water or groundwater under direct influence of surface water (GWUDI) systems that serve a population of 10,000 or more. The IESWTR builds on the Surface Water Treatment Rule by adding protection from Cryptosporidium. The rule is designed to optimize treatment reliability and enhance physical removal efficiencies to minimize the Cryptosporidium levels in finished water.
The rule establishes a Maximum Contaminant Level Goal (MCLG) of zero for Cryptosporidium and requires 2-log removal requirements for systems that filter. For unfiltered systems, Cryptosporidium must be included in watershed control requirements. The IESWTR requires sanitary surveys for all public water systems (regardless of size) using surface water or GWUDI. The Rule also requires covers for all new finished water storage facilities and includes disinfection profiling and benchmarking provisions to ensure systems provide continued levels of microbial protection while taking the necessary steps to comply with the Disinfection By-Products standards.
Long Term 1 Enhanced Surface Water Treatment Rule (2002)
The Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR) is similar to the IESWTR as applied to small systems, serving less than 10,000 people, using surface water or groundwater under the direct influence of surface water. This rule became effective March 2002.
Published in December 2005, the Long Term 2 Surface Water Treatment Rule (LT2) applies to surface water or groundwater under direct influence of surface water (GWUDI) systems, increasing the regulation of Cryptosporidium. LT2 also addresses the regulation of Cryptosporidium, Giardia and Viruses in open reservoirs.