FIGURE ES-2 The Allegheny, Monongahela, and Ohio Rivers in Allegheny County in southwestern Pennsylvania; shaded areas include the 83 Allegheny County communities serviced by the Allegheny County Sanitary Authority (ALCOSAN), including the City of Pittsburgh.

Since the late 1950s, the development of sewage treatment plants throughout the region—the largest of which is operated by the Allegheny County Sanitary Authority (ALCOSAN) and serves the City of Pittsburgh and 82 other communities in Allegheny County (see Figure ES-2)—has alleviated downstream pollution in the Ohio River from the municipal sewers that previously discharged directly to local waterways. Yet releases of untreated sewage and surface runoff, especially on wet weather days and due to failing sewers, continue to degrade the quality of waters and impair their value for habitat, recreation, and water supply. Sewage-related water quality problems also persist in dry weather because of aging and deteriorating on-site sewage treatment and disposal (“septic”) systems and sewage pipes that may be a significant source of contamination to groundwater supplies. These problems threaten the region’s public health, environment, economy, and image. For example, there has been a steady rise in the last decade in the number of days of the summer recreational season that the Allegheny County Health Department (ACHD) has issued river advisories (i.e., when rainfall in the region is great enough to potentially cause sewer overflows and lead to excessive levels of bacterial indicator organisms1) that recommend restricted recreational contact exposure. Indeed, the City of Pittsburgh, ALCOSAN, and other communities in the region face extensive and costly regulatory


Because it is impractical to test waters for all possible pathogenic microorganisms, the microbial quality of water is often assessed through the use of indicator microorganisms (usually bacteria). Although such fecal indicator bacteria are generally not pathogenic, they provide estimates of the amount of feces and, indirectly, the presence and quantity of fecal pathogens in water (see Chapter 3 for further information).

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