There are indications that the CSO problem has worsened in the last decade in southwestern Pennsylvania. Table 4-11 provides the total number of advisories and days affected by advisories for the summer recreational season in Allegheny County. River advisories are issued when rainfall in the region is high enough to potentially cause sewer overflows and lead to unsafe bacterial concentrations in the river. When an alert is in effect, marinas and docks fly an orange and black CSO sign to alert recreational users of potentially unsafe conditions. The Allegheny County Health Department (ACHD) recommends restricted recreational exposure during advisories (e.g., anglers are advised to wash their hands after fishing and not to cut fish line with their teeth). As shown in Table 4-11, there has been a steady rise in the number of days that the water is considered impaired and restriction of body contact recreation is recommended by the ACHD. As noted previously, the ACHD is conducting a study of the river quality and human health by evaluating the health status of rowers who use the river for practice and competition (ACHD, 2004). Initial data are expected in October 2004.

One of the reasons for increasing CSOs in Allegheny County is the aging collection system and the problem of infiltration. Although many wet weather stormwater flows are directed into sewer pipes in the combined systems, many additional flows find their way into the system during wet and dry weather. Figure 4-5 shows possible sources of infiltration and inflow (I/I) into a collection system. The source of infiltration and inflow in sewer systems is site specific. In some locations, foundation drains are connected to the sewer lines. In other areas, rain leaders (roof gutter drains and areaway drains) are connected to the sewer lines. In many areas, house laterals (the component of the system owned by individual homeowners) show significant deterioration, allowing groundwater to enter sewer pipes.

Unlike combined systems, dedicated sanitary sewer systems were designed to carry only sanitary waste. However, pipe cracks and illegal connection of “French drains” or roof collection systems can add stormwater to sanitary systems. When significant infiltration occurs, sanitary sewer overflows can take place, especially during rain events. SSOs are illegal in the United States under the federal CWA. Since the sanitary system was not designed to overflow into local waterways, SSOs result in groundwater contamination, backups of sewage into basements, and overflows through manhole covers (see Figure 4-6).