Unfortunately, raw sewage discharges are still common in our area. Many of these occur through Combined Sewage Overflows (CSOs) and Separate Sewer Overflows (SSOs). Overflows from SSOs are illegal and unpermitted discharges and may occur as sewage backups in residences or businesses, discharges from manholes or overflows from control structures. Early in 1997, the United States Environmental Protection Agency (EPA) ordered many municipalities within the Allegheny County Sanitary Authority (ALCOSAN) service area to provide information about their sewer systems with full intent to enforce the Clean Water Act. The EPA goal is to end all SSO overflows and bring municipalities into compliance with the Act.
The Gateway Engineers, Inc. (Gateway) provide municipal engineering services to several communities ordered to provide sewer information to the U.S. EPA. EPA orders demand an extensive collection of flow data from the sewers under study. Gateway has installed flow monitors to assist many municipalities in complying. In addition, several communities have voluntarily undertaken sewage studies and installed flow monitors.
Flow Analysis
The flow monitoring devices have been installed at or above sewer overflow structures to determine precisely what quantities of sewage are produced at all times of the day. The monitors are set to take readings every 15 seconds and to record the averages of these readings every 15 minutes. Each week, representatives make site visits to "upload" data from monitors and inspect the monitoring devices.The data is then analyzed and reports are prepared monthly for the EPA and the Allegheny County Health Department (ACHD). The monthly reports include census data for each watershed area and allow a determination of "per capita" flow quantity. The residential per capita sewage allowance is a peak flow rate of 250 gallons per person per day and the commercial allowance is 2.5 times the water consumption. If sewer lines carry flow from municipal communities, the EPA allowance must be met before the combined sewage would reach the ALCOSAN interceptor. Due to this requirement, the EPA and the ACHD suggest communities join together by watershed area to gather and prepare the required data. Some additional study requirements are shown in Table 1.
It is evident from these requirements that the EPA order is a labor-intensive directive. The EPA has given the ACHD authority to issue orders and assist communities with flow monitoring requirements.
The sewage monitoring study program is ordered to continue until sewage flow at the selected study points is at or below the allowable flow rates for eight consecutive months. This may be a difficult goal for some communities to achieve because of old and deteriorating sewer systems. Older systems tend to have many problems with inflow and infiltration (I/I). Many older systems also have illegal connections from roof and driveway drains.
Rain flow data collection is very important in identifying I/I problems. Several Gateway communities have instructed us to install rain gauges to quantify precipitation amounts and compare these quantities with peak monthly flow data. Gateway also assists communities in videotaping sewer lines to identify problem areas and in rehabilitating, replacing or redesigning sewers as necessary. Dye testing may identify illegal storm water connections to be removed. With proper design and maintenance, the EPA requirements can be met.
The EPA fully intends to carry out the Clean Water Act as authorized. All data provided must be "legally defensible" and will be used to determine violators of the Act. Failure to respond to the EPA requests is punishable under section 309 of the Act. It is our goal to assist the communities we represent in meeting the EPA demands as cost efficiently and in as timely a manner as possible. Together we can preserve our environment and provide our communities and families with safe and clean waterways to enjoy for years to come.
About the Author:
Amy Fardo Patsey, E.I.T., holds a Civil Engineering degree from the University of Pittsburgh and serves as engineering project manager for The Gateway Engineers, Inc., in Pittsburgh, PA. She sits on the board of directors for the Pennsylvania Society of Professional Engineers and is past treasurer and vice president of the national Society of Women Engineers.Table 1: Flow Monitoring Compliance Requirements
- Provide peak and daily flow totals for the month.
- Provide census data for the watershed area.
- Provide plan views and profiles predicting the selected monitoring points and the adjacent upstream and downstream manholes and connecting pipes.
- Submit flow monitoring data in ASCII-formatted files to the ACHD.
- Check monitor sites after every storm event producing more than one inch of rainfall.
- Measure depth and velocity profile readings at every site visit to calculate calibration coefficients. The coefficients should be adjusted monthly when data is submitted.
- Take dry-weather measurements at varying times of the day. Half of the readings should be made during peak flow times (7p;9 a.m. and 7p;10 p.m.). At least five measurements should be taken between 2p;5 a.m.
- Take measurements for at least 12 rainfalls of varying depth, intensity and duration.
- Track weather reports to schedule measurement days. Doppler radar is suggested to predict when storms will peak.
- Record three measurements each of rising and falling flow depths during storm events at 15 minute intervals.
- The morning after a storm event, take readings to observe infiltration effects.
- Prepare various plots for submissions.
- Submit data for all commercial and industrial users' flow estimates.
- Document quality reviews required by the municipal engineer.
- Install and maintain rain gauges. Locations of gauges must be submitted for GIS (Geographic Information Systems) mapping. These must be recording-type gauges.
- Submit data files of rainfall information in a specified format.
- Submit mapping of the entire sewer system.
