Last week, the Lehigh Valley received record rainfall in the amount of more than 8 inches beginning on Thursday, September 30, and continuing overnight into Friday, October 1, 2010.
For Lehigh County Authority (LCA) and the municipalities that are connected to its regional sewer system, the storm brings the issue of leaking sewer lines into sharp focus. During the storm, sewer flows increased rapidly over a few short hours from a normal flow of about 7 million gallons per day to approximately 20 million gallons per day on Friday.
LCA now has three facilities in place to address “wet weather flow” like this, including a pump station in the Spring Creek Road area of Lower Macungie Township, a pump station in Allentown’s Lehigh Parkway area, and a new flow equalization basin (FEB) in Fogelsville. The FEB project was just completed and put into full operation earlier in the week, so this storm event was its first use. While LCA plans to analyze the FEB’s operation during last week’s storm to learn how to optimize its use during wet weather events, officials say the basin was successful in holding back up to 3 million gallons of flow during the peak of the rain event, which may have helped to reduce overflows downstream of the facility.
All three facilities were working at full capacity to handle the high flows brought on by the storm. However, the quick onslaught of the storm overwhelmed the system in a few areas, causing sewer manholes to overflow in the Lehigh Parkway area, just upstream of the pump station located there. Four of LCA’s sewer manholes were overflowing in addition to other non-LCA sewer manholes that were observed overflowing during the storm event. Because the municipal, LCA and Allentown pipe networks are an interconnected system, overflows may have been experienced in other locations throughout the system as well, in addition to possible bypassing of the Allentown treatment plant.
Based on operational data and field observations, LCA believes the overflows began at about 3:30 a.m. on Friday and continued intermittently until about 2:30 p.m. On Friday afternoon, LCA crews spent time in the Little Lehigh Parkway raking up debris caused by the Little Lehigh Creek flooding and the sewer manhole overflows, and spreading lime to neutralize the affected areas and control odors at any of manholes that showed evidence of overflows. Crews will continue to work on the affected manholes to repair damage caused by the force of water flowing through the system.
LCA crews also spent Friday afternoon and Saturday inspecting manholes on the Western Lehigh Interceptor upstream of the City’s Little Lehigh Parkway. No evidence of sewer overflows was observed upstream of the area that was inundated on Friday.
Sewer overflows occur in this region during storm events due to a high rate of rainwater entering the sewer system, typically through a combination of unauthorized connections such as sump pumps, roof drains and floor drains, manholes that are not designed to prevent rainwater leakage into the system, leaking private lateral sewer lines, public sewer lines that allow groundwater to enter the system, and aging stormwater systems that do not adequately contain stormwater runoff. Sanitary sewer systems are not designed to handle stormwater, and yet the flows experienced during rain events indicate that rainwater inflow is the primary cause of these peak flows and subsequent overflows.
In late 2009, the U.S. Environmental Protection Agency issued an order for all the municipalities using the regional sewer system that flows to the City of Allentown treatment plant to eliminate sewer system overflows that have plagued the system for quite some time. Municipalities throughout the region have their own sewer systems providing service to residents and businesses, and connect into LCA’s or Allentown’s regional interceptors to transport their wastewater to the treatment plant.
LCA and the municipalities in Western Lehigh County are actively pursuing the investigation and rehabilitation of sewer systems to eliminate such overflows. The Sewer Capacity Assurance and Rehabilitation Plan (SCARP) was adopted by LCA and the municipalities it serves in 2009, and they are now working through a partnership approach on programs to address high-priority areas identified through the flow-monitoring work conducted over the past three years.
Municipalities included in this partnership have already begun work in their communities to identify homes with unauthorized connections or sewer lines and manholes that need to be prepared. LCA has recently completed the construction of the FEB to help contain peak flows during storm events, as well as pursuing a flow modeling program, interceptor rehabilitation work, and providing overall leadership and support for the municipalities involved in the partnership. It is expected that this work will continue for several years before significant improvements will be realized, as the problem stems from tens of thousands of individual sewer connections that must be inspected and addressed if they are contributing rainwater to the system.