Inflow & Infiltration Reduction

Borough of Orwigsburg Orwigsburg, PA



In 2004, the Borough of Orwigsburg (Orwigsburg) completed an upgrade project to increase the capacity of their wastewater treatment plant (WWTP). A few years later they found themselves within 10% of the maximum capacity at the WWTP and with a collection system wrought with backups and overflows during wet weather. The added flow to the plant and collection system issues were due to inflow & infiltration (I&I) of groundwater and rainwater into the system. Fearing millions spent on another costly plant expansion, Orwigsburg decided to tackle their I&I problem head-on.

In 2006, we began assisting Orwigsburg with a strategic 10-year I&I reduction plan that fit within their capital budget. Over that time, a series of projects were designed and implemented that ultimately resulted in a 42% reduction (342,000 GPD) of effluent to the WWTP, returning capacity to the plant and collection system. The reduction has eliminated the need for designed capacity upgrades for the plant and PADEP effluent discharge permit increases, saving the borough millions of dollars.

Solution Details

The first step in an I&I battle is to understand the system. Like many systems, data for Orwigsburg was scattered and sporadic, with lots of data on some areas and little to none on others. A system-wide manhole inspection was performed with GPS verification to get a snapshot of the system’s current condition. That data was then converted into a GIS system map.

After we had a better understanding of the system, several small I&I projects were completed along with a house to house inspection. The low cost projects improved I&I by identifying and removing illegal hookups that diverted rain and groundwater into the sanitary sewer system. After these projects were completed, there were no more sewer overflows during rain events in known problem areas.

The largest project was the WWTP interceptor replacement and relocation. The main interceptor was an old 12” clay pipe that traversed waterlogged areas such as a stream bed wetlands as it made a straight line to the WWTP, exacerbating infiltration. Additionally, the existing route created a large right-of-way (ROW) Orwigsburg needed to maintain for access.

The interceptor was replaced with an 18” PVC interceptor and re-routed along a roadway, eliminating the ROW access issue, removing the interceptor from the high groundwater areas, and allowing for the abandonment of a parallel system branch, prone to backups. The new interceptor eliminated 200,000+ GPD of I&I flow immediately upon its commissioning.

With the comprehensive I&I program executed, Orwigsburg has regained both WWTP and collection system capacity, eliminating the need for expansions in the foreseeable future that would have cost millions of dollars. Heavy rain events no longer have a significant impact on WWTP flows, and customers within this area are no longer subjected to SSOs / backups.

What They Said

"Entech has helped the Borough develop and navigate a system-wide home inspection program, with over 1,200 connections, which has reduced our 3-month maximum flow rate by over 150,000 gpd."

-Borough Manager

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42% flow reduction (2004/2015)

194 illegal system connections identified

3,127 lf of interceptor replaced

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