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Little Patuxent Interceptor Sewer. Howard County, Maryland.

The existing interceptor sewer, constructed in the 1960s, is nearly at capacity. The proposed interceptor sewer would parallel the existing pipeline for approximately 10.4 miles.

The new pipeline was located parallel to an existing interceptor and to the Little Patuxent River. In order to best utilize the existing pipeline, several complex junction structures were designed. During construction, the existing sewer remained in service, requiring full bypass of the flow. Because the majority of the parallel sewer was located in the 100-year flood plain and in a close proximity to the Little Patuxent River, environmental permitting and pipeline routing were key. The design included features for limiting inflow and infiltration to the system during wet weather and flood events, including raised, bolted manhole covers, and pressure-rated pipe. WRA worked with Howard County engineers and a team of consultants to design the parallel sewer system, and was directly responsible for design of Contracts 6, 7 and 8 (a total of 18,000 linear feet).

Little Patuxent Interceptor Sewer
Project Highlights


Survey efforts for this project included: topographic and boundary surveys, easement plats and stream mitigation plats. Surveys were tied to Maryland State Plane Coordinate System NAD 83 and NAVD 88 benchmarks using control supplied by the Howard County Survey Office.


A subsurface investigation, geotechnical design and advice during construction were provided for the 36-inch parallel gravity sewer. The project included considerations for multiple stream crossings, a complex junction structure and pipeline construction near an existing bridge foundation.


WRA’s Highway Design group designed access points for construction vehicles, ensuring that they could navigate the required grades and turns to access the site, and checked vertical clearances to ensure construction equipment could navigate under bridges along the Interceptor alignment.