Little Patuxent Interceptor Sewer Rehabilitation
The Little Patuxent Sewershed in Howard County, Maryland encompasses approximately 49-square miles in central Howard County and includes the Columbia Town Center. The existing Little Patuxent Interceptor generally follows the alignment of the Little Patuxent River spanning from north of Interstate 70 south to the Little Patuxent Water Reclamation Plant. In order to address current and future capacity needs, Howard County contracted with George, Miles & Buhr, LLC (GMB) to study the existing Little Patuxent Interceptor Sewer and evaluate its capability of handling current and future anticipated flows and recommend measures to address those needs.
A hydraulic model was developed to analyze the existing sewer system comprised of the physical sewer system data (sewer pipes 12-inch diameter and larger with accompanying manholes) and the hydraulic information (flows and hydraulic conditions). The flow metering program consisted of 21 flow meters and 6 rain gauges which were operated and maintained for 4 months. GMB analyzed the flow meter data to determine wastewater flows and patterns broken into the three components of sewage flow, groundwater infiltration, and rainfall-dependent infiltration and inflow (RDII) for use in the hydraulic model.
GMB provided design and bidding phase services for the Little Patuxent Parallel Interceptor Sewer from the recommendations of the study including the evaluation of multiple alternative alignments and trenchless technologies for the preparation of bid-ready plans and specifications. The construction contracts were phased into five (5) separate contracts to construct approximately 21,900 linear feet of new 30-inch diameter through 42-inch diameter parallel interceptor sewer. The sewer originates at the tie-in to the existing Little Patuxent Interceptor just north of the Little Patuxent Water Reclamation Plant and runs north / upstream and generally parallel to the existing Little Patuxent Interceptor to just south of the Maryland Route 32 crossing at Guilford Road. The sewer alignment included several river crossings and traversed heavily wooded areas, rock outcroppings, wetland areas and historic preservation areas. Project included environmental permitting for multiple river crossings, bypass pumping, blasting precautions, construction access, and 380 LF of hand dug 8-foot horseshoe tunnel through 55,000 psi amphibolite bedrock.
As part of an on-call contract, GMB provided preliminary engineering services, design, bidding and construction phase services for rehabilitation of the original Little Patuxent Interceptor Sewer. This project involved preparation of bid-ready plans and specifications to rehabilitate approximately 17,000 LF of existing 27-inch diameter through 36-inch diameter interceptor sewer and 36 manholes. The design called for the use of Cured-In-Place Pipe (CIPP) lining of the interceptor and spray-on resin lining of the manholes. Since the rehabilitation project is following up on the earlier work installing the parallel interceptor, the rehabilitation efforts took advantage of existing access roads as much as possible and required only one new access point.