Project Summary
Current Phase: Design
Total Estimated Cost: $2,582,000.00
Funding Source: Combined Sewer Wet Weather Mitigation
Project Description
The Colonial Avenue Sanitary Sewer Separation Project will separate sanitary flow from the combined sewer system to prevent sewer backups and basement flooding within Bashford Avenue, Powhatan Street, Second Street, Colonial Avenue, and Vernon Street
This project is expected to mitigate the potential for sewer basement backups and basement flooding within the Westover neighborhood. During severe storm events, sanitary sewer capacity exceeds causing basement sewer backups, backyard and back-alley flooding. Several residences in the Westover neighborhood area have reported sewer backups and flooding during storm events because the current sewers are unable to convey the collected sewage.
A 10-inch-diameter sanitary sewer and 12-inch-diameter storm sewer are located in the back alley of Powhatan Street and Colonial Avenue houses. These pipe networks discharge into separate combined sewer mains that convey flow to AlexRenew’s wastewater treatment plant.
The City tasked an engineering consultant to conduct drainage surveys, model storm and sanitary flows, identify capacity deficiencies, and propose solutions. One of the proposed solutions involves separating the sanitary sewer from the combined sewer system and connecting it to a separate sanitary trunk sewer.
Stormwater improvements have also been identified to address local flooding concerns, but are outside the scope of this project and will be considered following implementation of the sewer separation project and subsequent monitoring.
Progress Update
The planning for the Colonial Avenue Sanitary Sewer Separation project is complete, and the project is currently in the design stage. The City is in the process of procuring a design contractor to produce the design plans and construction drawings. Upon awarding a contract to a design firm, the City plans to meet with residents and stakeholders. Notices will be distributed to residents prior to the start of work.
Project Funding
Total Estimated Cost: $2,582,000.00
Funding Source: Combined Sewer Wet Weather Mitigation
Funding Breakdown
This project is funded using Sanitary Sewer enterprise Fund Revenues and is programmed in the City’s Capital Improvement Program.
Schedule
Planning: Fall 2023 - Fall 2024
Design: Fall 2024 - Fall 2025
Construction: Fall 2025 - Spring 2027
Planning Phase
During the planning phase, the City identified a need for isolation of sanitary sewage prior to connecting to the combined sewer system to address the sewer backup issues. The primary task is to disconnect the sanitary sewer along Colonial Avenue that flows to the manhole located near the intersection of Colonial Avenue and Vernon Street to reverse the sanitary sewer flows and redirect flows to the existing AlexRenew trunk sewer (along N Fayette Street). The new route will align with the existing rights-of-way. The work will also include the installation of new manholes along N. Henry Street and First Street.
The City performed an investigation to assess the current conditions and the sanitary sewer network within the neighborhood. This work included locating cross connections between stormwater and sanitary system, carrying out field investigations of the neighborhood, and developing a hydraulic model of the sanitary sewer system.
The City also investigated private connections defined as drainage fixtures connected to the sanitary sewer system that do not primarily discharge wastewater, such as sump pumps, roof drains, and roof leaders. The analysis indicates that the sanitary sewer networks associated with Westover lack adequate capacity to manage the intense storm events of recent years. The increased sewage backups and basement flooding are attributed to old infrastructure, the design criteria in place at the time of construction, and the impact from climate change.
Planning Overview
- Field Investigation – includes resident interview results and dye test procedures, results, and analysis.
- Detailed Survey – all storm, sanitary and combined sewers in the area have been surveyed in order to determine sewer capacity and confirm feasibility of solutions
- Conceptual Design – includes a list of design requirements, existing condition descriptions, proposed alignment alternatives, model assumptions and development, recommendations, and coordination.
- Opinion of Probable Construction Cost – includes an estimated cost of the conceptual design.
Planning Public Outreach
Residents were actively involved through interviews, providing valuable information on sewage backup and flooding events. Their input influenced the study's recommendations and conceptual design.
Contact
Wael Eltayeb, P.E.
Project Manager
Department of Project Implementation
703.746.4217 (Office)
703.512.6253 (Direct)
Wael.eltayeb@alexandriava.gov