Western Slopes Drainage Study and Design

CHALLENGE:

In 2017, a severe flood event devastated the Village of Mundelein, affecting residents and businesses in the downtown area near Division Street and US 45 (Lake Street). The Village enlisted HR Green to investigate the causes of the flooding and to prepare the Western Slopes drainage study and design.

The upstream watershed, encompassing approximately 1,200 acres of urbanized land, funneled stormwater into a single 54-inch storm sewer that lacked the capacity to handle even a two-year storm event. This inadequacy led to significant residential flooding, infrastructure damage, and road closures. Seavey Ditch, the project’s ultimate outlet, is a regulatory floodway, and increasing its flow would impact downstream communities in Vernon Hills. Therefore, the project required a solution that alleviated flooding in Mundelein while maintaining or reducing downstream flows.

SOLUTION:

HR Green conducted a comprehensive drainage study and developed four potential solutions. The preferred alternative utilized a combination of strategically placed detention and conveyance improvements. HR Green worked with the Village to balance cost and level of service (LOS). A key accomplishment was the adaptive reuse of the existing 54-inch storm sewer along Division Street, which was in good condition. An additional 72-inch pipe, instead of the required 96-inch pipe, was proposed in parallel to the 54-inch pipe with equalizing cross-connections to reduce costs while providing the desired LOS for flood reduction. To mitigate increased flow, a 38-acre-feet wetland detention basin was proposed on an adjacent brownfield site. The basin also provides water quality and recreational and educational benefits in the watershed.

HR Green then developed the preliminary and final engineering plans for the preferred alternative.  The design team navigated critical design aspects during the preliminary design stage, coordinating with IDOT, IDNR-OWR, LCSMC, and the Park District, and addressing geotechnical and utility conflicts. HR Green also helped the Village secure $500,000 in cost participation from IDOT for improvements within the US 45 right-of-way.

Key project components included:

• Installation of a 72-inch RCP storm sewer parallel to the existing 54-inch pipe.
• Construction of three pre-cast box culverts and associated end sections.
• Development of new storm sewer structures, junction chambers, and adjustments to water and sanitary mains.
• Surface improvements, including sidewalks, curb and gutter, pavement patching, replacement, and resurfacing.
• Comprehensive traffic management plans for US Route 45 during construction.

BENEFIT: 

The Western Slopes drainage project was completed with a winning bid approximately 10% below the engineer’s estimate. The project provides regional benefits by attenuating peak flows in the 38-acre-feet detention basin and improving water quality by reducing sediment and pollutant transport downstream.