Microtunneling beneath I-215 to close the gap on Perris Valley Pipeline

Completing a critical water connection for Riverside County

The north and south reaches of the Perris Valley Pipeline were constructed more than a decade ago to expand water delivery to the Eastern and Western Municipal Water Districts of Riverside County in California.

However, the segment crossing under Interstate 215 (I-215) could not be constructed at the time because of complex ground conditions and higher-than-anticipated groundwater inflows. Completing this final connection was essential to improving regional water delivery capacity and supporting a more reliable supply for growing communities east of Los Angeles.

The I-215 crossing involved construction of approximately 3,000 linear feet of 97-inch (2.46m) diameter steel water transmission pipeline. Most of the work was delivered through three microtunnel drives and four tunnel access shafts, with the final drive passing beneath I-215 and railway corridors.

The project’s location created several technical and logistical challenges, including maintaining traffic along Van Buren Boulevard; coordinating with adjacent property owners, Caltrans, rail stakeholders, and permitting agencies; protecting active transportation infrastructure; and managing groundwater and potential contaminants. To reduce disruption at the surface and safely complete the crossing, the project team used a 123-inch (3.12m) microtunnel boring machine to install large-diameter casing below ground.

Perris Valley Pipeline alignment (image credit: MWD)

Supporting delivery of a challenging underground crossing

Mott MacDonald joined the project team in 2023 to provide specialized tunnel and shaft expertise in support of MWD’s Construction Management Unit. As a prime construction management partner, we provided technical support to help MWD and contractor J.W. Fowler progress the final segment connecting the north and south reaches of the Perris Valley Pipeline.

We helped the team navigate the complexities of large diameter microtunneling, shaft construction, and groundwater treatment, drawing on our expertise across tunneling, geotechnical engineering, permitting, and stormwater management. We provided construction inspection, tunnel engineering support, technical review, and risk management services for the project.

To support safe and efficient delivery, we established observation protocols, analyzed instrumentation and microtunnel boring machine data, and provided recommendations to address emerging field conditions. We also introduced additional ground movement monitoring and enhanced stakeholder coordination measures, helping strengthen collaboration and manage risks throughout this complex underground crossing.

Minimizing disruption while maximizing impact

The completed Perris Valley Pipeline I-215 Crossing connects the final segment of a major water delivery pipeline, improving regional water delivery capacity, strengthening system reliability, and supporting the long-term needs of growing communities in Southern California. The project also demonstrates how trenchless construction can help deliver essential infrastructure while minimizing surface disruption in busy transportation corridors.