Los Angeles doesn’t hold still, and neither does its underground infrastructure. Between drought cycles, atmospheric rivers, and ongoing seismic activity, the city’s aging sewer infrastructure absorbs more movement than almost any other major metro in the country.
For engineers and contractors managing sewer rehabilitation across LA County, inflow and infiltration (I&I) isn’t a seasonal problem. LASAN operates under a consent decree that keeps I&I reduction as a constant priority, and the back-to-back atmospheric river events of the past two winters have made the stakes even clearer.
Same Headache, Two Different Sources
Cracked pipes, failing joints, and deteriorated manholes let groundwater seep into the system, that’s infiltration doing what it does. Inflow shows up differently, riding in through roof drains, yard connections, and other surface points wired straight into the sanitary line.
Every gallon that shouldn’t be there is a gallon eating into sewer capacity you need during the next storm. When saturation events hit LA County hard, as they did during the recent atmospheric river seasons, systems already carrying excess I&I get pushed toward overflow faster.
What the Mainline Fix Leaves Behind
LA County contractors reach for CIPP whenever a mainline needs structural renewal without tearing up a major arterial, and it’s a proven approach for exactly that job. What it doesn’t do is guarantee the surrounding pipe network behaves.
Contractors sometimes line a main and watch infiltration numbers barely budge. The culprit is usually the basin itself: expansive clay soils and seismic micro-movement stress laterals, connections, and manholes on their own timeline, unrelated to whatever happened at the mainline.
Common infiltration sources across LA’s neighborhoods include:
- Deteriorated laterals running beneath older San Fernando Valley and Eastside properties
- Failed main-to-lateral connections stressed by expansive soil movement
- Cracked host pipes near fault lines and areas with ongoing seismic micro-movement
- Manhole joint failures allowing groundwater intrusion near coastal zones
- Root intrusion into aging clay and concrete pipe throughout inland neighborhoods
Matching the Fix to the Actual Defect
Engineers here lean on a mix of CCTV footage, flow monitoring, and smoke testing precisely because LA’s soil behavior varies so much that a single inspection pass can miss where the real leak sits, the main, the lateral, the connection, or the structure itself.
Once the defect is confirmed, the fix should follow it, not a standard playbook. Trunk-line deterioration calls for mainline CIPP; a compromised private or public lateral needs full-length lining; a lateral connection knocked loose by soil movement needs targeted repair at that joint; a manhole cracked by seismic activity or coastal groundwater pressure needs structural rehab; and an isolated active leak at a joint is often best resolved with injection grouting rather than a full relining pass.
What’s at Stake for Engineers and Contractors
LA County utilities are footing a growing bill to pump and treat groundwater that shouldn’t be in the system, a cost made worse as wildfire recovery and rebuilding accelerate infrastructure demand across the region. Sewer overflows during heavy rain carry real regulatory and reputational consequences under LASAN’s consent decree framework.
Treating the collection system as one connected network, not a set of isolated pipe segments, is what makes an I&I reduction program hold up in a basin this dynamic. A relined main answers to LASAN’s spec on paper; laterals, connections, and manholes rehabbed in the same cycle are what actually keep infiltration numbers down through the next atmospheric river season.
Find a WRT-certified installer serving LA County to assess your collection system’s full scope of I&I sources.
