Sump Pump Design in Altadena - LA County Standards
When does an Altadena property need a sump pump? We follow LA County standards for design and try to avoid pumps whenever gravity drainage can work instead.
The LA County Sump Pump Manual outlines three cases where a sump pump becomes necessary. Case A is when flows would naturally travel to a downstream property but no drainage facilities exist to accept them. Case B happens when the finished floor sits above sump overflow elevations but ponding depth would exceed allowable limits. Case C is when the finished floor sits below the sump overflow elevation, such as with subterranean parking.
We see all three scenarios play out in Altadena fire rebuilds. The county requires a hydrology study for the Q50 to determine sump volume and pump sizing. The design must show sufficient offsite topography to understand the drainage pattern. If your drainage area is 10 acres or less, LA County provides the HydroCalc Calculator to calculate flows.
The key thing we tell homeowners: pumps are expensive to maintain and depend on electricity. If we can route water downhill to the street or an existing storm drain, that is always the better solution. Sometimes the grade just does not work out and a pump becomes necessary.
On Altadena fire rebuilds specifically, we often use a hydrology report to show the pre-fire drainage pattern compared to post-fire conditions. If we can demonstrate that post-development Q does not exceed pre-fire Q, we can sometimes avoid requiring a pump altogether. The key is showing the site drains the same way it did before the fire and that we are not increasing cross-drainage to neighboring properties.
When a pump is required, LA County mandates a duplex system with two pumps. Each pump must handle the design flow with a factor of safety of 1.25. The system activates both pumps as water rises, preventing either from sitting idle and deteriorating. The sump basin must be at least 15 inches in diameter and 18 inches deep with a fitted cover.
If you are in plan check and LADBS or LA County is asking for a sump pump design, give us a call. We can review your site, check the grades, and determine if there is a gravity solution first.
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