To keep up with a growing student population, Sacramento State University is planning and building additional facilities and recently broke ground on a new parking structure. In keeping with their dedication to low impact development (LID), the addition of the parking structure included stormwater planters to capture and treat runoff for the purpose of meeting stormwater quality requirements. What was a great design on paper (in 2 dimensions) wasn’t practically possible because the invert of the stormwater planters was lower than the existing storm drain outfall which could lead to standing water and vector (mosquito) issues.
It fell to the project engineer to find a solution to mitigate these issues. As luck would have it, Siegfried Engineering had just been through one of Torrent Resources’ Lunch & Learn Presentations and had MaxWell® drywells on their minds. Torrent’s dual chambered drywell, known as the Maxwell Plus®, was the perfect solution to both problems. The Maxwell Plus would be used to prevent standing water (vector hazard) and supply additional groundwater infiltration on the site. As a bonus, the drywell provided a higher discharge elevation to the arboretum, which includes a sump pump to discharge to the American River.
The overall design depth of the drywell was set at 25’ to maintain a minimum 10’ separation from groundwater, which was at least 35’ below the project site according to the project soils report. But construction projects often encounter unforeseen circumstances and this one was no different. During drilling operations, the Torrent crew ran into groundwater at a depth of 24’, which halted construction. After coordinating with Siegfried Engineering and the contractor, the plan of action was to shorten the overall depth to 14’, because the 10’ separation was still required, and adjust the chamber depths accordingly. Though the deign depths were modified due to field conditions, the overall functionality of the system remains the same.