As part of an on-call contract, Skilling Connolly worked with the City to complete stormwater basin design in support of a proposed roundabout. We oversaw a geotechnical investigation which determined the infiltration capacity of vicinity soils. Due to the presence of poor soils, advanced infiltration techniques were proposed. To determine if deep infiltration trenches would improve infiltration rates, a pilot infiltration test was conducted. We designed a deep infiltration trench pilot project (Pilot Infiltration Test – PIT) which was installed in the existing fire station storm basin. The basin was then flooded for approximately eight hours while ground water levels were monitored. Based on the test results it was determined that deep trenches would improve infiltration and allow for treatment of new stormwater from the roundabout, therefore we went forward with completing PS&E for these facilities.Based on the results of the PIT test, a final infiltration design was completed.  This required working closely with City staff as they completed final roundabout design.  During final design, it was determined that standard side slopes would not facilitate the necessary road geometry and that retaining walls within the stormwater basins would be required.  Working with the City, Skillings Connolly designed retaining walls that took into consideration the saturated conditions of the stormwater basin.