Dry Well System
The design of the dry well system consists of a treatment train of three components: a vegetated pretreatment feature, sedimentation well, and the dry well itself, as depicted in the diagram below. The vegetated pretreatment feature stored and filtered stormwater for a minimum of 7-minutes and reduced peak discharge rates and total runoff by using soil amendments to increase infiltration. The second stage of pretreatment, the sedimentation well, trapped and filtered additional sediment before runoff was discharged into the dry well. The dry well itself was designed to capture any remaining suspended solids by including both sand and gravel layers at the top of the well. While the pervious layers will facilitate a high infiltration rate, the clay layer in the vadose zone will cause stormwater to move horizontally to obtain further treatment of potential contaminants and will function as a final step of attenuation.
The project's dry well system to the left is composed of a (left to right) vegetated pre-treatment feature, sedimentation well and a dry well.
Monitoring Well Network
At each site three groundwater monitoring wells were constructed: one upgradient and two downgradient of the dry well. The upgradient well was constructed approximately 150 to 300 feet from the dry well and provided information on the baseline groundwater quality. The two downgradient wells, located about 100 feet from the dry well, permitted the assessment of the affects, if any, of influent stormwater on groundwater quality. In addition, one downgradient vadose zone well was constructed about 5 feet from the dry well. The vadose zone well aided in tracing the movement of contaminants that might pass through the dry well.
The figures below show the layout of the dry well and monitoring networks at the Strawberry Creek Water Quality Basin and the City’s Corporation Yard.