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1 <br /> ' Proposed James Monroe Elementary School Replacement Subsw face Exploration, Geologic Hazards, andRevised Geotechnical Engineering Report <br /> Everett, Washington Project and Site Conditions <br /> ' 4.4 Infiltration.Potential/Detention Considerations <br /> I • The site was observed to be underlain by lodgement till sediments at each of the boring <br /> locations. Lodgement till is characterized by low infiltration rates, and is not suitable for use <br /> as a conventional infiltration receptor. On some recent projects, we have seen Low Impact <br /> ' Development (LID) features used on sites underlain by lodgement till. Examples have <br /> included the use of permeable pavement and water quality rain gardens. Where permeable <br /> pavement is placed above lodgement till, we typically recommend a storage layer often <br /> ' consisting of 18 inches of open graded crushed rock, as well as a conventional surface water <br /> management infrastructure to handle surface water when the infiltration capacity and storage <br /> capacity of the permeable paving are exceeded. Water quality rain gardens are sometimes used <br /> to treat parking lot runoff prior to disposal, and do not rely on infiltration to achieve their <br /> intended purpose. Current project plans do not include LID features. We are available to <br /> provide situation-specific recommendations if LID features are implemented on this project. <br /> ' We are also working with the design team to investigate potential use of Underground Injection <br /> Control (UIC) wells for storm water disposal. That work is ongoing and will be presented <br /> separately from this report. <br /> • <br /> 1 <br /> 1 <br /> 1 <br /> 1 <br /> ' October 5, 2009 ASSOCIATED EARTH SCIENCES, INC. <br /> 13WG1(d-K090312/13-Projeus1200903121KEiWP Page 5 <br />