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EAST LAKE CENTER A 40-acre retail commercial development site anchored by Home Depot, Fred Meyer and Walgreen’s in Issaquah, WA. The scope of work included installation of 36,000 lineal feet of sewer, storm, and water piping as well as the construction of water detention and quality systems. This project was completed between July 1999 and April 2000 at a cost of $2.8 million. Spotlight Site water quality control and management, coupled with unsuitable trench backfill. Problem The project schedule dictated that utility piping be installed during the wet winter season. Site materials were extremely moisture sensitive, silty clay soils with over-optimum moisture content that could not be acceptably recompacted. Import of trench backfill would also require exporting the unsuitable trench spoils, and import/export would cause a serious budget over-run. In addition, the site experienced serious water quality management issues as a result of excessive offsite surface water that drained across the site and emptied directly into watercourses leading to Lake Sammamish. Solution Sajasa utilized Kiln Dust/Cement mixture treatment to dry trench spoils to achieve compaction of the native soils. The use of Kiln Dust/Cement accentuated the concern over site surface waters running directly into Lake Sammamish as a result of the added PH risk. To mitigate the potential of contaminated water escaping the site, a water collection system was designed and installed to allow retention, treatment and testing prior to release from the site. Using a 6" high lift diesel pump, water was pumped more than 2,000 lineal feet, with a head of 500 vertical feet, into a large detention and filtering pond. This allowed settling of silt particles and neutralization of PH levels prior to discharge. Results The project continued on schedule despite wet winter weather and silty clay backfill. This was accomplished without the use of imported trench backfill while avoiding an unacceptable discharge of silty or high PH level run-off water.Acknowledgements
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