Oct 03, 2008

Protecting Elliot Bay

Waterfront property on the shores of Puget Sound in Seattle is currently undergoing revitalization efforts to attract some of the major Web-based companies to develop branch campuses in the area. One of the area projects is redeveloping a site that was previously occupied by a producer of dairy products.

The owner voluntarily agreed to clean up the site in preparation for the construction of two four-story commercial buildings, a plaza and an underground parking facility that will be up to 20 ft below existing grade.

The 2.25-acre site is located at the base of a large hill and 700 ft from the shoreline of Elliot Bay. The proximity to the Puget Sound and the surrounding steep slopes create challenges for both groundwater and surface water discharge. The site required a maximum of 7 mL to 1 L settleable solids and a pH of 12 (due to the permit issued by King County Industrial Waste Office) prior to discharge to the municipal wastewater system.

Eliminating Pollutants

Initial environmental analysis of the site revealed high levels of petroleum and chlorinated hydrocarbons in the soil. The contaminants came from up-gradient industrial sources and a facility adjacent to the project. Along with hydrocarbons, significant levels of heavy metals, petroleum products and arsenic have been found.

As part of the remediation process and to allow for subgrade construction, dewatering wells were installed around the interior of the project. Contaminated groundwater is extracted from these wells and pumped to a revolutionary treatment system.

A modularized, 350-gal-per-minute treatment system , consisting of chitosan flocculant and a series of filters with specific media to address each pollutant of concern, was installed. Chitosan is added to the system as water passes over a dry chitosan flocculant that dissolves into the system. The chitosan addition to the system is to address sediment removal prior to filtration through the granulated activated carbon (GAC). Many contaminants associated with the fine sediment are removed at this point.

Once the sediment is removed, the GAC filters act as a polishing filter to remove any further contamination prior to discharge.

Automation

Clear Water Compliance Services was chosen by Malcolm Drilling Co. Inc., the shoring and dewatering contractor, as the treatment service provider for this project. For the past 10 years, Clear Water has been treating groundwater and storm water on construction sites, but the company has not gone to an automated system because of regulatory restrictions and the high variability of storm water and environmental influences that can affect treatment.

However, due to some advancements in technology and treatment experience, the company was able to automate the system for this project.

Daily site checks are required, but only for maintenance purposes and to conduct a confidence check on settleable solids. The system monitors turbidity and water levels in the wells and shuts on and off accordingly. Discharge limits are set on the system according to the permit. If recorded monitoring limits are outside the set perimeters, the system will notify the supervisor and stop the water from discharging to sanitary.

The use of an automated system has greatly reduced operational labor costs and increased efficiency of treatment on site. With an automated system, clients are able to save money in labor costs and stay in water quality compliance.

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