Specialized Sediment Removal - Industrial Facility Pond

Date Completed: April 7, 2015
Category: general

In Spring of 2013, Allied was awarded a contract to remove and dispose of oil-impacted sediment from a firewater holding pond operated by a global manufacturer of industrial and agricultural chemicals. The facility was located in northwest Ohio. Allied’s unique approach, employing specialized SCUBA diving techniques, vacuum extraction, and passive sediment dewatering, was selected over competitors’ traditional mechanical dredging methods. Allied’s specialized approach was considered superior for multiple reasons:

• being safer when working around submersed pond equipment pumps and aerators,
• providing more precise depth control,
• eliminating the need to drain the pond, and
• being considerably less expensive than traditional methods.

Allied began project planning, including an assessment of the pond and sediment conditions, in spring of 2013. The assessment included evaluation of the sediment composition and chemistry, as well as mapping of the sediment depth, thickness and volume. The pond surface area was determined to be 1.9 acres, with an average sediment thickness of 4 feet and a maximum thickness of 12 feet. The sediment removal project focused on approximately one acre of the pond bottom. Contaminants of concern within the sediments consisted of low concentrations of petroleum hydrocarbons.

Allied compiled this information and prepared an effective work plan, diving plan, and site-specific safety plan for the project. It was determined that the sediment would be collected into a series of geotextile containers (bags) to allow passive dewatering. To increase the precipitation and dewatering efficiencies, Allied made the decision to condition the collected sediment with a specialized polymer. The excess water would be drained from the geotextile containers and would be discharged to an adjacent process pond, per client specifications. The remaining sediment would be excavated from the geotextile bags, loaded into sealed roll-off boxes, and transported to an approved off-site landfill for disposal as non-hazardous waste.

Equipment was mobilized to the project site and sediment removal began in September 2013. Work continued through mid-November when diving activities were suspended due to freezing conditions. Following the spring thaw, work commenced in mid-April. The diving/sediment removal phase of the project was completed on June 27, 2014. The filled geotextile containers were allowed to passively dewater for 25 days. The dewatering process was confirmed complete by a standard paint filter test and excavation of the collected sediment began on July 21, 2014. The excavation and transport of sediment continued through August 29, 2014. The overall project length, from planning through completion, was 17 months (510 days).

In total, 110 days were dedicated to diving/sediment removal. The in-situ volume of sediment removed from the pond was estimated to be 9,837 yd³. The average rate of sediment removal was approximately 80 yd³ per day (approximately 19 tons of dewatered sediment per day). The estimated volume of pond capacity restored was 1.99 million gallons.