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  Soil stabilisation  

TENAX MS multi-layer bi-oriented geogrids for closure of a wastewater treatment impoundment, Alabama

 

 

PRODUCTS:

TENAX MS multi-layer geogrids

 

Location:

Phoenix, Alabama

Owner:

Mead Corporation

Project:

Mr. Kent Nilsson, PE, RMT, Inc.

 

Problem
The Mead Corporation has considered closing unlined wastewater treatment impoundments, including a 2.8 hectars strong waste pond at the Mahrt, Alabama mill.
The Mahrt strong waste pond contains a mixture of spent liquor, fiber and some ash. In addition to receiving the occasional liquor spill material; the pond receives some storm water.

The pond is frequently covered with some depth of water, and any exposed solids are typically weak and unstable. The pond would be closed under guidelines promulgated by the Water Division of the Alabama Department of Environmental Management (ADEM).

One requirement stipulates that any cap should maintain a minimum slope of 5 percent. For the 2.8 hectars impoundment, this would require significant earth fill volumes. However, the guidelines allow some variance in the stipulated closure approach provided the closure method provides equal or better protection of the groundwater.

Mead’s proposed concept involved the use of ash as a construction material in covering the solids in place. The landfill operator would use ash as a fill to construct the cover incrementally, without double handling of material. This would save significant construction costs and preserve valuable landfill airspace.


 

TENAX MS multi-layer bi-oriented geogrids for closure of a wastewater treatment impoundment, Alabama

 

Solution
A demonstration project for the closure concept was performed using ash and a multi-layer geogrid for bridging the soft solids. The closure strategy was successfully demonstrated and a closure concept developed. A closure design concept was developed for the unlined pond to achieve:

  • Facilitate preparation of future phase closure plan for the existing impoundment to comply with/ADEM’s guidelines for industrial wastewater impoundments;
  • Stabilize the existing ground surface of the impoundment with a multi-layer geogrid to prepare for the additional fill material for closure; and
  • Utilize on site ash as a fill material to facilitate closure of the existing impoundment.


Conclusions
The use of a multi-layer geogrid to stabilize the existing ground surface of the impoundment to prepare for the additional fill material for closure was considered a success. With the geogrid reinforcement at the base of the ash layer, the geogrid was able to withstand heavy equipment and loads, which is critical for the short term and long term closure activities of the impoundment.

At an economic standpoint, the amount of airspace saved for the mill’s landfill by using the industrial wastewater impoundment for ash fill was estimated to be around 100.000 m3. The mill produces around 135.000 m3 per year, which is about an 8-month savings of valuable landfill airspace.


 

 

 

 

 

Applications:

Permanent and semi-permanent loads spread over large areas

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