ASCE webinars are great for us. We are in a remote location and it is difficult to get quality training for our staff without much expense.  -  Anonymous Attendee

Purpose and Background

Surface impoundments are used to contain (either temporarily or permanently) all types of liquids and quasi-liquids. In addition to the obvious (potable water, industrial waters, grey waters, various sludges) there are 206,000 hazardous liquid impoundments in America. Quasi-liquids like sewage sludge, dredged sediments, and coal combustion residuals are also necessarily contained materials. For all of these materials, geomembranes as a single or double-lined barrier system hold the key toward a successful containment system. After a brief background, this webinar progresses step-by-step through the design process of surface impoundments. The progression begins with geometric considerations and then deciding upon a preferred cross-section. Regulations, where appropriate, will be mentioned. The all-important choice of geomembrane type is addressed using a benefit-to-cost analysis for resin type and this is then followed by an analytic design for thickness. Details regarding subgrade stability and cover soil stability are then presented. The termination of the geomembrane insofar as runout and anchor trench design, are presented. Lastly, allowable leakage values and details of the relatively new electrical leak location survey are presented.

Primary Discussion Topics

This webinar, an essential aspect of geosynthetic material applications focuses on the following segments:

• Background
  o typical applications
  o exposed vs. covered conditions
  o appurtenances
• Geometric Considerations
  o need for borings
  o general volumetric equation
  o typical cross sections
  o uplift considerations, i.e., whales
  o avoidance of whales
  o underdrain possibilities
  o venting options
• Geomembrane Selection
  o major (and minor) issues
  o benefit quantification
  o benefit/cost example
  o generic specifications
• Thickness Considerations
  o regulations
  o survivability
  o analytic model
  o numeric example
• Stability Issues
  o soil subgrade instability
  o exposed lifetime of different geomembranes
  o cover soil stability
  o numeric examples
• Geomembrane Termination Details
  o runout calculations
  o anchor trench details
  o V-trench considerations
• Leakage Through Holes
  o regulatory survey
  o calculated values
  o electrical leak location surveys

Learning Outcomes

• Recognize the scope and range of lined surface impoundments
• Understand the appropriate design methodology geomembranes for surface impoundments
• Learn appropriate site selection methods; various optional geosynthetic cross-sections; idiosyncrasies of different geomembrane types; various design details (thickness, soil stability, anchor trenches); as well as leakage scenarios
• Understand the various regulatory agency allowable leakage rates
• Know the electrical leak location survey method will be described and discussed

Webinar Benefits

• Understanding the scope and range of lined surface impoundments
• Discuss the various optional cross-sections vis-à-vis different geosynthetic materials, including geomembranes, geosynthetic clay liners, geotextiles, geonets, and geocomposites
• Present design models (with numeric examples), for geomembrane thickness, subgrade stability, cover and stability, runout and anchor trench design
• Learn various regulatory agency allowable leakage rates and most importantly describe the relatively recent method of leak location, which is conducted before the surface impoundment is put into service

Assessment of Learning Outcomes

Students' achievement of the learning outcomes will be assessed via a short post-assessment (true-false, multiple choice and fill in the blank questions).

Intended Audience

• Federal, state and regional environmental, geoenvironmental, geotechnical and hydraulic engineers
• Engineers from municipal districts and townships
• Private and municipal owners of all types of surface impoundments
• General civil consulting engineers
• Testing laboratories servicing these organizations
• Manufacturers and representatives of geosynthetic materials
• Contractors and installers servicing these applications; academic and research groups
• Others desiring technically related information on this important aspect of our environmental protection

Webinar Outline

• Background
• Geometric considerations
• Typical cross sections
• Geomembrane selection
• Thickness considerations
• Subgrade and cover soil stability
• Runout and anchor trench considerations
• Leakage through geomembrane holes
• Summary and conclusion