Richard N. Downer

To the Technical Advisory Committee (TAC)

The EE/CA is a Concept Report and Final Design will come later. As I see the scenario,

1. The State and EPA have already agree there is a problem, namely, Acid Mine Drainage (AMD)
2. EPA has agreed to do something about the AMD, namely, declare the Elizabeth mine a Superfund Site.
3. Using the EE/CA EPA has put forth 5 possible solutions.
4. The Elizabeth Mine Community Advisory Group (EMCAG) now has the option of agreeing to one of the 5 alternatives or suggesting modifications to one of these 5 alternatives.
5. Once an alternative is agreed upon, EPA will move toward Final Design, namely, acquiring extensive site data, doing computations, drawing up plans, running tests and preparing bid documents.
6. Only as Final Design progresses will the exact shape, size, location of the elements become known, first to the EPA designers and then to the community.
7. Only after the contract has been let will the community really know the location of the borrow pits and what the truck traffic will be.

From an engineering point of view, future Operation and Maintenance Costs would be a lot lower if TP-3 were also covered. That said, and realizing that the community wants to preserve TP-3, the trick is to minimize the AMD coming off TP-3.

It is my professional opinion that EPA can design and build a set of diversion ditches that will effectively cut of all surface water flow and shallow groundwater flow onto TP-3, TP-2 and TP-3. Diversion ditches are a well-known, tried and proved technology for collecting both surface and shallow groundwater water. Variations, sometimes called "French Drains", have been used successfully for centuries to de-water agricultural fields, areas around leach fields, wetlands.

Using the new geo-synthetics, EPA can construct nearly maintenance-free channels. Properly sized rip rap will armor the sides and bottom. Properly chosen geotextiles will maintain separation between the native soils and the rip rap. Submerged vertical geomembrane walls will act as hydraulic barriers to groundwater flow. These technologies have been used by Highway Departments throughout the U.S. for many years.

It is my professional opinion that the multilayer caps proposed for Alternatives 2B and 2C represent the latest in confinement technology. Prior to the 1980's the predominate liner material for achieving landfill leachate confinement was compacted clay. However, they have four drawbacks:

1. Compacted clay Liners (CCL’s) must be typically 24 to 60 inches thick to adequately assure minimum infiltration.
2. Clay liners have been shown to suffer from subsequent shrinkage and cracking.
3. CCL’s take up space, add volume.
4. CCL’s are difficult and time-consuming to place.

By the 1990's EPA and nearly all States had adopted landfill confinement regulations that allowed for geomembranes and geosynthetic clay liners (GCL’s). The proposed cap for Alternatives 2B and 2C is very similar to the cap that was used to close the landfill at Post Mills, VT. The Post Mills closure used 6 inches of topsoil, 6 inches of common fill and 12 inches of granular drainage material over a 40 mil LLDPE geomembrane and a GCL for a total of 24 inches of cover. Alternatives 2B and 2C propose 30 inches of soil cover. During the Final Design, EPA may be able to reduce the depth of soil to 24 inches, thus, cutting the estimated number of truck loads by 25%.

We now have functioning geomembranes that have been installed for over 40 years. Elevated Temperature and Arthenius Modeling have shown that the antioxidant depletion time for HDPE geomembranes is approximately 200 years. Conclusion - Geomembranes, if properly installed, should last a very long time.

It is my professional opinion that Alternatives 3B, 3C and 3D will have great difficulty passing or receiving variances from the Vermont Solid Waste Management Rules. They do not appear to meet the minimum guidelines for infiltration.

It is my professional opinion that Roller Compacted Concrete (RCC) can be safely used to provide stability to the faces of TP- and TP-2. RCC has been used in the construction of and repair of water dams world wide. A check of the Web found numerous references to the use of RCC. Of note: The City of San Diego is starting a "308 foot high dam which will provide water if an earthquake or other disaster disrupts the water supply from the Colorado River and northern California."

As stated by Ed Hathaway from EPA it is difficult in a "free enterprise society" to know just where the borrow will come from. The contractors have the option (requirement) of finding the source. They will always use a source that minimizes their costs (bid). I think the community can with the help of local contractors and geologists make some good guesses as to the location of future borrow pits. I suggest the CAG start making x’s on a map where there are know deposits of gravel. It may soon become apparent where the majority of the future pits will be located.

I have numerous geosynthetic samples which you can touch and feel.

I invite your specific questions.

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