using System.Configuration;
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.
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String value = ConfigurationManager.AppSettings["Param_1"].ToString();
The web.config file would contains something like this:

For more information, go to the following links:
http://www.dotnetfunda.com/articles/article13.aspx
The following link show how to read the root web.config file instead of the one in the virtual directory:
http://msdn.microsoft.com/en-us/library/610xe886.aspx