Migrate text field with multiple values
You should implement prepareRow() method in your migration class. Inside prepareRow() you can read both source fields and add them to an array.
I will provide an example:

public function prepareRow($row) {
  $row-&gt;text1 = array($row-&gt;text1, $row-&gt;text2);
}


Now your source field "text1" will contain both values and it can be mapped to "field_text". "text2" has to be set to DNM (do not map).