Grouping over a list of dictionaries
You don't need neither Select and can get the same result by using only GroupBy:

var valuePairs = sharePointResult
    .GroupBy(
        dict =&gt; dict["PA"], 
        dict =&gt; int.Parse(dict["TO"]), 
        (key, items) =&gt; new
        {
            PA = key,
            Sum = items.Sum(f =&gt; f)
        });


where the parameters are respectively:

.GroupBy(keySelector, elementSelector, resultSelector);


I used int.Parse for testing - it's not a part of my review ;-)