Get total in HH:MM format from the dataset

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C#

ASP.NET

CREATE procedure St_Proc_GetUserReportforCurrentDayTask                        
@userID int                        
as                        
    Begin                        
        set NoCount on;                        
        DECLARE @TODAY DATE                          
        SET @TODAY = CONVERT(VARCHAR(10), GETDATE(), 111)                        
        select  CONVERT(VARCHAR,production.CalendarDate,101) + RIGHT (CONVERT(VARCHAR,production.CalendarDate , 100 ) ,7) as Date,                         
        RegionAndProjectInfo.RegionProjectName as Region ,                        
        County.CountyName as County,                        
        WorkType.WorkTypeName as WorkType,                        
        Task.TaskName as Task,            
        Production.VolumeProcessed as 'Volumes Processed',                        
        Production.TimeSpent as 'Duration'                        
        from Production                         
        inner join RegionAndProjectInfo                        
        on                        
        RegionAndProjectInfo.RegionProjectID=Production.RegionProjectID                        
        inner join County                        
        on                         
        County.CountyID=Production.CountyID                        
        inner join WorkType                        
        on                        
        WorkType.WorkTypeID=Production.WorkTypeID                        
        inner join Task                        
        on                        
        Task.TaskID=Production.TaskID                        
        where Production.UserID=@userID and CalendarDate >= @TODAY                        
    End

From the above Stored Procedure i am filling a Dataset.After that i am binding this Dataset to a grid view. In the dataset ,the Column Duration contains Data in HH:MM Format(example-01:00,12:45,02:59 etc).Is there a way that i can get the total of Duration in HH:MM format from the dataset itself.I dont want to query again from the Database to get the Sum of the Duration.