public void RunMergeGeoProcess(ILayer SourceLayer1, ILayer SourceLayer2, string ResultFeatureClassName, string GeoDBAbsFileName)
    {

        IFeatureLayer featureLayerSource1 = (IFeatureLayer)SourceLayer1;
        IFeatureLayer featureLayerSource2 = (IFeatureLayer)SourceLayer2;


        _geoProcessor.SetEnvironmentValue("Workspace", GeoDBAbsFileName);
        //_gpParams.Add(featureLayerSource1);
        ////_gpParams.Add(featureLayerSource2);

        IWorkspace refWS = ((IDataset)featureLayerSource1.FeatureClass).Workspace;
        string dbPath = refWS.PathName;

        IDataset myDS1 = featureLayerSource1.FeatureClass as IDataset;
        string mysDS1 = dbPath + "\" + myDS1.Name;
        IDataset myDS2 = featureLayerSource2.FeatureClass as IDataset;
        string mysDS2 = dbPath + "\"+ myDS2.Name;

        string myResult = dbPath + "\" + ResultFeatureClassName;

        string param1 = "[" + mysDS1 + ", " + mysDS2 + "]";

        _gpParams.Add(param1);
        _gpParams.Add(myResult);


        try
        {
            _geoProcessor.OverwriteOutput = true;
            _geoProcessor.Execute("Merge_management", _gpParams, null);
            //returnMessages(_geoProcessor);
        }
        catch (Exception ex)
        {
            MessageBox.Show("There was a GeoProcessing Error." + ex.ToString());
            returnMessages(_geoProcessor);
        }

        _gpParams.RemoveAll();

    }

public void RunMergeGeoProcess(ILayer SourceLayer1, ILayer SourceLayer2, string ResultFeatureClassName, string GeoDBAbsFileName)
    {

        IFeatureLayer featureLayerSource1 = (IFeatureLayer)SourceLayer1;
        IFeatureLayer featureLayerSource2 = (IFeatureLayer)SourceLayer2;

        _geoProcessor.SetEnvironmentValue("Workspace", GeoDBAbsFileName);

        IWorkspace refWS = ((IDataset)featureLayerSource1.FeatureClass).Workspace;
        string dbPath = refWS.PathName;

        IDataset myDS1 = featureLayerSource1.FeatureClass as IDataset;
        string mysDS1 = dbPath + "\" + myDS1.Name;
        IDataset myDS2 = featureLayerSource2.FeatureClass as IDataset;
        string mysDS2 = dbPath + "\" + myDS2.Name;

        string myResult = dbPath + "\" + ResultFeatureClassName;
        string param1 =  mysDS2 + ";" + mysDS1  ;
        _gpParams.Add(param1);
        _gpParams.Add(myResult);

        try
        {
            _geoProcessor.OverwriteOutput = true;
            _geoProcessor.Execute("Merge_management", _gpParams, null);
            //returnMessages(_geoProcessor);
        }
        catch (Exception ex)
        {
            MessageBox.Show("There was a GeoProcessing Error during the Merge Operation." + ex.ToString());
            //returnMessages(_geoProcessor);
        }

        _gpParams.RemoveAll();

    }

private void Intersect(List<string> LayerNames, string OutputLayerLocation)
    {
        Intersect inter;
        StringBuilder sb;
        Geoprocessor gg;

        sb = new StringBuilder();

        foreach (string LayerName in LayerNames)
        {
            sb.Append(LayerName);
            sb.Append(";");
        }

        sb.Length--;

        inter = new Intersect();
        inter.in_features = sb.ToString();
        inter.out_feature_class = OutputLayerLocation;

        gg = new Geoprocessor();
        gg.OverwriteOutput = true;
        gg.ProgressChanged += new EventHandler<ESRI.ArcGIS.Geoprocessor.ProgressChangedEventArgs>(gg_ProgressChanged);
        gg.ToolExecuted += new EventHandler<ToolExecutedEventArgs>(gg_ToolExecuted);
        gg.MessagesCreated += new EventHandler<MessagesCreatedEventArgs>(gg_MessagesCreated);

        gg.ExecuteAsync(inter);
    }