How can I pass json data returned from a webservice into D3.json(...)?

Thank you for your help so far! I was able to successfully build my webservice and NVD3.js stacked area chart. However, I have been struggling without any success in passing json data from my webservice into my NVD3.js graph. On my webform, I select two dates for an interval and click a "go" button.

I feel that it is something obvious that I am missing. If not possible, is there a way of saving the json data retued from my webservice into a regular file (e.g. myFile.json), so that I can pass it in my graph? Thank you very much for your help! Here is my latest attempt:

<script type="text/javascript">
        $(document).ready(function(){
            $("#btGO").click(function(){
                var startDate = $("#startDate").val();
                var endDate = $("#endDate").val();

                $.ajax({
                    url: "dataWebService.asmx/getCasesForDateInterval",
                    method: "post",
                    data: {
                        startDate: startDate,
                        endDate: endDate
                    },
                    dataType: "json",
                    contentType: "application/json",
                    success: function (data) {
                        //This is where I attempt to pass my json data
                        d3.json(data, function (error, data) {
                            nv.addGraph(function () {
                                var chart = nv.models.stackedAreaChart()
                                              .x(function (d) { retu d[0] })
                                              .y(function (d) { retu d[1] })
                                              .clipEdge(true)
                                              .useInteractiveGuideline(true);

                                chart._options.controlOptions = ['Expanded', 'Stacked'];

                                chart.xAxis
                                    .showMaxMin(true)
                                    .tickFormat(function (d) { retu d3.time.format('%x')(new Date(d)) });

                                chart.yAxis
                                    .tickFormat(d3.format(',.0f'));

                                d3.select('#chart svg')
                                  .datum(data)
                                    .transition().duration(500).call(chart);

                                nv.utils.windowResize(chart.update);

                                retu chart;
                            });
                        });
                    }
                });

            });
        });
     </script>

Here is my webservice:

    [WebMethod]
     public string getTotalForDateInterval(string startDate, string endDate)
    {
    string cs = ConfigurationManager.CoectionStrings["vetDatabase_Wizard"].CoectionString;
    List<keyValues> master = new List<keyValues>();

    using (SqlCoection con = new SqlCoection(cs))
    {
        SqlCommand cmd = new SqlCommand("sp_CountAndGroupByDate", con);
        cmd.CommandType = CommandType.StoredProcedure;

        //Linking SQL parameters with webmethod parameters
        SqlParameter param1 = new SqlParameter()
        {
            ParameterName = "@startDate",
            Value = startDate
        };

        SqlParameter param2 = new SqlParameter()
        {
            ParameterName = "@endDate",
            Value = endDate
        };

        cmd.Parameters.Add(param1);
        cmd.Parameters.Add(param2);
        con.Open();

        //Get time in milliseconds
        DateTime start = DateTime.ParseExact(startDate, "yyyy-MM-dd", System.Globalization.CultureInfo.InvariantCulture);
        DateTime end = DateTime.ParseExact(endDate, "yyyy-MM-dd", System.Globalization.CultureInfo.InvariantCulture);
        DateTime utime = DateTime.ParseExact("1970-01-01", "yyyy-MM-dd", System.Globalization.CultureInfo.InvariantCulture);

        long startMilliseconds = (long)((start - utime).TotalMilliseconds);
        long endMilliseconds = (long)((end - utime).TotalMilliseconds);
        const long oneDayInMilliseconds = 86400000;

        //Declare temp dictionary to store the lists
        Dictionary<string, List<long[]>> temp = new Dictionary<string, List<long[]>>();
        string[] buildings = { "SSB", "GEN", "LYM", "LUD", "GCC", "MAC", "MMB" };

        //Create building lists and initialize them with individual days and the default value of 0 
        foreach (string building in buildings){
            temp.Add(building, new List<long[]>());
            for (long j = startMilliseconds; j <= endMilliseconds; j = j + oneDayInMilliseconds){
                long[] timeTotal = { j, 0 };
                temp[building].Add(timeTotal);
            }
        }

        SqlDataReader rdr = cmd.ExecuteReader();
        while (rdr.Read())
        {

            //Remove time from dateTime2 and assign totals for appropriate date
            string s = (rdr["dateOpened"].ToString()).Substring(0, 10);
            DateTime dateOpened = DateTime.ParseExact(s, "yyyy-MM-dd", System.Globalization.CultureInfo.InvariantCulture);
            long time = (long)((dateOpened - utime).TotalMilliseconds);
            long total = (long)Convert.ToInt32(rdr["total"]);

            string buildingName = rdr["building"].ToString();
            int index = temp[buildingName].FindIndex(r => r[0].Equals(time));
            temp[buildingName][index][1] = total;
        }
            //add all the keyValue objects to master list
            for (int i = 0; i < buildings.Length; i++)
            {
                keyValues kv = new keyValues();
                kv.key = buildings[i];
                kv.values = temp[kv.key];
                master.Add(kv);
            }

      }
    JavaScriptSerializer js = new JavaScriptSerializer();

    //Serialize list object into a JSON array and write in into the response stream
    string ss = js.Serialize(master);
    retu ss;

}