Have you thought about using a form to enter the parameters and then using
those as criteria in the crosstab query?  The criteria would be somthing like
this ---
  [Forms]![YourFormName]![YourTextBoxName]

I'm assuming Site Name is a row heading in the crosstab query.

Create an unbound form with a multi-select list box, lstSites, of all site
names and a button with code along these lines in its Click event procedure:

   Dim varItem As Variant
   Dim strSiteList As String
   Dim strCriteria As String
   Dim ctrl As Control
   
   Set ctrl = Me.lstSites
   
   If ctrl.ItemsSelected.Count > 0 Then
       For Each varItem In ctrl.ItemsSelected
           strSiteList = strSiteList & ",""" & ctrl.ItemData(varItem) & """"
       Next varItem
       
       ' remove leading comma
       strSiteList = Mid(strSiteList, 2)
       
       strCriteria = "[Site Name] In(" & strSiteList & ")"
       
       DoCmd.OpenReport "YourReportNameGoesHere", _
           View:=acViewPreview, _
           WhereCondition:=strCriteria
   Else
       MsgBox "No Sites Selected", vbInformation, "Warning"
   End If

The user can select one or more sites from the list, then click the button
to open the report for just that site or sites.  Setting the MultiSelect
property of the list box to 'Extended' would probably be best as this would
enable the user to Shift + click to select a contiguous range of sites or
Ctrl + click to select non-contiguous sites.  Or you could include a Select
All button with:

   Dim n As Integer
   
   For n = 0 To Me.lstSites.ListCount - 1
       Me.lstSites.Selected(n) = True
   Next n

If you want a Clear Selections button use:

   Dim n As Integer
   
   For n = 0 To Me.lstSites.ListCount - 1
       Me.lstSites.Selected(n) = False
   Next n

Ken Sheridan
Stafford, England