LINQ performance over several hundred records

in the following code I have commented out the line that SLOWS my page down. I did some speed test to show that CONTAINS

LINQ expression is the problem.

Does anyone know how to change this line to be more efficient using something else. I am also curious as to why it is so slow.

Any ideas (thanks in advance):

    var allWaste = _securityRepository.FindAllWaste(userId, SystemType.W);
    var allWasteIndicatorItems = _securityRepository.FindAllWasteIndicatorItems();

    // First get all WASTE RECORDS
    var searchResults = (from s in allWaste
                         join x in allWasteIndicatorItems on s.WasteId equals x.WasteId
                         where (s.Description.Contains(searchText)
                         && s.Site.SiteDescription.EndsWith(searchTextSite)
                         && (s.CollectedDate >= startDate && s.CollectedDate <= endDate))
                         && x.EWC.EndsWith(searchTextEWC)
                         select s).Distinct();

    var results = searchResults.AsEnumerable();

    if (hazardous != "-1") 
    {
        // User has requested to filter on Hazardous or Non Hazardous only rather than Show All
        var HazardousBoolFiltered = (from we in _db.WasteIndicatorItems
        .Join(_db.WasteIndicators, wii => wii.WasteIndicatorId, wi => wi.WasteIndicatorId, (wii, wi) => new { wasteid = wii.WasteId, wasteindicatorid = wii.WasteIndicatorId, hazardtypeid = wi.HazardTypeId })
        .Join(_db.HazardTypes, w => w.hazardtypeid, h => h.HazardTypeId, (w, h) => new { wasteid = w.wasteid, hazardous = h.Hazardous })
        .GroupBy(g => new { g.wasteid, g.hazardous })
        .Where(g => g.Key.hazardous == true && g.Count() >= 1)
                                     select we).AsEnumerable(); // THIS IS FAST

        // Now join the 2 object to eliminate all the keys that do not apply
        if (bHazardous)
            results = (from r in results join x in HazardousBoolFiltered on r.WasteId equals x.Key.wasteid select r).AsEnumerable(); //This is FAST
        else
            results = (from r in results.Where(x => !HazardousBoolFiltered
                .Select(y => y.Key.wasteid).Contains(x.WasteId)) select r).AsEnumerable(); // This is DOG SLOW 10-15 seconds !--- THIS IS SLOWING EXECUTION by 10 times --!


    }


    return results.AsQueryable();