Index: Ringtoets/GrassCoverErosionOutwards/src/Ringtoets.GrassCoverErosionOutwards.Data/GrassCoverErosionOutwardsFailureMechanismExtensions.cs
===================================================================
diff -u -r871a2151d7a49d6f50699b6dea82c3e20ba6e409 -rcff4b928800b2a49ccaaaa49e7c87755d79b0169
--- Ringtoets/GrassCoverErosionOutwards/src/Ringtoets.GrassCoverErosionOutwards.Data/GrassCoverErosionOutwardsFailureMechanismExtensions.cs	(.../GrassCoverErosionOutwardsFailureMechanismExtensions.cs)	(revision 871a2151d7a49d6f50699b6dea82c3e20ba6e409)
+++ Ringtoets/GrassCoverErosionOutwards/src/Ringtoets.GrassCoverErosionOutwards.Data/GrassCoverErosionOutwardsFailureMechanismExtensions.cs	(.../GrassCoverErosionOutwardsFailureMechanismExtensions.cs)	(revision cff4b928800b2a49ccaaaa49e7c87755d79b0169)
@@ -21,8 +21,11 @@
 
 using System;
 using System.Collections.Generic;
+using System.ComponentModel;
 using System.Linq;
-using Core.Common.Util.Extensions;
+using Core.Common.Base.Data;
+using Ringtoets.Common.Data.AssessmentSection;
+using Ringtoets.Common.Data.Contribution;
 using Ringtoets.Common.Data.Hydraulics;
 
 namespace Ringtoets.GrassCoverErosionOutwards.Data
@@ -33,31 +36,64 @@
     public static class GrassCoverErosionOutwardsFailureMechanismExtensions
     {
         /// <summary>
-        /// Sets <see cref="GrassCoverErosionOutwardsFailureMechanism.HydraulicBoundaryLocations"/> 
-        /// based upon the <paramref name="hydraulicBoundaryLocations"/>.
+        /// Gets the normative assessment level for a <see cref="HydraulicBoundaryLocation"/>.
         /// </summary>
-        /// <param name="failureMechanism">The <see cref="GrassCoverErosionOutwardsFailureMechanism"/> to update.</param>
-        /// <param name="hydraulicBoundaryLocations">The hydraulic boundary locations to use.</param>
-        /// <exception cref="ArgumentNullException">Thrown when any parameter is <c>null</c>.</exception>
-        public static void SetGrassCoverErosionOutwardsHydraulicBoundaryLocations(this GrassCoverErosionOutwardsFailureMechanism failureMechanism,
-                                                                                  IEnumerable<HydraulicBoundaryLocation> hydraulicBoundaryLocations)
+        /// <param name="assessmentSection">The assessment section to get the normative assessment level from.</param>
+        /// <param name="failureMechanism">The failure mechanism to get the normative assessment level from.</param>
+        /// <param name="hydraulicBoundaryLocation">The hydraulic boundary location to get the normative assessment level for.</param>
+        /// <returns>The normative assessment level or <see cref="RoundedDouble.NaN"/> when:
+        /// <list type="bullet">
+        /// <item><paramref name="hydraulicBoundaryLocation"/> is <c>null</c>;</item>
+        /// <item><paramref name="hydraulicBoundaryLocation"/> is not part of <paramref name="failureMechanism"/>;</item>
+        /// <item><paramref name="hydraulicBoundaryLocation"/> is not part of <paramref name="assessmentSection"/>;</item>
+        /// <item><paramref name="hydraulicBoundaryLocation"/> contains no corresponding calculation output.</item>
+        /// </list>
+        /// </returns>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="failureMechanism"/>
+        /// or <paramref name="assessmentSection"/> is <c>null</c>.</exception>
+        /// <exception cref="InvalidEnumArgumentException">Thrown when <paramref name="assessmentSection"/>
+        /// contains an invalid value of <see cref="NormType"/>.</exception>
+        /// <exception cref="NotSupportedException">Thrown when <paramref name="assessmentSection"/>
+        /// contains a valid value of <see cref="NormType"/>, but unsupported.</exception>
+        public static RoundedDouble GetNormativeAssessmentLevel(this GrassCoverErosionOutwardsFailureMechanism failureMechanism,
+                                                                IAssessmentSection assessmentSection,
+                                                                HydraulicBoundaryLocation hydraulicBoundaryLocation)
         {
             if (failureMechanism == null)
             {
                 throw new ArgumentNullException(nameof(failureMechanism));
             }
-            if (hydraulicBoundaryLocations == null)
+
+            if (assessmentSection == null)
             {
-                throw new ArgumentNullException(nameof(hydraulicBoundaryLocations));
+                throw new ArgumentNullException(nameof(assessmentSection));
             }
 
-            failureMechanism.HydraulicBoundaryLocations.Clear();
-            if (!hydraulicBoundaryLocations.Any())
+            NormType normType = assessmentSection.FailureMechanismContribution.NormativeNorm;
+
+            if (!Enum.IsDefined(typeof(NormType), normType))
             {
-                return;
+                throw new InvalidEnumArgumentException(nameof(normType),
+                                                       (int)normType,
+                                                       typeof(NormType));
             }
 
-            failureMechanism.HydraulicBoundaryLocations.AddRange(hydraulicBoundaryLocations);
+            IEnumerable<HydraulicBoundaryLocationCalculation> calculations;
+
+            switch (normType)
+            {
+                case NormType.Signaling:
+                    calculations = failureMechanism.WaterLevelCalculationsForMechanismSpecificSignalingNorm;
+                    break;
+                case NormType.LowerLimit:
+                    calculations = failureMechanism.WaterLevelCalculationsForMechanismSpecificLowerLimitNorm;
+                    break;
+                default:
+                    throw new NotSupportedException();
+            }
+
+            return calculations.FirstOrDefault(c => ReferenceEquals(c.HydraulicBoundaryLocation, hydraulicBoundaryLocation))?.Output?.Result
+                   ?? RoundedDouble.NaN;
         }
     }
 }
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