Index: Ringtoets/Piping/src/Ringtoets.Piping.Data/DerivedPipingInput.cs
===================================================================
diff -u -r0cdb24eee9b746ab5d21381ca51c6836dd460292 -rf5e6d6dbc89bb2059883a47a7be9ab944b4825d6
--- Ringtoets/Piping/src/Ringtoets.Piping.Data/DerivedPipingInput.cs	(.../DerivedPipingInput.cs)	(revision 0cdb24eee9b746ab5d21381ca51c6836dd460292)
+++ Ringtoets/Piping/src/Ringtoets.Piping.Data/DerivedPipingInput.cs	(.../DerivedPipingInput.cs)	(revision f5e6d6dbc89bb2059883a47a7be9ab944b4825d6)
@@ -298,11 +298,23 @@
                 return true;
             }
 
-            var belowPhreaticLevelDeviation = consecutiveAquitardLayers[0].BelowPhreaticLevelDeviation;
-            var belowPhreaticLevelShift = consecutiveAquitardLayers[0].BelowPhreaticLevelShift;
+            return consecutiveAquitardLayers.All(currentLayer => AreShiftAndDeviationEqual(
+                currentLayer, 
+                consecutiveAquitardLayers[0], 
+                deviationNumberOfDecimals, 
+                shiftNumberOfDecimals));
+        }
 
-            return consecutiveAquitardLayers.All(al => AlmostEquals(belowPhreaticLevelDeviation, al.BelowPhreaticLevelDeviation, deviationNumberOfDecimals) &&
-                                                       AlmostEquals(belowPhreaticLevelShift, al.BelowPhreaticLevelShift, shiftNumberOfDecimals));
+        private bool AreShiftAndDeviationEqual(PipingSoilLayer currentLayer, PipingSoilLayer baseLayer, int deviationNumberOfDecimals, int shiftNumberOfDecimals)
+        {
+            var belowPhreaticLevelDeviationBase = new RoundedDouble(deviationNumberOfDecimals, baseLayer.BelowPhreaticLevelDeviation);
+            var belowPhreaticLevelShiftBase = new RoundedDouble(shiftNumberOfDecimals, baseLayer.BelowPhreaticLevelShift);
+
+            var belowPhreaticLevelDeviationCurrent = new RoundedDouble(deviationNumberOfDecimals, currentLayer.BelowPhreaticLevelDeviation);
+            var belowPhreaticLevelShiftCurrent = new RoundedDouble(shiftNumberOfDecimals, currentLayer.BelowPhreaticLevelShift);
+
+            return belowPhreaticLevelDeviationCurrent == belowPhreaticLevelDeviationBase &&
+                   belowPhreaticLevelShiftCurrent == belowPhreaticLevelShiftBase;
         }
 
         private static double GetWeightedMeanForVolumicWeightOfCoverageLayer(PipingSoilLayer[] aquitardLayers, PipingSoilProfile profile, double surfaceLevel)
@@ -355,11 +367,6 @@
             return new PipingSoilLayer[0];
         }
 
-        private bool AlmostEquals(double a, double b, int numberOfDecimals)
-        {
-            return Math.Abs(a - b) < 0.5 * Math.Pow(10.0, -numberOfDecimals);
-        }
-
         private static double GetThicknessTopAquiferLayer(PipingSoilProfile soilProfile, RingtoetsPipingSurfaceLine surfaceLine, RoundedDouble exitPointL)
         {
             try
Index: Ringtoets/Piping/test/Ringtoets.Piping.Data.Test/DerivedPipingInputTest.cs
===================================================================
diff -u -r0cdb24eee9b746ab5d21381ca51c6836dd460292 -rf5e6d6dbc89bb2059883a47a7be9ab944b4825d6
--- Ringtoets/Piping/test/Ringtoets.Piping.Data.Test/DerivedPipingInputTest.cs	(.../DerivedPipingInputTest.cs)	(revision 0cdb24eee9b746ab5d21381ca51c6836dd460292)
+++ Ringtoets/Piping/test/Ringtoets.Piping.Data.Test/DerivedPipingInputTest.cs	(.../DerivedPipingInputTest.cs)	(revision f5e6d6dbc89bb2059883a47a7be9ab944b4825d6)
@@ -801,6 +801,43 @@
         }
 
         [Test]
+        public void SaturatedVolumicWeightOfCoverageLayer_MultipleLayersInequalStandardDeviationOrShiftButEqualWhenRounded_ReturnsWithWeightedMean()
+        {
+            // Setup
+            var input = PipingCalculationFactory.CreateInputWithAquiferAndCoverageLayer();
+            var derivedInput = new DerivedPipingInput(input);
+            var belowPhreaticLevelMeanA = 2.5;
+            var belowPhreaticLevelMeanB = 3.4;
+            input.StochasticSoilProfile.SoilProfile = new PipingSoilProfile("", -2.0, new[]
+            {
+                new PipingSoilLayer(2.5)
+                {
+                    BelowPhreaticLevelDeviation = 1.014,
+                    BelowPhreaticLevelShift = 1.014,
+                    BelowPhreaticLevelMean = belowPhreaticLevelMeanA
+                },
+                new PipingSoilLayer(-0.5)
+                {
+                    BelowPhreaticLevelDeviation = 1.006,
+                    BelowPhreaticLevelShift = 1.006,
+                    BelowPhreaticLevelMean = belowPhreaticLevelMeanB
+                },
+                new PipingSoilLayer(-1.5)
+                {
+                    IsAquifer = true
+                }, 
+            }, SoilProfileType.SoilProfile1D, 0);
+
+            // Call
+            var result = derivedInput.SaturatedVolumicWeightOfCoverageLayer;
+
+            // Assert
+            Assert.AreEqual((belowPhreaticLevelMeanA * 2.5 + belowPhreaticLevelMeanB * 1.0) / 3.5, result.Mean, result.Mean.GetAccuracy());
+            Assert.AreEqual((RoundedDouble) 1.01, result.Shift);
+            Assert.AreEqual((RoundedDouble)1.01, result.StandardDeviation);
+        }
+
+        [Test]
         public void DarcyPermeability_NoSoilProfile_ReturnsNaNForParameters()
         {
             // Setup