Index: Demo/Ringtoets/test/Demo.Ringtoets.Test/Commands/AddNewDemoAssessmentSectionCommandTest.cs
===================================================================
diff -u -r3254da22c99c7eb680cdb838519684ce314afb0a -r124e30d6f914a8e154ae8de0827ca363c89bba64
--- Demo/Ringtoets/test/Demo.Ringtoets.Test/Commands/AddNewDemoAssessmentSectionCommandTest.cs	(.../AddNewDemoAssessmentSectionCommandTest.cs)	(revision 3254da22c99c7eb680cdb838519684ce314afb0a)
+++ Demo/Ringtoets/test/Demo.Ringtoets.Test/Commands/AddNewDemoAssessmentSectionCommandTest.cs	(.../AddNewDemoAssessmentSectionCommandTest.cs)	(revision 124e30d6f914a8e154ae8de0827ca363c89bba64)
@@ -420,7 +420,7 @@
                             GetAccuracy(inputParameters.PhreaticLevelExit));
             Assert.AreEqual(0.011453, PipingSemiProbabilisticDesignValueFactory.GetDiameter70(inputParameters).GetDesignValue(),
                             GetAccuracy(inputParameters.Diameter70));
-            Assert.AreEqual(1.179897, PipingSemiProbabilisticDesignValueFactory.GetDarcyPermeability(inputParameters).GetDesignValue(),
+            Assert.AreEqual(1.179895, PipingSemiProbabilisticDesignValueFactory.GetDarcyPermeability(inputParameters).GetDesignValue(),
                             GetAccuracy(inputParameters.DarcyPermeability));
             Assert.AreEqual(17.5, PipingSemiProbabilisticDesignValueFactory.GetSaturatedVolumicWeightOfCoverageLayer(inputParameters).GetDesignValue(),
                             GetAccuracy(inputParameters.SaturatedVolumicWeightOfCoverageLayer));
Index: Ringtoets/Piping/src/Ringtoets.Piping.Data/DerivedPipingInput.cs
===================================================================
diff -u -r3254da22c99c7eb680cdb838519684ce314afb0a -r124e30d6f914a8e154ae8de0827ca363c89bba64
--- Ringtoets/Piping/src/Ringtoets.Piping.Data/DerivedPipingInput.cs	(.../DerivedPipingInput.cs)	(revision 3254da22c99c7eb680cdb838519684ce314afb0a)
+++ Ringtoets/Piping/src/Ringtoets.Piping.Data/DerivedPipingInput.cs	(.../DerivedPipingInput.cs)	(revision 124e30d6f914a8e154ae8de0827ca363c89bba64)
@@ -283,8 +283,11 @@
                 numberOfDecimals))
             {
                 PipingSoilLayer topMostAquiferLayer = aquiferLayers.First();
-                double deviationFraction = (topMostAquiferLayer.PermeabilityDeviation / topMostAquiferLayer.PermeabilityMean);
 
+                var permeabilityDeviation = new RoundedDouble(numberOfDecimals, topMostAquiferLayer.PermeabilityDeviation);
+                var permeabilityMean = new RoundedDouble(numberOfDecimals, topMostAquiferLayer.PermeabilityMean);
+                double deviationFraction = (permeabilityDeviation / permeabilityMean);
+
                 var weightedMean = new RoundedDouble(numberOfDecimals,
                                                      GetWeightedMeanForDarcyPermeabilityOfAquiferLayer(aquiferLayers,
                                                                                                        input.StochasticSoilProfile.SoilProfile,
@@ -374,7 +377,7 @@
                 return true;
             }
 
-            return distributions.All(currentLayerDistribution => AreDeviationAndFractionEqual(
+            return distributions.All(currentLayerDistribution => AreDeviationAndMeanFractionEqual(
                 currentLayerDistribution,
                 distributions[0]));
         }
@@ -418,7 +421,7 @@
                    currentLayerDistribution.Shift == baseLayerDistribution.Shift;
         }
 
-        private static bool AreDeviationAndFractionEqual(LogNormalDistribution currentLayerDistribution, LogNormalDistribution baseLayerDistribution)
+        private static bool AreDeviationAndMeanFractionEqual(LogNormalDistribution currentLayerDistribution, LogNormalDistribution baseLayerDistribution)
         {
             var baseLayerDeviationFraction = (baseLayerDistribution.StandardDeviation / baseLayerDistribution.Mean);
             var currentLayerDeviationFraction = (currentLayerDistribution.StandardDeviation / currentLayerDistribution.Mean);
Index: Ringtoets/Piping/test/Ringtoets.Piping.Data.Test/DerivedPipingInputTest.cs
===================================================================
diff -u -r3254da22c99c7eb680cdb838519684ce314afb0a -r124e30d6f914a8e154ae8de0827ca363c89bba64
--- Ringtoets/Piping/test/Ringtoets.Piping.Data.Test/DerivedPipingInputTest.cs	(.../DerivedPipingInputTest.cs)	(revision 3254da22c99c7eb680cdb838519684ce314afb0a)
+++ Ringtoets/Piping/test/Ringtoets.Piping.Data.Test/DerivedPipingInputTest.cs	(.../DerivedPipingInputTest.cs)	(revision 124e30d6f914a8e154ae8de0827ca363c89bba64)
@@ -765,7 +765,7 @@
             PipingInput input = PipingInputFactory.CreateInputWithAquiferAndCoverageLayer();
             var derivedInput = new DerivedPipingInput(input);
             var random = new Random(21);
-            double belowPhreaticLevelMean = random.NextDouble();
+            double belowPhreaticLevelMean = 0.1 + random.NextDouble();
             double deviation = random.NextDouble();
             double shift = random.NextDouble();
             input.StochasticSoilProfile.SoilProfile = new PipingSoilProfile("", 0.0, new[]
@@ -798,8 +798,8 @@
             PipingInput input = PipingInputFactory.CreateInputWithAquiferAndCoverageLayer();
             var derivedInput = new DerivedPipingInput(input);
             var random = new Random(21);
-            var belowPhreaticLevelMeanA = random.NextDouble();
-            var belowPhreaticLevelMeanB = random.NextDouble();
+            var belowPhreaticLevelMeanA = 0.1 + random.NextDouble();
+            var belowPhreaticLevelMeanB = 0.1 + random.NextDouble();
             double deviation = random.NextDouble();
             double shift = random.NextDouble();
             input.StochasticSoilProfile.SoilProfile = new PipingSoilProfile("", -2.0, new[]
@@ -846,8 +846,8 @@
             PipingInput input = PipingInputFactory.CreateInputWithAquiferAndCoverageLayer();
             var derivedInput = new DerivedPipingInput(input);
             var random = new Random(21);
-            var belowPhreaticLevelMeanA = random.NextDouble();
-            var belowPhreaticLevelMeanB = random.NextDouble();
+            var belowPhreaticLevelMeanA = 0.1 + random.NextDouble();
+            var belowPhreaticLevelMeanB = 0.1 + random.NextDouble();
             double deviation = random.NextDouble();
             double shift = random.NextDouble();
             input.StochasticSoilProfile.SoilProfile = new PipingSoilProfile("", -2.0, new[]
@@ -1124,9 +1124,9 @@
             PipingInput input = PipingInputFactory.CreateInputWithAquiferAndCoverageLayer();
             var derivedInput = new DerivedPipingInput(input);
             var random = new Random(21);
-            double mean = random.NextDouble();
+            double mean = 0.1 + random.NextDouble();
             double deviation = mean / 2;
-            double mean2 = random.NextDouble();
+            double mean2 = 0.1 + random.NextDouble();
             double deviation2 = mean2/2;
             input.StochasticSoilProfile.SoilProfile = new PipingSoilProfile("", 0.0, new[]
             {
@@ -1148,7 +1148,7 @@
             var result = derivedInput.DarcyPermeability;
 
             // Assert
-            var weightedMean = 0.885136;
+            var weightedMean = (mean * 0.5 + mean2) / 1.5;
             Assert.AreEqual(weightedMean, result.Mean, result.Mean.GetAccuracy());
             Assert.AreEqual(weightedMean / 2, result.StandardDeviation, result.StandardDeviation.GetAccuracy());
         }
@@ -1160,7 +1160,7 @@
             PipingInput input = PipingInputFactory.CreateInputWithAquiferAndCoverageLayer();
             var derivedInput = new DerivedPipingInput(input);
             var random = new Random(21);
-            var permeabilityMean = random.NextDouble();
+            var permeabilityMean = 0.1 + random.NextDouble();
             var permeabilityDeviation = random.NextDouble();
             input.StochasticSoilProfile.SoilProfile = new PipingSoilProfile("", -2.0, new[]
             {
@@ -1177,7 +1177,7 @@
 
             // Assert
             var expectedMean = new RoundedDouble(6, permeabilityMean);
-            var expectedDeviation = new RoundedDouble(6, expectedMean * (permeabilityDeviation / permeabilityMean));
+            var expectedDeviation = new RoundedDouble(6, permeabilityDeviation);
             Assert.AreEqual(expectedMean, result.Mean);
             Assert.AreEqual(expectedDeviation, result.StandardDeviation, result.StandardDeviation.GetAccuracy());
         }
@@ -1304,7 +1304,7 @@
             PipingInput input = PipingInputFactory.CreateInputWithAquiferAndCoverageLayer();
             var derivedInput = new DerivedPipingInput(input);
             var random = new Random(21);
-            var diameterD70Mean = random.NextDouble();
+            var diameterD70Mean = 0.1 + random.NextDouble();
             var diameterD70Deviation = random.NextDouble();
             input.StochasticSoilProfile.SoilProfile = new PipingSoilProfile("", -2.0, new[]
             {