diff --git a/src/main/java/gov/usgs/earthquake/nshmp/calc/ReturnPeriod.java b/src/main/java/gov/usgs/earthquake/nshmp/calc/ReturnPeriod.java
deleted file mode 100644
index 2dfd70da20b4bec05e163bc1600da66678404a0a..0000000000000000000000000000000000000000
--- a/src/main/java/gov/usgs/earthquake/nshmp/calc/ReturnPeriod.java
+++ /dev/null
@@ -1,89 +0,0 @@
-package gov.usgs.earthquake.nshmp.calc;
-
-import com.google.common.base.MoreObjects;
-
-import gov.usgs.earthquake.nshmp.Maths;
-import gov.usgs.earthquake.nshmp.mfd.Mfds;
-
-/**
- * Identifiers of common return periods, also referred to in PSHA as
- * probabilities of exceedance.
- *
- * <p>Each identifier is structured as follows, for example {@code PE2IN50}:
- *
- * <ul><li>Reads as a 2% Poisson probability of exceeding some measure of ground
- * motion in a 50 year period.</li>
- *
- * <li>Is equivalent to an annual rate of occurrence of ~0.000404 (see
- * {@link #annualRate()}).</li>
- *
- * <li>Or once every 2475 years or so (see {@link #duration()} ).</li></ul>
- *
- * <p>Note that the {@link Mfds} class includes useful static utilities for
- * working with Poisson probabilities, rates, and time spans.
- *
- * @author U.S. Geological Survey
- * @see Mfds
- */
-public enum ReturnPeriod {
-
-  /** A 1% probability of exceedance in 10,000 years. */
-  PE1IN10000(0.000001),
-
-  /** A 1% probability of exceedance in 1,000 years. */
-  PE1IN1000(0.00001),
-
-  /** A 1% probability of exceedance in 100 years. */
-  PE1IN100(0.000101),
-
-  /** A 1% probability of exceedance in 50 years. */
-  PE1IN50(0.000201),
-
-  /** A 2% probability of exceedance in 50 years. */
-  PE2IN50(0.000404),
-
-  /** A 5% probability of exceedance in 50 years. */
-  PE5IN50(0.001026),
-
-  /** A 10% probability of exceedance in 50 years. */
-  PE10IN50(0.002107),
-
-  /** A 40% probability of exceedance in 50 years. */
-  PE40IN50(0.010217);
-
-  private double annualRate;
-
-  private ReturnPeriod(double annualRate) {
-    this.annualRate = nameToAnnRate(name());
-  }
-
-  @Override
-  public String toString() {
-    return MoreObjects
-        .toStringHelper(getClass().getSimpleName() + "." + name())
-        .add("annualRate", annualRate)
-        .add("duration", duration())
-        .toString();
-  }
-
-  /**
-   * Return the annual rate of occurrence represented by this time period.
-   */
-  public double annualRate() {
-    return annualRate;
-  }
-
-  /**
-   * Return the duration (number of years spanned) by this return period.
-   */
-  public int duration() {
-    return (int) Math.rint(1.0 / annualRate);
-  }
-
-  private double nameToAnnRate(String name) {
-    String[] values = name.substring(2).split("IN");
-    double prob = Double.parseDouble(values[0]) / 100.0;
-    double time = Double.parseDouble(values[1]);
-    return Maths.probabilityToRate(prob, time);
-  }
-}
diff --git a/src/main/java/gov/usgs/earthquake/nshmp/model/ClusterRuptureSet.java b/src/main/java/gov/usgs/earthquake/nshmp/model/ClusterRuptureSet.java
index fa5f562c0b4d544b26b46963fc66d5f81256bb10..778b86e4e085b9076d3309fdab270301746caff1 100644
--- a/src/main/java/gov/usgs/earthquake/nshmp/model/ClusterRuptureSet.java
+++ b/src/main/java/gov/usgs/earthquake/nshmp/model/ClusterRuptureSet.java
@@ -97,7 +97,7 @@ public class ClusterRuptureSet extends AbstractRuptureSet<ClusterSource> {
     private ModelData data; // holds cluster rate-tree
     private ClusterSource source;
 
-    Builder() {
+    private Builder() {
       super(SourceType.FAULT_CLUSTER);
     }
 
diff --git a/src/main/java/gov/usgs/earthquake/nshmp/model/FaultRuptureSet.java b/src/main/java/gov/usgs/earthquake/nshmp/model/FaultRuptureSet.java
index b51ca5cced19e967fb32544605ea26162b26e9cf..5d39ab35d8f875952275dce771ce480627ca0b8b 100644
--- a/src/main/java/gov/usgs/earthquake/nshmp/model/FaultRuptureSet.java
+++ b/src/main/java/gov/usgs/earthquake/nshmp/model/FaultRuptureSet.java
@@ -162,7 +162,7 @@ public class FaultRuptureSet extends AbstractRuptureSet<FaultSource> {
     private List<Integer> sectionIds;
     private Optional<Map<String, ?>> ruptureProps = Optional.empty();
 
-    Builder() {
+    private Builder() {
       super(SourceType.FAULT);
     }
 
diff --git a/src/main/java/gov/usgs/earthquake/nshmp/model/InterfaceRuptureSet.java b/src/main/java/gov/usgs/earthquake/nshmp/model/InterfaceRuptureSet.java
index 052bc3a700d995a6a59ab6a0d37a06af0961c18c..a0211f848e70b0af088ea499179066b2a457373b 100644
--- a/src/main/java/gov/usgs/earthquake/nshmp/model/InterfaceRuptureSet.java
+++ b/src/main/java/gov/usgs/earthquake/nshmp/model/InterfaceRuptureSet.java
@@ -131,7 +131,7 @@ public class InterfaceRuptureSet extends AbstractRuptureSet<InterfaceSource> {
     private Mfd mfdTotal;
     private GriddedSurface surface;
 
-    Builder() {
+    private Builder() {
       super(SourceType.INTERFACE);
     }
 
diff --git a/src/main/java/gov/usgs/earthquake/nshmp/model/SystemRuptureSet.java b/src/main/java/gov/usgs/earthquake/nshmp/model/SystemRuptureSet.java
index 8c49c02879fd4a696f4e3e904b2898780861fd00..4bc773ef16c31e483704cb2765bc12d8e4f34dd3 100644
--- a/src/main/java/gov/usgs/earthquake/nshmp/model/SystemRuptureSet.java
+++ b/src/main/java/gov/usgs/earthquake/nshmp/model/SystemRuptureSet.java
@@ -417,7 +417,7 @@ public class SystemRuptureSet extends AbstractRuptureSet<SystemRuptureSet.System
     private double mMin = Double.POSITIVE_INFINITY;
     private double mMax = Double.NEGATIVE_INFINITY;
 
-    Builder() {
+    private Builder() {
       super(SourceType.FAULT_SYSTEM);
     }