C#

public interface IHazardLocation {}
public interface IHazardLocations : IEnumerable<IHazardLocation> {}
public interface IClusterHazardLocations : IHazardLocations { }

    [Serializable]
    public class ClusterHazardLocation : IClusterHazardLocation
    {
        public ICluster Cluster { get; }

        /// <summary>
        /// for serialization only!
        /// </summary>
        [UsedImplicitly]
        public ClusterHazardLocation()
        { }
        public ClusterHazardLocation(ICluster _cluster)
            : this()
        {
            Cluster = _cluster;
        }
    }

    [Serializable]
    public class ClusterHazardLocations : IClusterHazardLocations
    {
        [NotNull]
        private readonly List<IClusterHazardLocation> m_Locations;

        public ClusterHazardLocations()
        {
            m_Locations = new List<IClusterHazardLocation>();
        }
        public ClusterHazardLocations([NotNull] params IClusterHazardLocation[] _locations)
        {
            m_Locations = _locations.ToList();
        }
        public ClusterHazardLocations([NotNull] IEnumerable<IClusterHazardLocation> _locations)
        {
            m_Locations = _locations.ToList();
        }
        IEnumerator IEnumerable.GetEnumerator()
        {
            return ((IEnumerable<IHazardLocation>)m_Locations).GetEnumerator();
        }
        public IEnumerator<IHazardLocation> GetEnumerator()
        {
            return ((IEnumerable<IHazardLocation>)m_Locations).GetEnumerator();
        }
        // rename to Add to cause WCF failure
        public void AddHazardLocation(IHazardLocation _other)
        {
            if (_other is IClusterHazardLocation tmp)
            {
                m_Locations.Add(tmp);
            }
        }
    }