def pd6(shellmound_model):
    """Perioddata defined with month-end frequency
    """
    m = shellmound_model
    # month end vs month start freq
    m.cfg['tdis']['perioddata']['freq'] = '6M'
    m.cfg['tdis']['options']['start_date_time'] = '2007-04-01'
    m.cfg['tdis']['perioddata']['end_date_time'] = '2015-10-01'
    m.cfg['tdis']['perioddata']['nstp'] = 15
    m._perioddata = None
    pd6 = m.perioddata.copy()
    return pd6