Do you currently work with a local authority?
If not, it certainly will be an uphill struggle- as although 'outsiders' can apply for such vacancies, this is a promotional grade for 'insiders' i.e. clerical officers and persons acting as Assist Staff Officer
Have you looked at http://www.environ.ie (www.environ.ie), the council's annual report, annual financial statement, budget, minutes of recent meetings, local government act 2001, planning and development acts 2000 onwards, etc
Hope that gets you started- not impossible, but not easy! Well worth doing some prep for it- how long before your interview?