One of the most popular forms of evaluation is the organisation of surveys among the target population. Systematic surveys are the only means of getting a representative cross-section of the people who have been exposed to the communication.
There is not much value in conducting surveys of the total population (although polling companies will tell you otherwise), unless you had launched a nation-wide, multichannel communication programme.
Rather, risk communicators should direct the questionnaire to the targeted audiences. Members of the audience will be the only ones directly exposed to your programme. Even then, most of the audience may not remember anything if asked some time after the event. In contemporary societies there is an abundance of information floating around. More than 99% of everything that one receives is forgotten within minutes or hours.