Linda, The realities of your situation lies with your county health department. No matter what, if you do not adhear to these regulations, you are asking for possible trouble.
Your county health agent will give you all the information you need. At a "minimum", follow these regulations. Failure to do so could create future issues and fines. Did you know that when you go to sell your home, in most areas, if your septic system does meet minimum regulations, you will not be able to sell your home until these issues are resolved?
Lagoons can work very well. If it is in good shape, you will probably be quite happy with it. Go to the county and get the pamphlets and go go go.