I am familiar with the process of installing/designing septic systems (in Mass). This is a link to the DEP website that might be of use to you... it is always good to explore your options!!!
http://www.mass.gov/dep/brp/wwm/file...alap.htm#septi
Even though this link is for MA... it really is a good tool for looking at different types of sysems available and the work involved with putting one in (parts/maintenance contracts/installation).
Good luck.