Get your local health department in on what is going on. You need to find out why the 4 yr. old lateral field failed. You could put in a new one of a different type like rock and pipe vs what was there and it could fail in 4 yrs. Is that what you want? it could be that the ground you are putting untreated effluent into needs secondary treatment like An ATU, Recirc sand filter, single pass sand filter, many other on the market. These are just a few. Get a good sight evaulation.