Seller fraud

I bought a 17 space park in Oregon March 2007. I’m set to close escrow on the sale of the park in a week. The buyer’ bank asked for a septic inspection. After the inspection it came to light that 10 out of 12 septic tanks are failing and must be replaced before the sale can go thru. The inspector said that most of the tanks hadn’t been pumped in 20 years. Replacing all 10 tanks is going to cost me $24,000. When I bought the park my bank insisted on documentation on the septic system. The seller from took several years of septic tank service receipts( most were for snaking out the line between the mobiles and their respective tanks) and whited out the receipts and forged pumping receipts for all the tanks. We went back to the different tank pumping companies and got the original, undoctored receipts and found that not only had tanks not been pumped but some tanks were listed on the receipts as failing and needed replacing. The woman’s forged receipts were good enough to fool me and my bank. I think I have a civil case and a criminal case here. Thoughts anyone ? How should I deal with the woman who sold me the park ?