Need filters to existing casing underground

Sir, we need filter screens for already existing PVC bore casing at 60 feet depth. Existing bore casing is of 390 feet depth & 5 inch diameter. Filter pipes installed at 250 feet depth are giving sweet water that was present at upper layer of 60 to 80 feet, but we need salt water for our aquaculture. Is it possible now to put filters underground? Can anyone provide this service?

Laxman, ph: 8008150555