When the grapefruit and lemon trees bloom on Jim Seley’s farm, the white blossoms fill the air with their sweet scent. He and his son, Mike, manage the business, and they hope to pass it on to the next generation of Seleys.  But the farms of Borrego Springs, like the town and its golf courses, rely completely on groundwater pumped from the desert aquifer. And it’s unclear whether farming will be able to survive in this part of the Southern California desert west of the Salton Sea in San Diego County. The aquifer beneath Borrego Springs has been declining for decades due to overpumping.