North Marin Water District has struggled with salinity issues in its wells for decades because of their proximity to Tomales Bay. This month, it finally secured a $1.5 million grant to help remedy the problem by incorporating a new well into the system. The agency has observed salinity problems at its two wells, which draw groundwater influenced by the bay during high tides, since the 1970s; it copes by timing pumping to avoid high tides,…