A young man with his girlfriend stood in the shade under an awning at the side of an RV truck parked near Barnard Park in Hartford on a recent Tuesday morning. Holding a bag in one hand and reaching through an opening in a screened door with the other, he dropped empty, used syringes into a medical waste bucket. “Eighty-eight, eighty-nine, ninety,” he counted, each needle making a thunk as it disappeared into bright red plastic.