An environmental investigation of the mineralogical, geotechnical, hydrogeologic and botanical properties of subsurface flow constructed wetlands in Akumal Mexico

Akumal is one of the few locations where subsurface flow constructed wetland systems can be compared directly without major differences in environmental setting. These systems in Akumal have highly variable geotechnical properties and performance and most systems are not well functioning. A basic water quality survey indicates SFCW effluent in no case meets UNEP or USEPA guidelines for ammonia or phosphate for sensitive waters. Systems are undersized and many are planted with less than optimal vegetation. Aggregate is generally too coarse and pores are commonly occluded with organic matter. The mineralogy of the locally sourced aggregate used in the systems is dominated by calcite, aragonite, quartz, boehmite and chlorite and is generally beneficial for improving the water quality of the systems; however, dissolution is observed and is of some concern. Major systematic retrofit efforts to improve these systems are warranted and should focus on better vegetation choices, use of locally sourced smaller and less soluble aggregate, exclusive use of the local limestone source containing boehmite, more frequent exchange of the aggregate, and an increase of overall cell size. The systems in Akumal are a classic example of a technological solution to an environmental problem caused by human development that has outpaced the designed capacity for wastewater treatment. This investigation serves as a baseline for numerous future interdisciplinary investigations and outlines challenges facing coastal communities attempting to use subsurface flow constructed wetlands.