Investigating pesticide transport in the León-Chinandega aquifer, Nicaragua

Abstract

Nicaragua's Leon-Chinandega aquifer has seen extensive contamination by persistent organochlorine pesti- cides applied over decades of intensive agricultural activity. Models of flow and transport of a 330 km 2 sub-region of the aquifer were developed to test conceptual models of contaminant transport, to constrain the value of certain key transport parameters, and to investigate contamination- related concerns raised in past studies. To support these models, a variety of hydrogeologic and geochemical data were collected. It was concluded that the organochlorine pesticides seen in groundwater originate in soils, and are transported to the water table through widespread preferential flow, through shortcutting around wells, or through wind-blown particles delivered to poorly protected hand-dug wells. The distribution coefficient (Kd )o f these pesticides is estimated to be between 0.1 and 100 ml/g and the concentration of pesticides being delivered to the water table is estimated to be between 10 2 and 10 5 ng/L. It was found that the distribution and concentration of pesticides in the aquifer would be affected by an increase in groundwater abstraction within the region. Resume L'aquifere du Leon-Chinandega au Nicaragua a ete soumis a des contaminations etendues par des pesticides organochlores persistants qui ont ete repandus pendant des dizaines d'annees d'agriculture intensive. Des modeles d'ecoulement et de transport d'une sous- region de 330 km 2 de l'aquifere ont ete construits pour