Groundwater flow model and particle track analysis for selecting water quality monitoring well sites, and soil sampling profiles

Researchers often use only surface drainage (imperical method) as a tradition to locate sites for installation of water quality monitoring wells, and soil sampling profile for pollution studies in urban areas. They neglect that structural development may have altered the natural surface drainage. This paper demonstrates an advanced method; combining surface imperical method with a three-dimensional groundwater flow model and particle track analysis. This was performed using transient MODFLOW and MODPATH codes, as a first step in a pollution study of Owerri urban areas. Result was more reliable, showing diverging flows at Orji and Nekede auto-mechanic villages (MVs) due to relatively high elevation with the surroundings, and southward flow at the Obinze municipal waste dump (MWD). There were vertical flows at the sewage dumps (mangrove swamp areas) between Egbeda and Umuapu, and convergent flows along stream valleys. Particle tracking show an extended capture zone lying southeast. A total of eight water quality monitoring wells (WQ) was then recommended according to the directions of groundwater flow and particle releases from three tracking wells (ABC). WQ1: SE of Orji MV, WQ2: SE of Nekede MV, WQ3: south of Obinze MWD, WQ4: west of Egbeda, and WQ5: east of Umuapu. WQ6: NE of well A, WQ7: SW of well B, and WQ8: NE of well C. Soil sampling profiles; MVs: SE, MWD: South and sewage dumps: East and West. Distance of monitoring wells will vary according to the proximity of human settlements and shallow domestic wells (37m-55m) to the sites.