ASSESSING BOREHOLE GEOPHYSICAL DATA BY SIMULATING BOREHOLE FLOW IN FRACTURED BEDROCK AQUIFERS

A computer program was prepared, using the python scripting language, to assist with the analysis of borehole flow data collected using a heat pulse flowmeter. This computer model, based on methodology published by F. Paillet in 1999, utilizes flow profiles collected under two states, typically pumped and ambient conditions. Transmissivity and far-field hydraulic head for individual fractures can be quantified by calibrating this model to both measured flow profiles. The calibration process, previously completed through a trial-and-error process, has been interfaced with open-source optimization modules that automate this process. The borehole flow model has been used to characterize the hydraulic properties of a fractured granite aquifer where deicing salts have impacted the groundwater system. At this Jonesboro, Maine study area, borehole geophysical logs were collected in two wells (119 and 121). Based on flowmeter logs, Well 119 has three clear inflow locations at about 30m, 43 m, and 55 m below the ground surface. Preliminary modeling results indicate these fractures have transmissivities of 5.74e-6, 2.74e-5, and 2.50e-5 sq. m/sec., respectively. The simulated difference in far-field head between these fracture zones was expectedly small, with negligible values of less than 1e-4 m in these models. Well 123, located about 150 m to the west of Well 119, appears to have only two hydraulically active fracture zones at about 33 m and 43 m below grade with order of magnitude lower transmissivities.