A test‐stand experiment was conducted on neutron probe measurements using steel and Schedule 40 PVC access tubes to determine the effect of backfill grout in boreholes. The experiment used a moveable simulated vadose zone. Access tubes and grout do have masking effects on vadose zone measurements, but vadose zone moisture was detected through all configurations tested. Steel tubing has a smaller masking effect than PVC tubing. The masking effect of grout increased with borehole diameter. Although this experiment produced numerical results, conclusions drawn are qualitative in nature, rather than a quantitative calibration of the technique.

Agricultural irrigation with wastewater is widely established in Mexico. The city of León is the centre of the Mexican tanning industry, and produces wastewater with a significant component of industrial effluent. The city is one of the fastest growing in Mexico and is highly dependent on groundwater for public supply. Much of this is drawn from aquifers around the city, including those beneath the wastewater area. The sources of recharge to these aquifers and the types of pollutants are reviewed. Regionally, groundwater levels are falling as a result of excessive groundwater abstraction but, within the area of wastewater irrigation, groundwater levels are maintained close to the ground surface. Groundwater sampling from existing boreholes, surface geophysics, soil sampling and the drilling of cored investigation boreholes have been able to characterize a body of shallow, polluted groundwater beneath the wastewater area, and contrast this with the regional groundwater quality. The most immediate threat to public supply from pollutants originating in the wastewater is posed by salinity. The predicted consequences of various management options for reducing the impact of wastewater on the quality of deeper groundwater are briefly discussed.

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