USING DRILL CUTTINGS TO IDENTIFY ARSENIC RISK DURING WELL CONSTRUCTION IN UNCONSOLIDATED AQUIFERS

High amounts of arsenic in groundwater poses a health risk in parts of Minnesota. The relationship between arsenic concentration and aquifer material is not well understood. Research on this relationship has been limited to drill core rather than the easier to obtain drill cuttings. This study examines cuttings from five sand and gravel wells and arsenic concentrations in water from the aquifers tapped by these wells. The cuttings were examined, photographed, and classified using a grain count system similar to Hobbs (1998). The preliminary results obtained from this study suggest a correlation between lithic sand and arsenic concentration. While additional research is necessary to confirm these results, it appears possible to use cuttings to identify high-arsenic aquifers during well construction where local aquifer As- concentrations are known. When a new well is constructed, water quality testing typically occurs after the well is completed. Often the presence of arsenic concentrations that exceed the maximum contaminant level (MCL) of 0.01mg/L comes as a surprise to the well owner. Identifying aquifers with high arsenic concentration during construction would provide the well owner with the opportunity to change the design of the well or the water system before the system is operational, mitigating the risk of arsenic exposure and/or the cost of water treatment.