MONTANA DEPARTMENT OF AGRICULTURE: A GIS METHOD FOR AGRICULTURAL CHEMICAL GROUNDWATER MONITORING WELL SITE SELECTION

Monitoring for agricultural chemicals in groundwater is often reactionary to known contamination events or focused in regions with geographic attributes specifically vulnerable to leaching from agricultural activities. Access to many of the wells utilized in the Montana Department of Agriculture’s, Groundwater Protection Program: Permanent Monitoring Well Network (PMWN) have come from the opportunistic expansion of monitoring sites, where monitoring has been requested by concerned citizens or other state agencies. This has led to a lack in relatable land use and geographic conditions between monitoring wells, and a low correlatability between monitoring well environments and groundwater sample analytical results. The Agricultural Land Use – Crop Frequency – Soil Residency (ACSR) data layer model uses a dynamic confluence window to compare the agricultural land use, crop type history, soil depth and soil saturated conductivity around a point to identify areas that are representative of the average agricultural conditions of a WBDHU12, Project Area, and the PMWN. Using the resulting heat maps, new monitoring wells can be developed with a level of consideration for how a given location fits into the agricultural environment of the region as well as a new sites relatability to the existing permanent monitoring well network.