GROUNDWATER QUALITY INDICATORS IN THE GREAT LAKES BASIN

The Great Lakes Water Quality Agreement (GLWQA) was signed in 1972 to coordinate the actions of Canada and the United States “...to restore and maintain the chemical, physical, and biological integrity of the Waters of the Great Lakes” (https://binational.net). The 2012 GLWQA amendment recognized and incorporated groundwater as an important component of Great Lakes water quality. The 2012 GLWQA, organized as a series of Articles and Annexes, describes the objectives of the GLWQA, defines principles and approaches, and lays out the structure and process for its implementation. Annex 8 pertains to groundwater.

A major Annex 8 groundwater product was the 2016 “Groundwater Science Relevant to the Great Lakes Water Quality Agreement: A Status Report.” The report noted that within the Great Lakes Basin, different aspects of groundwater science are conducted by myriad entities: various levels of government, non-government organizations, academic institutions, and the private sector. Groundwater quality concerns were summarized in broad contaminant categories: nutrients, salts, metals, radionuclides, and organic compounds. Nutrients and salts, specifically nitrate and chloride, were identified as indicators of anthropogenic water quality impacts. Therefore, nitrate and chloride, termed the “groundwater quality indictors,” were selected for assessment of occurrence and monitoring of trends for the State of the Lakes Progress Reports organized under Annex 10, Science.

The groundwater quality indicators were last reported in the 2019 Progress Report. Because many entities collect and store groundwater quality data, it is a challenge to identify data sources, obtain data, perform data quality assurance, and compile data into a consistent format with consistent metadata. In the 2019 Progress Report, limited financial resources resulted in a groundwater data set with limited geographic coverage and little to no temporal record. The groundwater quality indicators were assessed as in fair condition and undetermined trend. Large areas of the basin had little available groundwater data. USGS is currently working on an update to the groundwater quality indicators for the 2022 Progress Report. We aim to have a more comprehensive spatial and temporal data set with which to evaluate condition and trends.