05/31/2000 Env Bd Packet - Laserfiche WebLink

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Ground Water Monitoring and Assessment Program (GWMAP), June 1998 particularly valuable data for managers at sites that are otentially contaminated. Thus, higher or lower values than background can be investigated and assessed. Also, chemicals with the greatest risk of exceeding the various drinking water criteria have been identified for the principal aquifers. This information will help managers make informed decisions about risk, aquifer use, and resource protection. What doesn't the study tell us? For aquifers in which less than about 15 wells were sampled, the summary data should not be used as background information unless additional data from other sources exist for the aquifer of concern. Most sampled wells were completed in the middle and lower portions of aquifers. The data therefore do not provide a good picture of water quality in the upper portions of these aquifers. This will be of most concern for unconfined aquifers which receive direct recharge, such as unprotected areas of the Prairie du Chien and Jordan aquifers, fractured bedrock aquifers near the land surface, and surficial drift aquifers. GWMAP is conducting an increasing amount of monitoring in shallow systems to fill in these data gaps. Ilkamples were not filtered. The samples provide a good indication of what is being consumed by humans, but geochemical interpretations are difficult. The greatest concern is with chemicals which were highly correlated with suspended solids, such as iron and manganese. Seasonal and spatial effects are unknown. Seasonal effects on water quality should be small, since most samples were from deeper portions of the aquifers. Assessing spatial patterns would require a denser sampling network and knowledge of geologic materials. Spatial effects are best studied in small geographic areas for naturally- occurring chemicals which pose a potential water quality concern. What is the future of the baseline study? iecause background water vality should not change over time, there is no need to continue the baseline program at the same level. However, the following components of a statewide baseline program should be established. Additional samples should be collected from the Sioux Quartzite, Cedar Valley, Mt. Simon, Hinckley, St. Lawrence, and Franconia aquifers. The final sample size for these aquifers should be approximately 20. These samples do not need to be collected within GWMAP grids. Upon completion of the additional sampling, the data should be reanalyzed and new summary statistics generated. A statewide baseline database should be established and maintained in a central location. Some of the key features of this database are listed below. • Minimum quality assurance/quality control (QA/QC) criteria need to be established for data entered into the database. • Additional fields should be created for the data, including land use. • Data from non -GWMAP past and future studies should be entered. Other likely data sources include US Geological Survey investigations, Minnesota Geological Survey and Department of Natural Resources studies including county atlases and regional assessments, and regional data. • Data from regulated sites should be entered when the data are considered to represent background (i.e. upgradient wells) water quality. 9 8 7 6 c 5 W V 0 4 3 2 0 Percent exceeding health -based drinking water standards boron manganese nitrate berillium Baseline Water Quality of Minnesota's Principal Aquifers Page 3