Long-Term Nitrate Monitoring in Sensitive Sand and Gravel Aquifers in Minnesota Jim Stockinger, Erin Eid, Jennifer Maloney and Mike Trojan Minnesota Pollution Control Agency Ground Water Monitoring and Assessment Program

Purpose of Presentation Proposal for Statewide Ambient Monitoring Midwest GW Conference provides: Outlet to get information out, build support and gain cooperators Source of valuable feedback

Objectives for a Statewide Ambient Program Is Minnesota’s Ground Water Getting Better or Worse? Evaluate the Effectiveness of Ground Water Programs Impacts from Human Activity

STATEWIDE BASELINE ASSESSMENT OF GROUND WATER QUALITY (1992-96) CHEMICALS/AQUIFERS OF CONCERN HUMAN EFFECTS (LAND USE STUDIES) LONG-TERM, TREND MONITORING EFFECTIVENESS OF BMPS

Nitrate-Sensitive What is a Nitrate-Sensitive Aquifer? An aquifer in which nitrate will not be denitrified. Based upon the following criteria: Eh > 250 mV Dissolved Oxygen > 1 ppm Iron < 0.7 ppm

Location of Nitrate-Sensitive Aquifers Glacial Bedrock Hydrogeology Sensitive Nitrate Sensitive

Why the Sand and Gravel Aquifers? 18% of Wells Sampled from Nitrate-Sensitive, Sand and Gravel Aquifers Exceed the Nitrate Standard of 10ppm Important Source of Drinking Water Economically Feasible to Study Them

Objectives to Ambient Monitoring of Nitrate Determine if Nitrate Concentrations are Increasing or Decreasing with Time Determine if a Correlation Exist Between Land Use and Nitrate Concentrations in Shallow Ground Water Determine if Contamination of Shallow Ground Water Represents a Drinking Water Risk.

Study Design Domestic Wells Network of 100 Domestic Wells Screened deeper within the aquifer Represents drinking water supply (receptor) Network of 100 Domestic Wells 6 land use categories Irrigated and Non-Irrigated Agriculture, Sewered and Unsewered Residential, Commercial, and Undeveloped

Study Design Shallow Monitoring Wells Nested Monitoring Wells Screened across water table Represents most recent and vulnerable water Nested Monitoring Wells Screened 10 feet below water table Allows for a profile of the aquifer

Monitoring Wells Domestic Well Infiltration

Implementation Selection of Candidate Wells Sampling Compile list of candidate domestic wells Obtain permissions for well owners Sampling Sample up to 200 domestic wells Field verify land use

Implementation Selecting Monitoring Locations Uniformed Land Use within a 1/2 Mile Cooperative Land Owner Selecting Monitoring Well Locations Monitoring wells located within a 1/4 mile of the Domestic well

Typical Site Layout

Sampling Schedule and Parameters Sample Annually Between July 1st and August 15 Period of 20 or more years Field Parameters Oxidation-reduction potential Dissolved oxygen Reduced iron and manganese Laboratory Analysis Nitrate, Chloride, TOC

Focus Areas Watershed Level Address local land use issues Area actively implementing BMPs Surface water component can be added

Local Land Use Issues Septic systems Manure storage Irrigated agriculture Row crop agriculture Land application of manure Conversion of CRP land Residential fertilizers

WATERSHED LEVEL Residential development along rivers Row crop agriculture Currently not threatened Primarily bedrock aquifers Irrigated agriculture; residential development

Focus Areas Areas of On-going Studies Incorporate existing monitoring wells Existing data

Manure management studies Land use studies Septic system studies Manure management studies Geochemical studies Agricultural BMPs ON-GOING STUDIES

Additional Benefits of Study Compilation of Existing Ground Water Data Bases GIS Coverages Land use, land use changes, geologic and hydrogeologic

Resources GWMAP Can Provide Resources Needed Analytical Dollars Data Analysis / Reporting Resources Needed Assistance with locating study sites Dollars for installing monitoring wells Assistance with sampling

Time Frame Domestic Well Network Monitoring Well Network 1 month to identify candidate wells 2 months to obtain permissions and sample Monitoring Well Network Several years to install entire network Install 15 to 20 well nest per year