GROUND WATER MONITORING TO EVALUATE EFFECTS OF LAND USE ON WATER QUALITY Mike Trojan Erin Eid Jennifer Maloney Jim Stockinger Minnesota Pollution Control Agency

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

OUTLINE Design Results Applications

Why study land use? Helps focus statewide trend and effectiveness monitoring No comprehensive studies found in the literature Shift in Agency focus to pollution prevention and sustainability Local ground water organizations desire this information

STUDY DESIGN Objectives Study Area Monitoring Network Design Parameters Sampling Frequency Data Analysis THESE WERE DETERMINED BEFORE ANY DRILLING OR SAMPLING

Objectives (stated as hypotheses) Concentrations of analytes do not differ under irrigated agriculture, nonirrigated agriculture, unsewered residential, sewered residential, commercial/industrial, and undeveloped land uses Concentrations of analytes do not change following a change in land use Concentrations of analytes do not change with time within an individual land use

Where to Conduct Study Aquifers vulnerable to contamination All required land uses present Changing land uses Results applicable to other areas Existing data existed Local cooperation

Monitoring Network Design 3 shallow wells directly under each land use (irrigated and nonirrigated agriculture, sewered and unsewered residential, commercial, undeveloped) additional wells at various depths surface water monitoring weather station continuous water level measurements

Parameters 39 inorganic chemicals 66 Volatile Organic Compounds (VOCs) pesticides and pesticide metabolites field measurement of oxidation-reduction potential, temperature, pH, specific conductance, dissolved oxygen, and water level

Sampling Frequency and Data Analysis Quarterly sampling in March, May, August, and October Monthly sampling in a subset of wells Nonparametric methods for comparing land uses, depths, year and month of sampling, for evaluating trend, and for correlation analysis

Adjustments to Monitoring Network Dropped VOCs in agricultural areas after 1 year Sampled for agricultural pesticides in urban areas in May, 1999 Sampled for Polynuclear Aromatic Hydrocarbons in March, 1999 Slug tests in monitoring wells Conducted a geoprobe study in 1998 Sampled for tritium, N-15 summer 1998

RESULTS

Nitrate concentrations exceeded the MCL under irrigation and were elevated under unsewered land use MCL = 10

Nitrate decreased with depth even though tritium is present 1960’s1970’s1980’s1990’s

Nitrate concentrations in mg/L 0.5 to 3 3 to 5 5 to 10 More than 10 Ground water flow Mississippi River 0 ft 20 ft 6 miles Wells Denitrification occurs rapidly between 10 and 25 feet NO3/Cl ratios }

Concentrations of chloride, total solids, and nitrate were higher in ground water than in surface water

VOCs were primarily detected in urban settings

Solvents and fuel oils accounted for two-thirds of VOC detections

Metabolites accounted for most of the pesticide detections

Total dissolved solids are higher in urban areas aaabbc

Other Results Concentrations of arsenic, boron, chloride, phosphorus, potassium, and sulfate were higher under all land uses compared to undeveloped Concentrations of heavy metals, VOCs, pesticides, and nitrate vary with season Only nitrate approached its drinking water standard

Recommendations for local application Different land uses are compatible Screen domestic wells more than 50 feet below water table Ensure that supply wells do not mix upper and lower portions of aquifer Maintain riparian buffers adjacent to surface waters

Outreach Distributed over 500 reports and fact sheets Presented results at 6 conferences and to several ground water resource groups Modeling scenarios Used results to focus on specific land use issues

Modeling to predict impacts from land use If all agricultural land became irrigated, would residential areas be impacted?

< 0.5 ppm 0.5 ppm to 1 1 to 3 ppm 3 to 10 ppm > 10 ppm River Initial Condition Irrigated area

< 0.5 ppm 0.5 ppm to 1 1 to 3 ppm 3 to 10 ppm > 10 ppm River Ground water flow 5 years Irrigated area

< 0.5 ppm 0.5 ppm to 1 1 to 3 ppm 3 to 10 ppm > 10 ppm River Ground water flow 15 years Irrigated area

< 0.5 ppm 0.5 ppm to 1 1 to 3 ppm 3 to 10 ppm > 10 ppm River Ground water flow 25 years Irrigated area

We have used results from this study to begin new studies Impacts from septic systems - 3 study areas Transition from agricultural to unsewered land use - 2 studies Affects of aquifer geochemistry on distribution of nitrate, VOCs, and pesticides - 3 studies Impacts of agricultural BMP’s on ground water quality - 1 study

groundwater/gwmap