GROUND WATER MONITORING TO EVALUATE EFFECTS OF LAND USE ON WATER QUALITY Mike Trojan Erin Eid...
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Transcript of GROUND WATER MONITORING TO EVALUATE EFFECTS OF LAND USE ON WATER QUALITY Mike Trojan Erin Eid...
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 (1992-96)
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 - 1998
• 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
0
5
10
15
20
Med
ian
(pp
m)
Irrigated Unsewered Nonirrigated
Sewered Commercial Undeveloped
MCL = 10
Nitrate decreased with depth even though tritium is present
0
30
60
0 40 80 120
Depth below water table (feet)
TU
s o
r p
pm
Tritium Nitrate
1960’s1970’s1980’s1990’s
Nitrate concentrations in mg/L0.5 to 3
3 to 55 to 10More than 10
Ground water flow
Mississippi River
0 ft
20 ft
6 milesWells
Denitrification occurs rapidly between 10 and 25 feet
0.080.07
0.005
0.001
NO3/Cl ratios}
0.1
1
10
100
1000
surface water ground water
Concentrations of chloride, total solids, and nitrate were higher in ground water than in surface water
VOCs were primarily detected in urban settings
0
2
4
6
8
No.
det
ecti
ons
Commercial Sewered Irrigated
Nonirrigated Unsewered Undeveloped
Solvents and fuel oils accounted for two-thirds of VOC detections
0
5
10
15
20
25
Wel
ls d
etec
ted
Chlorinated solvents Chloroform CFCs BTEX
Metabolites accounted for most of the pesticide detections
0
20
40
60
To
tal
no
. o
f
det
ecti
on
s
Parent Metabolites
Triazines Acetanalides Prometon Dicamba
Total dissolved solids are higher in urban areas
200
400
600
mg/L
Commercial Sewered Irrigated
Unsewered Nonirrigated Undeveloped
a a a b b c
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
Http://www.pca.state.mn.us/water/
groundwater/gwmap