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