Prepared by the Central Wisconsin Groundwater Center University of Wisconsin-Stevens Point

Transcription

1 CONTAMINANT SOURCE ASSESSMENT AND MANAGEMENT USING GROUNDWATER FLOW AND CONTAMINANT MODELS IN THE STEVENS POINT - WlDTING - PLOVER WELLHEAD PROTECTION AREA Prepared by the Central Wisconsin Groundwater Center University of Wisconsin-Stevens Point 1997

2 CONTAMINANT SOURCE ASSESSMENT AND MANAGEMENT USING GROUNDWATER FLOW AND CONTAMINANT MODELS IN THE STEVENS POINT - WIllTING - PLOVER WELLHEAD PROTECTION AREA prepared by David I. Mechenich, Data Management Specialist George I. Kraft, Director in partnership with Portage County Planning and Zoning Department USDA Stevens Point-Whiting-Plover Wellhead Protection Project for the Village of Whiting Village of Plover City of Stevens Point Central Wisconsin Groundwater Center Cooperative Extension Service College of Natural Resources, University of Wisconsin-Stevens Point January 1, 1997

3 ii ACKNOWLEDGMENTS This project was a collective effort between many people and agencies. The Village of Whiting, Thomas Hagen and Cletus Tepp in particular, sponsored this project and took the local lead role. The Portage County Planning Department, especially Ray Schmidt, coordinated this joint effort. Portage County and the Communities ofstevens Point, Whiting, and Plover are commended for their foresighted and responsible efforts to protect and manage our groundwater resources. Greg Disher ofthe Stevens Point Water and Sewage Department, Jeff Schlegel of the Whiting Water Utility, and Dave Fritsch of the Plover Water Department provided excellent cooperation and assistance with information needed in this study. Bill Ebert, USDA Stevens Point-Whiting-Plover Wellhead Protection Project, contributed his expertise and agricultural management data on the Stevens Point-Whiting-Plover recharge areas. Norm Bushor, Portage County Planning Department, applied GIS expertise to the land use analysis essential to the project. Thanks to reviewers Professors Larry.Bundy and Fred Madison, UW-Madison Soil Science Department, Professor Ken Bradbury, WGNHS, and Christine Mechenich, Central Wisconsin Groundwater Center, for their assistance and advice. We would like to acknowledge and thank our student help, especially Heather Barlow for her outstanding assistance with land use mapping, and Dave Johnston for his talented graphics. And finally, we wish to thank the US EPA-Region 5 and Bill Ryan for funding this work and contributing to the informed management of our groundwater resources.

4 iii CONTENTS List of Figures iv List oftables vii List of Appendices viii List of Archives ix Executive Summary ~ x Chapter 1. Introduction Chapter 2. Study Area Characterization Chapter 3. Groundwater Flow Modeling 3-1 Chapter 4. Zone-of-Contribution Delineation Chapter 5. Nitrate Loading to Groundwater 5-1 Chapter 6. Predicted Nitrate Concentrations at the Municipal Wells 6-1 Chapter 7. Conclusions , 7-1 References References-l

5 iv FlGURES 1.1 Location of study area Nitrate-N concentrations at Village of Whiting well Nitrate-N concentrations in Little Plover River baseflow, from sampling at Hoover Road The Stevens Point, Whiting, and Plover study area The Stevens Point, Whiting, and Plover municipal wellfields Pleistocene geology of the Stevens Point, Whiting, and Plover area Water table elevation from Lippelt and Hennings Example well logs for the Stevens Point, Whiting, and Plover municipal wellfields Water-level hydrograph for well Pt Land use in the Stevens Point, Whiting, and Plover area Location of wells included in the Stevens Point, Whiting, and Plover well log database Bedrock elevation in the Stevens Point, Whiting, and Plover area lOA 2.lOB Hydraulic conductivity (x 10-4 m/s) calculated from specific capacity data for the Stevens Point, Whiting, and Plover area 2-25 Hydraulic conductivity (log m/s) calculated from specific capacity data for the Stevens Point, Whiting, and Plover area Composite water table map for the Stevens Point, Whiting, and Plover area Design of the MODFLOW model for the Stevens Point, Whiting, and Plover study area Point calibration targets for the Stevens Point, Whiting, and Plover MODFLOWmodel Hydraulic conductivity zones for the calibrated Stevens Point, Whiting, and Plover model " " A Changes in hydraulic conductivity (ftls) for calibration ofthe Stevens Point, Whiting, and Plover model B Changes in hydraulic conductivity (percent) for calibration ofthe Stevens Point, Whiting, and Plover model Recharge zones for the calibrated Stevens Point, Whiting, and Plover model '

6 3.6A Changes in recharge (inches) from 10 inches/year for calibration of the Stevens Point, Whiting, and Plover mod~l B Changes in recharge (percent) from Winches/year for calibration of the Stevens Point, Whiting, and Plover model Adjustments to bedrock elevation for calibration of the Stevens Point, Whiting, and Plover model Water table contours for the calibrated Stevens Point, Whiting,and Plover model and the composite target ; Head residuals for the calibrated Stevens Point, Whiting, and Plover model Measured heads versus simulated heads for the calibrated Stevens Point, Whiting, and Plover model Sensitivity analysis for the Stevens Point, Whiting, and Plover model Comparison of the water table calculated for no municipal well pumpage, year 2005 average daily pumpage, and year 2005 maximum cl1lily pumpage Cumulative basetlow in the Little Plover River under three pumping scenarios ' Cumulative additions to the Plover River basetlow under three pumping scenarios Starting locations for particles used to delineate zones-of-contribution Zones-of-contribution and times-of-travel for the Stevens Point, Whiting, and Plover municipal wellfields using MODPATH Comparison of zone-of-contribution delineations for the Plover municipal wellfield Comparison of zone-of-contribution delineations for the Whiting municipal wellfield Comparison of zone-of-contribution delineations for the Stevens Point wellfields ' Estimated nitrogen loading for crops in the Stevens Point, Whiting, and Plover area under conventional and BMP agriculture Estimated nitrogen loading average and range for c...ops in the Stevens Point, Whiting, and Plover area under conventional agricultural management Estimated nitrogen loading average and range for crops in the Stevens Point, Whiting, and Plover area under BMP agriculture Thirty year zones-of-contribution for the Stevens Point, Whiting, and Plover municipal wells 6-2 v

7 6.2 Relationship between zone-of-contribution and time-of-travel for the Stevens Point, Whiting and Plover municipal wells Land use in the 30year zones-of-contribution for the Stevens Point, Whiting, and Plover municipal wells Groundwater recharge in the 30 year zones-of-contribution for the Stevens Point, Whiting, and Plover municipal wells Predicted steady-state nitrate-n concentrations under existing land use Nitrate loading sources for the Stevens Point, Whiting, and Plover municipal wells under conventional and BMP agriculture 6-14 C.l Revised bedrock topography for the alternate bedrock model C-2 C.2 Water table contours for the original calibrated model, the revised bedrock model, and the composite calibration target C-3 C.3 Comparison of 30 year zones-of-contribution for revised bedrock model and original model C-5 C.4 Final hydraulic conductivity zones for the alternate hydraulic conductivity model C-6 C.5 'Water table contours for the original calibrated model, the alternate hydraulic conductivity model, and the composite calibration target C-8 C.6 Comparison of 30 year zones-of-contribution for revised hydraulic conductivity model and original model C-9 C.7 Adjustments to bedrock elevation for the alternate treatment of bedrock highs model C-11 C.8 Water table contours for the original calibrated model, the alternate bedrock high model, and the composite calibration target...,... " C-12 C.9 Comparison of30 year zones-of-contribution for revised bedrock high model and original model C-13 vi

8 vii TABLES 2.1 Hydraulic conductivity (K) and specific yield (SY) from pump tests for the SWP area Typical ranges for hydraulic conductivity for unconsolidated materials Table structure for well log database Hydraulic conductivity calculated from specific capacity data for the SWP area Comparison ofhydraulic conductivity determined from pump tests and specific capacity data Hydraulic conductivity calculated from specific capacity data for wells located in flat sand and gravel outwash in the Stevens Point, Whiting, and Plover area Residuals for the calibrated SWP model Calibration levels for active cells in the SWP model Municipal wellfield pump rates Water balance for zones-of-contribution for the Stevens Point, Whiting, and Plover wellfields Fertilizer-N applied to crops in the study area under best management practices (BMP) and conventional practices (CON) Crop yield and harvested-n per acre for crops grown instudy area Summary of N outputs :......, Calculated N loading to groundwater from each crop (Nc.J Summary of land use in the 30 year time-of-travel zone-of-contribution Average crop census for the 30 year TOT areas Average nitrate-n loading for various land uses on a per acre basis Water budget for 30 year zones-of-contribution for concentration calculations Predicted steady-state nitrate-n concentrations under existing land management '.' Some comparisons for evaluating potential management schemes " 6-16 C.l Calibration residuals for the alternate bedrock model C-4 C.2 Calibration residuals for the alternate hydraulic conductivity model C-7 C.3 Calibration residuals for the alternate treatment ofhigh bedrock areas C-IO

9 _..._...,."".._.... "'.".' viii APPENDICES A MODFLOW INPUT FILES A-I B MODPATH INPUT FILES B-1 C ALTERNATE MODEL CALffiRATIONS C-l

10 ix ARcmVES Archives are voluminous collections of data that are maintained at the Central Wisconsin Groundwater Center. They are available for i~ction there, or information from them can be furnished upon request. 1 Database containing well log and construction report data for 694 wells. 2 AutoCAD format land use mapping.