Groundwater Fluxes Across Interfaces (2004)

Chapter: Appendix B: Hydrogeology of Door County

« Previous: Appendix A: Workshop Agenda
Suggested Citation: "Appendix B: Hydrogeology of Door County." National Research Council. Groundwater Fluxes Across Interfaces. Washington, DC: The National Academies Press, 2004.
Page 71
Suggested Citation: "Appendix B: Hydrogeology of Door County." National Research Council. Groundwater Fluxes Across Interfaces. Washington, DC: The National Academies Press, 2004.
Page 72
Suggested Citation: "Appendix B: Hydrogeology of Door County." National Research Council. Groundwater Fluxes Across Interfaces. Washington, DC: The National Academies Press, 2004.
Page 73

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Appendix B Groundwater Recharge and Discharge on Wisconsin's Door Peninsula Based on a talk given at the workshop by Kenneth R. Bradbury Wisconsin Geological and Natural History Survey The workshop on "Groundwater fluxes across interfaces" was held in Egg Harbor, Wisconsin, which is situated on the Door Peninsula (Figure B-1~. The hydrogeology of the Door Peninsula illus- trates the complexity and importance of flow across interfaces - groundwater recharge and discharge processes. A rocky peninsula between Lake Michigan and Green Bay, the Door Peninsula is character- ized by rugged rocky shorelines and sandy beaches. The scenery along with the mild climate, abundant natural resources, and a small-town feel have made the Door Peninsula one of the most popular tourist destinations in the midwestern United States. All residents of the county depend on groundwater, but groundwater quality problems have plagued the county for many years. Bacteria and nitrate exceed drinking water standards in about 30 percent of the private wells in the county, and private well owners often report turbid or muddy water in their wells during certain times of the year (Bradbury and Mul- doon, 19921. Other groundwater contaminants include agricultural chemicals, pesticide residues from cherry and apple orchards, and petroleum and other non-aqueous phase liquids. Much of the charm of the Door Peninsula, and its groundwater problems, are directly related to its unique geology - a combination of Paleozoic bedrock and Pleistocene modifications. SiTurian-age dolomites form the backbone of the peninsula and dip gently eastward into the Michigan Basin (Figure B-2~. In the Late Pleistocene, continental glaciers covered the area, and when they retreated they left behind a unique landscape. On the western side of the county the Silurian escarpment forms high cliffs along the Green Bay shoreline; only a few miles to the east the land meets Lake Michigan with sandy beaches and diverse wetlands. In between, in the uplands of the county, glaciers removed most of the soil, so that in most places the bedrock is less than two meters below the surface and in many places it is exposed at the land surface. The dolomite contains both near-horizontal and vertical fractures (Mul- doon et al., 2001~. These fractures are extensive, and the vertical Fractures are easily visible from the air, particularly under alfalfa fields in dry weather. The combination of thin soils and fractured rock makes groundwater in the county extremely vulnerable to contamination. Groundwater flow in the Door Peninsula is conceptually simple, with recharge occurring in the uplands along the crest of the peninsula, and discharge occurring in springs and seeps along the Green Bay and Lake Michigan shorelines. In detail, however, both the recharge and discharge processes are 71

72 Apperld~c B G:reen: B~ >',~ 2 ~~ 5~ ) av ~ lie H ~ ~..~.CMQ.~.r.,~...,..,C..,~o~.,. am. A: -- - N ~ - in.. at.: ~ Lake MI~GhI~9a:n ~ ~2- 4: :.~: 8:: :10~ Miles ~17 H I 1~ Q 2~:4::6::~:10 Kilometers 1_ H H 1 Canada ~ I FIGURE B-1 Location of the Door Peninsula in eastern Wisconsin, extending out into Lake Michigan. E.H. is Egg Harbor, the site of the workshop. SOURCE: Adapted from Kenneth R. Bradbury, Wisconsin Geological and Natural History Survey, written commun., 2002. ~ -—D- ~ quite complex. Groundwater recharge is rapid, transient, and often focused in discrete depressions where open vertical fractures or solution features occur at the land surface. Most annual recharge occurs over a few weeks following spring rains and snowmelt; during this period groundwater levels often rise by tens of meters. Thermal and geochemical data collected during specific recharge events show that recharge water can move from the land surface to tens of meters below the water table in a matter of hours or days. Once in the aquifer, groundwater flow is generally horizontal along bedding-plane fractures that have been widened by solution (Rayne et al., 2001~. Flow rates in this fractured dolomite can be extremely rapid - on the order of 10 km/yr. These rapid flow rates mean that local private and municipal water supply wells are extremely vulnerable to contamination from surface sources, and that contributing areas for local wells can be very large. Groundwater not captured by wells in the Door Peninsula discharges to discrete shoreline springs, local wetlands, and as diffuse flow through offshore lake sediments. In general, springs occur where conductive horizontal or vertical factures intersect the shoreline. Locally, hydraulic gradients in the discharge zone can be high enough to create flowing wells, sand boils and measurable thermal anomalies,

Appendix B 73 Cross se~ion:.thro.u~g~h~th:~.e. Door Penins:u:la. recharge Green l l l :La~ke Michi:g~a:n:- "sandstone"~: aqu~ifer discharge idea FIGURE B-2 West-to-east cross section of the Door Peninsula. SOURCE: Kenneth R. Bradbury, Wisconsin Geological and Natural History Survey, written common., 2002. but over large areas of the lakebed the upward groundwater discharge through lake sediments is slow and difficult to measure. In this environment, closing the water budget - balancing recharge processes with dis- charge processes - is extremely challenging, yet understanding recharge and discharge processes is essential for solving local groundwater contamination problems and for making wise land-use management decisions for the area.

Next: Appendix C: Agency Interest in Groundwater Fluxes »
Groundwater Fluxes Across Interfaces Get This Book
Buy Paperback | $35.00
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

Estimates of groundwater recharge and discharge rates are needed at many different scales for many different purposes. These include such tasks as evaluating landslide risks, managing groundwater resources, locating nuclear waste repositories, and estimating global budgets of water and greenhouse gasses. Groundwater Fluxes Across Interfaces focuses on scientific challenges in (1) the spatial and temporal variability of recharge and discharge, (2) how information at one scale can be used at another, and (3) the effects of groundwater on climate and vice versa.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook,'s online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
  9. ×

    And that's about it! What do you think of the new OpenBook? Click the Feedback button and tell us. Happy reading!

    « Back Done