Ground Water Conditions around the Lathers Property

Town of Waukesha

Douglas S. Cherkauer PhD, PG, PH

November 15, 2007

Tonight’s presentation

• Site specific issues at Lathers site– My report and what it means

• Overview of what a ground-water using community needs to do to understand and protect its water supply resource– Status of the Town’s monitoring program

• Discussion

1. Lathers site issues that need addressing

• What extraction rate can the aquifer sustain?

• Where will the water pumped come from?

• What impacts will the removal of water cause?– Drawdowns and effects on local wells– Effects on surface waters– Impacts on ground water quality

• Are these impacts acceptable?

Adequacy of available information

• Some useful information exists, but not enough for complete answers.

• The greatest weaknesses include:– Accurate 3D distribution of geologic materials– Conductivities of those materials – especially

links between aquifer and surface waters– 3D distribution of existing ground water levels– Depths of existing wells (and pump positions)

Role of report done for Town

• Examine existing information to provide an interpretation of geology at and around the site

• Make some preliminary calculations of drawdowns using the existing (but incomplete) data

• Present recommendations as to what needs to be done to allow better answers to the Town’s concerns

Conclusions about site geology

• There is substantial coarse grained (aquifer) material under the Lathers site

• 8 of the 12 test borings on site encountered sand at the surface

• There is a strong likelihood of a hydraulic connection between any well constructed on site and the Fox River (and probably Vernon Marsh)

Assumptions: Aquifer is homogeneous and laterally extensive;Well pumped at 1.5 mgd;

NO interconnection to surface waters (aquifer confined)Cautions: These are likely upper limits & are in the aquifer (not surface waters).

Assumptions: Aquifer is homogeneous and laterally extensive;Well pumped at 1.5 mgd;

NO interconnection to surface waters (aquifer confined)Cautions: These are likely upper limits & are in the aquifer (not surface waters).

What impacts are likely?

• Wells - drawdowns from the site will reach nearby wells, but whether this will cause problems is site specific and can’t be answered today.

• Fox River – will lose some water, but it would be returned upstream

• Vernon Marsh – some water will likely be pulled from the northern marsh. How much can’t be determined today, but this water will NOT be returned.

• Water quality – can’t assess at present.

Are there currently answers to the questions?

• Sustainable pumping

• Source of the pumped water

• Impacts– Drawdowns– Surface water– Water quality

• Acceptability of impacts

• Without more testing and a reliable flow model, definitive answers to first two are difficult

• Conservative drawdowns can be estimated, but the link between aquifer and surface waters needs to be accurately defined

• Can’t be assessed until more information is available.

2. Assuring local water supply

• Monitor water levels

• City should assure residents within any well’s impact zone that they will correct water problems they cause

• Town needs to work with City to:– get adequate information– create a good flow model – use that model to test and optimize possible well

scenarios

Additional steps to protect supply

• Land use plan and zoning needs to be consistent with ground water protection– Cluster development with open space for

recharge– Avoid impervious surfaces, curb/gutter, sewers– Minimize road salt, other contaminants

• Require developments to quantify water needs and to show they can live with available supply (Example: Richfield ground water ordinance)

Monitoring Program Status

• Over 50 volunteers– 25 selected as initial set (based on location)– 22 are in backup set– Others too far away for present program

• Initial set– Test for bacteria– If pass, then water level will be measured

bimonthly – during work day when well inactive– Reports and data archiving; future survey– Actual schedule unknown at present (email

helpful)

Monitoring Program Status (2)

• Backup set– If any of initial set fail bacteria test, or if their

well is inaccessible, we’ll select a nearby home from backup set to replace it.

– Will be contacted for permission– After inclusion, the steps for the initial set will

be followed.

• If any volunteer wants to opt out, they need merely to call Town contact

Additional thoughts

• Other nearby communities dependent on private wells should consider initiating a similar program

• Having long-term, consistent monitoring record is best way to identify areas where problems may be developing

• Examples: Mequon and Richfield

Southeastern Mequon – dolomite aquifer

Over 150 feet of drawdownin parts of the aquifer(effectively confined)

Lake water nowavailable in parts of city

Jun

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4

Jun

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5

Jun

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6

Jun

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Private wells are inboth dolomite and

sand & gravel –unconfined

Questions?