Ground Water Conditions around the Lathers Property Town of Waukesha Douglas S. Cherkauer PhD, PG,...

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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Private wells are inboth dolomite and

sand & gravel –unconfined

Questions?