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Gem Lake News Page 3 of 6
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<br />Hydrology 101 and Gem Lake’s
<br />Well Situation (Continued from pg.1)
<br />
<br />In the past few months, the MPCA and MDH have
<br />continued testing, monitoring and following up leads as
<br />to where the problem may have started. The problem is
<br />multi-dimensional, and a lot of the same questions have
<br />emerged from citizens who are trying to understand the
<br />science behind this situation. Why did the problem
<br />emerge generally in one area of the city? Is the
<br />contamination moving? Why did one neighbor have a
<br />slightly contaminated well, while another nearby did
<br />not? Is the situation stable? Can wells heal themselves,
<br />so to speak?
<br />
<br />Following are a few general answers to these
<br />questions:
<br />
<br />Why did the problem show up in one area of the
<br />city? 1,4 dioxane was initially detected in residential
<br />wells located in the vicinity of Haven Lane and Tessier
<br />Road as part of testing done by Water Gremlin. Based
<br />on these detections, additional testing was completed
<br />to determine the extent of the contamination in Gem
<br />Lake. As testing continued, 1,4 dioxane contamination
<br />was detected in additional wells to the southwest of the
<br />initial detections, towards Little Fox Lane and LaBore
<br />Road.
<br />
<br />The highest concentrations of 1,4 dioxane were
<br />detected in the area around Haven Lane and Tessier
<br />Road. The groundwater contamination appears to have
<br />migrated to the southwest, based on lower 1,4 dioxane
<br />detections in residential wells in this direction. The
<br />distributions of contamination indicated that the source
<br />may be located north of Haven Lane and Tessier Road
<br />area of Gem Lake.
<br />
<br />Is the contamination moving? At present the problem
<br />appears to be fairly stable and confined to the western
<br />portion of Gem Lake. There have been no
<br />exceedances of the HRL for 1,4 dioxane in the northern
<br />or eastern portions of Gem Lake. As the pattern of well
<br />contamination emerged, it might have seemed like the
<br />pollution was moving around with ease, but the
<br />situation is a bit more complex. The contamination is
<br />dissolved in the groundwater, and therefore moves in
<br />the same direction the groundwater is flowing beneath
<br />the surface, which is generally to the southwest in this
<br />area of Ramsey County. The rate of groundwater
<br />movement, or “flow”, beneath the surface is generally
<br />much slower than water flowing in a river or stream at
<br />the surface.
<br />
<br />
<br />
<br />Why did one neighbor have well contamination,
<br />and another nearby had none? Here is where the
<br />real complexity emerges. We tend to think of the
<br />ground beneath us in terms of north, south, east and
<br />west, as though it is two- dimensional. In reality, the
<br />ground beneath us is like a three-dimensional layer
<br />cake. It is made up of multiple layers of gravel, sand,
<br />clay, bedrock, and other materials. The bedrock is
<br />generally very deep, and other materials (sand, gravel,
<br />clay) are layers on top of the bedrock, deposited as the
<br />glaciers receded from the area.
<br />
<br />The majority of residential wells in Gem Lake are set in
<br />the sand and gravel layers, with a few set in the deeper
<br />bedrock layers. However, the wells are not all set at the
<br />same depth, even in the sand and gravel layers. There
<br />are likely different concentrations of the 1,4 dioxane
<br />contamination in the different sand and gravel layers in
<br />the area. Therefore, the 1,4 dioxane levels may be
<br />higher in one well than another well right next door
<br />because that well is set in a different water bearing
<br />layer, that has a higher 1,4 dioxane level.
<br />
<br />Is the situation stable? Can wells heal themselves?
<br />The ground way below us is usually a mixture of gravel,
<br />sand, clay and other material. The water beneath us
<br />finds a pathway through it and can be somewhat
<br />filtered by what it is traveling through. As contamination
<br />travels through the ground, the groundwater dilutes the
<br />contamination to a certain degree, depending on how
<br />much and what type of contamination is present.
<br />Private wells don’t generally heal themselves, although
<br />contamination can become more diluted, depending
<br />upon a lot of factors. Some private well owners do
<br />extensive filtration of their well water, which can have
<br />an effect on water quality. Additional on-going testing
<br />by the MPCA will evaluate the stability of the
<br />groundwater contamination and determine if any
<br />additional wells may potentially be at risk from 1,4
<br />dioxane.
<br />
<br />Will the MPCA be able to determine where the
<br />pollution came from? How long will it take to find
<br />out? A generation ago, there were very few rules about
<br />what could and couldn’t be buried when it came to
<br />pollution and harmful chemicals.
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<br />(story concluded on page 5)
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