BOARD00158

• Board Meeting Date: 12/12/1973
• Description: Agenda or Table of Contents, Minutes, Memos
• Board Meetings - Doc Type: Meeting

One of the things we set out to do is to inventory the wells in the
area for which we could find adequate records. The reason we have to
have adequate records is that we need to know which geological units
the wells tap. If we know that, then if we do find some interesting
chemical characteristics in some of these waters then there should
be transfer value from one area to another because they are not going
to have a well every square mile. There really aren't that many there.

(slide) Just briefly, this is a geologic map that is taken from a
published geologic map of the area. The units here - this would be
alluvium, this is a Wasatch formation, the blue is the Mancos shale
and the green is the Dakota sandstone. Now there are o~her units
that you are probably familiar with that do yield water to wells, but
they are not on this map. In the big area up in here, of course, has
some crystal rock in it. \~e have inventoried a number of wells and
springs and we have collected water samples from them for chemical
analysis and we found some very interesting characteristics in some
of these waters. You will notice here I have a little dot for a well,
a dot with a tail for a spring, and this is a stream with a triangle.
The red dots represent wells that have more than the recommended
rejection limit for driru~ing water of selenium in them. The recom-
mended rejection limit is ten micrograms per liter of selenium and
these wells are all greater. The largest one, which is 120 down here
at the bottom, happens to be at a recreational site public supply
well. I sent them a letter last week and told them what they had
there. It probably won't cause the casual user any problem, but the
people who live there could develop some physiological difficulties
if they continue to use that kind of water on a regular basis.

(slide) Now I will get on to my next slide. Before I do that, let
me point out that two of these high selenium values are in the
Wasatch formation and we haven't got up to this area yet, but perhaps
we will find the same thing. This selenium value comes out in the
Entradas, this one comes out of the Mancos and this one comes out of
Dakota sandstone. So it is not concentrated in just one formation.
It exists throughout the area. One of the things we found out
besides the fact that there is selenium is the fact that there are
high concentrations of dissolved solids in the water.

(slide) This is the Mancos shale which is generally not considered to
be an aquifer. It is a pretty fair aquifer in part of this area. It
yields perhaps 10 to 15 gallons a minute of water to domestic wells.
That is a lot of water down in southwest Colorado. And the quality
is not bad in some places.

I believe that the gravel was probably dry before surface irrigation

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