BOARD00632

• Board Meeting Date: 8/16/1972
• Description: Agenda or Table of Contents, Minutes, Memos
• Board Meetings - Doc Type: Meeting

presents the quality of water existing in the aquifer at that point
and time. You can see within the small area that it actually is
a very complex pattern of dissolved solids concentrations. We
observe very marked changes in water quality over a very short dis-
tance. For example, beneath the canal in the central part of the I
study area we have dissolved solids of less than 1,000 parts per
million or mg/l, and this increases to over 3,500 milligrams per
liter in a distance of less than one mile. The water quality pattern
itself appears to be a function of several factors, but the major ones
appear to be the location of areas of heaviest irrigation which would
be this area east of La Junta, and also the direction of ground water
flow indicated by some of these arrows, which are perpendicular to
the water table contours. The position of the river itself also
appears to play some role in the water quality pattern observed with-
in the study area.

(Slide) Now, if you will remember on the flow chart, I showed you the
first step in the actual calculations was to determine the new water
table elevations. In the model that we are using, a working and
satisfactory hydrologic model is a prerequisite to the water quality
model. One measure of how good our hydrologic model is, is to
compare the observed and calculated water table elevation for the end
of the study period. That is, after a period of one year has elapsed.
So from March I, 1972, you can see that the water table contours, the
water table elevations measured in the field, shown in blue, compared
quite well with those calculated by the computer model. We were
able to predict the observed water table elevations throughout the
aquifer within half a foot approximately 90 percent of the time.
(Slide) Since we ran the model on a monthly basis, we were able to
compare, or look at changes in water table elevations as a function
of time. This slide shows you a comparison of observed and calculated
water table elevations for one observation point in the aquifer or
in the study area. And again, you see that the model is predicting
the trends and the changes which were observed in the field.

(Slide) What we are really interested in - the purpose of the study
was to look at the quality of water in the aquifer. This map shows
you first of all the actual dissolved solids concentration which was
observed in the study area after a period of one year. The water
quality pattern is indicated again by these contour lines and you see
that the shape of the pattern, or the pattern itself, is fairly
similar to what it was a year ago, that is, in 1971, but it is not a
static pattern. It is changing and there are differences, noticeable
differences, between '71 and '72. What I did was to shade in either

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