PERMFILE60752

• Permit No: C1989074
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit F Hydrology
• Media Type: D
• Archive: No

8.0 GROUNU-WATER QUALITY--Continued
8.2 pH and Specilic Conductance
pH and Specific Conductance Vary Among and Within Aquifers
pH and specific conductance are easily measurable properties o/ground water
that allow estimates of the acidity and dissolved-solids concentration.
The pH of water is a measure of acidity. A pli
of less than 7.0 is acidic; 7.0 is neutral; more than 7.0
is alkaline. Information on the pli of ground a~atcr
is sparse. The pH of growtd water in areas where it is
known or can be reasonably inferred from existing
data is shown in figure 8.2-I. The pH of ground
water in wells and springs ranges from F.6 to 9.3.
Marked variations in pH occur within distances of
less than a mile. Variations in pH cannot be correlat-
ed with ratios of sulfate to bicarbonate or chloride to
bicarbonate.
Ground water in Cretaceous to Tertiary transi-
tional and terrestrial formations is more alkaline
than in Cretaceous marine formations. The pH of
ground water in the coal-bearing Vcrmejo and Raton
Formations most commonly ranges from 7.5 to 8.0,
but it exceeds 8.0 in the vicinity of some active or
abandoned coal mines. However, it cannot be prov-
en that mining raises the pH of ground water since
the pH of mine discharge, ranging from 7.3 to 9.2, is
in the same range as that of ground cvatcr from
undisturbed bedrock. The pH of ground water in rite
Cuchara and Poison Canyon Formations mast com-
monly ranges from 7.5 to 8A nonh of the Spanish
Peaks and 6.5 l0 7.5 south of the Spanish I'caks. Tltc
pH of ground water in the Devils Holc and liucrfano
Formations, Parasiia Conglontcrmc and Trinidad
Sandstone most commonly ranges from 7.0 to R.O.
The pH of ground water in Cretaceous marine for-
mations most commonly ranges from 7.0 to 8.0 and
tends to he slightly greater in shale than in limestone
or sandstone.
Specific conductance is an indicator of dis-
solved-solids concentration; like pH, it is an easily
measured property of ground water that can he used
to estimate water-quality characteristics which are
more difficult and expensive to ascertain. Areas
where the dissolved-solids concentration in ground
water is known or can be reasonably inferred from
analyses are shown in figure 8.2-2, and graphs of
specific conductance versus dissolved-solids concen-
tration prepared from these analyses are shown in
figure 8.2-3. These graphs can be used to estimate
the dissolved-solids concentrations in parts of Area
61 where chemical analyses are not available. From
figure 8.2-3, it can be seen that for any specific
conductance the dissolved-solids concentrations gen-
erally will be greatest in shale and limestone forma-
tions, less in shale and sandstone formations, and
Icast in sandstone formations and alluvium.
The similarity of specific conductance/
dissolved-solids ratios in Purgatoire drainage alluvi-
um and sandstone formations suggests that much of
the water in the alluvium (lowed in from sandstone.
In the area sampled, the Purgatoire drainage is
underlain by the Poison Canyon and Raton Forma-
tions, which contain sandstone and shale. Specific
conductance/dissolved-solids ratios indicate that wa-
ter from these formations is transmitted principally
by the sandstone layers.