WSP11265

• File Number: 8274.400
• Description: Colorado River Basin Salinity Control - General Basinwide Salinity Issues - NPDES
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 2/21/1995
• Title: Pine River Investigative Team Report - February 21 1995
• Water Supply Pro - Doc Type: Report/Study

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findings of the Team. The following is a brief summary of those findings and the
conclusions drawn.

The geologic subcommittee of the investigative team prepared a report for the general
committee (Appendix A) and also submitted extensive comments on the
aforementior'led Amoco report (Appendix G) including numerous findings and
determinatiohs. Following an independent geological analysis of all pertinent
information, the geologic subcommittee found "there are no positively identified barriers
to reservoir fluid flow in the area." The subcommittee recognizes the Northwest- and
Northeast-trending features identified by Amoco, but also has identified numerous
north-south fraotures and lineaments (see also the lineament review ofARI included
as Appendix G). Further, a fairly straightforward interpretation ofthe structural and
geomorphic elements of the study area yields a: fault, or fault zone, roughly parallel to
the Pine River which is consistent with the permeable zone modeled in the reservoir
simulation.

The subcom~ittee also analyzed precipitation data to determine if the theory advanced
by Amoco of diminished groundwater recharge at the outcrop as the cause of seepage
was reasonable. The findings did not support the diminished recharge theory. The
"four- to five-year dry period" interpreted by Amoco is not present in the precipitation
data from the nearest (Vallecito) gauge. When precipitation measurements are
examined, only one year was substantially below the average of 26 inches overthelast
fourteen years. Further, a closer review of the precipitation data reveals that between
1979 and 1992,11 of the 14 years experienced above average precipitation, and 10
of the last 14 years are even above the "trend" described in Amoco's report. Also it is
critical to note that during 1992, the year preceding the first report of seepage,
precipitation Was well above average. In fact, 1992 is the 6th wettest year recorded in
the past 43 years, Therefore, lowering of the water table due to precipitation rates is
not supported by the data from the Vallecito gauge.

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The geologic subcommittee also analyzed groundwater chemistry data from the study

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