WSP06480

• File Number: 8546.200
• Description: AWDI - Mailing Lists/Correspondence
• State: CO
• Basin: Rio Grande
• Water Division: 3
• Date: 6/6/1983
• Title: The San Luis Valley Groundwater Dispute
• Water Supply Pro - Doc Type: Report/Study

o
eXl
0Ci
_-I
~ ")
-"t, ~,":,j

~v
(,) C
\~~~ v~
~~,
/?:;~j:
j/\

the effect that diversions of groundwater from the
artesian, confined aquifer, probably throughout most of
the San Luis Valley, was having a depletive effect on
surface stream flows, particularly on the Conejos River.
The assertion was that with pumping came declines in the
artesian pressure and, therefore, increases in recharge
into the aquifer from the stream in the recharge areas
around the periphery of the confining layer (around the
edges of the San Luis Valley); and reductions in the
flows into the surface streams from springs thought to be
fed from the confined aquifer.

1. U.S.G.S. Circular 18 was published in 1973, strongly
suggesting the direct hydraulic connection between
the confined aquifer throughout the San Luis Valley
as whole with the. Conejos River.

2. Further U.S.G.S. work on an analog computer model of
the San Luis Valley resulted in the publication of
Circular 29 in 1975. This publication produced the
first estimates of the order of magnitude of that
impact, suggesting that it was significant. And
sensitivity runs on the analog model gave important
basis for the conclusion that these effects were
material, regardless of the uncertainties about the
degree of hydraulic connection.

3. As a result of this general understanding of the
geologic situation, the State Engineer's Office
began to disallow new well permits from the
connfined aquifer.

4. The working leading to Circular 29 also developed
and utilized assumptions concerning the leakage of
water between the confined and unconfined aquifer
and developed and utilized assumptions concerning
the lowering of the unconfined aquifer water table
and the resultant salvage of non-beneficial use.
That model predicted, for example, assuming the
pumping of 5 million acre-feet over a 50-year period
from the confined aquifer, 38 percent or 1,900,000
acre-feet would be derived from salvaged evapotrans-
piration; 28 percent or 1,400,000 acre-feet would
be derived from groundwater storage; 12 percent or
600,000 acre-feet would be derived from the flow of
the Rio Grande; and 22 percent or 1,100,000 acre-
feet would be derived from the Conejos.

B. Following the lead of the State Engineer, parties
primarily from the Conejos area became increasingly
concerned over the impact of groundwater use on the
surface streams, and the call for regulation began to be
heard. Parties from other areas were less vocal. The
Conejos area was typified by more traditional methods of

-7-