University of Colorado Law School University of Colorado Law School

Colorado Law Scholarly Commons Colorado Law Scholarly Commons

Uncovering the Hidden Resource: Groundwater Law, Hydrology, and Policy in the 1990s (Summer Conference, June 15-17)

1992

6-15-1992

Exporting Ground Water from Colorado’s San Luis Valley: AWDI’s Exporting Ground Water from Colorado’s San Luis Valley: AWDI’s

Nontributary Claim Nontributary Claim

Eric J. Harmon

Follow this and additional works at: https://scholar.law.colorado.edu/groundwater-law-hydrology-policy

Part of the Courts Commons, Hydraulic Engineering Commons, Litigation Commons, Natural

Resources Law Commons, Natural Resources Management and Policy Commons, Science and

Technology Law Commons, State and Local Government Law Commons, Water Law Commons, and the

Water Resource Management Commons

Citation Information Citation Information Harmon, Eric J., "Exporting Ground Water from Colorado’s San Luis Valley: AWDI’s Nontributary Claim" (1992). Uncovering the Hidden Resource: Groundwater Law, Hydrology, and Policy in the 1990s (Summer Conference, June 15-17). https://scholar.law.colorado.edu/groundwater-law-hydrology-policy/6

Reproduced with permission of the Getches-Wilkinson Center for Natural Resources, Energy, and the Environment (formerly the Natural Resources Law Center) at the University of Colorado Law School.

Eric J. Harmon, Exporting Ground Water from Colorado’s San Luis Valley: AWDI’s Nontributary Claim, in UNCOVERING THE HIDDEN RESOURCE: GROUNDWATER LAW, HYDROLOGY, AND POLICY IN THE 1990S (Natural Res. Law Ctr., Univ. of Colo. Sch. of Law 1992). Reproduced with permission of the Getches-Wilkinson Center for Natural Resources, Energy, and the Environment (formerly the Natural Resources Law Center) at the University of Colorado Law School.

EXPORTING GROUND WATER FROM COLORADO'S SAN LUIS VALLEY:

AWDI'S NONTRIBUTARY CLAIM

Eric J. Harmon, P.E.HRS Water Consultants, Inc.

Lakewood, Colorado

Uncovering the Hidden Resource:Groundwater Law, Hydrology, and Policy in the 1990's

Natural Resources Law CenterUniversity of Colorado at Boulder

June 15-17, 1992

1

iCl

EXPORTING GROUND Han FROM THE SAN LUIS VALLEY: AWDI'S NONTRIBUTARY CLAIM

I. INTRODUCTION

The San Luis Valley is the largest intermontane basin inColorado, comprising about 3,500 sq mi. It includes the entiredrainage basin of the Rio Grande River and its tributaries inColorado. The valley extends from Poncha Pass (near the town ofPoncha Springs), in the north, to Antonito, at the New Mexicoborder, in the south. It extends from the town of Del Norte inthe west to La Veta Pass, near the town of Fort Garland, in theeast.

The primary aquifers of the San Luis Valley are relativelyevenly distributed under much of the valley floor. They arethickest in the east-central part of the valley, in the Hooper -Center area, are thinner near the valley edges, and arenonexistent in the mountainous areas that form the west, north,and east boundaries of the valley.

American Water Development, Inc. (AWDI) applied to theColorado Division 3 Water Court for a water right for 200,000acre-feet per year of ground water, most of which would be pumpedfrom the east-central part of the valley. Following 29 days oftrial during October-November, 1991, the trial court foundagainst the applicant, in that AWDI's proposed withdrawals wouldmaterially injure vested and decreed water rights in the San LuisValley. As of this writing (May, 1992) the applicant hasappealed the trial court's decision to the Colorado SupremeCourt.

II. THE GROUND WATER SYSTEM

A. Description of Aquifers

Two principal aquifers underlie the San Luis Valley. Bothaquifers are composed of unconsolidated sand and gravelinterbedded with silt and clay layers. The shallower of these,called the unconfined aquifer, varies from zero thickness nearthe valley edges to a maximum of about 200 feet near the towns ofCenter, Hooper, and Mosca. The deeper aquifer, termed theconfined aquifer, extends downward from the top of a series ofblue-gray' clay layers that separate the two aquifers, to thebottom of the unconsolidated basin-fill sediments. The clay

1

layers are thickest near the center of the basin, becomingthinner and less continuous near the basin margins. At the edgesof the San Luis Valley, including most of southern CostillaCounty, the clays are not present. The aggregate thickness ofthese clay layers typically ranges from 150 to 250 feet, thoughthere are areas in the east-central valley where the aggregatethickness of the clay beds exceed 1000 feet, and are found atdepths exceeding 1500 feet.

The thickness of the confined aquifer basin-fill sedimentsis not well defined, but it reaches at least 2500 feet in someplaces, and probably averages over 1500 feet. Recent studiesindicate that the deepest economically recoverable ground waterin the confined aquifer lies at depths of 2000 to 3000 feet dueto indications of poor water quality, reduced hydraulicconductivity, and high well completion and water pumping costsbelow that depth.

B. Ground Water Recharge and Discharge

Recharge of the major aquifers occurs at the edges of thebasin, where runoff of rain and snowmelt in the mountains flowsonto the permeable valley sediments and infiltrates to theaquifers. Recharged ground water moves slowly toward the centerof the basin and then upward, to discharge at the surface. Thisdischarge ultimately flows into the Rio Grande River and itstributaries or rises into a closed basin called the "sump area,"which lies in the east-central portion of the valley between thetowns of Mosca and Blanca. In this sump area there is no outletfor surface-water flow from the unconfined aquifer.Evapotranspiration in the San Luis Valley, including the closedbasin, is estimated by some researchers to exceed two millionacre-feet per year.

In addition to natural ground water discharge, approximately800,000 acre-feet of ground water are used for irrigation. (Anadditional 1,200,000 acre-feet per year of surface water fromcanal diversions is also used for irrigation). Surfacediversions and irrigation return flows constitute a major sourceof recharge to the unconfined aquifer of the valley.

The greatest amount of pumping occurs in the mostintensively irrigated area, which is the west-central part of thevalley, in the Alamosa - Hooper - Center - Monte Vista area.

2

PM About half of this ground water is taken from the deeper aquifer.Some of this ground water from the deeper aquifer recharges theshallower aquifer since not all of the water is used by thecrops. Also, there is evidence that artesian pressure issufficient to cause relatively minor amounts of upward leakage ofground water from the confined aquifer into the unconfinedaquifer via leakage through the intervening clay layers. Both ofthese processes act to raise the water table in the unconfinedaquifer in the central portion of the San Luis Valley to within afew feet of ground surface. Several thousand acres ofpotentially arable land are not in farm production due towaterlogging caused by these processes. The Closed Basin Projectcurrently under way in the sump area is designed to lower thewater table, thereby reducing water lost by evapotranspiration.

C. Aauifer and Well Characteristics

Porosity in both major aquifers typically is about 30% andconsists entirely of void space between the sand and gravelgrains. Because the shallower aquifer is unconfined, wellscompleted in it do not flow. In the west-central San Luis Valley,production rates from pumping irrigation wells completed in theshallow aquifer range up to 1,000 gallons per minute (gpm).Irrigation wells in the deeper, confined aquifer in the same areatypically flow at rates up to 2,000 gpm, with many wellsreportedly producing as much as 3,000 to 4,000 gpm. Elsewhere inthe valley, wells completed in the unconfined aquifer typicallyproduce an average of 500 gpm, and wells in the confined aquifertypically produce an average of 800 to 1,000 gpm. The volume ofeconomically recoverable ground water in storage in the two majoraquifers of the San Luis Valley is estimated to be on the orderof 100 million acre-feet, over 75 percent of it in the confinedaquifer. An estimated 1800 large-capacity wells in the valleyare in the unconfined aquifer, and are less than 300 feet indepth. By contrast, there are an estimated 800 large-capacityirrigation wells (and over 9000 small-capacity irrigation, stock,and domestic wells) which draw water from the confined aquifer.Wells which produce from the confined aquifer range in depth from300 feet to over 2000 feet.

3

p, Water Quality

In general, the water quality in the unconfined aquifer andthe upper portion of the confined aquifer is acceptable for mostagricultural, domestic, and municipal uses. In the unconfinedaquifer, ground water usually contains less than 500 milligramsper liter of total dissolved solids (mg/1 TDS), with a trendtoward better water quality (lower TDS) near the valley edges,and poorer water quality (higher TDS) near the center of thevalley. In clay-rich soils near the valley center, there is amoderate to high sodium-hazard potential for irrigation.

In the confined aquifer above a depth of about 2,000 to3,000 feet (shallower depths near the valley edges, and deepernear the center) the water quality follows the same margin-to-center pattern, with approximately the same TDS concentrationsand dominant ions as in the unconfined aquifer. Below 2,000 to3,000 ft, water quality degrades abruptly to a TDS concentrationaveraging 3,000 mg/1 or greater. Water from below those depthsis too salty for most uses without prior treatment.

L. Water Use

Extensive use of ground water in the San Luis Valley datesfrom the late 1800s, when a large number of low- to moderate-production flowing wells were completed in the upper few hundredfeet of the confined aquifer. These wells were used forirrigation and stock watering, as well as for municipal supply.By 1891, there were an estimated 2,000 flowing wells in thevalley.

There are presently about 12,000 permitted wells in the SanLuis Valley and the surrounding mountainous areas in the RioGrande drainage of Colorado. Although no exact figures areknown, an estimated 5,000 to 6,000 wells are for irrigation,4,000 to 5,000 are for individual domestic water supplies, about1,000 to 2,000 are stock wells, and several dozen are municipalwells.

Currently, irrigated agriculture demands about two millionacre-feet of water per year, of which an estimated 800,000 acre-feet is ground water. Municipal and individual domestic wells inthe San Luis Valley demand an estimated 11,000 acre-feet per

4

year. The Rio Grande Compact, an interstate agreement providingfor delivery of Rio Grande River water to New Mexico and Texas,causes an annual demand averaging about 305,000 acre-feet peryear. At present, industrial consumption of water in the valley

is virtually nil.

II. PHYSICAL BASIS OF AWDI'S NONTRIBUTARY CLAIM

In its amended application filed with the Division 3 WaterCourt, AWDI sought 117 wells on the Baca Grant and adjacentproperty in the east-central part of the San Luis Valley andanother 15 wells near Villa Grove in the north end of the valleyfrom which 200,000 af/y, in the aggregate, was to be pumped. Allwells were to be perforated between 200 and 2500 feet belowground surface, indicating that the water was to be drawn fromthe confined aquifer. The applicant stated that the source ofwater was the "San Luis Valley Aquifer", a nonstandarddesignation.

AWDI contended that the water proposed to be pumped wasnontributary, as determined by the effect of the pumping onnatural streams. The applicant argued that this impact was to bedetermined only upon surface flows, and not at all uponhydraulically connected alluvium; that very few streams in thevalley were in connection with the aquifer system and, further,that once the streams enter the valley from the surroundingmountains they lose the characteristics by which they areidentifiable as natural streams (i.e., that they do not havedefinite beds, banks, and channels).

AWDI maintained that much of the water to be gained by itspumping would be salvaged evapotranspiration losses by loweringthe near-surface water table in the sump area, in a directcomparison to the U.S. Bureau of Reclamation's Closed BasinProject centered a few miles southwest of AWDI's Baca Ranchproperty:

"The Closed Basin Project was designed to primarilyharvest water lost through evapotranspiration. TheBaca Project operates on the same principle." (BacaProject Fact Sheet, American Water Development, Inc.,August 20, 1990).

Since the proposed project's wells were to be completed in

5

the confined aquifer below 200 feet, there is an implication : ofnot only regionally-high.. water table (which is well documented)but strong' drawdown effects in the unconfined aquifer due topumping' the confined aquifer.

A third major point propounded by AWDI was that the impacton: existing' wells would be minimal':

"Of the 6114. total wells in the San Luis Valley, 5858(94%) will not be, impacted by the Baca. Project.Approximately 179 wells, will incur higher pumping: costsand another 77 wells may be affected, to such an extentthat they will have to be deepened or replaced with analternate: source of water." (Baca Project Fact Sheet,American. Water Development, Inc., August. 20', 1990).

These arguments, made by AWDI as the physical framework ofits nontributary claim, placed the applicant on a technicalrazor's edge. On the one hand, AWDI claimed that its pumpingwould be nontributary, that few streams. on the Valley floor werehydraulically connected to the underlying; aquifer system (thosefew' which remained., in its opinion, as "natural streams"): andthat well-interference effects would be. minimal. On the otherhand,: AWDI claimed that a, significant amount of its water wouldderive from salvaged, evapotranspiration due to lowering of theregional water table. Of necessity, an application amountultimately reaching 200,000 af/y would require rigorous attention.to. technical detail with regard to hydrologic issues. By makingits application on the basis of this. seemingly contradictoryphysical framework, however, AWDI made its burden. of proof onhydrologic and physical issues even more difficult.

III. PHYSICAL AND HYDROLOGIC ISSUES.

A. Hydrologic Role 2f Faulting

AWDI made the argument that faults„ which are prevalent inthe geologic materials comprising the San: Luis. Valley, largelyact to enhance vertical. connection between aquifer layers in thesubsurface. AWDI presented testimony that such faults areprevalent particularly in the Baca , Grant area of the valley, and.that they serve: to provide, an avenue of hydraulic connectionbetween the confined aquifer and the unconfined aquifer. Thesignificance of the argument lies in the effect of pumping; such a'

6

(Th large volume of ground water in a relatively concentrated area.Faults which act as water-movers, that is, enhance the verticalconnection, tend to distribute the pumping effect verticallythroughout the stack of materials, and to reduce the lateralspread of drawdown or piezometric head decline.

Objectors to the application contended that the action offaults was localized, material-specific and depth-specific. Inhard, crystalline or well-cemented rock materials, faulting caninduce enhancement of hydraulic conductivity (K), that is, theease with which water can move through the material. Inrelatively soft, unconsolidated materials, the objectors pointedout, faulting tends not to enhance K, and may serve to reduce it.Further, the objectors argued in trial that where enhancement ofK may exist, it was not as pervasive as the applicant claimed.

Es Depth of "Active/Passive" Interface

On the basis of seismic data, coupled with well-log data

(s\ from some of the few deep oil and gas test wells in the San LuisValley, AWDI interpreted that the hydraulic conductivity (K)remained relatively high (i.e. "active" in terms of ground water

• movement) to about 7000 feet below ground surface in the vicinityof the Baca Grant. The objectors, using many of the same datasources, presented an alternate interpretation in which thehydraulic conductivity beneath most of the valley, including theBaca Grant, decreases significantly below about 2500 feet depth.

As with the faulting issue, the significance of thesearguments is that a thicker "active " (high-K) zone would allowmore water to be drawn from beneath the Baca wellfield area, andthereby would reduce the lateral spread of drawdown andpiezometric head decline.

C. Streams and Hydraulic Connection

Much time and effort during the October-November, 1991,trial of AWDI's nontributary claim was spent by both theapplicant and the objectors in arguing the nature of the surfacestreams in the San Luis Valley. At issue was not only whetherthe streams were "natural streams" by law, but also whether thestreams were in hydraulic connection with the unconfined aquifer.

As discussed above, AWDI contended that most streams Werenot in hydraulic connection with the u•confimed aquifer. theobjectors, on the other hand, presented testimony that may Ofthe streams on the floor of the valley were indeed in connectichwith the unconfined aquifer. Each side presented evidencesupport their contentions. In addition, for several Mai&streams including certain reaches of the Rio Grande, the CenejOisRiver, and Saguache Creek, arguments were made concerning themagnitude of streambed conductance. This is a qUahtity Whithdescribes how readily Water can be transmitted thrtiligh astreambed in response to falling or rising water table.

If a stream is not in hydraulic connection With anunderlying aquifer, then drawdown due to pumping in that aquiferwill not induce greater downward leakage and consequent lossstreamf low. Likewise, a low streambed conductance redttiCtSdownward leakage of water, slowing the loss of streaMfloW.

D. Ouantification gf Inflow and Outflow

Several parameters related to the quantity of water whichflows into and out of the San Luis Valley on an annual basis wereat issue during the trial of the nontributary claim. theseincluded evapotranspiration (ET), irrigation consumptive use, andground-water inflow to the valley from the surrounding Mountainranges. These parameters, particularly the magnitude anddistribution of ET, were key to the applicant's argument thatapproximately 89 percent of its total withdrawal at the end of100 years of pumping would be due to ET salvage (Findings ofFact, Conclusions of Law, and Decree, Case No. 86CW46, WaterDivision 3, State of Colorado, February 10, 1992, p. 74).

In addition, each of the inflow and outflow parameters wereused by the applicant and the objectors in support of theirrespective views of the ground water system Of the San LuisValley. These parameters received particular scrutiny in thenumerical models entered as evidence in the trial of thenontributary claim.

8

IV. NUMERICAL MODEL: SCALPEL OR BLUDGEON?

Computerized numerical modeling, used by AWDI to support itsclaim and by objector State of Colorado in opposition to theclaim, makes use of inflow and outflow parameters, streams,aquifer layering, hydraulic conductivity (K) and storativity (S),piezometric head, and historical ground-water withdrawals as ameans of simulating an aquifer system by which predictions ofpumping effects can be made. A polygonal (often orthogonal)geometric framework of grid cells is constructed, and each cellor node is assigned representative physical parameters.

AWDI used a multi-layer numerical model of the San LuisValley as the technical centerpiece of its nontributary claim.Likewise, objector State of Colorado constructed its ownnumerical model of the valley. The applicant and the objectorspresented extensive evidence at trial in support of theirrespective models, and took pains to denigrate the opposingside's model.

Numerical ground water models used as predictive tools,particularly for projects as large as AWDI's, impartunprecedented demands for quality data and technical care toarrive at a valid result. Models are mathematically complex anddemand careful calibration, validation, and error-checking. Aspredictive tools, models are nonunique: more than one modelframework or set of values can arrive at a virtually identicaldistribution of piezometric head or ground-water flow. Models,especially complex ones, therefore demand significant investmentof funds and effort in data collection and interpretation to makesure that the modeler's concept of a ground water system is asfactually reflective of physical reality as possible. Sadly, thenature of predictive models is such that it is easier to usethem to support preconceived notions than it is to follow anobjective course of data collection, interpretation, modelconceptualization, verification, and prediction.

The power and flexibility of numerical models assures thatthey will continue to be used to assess impacts of waterdevelopment projects. If models are to be useful tools forprediction, then technical experts, attorneys, managers, and,most importantly, the courts, must begin to understand ground-water modeling in terms of capabilities as well as pitfalls.

V. SELECTED REFERENCES 2li ME ZUIS VALLEY HYDROGEOLOGY

Burroughs, R.L., 1981, A Summary of the Geology of the San LoisBasin, Colorado-New Mexico, With Emphasis on the GeothermalPotential for the Monte Vista Graben. Colorado Geological surveySpecial Publication No. 17, 30p.

Emery, P.A., R.J. Snipes, J.M. Dumyer, J.M. Klein, 1973, Water inthe San Luis Valley, South-central Colorado. Colorado WaterConservation Board Water-Resources Circular 18, 26p.

Hanna, T.M., and E.J. Harmon, 1989, An Overview of theHistorical, Stratigraphic, and Structural Setting of the AquiferSystem of the San Luis Valley. in Harmon, E.j., ed., Water inthe Valley: Colorado Ground Water Association 8th Annual FieldTrip Guidebook, pp.1-34.

HRS Water Consultants, Inc., 1987, San Luis Valley ConfinedAquifer Study (Phase I) Final Report. Prepared for the ColoradoWater Resources and Power Development Authority, 250 pp(approx.). (-\

Huntley, D., 1976, Ground-water Recharge to the Aquifers of theNorthern San Luis Valley, Colorado. Geological Society ofAmerica Bulletin Part II, v. 90, pp. 1196-1281.

Leonard, G.J., and K.R. Watts, 1989, Hydrogeology and SimulatedEffects of Ground-Water Development on an Unconfined Aquifer inthe Closed Basin Division, San Luis Valley, Colorado. U.S.Geological Survey Water-Resources Investigations Paper 87-4284,41p.

Powell, W.J., 1958, Ground-Water Resources of the San LuisValley, Colorado. U.S. Geological Survey Water Supply Paper1379. 284 p.

Siebenthal, C.E., 1910, Geology and Water Resources of the SanLuis Valley, Colorado. U.S. Geological Survey Water Supply Paper240, 124 p.

10