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LC Action Plan Discussion Draft January 18,2019 Proposed Las Cruces Water-Supply Action Plan based on Las Cruces Utilities 40-Year Water Development Plan, 2017 Annie McCoy and John Shomaker John Shomaker&Associates,Inc. Las Cruces Utilities (LCU) contracted with John Shomaker & Associates, Inc. (JSAI) to prepare an action plan for water-supply development based on projected water demand and potential sources for alternate supply identified in the City of Las Cruces 40-Year Water Development Plan (JSAI, 2017). This action plan contemplates a 10-year timeframe for further water supply development,with broader consideration of the 20-year timeframe. Limitations of Existing Supply and Need to Develop Alternate Supply Development of an alternate supply may eventually become necessary due to water-level declines and the transition from a system that has been closer to equilibrium with recharge, to one in which groundwater pumping is primarily from storage (discussed in the 40-Year Plan among the physical limitations), but may also be triggered much sooner by legal constraints arising from Texas v. New Mexico & Colorado, Original No. 141 (discussed among the legal and administrative constraints). Water-level declines must be managed in order to avoid eventual irreversible subsidence and compaction of the aquifers,which would result in diminished capacity for aquifer recharge. Water- level declines may also be accompanied by a decrease in groundwater quality. In terms of physical limitations, the threshold of irreversible subsidence and water quality thresholds would likely not be reached within the 10-year timeframe; however, as recommended in the 40-Year Plan (JSAI, 2017), a drawdown warning indicator should be developed within the 10-year timeframe in order to ensure protection of the aquifers in the case that the drawdown threshold is approached, and to trigger actions toward an alternate supply. The 40-Year Plan outlines some possible approaches to development of a drawdown warning indicator. It is possible that an excessive-drawdown warning might be approached within the 20-year timeframe,particularly in Jornada sub-basin aquifer of the East Mesa. Legal and administrative constraints associated with Texas v. New Mexico & Colorado, Original No. 141, could arise within the 10-year timeframe. One potential outcome of the litigation may be that New Mexico loses state jurisdiction over all surface water and groundwater in the Lower Rio Grande, under the assumption that all groundwater is hydrologically connected with, and considered to be part of, Rio Grande Project water, which might threaten the viability of Las Cruces' water supply by requiring that the City enter into a water-supply contract with the United States to divert groundwater in the Lower Rio Grande for municipal use. Las Cruces may lose the early, pre-EBID, priority that has been recognized by the State Engineer. 2 Water Demand Table 1 presents a summary of City of Las Cruces water demand projections in terms of total diversions under low-,medium-, and high-growth scenarios, as presented in the 40-Year Plan(JSAI, 2017). The water demand projections are based on projected population growth and projected total gallons per capita day (GPCD) use, and should be updated from time to time based on changing circumstances. A summary of Las Cruces water rights and permits is also presented in Table 1 for comparison with demand. Although projected water demand exceeds the amount of the LRG-430 et al. base water right, it is clear that development of an alternate supply is generally based on physical limitations and potential legal and administrative limitations, as opposed to deficiency in the amount of existing water rights and permits. Water Rights Acquisition to Develop Alternate Supply As discussed above, legal and administrative constraints could potentially require that the City enter into a water-supply contract with the United States to divert groundwater in the Lower Rio Grande for municipal use, despite the fact that the City's groundwater use under LRG-430 et al. was initiated more than 100 years ago, prior to the Rio Grande Project. Although a contract with the U.S. may prove to be entirely feasible, the complexity and timing of the process, and the possible roadblocks involved, are not predictable. It is therefore reasonable that Las Cruces develop a plan of action that includes acquisition of groundwater rights to develop alternate supply up to the amount of the LRG-430 et al. base water right, 21,869 acre-feet per year, within the 10- to 20-year timeframe. This would require engagement with existing water-rights holders in a basin in which the groundwater is not potentially subject to designation as Rio Grande Project water. The 40-Year Plan contemplates lease or purchase,primarily of agricultural water rights, in the Corralitos Basin, the Nutt-Hockett Basin, and the Mimbres Basins. It is difficult to know how the designation as Rio Grande Project water might be applied with respect to each of these. All three are within the boundary of the Rio Grande Project as shown on a Bureau of Reclamation Albuquerque Area Office map dated 2002. On the other hand, the Corralitos Basin is only partly within the surface drainage of the Rio Grande and some surface water discharges to surface evaporation within the basin itself and to the closed Mimbres Basin. Surface water in the Nutt- Hockett Basin discharges to the closed Uvas Valley basin. In the Mimbres closed basin,the surface flows in pre-development conditions reached Laguna Guzman in Mexico, but there is no surface water discharge from the basin under present conditions. None of the three basins is represented in the newly released U.S. Geological Survey groundwater flow model of Rio Grande transboundary region (Hanson et al., 2018). Even so, although the Corralitos and Nutt-Hockett Basins are separated by low-permeability geologic materials from the Palomas and Mesilla groundwater basins in the inner valley of the Rio Grande, which are closely connected with Rio Grande flows, natural groundwater discharge from the 3 Corralitos Basin is tributary to the Mesilla Basin, and that from the Nutt-Hockett Basin is tributary to the groundwater in the Palomas Basin. Table 1. City of Las Cruces water demand projections [projected population * projected total GPCD water use], and summary of existing water rights City of Las Cruces water demand projections high growth, medium growth, low growth, year ac-ft/yr ac-ft/yr ac-ft/yr 2020 24,186 23,601 23,145 2030 28,797 26,759 25,057 2040 34,293 30,343 26,672 City of Las Cruces summary of existing water rights NMOSE File No. water-right diversion amount, status ac-ft/yr pre-basin, LRG-430 et al. conditional use of 21,869 return flow a LRG-3283 through LRG-3285,LRG- permitted, 3288 through LRG-3296 new appropriations, 10,200 East Mesa permit minimal offsets required permitted, LRG-3275 et al. new appropriations, 8,000 West Mesa permit offsets required LRG-389,LRG-399,LRG-5818 et al., permitted, LRG-5039 et al.,LRG-47 et al., new appropriations, 11,110 LRG-48 et al.,LRG-50 et al., LRG-1882 et al., LRG-4278 offsets required ac-ft/yr-acre-feet per year NMOSE—New Mexico Office of the State Engineer a In periods of drought in which EBID allotment to irrigators is less than 2 ac-ft/ac,Las Cruces is not to consumptively use treated effluent derived from LRG-430 wells,but instead must return effluent to stream system. b Total of 100 ac-ft/yr in offsets required after 40 years,total of 644 ac-ft/yr in offsets required after 100 years. ° Amount of water that may be diverted re-evaluated and determined by NMOSE annually subject to any offset debt from previous calendar year(s)and anticipated availability of offsets in the current calendar year,pursuant to Return Flow Plan(JSAI,2009). 4 Several alternative ways of securing an imported supply present themselves, including purchase and holding in reserve,purchase and lease-back, and"dry-year option" agreements. The choice would rest on several factors,probably the most important being whether the supply would be needed every year, or only during times of low supply within the existing Las Cruces system. The first reaction to most efforts to acquire water for export to another basin is generally strongly negative, and a plan that would keep the local economy whole would be much easier to carry out than one that would erode economic activity. Establishment of an option agreement program would be an approach in which Las Cruces enters into contracts with one or more irrigators and pays an annual fee for the option of taking the water in a given year, and paying the irrigator some previously agreed-upon compensation for that year's crop. Engagement with water rights holders in nearby basins and establishment of an option agreement program would be preceded by a ranking study of alternatives for groundwater importation. Potential factors for the ranking study would include: • Amount of water potentially available. • General feasibility. o Distance to existing Las Cruces Utilities water-supply infrastructure. o Potential capital and OM&R costs. o Land ownership and right-of-way. o Potential legal and administrative impediments. The amount of water potentially available would be of first importance in a ranking study. The 40-Year Plan has outlined the amounts of water potentially available based on existing water rights, as follows. • Corralitos Basin: The maximum transfer associated with the LRG-468 et al. water right would likely be 1,651 ac-ft/yr, but the State Engineer may not accept that full amount. The longevity of the supply has not been estimated, and some further groundwater study would be needed. • Nutt-Hockett Basin: Pumping for irrigated agriculture was estimated by the NMOSE to be 17,185 ac-ft/yr in 2010 (NMOSE, 2013), of which 13,493 ac-ft/yr was consumptively used (net pumping) and would presumably represent the maximum that could be exported from the basin. • Mimbres Basin: JSAI has estimated net pumping, that is, the consumptive-use amount that might be physically transferrable, for irrigated agriculture in the Deming area of the Mimbres Basin, to range from 12,000 to 18,000 ac-ft/yr. A previous study by JSAI (2004) evaluated the physical availability of water supply in the Corralitos and Nutt-Hockett Basins. This study could be updated based on more-recently available data from New Mexico Office of the State Engineer, and other sources. A similar study could be performed for specific area(s) in the Mimbres Basin. 5 It is important to remember that these three groundwater sources receive very little recharge, as compared with the basin-fill aquifer system of the Mesilla groundwater basin with its direct connection to the flows of the Rio Grande, and for that reason the physical supply is renewable to a much smaller degree. For a ranking study to be particularly useful, the amount of water potentially available would be based on the existence of specific water right holders interested in lease or purchase of rights, or participating in an option agreement program, and the amounts of the specific rights. The amounts of the specific rights that could be successfully transferred to municipal use may require further study on a case-by-case basis to consider factors such as whether the rights have been licensed, and if not, how much appears to have been beneficially used in recent years, and the like. Thus, a ranking study should be followed by the process of engagement with water rights holders and development of an option agreement program. More detailed feasibility study may then be performed for the highest-ranking alternative(s). Utilize Reclaimed Wastewater for Alternate Supply Las Cruces would like to make use of reclaimed wastewater for alternate supply, and one potential way would be through an aquifer storage and recovery(ASR)project with well injection, as identified in the 40-Year Plan. However, the current regulatory environment poses major challenges that may discourage ASR as an approach. Treating the water to be injected to drinking- water quality, as would probably be required, can be cost-prohibitive. Extremely comprehensive demonstrations and pilot testing, as required by State Engineer ASR regulations (at Sec. 19.25.8 NMAC), may also be cost-prohibitive. LCU should therefore engage with regulatory agencies to explore other approaches,possibly with other levels of water treatment. For example, if it can be determined through groundwater-flow calculations or modeling that wastewater applied in spreading basins,rather than through injection well(s),would reach the water table soon enough to provide a meaningful offset to drawdown due to pumping from supply wells, then a conventional return-flow plan associated with the existing permits might be acceptable to the State Engineer, and a discharge plan based on New Mexico Environment Department (NMED) groundwater discharge standards under Sec. 20.6.2 NMAC would presumably be acceptable to NMED. The 40-Year Plan provided an estimate of the amount of water potentially available based on under-utilization of the East Mesa water reclamation facility in winter months,equating to about 340 ac-ft/yr based on data from 2011 to 2015. The fact that this amount is relatively small compared with potential amounts of water available from groundwater importation projects may make reclaimed wastewater a secondary priority as compared with water rights acquisition as discussed above, except that with some change in the regulatory situation, the use of reclaimed wastewater might be established at relatively small cost. 6 Pilot Projects It is likely that any of the approaches to alternate supply discussed in the sections above (potential groundwater importation projects or utilization of reclaimed wastewater)would require a pilot project to verify the amount of water potentially available, and general feasibility. Groundwater Importation: For the discussion below, it is assumed that groundwater from the Corralitos, Nutt-Hockett, and Mimbres Basins would not be considered Rio Grande Project water, and would be transferrable under State Engineer jurisdiction. The effect on Rio Grande flows attributable to pumping from these basins to Las Cruces is assumed to be fully accounted for if no more than the consumptive-use portion of any existing right would be conveyed to Las Cruces. For a potential groundwater importation project, the objectives of a pilot project would include: • Determine whether existing wells have capacity to produce the amount of water potentially available based on water rights, with water quality that conforms to municipal drinking water standards. All of the rights are irrigation rights, and the wells were constructed as irrigation wells which, at a minimum, would require some rehabilitation and construction of surface seals to conform with NMED regulations. As a practical matter, most of the wells are relatively old now, and probably would be replaced if the rights were acquired by Las Cruces for public supply. • If existing wells are not adequate in terms of water quantity and quality,determine whether new wells completed at the site could produce water of adequate quantity and quality. Reclaimed Wastewater: For a potential reclaimed wastewater project, the objectives of a pilot project would include: • Determine whether the water can be successfully returned to the water table and recovered for later use, considering both physical return of the water and State Engineer accounting. • Determine whether the proposed water treatment and aquifer-return approach is protective of environmental and human health standards. Summary of Suggested Action Items Below is a sequence of potential water-supply development action items based on discussions in the sections above. 7 Ten-Year Timeframe • Develop the drawdown warning indicator,based on the water-level monitoring program as described in the 40-Year Plan. It could be defined as a 5- or 10-year running average water-level decline rate in a well or a group of wells that would lead to water-level declines approaching the drawdown threshold near the end of the 40-year planning period, or an acceleration of the rate of water-level decline. • Update to the next level the study of availability of water supply in the Corralitos and Nutt- Hockett Basins. Prepare a similar study for specific area(s) in the Mimbres Basin. o Develop a database from State Engineer records of water rights in the three basins, including owners,locations of wells,consumptive-use amounts,priority dates,well capacities, ages of wells,whether wells are in a Critical Management Area(for the Mimbres Basin), water-use history (from records and aerial photography), water quality, and related information. o Refine the estimate of water available from the Corralitos Basin. Although small, this is the closest to the existing infrastructure and presumably would provide water at the least cost. Much of the information necessary would come from recent work by John Hawley and his colleagues (Hawley et al., 2018) and the USGS (Sweetkind, 2017), but it may also be necessary to conduct pumping tests, which would require permission of the well-owner. o Identify potential pipeline routes, generally following public rights of way. o Prepare a"strawman" development plan with a preliminary list of rights prioritized according to their suitability for acquisition by Las Cruces, considering size of the right, well capacity, need for new wells, water quality, distance from LCU infrastructure, and other such factors. o Prepare planning-level cost estimates for water-right acquisition, rights of way, capital costs of infrastructure, and annual OM&R costs. • Explore the potential for a reclaimed wastewater project. o Engage with regulatory agencies, primarily the NMED and the State Engineer, to explore approaches to utilization of reclaimed wastewater. o Carry out groundwater calculations to determine what approach would be necessary to return reclaimed water to the aquifer(whether an infiltration basin would suffice, or injection well(s)would be required). o Meet with NMED to discuss water-quality standards. Ten-to Twenty-Year Timeframe • Update water demand projections as needed based on changing circumstances • Complete a ranking study of alternatives for groundwater importation. 8 • More detailed case-by-case feasibility study for the highest-ranking alternative(s) for groundwater importation. • Engage with water-rights holders in the Corralitos Basin,Nutt-Hockett Basin,and Mimbres Basin. • Establish an option agreement program or acquire water rights to develop an alternate supply up to the amount of the LRG-430 et al. base water right, 21,869 ac-ft/yr. • Pilot project selection and design. References Cited Hanson, R.T., Ritchie, A.B., Boyce, S.E., Galenter, A.E., Ferguson, IA., Flint, L.E., and Henson, W.R.,2018,Rio Grande transboundary integrated hydrologic model and water-availability analysis, New Mexico and Texas, United States, and northern Chihuahua, Mexico: U.S. Geological Survey Open-File Report 2018-1091. Hawley, J.W., Swanson, B.H., Walker, J.S., and Glaze, S.H., 2018, Hydrogeologic framework of the Mesilla Basin region of New Mexico, Texas and Chihuahua (Mexico)—advances in conceptual and digital model development: New Mexico Water Resources Research Institute, Technical Completion Report No. 363. [JSAI] John Shomaker & Associates, Inc., 2004, Aquifer storage and recovery assessment,Nutt- Hockett Basin, Dona Ana, Luna, and Sierra Counties, and Corralitos Basin, Dona Ana County, New Mexico: consultant's report prepared for City of Las Cruces, New Mexico, and Lower Rio Grande Water Users Organization, 29 p. plus figures and appendices. [JSAI] John Shomaker & Associates, Inc., 2017, City of Las Cruces 40-Year Water Development Plan: consultant's report prepared by JSAI for Las Cruces Utilities, April 2017, 68 p. plus appendices. [NMOSE] Longworth, J.W., Valdez, J.M., Magnuson, M.L., and Richard, K., 2013, New Mexico Water Use by Categories 2010:New Mexico State Engineer Office,Technical Report 54. Sweetkind, D.S., 2017, Three-dimensional hydrogeologic framework model of the Rio Grande transboundary region of New Mexico and Texas,USA,and northern Chihuahua,Mexico: U.S. Geological Survey Scientific Investigations Report 2017-5060.