POTABLE REUSE IN THE PERMIAN BASIN David W. Sloan, Freese and Nichols, Inc., Fort Worth, TX Chris Wingert, Colorado River MWD, Big Spring, TX Ignacio Cadena, Freese and Nichols, Inc., Fort Worth, TX

Abstract The Permian Basin of West Texas has always been challenged with water supply issues, but like much of the Southwestern U.S., the area has lately been subject to extended periods of low rainfall. Long term drought conditions have resulted in dangerously low reservoir levels, and prompted providers to consider new sources. Water reuse has been practiced there for decades, but new concepts are now being implemented to increase the use of this resource. The Colorado River Municipal Water District (CRMWD) supplies water to its member cities of Big Spring, Snyder and Odessa, as well as several customer cities including Midland. They have launched an ambitious water reclamation initiative with a goal to “reclaim 100 percent of the water, 100 percent of the time.” Key components of this concept include:  Facilities to capture effluent prior to discharge  Local and regional treatment facilities to re-purify the water captured  Blending facilities to combine the reclaimed water with other water supplies A feasibility study completed in 2005 included the following:  An inventory of effluent quantity and quality  Determination of quality requirements for various blending scenarios  Initial coordination with state regulators  Concept-level cost estimates  Development of a public information strategy Although treatment and transmission costs will be significant, the CRMWD anticipates significant potential savings over other raw water source development options and a reduction in long-distance pumping costs. Three separate projects are envisioned, with a potential net average yield of 13 million gallons per day. The District has proceeded with implementation of the first project, to be located near their headquarters in Big Spring, Texas. This project will intercept up to 2.5 million gallons per day of filtered secondary effluent from the City of Big Spring Wastewater Treatment Plant and transfer it to an adjacent treatment site. At the District’s facility the water will be treated with membrane filtration, reverse osmosis and advanced oxidation prior to blending with raw surface water in the District’s raw water transmission pipeline. Pilot testing was completed in October 2009. Final design is now complete, subject to regulatory review, and construction is to begin in the spring of 2011. Facility startup is anticipated in 2012. Public education has been ongoing since the feasibility study along with recurring consultations with state drinking water regulators at the Texas Commission for Environmental Quality.

Big Spring

Figure 1 – CRMWD Service Area

Background The Permian Basin, like much of the Western United States, has been subjected to an unprecedented period of drought during the past twelve years. Reservoir levels have been very low for several years, and it appears that West Texas runoff response and reservoir yields are fundamentally different than records indicated when the principal reservoirs were originally planned on the Upper Colorado River. The Colorado River Municipal Water District (CRMWD) is therefore pursuing new supplies and alternatives to continue providing a reliable and sustainable water supply to its member and customer cities. The treated wastewater currently discharged by cities in the District’s service area has been identified as a feasible source and the first of three potential projects is now being developed to augment existing CRMWD supplies.

Feasibility Study A feasibility study was completed in 2005, which examined the capture and purification of effluent currently discharged by the member cities of Odessa, Big Spring and Snyder and the major customer city of Midland. Odessa and Midland were considered as a potential combined project, while Snyder and Big Spring were considered as independent projects. All were considered technically and economically viable, but the Big Spring project was considered to be the easiest to implement and to

have the quickest payback. The factors favoring the Big Spring project included a ready destination for the reverse osmosis concentrate, relatively short transmission distances and an available location within minutes of the District’s headquarters. Approximately 2.5 million gallons per day of effluent are available for reclamation, using a proven treatment sequence of membrane filtration, reverse osmosis and ultraviolet disinfection/oxidation. An illustration of the project concept is provided in Figure 2.

J.B. Thomas Reservoir Big Spring Water Treatment Plant

Big Spring Big Spring Wastewater Treatment Plant

CRMWD Raw Water Production Facility

E.V. Spence Reservoir

RO Concentrate

Beals Creek Red Draw Reservoir

Figure 2 – Big Spring Project Concept

Drivers for Direct Blending Blending reclaimed water into public water supplies has been a source of numerous controversies within the water industry and among the general public. Many agencies and utilities have avoided these controversies by implementing non-potable reuse, supplying reclaimed water for landscape and turf irrigation, cooling towers and industrial processes. Issues that persuaded the District to pursue potable reuse include:  Non-potable reuse is usually heavily seasonal, limiting the overall volume saved from reuse facilities.  Few large-potential customers are available to the District for non-potable reuse.  Low-density development makes transmission distances greater and distribution systems more expensive.  Arid conditions have restricted landscape irrigation, reducing potential demand.  High dissolved solids, especially chloride concentrations, limit reclamation without desalination.

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Blending offers the opportunity for year-round use, reduced transmission distance and improvement in raw water salinity. Conventional raw water sources available in the region are generally distant and lower in elevation than customers, resulting in high delivery costs.

A reality that must be recognized is the prevalence of unplanned potable reuse. This occurs whenever municipal wastewater effluent is discharged to a water body that serves as a public water source. This is a common occurrence; in fact many reservoirs in Texas and elsewhere consider return flows as a significant component of their available yield. While this type of reuse may go unnoticed by the general public, the potential for recirculating human disease agents is the primary basis for modern water disinfection practice. Blending represents an acceleration of this scenario, substituting additional treatment for time and travel within the receiving stream and other water bodies. Several locations in Texas have developed and in some cases implemented plans for indirect potable reuse. In the North Central part of the state, near the Dallas-Fort Worth Metroplex, large projects will take effluent-dominated flows and pass the water through constructed wetlands for polishing, providing multiple benefits along with the water supply augmentation. This approach has been viewed favorably in North Central Texas, but was not as well suited to the Permian Basin area, due to high evaporative losses and the high dissolved solids present both in current surface water and in the available effluent sources. Desalination was deemed a necessary step for large-scale water reclamation, and with the use of fullstream reverse osmosis came the opportunity to shorten the reuse circle. The District’s network of longdistance, large diameter pipelines presented a convenient means of blending high quality reclaimed water with other sources and conveying the blended product to the member and customer cities. Pilot testing of the membrane filtration and reverse osmosis processes confirmed that the product water will be superior to the current raw water in most respects, and will make up only about 15 percent of the blended water in the pipeline during low demand periods, and as low as five percent during summertime high demand periods.

Concentrate Disposal The reverse osmosis process selected for desalination will produce two liquid streams: the desalinated product water (permeate), and a second stream containing the salts and other contaminants separated from the product water. This stream, referred to as reject, brine or concentrate, is usually difficult to dispose and represents a significant obstacle to most desalination operations. It is still mostly water (9899.5 percent by weight) but is unfit for most uses and potential discharge locations. It represents a significant fraction of the original water source (10-35 percent), so its disposition is far from trivial, especially for large projects. Typical disposal alternatives include the following: 

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Evaporation -- In a dry area such as the Permian Basin, it is natural to consider evaporation for disposal of unwanted water, and it is a viable alternative for small quantities. However, for large quantities of concentrate such as those contemplated in this project, evaporation would require a very large area. Discharge -- Historically, most desalination concentrate has been discharged to the ocean, a sanitary sewer system or to a stream. This is the simplest form of disposal and is preferable when a suitable discharge location is available.

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Dedicated Disposal Well -- Deep saline aquifers have been used in many locations for disposal of various waste streams, including oil field brines, cooling water blowdown, and desalination concentrate. Where favorable conditions exist, this method is attractive due to its minimal impact on the environment and potentially large capacity for receiving liquid wastes. Unfortunately, the regulatory framework makes permitting and constructing injection wells a lengthy and expensive process. Conjunctive Use With Oil Field Operations -- A promising variant of disposal wells is the joint use and disposal of concentrate in oil extraction operations. Zero Liquid Discharge -- Technology also is available for recovering additional water from desalination concentrate, increasing the yield from the original source and greatly reducing the volume of waste for disposal.

The Big Spring Wastewater Treatment Plant (WWTP) currently discharges treated effluent to Beals Creek, a naturally brackish stream in the Colorado basin. Due to its high salinity, the District constructed a channel dam and off-channel reservoir to divert and store the flow from Beals Creek for improvement of the water quality in the District’s reservoirs on the Colorado River. The stored water is either sold to oil interests for secondary recovery of oil from mature fields, or is allowed to evaporate. Since the stream is already subject to high salinity, the District was able to obtain a discharge permit for the concentrate, at a location near the project site.

Regulatory Consultations Regulatory agencies are faced with the challenge of developing criteria for the safe use of reclaimed water to augment potable water supplies. The regulatory challenge is to ensure that high quality water supplies are maintained regardless of their source. The Texas Commission on Environmental Quality’s (TCEQ) rules for use of reclaimed water do not provide specific requirements for supplementing public water supplies. However, in an initial meeting with TCEQ, the agency’s overriding guidance was that the finished water provided to consumers must meet TCEQ’s Rules and Regulations for Public Water Systems, also known as the Primary Drinking Water Standards. Texas regulators have been generally supportive of the project, including assembling representatives from multiple departments and working groups for meetings to facilitate free-ranging discussions without passing the buck down the hall when a line of responsibility was crossed. In exchange, the District has been open with its plans and questions, allowing potentially contentious issues to surface earlier rather than later. Several specific regulatory actions were required in the development of the project, including:    

Reclaimed Water Use Authorization. This authorization from the TCEQ reuse group governs the transfer of water from the City of Big Spring to CRMWD. The City was required to obtain this authorization from TCEQ. Concentrate Discharge Permit. An industrial discharge permit (TPDES) was required for the District to discharge the reject from the RO process into Beals Creek. Industrial Pretreatment Permit. The membrane filtration backwash waste will be returned to the head of the City’s wastewater treatment plant, requiring the District to obtain a pretreatment permit from the City of Big Spring. Membrane Pilot Study. Although not stipulated by published rules since the product water is not represented as potable water, the District submitted to the TCEQ’s membrane treatment

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guidelines, providing a pre-pilot protocol for review prior to beginning the pilot testing, and submitting the pilot study report for review upon completion. Plans and Specification Review. Similarly, published rules do not specifically speak to review of facilities producing water for blending. However, TCEQ will use its prerogative to review the plans and specs prior construction.

The reclaimed water use authorization and concentrate discharge permit have been in hand for over a year. The City pretreatment permit is anticipated within the next few weeks, and final plans and specifications have been submitted for TCEQ review. In May 2010, the TCEQ approved the pilot study report, paving the way for the District to award a contract for supply of the MF and RO membrane systems. The TCEQ used the pilot study approval as an opportunity to approve the purified water as a municipal drinking water source and set out ground rules on several design and operating parameters for the project. Some key requirements stipulated with the source approval:        

Influent quality shall be consistent with the piloted influent water quality, including o turbidity shall be less than 10 NTU; o chlorine residual shall be greater than 1 mg/l. Membrane filtration and reverse osmosis processes shall be operated consistent with the piloted operation, including flux limitations, chemical preparation, cleaning intervals and integrity testing. Continuous monitoring of membrane filtrate turbidity and reverse osmosis permeate conductivity to provide indirect indication of process integrity The facility must be under the supervision of a Class B licensed operator. The facility is designed to contribute 10-15 percent of the total water in the raw water pipeline. Public water systems receiving water from the facility shall be notified. Applicable portions of surface water treatment requirements are stipulated. Required monitoring and record keeping are stipulated.

Energy Use and Savings The Raw Water Production Facility will require a significant energy input to produce a high quality product suitable for blending. All three of the treatment processes are energy-intensive, especially the critical reverse osmosis step. However, this must be placed in context with the high energy cost of existing supplies and other potential supplies. Based on guaranteed performance of the membrane supplier, the microfiltration and reverse osmosis treatment will use about 3.55 kilowatt-hours/1000 gallons of product water produced. Estimated UV oxidation operation adds about 0.39 kWh/1000 gallons and pumping to and from the reclamation facility will increase the total to about 5.34 kWh/1000 gallons reclaimed. By comparison, lifting water from Lake Spence to Big Spring requires about 4.2 kWh/1000 gallons under normal conditions. Currently the water level in Lake Spence is so low that a barge mounted pump station is required to lift water into the permanent intake structure. The power consumption for the barge operation is not readily available, but it is apparent that lifting water to Big Spring requires almost as much energy as processing effluent from the wastewater treatment plant.

On the discharge side, the District currently uses about 0.84 kWh/1000 gallons to divert water from Beals Creek to keep it out of the Colorado River. Each gallon reclaimed represents a gallon of water removed from Beals Creek, thereby avoiding the need to divert it downstream. Adding this to the normal pumping requirement from Lake Spence yields a total of 5.04 kWh of avoided energy per 1000 gallons of reclaimed product water, comparable to the energy requirement for the total reclamation process.

Public Acceptance Some of the biggest challenges to the successful implementation of potable reuse have been related to public acceptance. Major projects with extensive planning and research have been pursued only to stumble in the political arena for lack of public acceptance. These high-profile public rejections have certainly been on the minds of the project planners and designers throughout the development of the project, but the District has been successful thus far with a very simple and direct approach to public education. CRMWD officials have been forthcoming with information about the project, using radio interviews, newspaper articles, internet sites and public meetings to simultaneously convey the severity of water supply limitations and to describe the proposed reclamation concept in a straightforward way. Water scarcity is apparent in the landscape throughout the area, and many area residents are established in the region and understand the difficulty of obtaining adequate supplies. High chloride levels are a fact of life and serve to highlight the compromises inherent in water cost and quality. Public reaction has been muted and generally positive or at least neutral.

Conclusions The technology to provide high quality water suitable for drinking water supplies is reliable and relatively mature. The obstacles to pursuing direct blending with municipal source water should not be taken lightly, but the payoff can be a near-total use of a precious resource. CRMWD’s proposed Raw Water Production Facility in Big Spring, Texas has several advantages which are allowing it to proceed, but it is expected that this project will serve as a demonstration project for similar projects in the future as water demand continues to rise and supply choices continue to dwindle.