# XcelEnergy·M

August 20, 2015
Joe Kordzi EPA's South Central Region (Region 6) Air Planning Section (6PD-L) Environmental ProtectionAgency 1445 Ross Avenue Suite 1200 Dallas, Texas 75202-2733 DocketNo. EPA-R06-0AR-2014-0754
Re: Proposed Approval/Disapproval ofTexas and OklahomaRegional Haze State ImplementationPlans; Federal Implementation Plan for Regional Haze
Dear Mr. Kordzi:
Southwestern Public Service Company ("SPS") d/b/a Xcel Energy ("Xcel Energy") respectfully submits the following response to your request regarding water availability at Tolk Station, as discussed in Xcel Energy's comments dated April 20, 2015, submitted on the U.S. Environmental Protection Agency ("EPA") proposed rule partly approving and partly disapproving the Texas State Implementation Plan ("SIP") addressing regional haze and proposing a Federal Implementation Plan ("FIP"). 

### See 79 Fed. Reg. 74,818 (Dec. 16, 2014) (the "Proposal"). Additionally, Xcel Energy is providingthe informationyourequested regarding the mercury controls inplace at Tolle Station. Background. The well:field serving SPS' Tolle and Plant X generating stations includes approximately 46,668 acres of water rights 1

, 73 high-capacity production wells, and associated conveyance infrastructure. The plants have a combined annual demand ranging between 3.5 billion gallons (BG) (11,000 acre-feet) and 5.2 BG (15,900 acre-feet) ofwater. The average saturated thickness of the aquifer underlying the SPS well:field is approximately 60 feet2 from about 80 feet in 2010, depleting at an average rate ofapproximately 4 feet per year since 20103

. HighPlains Underground Water DistrictNo. 1 (HPWD) regulates groundwaterproduction in the region and, pursuant to rules adopted by HPWD on March 13, 2015, groundwater production is limited to 18 inches per acre, per year, unless a producer is eligible for certain agricultural alternative compliance mechanisms. This rule specifies a regulatory production limit as a ceiling on water production. However, the actual water availability is driven by the physical characteristics of the

1 SPS believes that this number is reflective oftitled water rights acreage andhas beenused inprevious aquifer studies, includingthe recent Rose acquisition of3,108 acres. 2 Average saturatedthickness based onJune 2015 calculation. 3 Based on observed average saturatedthickness decline in SPS' wellfield since 2010.Mr. Joe Kordzi 2 August 20,2015 underlying aquifer, and the aquifer cannot sustain the level of production authorized by the rule, as demonstrated below.
Water Availability Problems. In 2004, SPS' wellfield was capable ofproducing in excess of 15,000 gallons per minute (gpm) using 54 wells (average well productivity of275 gpm). Currently, the wellfield produces approximately 12,000 gpm using 73 wells (average well productivity of 165 gpm). The aquifer underlying the wellfield is increasingly unable to support these production rates, due to the reduction in both aquifer transmissivity4 and the active screened length5 at each well, both ofwhich are driven bythe overall decline inregional saturatedthickness6

. Well production is impacted by the reduction in transmissivity increasing the "cone of depression"7inthe groundwater table surroundingthe pumped well, withthe most significant depression effect immediately adjacentto the well. As the "cone ofdepression" draws the watertable down toward the aquifer floor, the pump eventually breaks suction and introduces air and sand into the well. This effect becomes especially pronounced when the aquifer saturated thickness reaches 40 feet8

. At this thickness, wells become unable to produce water at reasonable rates and are effectively "dry", though water remains in the aquifer. As more wells reach this threshold, the productivity ofthe entire wellfield becomes increasinglyrestricted.
Water Availability and its Impact on Plant Operations. Considering the physical limitations ofthe aquifer, described above, the estimated water available from the SPS wellfield can be computed as follows: wellfield acreage multiplied by the productive saturated thickness (60-foot average thickness minus 40-foot productivity limit) multiplied by the specific yield ofthe aquifer (0.15 9; the estimated fraction ofthe bulk aquifer volume that will yield water). The available water is further reduced because the western 1/3 ofthe aquifer has an estimated average saturated thickness ofless than 50 feet, has no existing production wells, and is thus currently uneconomical to develop due to the projected short lifespan of wells (less than 10 usable feet of saturation) which would be constructed in this area [(46,668*20*0.15)*2/3].
The calculation described estimates thatthe total recoverable water availability ofthe wellfield is approximately 30.5 BG or 94,000 acre-feet. The simplified calculationprovided above does not include the effects ofaquifer hydraulics, the significant water usage by agricultural water users neighboring the SPS wellfield, or the effect ofwater flowing into or out ofthe SPS wellfield, (which is estimated to be relatively small), which can onlybe predictedthroughthe use ofcomplex groundwater modeling tools.
The addition ofdry scrubbers to the units at Tolk Stationwouldbe expectedto increase the water demand by approximately 380 million gallons (MG)(l,l65 acre-feet) annually, or between 9% and 12% ofthe plants' water demand in recent years. A requirement to add dry scrubbers at Tolk Station would

4Transmissivity is defined as the hydraulic conductivity multipliedbythe saturatedthickness ofthe aquifer. 5 Active screened length is the length ofwell screen in contactwiththe saturated portion ofthe aquifer and able to produce groundwater. 6 Saturatedthicknessis the portion ofthe aquifer which contains waterthat can be producedby a groundwater well 7 A cone ofdepression is created bygroundwater pumping. The most significant effect is closestto the well, and the effect decreases with distance away from the well. Cone dimensions are determined based onphysical properties ofthe aquifer, pumping rate, etc. 8 40-footthresholdbased on informationprovidedby SPS' groundwater consultant in various studies andreports. 9 Specific yieldbased on informationprovided by SPS' groundwater consultant in various studies and reports.Mr. Joe Kordzi 3 August 20, 2015
contribute substantially to the cost of new watet: rights acquisition and the associated wellfield development that will be required to operate the plant in the future, assuming that the water can be acquired from cunent agricultural operations. Further depletion of this aquifer in order to add dry scrubbers would have a critical adverse non-air quality impact in an area already impacted by limited water resources and availability. 

### Mercury Control Technology at Tolk Station. In reference to the request for information regarding mercury controls, Tolk Station employs activated carbon injection on both units to comply with the mercury standards under the Mercury and Air Toxics Standards (MATS). This system is composed ofthe pneumatic transpmi ofbrominated active carbon to lances injected in the ductwork downstream ofthe preheater. The brominated activated carbon is stored in silos on site. Feed rates are adjusted based on compliance with the mercury limits under MATs.
Xcel Energy appreciates EPA's consideration ofthisresponse to EPA's informationrequest in its effmis to finalize the rule. Additionally, Xcel Energy requests thatthis letterbe added to DocketNo. EPA-R06-0AR-2014-0754. Ifyou shouldhave any questions, please contact me at 303-571-2762 or Ann Seha at 612-215-4619. Very truly yours, 

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JeffWest Director, Environmental Services Xcel Energy Inc.