Xcel Energy·M 

August 20, 2015 

Joe Kordzi 

EPA's South Central Region (Region 6) 

Air Planning Section (6PD-L) 

Environmental Protection Agency 

1445 Ross A venue 

Suite 1200 

Dallas, Texas 75202-2733 

Docket No. EPA-R06-0AR-2014-0754 

Re: Proposed Approval/Disapproval of Texas and Oklahoma Regional Haze State 

Implementation Plans; 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 

providing the information you requested regarding the mercury controls in place 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) of water. 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 of approximately 4 feet per year since 20103

. 

High Plains Underground Water District No. 1 (HPWD) regulates groundwater production 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 of titled water rights acreage and has been used in previous aquifer studies, 

including the recent Rose acquisition of 3,108 acres. 2 Average saturated thickness based on June 2015 calculation. 3 Based on observed average saturated thickness 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 of producing 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 of which are 

driven by the overall decline in regional saturated thickness6

. 

Well production is impacted by the reduction in transmissivity increasing the "cone of 

depression" 7 in the groundwater table surrounding the pumped well, with the most significant depression 

effect immediately adjacent to the well. As the "cone of depression" draws the water table 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 of the entire wellfield 

becomes increasingly restricted. 

Water Availability and its Impact on Plant Operations. Considering the physical limitations 

of the 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 of the aquifer (0.159

; the estimated 

fraction of the bulk aquifer volume that will yield water). The available water is further reduced because 

the western 1/3 of the aquifer has an estimated average saturated thickness of less 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 that the total recoverable water availability of the wellfield is 

approximately 30.5 BG or 94,000 acre-feet. The simplified calculation provided above does not include 

the effects of aquifer hydraulics, the significant water usage by agricultural water users neighboring the 

SPS wellfield, or the effect of water flowing into or out of the SPS wellfield, (which is estimated to be 

relatively small), which can only be predicted through the use of complex groundwater modeling tools. 

The addition of dry scrubbers to the units at Tolk Station would be expected to increase the water 

demand by approximately 380 million gallons (MG)(l,l65 acre-feet) annually, or between 9% and 12% 

of the plants' water demand in recent years. A requirement to add dry scrubbers at Tolk Station would 

4 Transmissivity is defined as the hydraulic conductivity multiplied by the saturated thickness of the aquifer. 

5 Active screened length is the length of well screen in contact with the saturated portion of the aquifer and able to produce 

groundwater. 

6 Saturated thickness is the portion of the aquifer which contains water that can be produced by a groundwater well 7 A cone of depression is created by groundwater pumping. The most significant effect is closest to the well, and the effect 

decreases with distance away from the well. Cone dimensions are determined based on physical properties of the aquifer, 

pumping rate, etc. 8 40-foot threshold based on information provided by SPS' groundwater consultant in various studies and reports. 9 Specific yield based on information provided 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 of the pneumatic transpmi of brominated active carbon to lances injected in the ductwork 

downstream of the 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 ofthis response to EPA's information request in 

its effmis to finalize the rule. Additionally, Xcel Energy requests that this letter be added to Docket No. 

EPA-R06-0AR-2014-0754. If you should have any questions, please contact me at 303-571-2762 or 

Ann Seha at 612-215-4619. 

Very truly yours, 

rv& 

Jeff West 

Director, Environmental Services 

Xcel Energy Inc.