Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

HAZARDOUS RANKING SYSTEM (HRS) DOCUMENTATION RECORD

REVIEW COVER SHEET

SITE NAME: WEST COUNTY ROAD 112 GROUND WATER

CONTACT PERSON:

Documentation: Brenda Cook, USEPA 214/665-7436

 Region 6 NPL Coordinator 

Pathway, Components, or Threats Not Evaluated

Surface Water Pathway

The Surface Water Pathway was not scored because the inclusion of this pathway would not 

significantly affect the Site score.

Soil Exposure Pathway

The Soil Exposure Pathway was not scored because the inclusion of this pathway would not 

significantly affect the Site score.

Air Migration Pathway

The Air Migration Pathway was not scored because the inclusion of this pathway would not 

significantly affect the Site score.
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

1 

HRS DOCUMENTATION RECORD

Name of Site: West County Road 112 Ground Water 

Date Prepared: October 2010 

CERCLIS Site ID Number: TXN 000 606 992 

Site Specific Identifier: Unidentified Ground Water Plume 

Street Address of Site*: Intersection between County Road 112 and County Road 1205. 

City, County, State: Midland, Midland County, Texas 79706 

General Location in the State: 

The West County Road 112 Ground Water Site is located two blocks south of Interstate 20 

(I-20) in the southwest quadrant of the I-20 and Cotton Flat Road intersection, outside and 

immediately to the southwest of the city limits of Midland (see Figure 1a for Regional 

Location Map, Figure 1b for Site Topographic Map, Figure 1c for Site Location and 

Surrounding Land Use Map, and Figure 1d for Ground Water Sample Location Map). 

Topographic M ap: U.S. Geological Survey 7.5 Minute Topographic Map, Southeast 

Midland Quadrangle. Photo revised 1995. 

Latitude: 31.964129O Longitude: -102.094921O

EPA Region: 6 

*The street address coordinates, and contaminant locations presented in this Hazard Ranking 

System (HRS) documentation record identify the general area in which the site is located. 

They represent one or more locations that the U.S. Environmental Protection Agency (EPA) 

considers to be part of the site based on the screening information EPA used to evaluate the 

site for National Priority List (NPL) listing. EPA lists national priorities among the known 

"releases or threatened releases" of hazardous substances; thus, the focus is on the release, 

not precisely delineated boundaries. A site is defined as where a hazardous substance has 

been "deposited, stored, placed, or otherwise come to be located." Generally, HRS scoring 

and the subsequent listing of a release merely represent the initial determination that a certain 

area may need to be addressed under the Comprehensive Environmental Response, 

Compensation, and Recovery Act (CERCLA). Accordingly, EPA contemplates that the 

preliminary description of facility boundaries at the time of scoring will be refined as more 

information is developed as to where the contamination has come to be located. 

Pathway Scores: 

Ground Water Migration Pathway – 100.00 

Surface Water Migration Pathway – NS

Soil Exposure Pathway – NS

Air Migration Pathway – NS
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

2 

**NS = Not Scored 

(** Pathways were evaluated but not scored due to their minimal contribution to the overall 

site score)

HRS SITE SCORE: 50.00
1

1

 

 

 

 

 

 

 

 

 

 

 

 

 

2 !!

Site center 

Midland Midland

§ ̈¦20 

§ ̈¦20 

UV349 

UV349 

UV158 

UV158 

UV158 

UV58 

UV58 

Illinois 

349 

Front 

Wall 

20e 

1200 

Midkiff 

1210 

158 

Midland 

Gist

Thomason 

Lamesa 

A 

Florida 

Francis 

Rankin 

Louisiana 

Cotton Flat 

Garfield 

80 

Andrews 

349 Big Spring Big Spring 

Andrews 

Garden City Cloverdale

Industrial 

Industrial

Lee 

Marienfeld 

Lamesa 

158 

Illinois 

Garfield 

Figure 1a: Regional Location Map
 μ
 West County Road 112

Groundwater Plume

Midland, Texas

(Midland County)

TXN000606992 

2 !!

Subject Area 

Odessa Odessa

£¤385 

Midland Midland

This map was generated by the Remediation Division of the Texas

Commission on Environmental Quality. It is intended for illustrative 

or informational purposes only, and is not suitable for legal,

engineering, or survey purposes. This map does not represent an 

on-the-ground survey conducted by or under the supervision of a 

registered professional land surveyor. In cases where property

boundaries are shown, it only represents their approximate relative

0 0.25 0.5 1 1.5 2 2.5 3 3.5 4 4.5 location. No claims are made to the accuracy or completeness of the

Miles data or to its suitability for a particular use. For more information 

concerning this map, contact the Remediation Division at 800-633-9363. 

The base data set is UTM Zone 13, 0.5 Meter Resolution, Natural Color, NAD 1983 (Ref. 128, pp. 1-4) 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

2 !!

Site center 

Figure 1b: Site Location Topographic Map
 μ
 West County Road 112

Groundwater Plume

Midland, Texas

(Midland County)

TXN000606992 

2 !!

Subject Area 

Odessa Odessa

£¤385 

Midland Midland

This map was generated by the Remediation Division of the Texas

Commission on Environmental Quality. It is intended for illustrative 

or informational purposes only, and is not suitable for legal,

engineering, or survey purposes. This map does not represent an 

on-the-ground survey conducted by or under the supervision of a 

registered professional land surveyor. In cases where property

boundaries are shown, it only represents their approximate relative 0	 0.25 0.5 1 1.5 2 2.5 location. No claims are made to the accuracy or completeness of the

Miles data or to its suitability for a particular use. For more information

The base data set is U.S. Geological Survey 7.5 Minute Topographic Map, Southwest Midland Quadrangle. concerning this map, contact the Remediation Division at 800-633-9363. 

Available from Texas Natural Resources Information System (TNRIS), Data Search and Download. 
Figure 1c: Site Location and Surrounding Land Use Map 
 N 

E 


s 

Legend

* State Superfund Site 

o Corrective Action Site 

• Public Water Supply Well 

... LPST Site 

Miles 

o 1 2 3 4 5 6 7 8 9 10 11 


The base data set is UTM Zone 13,0.5 Meter Resolution, Natural Color, NAD 1983 (Ref. 128, pp. 1-4) 

West County Road 112 

Groundwater Plume 

Midland, Texas 

(Midland County) 

TXN000606992 

Subject Area 

I'­

'­

~ ~ r\ ~;;:; " / 

"'/ ';( C J' 

/ ):., r­

"- ~~v 

~ 

'" \ 

\ 

'--J. ~ 

This map was generated by the Remediation Division of the Texas 

Commission on Environmental Quality. It is intended for illustrative 

or informational purposes only, and is not suitable for legal, 

engineering, or survey purposes. This map does not represent an 

on-the-ground survey conducted by or under the supervision of a 

registered professional land surveyor. In cases where property 

boundaries are shown , it only represents their approximate relative 

location. No claims are made to the accuracy or completeness of the 

data or to its suitability for a particular use. For more information 

concerning this map, contact the Remediation Division at 800-633-9363. 
Figure 1d: Groundwater Sample Locations 


Legend 

Sampled Groundwater Wells 

Site Center 

N 


w E 

s 


West County Road 112 

Groundwater Plume 

Midland, Texas 

(Midland County) 

TXN000606992 

Subject Area 

fen 

» 

N /, 

[ "" t>< ry 

"J~ " \ .rY 

\ 

--J. 

This map was generated by the Remediation Division of the Texas 

Commission on Environmental Quality. Jt is intended for inustrative 

or informational purposes only. and is not suitable for legal, 

engineering , or survey purposes_ This map does not represent an 

on-lheiJround survey conducted by or under the supervision of a 

registered professional land surveyor. In cases where property 

boundaries are shown , it only represents their approximate relative 

Iocation_ No daims are made to the accuracy or completeness of the 

data or to its sufability for a particular use_ For more informalion 

conceming Ihis map. conlacllhe Remedialion Division al800-633-9363 

o 0.25 0.5 1 1.5 2 2.5 

_C:::::=::::J_==:::J__C::==========:::::J__C::==========:::::JI Miles 

The base data set is UTM Zone 13, 0.5 Meter Resolution , Natural Color, NAD 1983 (Ref. 128, pp. 1-4) 

Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

7 

WORKSHEET FOR COMPUTING HRS SITE SCORE

S S2

1. Ground Water Migration Pathway Score (Sgw) 100 10,000 

(from Table 3-1, line 13) 

2a. Surface Water Overland/Flood Migration NS

 Component (from Table 4-1, line 30) 

2b. Ground Water to Surface Water Migration NS

 Component (from Table 4-25, line 28) 

2c. Surface Water Migration Pathway Score (Ssw) NS

 Enter the larger of lines 2a and 2b as the 

pathway score.

3. Soil Exposure Pathway Score (Ss) NS

(from Table 5-1, line 22) 

4. Air Migration Pathway Score (Sa) NS

(from Table 6-1, line 12) 

5. Total of Sgw

2 + Ssw2 + Ss2 + Sa2

 10,000 

6. HRS Site Score Divide the value on line 5 

 by 4 and take the square root. 50.00 

NS = Not Scored
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

8 

TABLE 3-1 

GROUND WATER MIGRATION PATHWAY SCORESHEET

Factor Categories and Factors Maximum Value Value Assigned

Likelihood of Release to an Aquifer

1. Observed Release 550

2. Potential to Release

550

2a. Containment 10

2b. Net Precipitation 10

2c. Depth to Aquifer 5

2d. Travel Time 35

2e. Potential to Release

(Lines 2a(2b + 2c + 2d)) 500

3. Likelihood of Release

(Higher of Line 1 and 2e) 550 550

Waste Characteristics

4. Toxicity/Mobility *

5. Hazardous Waste Quantity

10,000

*

6. Waste Characteristics

100

100 32

Targets

7. Nearest Well 50

8. Population:

50

8a. Level I Concentrations **

8b. Level II Concentrations

533

**

8c. Potential Contamination

10.48

**

8d. Population (Lines 8a + 8b + 8c)

17.8

**

9. Resources

561.28

5 0

10. Wellhead Protection Area 20 0

11. Targets (Lines 7 + 8d + 9 + 10) ** 611.28

Ground Water Migration Score for an Aquifer

12. Aquifer Score

((Lines 3 x 6 x 11)/82,500)

100

100

Ground Water Migration Pathway Score

13. Pathway Score (Sgw), (Highest value from Line 12 for all 

aquifers evaluated)

100 100
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

9 

REFERENCE LISTING

Reference

1. U.S Environmental; Protection Agency. Federal Register – 40 CFR Part 300; Hazard Ranking System; 

Final Rule, Volume 55, No. 241, December14, 1990.

Number Description of the Reference

2. RESERVED 

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http://epa.gov/superfund/sites/npl/hrses/tools/scdm.htm. 1-3 excerpted pages. 

4. RESERVED

5. Sattman Soule, Danielle. Texas Commission on Environmental Quality Project Manager. Field 

Notebook from West County Road 112 Ground Water: Book 1. July 20-23, 2009. 29 pages.

6. Palmie, April. Texas Commission on Environmental Quality Project Manager. Field Notebook from 

West County Road 112 Ground Water: Book 2. July 20-23, 2009. 18 pages.

7. U.S. Geological Survey, Water-Resources Investigation Report 94-4039. Geologic History and 

Hydrogeologic Setting of the Edwards-Trinity Aquifer System, West-Central Texas. Rene A. Barker, 

Peter W. Bush, and E.T. Baker, Jr. 1994. 55 pages.

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2010. 16 pages.

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Texas. Johan August Udden Memorial Edition. 1976. 7 excerpted pages.

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http://quickfacts.census.gov/qfd/index.html. Accessed May 19, 2009. 9 pages.

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pages.
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

10

18. WCR 112 TCEQ – SSDAP Sampling Field Notebook # 4. June 16, 2009 through July 16, 2009. 95 

pages.

19. WCR 112 TCEQ – SSDAP Sampling Field Notebook # 5. June 16, 2009 through July 16, 2009. 107 

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Database: Water Well Data and Logs. Available at 

http://wiid.twdb.state.tx.us/ims/wwm_drl/viewer.htm?appno=1. Accessed January 12, 2010. 10 

pages. 

21. WCR 112 TCEQ – SSDAP Sampling Field Notebook # 6. September 15, 2009 through January 6, 

2010. 117 pages. 

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38 pages.

23. WCR 112 TCEQ – SSDAP Sampling Field Notebook # 7. September 15, 2009 through January 6, 

2010. 107 pages. 

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System, EPA 540-F-95-034, OSWER Publication 9320.8-01FS, September 1998. 5 pages.

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26. WCR 112 TCEQ – SSDAP Sampling Field Notebook # 8. September 15, 2009 through January 6, 

2010. 64 pages.

27. Xenco Laboratories. Analytical Report 332384 for Shaw E & I, Inc: WCR 112 Midland TX. May 15, 

2009. 77 pages.

28. Xenco Laboratories. Analytical Report 332487 for Shaw E & I, Inc: WCR 112 Midland TX. May 15, 

2009. 115 pages.

29. Xenco Laboratories. Analytical Report 332667 for Shaw E & I, Inc: WCR 112 Midland TX. May 18, 

2009. 116 pages.

30. Xenco Laboratories. Analytical Report 332803 for Shaw E & I, Inc: WCR 112 Midland TX. May 19, 

2009. 100 pages.

31. Xenco Laboratories. Analytical Report 333163 for Shaw E & I, Inc: WCR 112 Midland TX. May 20, 

2009. 32 pages.

32. Xenco Laboratories. Analytical Report 333288 for Shaw E & I, Inc: WCR 112 Midland TX. May 21, 

2009. 26 pages.

33. WCR 112 TCEQ – ESI Sampling Field Notebook # 1. February 1, 2010 through February 11, 2010. 

101 pages.

34. Xenco Laboratories. Analytical Report 333460 for Shaw E & I, Inc: WCR 112 Midland TX. May 22, 

2009. 24 pages.
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

11

35. Xenco Laboratories. Analytical Report 334577 for Shaw E & I, Inc: WCR 112 Midland TX. June 5, 

2009. 23 pages.

36. Xenco Laboratories. Analytical Report 334969 for Shaw E & I, Inc: WCR 112 Midland TX. June 10, 

2009. 17 pages.

37. Xenco Laboratories. Analytical Report 335094 for Shaw E & I, Inc: WCR 112 Midland TX. June 11, 

2009. 21 pages.

38. Xenco Laboratories. Analytical Report 335246 for Shaw E & I, Inc: WCR 112 Midland TX. June 12, 

2009. 17 pages.

39. WCR 112 TCEQ – ESI Sampling Field Notebook # 2. February 1, 2010 through February 18, 2010. 49 

pages.

40. Xenco Laboratories. Analytical Report 335618 for Shaw E & I, Inc: WCR 112 Midland TX. June 17, 

2009. 16 pages.

41. Xenco Laboratories. Analytical Report 335713 for Shaw E & I, Inc: WCR 112 Midland TX. June 18, 

2009. 16 pages.

42. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 344700, 344875, 344876, 344898, 344997, 344999, 345000, 345597, 345867, 

345944 and 346081 Analytical Package(s) for September 15 through 25, 2009 Ground Water Sampling 

Event at West County Road 112, Midland, Texas. December 14, 2009. 18 pages.

43. Xenco Laboratories. Analytical Report 335882 for Shaw E & I, Inc: WCR 112 Midland TX. June 19, 

2009. 16 pages.

44. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 350780, 350925 and 353327 Analytical Package(s) for November 3, 4 and 24, 2009 

Ground Water Sampling Event at West County Road 112, Midland, Texas. January 12, 2010. 7 pages.

45. Shaw Environmental, Inc. Data Validation Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 344700, 344875, 344876, 344898, 344997, 344999, 345000, 345597, 345867, 

345944 and 346081 Analytical Package(s) for September 15 through 25, 2009 Ground Water Sampling 

Event at West County Road 112, Midland, Texas. January 4, 2010. 31 pages.

46. Shaw Environmental, Inc. Data Validation Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 350780, 350925 and 353327 Analytical Package(s) for November 3, 4 and 24, 2009 

Ground Water Sampling Event at West County Road 112, Midland, Texas. January 18, 2010. 6 pages.

47. Xenco Laboratories. Analytical Report 336372 for Shaw E & I, Inc: WCR 112 Midland TX. June 29, 

2009. 18 pages.

48. Xenco Laboratories. Analytical Report 336428 for Shaw E & I, Inc: WCR 112 Midland TX. June 26, 

2009. 12 pages.

49. Xenco Laboratories. Analytical Report 336793 for Shaw E & I, Inc: WCR 112 Midland TX. July 1, 

2009. 27 pages.

50. Xenco Laboratories. Analytical Report 336906 for Shaw E & I, Inc: WCR 112 Midland TX. July 2, 

2009. 17 pages. 

51. Xenco Laboratories. Analytical Report 336930 for Shaw E & I, Inc: WCR 112 Midland TX. July 2, 

2009. 12 pages.
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

12

52. Xenco Laboratories. Analytical Report 337310 for Shaw E & I, Inc: WCR 112 Midland TX. July 8, 

2009. 19 pages. 

53. Xenco Laboratories. Analytical Report 337435 for Shaw E & I, Inc: WCR 112 Midland TX. July 9, 

2009. 19 pages.

54. Xenco Laboratories. Analytical Report 346081 for Shaw E & I, Inc: WCR 112 Midland TX. December 

9, 2009. 20 pages.

55. Xenco Laboratories. Analytical Report 350780 for Shaw E & I, Inc: WCR 112 Midland TX. December 

14, 2009. 27 pages.

56. Xenco Laboratories. Analytical Report 337608 for Shaw E & I, Inc: WCR 112 Midland TX. July 13, 

2009. 12 pages.

57. Xenco Laboratories. Analytical Report 350925 for Shaw E & I, Inc: WCR 112 Midland TX. December 

14, 2009. 20 pages.

58. Xenco Laboratories. Analytical Report 337963 for Shaw E & I, Inc: WCR 112 Midland TX. July 16, 

2009. 17 pages.

59. Xenco Laboratories. Analytical Report 353327 for Shaw E & I, Inc: WCR 112 Midland TX. December 

14, 2009. 13 pages.

60. Xenco Laboratories. Analytical Report 338085 for Shaw E & I, Inc: WCR 112 Midland TX. July 16, 

2009. 22 pages.

61. Xenco Laboratories. Analytical Report 338182 for Shaw E & I, Inc: WCR 112 Midland TX. July 17, 

2009. 16 pages.

62. Xenco Laboratories. Analytical Report 338183 for Shaw E & I, Inc: WCR 112 Midland TX. July 17, 

2009. 12 pages.

63. Xenco Laboratories. Analytical Report 339141 for Shaw E & I, Inc: WCR 112 Midland TX. July 30, 

2009. 11 pages.

64. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 332384 Analytical Package(s) for May 11, 2009 Ground Water Sampling Event at 

West County Road 112, Midland, Texas. July 21, 2009. 50 pages. 

65. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 332387 Analytical Package(s) for May 12, 2009 Ground Water Sampling Event at 

West County Road 112, Midland, Texas. July 23, 2009. 79 pages.

66. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 332667 Analytical Package(s) for May 13, 2009 Ground Water Sampling Event at 

West County Road 112, Midland, Texas. July 24, 2009. 105 pages.

67. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 332803 Analytical Package(s) for May 14, 2009 Ground Water Sampling Event at 

West County Road 112, Midland, Texas. July 27, 2009. 81 pages.

68. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 333163 Analytical Package(s) for May 19, 2009 Ground Water Sampling Event at 

West County Road 112, Midland, Texas. July 28, 2009. 10 pages.
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

13

69. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 333288 and 3333289 Analytical Package(s) for May 20, 2009 Ground Water 

Sampling Event at West County Road 112, Midland, Texas. July 28, 2009. 9 pages.

70. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 333460 Analytical Package(s) for May 21, 2009 Ground Water Sampling Event at 

West County Road 112, Midland, Texas. July 30, 2009. 8 pages.

71. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 334577 Analytical Package(s) for June 4, 2009 Ground Water Sampling Event at 

West County Road 112, Midland, Texas. July 31, 2009. 6 pages. 

72. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 334969 Analytical Package(s) for June 9, 2009 Ground Water Sampling Event at 

West County Road 112, Midland, Texas. June 18, 2009. 6 pages.

73. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 335094 Analytical Package(s) for June 10, 2009 Ground Water Sampling Event at 

West County Road 112, Midland, Texas. August 6, 2009. 6 pages.

74. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 335246 Analytical Package(s) for June 11, 2009 Ground Water Sampling Event at 

West County Road 112, Midland, Texas. August 3, 2009. 5 pages.

75. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 335589 and 335618 Analytical Package(s) for June 16, 2009 Ground Water 

Sampling Event at West County Road 112, Midland, Texas. August 4, 2009. 6 pages.

76. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 335713 and 335741 Analytical Package(s) for June 17, 2009 Ground Water 

Sampling Event at West County Road 112, Midland, Texas. August 10, 2009. 6 pages.

77. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 335882 and 335899 Analytical Package(s) for June 18, 2009 Ground Water 

Sampling Event at West County Road 112, Midland, Texas. July 30, 2009. 6 pages.

78. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 336260, 336282, 336372 and 336428 Analytical Package(s) for June 23-24, 2009 

Ground Water Sampling Event at West County Road 112, Midland, Texas. August 17, 2009. 9 pages.

79. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 336793 Analytical Package(s) for June 30, 2009 Ground Water Sampling Event at 

West County Road 112, Midland, Texas. July 16, 2009. 6 pages.

80. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 336906 and 336930 Analytical Package(s) for July 1, 2009 Ground Water Sampling 

Event at West County Road 112, Midland, Texas. July 20, 2009. 6 pages.

81. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 337310, 337312 and 337315 Analytical Package(s) for July 7, 2009 Ground Water 

Sampling Event at West County Road 112, Midland, Texas. August 18, 2009. 6 pages. 

82. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 337435 and 337457 Analytical Package(s) for July 8, 2009 Ground Water Sampling 

Event at West County Road 112, Midland, Texas. August 5, 2009. 6 pages.
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

14

83. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 337567 and 337608 Analytical Package(s) for July 9, 2009 Ground Water Sampling 

Event at West County Road 112, Midland, Texas. August 6, 2009. 18 pages. 

84. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 337912 and 337963 Analytical Package(s) for July 14, 2009 Ground Water 

Sampling Event at West County Road 112, Midland, Texas. August 17, 2009. 7 pages.

85. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 338035 and 338085 Analytical Package(s) for July 15, 2009 Ground Water 

Sampling Event at West County Road 112, Midland, Texas. August 7, 2009. 7 pages.

86. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 338182 and 338183 Analytical Package(s) for July 16, 2009 Ground Water 

Sampling Event at West County Road 112, Midland, Texas. August 11, 2009. 6 pages.

87. Shaw Environmental, Inc. Data Review Memorandum: e-Lab Analytical Inc., (Xenco) Laboratory 

Report Number(s) 339141 Analytical Package(s) for July 29, 2009 Ground Water Sampling Event at 

West County Road 112, Midland, Texas. August 12, 2009. 5 pages.

88. Johnson, Lloyd. Texas Commission on Environmental Quality - Quality Assurance/Technical 

Support. Interoffice Memorandums: Data Quality Audit and Review. October 16, 2009 and March 1, 

2010. 10 pages

89. U.S. Environmental Protection Agency Region 6 Laboratory. Final Analytical Report: West County 

Road 112 Ground Water. August 25, 2009. 266 pages.

90. Texas Commission on Environmental Quality. Water Well Surveys From WCR 112 Area Residents. 

63 pages.

91. U.S. Environmental Protection Agency Region 6 Laboratory. Final Analytical Report: West County 

Road 112 Ground Water. March 8, 2010. 70 pages.

92. Xenco Laboratories. Analytical Report 344700 for Shaw E & I, Inc: WCR 112 Midland TX. December 

9, 2009. 29 pages. 

93. Xenco Laboratories. Analytical Report 344875 for Shaw E & I, Inc: WCR 112 Midland TX. December 

9, 2009. 23 pages.

94. Xenco Laboratories. Analytical Report 344876 for Shaw E & I, Inc: WCR 112 Midland TX. December 

9, 2009. 23 pages.

95. Xenco Laboratories. Analytical Report 344898 for Shaw E & I, Inc: WCR 112 Midland TX. December 

9, 2009. 23 pages.

96. Xenco Laboratories. Analytical Report 344997 for Shaw E & I, Inc: WCR 112 Midland TX. December 

9, 2009. 21 pages.

97. Xenco Laboratories. Analytical Report 344999 for Shaw E & I, Inc: WCR 112 Midland TX. December 

9, 2009. 19 pages.

98. Xenco Laboratories. Analytical Report 345000 for Shaw E & I, Inc: WCR 112 Midland TX. December 

9, 2009. 18 pages.
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

15

99. Xenco Laboratories. Analytical Report 345597 for Shaw E & I, Inc: WCR 112 Midland TX. December 

9, 2009. 20 pages.

100.Xenco Laboratories. Analytical Report 345867 for Shaw E & I, Inc: WCR 112 Midland TX. December 

9, 2009. 27 pages.

101.Xenco Laboratories. Analytical Report 345944 for Shaw E & I, Inc: WCR 112 Midland TX. December 

9, 2009. 28 pages.

102.Sattman Soule, Danielle. Texas Commission on Environmental Quality Project Manager. Note to File: 

West County Road 112 Anion Exchange Filtration Systems. March 24, 2010. 3 pages.

103.Hammitt, Christine. Texas Commission on Environmental Quality. IOM at the West County Road 

112 Site from 3/3/09 to 5/1/09. May 1, 2009. 11 pages. 

104.Sattman Soule, Danielle. Texas Commission on Environmental Quality Project Manager. Note to File: 

West County Road 112 Groundwater Site Summary November 2009 site update. March 24, 2010. 3 

pages.

105.Sattman Soule, Danielle. Texas Commission on Environmental Quality Project Manager. ESI 

Workplan. January 2010. 74 excerpted pages.

106.Palmie, April. Texas Commission on Environmental Quality Project Manager. SI Report. February 

2010. 50 excerpted pages.

107.Sattman Soule, Danielle. Texas Commission on Environmental Quality Project Manager. ESI Report. 

Placeholder.

108.Texas Commission on Environmental Quality. HRS Level One and Two Photo Log: West County 

Road 112 Ground Water Plume. March 2010. 74 pages.

109.Texas Water Development Board. Well Locations Data from Texas Water Development Board 

Groundwater Database. March 2010. Available at 

http://wiid.twdb.state.tx.us/ims/wwm_drl/viewer.htm?DISCL=1. 20 pages.

110.Banks Environmental Data. Water Well Report. May 2009. 73 pages.

111.Musick, Robert. Texas Commission on Environmental Quality Project Manager/Work Leader. Note to 

File: Regarding Water Bearing Units (WBUs) in the West County Road 112 Site Area. April 7, 2010. 2 

pages.

112.Texas Commission on Environmental Quality. Quality Assurance Project Plan for Texas Commission

on Environmental Quality-Preliminary Assessment and Site Inspection Program (Number V96665501-0). February 1, 2010. 218 pages.

113.Texas Water Commission. B&W Welding and Construction Site Investigation. August 31, 1987. 142 

pages.

114.Texas Commission on Environmental Quality. Schlumberger Technology Corporation Notice of 

Registration (SWR # 33591). March 15, 2010. 31 pages. 

115.Danielle Schleman. Texas Commission on Environmental Quality Project Manager. Approval of 

Affected Property Assessment Report. February 3, 2009. 15 pages.

116.Williams Paving and Excavation. January 2010. Available at 

http://www.wiliamspavingandexcavation.com. 1 page.
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

16

117.Arcadis. Twelfth Annual Report 2007 Groundwater Quality Assurance Plan For The Agreed Order Of 

7-13-94 (SWR 33591). January 2008. 25 pages.

118.Texas Speleological Society. Texas Karst and Pseudokarst Region Map. May 2010. Available at 

http://www.utexas.edu/tmm/sponsored_sites/tss/images/tk1/gif. 1 page.

119.Texas Water Development Board. Midland County Major Aquifer Extent Map. May 2010. Available 

at http://www.twdb.state.tx.us/home/index.asp. 1 page.

120.Texas Commission on Environmental Quality. Water System Data Sheet. July 20, 2010. Available 

at http://www10.tceq.state.tx.us/iwud/pws/index.cfm?fuseaction=ListPWS&Command=list. 20 pages.

121.Xenco Laboratories. Analytical Report 329551 for TCEQ-Region 7: WCR 112 Midland TX. April 9, 

2009. 9 pages.

122.Sattman Soule, Danielle. Texas Commission on Environmental Quality Project Manager. Note to File: 

City of Midland’s Water Distribution Lines. July 21, 2010. 2 pages.

123.Texas Commission on Environmental Quality. Water System Data Sheet. July 21, 2010. Available 

at http://www10.tceq.state.tx.us/iwud/pws/index.cfm?fuseaction=ListPWS&Command=list. 20 pages.

124.Sattman Soule, Danielle. Texas Commission on Environmental Quality Project Manager. Health and 

Safety Plan. January 2010. 29 excerpted pages.

125.Arcadis. Schlumberger Technology Corporation Agreed Order of 7/13/94 (Dowell Midland Facility). 

May 21, 2009. 5 pages.

126.Eden, Daniel J., Texas Water Commission. Correspondence to Honorable William B. Ahders and 

James H. Humphries, Jr. M.D. July 19, 1991. 2 pages.

127.Lear Corporation. Bankruptcy Notice Regarding the Former Lear Corporation Facility located at 4 

South Industrial Loop. September 2, 2009. 1 page.

128.TNRIS. Top-2008/2009 0.5 Meter DOQQ Metadata. August 2009. 4 pages.

129.Sattman Soule, Danielle. Texas Commission on Environmental Quality Project Manager. Note to File: 

Water Well Survey for 3109 South County Road 1200. July 22, 2010. 1 page.

130.Environmental Lab of Texas/XENCO Laboratories. Laboratory sheets. 55 pages.

131.XENCO Laboratories. Data Package for WCR 112, Chromium by Method SW 6010C sequence 

120409B. 2009. 56 pages.

132.XENCO Laboratories. Data Package for WCR 112, Chromium by Method SW 6010C sequence 

120509A. 2009. 56 pages.

133.XENCO Laboratories. Data Package for WCR 112, Chromium by Method SW 6010C sequence 

120609A. 2009. 33 pages.

134.Warren, Christy. U.S. Environmental Protection Agency, Region 6 Laboratory, Sample Control 

Center. Email to Brenda Nixon Cook, U.S. Environmental Protection Agency, Region 6 NPL 

Coordinator regarding analytical data detection limits. August 6, 2010. 2 pages.

135.Cook, Brenda. U.S. Environmental Protection Agency, Region 6 NPL Coordinator. Note to File: 

West County Road 112 Ground Water Source 1 Sample Locations. August 18, 2010. 4 pages.
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

17

SITE DESCRIPTION

The West County Road 112 Ground Water site is designated as a contaminated ground water

plume originating from unknown sources composed of hazardous substances that released 

into the Edwards-Trinity aquifer. The center of the plume is designated as 2604 West 

County Road 112, Midland, Texas (2604 W CR 112). The plume currently extends 1 1⁄4 

miles from the center of the site at its farthest documented point and is situated under 

approximately 260 acres of residential and commercial land (Figures 1a through 1d). 

Based on the results of the domestic water well located at 2604 W CR 112, ground water

samples were collected from April 2009 to November 2009. The ground water plume 

contains elevated inorganic compounds of chromium and chromium VI, which exceeded

three times the background level (See Tables 6-12 of this HRS documentation record). The 

plume extent is based on delineation of sample points as shown in Figure 2.

As of November 9, 2009, concentrations of chromium in the ground water at the Site 

exceeded the United States Environmental Protection Agency (EPA) maximum contaminant 

limit (MCL) of 0.1 mg/L for total and hexavalent chromium in 47 active domestic water 

wells (Ref. 102, pp.1-3). 

The Site is surrounded by residential properties to the south and east, and by commercial and 

residential properties to the north and west. All residences and commercial businesses south 

of I-20 receive ground water from private water wells drilled to depths between 60 and 100 

feet below ground surface (bgs) (Ref. 110, pp.3-5; Ref. 20, p. 10). The ground water is the 

sole source of water in this area; the City of Midland does not provide city water south of I20. Several households purchase drinking water, but all households use the ground water for 

bathing and other domestic purposes. There are no city water distribution lines within 1 1⁄4

miles of the Site (Ref. 122, pp. 1-2). Properties north of I-20 currently receive water from 

the City of Midland (PWS 1650001) (Ref. 123, p. 1; Figure 1c of this HRS documentation 

Record). 
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

18

SOURCE DESCRIPTION

2.2 Source Characterization

2.2.1

Number of the source: 1 

Name and description of the source: Other – Ground Water Plume with No Identified Source 

The chromium contamination was reported to the TCEQ when a resident complained of 

yellow water to the TCEQ Region 7 office (Ref. 103, pp. 1-3). The regional office 

immediately collected ground water samples from a domestic water well at 2604 West 

County Road 112 on April 8, 2009 (Ref. 103, pp. 1-3). The concentrations of hexavalent 

chromium in these samples exceeded the MCL of 0.1 mg/L for chromium (Ref. 3, pp. 1-3; 

Ref. 103, p. 3; Ref. 121, p. 4).

On April 20, 2009, and April 29, 2009, the TCEQ Region 7 office and TCEQ Superfund Site 

and Discovery and Assessment Program (SSDAP) personnel collected additional ground 

water samples from water wells, located on West County Road 112 and West County Road 

110, surrounding the well located at 2604 West County Road 112 (Ref. 103, pp. 7-9). On 

May 4, 2009, SSDAP continued collecting ground water samples from water wells within 1 

1⁄4 mile north and south and 1⁄2 mile east and west of the center of the site (2604 W CR 112) 

(Figure 1d). By November 4, 2009, SSDAP collected ground water samples from 234 water

wells (Ref. 104, p. 1). 

From July 20, 2009, through July 23, 2009, TCEQ conducted a Site Inspection (SI) (Ref. 

106, p. 15). 30 of the 234 drinking water wells were sampled during the SI (Ref. 106, pp. 18-

19). The SI also included collection and analysis of five soil samples (including one 

duplicate) from the center of the site and from surrounding residential areas (Ref. 106, pp. 

15-16). Three soil samples were collected at a depth of 0-6 inches, and one sample was 

collected from a depth of five feet below the ground surface (bgs) (Ref. 106, pp. 15-16). 

None of the soil samples collected met observed release criteria (Ref. 89, pp. 158-177; Ref. 

106, p. 23). Ground water samples from 26 drinking water well locations met the observed 

release criteria for chromium (Ref. 89, pp. 6-157; Ref. 106, pp. 38-40). For the samples 

meeting the observed release criteria, all but one sample exceeded the SCDM health based 

benchmark for chromium of 0.1 mg/L (Ref. 3, pp. 1-3).

The TCEQ continued investigating for a potential source or sources at the site by conducting

an Expanded Site Inspection (ESI) during February 1-10, 2010 (Ref. 105, pp. 45-49; Ref. 

107, p. 10). The ESI involved sampling a total of 23 monitor wells screened in the Ogallala 

and Edwards-Trinity aquifers and collecting 8 soil samples at the center of the site (2604 W 

CR 112) to determine a pattern of chromium concentrations to identify a point of release

(Ref. 107, pp. 10 and 13). 

Source Identification
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

19

Before soil samples were collected at the center of the site (2604 W CR 112), the TCEQ 

conducted ground-penetrating radar and electromagnetic pulse surveys (Ref. 107, p. 13). 

These surveys were used to search for buried metal consistent with buried drums. Soil 

samples were collected based on the results of the ground-penetrating radar and 

electromagnetic pulse surveys (Ref. 107, p.13). The ground-penetrating radar and 

electromagnetic pulse surveys report concluded three anomalies were present, in the 

backyard of 2604 W CR 112, which potentially could indicate the presence of buried drums

(Ref. 107, p. 13). Surface structures may have limited the effectiveness of the surveys. 

Based on the findings of the ground- penetrating radar and electromagnetic pulse surveys 

eight soil samples, including one field duplicate sample, were collected in areas where buried 

drums could have been located (Ref. 107, p. 13). However, no drums were found during the 

soil sampling and the sample results indicated no sources of chromium contamination were 

identified (Ref. 107, p.13). 

A total of 23 monitoring wells were sampled to identify potential source locations for the ESI

(Ref. 107, p. 10). The TCEQ opted to use 18 existing monitoring wells within the potential 

source area as part of the ESI; however, TCEQ installed five new monitoring wells for 

further plume definition and potential source identification (Ref. 107, p. 10). Two of the five 

monitoring wells were installed north of the 32 E. Industrial Loop located hydraulically upgradient of the known chromium plume to establish background values for the Site (Ref. 107, 

p. ). The remaining three monitoring wells were installed near the center of the site (2604 W 

CR 112) on properties at 2406 W CR 112; 2700 W CR 112; and 2601 W CR 112 (Ref. 107, 

p. 11). These wells were installed to evaluate for a potential source of the chromium release 

in the vicinity of the highest known chromium ground water contamination (Ref. 107, p. 10). 

Four of the five monitoring wells were installed by the TCEQ in the uppermost aquifer, the

Ogallala aquifer, and one monitoring well was installed in the Edwards-Trinity aquifer 

(below the Ogallala aquifer) (Ref. 107, pp. 10-11). All wells were installed using an air 

rotary drilling system (Ref. 33, p. 2). The shallow monitoring wells installed in the Ogallala 

aquifer were drilled to a target depth of approximately 35 to 60 feet bgs (Ref. 107, p. 10). 

The wells installed in the Ogallala aquifer were completed with 4-inch PVC casing with fully 

penetrating 0.020 inch slotted screen. The deep monitoring well installed in the EdwardsTrinity aquifer was drilled to a target depth of approximately 79 feet bgs (Ref. 107, p. 11). 

The well was advanced at a diameter of 12 1/4 inches to 35 feet bgs and 8-inch steel casing 

was installed and cemented to isolate the Ogallala aquifer (Ref. 33, p. 1-3). Once the cement 

had cured, the bore hole was advanced at a diameter of 7 7/8 inches from 35 to 79 feet bgs. 

The well was then completed with 4-inch PVC casing with fully penetrating 0.0020 inch 

slotted screen for the Edwards-Trinity aquifer (Ref. 33, p.5). 

A total of 26 ground water samples, including three field duplicate samples, were collected 

from 23 monitoring wells during the ESI (Ref. 107, p. 14). Ground water samples were 

collected to evaluate the possible source areas for a release of chromium into the West 

County Road 112 ground water plume. Four locations were identified as possible source(s) 

of the chromium contamination. Up-gradient and down-gradient ground water samples were 

collected at all four source locations (Ref. 107, p. 14). 
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

20

• Two up-gradient (GW-13 & GW-14) and 2 down-gradient (GW-20 & GW-20A) 

ground water samples were collected in the Ogallala aquifer (GW-13 & GW-20) 

and Edwards-Trinity aquifer (GW-14 & GW-20A) to determine if a release 

occurred at the Schlumberger Technology Corporation facility located at 432 E. 

Industrial Loop (Ref. 107, pp. 19, 24). 

• One up-gradient (GW-105) and 5 down-gradient (GW-4l, GW-E, GW-41, GW55, & GW-15) ground water samples were collected in the Ogallala aquifer to 

determine if a release occurred at the B&W facility located at 4 S. Industrial Loop 

(Ref. 107, pp. 19, 24). 

• Five up-gradient (GW-41, GW-55, GW-10, GW-11 & GW-12) and 3 downgradient (GW-07, GW-08, & GW-09) samples were collected in the Ogallala 

aquifer (GW-41, GW-55, GW-10, GW-11, GW-07, & GW-08) and EdwardsTrinity aquifer (GW-12 & GW-09) to determine if a release occurred at the 

Williamson Gravel Pit located at the corner of S CR 1205 and Harris Ave (Ref. 

107, pp. 19, 24). 

• Four up-gradient (GW-01, GW-04, GW-05,& GW-06) and two down-gradient 

(GW-02 & GW-03) samples were collected in the Ogallala aquifer (GW-01, GW04, GW-05, GW-02, & GW-03) and Edwards-Trinity aquifer (GW-06) to 

determine if a release occurred at the center of the site located at 2604 W CR 112 

(Ref. 107, pp. 19, 24). 

The ESI sampling data indicates that the first uppermost aquifer (Ogallala aquifer) was 

impacted with chromium at the B&W facility, but not at the Schlumberger Technology 

Corporation facility or the Williamson Gravel Pit (Ref. 107, pp. 25, 30, 31). The data also 

indicates that the chromium concentrations increase in the Ogallala aquifer in a downgradient direction starting near the B&W facility and culminate with the highest values 

observed at 2601 West County Road 112, just south of the center of the site (Ref. 107, p. 31). 

The data establishes that no elevated chromium contamination was observed in the Ogallala

aquifer from the background wells in the vicinity of the Schlumberger Technology 

Corporation facility and Williamson Gravel Pit. The data suggests that the area defined by 

the north at the B&W facility via Interstate 20 to the center of the site (2604 W CR 112) is a 

likely source area for the point of release of chromium to the Ogallala aquifer (Ref. 107, p. 

31). Because of the up-gradient concentration patterns observed in the analytical data from

the Ogallala aquifer wells and soil data collected at the site center (2604 W CR 112), no 

known source or sources were identified within the current Site area (Ref. 107, p. 31). The 

ESI data does not conclusively identify a point of release and suggests there may be a source 

or sources of chromium in an area bound by the B&W facility to the north (up-gradient) and 

the center of the site to the south (down-gradient) (Ref. 107, p. 31). 

Adequate documentation attributing the hazardous substances to one or more of the potential 

source areas from the SI and ESI has not been identified. Therefore, a ground water plume 
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

21

with no identified source was used for HRS scoring. The ground water plume with no 

identified source was characterized as the site source based on the following:

• The extent of the plume was estimated solely by sampling, using the criteria for an 

observed release to the Ground Water Migration Pathway (Ref. 1, Section 2.2). 

• The level of effort to identify the original source(s) of the hazardous substances by an 

ESI conducted on February 1- 10, 2010 (Ref. 24, p. 2). 

Location of the source, with reference to a map of the site:

See Figure 2, Source Area Map. Also, see Reference 134 for source sample locations. 

Source type for HRS evaluation purposes:

Other - Ground Water Plume with No Identified Source. 

Containment

Gas release to air: The air migration pathway was not evaluated; therefore, gas containment 

was not evaluated.

Particulate release to air: The air migration pathway was not evaluated; therefore, particulate 

containment was not evaluated. 

Release to ground water: The Containment Factor Value for the ground water migration 

pathway was evaluated for “All Sources” for evidence of hazardous substance migration 

from source area (i.e., source area includes source and any associated containment 

structures). The applicable containment factor value was determined based on existing 

analytical evidence of hazardous substances in ground water samples from private and public 

wells (Table 1). Therefore, based on no liner and evidence of a release, the highest Ground 

Water Migration Pathway Containment Factor Value of 10 was assigned to Source No. 1 as 

specified in Table 3-2 of the HRS (Ref. 1, Section 3.1.2.1). 

Release to surface water overland/flood migration component: The surface water pathway 

was not scored; therefore, surface water overland/flood migration component containment 

was not evaluated.
- -

Fi N 

E 

s 

West County Road 112 

Groundwater Plume 

Midland, Texas 

(Midland County) 

TXN000606992 

....

..... 

Subject Area 

~ 

\.j" 

.} 

~r /. '" ~ \..... J " Vv' 

'-­

\ 

'" 

This map was generated by the Remediatioo Division of the Texas 

Commission on Environmental Quality. It is intended for illustrative 

or informational purposes only, and is not suitable for legal, 

engineering. or survey purposes. This map does not represent an 

on-the-ground survey conducted by or under the supervision of a 

registered professional land surveyor. In cases where property 

boundaries are shown , it only represents their approximate relative 

location . No claims are made 10 the accu racy or completeness of the 

data or 10 ils suilabiity for a particular use. For more information 

concerning this map, contact the Remediation Division at BOO -633-9363. 

Legend 

@ Site Center 

Groundwater Chromium Plume 

Level 

Background Well 

• Level 1 Concentration 

Level 2 Concentration 

1.5 1.75 2 2.25 2.5 2.75 3 

Miles 

o 0.125 0.25 0.5 0.75 1 1.25 


The base data set is UTM Zone 13, 0.5 Meter Resolution , Natural Color, NAD 1983 (Ref. 128, pp. 1-4) 

Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

23

2.2.2 Hazardous Substances Associated With A Source

The ground water plume with no identified source, Source 1, contains measured levels of 

chromium and specifically chromium VI, for which observed releases were established 

within the Edwards-Trinity aquifer, the aquifer being evaluated for the Ground Water 

Migration Pathway. These hazardous substances were detected above the background level 

(see Table 5 and Table 6) in samples collected by the TCEQ in 2009, including the SI tasked 

to the TCEQ by the USEPA, which are given in Table 1 below. All field work was 

conducted as outlined in the work plan, including the Expanded Site Inspection Health and 

Safety Plan (HASP), and the TCEQ/EPA approved Quality Assurance Project Plan (QAPP) 

for TCEQ Preliminary Assessment/Site Inspection Program: Federal Grant Identification 

Number V-96665501-0 (Ref. 112; Ref. 124). All deviations from the work plan and/or 

QAPP were noted in the field notebooks. The laboratories that tested the samples for the 

West County Road 112 Ground water site were:

• Xenco, Odessa, Texas – 12600 West Interstate 20 East, Odessa, Texas 79765 (Tables 

5-9 and Tables 11-12) 

• EPA Region 6, Houston – 10625 Fall Stone Road, Houston, Texas (Table 10) 

The water samples were analyzed by methods CLP ILM05.3, SW6010, and SW846 for 

inorganic drinking water analysis (See Table 1 and Table 5 through Table 12) The analytical 

results documented inorganic compounds of chromium and chromium VI greater than or 

equal to the background sample(s) quantitation limit, if not detected in background samples

(see Table 5 through Table 12). 

Not all of the depths for the water wells are specified due to lack of information known by 

the well owner; however, according to residents and local well drillers, the common drilling 

practice in the site area is to install wells to the bottom of the Edwards-Trinity aquifer at a 

depth of approximately 100 feet bgs (Ref. 111, pp. 1-2). Most wells in the site vicinity are 

screened over the two aquifers identified as the Ogallala (uppermost) and Edwards-Trinity 

aquifers to maximize the production of drinking water for the residences (Ref. 111, pp. 1-2). 

Most pumps in the domestic wells were placed in the Edwards-Trinity aquifer near the 

bottom of the well and the well is usually screened across both aquifers to maximize ground 

water production (Ref. 111, p. 2). For the purpose of this record only those wells installed in 

the Edwards-Trinity aquifer were included in the Ground Water Migration Pathway Score.

The chromium is present in the drinking water wells due to a release at the Site. The ground

water samples were collected from a faucet located on or near the well or from port A of the 

anion exchange filtration system (port A is located before the ground water from the well 

enters the anion exchange filtration system). 
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

24

Well ID**

Well Depth (feet)

Below Ground Surface 

and above Mean Sea 

Level (msl)*

Date 

Collected

Contaminant 

Detected

Reference

GW-005

100 (Ref. 90, p.1)

2695 msl ***

6/30/2009 Chromium VI Ref. 18, p. 39; Ref. 135, p. 1

GW-011 80 (Ref. 90, p. 2)

2712 msl ***

5/11/2009 Chromium VI Ref. 16, p. 50; Ref. 135, p. 1

GW-137 6/4/2009 Chromium VI Ref. 16, p. 85; Ref. 135, p. 1

GW-011 9/16/2009 Chromium Ref. 23, p. 13; Ref. 135, p. 1

GW-19 7/20/2009 Chromium Ref. 6, p. 5; Ref. 135, p. 1

GW-020 87 (Ref. 90, p. 4)

2704 msl ***

5/11/2009 Chromium VI Ref. 16, p. 51; Ref. 135, p. 1

GW-135 6/4/2009 Chromium VI Ref. 16, p. 77; Ref. 135, p. 1

GW-020 9/16/2009 Chromium Ref. 23, p. 13; Ref. 135, p. 1

GW-20 7/20/2009 Chromium Ref. 5, pp. 7-8; Ref. 135, p. 1

GW-023 70 (Ref. 90, p. 3)

2722 msl ***

5/12/2009 Chromium VI Ref. 16, p. 53; Ref. 135, p. 1

GW-138 6/4/2009 Chromium VI Ref. 16, p. 84; Ref. 135, p. 1

GW-023 9/16/2009 Chromium Ref. 23, p. 15; Ref. 135, p. 1

GW-28 7/20/2009 Chromium Ref. 5, pp. 9-10; Ref. 135, p. 1

GW-029

80 (Ref. 90, p. 7)

2706 msl ***

6/9/2009 Chromium VI Ref. 17, p. 77; Ref. 135, p. 1

7/1/2009 Chromium Ref. 19, p. 35; Ref. 135, p. 1

9/17/2009 Chromium Ref. 21, p. 45; Ref. 135, p. 1

GW-042 63 (Ref. 90, p. 9)

2727 msl ***

5/12/2009 Chromium VI Ref. 16, p. 56; Ref. 135, p. 1

GW-139 6/4/2009 Chromium VI Ref. 16, p. 86; Ref. 135, p. 1

GW-042 9/16/2009 Chromium Ref. 23, p. 15; Ref. 135, p. 1

GW-31 7/20/2009 Chromium Ref. 5, pp.13-1; Ref. 135, p. 14

GW-044 62 (Ref. 90, p. 11)

2727 msl ***

5/12/2009 Chromium VI Ref. 12, p. 4; Ref. 135, p. 1

GW-140 6/4/2009 Chromium VI Ref. 16, p. 87; Ref. 135, p. 1

GW-044 9/16/2009 Chromium Ref. 26, p. 11; Ref. 135, p. 1

GW-21 7/20/2009 Chromium Ref. 6, pp. 4-5; Ref. 135, p. 1

GW-046 70 (Ref. 90, p. 15)

2729 msl ***

5/12/2009 Chromium VI Ref. 12, p. 3; Ref. 135, p. 1-2

GW-142 6/4/2009 Chromium VI Ref. 16, p. 78; Ref. 135, p. 2

GW-046 9/16/2009 Ref. 26, p. 11; Ref. 135, p. 2

GW-29 7/20/2009 Chromium Ref. 6, pp. 9-11; Ref. 135, p. 2

GW-047 65 (Ref. 103, p. 3)

2725 msl ***

5/12/2009 Chromium VI Ref. 12, p. 5; Ref. 135, p. 2

GW-143 6/4/2009 Chromium VI Ref. 16, p. 88; Ref. 135, p. 2

GW-047 9/23/2009 Ref. 21, p. 63; Ref. 135, p. 2

GW-14 7/20/2009 Chromium Ref. 5, p. 11-12; Ref. 135, p. 2

GW-27 Not specified 7/20/2009 Chromium Ref. 6, p. 7; Ref. 135, p. 2

GW-053

100 (Ref. 90, p. 16)

2677 msl ***

5/13/2009 Chromium VI Ref. 12, p. 7; Ref. 135, p. 2

7/1/2009 Chromium Ref. 50, p. 8; Ref. 135, p. 2

9/24/2009 Chromium Ref. 21, p. 73; Ref. 135, p. 2

9/23/2009 Chromium Ref. 21, p. 65; Ref. 135, p. 2

GW-057

96 (Ref. 90, p. 18)

2684 msl ***

5/13/2009 Chromium VI Ref. 12, p. 11; Ref. 135, p. 2

7/1/2009 Chromium Ref. 18, p. 41; Ref. 135, p. 2

9/24/2009 Chromium Ref. 21, p. 83; Ref. 135, p. 2

GW-058

65 (Ref. 90, p. 19)

2726 msl ***

5/13/2009 Chromium VI Ref. 16, p. 65; Ref. 135, p. 2

7/1/2009 Chromium Ref. 18, p. 41; Ref. 135, p. 2

11/4/2009 Chromium Ref. 21, p. 95; Ref. 135, p. 2

GW-064 Not specified

5/13/2009 Ref. 16, p. 62; Ref. 135, p. 2

7/1/2009 Ref. 19, p. 43; Ref. 135, p. 2

9/23/2009 Ref. 21, p. 71; Ref. 135, p. 2

11/3/2009 Ref. 55, p. 10; Ref. 135, p. 2
Hazard Ranking System Document Record West County Road 112 Ground Water

October 2010 TXN 000 606 992

25

Well ID**

Well Depth (feet)

Below Ground Surface 

and above Mean Sea 

Level (msl)*

Date 

Collected

Contaminant 

Detected

Reference

GW-066

68 (Ref. 90, p. 20)

2718 msl ***

5/13/2009 Chromium VI Ref. 12, p. 12; Ref. 135, p. 2

GW-083

80 (Ref. 90, p. 22)

2710 msl ***

5/13/2009 Chromium VI Ref. 16, p. 66; Ref. 135, p. 2

11/3/2009 Chromium Ref. 17, p. 47; Ref. 135, p. 2

GW-091

100 (Ref. 90, p. 24)

2709 msl ***

5/19/2009 Chromium VI Ref. 12, p. 21; Ref. 135, p. 2

GW-091 6/10/2009 Chromium VI Ref. 17, p. 81; Ref. 135, p. 2

GW-091 9/16/2009 Chromium Ref. 26, p. 13; Ref. 135, p. 2

GW-08 7/21/2009 Chromium Ref. 5, p. 13; Ref. 135, p. 2

GW-092

80 (Ref. 90, p. 25)

2710 msl ***

5/19/2009 Chromium VI Ref. 12, p. 19; Ref. 135, p. 2

GW-092 6/9/2009 Chromium VI Ref. 17, pp. 75-77; Ref. 135, p. 2

GW-092 9/16/2009 Chromium Ref. 23, p. 17; Ref. 135, p. 2

GW-13 7/21/2009 Chromium Ref. 6, p. 8; Ref. 135, p. 2

GW-093

90 (Ref. 90, p. 26)

2700 msl ***

5/19/2009 Chromium VI Ref. 12, p. 24; Ref. 135, p. 2

GW-093 6/9/2009 Chromium VI Ref. 17, p. 75; Ref. 135, p. 2

GW-093 9/16/2009 Chromium Ref. 23, p. 17; Ref. 135, p. 2

GW-12 7/21/2009 Chromium Ref. 21, p. 22; Ref. 135, p. 3

GW-098

80 (Ref. 90, p. 29)

2710 msl ***

5/21/2009 Chromium VI Ref. 17, pp. 47-49; Ref. 135, p.3

6/9/2009 Chromium VI Ref. 17, p. 75; Ref. 135, p. 3

9/22/2009 Chromium Ref. 21, p. 59; Ref. 135, p. 3

GW-099

80 (Ref. 90, p. 30)

2709 msl ***

5/19/2009 Chromium VI Ref. 12, p. 28; Ref. 135, p. 3

6/10/2009 Chromium VI Ref. 17, p. 83; Ref. 135, p. 3

9/17/2009 Chromium Ref. 26, p. 19; Ref. 135, p. 3

GW-102

78 (Ref. 90, p. 32)

2705 msl ***

5/20/2009 Chromium VI Ref. 17, pp. 17-19; Ref. 135, p. 3

6/10/2009 Chromium VI Ref. 17, p. 85; Ref. 135, p. 3

GW-103

120 (Ref. 90, p. 33)

2684 msl ***

5/20/2009 Chromium VI Ref. 12, p. 30; Ref. 135, p. 3

6/10/2009 Chromium VI Ref. 17, pp. 83-85; Ref. 135, p. 3

9/17/2009 Chromium Ref. 21, p. 43; Ref. 135, p. 3

GW-104 80 (Ref. 90, p. 34)

2706 msl ***

5/21/2009 Chromium VI Ref. 17, p. 45; Ref. 135, p. 3

GW-104 6/10/2009 Chromium VI Ref. 17, p. 85; Ref. 135, p. 3

GW-104 6/30/2009 Ref. 19, p. 32; Ref. 135, p. 3

GW-11 7/22/2009 Chromium Ref. 88, pp. 1-10; Ref. 135, p. 3

GW-104 9/17/2009 Chromium Ref. 21, p. 39; Ref. 135, p. 3

GW-126 80 (Ref. 90, p. 42)

2696 msl ***

5/20/2009 Chromium VI Ref. 17, pp. 25-27; Ref. 135, p. 3

GW-126 6/11/2009 Chromium VI Ref. 17, p. 89; Ref. 135, p. 3

GW-126 9/17/2009 Ref. 23, p. 19; Ref. 135, p. 3

GW-15 7/22/2009 Chromium Ref. 5, pp. 37-38; Ref. 135, p. 3
Hazard Ranking System Document Record West County Road 112 Ground Water

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Well ID**

Well Depth (feet)

Below Ground Surface 

and above Mean Sea 

Level (msl)*

Date 

Collected

Contaminant 

Detected

Reference

GW-150

80 (Ref. 90, pp. 

46,47)

2691 msl ***

6/9/2009 Chromium VI Ref. 16, p. 89; Ref. 135, p. 3

7/1/2009 Chromium Ref. 19, p. 43; Ref. 135, p. 3

7/14/2009 Chromium Ref. 19, p. 85; Ref. 135, p. 3

9/24/2009 Chromium Ref. 21, pp. 75-77; Ref. 135, p. 3

GW-151

80 (Ref. 90, pp. 

46,47)

2690 msl ***

6/9/2009 Chromium VI Ref. 16, p. 90; Ref. 135, p. 3

11/3/2009 Chromium Ref. 44, p. 5-6; Ref. 135, p. 3

GW-152

70 (Ref. 90, pp. 

46,47)

2699 msl ***

6/9/2009 Chromium VI Ref. 16, p. 91; Ref. 135, p. 3

9/23/2009 Chromium Ref. 21, pp. 63-65; Ref. 135, p. 3

GW-160

90 (Ref. 90, p. 49)

2708 msl ***

6/11/2009 Chromium VI Ref. 17, pp. 89-91; Ref. 135, p. 3

GW-34 Not Specified 7/22/2009 Chromium Ref. 5, pp. 39-40; Ref. 135, p. 3

GW-260

90 (Ref. 90, p. 55)

2709 msl ***

7/29/2009 Chromium Ref. 63, p. 4; Ref. 135, p. 4

GW-261 Not specified 7/1/2009 Chromium VI Ref. 23, p. 21; Ref. 135, p. 4

GW-292

80 (Ref. 90, p. 56)

2699 msl ***

9/15/2009 Chromium Ref. 21, pp. 5-6; Ref. 135, p. 4

GW-293

140 (Ref. 90, p. 57)

2639 msl *** 9/15/2009 Chromium Ref. 21, pp. 7-8; Ref. 135, p. 4

GW-336

74 (Ref. 90, p. 62)

2715 msl ***

11/4/2009 Chromium Ref. 23, p. 75; Ref. 135, p. 4

GW-344

65 (Ref. 90, p. 63)

2753 msl ***

9/16/2009 Chromium Ref. 26, p. 9; Ref. 135, p. 4

Note:

* Ref. 111, pp. 1-2

** Some sample locations have multiple Sample IDs. However, the multiple Sample IDs correspond to the 

same sample location. The multiple Sample ID numbers are due to use of different Sample IDs during different 

sampling events at those sampling locations.

*** Well depth in feet above mean sea level (msl) was determined for each well by subtracting the feet below 

ground surface from the msl identified on the USGS Topographic Map, Southeast Midland 1:24,000, revised 

map dated 1974 obtained from TNRIS.
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2.2.3 Hazardous Substances Available to a Pathway

The containment factor value for Source 1 is greater than 0 (see Containment in Section 2.2.1

of this documentation record). The following hazardous substances associated with the 

ground water plume source can migrate via the ground water pathway:

Table 2: Hazardous Substance Available to a Pathway

Hazardous Substances

Air Pathway Ground 

Water 

Surface Water Soil Exposure

Gas Particulate Overland/

Flood

GW to 

SW Resident Nearby

Chromium NS NS Y NS NS NS NS

Chromium VI NS NS Y NS NS NS NS

Notes and Qualifiers:

NS = Not Scored

Y = Yes

2.3 

2.4 

Likelihood of Release

Refer to Section 3.1 of this documentation record for specific information related to 

Likelihood of Release to the Ground Water Pathway. 

2.4.1 

Waste Characteristics

Selection of Substance Potentially Posing Greatest Threat

The hazardous substances with the highest toxicity/mobility factor values available to the 

ground water migration pathway are chromium (10,000) and chromium VI (10,000). 

Therefore, chromium and chromium VI are the hazardous substances associated with this 

source posing the greatest hazard (Ref. 1, Sections 2.4.1.2, 3.2.1). 

Hazardous Waste Quantity

 

2.4.2.1 

2.4.2.1.1 

Source Hazardous Waste Quantity

Hazardous Constituent Quantity (Tier A)

2.4.2 

2.4.2.1.2 

 – Not Evaluated (NE)

The information available is not sufficient to evaluate Tier A as required in Section 2.4.2.1.1 

of the HRS, which is to determine mass of the hazardous substance present in the waste 

source. As a result, the evaluation of Hazardous Waste Quantity proceeds to the evaluation 

of Tier B, hazardous waste quantity (Ref. 1, Section 2.4.2.1.1). 

Hazardous Waste Stream Quantity (Tier B)

There is not sufficient information to evaluate Tier B which requires determining mass of the 

hazardous substance and additional CERCLA pollutants and contaminants that are allocated 

to the source as required in the HRS. (Ref. 1, Section 2.4.2.1.2) As a result the evaluation of 

 - NE
Hazard Ranking System Document Record West County Road 112 Ground Water

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Hazardous Waste Quantity proceeds to the evaluation of Tier C, volume (Ref. 1, Section 

2.4.2.1.2). 

2.4.2.1.3 Volume (Tier C) 

For the migration pathways, the source is assigned a value for volume using the appropriate 

Tier C equation from HRS Table 2-5 (Ref. 1, Section 2.4.2.1.3). The hazardous waste 

quantity for a plume site with no identified source can be determined by measuring the area 

within all observed release samples combined with the vertical extent of contamination to 

arrive at an estimate of the plume volume (Ref. 24, p. 4). 

However, the extent of the ground water plume is unknown because existing water wells are 

the only locations where chromium and chromium VI have been documented to date. 

Therefore, the volume of the ground water plume is assigned a volume hazardous waste 

quantity value greater than (>) 0. The value of >0 reflects that the volume is known to be 

greater than 0, but the exact amount is unknown. 

2.4.2.1.4 Area (Tier D)

2.4.2.1.5 

 - NE

The area measure (Tier D) cannot be evaluated because the hazardous waste quantity table in 

the HRS (Ref.1, Table 2-5) does not provide a divisor for source type “other” in this tier 

(Ref. 24, p. 4). 

Source Hazardous Waste Quantity Value

As described in the HRS, the highest value assigned to a source from among the four tiers of 

hazardous constituent quantity (Tier A), hazardous waste stream quantity (Tier B), volume 

(Tier C) or area (Tier D) was selected as the source hazardous waste quantity value (Ref. 1, 

Section 2.4.2.1). 

Table 3: Source Hazardous Waste Quantity Source 1 - Other - Ground Water Plume 

with No Identified Source

Tier Measure Migration Pathway (Ground Water) 

Tier A, Constituent Quantity NE

Tier B, Waste stream Quantity NE

Tier C, Volume > 0

Tier D, Area 0 

NE = Not Evaluated

Source No. 1, Other - Groundwater Plume with No Identified Source, Hazardous 

Waste Quantity Value: > 0
Hazard Ranking System Document Record West County Road 112 Ground Water

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SOURCE SUMMARY

The TCEQ SSDAP and Region 7 office conducted initial sampling and monitoring activities 

from April to November 2009 at the West County Road 112 Ground Water Site. During the 

initial assessment period, approximately 234 water wells were sampled (Ref. 104, p. 1). The 

source hazardous waste quantity and containment for the site is summarized in the table 

below. 

The hazardous constituent quantity data is not adequately determined for one or more sources 

for the site. The targets for the Ground Water Migration Pathway are subject to Level I 

concentrations (see Table 15 through Table 18). 

Table 4: Source Summary

Source 

Number

Source Hazardous 

Waste Quantity 

Value

Containment

Ground 

Water Surface Water Soil Exposure Gas Air Particulate

1 > 0 10 NE NE NE NE

TOTAL > 0

NE = Not Evaluated
Hazard Ranking System Document Record West County Road 112 Ground Water

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POSSIBLE SOURCES

The site is designated as a chromium contaminated ground water plume originating from an 

unknown source or sources. A number of known industries use or have historically used 

chromium and/or are located hydraulically up-gradient within one mile of the site. In 

addition, the center of the site was investigated as a possible source. The ESI focused on the 

following locations as possible sources of the chromium contamination: 

1. The Dowell Midland facility now known as the Schlumberger Technology 

Corporation is located north within 1 mile of the site boundary. The Dowell Midland 

facility, a division of Schlumberger Technology Corporation, is in the TCEQ’s 

corrective action program (SWR # 33591) due to a release of volatile organic 

compounds (VOCs) to the ground water (Ref. 126, p. 1). The Dowell Midland 

facility is monitoring ground water for VOCs, chloride, total petroleum hydrocarbons, 

nickel, sulfates, carbonate, bicarbonate, calcium, magnesium, sodium, potassium, and 

arsenic (Ref. 118, pp. 5; Ref. 126, p. 1). In 1994, the soil and ground water at the 

facility were tested for the presence of chromium. Because the analytical results for 

chromium were below action levels, the TCEQ determined no further action was 

warranted to monitor chromium in the ground water (Ref. 125, p. 1). The Notice of 

Registration (NOR) for industrial and hazardous waste at the above location does not 

indicate that chromium is or has been used at the facility (Ref. 114). Although the 

NOR for the facility does not indicate that chromium has been used or managed at the 

facility, it is hydraulically up-gradient of the site and is considered a possible source 

(Ref. 117, p. 23; see also Section 2.2.1 of this HRS documentation record). 

2. The B&W Welding and Construction facility (EPA ID No.TXD981055080) is an 

abandoned metal fabrication and welding facility located approximately 3⁄4 of a mile 

northwest of the center of the facility. The B&W Welding and Construction facility 

is hydraulically up-gradient of the site (Ref. 117, p. 22; see also Section 2.2.1 of this 

HRS documentation record). Since 1984, the site has been investigated for releases 

of chromium to soil and ground water (Ref. 113, pp. 7-8). An assessment conducted 

by Lear Corporation (SWR # 23041) identified a 100-foot-long by 40-foot-wide area 

of chromium impacted ground water at the B&W facility; however, according to Lear 

Corporation’s assessment, the source of the chromium release had not been identified 

onsite (Ref. 115, pp. 2-3). The Lear Corporation operated a plastic manufacturing 

plant and was cross-gradient from the B&W facility. The Lear Corporation had taken 

responsibility for the cleanup of the total and hexavalent chromium ground water 

contamination on the B&W site; however, the Lear Corporation has filed for 

bankruptcy and is no longer providing remedial actions at the B&W facility (Ref. 

127, p. 1). 

3. The Williamson Gravel Pit is located 3⁄4 of a mile north of the center of the site 

(Figure 1c). Local residents and a B&W Welding and Construction report have 

claimed that illegal disposal of chromium may have occurred at the Williams Gravel 

Pit, which is a caliche borrow pit (Ref. 113, pp. 6-7). The Williamson Gravel Pit is 
Hazard Ranking System Document Record West County Road 112 Ground Water

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located hydraulically up-gradient of the site and located hydraulically down-gradient 

of the B&W and Schlumberger Technology Corporation sites (Ref. 117, p. 23; see 

also Section 2.2.1 of this HRS documentation record). 

4. The center of the site (2604 West County Road 112) is the discovery location of the 

hexavalent chromium ground water contamination (Ref. 103, pp. 1-2). The TCEQ’s 

analytical results from the drinking water well (at 2604 WCR 112) indicate this 

location has the highest concentration of chromium (5.25 mg/L) detected in the 

ground water associated with the ground water chromium plume (Ref. 103, p. 3). The 

current residents bought the house in 2000 (Reference 103, pp. 6). When they moved 

into the dwelling, the external and internal property was in disarray (Ref. 103, pp. 

11). The current residents do not have any knowledge of wastes buried on their 

property; however, there were empty marked and unmarked 55-gallon drums on-site 

when the current residents moved into the house. The drums were later disposed of 

by the TCEQ’s contractor at a drum disposal facility. The center of the site is 

hydraulically down-gradient of the B&W facility, Williamson Gravel Pit, and 

Schlumberger Technology Corporation (Ref. 117, p. 23; see also Section 2.2.1 of this 

HRS documentation record).
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3.0 GROUND WATER MIGRATION PATHWAY

3.0.1 General Considerations

The primary drinking water aquifer in Midland County and underlying the Site is the 

Edwards-Trinity aquifer (Ref. 7, p. 5; Ref. 8, p. 18). The Edwards-Trinity aquifer is the most 

significant source of water on the Edwards Plateau, which covers approximately 23,000 

square miles in southwest Texas (Ref 8, p. 69). Most recharge to the Edwards-Trinity aquifer 

results from the infiltration of precipitation from land surface and seepage losses through 

stream beds and intermittent streams (Ref. 7, p. 44). An uncertain amount of crossformational flow from the Ogallala aquifer provides recharge to the Edwards-Trinity aquifer 

system in the northwestern portion of the aquifer (Edwards-Trinity aquifer near Site) (Ref. 8, 

p. 60). 

A secondary source of drinking water under the Site is the Ogallala aquifer, which 

stratigraphically overlies the Edwards-Trinity aquifer (Ref. 8, pp. 20, 73). The Ogallala 

Formation sediments often occur above the water table in Ector, Midland and Glasscock 

counties where saturated Cretaceous sediments (i.e., Trinity Group Formation of the 

Edwards-Trinity aquifer) form the predominant aquifer (Ref. 8, p. 69). Where significant 

saturated thickness occurs in Cretaceous sediments, the Trinity Group Antlers sand [EdwardTrinity aquifer] is the dominant aquifer material and it is difficult to differentiate between 

both aquifers [the Ogallala and Edward-Trinity aquifers] (Ref 8, p. 69). Although the 

Ogallala is not a major drinking water source in the vicinity of the Site, drinking water wells 

at the Site are typically screened in both aquifers to promote hydraulic communication

between the aquifers so water availability will be optimized (Ref. 9, p. 25; Ref. 111, p.2). 

The boundary between the two aquifers [Ogallala and Edwards-Trinity] is transitional and is 

not well defined in the Southern High Plains and the northwestern margin of the Edwards 

Plateau (the location of the Site) (Ref. 8, p.73). This area is where a transition occurs 

between the Southern Ogallala and Edwards- Trinity aquifers (Ref. 8, p. 69). Wells in the 

vicinity of the Site typically have a fine-grained layer (e.g., clay) or slate or shale layer that 

differentiates the Ogallala formation [aquifer] from the underlying Trinity Group Formation

of the Edwards-Trinity aquifer (Ref. 11, pp 5, 10, 13, 15; Ref. 33, pp. 3, 7; Ref. 39, pp. 3, 5, 

11, 17, 19; Ref 111, p. 1-2;). 

Average annual precipitation for Midland County is 15-20 inches per year (Ref. 11, p. 6). 

The center of the site is most likely on Arvana fine sandy loam soil of low relief and a typical 

profile of loamy eolian deposits up to 40 inches below ground surface. The soil is well 

drained with variable permeability (Ref. 12, pp. 1-4).

To understand the hydrogeologic or aquifer characteristics of the Ogallala and 

Edwards-Trinity aquifers, the geologic strata that compose the aquifers are described first. 

The geologic strata, from youngest to oldest, are: 
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Stratum: 1 

Stratum Name: Eolian

Post-Ogallala Formation sediments consist primarily of windblown (eolian) sand and silt, 

alluvium, and lucustrian deposits (playa lake deposits). Eolian sands occupy the largest 

surface area of the High Plains of Texas and are of both Pleistocene and Recent (Holocene) 

age. They are primarily fine-grained to silty, sometimes calcareous, and are derived from 

lacustrine, fluvial, and eolian deposits. These sands and silts form sheet or cover sand, 

dunes, and dune ridges with thicknesses generally ranging from 0 to 10 feet. Alluvium is 

present as fluvial floodplain and terrace sediments along the more active streams and rivers. 

The deposits consist of poorly sorted, often cross-bedded, gravel, sand, and silt. Lacustrine 

deposits, consisting primarily of clay and silt, line the bottom of the many playa lakes on the 

High Plains (Ref. 9, p. 33). 

At the West County Road 112 Ground Water Site, the surface and shallow subsurface 

deposits attributed to eolian or lucustrian deposits are typically encountered from the surface 

to a depth of about 15 feet. The deposits are typically brown sand, sandy silts, and silty 

sands (Ref. 11, pp 4, 5, 9, 12, 14; Ref. 39, pp. 3, 5, 11, 15, 19).

Geologic Stratum: 2 

Stratum Name: Caliche

Caliche deposits underlie much of the surface of the Southern High Plains of Texas and 

typically separate the Ogallala Formation from overlying eolian sediments of Pleistocene and 

Recent age deposits. Near the surface of much of the Texas High Plains are layers of 

resistant caliche known as “caprock”. Caliche occurs in both Ogallala and post-Ogallala 

sediments and is formed by the leaching of carbonate and silica from surface soils and the 

redeposition of the dissolved minerals layers below the surface. Although caliche layers 

occur primarily near the surface, deeper zones of caliche are also present (Ref. 9, p. 28). 

At the West County Road 112 Ground Water Site, significant caliche horizons are typically 

encountered near the ground surface in the soils at approximately 3 to 15 feet below ground 

surface (Ref. 11, pp 4, 5, 9, 12, 14; Ref. 39, pp. 3, 5, 11, 15, 19).

Geologic Stratum: 3 

Stratum Name: Ogallala Formation

Tertiary sediments - While deposition was occurring in the Gulf of Mexico in 

post-Cretaceous geologic history, widespread uplift and erosion was occurring in 

west-central Texas. A large volume of Cretaceous rock was removed from present day 

Midland County during late Mesozoic through early Cenozoic time (i.e., Paleocene, 

Miocene, and Pliocene), as the result of structural deformation, salt dissolution, and erosion 

along what is now the Pecos River Valley. Then, during the Cenozoic Era, a thick 
Hazard Ranking System Document Record West County Road 112 Ground Water

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succession of off-lapping deltaic deposits built the plains along the coast with detritus eroded 

from Paleozoic and Mesozoic rocks from the uplifted continental interior (Ref. 25, p. 20). 

The Ogallala Formation of late Miocene/Pliocene age unconformably overlies Cretaceous 

aged sediment (Ref. 9, p. 13). Ogallala sediments consist primarily of fine- to coarse-grained 

elastics from the southern Rocky Mountains to the west (Ref. 9, p. 13). The sands are 

generally tan, yellow, or reddish brown, medium- to coarse-grained, moderately- to wellsorted, unconsolidated quartz grains, interbedded with thin layers of clay and occasionally 

sandstone. Gravel commonly occurs in layers in the basal section of the Ogallala Formation 

and ranges in size from boulders to pea size. The gravel is usually associated with sand, silt, 

and clay and is occasionally cemented. Quartzite is the predominant rock type in the gravel, 

although a high percentage of limestone boulders and cobbles occur in the southern third of 

the study area along with weathered Cretaceous invertebrate fossils (Ref. 9, p. 27). 

At the West County Road 112 Ground Water Site, sediments attributed to the Ogallala 

Formation are typically encountered from approximately 10 feet to 60 feet bgs. These 

deposits are primarily sands, silty sands with clay and gravel deposits, which grade into 

sandstones in the deeper deposits. Often, the bottom confining layer will have clay, slate or 

shale to mark the top of the Trinity Group Formation (Ref. 11, p. 7; Ref. 39, pp. 9, 7, 21).

Geologic Stratum: 4 

Stratum Name

The Trinity Group is represented by the Antlers Formation in the southern part of the High 

Plains area. These rocks are considered to be equivalent to the Paluxy Sand of Central 

Texas, and are generally referred to as the “Trinity Sand” in the High Plains (Ref. 9, p. 24). 

In places, the Antlers forms a basal sand unit (aka. Basal Cretaceous Sands) in the 

Cretaceous system in the southeastern and southern portions of the High Plains (Ref. 8, p. 

49). It is a white to purple, loosely consolidated, fine- to coarse-grained, quartz sandstone, 

locally hard, and commonly interbedded with fine-grained yellow sand, green clay, and gray 

to pink siltstone. Scattered lenses of gravel occur throughout the unit, but a more persistent, 

basal conglomeratic unit with interbedded coarse sand is present in most sections. Where a 

sufficient saturated thickness of Ogallala sediments overlies the Antlers, the well completion 

interval usually encompasses both formations. In Ector, Midland, and part of Glasscock 

: Trinity Group Formation 

Early Cretaceous sediments - The Trinity Group rock record indicate a cyclic pattern of 

shoreline advance and retreat, superimposed upon an overall pattern of marine transgression 

(Ref. 25, p. 11). In early Cretaceous times, a broad continental shelf formed around a rifting 

and subsiding ancestral Gulf of Mexico basin. The Edwards and Trinity strata formed atop 

and landward of this continental shelf. As the sea level rose and advanced westward, inland 

alluvial plains deposited clastic materials along shorelines (Ref. 25, p. 11). The Trinity sands 

were formed west of the Llano uplift where "typically it amassed as a sprawling, braided 

stream deposit atop an eroded surface of the pre-Cretaceous rocks" (Ref. 25, p. 15). Shallow 

offshore environments also promoted the biogenic accumulation of calcium carbonate (Ref. 

25, p. 11). 
Hazard Ranking System Document Record West County Road 112 Ground Water

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Counties, the Antlers sand yields more water of acceptable quality than any other waterbearing formation. (Ref. 9, p. 25). 

At the West County Road 112 Ground Water Site, the Trinity Group is typically encountered 

from approximately 65 feet bgs to approximately 100 feet bgs. The Trinity Group is usually 

tan sandstone with layers of clay interbedded. Usually, the bottom confining unit is the red 

clays and shales of the Chinle Formation of the Dockum Group at approximately 100 feet 

bgs in the Site vicinity (Ref. 11, pp 6, 7, 13, 15; Ref. 39, pp. 7, 9, 13, 17, 21).

Geologic Stratum: 5 

Stratum Name: Dockum Group

Late Triassic sediments - During the late Triassic time, Paleozoic rocks were eroded from the 

surrounding high ground and deposited in low-lying fluvial, deltaic, and lacustrine 

environments as red beds of the Dockum Group (Ref. 7, pp. 14 and 16). The Upper Dockum 

Group is comprised of the Trecovas, Santa Rosa, and the uppermost Chinle formation, which 

underlies the Trinity Group at the site. The Chinle Formation consists of up to 600 feet of 

red, blue, and reddish brown clays and shales (Ref. 9, p. 22). At the West County Road 112 

Ground Water Site, the Chinle Formation of the Dockum Group is typically encountered 

below the Trinity Group at approximately 100 feet bgs depending on site-specific geology 

(Ref. 11, pp 1-16). 

Aquifer System

The aquifers that have been impacted by the West County Road 112 Ground Water Site are 

the Ogallala and the Edwards-Trinity aquifers (Ref. 7, p. 7; Ref. 25, p.3). Regionally, the site 

falls within an area where one major aquifer system ends and another one begins: The High 

Plains aquifer system, mainly the Ogallala Formation in the study area, overlies the eroded 

surface of the Trinity Group, mainly the Trinity Sands/Antlers Formation, which is at the 

extreme upgradient part of the Edwards-Trinity aquifer System (Ref. 10, p.8; Ref. 7, pp. 20-

21). Specifically, the Edwards-Trinity aquifer consists of Mesozoic (Cretaceous) formations, 

which are underlain by Paleozoic (Triassic) formations and overlain by Cenozoic (Tertiary

and Quaternary) formations (Ref. 7, pp. 20-21). 

The hydrogeologic units present at the site are as follows, from youngest to oldest: 

Hydrogeologic Stratum: 1 

Stratum Name: High Plains/Ogallala/Tertiary Aquifer

The Ogallala aquifer is located in Andrews, Ector, Glasscock, Howard, Martin, and Midland 

counties in the Edwards Plateau area. The Ogallala aquifer is composed primarily of sand, 

gravel, clay, and silt and generally has a saturated thickness of less than 100 feet in the 

Edwards Plateau area. The Ogallala aquifer partially overlies the Edwards–Trinity (Plateau) 

aquifer in the Edwards Plateau area (Ref. 8, p. 20). 
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As the ancestral Rocky Mountains were eroded during the Tertiary, southeasterly flowing 

streams carried and deposited sediments to their present day locations across the Texas High 

Plains and ending in Midland County. The earliest sediments, mainly gravel and coarse 

sand, filled the valleys cut in the Cretaceous, Triassic, and Permian surfaces (Ref. 22, p.17). 

The Ogallala Formation consists of red and yellow clay, silt, fine to coarse gray and buff 

colored sand, gravel and caliche (Ref. 22, p. 31). The fine to coarse sand, with the fine to 

medium grades predominate (Ref. 22, p. 32). In the Odessa-Midland area, the Ogallala 

Formation consists of reworked basal conglomerates of Triassic and Cretaceous fragments 

locally overlain by fine pink sandstone and/or caliche Acaprock@ with a maximum thickness 

of approximately 20 to 25 feet (Ref. 22, p. 32). Caprock consists of caliche cemented with 

silica, but containing many cracks and fractures (Ref. 14, pp. 3, 10) that allow water to 

recharge the Trinity Group. The top portion of the Ogallala Formation is layers of caliche 

formed by the leaching of calcium carbonate and silica from surface soils during the PlioPlestocene era. The caliche ranges in thickness from 20 to 35 feet, varies from crumbly to 

very hard and can be relatively impermeable in local areas. The caliche layer forms the 

Acaprock@ of the Texas High Plains region (Ref. 22, pp. 36-38). 

The Ogallala Aquifer will usually yield large amounts of water (Ref. 10, p. 8). However, at 

the site, the Ogallala and the Trinity aquifers are nearly indistinguishable (Ref. 8, p.73). 

Recharge to the Trinity Group (Edwards-Trinity aquifer) occurs indirectly by downward 

percolation or infiltration from the overlying Ogallala (Ref. 10, p. 16). Cross-formational 

recharge occurs most readily, where saturated sand and gravel beds in the Ogallala Formation 

abut against, or overlie porous and permeable parts of the Antlers (Ref. 10, p. 23). 

The Monahan’s Draw located to the south of the site and the Midland Draw located to the 

east of the site is within the High Plains/Ogallala/Tertiary aquifer system, which can 

influence the ground water flow direction in the area of the site.

Hydrogeologic Stratum: 2 

Stratum Name

The Edwards-Trinity aquifer system underlies about 42,000 square miles of west-central 

Texas in the Edwards Plateau and Trans-Pecos area (Ref. 7, pp. 5, 9). The aquifer is 

sometimes referred to as the Edwards-Trinity Plateau aquifer (Ref. 7, p. 9). The EdwardsTrinity aquifer is usually hydraulically connected to the Ogallala sediments where both are 

present (Ref. 8, p. 83). The Edwards-Trinity aquifer is primarily composed of the Trinity 

Group Sand in the West County Road 112 (site) area that typically consists of white to 

purple, loosely, consolidated, fine- to coarse grain well-sorted, unfossiliferous, quartz 

sandstone containing scattered lenses of quartz gravel (Ref. 22, p. 24). The sandstone can be 

cemented by silica. Lenses of red clay are scattered throughout (sometimes mistaken for the 

Upper Dockum - Triassic Red Beds) and a coarse conglomerate about 5 to 10 feet thick, 

consisting of red and black pebbles of chert and other quartz varieties generally occur at the 

base of the sandstone. In the Midland area, the Trinity Group Sand has been found to be 

medium to coarse rounded, white sand, locally ferruginous, weathering to a rust color, and

: Edwards-Trinity (Plateau) Aquifer
Hazard Ranking System Document Record West County Road 112 Ground Water

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containing white, black, and red pebbles scattered throughout, but particularly abundant at 

the base (Ref. 22, pp.22-24). 

The Trinity Group is primarily composed of sands from the Antlers and Maxim limestones 

(Ref. 8, p. 18; Ref. 13, p. 4). Permeable sands and gravels, and clays make up the Trinity 

Group Sands or Antlers Formation. From the northwestern part of the Edwards Plateau, 

water generally flows southeastward under hydraulic gradients that average about 10 

feet/mile (Ref. 25, pp. 34-41). Local exceptions to the regional pattern result from 

topographic and drainage variations and depressions in the ground water table caused by 

pumpage. The maximum hydraulic head occurs in northwestern Midland County at about 

3,100 feet above sea level. In Midland county, most recharge results from infiltration of 

precipitation from land surface and most discharge occurs through well withdraw. Water 

levels in Midland County have dropped 50 feet over last 50 years. Transmissivity values are 

approximately 5,000 feet2

/day (Ref. 25, pp. 34-41).

Hydrogeologic Stratum: 3 

Stratum Name: Upper Dockum or Chinle Formation 

The Dockum aquifer is located in the vicinity of the Site and extends to the north and to the 

northwest into New Mexico (Ref. 8, pp. 16-18). The Dockum aquifer consists of up to 700 

feet of sand and conglomerate with layers of silt and shale of the Dockum Group (Ref. 8, p. 

18). 

During the late Triassic time, Paleozoic rocks were eroded from the surrounding high ground 

and deposited in low-lying fluvial, deltaic, and lacustrine environments as red beds of the 

Dockum Group. The Upper Dockum Group is comprised of the Trecovas, Santa Rosa, and 

Chinle formations (Ref. 22, p.19). 

The Chinle formation is considered the upper part of the Dockum Group and it underlies the 

Trinity Group (Edwards-Trinity aquifer) at the West County Road 112 Ground Water site. 

The upper part of the Dockum contains the largest percentages of siltstone and shale (Ref. 

22, pp. 18-19). The thickness of Chinle Formation varies from 175 to 1,800 feet (Ref. 22, p. 

19). In Midland County, the Chinle or upper part has been reported to be approximately 600 

feet thick and dipping toward the west (Ref. 22, p. 20). The formation consists mainly of 

brick red to maroon and purple shale (Ref. 22, pp.18-19), and commonly referred to as Ared 

beds@. 

The underlying mudstone sequences in the Dockum Group are considered the lower 

confining layer to the Edward-Trinity Aquifer in the study area (Ref. 10, p. 18), and do not 

yield large quantities of water (Ref. 10, p. 8). 
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3.1 Likelihood of Release

3.1.1 Observed Release

An observed release was documented to the ground water pathway for the site by chemical 

analysis. To establish an observed release by chemical analysis, it requires analytical 

evidence of a hazardous substance in the media significantly above the background level. If 

the background concentration is not detected, or is less than the detection limit, an observed 

release is established when the sample quantitation limit equals or exceeds its own sample 

quantitation limit and that of the background sample (Ref. 1, Section 2.3, Table 2-3). 

Background Concentration 

Regional ground water flow through the Antlers Formation of the [Edward Trinity aquifer] is 

generally to the east-southeast in conformance with regional structure and dips (Ref. 10, p. 

18; Ref. 7, p 44). Another factor that influences ground water flow movement through the 

Antlers Formation [Edward-Trinity aquifer] are eroded channels cut into the late Triassic 

Formation [Dockum] (Ref. 10, p. 18). Two background samples were collected outside of 

the plume area and up-gradient to the Site based on regional ground water flow conditions 

(Ref. 10, p. 18; Ref. 7, p 44). These samples were collected in drinking water wells at depths 

similar to the depths of drinking water wells at the Site. Not all of the depths for the water 

wells are specified due to lack of information; however, according to residents and local well 

drillers, the common drilling practice in the area is to install wells within the Edwards/Trinity 

Formation to a maximum depth of approximately 100 feet bgs (Ref. 111, pp. 1-2). Thus, the 

background and release samples are likely from the same aquifer and have the same sample 

similarity. All samples were collected according to the EPA-approved state Quality 

Assurance Project Plan (QAPP) and sample locations were approved by the EPA (Ref. 112). 

Table 5 provides a summary of the background ground water samples collected. Table 6 

provides a summary of the designated background levels for the hazardous substances of 

concern for this site. 

Table 5: Background Ground Water Samples Collected

Sample ID* Sample Location Well Depth (feet) Date Collected Reference

GW-10 Drinking water well

3000 W I-20

located at 90 (Ref. 110, p. 3)

7/20/2009 Ref. 6, p. 2

GW-160 6/11/2009 Ref. 17, pp. 89-91

GW-22 Drinking water well located at 

3004 S CR 1207

68 (Ref. 90, p. 20)

7/20/2009 Ref. 6, p. 1

GW-066 5/13/2009 Ref. 12, p. 12

* Background sample locations have multiple Sample IDs. The multiple Sample IDs correspond to the same

sample location. The multiple Sample ID numbers were due to use of different Sample IDs during different 

sampling events at these sampling locations. 
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Table 6: Summary of Highest Constituents Detected in the Background Ground

Water Wells

Sample ID Organic Constituent

Highest 

Concentration 

[SQL] μg/L*

3 x Highest 

Background 

Concentration

Reference

GW-10 Chromium ND [10] NA + Ref. 6, p. 2; Ref. 89, pp. 8

& 238 

GW-160 Chromium VI ND [0.01 mg/L] NA _

Ref. 17, pp. 89-91; Ref. 

38, pp. 6 & 16; Ref. 74, p. 

5 

GW-22 Chromium ND [10] NA + Ref. 6, p. 1; Ref. 89, pp. 

20 & 238

GW-066 Chromium VI ND [0.01 mg/L] NA _ Ref. 12, p. 12; Ref. 29, pp. 

29 & 114; Ref. 29, p. 29

Notes: 

ND = Not Detected at the SQL.

[SQL] = Sample Quantitation Limit.

NA = Not applicable.

+ = Reported as Reporting Limit by Region 6 Laboratory. 

- = Reported as MQL UnAdj. by Xenco Laboratories.

* For all of the analyses the reporting limit in the references cited is the SQL based on the method detection limit (Ref. 134).

Given that all of the background samples have no detected chromium or chromium VI, the 

background level is ND [10 μg/L] and ND [0.01 mg/L] respectively. 

Contaminated Samples

The samples in Table 7 through Table 11 meet the observed release criteria and are presented 

below indicating hazardous substances with their concentrations and SQLs. These samples 

were qualified as “releases” based on the criteria in HRS Table 2-3 (Ref. 1, Section 2.3). 

Table 7: Contaminated Ground Water Pathway Drinking Water Samples Meeting 

Observed Release Criteria (May 2009 Results)

Sample Location Contaminant 

Detected

Conc. 

(mg/L)

SQL-

(mg/L)* Reference

GW-011-A Chromium VI 1.04 0.05 Ref. 27, pp. 20 & 75; Ref. 64, p. 31

GW-020-A Chromium VI 0.435 0.01 Ref. 27, pp. 26 & 75; Ref. 64, p. 37

GW-048-A Chromium VI 0.621 0.01 Ref. 27, pp. 5 & 75; Ref. 64, p. 12

GW-049-A Chromium VI 1.24 0.05 Ref. 27, pp. 15 & 75; Ref. 64, p. 25

GW-050-A Chromium VI 1.21 0.05 Ref. 27, pp. 10 & 75; Ref. 64, p. 18

GW-023-A Chromium VI 1.12 0.05 Ref. 28, pp. 16 & 112; Ref. 65, p. 26

GW-042-A Chromium VI 4.02 0.5 Ref. 28, pp. 55 & 114; Ref. 65, p. 65

GW-043-A Chromium VI 0.519 0.01 Ref. 28, pp. 6 & 112; Ref. 65, p. 14
Hazard Ranking System Document Record West County Road 112 Ground Water

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Table 7: Contaminated Ground Water Pathway Drinking Water Samples Meeting 

Observed Release Criteria (May 2009 Results)

Sample Location Contaminant 

Detected

Conc. 

(mg/L)

SQL-

(mg/L)* Reference

GW-044-A Chromium VI 1.81 0.05 Ref. 28, pp. 32 & 113; Ref. 65, p. 39

GW-045-A Chromium VI 1.23 0.05 Ref. 28, pp. 57 & 114; Ref. 65, p. 72

GW-046 Chromium VI 0.929 0.05 Ref. 28, pp. 22 & 112; Ref. 65, p. 32

GW-047 Chromium VI 4.56 0.5 Ref. 28, pp. 39 & 113; Ref. 65, p. 46

GW-057 Chromium VI 0.026 0.01 Ref. 29, pp. 19 & 114; Ref. 66, p. 30

GW-058 Chromium VI 0.052 0.01 Ref. 29, pp. 69 & 115; Ref. 66, pp. 92

GW-064 Chromium VI 0.041 0.01 Ref. 29, pp. 54 & 115; Ref. 66, pp. 74

GW-083 Chromium VI 0.02 0.01 Ref. 29, pp. 74 & 115; Ref. 66, p. 98

GW-081 Chromium VI 0.322 0.01 Ref. 30, pp. 54 & 102; Ref. 67, p. 74

GW-082 Chromium VI 0.017 0.01 Ref. 30, pp. 49 & 102; Ref. 67, p. 68

GW-086 Chromium VI 1.42 0.05 Ref. 30, pp. 29 & 101; Ref. 67, p. 42

GW-091-A Chromium VI 0.291 0.01 Ref. 31, pp. 4 & 29; Ref. 68, p. 7 

GW-092-A Chromium VI 0.437 0.01 Ref. 31, pp. 6 & 29; Ref. 68, p. 7

GW-093-A Chromium VI 0.109 0.01 Ref. 31, pp. 7 & 29; Ref. 68, p. 7

GW-095-A Chromium VI 0.202 0.01 Ref. 31, pp. 5 & 29; Ref. 68, p. 7

GW-096-A Chromium VI 0.223 0.01 Ref. 31, pp. 11 & 31; Ref. 68, p. 9

GW-097-A Chromium VI 0.207 0.01 Ref. 31, pp. 8 & 30; Ref. 68, p. 8 

GW-099-A Chromium VI 0.294 0.01 Ref. 31, pp. 10 & 30; Ref. 68, p. 8 

GW-100-A Chromium VI 2.34 0.05 Ref. 31, pp. 12 & 31; Ref. 68, p. 9

GW-101-A Chromium VI 1.51 0.05 Ref. 31, pp. 9 & 30; Ref. 68, p. 8 

GW-125-A Chromium VI 0.838 0.05 Ref. 31, pp. 13 & 31; Ref. 68, p. 9

GW-090-A Chromium VI 0.481 0.01 Ref. 32, pp. 4 & 24; Ref. 69, p. 7

GW-102-A Chromium VI 0.197 0.01 Ref. 32, pp. 7 & 25; Ref. 69, p. 7

GW-103-A Chromium VI 0.638 0.05 Ref. 32, pp. 5 & 24; Ref. 69, p. 7

GW-105-A Chromium VI 0.132 0.01 Ref. 32, pp. 6 & 24; Ref. 69, p. 7

GW-107 Chromium VI 0.03 0.01 Ref. 32, pp. 7 & 24; Ref. 69, p. 7
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Table 7: Contaminated Ground Water Pathway Drinking Water Samples Meeting 

Observed Release Criteria (May 2009 Results)

Sample Location Contaminant 

Detected

Conc. 

(mg/L)

SQL-

(mg/L)* Reference

GW-108 Chromium VI 0.151 0.01 Ref. 32, pp. 6 & 24; Ref. 69, p. 7

GW-126 Chromium VI 0.115 0.01 Ref. 32, pp. 8 & 25; Ref. 69, p. 8 

GW-127 Chromium VI 0.42 0.01 Ref. 32, pp. 8 & 25; Ref. 69, p. 8

GW-098 A Chromium VI 0.053 0.01 Ref. 34, pp. 7 & 23; Ref. 70, p. 7

GW-104 Chromium VI 0.448 0.01 Ref. 34, pp. 6 & 23; Ref. 70, p. 7

Note:

- = Reported as MDL UnAdj. or MQL Adj. by Xenco Laboratories.

* For all of the analyses the reporting limit in the references cited is the SQL based on the method detection limit (Ref. 134).

Table 8: Contaminated Ground Water Pathway Drinking Water Samples Meeting 

Observed Release Criteria (June 2009 Results)

Sample Location Contaminant 

Detected

Conc. 

(mg/L)

SQL-

(mg/L)* Reference

GW-137-A Chromium VI 1.1 0.05 Ref. 35, pp. 8 & 21; Ref. 71, p. 5

GW-135-A Chromium VI 0.473 0.01 Ref. 35, pp. 5-6 & 20; Ref. 71, p. 5

GW-138-A Chromium VI 1.12 0.05 Ref. 35, pp. 7 & 21; Ref. 71, p. 5

GW-139-A Chromium VI 2.11 0.05 Ref. 35, pp. 9 & 21; Ref. 71, p. 6

GW-136-A Chromium VI 0.605 0.01 Ref. 35, pp. 5 & 20; Ref. 71, p. 5

GW-140-A Chromium VI 1.5 0.05 Ref. 35, pp. 10 & 21; Ref. 71, p. 5-6 

GW-141-A Chromium VI 1.54 0.05 Ref. 35, pp. 4 & 19; Ref. 71, p. 5

GW-142-A Chromium VI 1.57 0.05 Ref. 35, pp. 6 & 20; Ref. 71, p. 5

GW-143-A Chromium VI 4.91 0.1 Ref. 35, pp. 9 & 21; Ref. 71, p. 6

GW-144-A Chromium VI 1.19 0.05 Ref. 35, pp. 7 & 20; Ref. 71, p. 5

GW-145-A Chromium VI 1.29 0.05 Ref. 35, pp. 4 & 19; Ref. 71, p. 5

GW-146-A Chromium VI 0.271 0.01 Ref. 35, pp. 7 & 20; Ref. 71, p. 5

GW-029-A Chromium VI 0.027 0.01 Ref. 36, pp. 7 & 16; Ref. 72, p. 5

GW-090-A Chromium VI 0.455 0.01 Ref. 36, pp. 4-5 & 15; Ref. 72, p. 5

GW-092-A Chromium VI 0.472 0.01 Ref. 36, pp. 6 & 16; Ref. 72, p. 5
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Table 8: Contaminated Ground Water Pathway Drinking Water Samples Meeting 

Observed Release Criteria (June 2009 Results)

Sample Location Contaminant 

Detected

Conc. 

(mg/L)

SQL-

(mg/L)* Reference

GW-093-A Chromium VI 0.18 0.01 Ref. 36, pp. 6 & 16; Ref. 72, p. 5

GW-098-A Chromium VI 0.057 0.01 Ref. 36, pp. 6 & 15-16; Ref. 72, p. 5

GW-150 Chromium VI 0.12 0.01 Ref. 36, pp. 4 & 15; Ref. 72, p. 5

GW-151 Chromium VI 0.068 0.01 Ref. 36, pp. 4 & 15; Ref. 72, p. 5

GW-153 Chromium VI 0.307 0.01 Ref. 36, pp. 5 & 15; Ref. 72, p. 5

GW-091-A Chromium VI 0.302 0.01 Ref. 37, pp. 7 & 19; Ref. 73, p. 5

GW-095-A Chromium VI 0.195 0.01 Ref. 37, pp. 6 & 19; Ref. 73, p. 5

GW-096-A Chromium VI 0.238 0.01 Ref. 37, pp. 7 & 19; Ref. 73, p. 5

GW-097-A Chromium VI 0.18 0.01 Ref. 37, pp. 7 & 19; Ref. 73, p. 5

GW-099-A Chromium VI 0.302 0.01 Ref. 37, pp. 5 & 18; Ref. 73, p. 5

GW-100-A Chromium VI 2.24 0.05 Ref. 37, pp. 4 & 18; Ref. 73, p. 5

GW-101-A Chromium VI 1.62 0.05 Ref. 37, p. 8; Ref. 73, p. 6

GW-102-A Chromium VI 0.193 0.01 Ref. 37, p. 6 & 18;Ref. 73, p. 5

GW-103-A Chromium VI 0.663 0.01 Ref. 37, pp. 5 & 18; Ref. 73, p. 5

GW-104-A Chromium VI 0.441 0.01 Ref. 37, pp. 9 & 20; Ref. 73, p. 6

GW-125-A Chromium VI 0.695 0.01 Ref. 37, pp. 4 & 18; Ref. 73, p. 5

GW-080-A Chromium VI 0.049 0.01 Ref. 38, pp. 4 & 15; Ref. 74, p. 5

GW-081-A Chromium VI 0.31 0.01 Ref. 38, pp. 4 & 15; Ref. 74, p. 5

GW-086-A Chromium VI 1.71 0.05 Ref. 38, pp. 5 & 15; Ref. 74, p. 5

GW-105-A Chromium VI 0.096 0.01 Ref. 38, pp. 5 & 15; Ref. 74, p. 5

GW-126-A Chromium VI 0.1 0.01 Ref. 38, pp. 6 & 15-16; Ref. 74, p. 5

GW-161 Chromium VI 0.025 0.01 Ref. 38, pp. 7 & 16; Ref. 74, p. 5

GW-108-A Chromium VI 0.117 0.005 Ref. 40, pp. 6 & 15; Ref. 75, p. 6

GW-176 Chromium VI 0.086 0.005 Ref. 41, pp. 6 & 15; Ref. 76, p. 5

GW-181 Chromium VI 0.034 0.005 Ref. 43, pp. 6 & 15; Ref. 77, p. 5

GW-187 Chromium VI 0.08 0.005 Ref. 43, pp. 6 & 15; Ref. 77, p. 5

GW-192 Chromium VI 0.032 0.005 Ref. 43, pp. 4 & 14; Ref. 77, p. 5

GW-194 Chromium VI 0.014 0.005 Ref. 43, pp. 5 & 14; Ref. 77, pp. 5

GW-196 Chromium VI 0.012 0.005 Ref. 43, pp. 5 & 14; Ref. 77, pp. 5
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Table 8: Contaminated Ground Water Pathway Drinking Water Samples Meeting 

Observed Release Criteria (June 2009 Results)

Sample Location Contaminant 

Detected

Conc. 

(mg/L)

SQL-

(mg/L)* Reference

GW-197 Chromium VI 0.031 0.005 Ref. 43, pp. 4 & 14; Ref. 77, pp. 5

GW-254-A Chromium VI 0.447 0.005 Ref. 45, p. 7; Ref. 78, p. 5-9; Ref. 95, pp. 8 & 

22

GW-259 Chromium VI 0.036 0.005 Ref. 19, pp. 23-25; Ref. 48, pp. 4 & 11; Ref. 

78, p. 8 

GW-005 Chromium VI 0.051 0.005 Ref. 49, pp. 9 & 25; Ref. 64, p. 12-50

GW-104 Chromium VI 0.437 0.005 Ref. 37, pp. 9 & 20; Ref. 73, pp. 5-6 

Note:

- = Reported as MDL UnAdj. or MQL Adj. by Xenco Laboratories.

* For all of the analyses the reporting limit in the references cited is the SQL based on the method detection limit (Ref. 134).

Table 9: Contaminated Ground Water Pathway Drinking Water Samples Meeting 

Observed Release Criteria (July 2009 Results)

Sample Location Contaminant 

Detected

Conc. 

(mg/L)

SQL-

(mg/L)* Reference

GW-029 Chromium VI 0.023 0.005 Ref. 50, pp. 4 & 15; Ref. 80, pp. 5-6 

GW-036 Chromium VI 0.013 0.005 Ref. 50, pp. 4 & 15; Ref. 80, pp. 5-6 

GW-038 Chromium VI 0.031 0.005 Ref. 50, pp. 5 & 15; Ref. 80, pp. 5-6 

GW-053 Chromium VI 0.018 0.005 Ref. 50, pp. 8 & 16; Ref. 80, pp. 5-6

GW-057 Chromium VI 0.027 0.005 Ref. 50, pp. 5 & 15; Ref. 80, pp. 5-6 

GW-058-A Chromium VI 0.051 0.005 Ref. 50, pp. 6 & 16; Ref. 80, pp. 5-6 

GW-064 Chromium VI 0.088 0.005 Ref. 50, pp. 6 & 16; Ref. 80, pp. 5-6 

GW-071 Chromium VI 0.008 0.005 Ref. 50, pp. 7 & 16; Ref. 80, pp. 5-6 

GW-082 Chromium VI 0.018 0.005 Ref. 50, pp. 7 & 16; Ref. 80, pp. 5-6 

GW-107 Chromium VI 0.035 0.005 Ref. 50, pp. 7 & 16; Ref. 80, pp. 5-6 

GW-150-A Chromium VI 0.124 0.005 Ref. 50, pp. 5 & 15; Ref. 80, p. 5

GW-261 Chromium VI 0.136 0.005 Ref. 51, pp. 4 & 11; Ref. 80, p. 5

GW-104-A Chromium VI 0.442 0.05 Ref. 58, pp. 5 & 16; Ref. 84, p. 5-6 

GW-150 Chromium VI 0.121 0.01 Ref. 58, pp. 5 & 16; Ref. 84, pp. 5-6 

GW-132 Chromium VI 0.012 0.005 Ref. 62, pp. 4 & 11; Ref. 86, p. 5

Note:

- = Reported as MQL UnAdj. by Xenco Laboratories.

* For all of the analyses the reporting limit in the references cited is the SQL based on the method detection limit (Ref. 134).
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Table 10: Contaminated Ground Water Pathway Drinking Water Samples meeting 

Observed Release Criteria (July 2009 SI Results)

Sample Location Contaminant 

Detected

Conc. 

(μg/L)

SQL+

(μg/L)* Reference

GW-20 Chromium 497 10 Ref. 88, pp. 5-6; Ref. 89, pp. 16 & 238 

GW-19 Chromium 1010 10 Ref. 88, p. 5; Ref. 89, pp. 12 & 238 

GW-28 Chromium 1040 10 Ref. 88, p. 6; Ref. 89, pp. 30 & 238

GW-27 Chromium 694 10 Ref. 88, p. 6; Ref. 89, pp. 26 & 238

GW-14 Chromium 4450 10 Ref. 88, p. 5; Ref. 89, pp. 38 & 240

GW-21 Chromium 1400 10 Ref. 88, p. 6; Ref. 89, pp. 42 & 240

GW-31 Chromium 3780 10 Ref. 88, p. 6; Ref. 89, pp. 50 & 240

GW-29 Chromium 1400 10 Ref. 88, p. 6; Ref. 89, pp. 46 & 240

GW-07 Chromium 110 10 Ref. 88, p. 5; Ref. 89, pp. 66 & 242

GW-13 Chromium 530 10 Ref. 88, p. 5; Ref. 89, pp. 74 & 242

GW-12 Chromium 191 10 Ref. 88, p. 5; Ref. 89, pp. 70 & 242

GW-08 Chromium 350 10 Ref. 88, p. 15; Ref. 89, pp. 94 & 244

GW-05 Chromium 217 10 Ref. 88, p. 5; Ref. 89, pp. 62 & 242

GW-03 Chromium 2510 10 Ref. 88, p. 5; Ref. 89, pp. 54 & 242

GW-04 Chromium 1980 10 Ref. 88, p. 5; Ref. 89, pp. 58 & 242

GW-16 Chromium 440 10 Ref. 88, p. 5; Ref. 89, pp. 102 & 244

GW-02 Chromium 239 10 Ref. 88, p. 5; Ref. 89, pp. 90 & 244

GW-09 Chromium 375 10 Ref. 88, p. 5; Ref. 89, pp. 98 & 244

GW-01 Chromium 431 10 Ref. 88, p. 5; Ref. 89, pp. 86 & 244

GW-11 Chromium 466 10 Ref. 88, p. 5; Ref. 89, pp. 128 & 247

GW-06 Chromium 116 10 Ref. 88, p. 5; Ref. 89, pp. 124 & 247

GW-17 Chromium 47.3 10 Ref. 88, p. 5; Ref. 89, pp. 132 & 247

GW-18 Chromium 313 10 Ref. 88, p. 5; Ref. 89, pp. 136 & 247

GW-15 Chromium 107 10 Ref. 88, p. 5; Ref. 89, pp. 112 & 246

GW-34 Chromium 491 10 Ref. 88, p. 5; Ref. 89, pp. 120 & 246

GW-25 Chromium 1140 10 Ref. 88, p. 6; Ref. 89, pp. 116 & 246

Note: 
Hazard Ranking System Document Record West County Road 112 Ground Water

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+ = Reported as Reporting Limit by Region 6 Laboratory. 

* For all of the analyses the reporting limit in the references cited is the SQL based on the method detection limit (Ref. 134).

Table 11: Contaminated Ground Water Pathway Drinking Water Samples meeting 

Observed Release Criteria (September 2009 Results)

Sample Location Contaminant 

Detected

Conc. 

(mg/L)

SQL-

(mg/L)* Reference

GW-104 Chromium 0.422 0.05 Ref. 98, pp. 4 & 16; Ref. 45, p. 21; Ref. 42, p. 

8 

GW-020 Chromium 0.508 0.05 Ref. 94, pp. 5 & 20; Ref. 45, p. 21; Ref. 42, 

p.8

GW-023 Chromium 1.01 0.05 Ref. 94, pp. 6 & 20-21; Ref. 45, p. 22; Ref. 42, 

p. 8

GW-042-A Chromium 3.62 0.05 Ref. 94, pp. 8 & 21; Ref. 45, p. 22; Ref. 42, p. 

9 

GW-043-A Chromium 0.668 0.05 Ref. 93, pp. 6 & 20; Ref. 45, p. 20; Ref. 42, p. 

7 

GW-044-A Chromium 1.71 0.05 Ref. 93, pp. 5 & 20; Ref. 45, p. 20; Ref. 42, p. 

7 

GW-045-A Chromium 1.5 0.05 Ref. 93, pp. 9 & 22; Ref. 45, p. 21; Ref. 42, p. 

8 

GW-046-A Chromium 1.11 0.05 Ref. 93, pp. 7, 20, & 22; Ref. 45, p. 20; Ref. 

42, p. 7 

GW-048-A Chromium 0.572 0.05 Ref. 95, pp. 10 & 22; Ref. 45, p. 23; Ref. 42, p

10

GW-049 Chromium 1.01 0.05 Ref. 95, pp. 5 & 21; Ref. 45, p. 23; Ref. 42, p. 

9 

GW-050-A Chromium 1.04 0.05 Ref. 95, pp. 6 & 21; Ref. 45, p. 23; Ref. 42, p. 

9 

GW-080-A Chromium 0.097 0.05 Ref. 93, pp. 7 & 21; Ref. 45, p. 21; Ref. 42, p. 

7 

GW-090-A Chromium 0.419 0.05 Ref. 95, pp. 9 & 22; Ref. 45, p. 23; Ref. 42, p. 

10

GW-091-A Chromium 0.335 0.05 Ref. 93, pp. 10 & 22; Ref. 45, p. 21; Ref. 42, 

p. 8 

GW-092-A Chromium 0.537 0.05 Ref. 94, pp. 9 & 21; Ref. 45, p. 22; Ref. 42, p. 

9 

GW-093-A Chromium 0.211 0.05 Ref. 94, pp. 10 & 21-22; Ref. 45, p. 22; Ref. 

42, p. 9

GW-094-A Chromium 0.127 0.05 Ref. 94, pp. 11 & 22; Ref. 45, p. 22; Ref. 42, 

p. 9

GW-095-A Chromium 0.21 0.05 Ref. 95, pp. 7 & 21; Ref. 45, p. 23; Ref. 42, p. 

10

GW-096-A Chromium 0.273 0.05 Ref. 93, pp. 11 & 22; Ref. 45, p. 21; Ref. 42, 

p. 8

GW-097-A Chromium 0.272 0.05 Ref. 95, pp. 4 & 20; Ref. 45, p. 22; Ref. 42, p. 

9 
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Table 11: Contaminated Ground Water Pathway Drinking Water Samples meeting 

Observed Release Criteria (September 2009 Results)

Sample Location Contaminant 

Detected

Conc. 

(mg/L)

SQL-

(mg/L)* Reference

GW-254-A Chromium 0.447 0.05 Ref. 95, pp. 8 & 22; Ref. 45, p. 23; Ref. 42, p. 

10

GW-019-A Chromium 0.17 0.05 Ref. 97, pp. 6 & 17; Ref. 45, p. 25; Ref. 42, p. 

11

GW-081-A Chromium 0.267 0.05 Ref. 97, pp. 7 & 17-18;Ref. 45, p. 25; Ref. 42, 

p. 12

GW-086-A Chromium 1.59 0.05 Ref. 97, pp. 8 & 18; Ref. 45, pp. 25; Ref. 42, 

p. 12

GW-099 Chromium 0.317 0.05 Ref. 45, p. 24; Ref. 42, p. 11

GW-100-A Chromium 1.96 0.05 Ref. 96, pp. 4 & 19; Ref. 45, p. 23; Ref. 42, p. 

10

GW-101-A Chromium 1.94 0.05 Ref. 96, pp. 5 & 19; Ref. 45, p. 24; Ref. 42, p. 

10

GW-102-A Chromium 0.27 0.05 Ref. 98, pp. 6 & 16; Ref. 45, p. 26; Ref. 42, p. 

12

GW-103-A Chromium 0.619 0.05 Ref. 98, pp. 6 & 16; Ref. 45, p. 26; Ref. 42, p. 

12

GW-104-A Chromium 0.422 0.05 Ref. 98, pp. 4 & 16; Ref. 45, p. 25; Ref. 42, p. 

12

GW-105-A Chromium 0.088 0.05 Ref. 96, pp. 10 & 20; Ref. 45, p. 24; Ref. 42, 

p. 11

GW-126-A Chromium 0.111 0.05 Ref. 97, pp. 4 & 17; Ref. 45, p. 24; Ref. 42, p. 

11

GW-146-A Chromium 0.241 0.05 Ref. 96, pp. 7 & 20; Ref. 45, p. 24; Ref. 42, p. 

11

GW-098-A Chromium 0.098 0.05 Ref. 99, pp. 5 & 20; Ref. 45, p. 26; Ref. 42, p. 

13

GW-047-A Chromium 4.51 0.05 Ref. 100, pp. 5 & 23; Ref. 45, p. 27; Ref. 42, 

p. 13

GW-064 Chromium 0.097 0.05 Ref. 100, pp. 8 & 24; Ref. 45, p. 27; Ref. 42, 

p. 14

GW-108-A Chromium 0.129 0.05 Ref. 100, pp. 4 & 23; Ref. 45, p. 27; Ref. 42, 

p. 13

GW-187 Chromium 0.101 0.05 Ref. 45, p. 27; Ref. 42, p. 14; Ref. 100, pp. 10 

& 25

GW-150-A Chromium 0.158 0.05 Ref. 101, pp. 5 & 24-25 ; Ref. 45, p. 28; Ref. 

42, p. 15

GW-176 Chromium 0.107 0.05 Ref. 59, pp. 4 & 12; Ref. 45, p. 30; Ref. 42, p. 

16

Note:

- = Reported as MDL UnAdj. or MQL Adj. by Xenco Laboratories.

* For all of the analyses the reporting limit in the references cited is the SQL based on the method detection limit (Ref. 134).
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Table 12: Contaminated Ground Water Pathway Drinking Water Samples meeting 

Observed Release Criteria (November 2009 Results)

Sample 

Location

Contaminant 

Detected

Conc. 

mg/L

SQLmg/L* Reference

GW-151 Chromium 0.073 0.05 Ref. 44, p. 3; Ref. 46, p. 4 ; Ref. 55, pp. 8 & 25

GW-299 Chromium 0.161 0.05 Ref. 44, p. 4; Ref. 46, p. 4-5; Ref. 55, pp. 13 & 

26

GW-313 Chromium 0.076 0.05 Ref. 44, p. 3; Ref. 46, p. 4-5; Ref. 55, pp. 11 & 

26

GW-058 Chromium 0.053 0.05 Ref. 44, p. 5; Ref. 46, p. 6; Ref. 57, pp. 6 & 19

Note:

- = Reported as MDL UnAdj. or MQL Adj. by Xenco Laboratories.

* For all of the analyses the reporting limit in the references cited is the SQL based on the method detection limit (Ref. 134).

Attribution

The site is designated as a contaminated ground water plume originating from unknown 

source(s) where chromium and chromium VI may have been released and percolated through 

the ground to the aquifer. When the source itself consists of a ground water plume with no 

identified source, no separate attribution is required (Ref.1, Sec. 3.1.1). 

Hazardous Substances Released

The following hazardous substances were released: 

Chromium and chromium VI. 

As specified in the HRS (Ref. 1, Section 3.1.1), an observed release factor value of 550 was 

assigned to the Edwards-Trinity aquifer since an observed release by chemical analysis was 

established in the Edwards-Trinity aquifer.

Observed Release Factor Value: 550
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3.1.2 

3.1.3 

Potential to Release

As specified in the HRS, since an observed release was established for the Edwards-Trinity 

aquifer, the potential to release was not evaluated (Ref. 1, Section 3.1.1). 

3.2 

Likelihood of Release Factor Category Value

As stated in the HRS, if an observed release is established for an aquifer, assign the observed 

release factor value of 550 as the likelihood of release factor category value for the aquifer 

(Ref. 1, Section 3.1.3). Since an observed release has been established for the aquifer, the 

Observed Release Factor Value of 550 is assigned as the likelihood of release factor category 

value.

3.2.1 

Waste Characteristics

Table 13: Toxicity/Mobility Factor Values

Toxicity/Mobility

The hazardous substances with the highest toxicity factor value available to the ground water

migration pathway are chromium and chromium VI, which both have a toxicity/mobility 

value of 10,000. Therefore, the following toxicity, mobility, and combined toxicity/mobility 

factor value has been assigned to the substances associated with Source No. 1, or present in 

the observed release, which has a containment value greater than 0.

Hazardous 

Substance

Toxicity Factor 

Value

Mobility Factor 

Value

Toxicity / Mobility

Value Reference

Chromium 10,000 1 10,000 Ref. 1, Sections 2.4.1.2, 3.2.1; Ref. 

3, pp. 1-3

Chromium VI 10,000 1 10,000 Ref. 1, Sections 2.4.1.2, 3.2.1; Ref. 

3, pp. 1-3

Documentation for Toxicity/Mobility Values

The Mobility Factor Value for all hazardous substances that meet the criteria for an observed 

release by chemical analysis to one or more aquifers underlying the source(s) at the Site, 

regardless of the aquifer being evaluated, is assigned a mobility factor value of 1 (Ref. 1, 

Section 3.2.1.2). 

Therefore, the hazardous substance with the highest toxicity/mobility factor value available 

to the ground water migration pathway is both chromium and chromium VI with a combined 

toxicity/mobility factor value of 10,000. 

Toxicity/Mobility Factor Value: 10,000
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3.2.2 

Table 14: Source Hazardous Waste Quantity Values

Hazardous Waste Quantity

According to Section 2.4.2.2 of the HRS, a pathway hazardous waste quantity factor value of 

100 was assigned because the hazardous constituent quantity data is not adequately 

determined for one or more sources, and targets for the Ground Water Migration Pathway are 

subject to Level I concentrations (Ref. 1, Section 2.4.2.2). 

Source Number Source Hazardous Waste Quantity 

Value

Hazardous Constituent Quantity Data 

Complete? 

1 > 0 NO

Total > 0

3.2.3 Waste Characteristics Factor Category Value

As specified in the HRS (Ref. 1, Section 3.2.3), the Hazardous Waste Quantity Factor Value 

of 100 was multiplied by the highest Toxicity/Mobility Factor Value of 10,000, resulting in a 

product of 1,000,000 (1.0E+06). Based on this product, a Waste Characteristics Factor Value 

of 32 was assigned from Table 2-7 of the HRS (Ref. 1, Section 2.4.3.1). 

Hazardous Waste Quantity Factor Value: 100

Waste Characteristics Factor Value: 32
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3.3

The primary aquifer being evaluated for the ground water pathway targets is the EdwardsTrinity aquifer. The ground water pathway targets for this aquifer have been impacted with 

chromium and chromium VI above a human health based benchmark. The number of target

wells subject to Level I concentration of chromium, which is the concentration above a 

benchmark, is given in Table 15. The population served is also given in Table 15. The 

average population per household of 2.62, which was determined from 2000 census when the 

population size of Midland was 94,996 (Ref. 15, p. 1), has been applied where the population 

size was not available from the water well survey. The 2008 estimated population in 

Midland is 104,768 (Ref. 15, p. 9). 

Ground water Pathway Targets

Table 15: Drinking Water Wells with Level I Concentration of Chromium

Well ID

Chromiu

m Conc. 

μg/L

(mg/L)

Benchmarks/Screening 

Concentrations (Ref. 3, pp. 1-3)

Population 

Served

MCL / Reference

MCLG

μg/L

(mg/L)

Cancer Risk 

Screen. 

Conc. μg/L

(mg/L)

Ref. Dose 

Screen. 

Conc. μg/L

(mg/L)

GW-08 350 100

(0.1)

NA 110

(0.11)

2 Ref. 5, p. 23-24; Ref. 88, p. 5; 

Ref. 89, pp. 94 & 244

GW-11 466 2.62

Ref. 19, p. 87; Ref. 88, pp. 5 & 

15; Ref. 84, pp. 5-7; Ref. 89, 

pp. 128 & 247

GW-12 191 4 Ref. 5, pp. 21- 22; Ref. 88, p. 

5; Ref. 89, pp. 70 & 242

GW-13 530 2.62 Ref. 6, p. 15; Ref. 88, p. 5; 

Ref. 89, pp. 74 & 242

GW-14 4,450 2.62 Ref. 5, p. 11-12; Ref. 88, p. 5; 

Ref. 89, pp. 38 & 240

GW-15 107 6 Ref. 5, pp. 37-38; Ref. 88, p. 

5; Ref. 89, pp. 112 & 246

GW-19 1,010 2.62 Ref. 6, p. 3; Ref. 88, p. 5; Ref. 

89, pp. 12 & 238

GW-20 497 2.62 Ref. 5, pp. 7-8; Ref. 88, p. 5; 

Ref. 89, pp. 16 & 238

GW-21 1,400 2.62 Ref. 6, p. 5; Ref. 88, p. 6; Ref. 

89, pp. 42 & 240

GW-27 694 2 Ref. 6, p. 4; Ref. 88, p. 6; Ref. 

89, pp. 20 & 238

GW-28 1,040 2.62 Ref. 5, pp. 9-10; Ref. 88, p. 6; 

Ref. 89, pp. 30 & 238

GW-29 1,400 2.62 Ref. 6, pp. 5; Ref. 88, p. 5; 

Ref. 89, pp. 46 & 240

GW-31 3,780 2.62 Ref. 5, pp. 13-14; Ref. 88, p. 6; 

Ref. 89, pp. 50 & 240

GW-34 491 2.62 Ref. 5, pp. 39-40; Ref. 88, pp. 

1-10; Ref. 89, pp. 120 & 246

GW-099-A (0.317) 2.62

Ref. 26, p. 19; Ref. 45, p. 24; 

Ref. 42, p. 11; Ref. 96, pp. 6 & 

19
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Table 15: Drinking Water Wells with Level I Concentration of Chromium

Well ID

Chromiu

m Conc. 

μg/L

(mg/L)

Benchmarks/Screening 

Concentrations (Ref. 3, pp. 1-3)

Population 

Served

MCL / Reference

MCLG

μg/L

(mg/L)

Cancer Risk 

Screen. 

Conc. μg/L

(mg/L)

Ref. Dose 

Screen. 

Conc. μg/L

(mg/L)

GW-102-A (0.27) 

100

(0.1)

NA 110

(0.11)

2.62

Ref. 21, p. 41; Ref. 98, pp. 6 & 

16; Ref. 45, p. 26; Ref. 42, pp. 

6-18

GW-103-A (0.619) 2.62

Ref. 21, p. 43; Ref. 98, pp. 6 & 

16; Ref. 45, p. 26; Ref. 42, p. 

12

GW-150-A (0.158) 2.62

Ref. 21, pp. 75-77; Ref. 101, 

pp. 5 & 24; Ref. 45, pp. 19-31; 

Ref. 42, p. 15

Total Population 

Served 50.68

NA= Not available. 

The numbers of targets for Level I concentration of chromium VI are given in Table 16. 

Those targets with Level I concentration of chromium VI that have already been accounted 

for in Level I concentration of chromium have not been considered. The population served is 

also given in the table. 

Table 16: Drinking Water Wells with Level I Concentration of Chromium VI

Well ID

Chromium 

VI 

Concentrat

ion mg/L

Benchmarks/Screening 

Concentrations

Population 

Served MCL / Reference

MCLG

mg/L

Cancer Risk 

Screen. 

Con. mg/L

Ref. Dose 

Screen. 

Conc.

mg/L

GW-261 0.136

NA NA 0.11

2.62

Ref. 18, p. 53; Ref. 51, 

pp. 4 & 11; Ref. 80, pp. 

5-6

Total Population Served 2.62

NA= Not available
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3.3.1 Nearest Well

According to Section 3.3.1 of the HRS, if one or more drinking water wells is subject to 

Level I concentrations, a Nearest Well Factor value of 50 is assigned. Level I concentrations 

have been documented in 19 wells within the ground water plume.

Level of Contamination (I, II, or potential): Level I 

Location of Well: Level I concentrations have been documented at 19 wells within the 

ground water plume. Well locations are identified in Table 1. 

For a well with Level I concentrations, a Nearest Well Factor Value of 50 is assigned (Ref. 1, 

Section 3.3.1). 

Nearest Well Factor Value: 50
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3.3.2 Population

3.3.2.1 

3.3.2.2 

Level of Contamination

Level I Concentration

The concentrations of hazardous substance shown in Table 15 and Table 16 include 

detections in drinking water wells that meet or exceed their corresponding benchmark 

concentrations; thus, these wells are associated with Level I concentrations (Ref. 1, Section 

3.3.2.1-3.3.2.2). 

Nineteen private wells within a one-mile radius of the Site contained Level I concentrations

of hazardous substances (see Table 15 and Table 16). All the private wells drew water from 

the Edwards-Trinity Aquifer (Ref. 111, pp.1-2). The residents depend upon their private 

wells for their daily water needs. TCEQ has installed 45 anion exchange filter systems due 

to the presence of chromium, as of November 2009 (Ref. 102, pp. 1-3). 

As specified in the HRS (Ref. 1, Section 3.3.2.2), the number of people served by drinking 

water from points of withdrawal subject to Level I concentrations were summed. Using the 

average population per household of 2.62 (Ref. 15, pp. 1-2) or the population from the water 

well survey where available, the total population counted from Level I wells is 53.30. The 

total of 53.30 was multiplied by 10, for a product of 533 (Ref. 1, Section 3.3.2.2). 

Population Served by Level I Well: 53.30

Level I Concentration Factor Value: 533
Hazard Ranking System Document Record West County Road 112 Ground Water

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3.3.2.3 Level II Concentration

The Level II concentration, which is the concentration above background but below the 

benchmark, was found in eight wells. As specified in the HRS, the number of people served 

by drinking water from points of withdrawal subject to Level II concentrations is summed up 

and the sum is assigned as the value for this factor. Table 17 below gives the list of ground

water wells with Level II concentration of chromium. The population served is also given in 

the table.

Table 17: Drinking Water Well with Level II Concentration of Chromium

Well ID

Chromium 

Conc. μg/L

(mg/L)

Benchmarks/Screening 

Concentrations

Population 

Served

MCL / Reference

MCLG

μg /L

(mg/L)

Cancer 

Risk 

Screen. 

Con. μg/L

(mg/L)

Ref. Dose 

Screen. 

Conc.

μg/L

(mg/L)

GW-098 (0.098) 

100

(0.1)

NA 110

(0.11)

2 

Ref. 21, p. 59; Ref. 99, pp. 5 & 

20; Ref. 45, p. 26; Ref. 42, p. 13, 

Ref. 90, p.29

GW-064 (0.097) 2.62 Ref. 21, p. 71; Ref. 100, pp. 8 & 

24; Ref. 45, p. 27; Ref. 42, p. 14

GW-151 (0.073) 17

Ref. 44, p. 3; Ref. 46, p. 4 ; Ref. 

55, pp. 8 & 25; Ref. 129, p. 1;

Ref. 90, pp. 46-47

GW-058 (0.053) 2.62 Ref. 21, p. 95; Ref. 44, p. 4; Ref. 

46, p. 4-6; Ref. 57, pp. 6 & 19

Total Population Served 24.24

NA= Not available

The number of targets for Level II concentration of chromium VI is given in Table 18. 

Those targets with Level II concentration of chromium VI, which have already been 

accounted for in Level II concentration of chromium have not been considered. 

Table 18: Drinking Water Well with Level II Concentration of Chromium VI

Well ID

Chromium 

Conc. 

mg/L

Benchmarks/Screening 

Concentrations

Population 

Served MCL / Reference

MCLG

mg/L

Cancer 

Risk 

Screen. 

Con. mg/L

Ref. Dose 

Screen. 

Conc.

mg/L

GW-029 0.027 NA NA 0.11 2.62 Ref. 17, p. 77; Ref. 36, pp. 7 & 

16; Ref. 79, p. 95

GW-005 0.051 2.62 Ref. 18, p. 39; Ref. 49, pp. 9 & 

25; Ref. 64, p. 12-50

GW-053 0.018 2.62 Ref. 50, pp. 8 & 16; Ref. 80, p. 5
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Table 18: Drinking Water Well with Level II Concentration of Chromium VI

Well ID

Chromium 

Conc. 

mg/L

Benchmarks/Screening 

Concentrations

Population 

Served MCL / Reference

MCLG

mg/L

Cancer 

Risk 

Screen. 

Con. mg/L

Ref. Dose 

Screen. 

Conc.

mg/L

GW-057 0.027 NA NA 0.11 2.62 Ref. 18, p. 41; Ref. 50, pp. 5 & 

15; Ref. 80, p. 5

Total Population Served 10.48

NA= Not Available

Level II Concentration Factor Value: 34.72

Population Served by Level II Well: 34.72
Hazard Ranking System Document Record West County Road 112 Ground Water

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3.3.2.4 Potential Contamination

The potential contamination factor was evaluated and scored. The ground water wells were 

identified from the well database in the TCEQ GIS servers and from the Texas Water 

Development Board (TWDB) (Ref. 109, pp. 1-20). The wells were researched within radii of 

0 to 0.5, 0.5 to1, 1 to 2, 2 to 3, and 3 to 4-miles of the site (see Figures 1c and 1d of this HRS 

documentation record). Using the average population per household of 2.62 (Ref. 15, p. 1),

the potential targets (Table 14) were calculated based on the number of wells located within 

each distance category and the weighted population assigned from Table 3-12 of the HRS. 

0 to 0.25-mile

The thirty wells located at 0 to 0.25-mile radius from the center of the site were all tested and 

accounted in Level I or Level II contamination according to the level of contaminants of 

concern (i.e., chromium and/or chromium VI) detected in those samples (see Tables 1, 15-16 

and Figures 1c and 1d of this HRS documentation record). 

0.25 to 0.5-mile

There were 12 domestic wells located at 0.25 to 0.5-mile radius of the site. Among the 12 

wells, only seven were considered for potential contamination as the rest were included in 

Level I or Level II contamination (see Tables 1, 17-18 and Figures 1c and 1d of this HRS 

documentation record). 

0.5 to 1-mile

At 1 to 0.5 to 1-mile of the site, four domestic ground water wells were located. All of them 

were considered as potential to contamination domestic wells (see Figures 1c and 1d of this 

HRS documentation record). 

1 to 2-mile

At 1 to 2-miles of the site, thirty-eight domestic ground water wells were located. Two 

public water supply (PWS) systems were found: 1) PWS with identification 1650077 with

two wells serving a population of 165 (Ref. 120, p. 1); and 2) PWS with identification 

1650111 with two serving wells for a population of 147 (Ref. 120, p. 5). Together with 38 

domestic wells (see Figures 1c and 1d of this HRS documentation record), the population at 1 

to 2-mile is 411.56. 

2 to 3-mile

Within 2 to 3 miles of the site, 42 domestic wells were found. There were four PWS systems 

located at a 2 to 3-mile radius of the Site, which are described below: 
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1) The PWS with identification 1650047 with five serving wells (Ref. 120, p.9), of which 

four wells are within 2 to 3-mile radius. None of the wells contributes more than 40% of the 

system’s total water supply; hence, the population served was equally apportioned to all the 

wells. Therefore, the total population served by the PWS, three-hundred (300), was divided 

by the total number of wells, five, giving a product of 60. Because there were four active 

wells located within 2 to 3-mile radius of this PWS, the population served is 240; 

2) The PWS system with identification 1650111 with one well, which is an inactive well, 

therefore, it was not considered; 

3) The PWS with identification 1650057 with two wells serving 234 people (Ref. 120, p. 13); 

and

4) The PWS with identification 1650084 with six active wells of which five are within 2 to 3-

mile radius (Ref. 120, p. 17). None of the wells contribute more than 40% of the system’s 

water. Therefore, the population served, which is 285, was equally apportioned to all six 

wells, which gives a population of 237.5 for the five wells within 1 to 2 miles. 

The total population served by PWS within a 2 to 3-mile radius of the Site is 711.5. Together 

with the domestic wells, the total population served located within a 1 to 2-mile radius of the 

Site is 821.54 (see Figures 1c and 1d of this HRS documentation record). 

3 to 4-mile

There were 33 domestic wells located in a 3 to 4-mile radius of the Site. No PWS were 

found in a 3 to 4-mile radius of the Site (see Figures 1c and 1d of this HRS documentation 

record). 

As specified in the HRS (Ref. 1, p. 51604), the number of people served by drinking water 

wells was determined within each ‘Other Than Karst’ distance category and a distanceweighted population value for each distance category was assigned. The distance weighted 

population values were summed for a total of 178, which was divided by 10 for a product of 

17.8. 

Table 19: Potential Contamination

Distance 

(Miles)

Potentially 

Contaminated

Domestic 

Wells

Potentially 

Contaminated

PWS Wells (Well 

ID)

Potentially 

Contaminated

Population

Weighted Population

0 to 0.25 0 NA 0*

0.25 to 0.5 7 NA 18.34** 11

0.5 to 1 4 NA 10.48 1

1 to 2 38 2 (ID: 1650077) 411.56 94 2 (ID: 1650111)

2 to 3 42

4 (ID: 1650047)

2 (ID: 1650057) 821.54 68

5 (ID: 1650084)

3 to 4 33 NA 86.46 4

Total 1,348.38 178

NA= Not applicable

* All wells within this distance category ring are already accounted for in Level I or II contamination sections 

of this HRS documentation record.
Hazard Ranking System Document Record West County Road 112 Ground Water

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** Only seven of the12 wells located in this distance category ring were considered subject to potential 

contamination as the rest were accounted for in the Level I or II contamination sections of this HRS 

documentation record.

3.3.3 Resources

No resources, as defined in HRS Section 3.3.3, were documented for the Edwards-Trinity 

and Ogallala aquifers (Ref. 1) 

3.3.4 Wellhead Protection Area

The Wellhead Protection Area (WPA) has not been evaluated at this time.

3.3.5 

3.4 

Calculation of Targets Factor Category Value

The target factor category value is calculated by determining the sum of the factor values for 

the nearest well (50), population (533 + 34.72 + 17.8), resources (0), and WPA (0) (Ref. 1, 

Section 3.3.5). 

Calculations: 50 + 585.52 + 0 + 0 = 611.28 

3.5 

Ground Water Migration Score for an Aquifer

The ground water migration score for an aquifer is calculated by multiplying the factor 

category values for likelihood of release (550), waste characteristics (32), and targets (646). 

Divided by 82,500, the resulting value (maximum value 100) is assigned as the ground water

migration pathway score (Ref. 1, Section 3.4). 

Calculations: (550 x 32 x 611.28) / 82,500 = 130.41 (100 maximum) 

Calculation of Ground Water Migration Pathway Score

The ground water migration pathway score is calculated by assigning the highest ground

water migration score for the aquifer being evaluated (100). 

Potential Contamination Factor Value: 17.8

Resource Factor Value: 0

Wellhead Protection Area Factor Value: NS
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3.5.1 Calculation of HRS Site Score

The HRS site score is calculated by using the root-mean-square equation which squares each 

pathway score then takes the sum of all pathways and divides the sum by 4 then takes the 

square root which is the site score (Ref. 1, Section 2.1.1). 

Calculations:

Pathway Squares

GW Pathway [100] = 10,000 

SW Pathway not scored = 0 

Soil Pathway not scored = 0 

Air Pathway not scored = 0 

Sgw + Ssw + Ss + Sa = 10,000 + 0 + 0 + 0 = 10,000 

10,000 / 4 = 2,500 

√ 2,500 = 50.00

HRS Site Score: 50.00