Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 000 6 06 992 

### HAZARDOUS RANKING SY STEM (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 Wa ter 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 s core.

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 0 00 606 992 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

Gen eral Location in the State: The West County Road 112 Ground W ater S ite 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 ( s ee 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 Locat ion Map).

Topographic M ap: U.S. Geological Survey 7.5 Minute Topographic Map, Southeast Midland Quadrangle. Photo revised 1995.

Latitude: 31.964129 O 

### Longitude : -102.094921 O



### 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 substanc e 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 W ater Migration Pathway – 100.00 Surface Water Migration Pathway

– NS Soil Exposure Pathway – NS Air Migration Pathway

– NSHazard Ranking System Document Record West County Road 112 Ground Water
October 2010 T XN 000 606 992 2 

### **NS = Not Scored (** Pathways w e re evaluated but not scored due to their minimal contribution to the overall site score)

HRS SITE SCORE: 50.001

1 

# ! ! 

# 2 Site center 

### Midland Midland



# §  ̈ ¦

20 

# §  ̈ ¦

20



# U V 349 

# U V 349



# U V 158 

# U V 158



# U V 158 

# U V

58



# U V

58 Illinois

349 Front

Wall

20e

1200 Midkiff

1210 1 5 8 Midland Gist Thomason Lamesa A

Florida

Francis Rankin Louisiana

Cotton Flat Garfield

80 Andrews

349 Big Spring

Big Spring Andrews

Cloverdale Garden City 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

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# 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

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# 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

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T his map was generated by the R emediation Division o f the T exas Commission on E nvironmental Quality. 

## Jt is intended f or inustrative

or informational purposes only

. and is not suitable f or legal

, engineering

, or survey purposes

_ 

### This map does not represent an

on

- lheiJround survey conducted by or under the supervision of a registered professional l a nd surveyor. In cases where property
boundaries are shown

, it 

### only represents their appro x imate relative
Iocation

_ No daims are made to the accuracy or completeness of the
data or to its sufability for a particular use

_ F or more in f ormalion conceming Ihis map

. conlacllhe Remedialion Division al800-633

- 9363 

# o 0.25 0.5 1 1.5 2 2.5

_C:::::=::::J_==:::J

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# C::==========:::::J

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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 0 00 606 992 7 

### WORKSHEET FOR COMPUTING HRS SITE SCORE

S S 2



### 1. Ground Water Migration Pathway Score (S gw 

### ) 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 Surfac e Water Migration NS Component (from Table 4-25, line 28)

2c. Surface Water Migration Pathway Score (S
sw 

### ) NS Enter the larger of lines 2a and 2b as the pathway score.

3. Soil Exposure Pathway Score (S
s 

### ) NS (from Table 5 -1, line 22)

4. Air Migration Pathway Score (S
a 

### ) NS (from Table 6 -1, line 12)

5. Total of S gw 2 

### + S
sw 2 

### + S
s 2 

### + S
a 2 

### 10,000

6. HRS Site Score Divide the value on line 5 by 4 and take the square root. 50.00

NS = Not ScoredHazard Ranking System Document Record West County Road 112 Ground Water
October 2010 T XN 000 606 992 8 TAB LE 3 -1
G RO UND 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 T ime 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

T argets

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 (S gw ), (Highest value from Line 12 for al l aquifers evaluated) 100 100Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 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

3. U. S. Environmental Protection Agency, Superfund Chemical Data Matrix (SCDM), EPA/540/R

96/028, OERR Publication 9345.1

- 21, June 1996. Available at http://epa.gov/superfund/sites/npl/hrses/tools/scdm.htm

. 1-3 excerpted page s.

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 C ommission 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 Settin g of the Edwards

- Trinity Aquifer System, West

- Central Texas. Rene A. Barker, Peter W. Bush, and E.T. Baker, Jr. 1994. 55 pages.

8. Texas Water Development Board. Report 360: Aquifers of the Edwards Plateau. Edited by Robert E. Mace, Edward S. Angle, and W illiam F. Mullican, III. February 2004. 10 3 excerpted pages.

9. Texas Department of Water Resources. Report 288: Evaluating the Ground

- Water Resources of the High Plains of Texas. Volume 1. May 1984. 33 excerpted pages.

10. Texas Water Development Board. Repor t No. 314: Hydrogeology of Lower Cretaceous Strata Under the Southern High Plains of Texas and New Mexico. J.A. Fallin. March 1989. 26 pages.

11. Elliot, Tom. Shaw E & I, Inc. Field Activity Daily Logs and Monitor Well Boring Logs. February 2010. 16 pages.

12. WCR 112 TCEQ

– SSDAP Sampling Field Notebook # 1. May 12, 2009 through May 21, 2009. 41

pages.

13. The University of Texas at Austin, Bureau of Economic Geology. Pecos Sheet, Geologic Atlas of Texas. Johan August Udden Memorial Edition. 1976. 7 excerpted p ages.

14. The Journal of Geology, Vol. 78, No. 3. Origin, Classification, and Geologic History of Caliche on the Southern High Plains, Texas and Eastern New Mexico. C. C. Reeves, Jr., Texas Tech University, Department of Geosciences. May 1970. 13 pages.

15. U. S. Census Bureau. State and County QuickFacts: Midland, Texas. Available at http://quickfacts.census.gov/qfd/index.html . Accessed May 19, 2009. 9 pages.

16. WCR 112 TCEQ

– SSDAP Sampling Field Notebo ok # 2. May 14, 2009 through June 9, 2009. 91

pages.

17. WCR 112 TCEQ

– SSDAP Sampling Field Notebook # 3. May 14, 2009 through June 11, 2009. 94

pages.Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 10 18. W CR 1 12 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

pages.

20. Texas Water Development Board. Water Information Integration and Dissemination Groundwater 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 pag es.

22. Texas Board of Water Engineers. Bulletin 6107: A Summary of the Occurrence and Development of Ground Water in the Southern High Plains of Texas. Prepared by the Geologic Survey United States Department of the Interior in cooperation with the Texas B oard of Water Engineers. September 1961. 38 pages.

23. WCR 112 TCEQ

– SSDAP Sampling Field Notebook # 7. September 15, 2009 through January 6, 2010. 107 pages.

24. U.S. Environmental Protection Agency. Evaluating Ground Water Plumes Under the Hazard Ranking
S ystem, EPA 540 -F- 95

- 034, OSWER Publication 9320.8

- 01FS, September 1998. 5 pages.

25. U.S. Geological Survey, Professional Paper 1421

- B. Hydrogeologic Framework of the Edwards

Trinity Aquifer System, West

- Central Texas. Rene A. Barker and Ann F. Ardis. 199 6. 42 pages.

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. Anal ytical 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 0 00 606 992 11 35. X enco Laboratories. A n alytical 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 Environm ental, 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 Sa mpling 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 Analy tical 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 Va lidation 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, 200 9 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 Midl and 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 0 00 606 992 12 52. X e n co 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. Analytica l 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. X enco 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 Rev iew 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 Me morandum: 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 Memorandu m: 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. 10 5 pages.

67. Shaw Environmental, Inc. Data Review Memorandum: e -L ab 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 Anal ytical 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 0 00 606 992 13 69. S ha w 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 Analyti cal 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., (Xenc o) 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) Labor atory 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

R eport 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) Labora tory 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) La boratory 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 An alytical 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 Analytica l 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 Analyt ical 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 0 00 606 992 14 83. S ha w Environmental, Inc. Data Review Memora ndum: 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 C ommission 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 Repo rt: 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: Wes t 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 0 00 606 992 15 99. X enco Laboratories. Analytical Report 345597 for Shaw E & I, Inc: WCR 112 Midland TX. December 9, 20 09. 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 Pro ject 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 pa ges.

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 Environ mental 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 Environme ntal 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. T exas W ater D evelopment B oard. Well Locations D ata 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 V

96665501

- 0). February 1, 2010. 218 pages.

113. Texas Water Commission. B&W Welding and Const ruction 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 Environme ntal 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.wiliamspavingande xcavation.com . 1 page.Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 16 117. A rcadis. 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 20 10

. Avail able 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. A vailable

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

124. Sattman Soule, Danielle. Texas Commission on Environme ntal 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. C orrespondence to Honorable William B. Ahders and James H. Humphries, Jr. M.D

. July 1 9 , 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. T NRIS. 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. Environmenta l 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 se quence 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 Co unty 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 0 00 606 992 17 

### S ITE DESCRIPTION

The West County Road 112 Ground W ater site is desi gnated as a contaminated ground water plume originating from unknown sources composed of hazardous substan ces that released
in to the Edwards- Trinity aquifer. The center of the plume is designated as 260 4 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 . T he gro und water plume contains elevated inorganic compounds of chromium and chromium VI, which exceed ed 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 Fi gure 2.

As of November 9, 2009, concentrations of chromium in the ground water at the S ite
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 S ite is surrounded by residential properties to the south and east

, and by commercial and residential prope r ties 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 su r face (bgs) (Ref. 110 , pp.3

- 5; Ref. 20, p. 10). The ground water is the
sole source of w a ter in this area; the City of Midland does not provide city water south of I

20. 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
mile s of the S ite (Ref. 122, pp. 1

- 2). Properties north of I

- 20 currently receive water from the City of Mi d land (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 0 00 606 992 18 

### SOURCE DESCRIPTION

2.2 Source Characterization

2.2.1

Number of the source: 1

Name and description of the source: Other – Ground W ater 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 do mestic 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, p p . 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 an d 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. 1 04, 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 dur ing 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. 1 5-16 ). None of the soil samples collected met observed release criteria (Ref. 89, pp. 158 -177; Ref. 106, p. 23 ). Ground water samp les 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 exceed ed 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 conduct ing

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 Edward s- Trinity a quifers and collecting 8 soil samples at the center of the site (2604 W CR 112) to determine a pattern of c hromium concentrations to identify a point of release (Ref. 107, pp. 10 and 13). Source IdentificationHazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 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.

B ased on the findings of the ground
- penetrating radar and electroma gnetic pulse surve ys

e ight soil samples, including one field duplicate sample, were collected in area s where buried
drums could have been located (Ref. 107, p. 13 ). However, no drums were found during the soil sampling and t he sample results indicate d no sources of chromium contamination were
identified (Ref. 107, p.13).

A total of 23 monitor ing 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 locate d hydraulically up

gradient of the known chromium plume to establish background values for the Site (Ref. 107

, p. )

. The remaining t hree monitor ing 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 monitor ing well s were installed by the TCEQ in the uppermost aquifer, the Ogallala aquifer, and one monitor ing 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 sys tem (Ref. 33, p. 2)

. The shallow monitor ing 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 wit h fully penetrating 0.020 inch slotted screen. The deep monitoring well installed in the Edwards

Trinity aquifer was drilled to a target depth of approximately 79 fe et 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 advance d 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. 0 020 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 po ssible 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 0 00 606 992 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 Edw ards

- Trinity a quifer (GW

- 14 & GW

- 20A) to determine if a release occurred at the Schlumberger Technology Corpor a tion 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, GW

55, & GW

- 15) ground water samples were collected in the Ogallala a quifer 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 down

gradient (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 Ed wards

Trinity aqui fer (GW

- 12 & GW -09) to determine if a release occurred at the
Williamson Gravel Pit located at the corner of S CR 1 205 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, GW

04, GW

- 05, GW

- 02, & GW

- 03) and Edwards- Trinity a quifer (GW -06) to
det ermine if a release occurred at the center of the site located at 2 604 W CR 112 (Ref. 107, pp. 19, 24).

The ESI sampling data indicates that the first uppermost aquifer ( Ogallala aquifer) was impacted with c hromium at the B& W facility , but not at the Schl umberger Technology Corpora tion facility or the Williamson Gravel Pit ( Ref. 107, pp. 25, 30, 31 ). The data also
indicates that the c hromium concentrations increase in the Ogallala a quifer in a down

gradient direction starting near the B& W facility and cul minate 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 c hromium contamination was observed in the Ogallala aquifer from the background wells in th e vicinity of the Schlumberger Technology Corpora tion facility and Williamson Gravel Pit. The data suggest s that the area defined by
the north at the B& W f acility via Interstate 20 to the center of the site (2604 W CR 112) is a likely source area for the point of release of c hromium 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 ) , n o known source or sources w ere identified within the current S ite 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 (u p- 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

sourc e areas from the SI and ESI has not been identified. Therefore, a grou nd water plumeHazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 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, w ith reference to a map of the site: See Figure 2, Source Area Map. Also, see Reference 134 for s ource s ample locations.

Source type for HRS evaluation purposes:
Other - Ground Water Plume with No Identified Source.

Containment
Gas release to air: The ai r 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 fa ctor 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 overla nd/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'

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# \ 

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This map was generated by the Remed i atioo Division of the Texas Commission on E nvironm ental Quality

. It 

## is in tended for illustrative

or informationa l purposes only

, and is not suitable for l ega l, 

## 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 whe r e property
boundaries are shown

, it only represents the i r app roxim ate relative
location

. No claims a r e made 10 the accu r acy or completeness of the


### data or 10 i ls 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 198 3 ( Ref

. 128

, pp

. 1

- 4 )Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 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 specificall y chromium VI, for which observed releases were established
within the Edwards

- Trinity aquifer , the aquifer being evaluated for the Ground W ater 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 t hat tested the samples for the West County Road 112 Ground water site were:

**•** Xenco, O dessa, Texas

– 12600 West Interstate 20 East, Odessa, Texas 79765 ( Table s 5-9 and Tables 11-12)

**•** EPA Re gion 6, Houston – 10625 Fall Stone Road, Houston, Texas ( Table 10 )

The water samples were analyzed by methods CLP ILM05.3, SW6010, and SW846 for
in organic 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
th e 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 a quifer at a depth of approximately 100 feet bgs (Ref . 1 11, pp. 1

- 2). M ost wells in the site vicinity are screened over the two aquifers ide ntified as the Ogallala (uppermost) and Edwards

- Trinity aquifers to maximize the production of drinking water for the residences (Ref. 1 11, pp. 1 -2).

M ost pumps in the domestic wells we re placed i n 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. 1 11, 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 S ite. 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 0 00 606 992 24 Well ID ** Well Depth (feet) Below Ground Surface

and above Mean Sea Level (msl) * Date
Collected Contaminant
Detected Refer ence

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

G W

- 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 ; Re f. 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 C hromium 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 C hromium 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)

267 7 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. 2Hazard 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 Refer ence

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 Chro mium 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 Chr omium 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 ; R ef. 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. 3Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 26 Well ID ** Well Depth (feet) Below Ground Surface

and above Mean Sea Level (msl) * Date
Collected Contaminant
Detected Refer ence

GW

- 150 80 (Ref. 90, pp. 46,47)

2691 msl *** 6/9/2009 Chromium VI R ef. 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 V I 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



### No t e: * 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.Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 27 

### 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 ). T he following hazardous substances associated with the ground water plume source can migrate via the ground water pathway:

T able 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 a nd Qualifiers:
NS = Not Scored

Y = Yes



### 2.3

2.4 L ikelihood 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 Ev alu ated (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 S tream Quantity (Tier B)

There is not sufficient information to evaluate Tier B which requires determining mass of the
haza rdous 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 - NEHazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 28 

### 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 sit e 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 wate r 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. Th e value of >0 reflects that the volume is known to be greater than 0, but the exact amount is unknown.

Area (Tier D) 2.4.2.1.4

2.4.2.1.5 - NE

The are a measure (Tier D) cannot be evaluated because the hazardous waste quantity table in
the HRS (Ref.1

, Table 2

- 5) d oes 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 N o 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: > 0Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 29 

### SOURCE SUMMARY

The TCEQ SSDAP and Region 7 office conduct ed initial sampling and monitoring activities from April to November 2009 at the West County Road 112 Ground W ater S ite. During th e initial asse ssment period, approximately 234 water wells were sampled (Ref. 104, p. 1 ). The source hazardous waste quantit y 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

concentr ations (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 EvaluatedHazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 30 

### POS SIBLE 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
follo wing locations as possible sources of the chromium contamination:

1. The Dowell Midland facility now known as the Schlumberger Tech nology Corpora tion is located north within 1 mile of the site boundary . The Do w ell Midland facility, a division of Schlumberger Technology Corpor a tion, is in the TCEQ’s corrective action program (SWR # 33591) due to a release of volatile organic

co mpounds (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, carbo n ate, 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 a c tion 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 d oes not indicate that chromium is or has been used at the facility (Ref. 11 4). 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 Construc tion facility (EPA ID No.TXD981055080 ) is an
abandoned metal fabrication and wel d ing 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 (Re f. 1 17 , 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. 1 1 3, pp. 7-8 ). An a s sessment conducted by Lear Corporation (SWR # 23041) identifie d 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. 1 15 , p p . 2 -3 ). The Lear Corporation oper ated 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 a c tions 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. 1 1 3, pp. 6

- 7). The Williamson Gravel Pit isHazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 31 

### located hydraulically up

- gradient of the site and located hydraulically d own

- gradient of the B&W and Schlumberger Technology Corpor a tion sites (Ref. 1 17 , 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 (5.2 5 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 (Refe r ence 103 , p p

. 6 ). When they moved into the dwelling, the external and internal property was in disarray (Ref. 103 , p p. 11 ). The current residents do not have any knowledge of wastes buried on their

pro p erty; 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. T he center of the site is hydraulically down

- gradient of the B&W facility, Williamson Gravel Pit, and Schlumberger Technology Corpor a tion (Ref. 1 17 , p. 23 ; see also Section 2.2.1 of this
HRS documentation record ).Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 32 

### 3.0 GROUND WATER MIGRATION PATHWAY

3.0.1 G eneral 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 cross

formational 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 [Edward

Trinity 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 optimize d (Ref. 9, p. 25 ; Ref. 111, p.2).

The boundary between the two aquifers [Ogallala an d 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 E dwards- 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 E dwards- 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 vari able pe rmeability (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:Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 33 

### Stratum : 1

Stratum Name: Eolian

Post- Ogallala Formation sediments consist primarily of windblown (eolian) sand and silt, alluvium, and lucustrian deposits ( playa lake d eposits) . 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 floodp lain 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 W est County R oad 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 typica lly 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

- Ogal lala sediments and is formed by the leaching of carbonate and silica from surface soils and the redeposition of the di s solved minerals layers below the surface. Although caliche layers occur primarily near the surface, deeper zones of caliche are also pre sent (Ref. 9, p. 28).

At the W est 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 hi s tory, 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 no w the Pecos River Valley. Then, during the Cenozoic Era, a thickHazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 34 

### 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).

T he 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). Th e sands are generally tan, yellow, or reddish brown, medium
- to coarse

- grained, moderately
- to well

sorted, unconsolidated quartz grains, interbedded with thin layers of clay and occ asionally 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,
al though 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 W est County R oad 112 Ground Water Site, sediments attributed to the Ogallala
Formation are typically encount ered from approximately 1 0 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 th e 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 fo rms a basal sand unit (aka. Basal Cretaceous Sands) in the
Cret a ceous system in the southeastern and southern portions of the High Plains (Ref. 8, p. 49). It is a white to pu r ple, loosely consolidated, fine
- to coarse

- grained, quartz sandstone, locally ha rd, and commonly interbedded with fine

- grained yellow sand, green clay, and gray to pink sil t stone. 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

su f ficient 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 Cret a ceous times, a broad continental shelf formed around a rifting and subsiding ance s tral 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 d e posited clastic materials along shorelines (Ref. 25, p. 11). The Trinity sands were formed west of the Llano uplift where "typically it amassed as a spra wling, braided stream deposit atop an eroded surface of the pre

- Cretaceous rocks" (Ref. 25, p. 15). Shallow
off shore environments also promoted the biogenic accumulation of calcium carbonate (Ref. 25, p. 11).Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 35 

### Counties, the Antlers sand yields more water of acceptable quality than any other water

bearing formation. (Ref. 9, p. 25).

At the W est 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 sand stone 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 Tri n ity 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 (R ef. 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

- Tri n ity 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 a quifer system, mainly the Ogallala Fo r mation 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 a quifer System (Ref. 10, p.8; Ref. 7, pp. 20

- 21). Specifically, the Edwards

- Trinity aq uifer 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 a quifer is located in Andrews, Ector, Glasscock, Howard, Martin, and Mi d land counties in the Edwards Plateau area. The Ogallala a quifer 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 a quifer partially overlies the Edwards

– Trinity (Plateau) aquifer in the Edwards Plateau area (Ref. 8, p. 20).Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 36 

### 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 en d ing 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 Oga l lala Formation c onsists 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

me dium grades predominate (Ref. 22, p. 32). In the Odessa

- Midland area, the Ogallala

F ormation consists of reworked basal conglomerates of Triassic and Cr e taceous fragments locally overlain by fine pink sandstone and/or caliche A c aprock @ with a max i mum 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 la y ers of caliche formed by the leaching of calcium carbonate and silica from surface s oils during the Plio

Plestocene 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

A c aprock @ 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 a quifers are nearly indistinguishable (Ref. 8, p.73). Recharge to the Trinity Group (Edwards

- Trinity a quifer) occurs indirectly by downward percolation or infiltration fr o m the overlying Oga l lala (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 per mea ble 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 a quifer system, which can influence the ground water flow dir ection in the area of the site.

Hydrogeologic Stratum : 2

Stratum Name

The Edwards

- Trinity a quifer 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 a quifer (Ref. 7, p. 9). The Edwards

Trinity a quifer is usually hydraulically connected to the Ogallala sediments where both are present (Ref. 8, p. 83). The Edwards

- Trinity aqui fer 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 conglo m erate about 5 to 10 feet thick, consisting of red an d 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) AquiferHazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 37 

### c ontaining 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 southeas t ward under hydraulic gradients that average about 10 feet/mile (Ref. 25, pp. 34

- 41). Local e xceptions 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 nort h western Midland County at about 3,100 feet above sea level. In Midland county, most r e charge results from infiltration of precipitation from land surface and most discharge o c curs through well withdraw. Water levels in Midland County have dropped 50 feet over last 50 years. Transmissivity values are approximately 5,000 feet 2 

### /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 a quifer) at the W est County Road 112 Ground Water s ite. The upper part of the Dockum contains the largest percen t ages 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 A r ed

b eds @

.

The underlying mudstone sequences in the Dockum Group are considered the lower

co n fining 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).Hazard Ranking System Document Record West County Road 112 Ground Water
October r 2010 T XN 000 606 992 38 

### 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
evidenc e 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 S ite. 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 acc ording 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 W ater Samples Collected

Sample ID* Sample Location Well Depth (feet) Date Collected Reference

GW

- 10 D rinking 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

.Hazard Ranking System Document Record West County Road 112 Grou n d Wa ter October 2010 TXN 00 0 606 992 39 

### Table 6: Summary of Highest Constituents Detected in the Background Ground
W ater Wells

S ample 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, p p

. 8
& 23 8

GW

- 160 Chromium VI ND [0.01 mg/L] NA

_ Ref. 17 , pp. 89

- 91; Ref. 38, p p . 6 & 16 ; Ref. 74, p.
5

GW

- 22 Chromium ND [10] NA + Ref. 6, p. 1; Ref. 89, p p

. 20 & 23 8

GW

- 066 Chromium VI ND [0.01 mg/L] NA

_ Ref. 12, p. 12; Ref. 29, p p

. 29 & 114; Ref. 29, p. 2 9

Notes : ND = Not Detected at the SQL. [SQL] = Sam ple Quantitation Limit. NA = Not applicable. + = Reported as Reporting Limit by Region 6 Laboratory

.

- = Reported as MQL UnAdj. b y Xenco Laboratories. * For all of the analyses the reporting limit in the references cited is the SQL based on the method dete ction 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 T able 2 -3 (Ref. 1, Section 2.3).

Table 7: Contaminated Ground W ater Pa thway Drinking Water Samples M eeting 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, p p . 20 & 75 ; Ref. 64, p. 31

GW

- 020 -A Chromium VI 0.435 0.0 1 Ref. 27, p p . 26 & 75 ; Ref. 64, p. 37

GW

- 048 -A Chromium VI 0.621 0.01 Ref. 27, p p . 5 & 75 ; Ref. 64, p. 12

GW

- 049 -A Chromium VI 1.24 0.05 Ref. 27, p p . 15 & 75 ; Ref. 64, p. 25

GW

- 050 -A Chromium VI 1.21 0.05 Ref. 27, p p . 10 & 75 ; Ref. 64, p. 18

GW

- 023 -A Chromium VI 1.12 0.05 Ref. 28, p p . 16 & 112 ; Ref. 65, p. 26

GW

- 042 -A Chromium VI 4.02 0.5 Ref. 28, p p . 55 & 114 ; Ref. 65, p. 65

GW

- 043 -A Chromium VI 0.519 0.01 Ref. 28, p p . 6 & 112 ; Ref. 65, p. 14Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 40 

### Table 7: Contaminated Ground W ater Pa thway Drinking Water Samples M eeting 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, p p . 32 & 113 ; Re f. 65, p. 39

GW

- 045 -A Chromium VI 1.23 0.05 Ref. 28, p p . 57 & 114 ; Ref. 65, p. 72

GW

- 046 Chromium VI 0.929 0.05 Ref. 2 8, p p . 2 2 & 112 ; Ref. 65, p. 32

GW

- 047 Chromium VI 4.56 0.5 Ref. 2 8, p p

. 39 & 113 ; Ref. 65, p. 46

GW

- 057 Chromium VI 0.026 0.01 Ref. 2 9, p p . 19 & 114 ; Ref. 66, p. 30

GW

- 058 Chromium VI 0.052 0.01 Ref. 29, p p . 69 & 11 5 ; Ref. 66, pp. 92

GW

- 064 Chromium VI 0.041 0.01 Ref. 29, p p . 54 & 11 5 ; Ref. 66, pp. 74

GW

- 083 Chromium VI 0.02 0.01 Ref. 29, p p . 74 & 11 5 ; Ref. 66, p. 98

GW

- 081 Chromium VI 0.322 0.01 Ref. 30, p p . 54 & 102 ; Ref. 67, p. 74

GW

- 082 Chromium VI 0.017 0.01 Ref. 30, p p . 49 & 102 ; Ref. 67, p. 68

GW

- 086 Chromium VI 1.42 0.05 Ref. 30, p p . 29 & 101 ; Ref. 67, p. 42

GW

- 091 -A Chromium VI 0.291 0.01 Ref. 31, p p . 4 & 29 ; Ref. 68, p. 7

GW

- 092 -A Chromium VI 0.437 0.01 Ref. 31, p p . 6 & 29 ; Ref. 68, p. 7

GW

- 093 -A Chromium VI 0.109 0.01 Ref. 31, p p . 7 & 29 ; Ref. 68, p. 7

GW

- 095 -A Chromium VI 0.202 0.01 Ref. 31, p p . 5 & 29 ; Ref. 68, p. 7

GW

- 096 -A Chromium VI 0.223 0.01 Ref. 31, p p . 11 & 31 ; Ref. 68, p. 9

GW

- 097 -A Chromium VI 0.207 0.01 Ref. 31, p p . 8 & 30 ; Ref. 68, p. 8

GW

- 099 -A Chromium VI 0.294 0.01 Ref. 31, p p . 10 & 30 ; Ref. 68, p. 8

GW

- 100 -A Chromium VI 2.34 0.05 Ref. 31, p p . 12 & 31 ; Ref. 68, p. 9

GW

- 101 -A Chromium VI 1.51 0.05 Ref. 31, p p . 9 & 30 ; Ref. 68, p. 8

GW

- 125 -A Chromium VI 0.838 0.05 Ref. 31, p p . 13 & 31 ; Ref. 68, p. 9

GW

- 090 -A Chromium VI 0.481 0.01 Ref. 32, p p . 4 & 24 ; Ref. 69, p. 7

GW

- 102 -A Chromium VI 0.197 0.01 Ref. 32, p p . 7 & 25 ; Ref. 69, p. 7

GW

- 103 -A Chromi um VI 0.638 0.05 Ref. 32, p p . 5 & 24 ; Ref. 69, p. 7

GW

- 105 -A Chromium VI 0.132 0.01 Ref. 32, p p . 6 & 24 ; Ref. 69, p. 7

GW

- 107 Chromium VI 0.03 0.01 Ref. 32, p p . 7 & 24 ; Ref. 69, p. 7Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 41 

### Table 7: Contaminated Ground W ater Pa thway Drinking Water Samples M eeting 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, p p . 6 & 24 ; Ref. 69, p. 7

GW -1 26 Chromium VI 0.115 0.01 Ref. 32, p p . 8 & 25 ; Ref. 6 9 , p. 8

GW

- 127 Chromium VI 0.42 0.01 Ref. 32, p p . 8 & 25 ; Ref. 69, p. 8

GW

- 098 A Chromium VI 0.053 0.01 Ref. 34, p p . 7 & 23 ; Ref. 70, p. 7

GW

- 104 Chromium VI 0.448 0.01 Ref. 34, p p . 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. 13 4).



### Table 8: Contaminated Ground W ater Pathway Drinking Water Samples M eeting 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 R ef. 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. 7 2 , p. 5

GW -0 90 -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. 5Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 42 

### Table 8: Contaminated Ground W ater Pathway Drinking Water Samples M eeting 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, p p . 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. 3 8, 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. 7 4, 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 Re f. 43, pp. 5 & 14; Ref. 77, pp. 5Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 43 

### Table 8: Contaminated Ground W ater Pathway Drinking Water Samples M eeting 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 0.4 47 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, p p . 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 t he reporting limit in the references cited is the SQL based on the method detection limit (Ref. 134).



### Table 9: Contaminated Ground W ater Pathway Drinking Water Samples M eeting Observed Release Criteria (July 2009 Results)

Sample Location Contaminant
Det ected Conc. (mg/L) SQL - (mg/L) * Reference

GW

- 029 Chromium VI 0.023 0.005 Ref. 50, p p

. 4 & 15 ; Ref. 80, pp. 5 -6

GW

- 036 Chromium VI 0.013 0.005 Ref. 50, p p . 4 & 15 ; Ref. 80, pp. 5 -6

GW

- 038 Chromium VI 0.031 0.005 Ref. 50, p p . 5 & 15 ; Ref. 80, pp. 5 -6

GW

- 053 Chromium VI 0.018 0.005 Ref. 50, p p . 8 & 16 ; Ref. 80, pp. 5 -6

GW

- 057 Chromium VI 0.027 0.005 Ref. 50, p p . 5 & 15 ; Ref. 80, pp. 5 -6

GW

- 058 -A Chromium VI 0.051 0.005 Ref. 50, p p . 6 & 16 ; Ref. 80, pp. 5 -6

GW

- 064 Chromium VI 0.088 0.005 Ref. 50, p p . 6 & 16 ; Ref. 80, pp. 5 -6

GW

- 071 Chromium VI 0.008 0.005 Ref. 50, p p . 7 & 16 ; Ref. 80, pp. 5 -6

GW

- 082 Chromium VI 0.018 0.005 Ref. 50, p p . 7 & 16 ; Ref. 80, pp. 5 -6

GW

- 107 Chromium VI 0.035 0.005 Ref. 50, p p . 7 & 16 ; Ref. 80, pp. 5 -6

GW

- 150 -A Chromium VI 0.124 0.005 Ref. 50, p p . 5 & 15 ; Ref. 80, p. 5

GW

- 261 Chromium VI 0.136 0.005 Ref. 51, p p . 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 -1 32 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. 13 4).Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 44 

### Table 10: Contaminated Ground W ater 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, p p

. 16 & 23 8

GW

- 19 Chromium 1010 10 Ref. 88, p. 5 ; Ref. 89, p p

. 12 & 23 8

GW

- 28 Chromium 1040 10 Ref. 88, p. 6 ; Ref. 89, p p

. 30 & 238

GW

- 27 Chromium 694 10 Ref. 88, p. 6 ; Ref. 89, p p

. 26 & 238

GW

- 14 Chromium 4450 10 Ref. 88, p. 5 ; Ref. 89, p p

. 38 & 2 40

GW

- 21 Chromiu m 1400 10 Ref. 88, p. 6 ; Ref. 89, p p

. 42 & 240

GW

- 31 Chromium 3780 10 Ref. 88, p. 6 ; Ref. 89, p p. 50 & 240

GW

- 29 Chromium 1400 10 Ref. 88, p. 6 ; Ref. 89, p p

. 46 & 240

GW

- 07 Chromium 110 10 Ref. 88, p. 5 ; Ref. 89, p p

. 66 & 242

GW

- 13 Chromium 530 10 Ref. 88, p. 5 ; Ref. 89, p p

. 74 & 242

GW

- 12 Chromium 191 10 Ref. 88, p. 5 ; Ref. 89, p p

. 70 & 242

GW

- 08 Chromium 350 10 Ref. 88, p. 1 5 ; Ref. 89, p p

. 94 & 244

GW

- 05 Chromium 217 10 Ref. 88, p. 5 ; Ref. 89, p p

. 62 & 242

GW

- 03 Chromium 2510 10 Ref. 88, p. 5 ; Ref . 89, p p

. 54 & 242

GW

- 04 Chromium 1980 10 Ref. 88, p. 5 ; Ref. 89, p p

. 58 & 242

GW

- 16 Chromium 440 10 Ref. 88, p. 5 ; Ref. 89, p p

. 102 & 244

GW

- 02 Chromium 239 10 Ref. 88, p. 5 ; Ref. 89, p p

. 90 & 244

GW

- 09 Chromium 375 10 Ref. 88, p. 5 ; Ref. 89, p p

. 98 & 244

GW

- 01 Chromium 431 10 Ref. 88, p. 5 ; Ref. 89, p p

. 86 & 244

GW

- 11 Chromium 466 10 Ref. 88, p. 5 ; Ref. 89, p p

. 128 & 247

GW

- 06 Chromium 116 10 Ref. 88, p. 5 ; Ref. 89, p p

. 1 24 & 247

GW

- 17 Chromium 47.3 10 Ref. 88, p. 5 ; Ref. 89, p p

. 132 & 247

GW

- 18 Chromium 313 10 Ref. 88, p. 5 ; Ref. 89, p p

. 136 & 247

GW

- 15 Chromium 107 10 Ref. 88, p. 5 ; Ref. 89, p p

. 112 & 246

GW

- 34 Chromium 491 10 Ref. 88, p. 5 ; Ref. 89, p p

. 120 & 246

GW

- 25 Chromium 1140 10 Ref. 88, p. 6 ; Ref. 89, p p

. 116 & 246

Note :Hazard Ranking System Document Record West County Road 112 Ground Water
October r 2010 T XN 000 606 992 45 + = Report ed 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. 13 4).



### Table 11: Contaminated Ground W ater Pathway Drinking Water Samples meeting
Obser ved Release Criteria (September 2009 Results)

Sample Location Contaminant
Detected Conc. (mg/L) SQL - (mg/L) * Reference

GW

- 104 Chromium 0.422 0.05 Ref. 9 8 , pp. 4 & 16 ; Ref. 45, p. 21; Ref. 42, p.
8

GW -0 20 Chromium 0.508 0.05 Ref. 94, pp. 5 & 20; Ref. 45, p. 21; Ref. 42, p.8

GW -0 23 Chromium 1.01 0.05 Ref. 94, pp. 6 & 20

- 21; Ref. 45, p. 22; Ref. 42, p. 8

GW -0 42 -A Chromium 3.62 0.05 Ref. 94, pp. 8 & 21; Ref. 45, p. 22; Ref. 42, p.
9

GW -0 43 -A Chromium 0.668 0.05 Ref. 93, p p . 6 & 20 ; Ref. 45, p. 20; Ref. 42 , p. 7

GW -0 44 -A Chromium 1.71 0.05 Ref. 93, p p . 5 & 20 ; Ref. 45, p. 20; Ref. 42, p.

7

GW -0 45 -A Chromium 1.5 0.05 Ref. 93, p p . 9 & 22 ; Ref. 45, p. 21; Ref. 42, p.
8

GW -0 46 -A Chromium 1.11 0.05 Ref. 93, p p . 7 , 20, & 22; Ref. 45, p. 20; Ref. 42, p. 7

GW -0 48 -A Chromium 0.572 0.05 Ref. 95, p p . 10 & 22 ; Ref. 45, p. 23; Ref. 42, p
10

GW -0 49 Chromium 1.01 0.05 Ref. 95, p p . 5 & 21 ; Ref. 45, p. 23; Ref. 42, p.
9

GW -0 50 -A Chromium 1.04 0.05 Ref. 95, p p . 6 & 21 ; Ref. 45, p. 23; Ref. 42, p.
9

GW -0 80 -A Chromium 0.097 0.05 Ref. 93, p p . 7 & 21 ; Ref. 45, p. 21; Ref. 42, p.

7

GW -0 90 -A Chromium 0.419 0.05 Ref. 95, p p . 9 & 22 ; Ref. 45, p. 23; Ref. 42, p.
10

GW -0 91 -A Chromium 0.335 0.05 Ref. 93, p p . 10 & 22 ; Ref. 45, p. 21; Ref. 42,

p. 8

GW -0 92 -A Chromium 0.537 0.05 Re f. 94, pp. 9 & 21; Ref. 45, p. 22; Ref. 42, p.
9

GW -0 93 -A Chromium 0.211 0.05 Ref. 94, pp. 10 & 21

- 22; Ref. 45, p. 22; Ref. 42, p. 9

GW -0 94 -A Chromium 0.127 0.05 Ref. 94, pp. 11 & 22; Ref. 45, p. 2 2 ; Ref. 42, p. 9

GW -0 95 -A Chromium 0.21 0.05 Ref. 95, pp. 7 & 21; Ref. 45, p. 23; Ref. 42, p.
10

GW -0 96 -A Chromium 0.273 0.05 Ref. 93, pp. 11 & 22; Ref. 45, p. 21; Ref. 42, p. 8

GW -0 97 -A Chromium 0.272 0.05 Ref. 95, pp. 4 & 20; Ref. 45, p. 22; Ref. 42, p.
9Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 46 

### Table 11: Contaminated Ground W ater Pathway Drinking Water Samples meeting
Obser ved 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 -0 19 -A Chromium 0.17 0.05 Ref. 97, pp. 6 & 17; Ref. 45, p. 25; Ref. 42, p.

11

GW -0 81 -A Chromium 0.267 0.05 Ref. 97, pp. 7 & 17

- 18;Ref. 45, p. 25; Ref. 42, p. 12

GW -0 86 -A Chromium 1.59 0.05 Ref. 97, pp. 8 & 18; Ref. 45, pp

. 25 ; Ref. 42, p. 12

GW -0 99 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 Chro mium 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 -0 98 -A Chromium 0.098 0.05 Ref. 99, pp. 5 & 20; Ref. 45, p. 26; Ref. 42, p.
13

GW -0 47 -A Chromium 4.51 0.05 Ref. 100, pp. 5 & 23; Ref. 45, p. 27; Ref. 42, p. 13

GW -0 64 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, p p . 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. 13 4).Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 47 

### Table 12: Contaminated Ground W ater Pathway Drinking Water Samples meeting Observed Release Criteria (November 2009 Results)

Sample
Location Contaminant
Detected Conc. mg/L SQL mg/L * Reference

GW

- 151 Chromium 0.073 0.05 Ref. 44, p. 3 ; Ref. 46, p. 4 ; Ref. 55, p p . 8 & 25

GW -2 99 Chromium 0.161 0.05 Ref. 44, p. 4 ; Ref. 46, p. 4 -5 ; Ref. 55, p p . 13 &
26

GW

- 313 Chromium 0.076 0.05 Ref. 44, p. 3 ; Ref. 46, p. 4 -5 ; Ref. 55, p p . 11 &
26

GW

- 058 Chromium 0.053 0.05 Ref. 44, p. 5; Ref. 46, p. 6; Ref. 57, p p . 6 & 19

Note:

- = Reported a s 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. 13 4).



### Attribution

The site is designated as a contaminated ground water plume origi nating 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 aqu ifer since an observed release by chemical analysis was
established in the Edwards- Trinity aquifer.

Observed Release Factor Value: 550Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 48 

### 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 o f 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 substance s 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, t he f ollowing toxicity, mobility

, and combined toxicity/mobility
factor value has been assigned to th e substance s 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 S ite, regardless of the a quifer being evaluated, is assigned a mobility factor value of 1 (Ref. 1, Section 3.2.1.2).

Therefore, t he 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: 10,000Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 49 

### 3.2.2

Table 1 4: 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 W ater Migration Pathway are subject to Level I concentrations (Ref. 1, Section 2.4.2.2).

S ource Number S ource Hazardous Was te Quantity
Value H azardous 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 b y 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 Characteristic s Factor Value: 32Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 50 

### 3.3

The primary aquifer being evaluated for the ground water pathway targets is the EdwardsTrinity aquifer

. The ground water pathway targets for th is 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 T able 15 . The average population per household o f 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

.

μ g/L (mg/L) Benchmarks/Screening
Concentrations (Ref. 3 , pp. 1 -3) Population
Served Reference MCL /
MCLG

μ g/L (mg/L) Cancer Risk
Screen.
Con c

. μg /L

(mg/L) Ref. Dose
Screen.
Conc. μ g/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 &
19Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 51 

### Table 15: Drinking Water Wells with Level I Concentration of Chromium

Well ID Chromiu
m Conc

.

μ g/L (mg/L) Benchmarks/Screening
Concentrations (Ref. 3 , pp. 1 -3) Population
Served Reference MCL /
MCLG

μ g/L (mg/L) Cancer Risk
Screen.
Con c

. μg /L

(mg/L) Ref. Dose
Screen.
Conc. μ g/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 number s 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 Reference MCL /
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 availableHazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 52 

### 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 Fac tor Value of 50 is assigned (Ref. 1, Section 3.3.1).

Nearest Well Factor Value: 50Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 53 

### 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
detecti ons 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 S ite conta ined Level I concentrations
of hazardous substances (see Table 15 and Table 16 ). All the private wells d rew water from
the Edwards- Trinity A quifer (Ref. 111, pp.1 -2). The residents depend upon their private wells for their daily water needs

. TCEQ has in stalled 4 5 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, t he 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: 533Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 54 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 t he 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 concent ration 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 . μ g/L

(mg/L) Benchmarks/Screening
Concentrations

Population
Served Reference MCL /
MCLG

μ g /L (mg/L) Cancer
Risk
Screen.
Con. μ g/L

(mg/L) Ref. Dose
Screen.
Conc.

μ g/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; Re f. 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

Tot al 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 concentratio n of chromium have not been considered.

Table 18: Drinking Water Well with Level II Concentration of Chromium VI

Well ID Chromium
Conc

.

m g/L Benchmarks/Screening
Concentrations Population
Served Reference MCL /
MCLG

mg /L Cancer
Risk
Screen.
Con. m g/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. 5Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 55 

### Table 18: Drinking Water Well with Level II Concentration of Chromium VI

Well ID Chromium
Conc

.
m g/L Benchmarks/Screening
Concentrations Population
Served Reference MCL /
MCLG

mg /L Cancer
Risk
Screen.
Con. m g/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: 34.72Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 56 

### 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 an d 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 conta minants 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 g round water wells were located. T wo 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 :Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 57 

### 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. B ecause 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 sys tem’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 ra dius 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 ‘ O ther T han Karst’ distance category and a distance

weighted 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 : Potenti al 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)

821.54 68 2 (ID: 1650057) 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 acco unted for in Level I or II contamination sections
of this HRS documentation record.Hazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 58 ** O n ly seven of the 12 we lls located in this distance category ring were considered subject to potential
contamination as the rest were accounted for in the Level I or II c ontamination sections of this HRS
documentation record.



### 3.3.3 Resources

No r esources, 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 W ater 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: NSHazard Ranking System Document Record West County Road 112 Ground Water
October 2010 TXN 0 00 606 992 59 

### 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, S ection 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

S gw 

### + S
sw 

### + S
s 

### + S
a 

### = 10,000 + 0 + 0 + 0 = 10,000 10,000 / 4 = 2,500

√ 2,500 = 50.00

HRS Site Sc ore: 50.00