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MEMO

To:

Lisa Dernbach, P.G., C.E.G., C.H.G. California Regional Water Quality Control Board, Lahontan Region (RWQCB)

Copies:

Anne Holden, RWQCB Iain Baker, PG&E

From:

Scott Seyfried, P.G. Isaac Wood, P.G.

Date:

November 7, 2014

Subject:

Plan for Enhancement of Lower Aquifer Remedy (Installation of EX-37) PG&E Hinkley Compressor Station, Hinkley, California

1.0 Introduction

This memorandum is submitted to the California Regional Water Quality Control Board, Lahontan Region (RWQCB) to present a plan to improve the effectiveness of the current extraction system for remediation of hexavalent chromium (Cr[VI]) in the Lower Aquifer at the Hinkley Compressor Station in Hinkley, California. The extent of Cr(VI) in the Lower Aquifer along with monitoring and Upper Aquifer extraction wells is shown on Figure 1. This memo presents a summary of Lower Aquifer remedial implementation to date, followed by a description of the proposed scope of work for installation of a new extraction well that targets extraction from both the Upper Aquifer and the Lower Aquifer.

2.0 Lower Aquifer Remedial Implementation and Effectiveness Evaluation

The plume map for Cr(VI) in the Lower Aquifer for the Third Quarter 2014 was presented on Figure 5-3 of the October 30, 2014 Third Quarter 2014 Groundwater Monitoring Report and Domestic Well Sampling Results (Third Quarter GMP Report, CH2M Hill, 2014) and is attached here for reference. Results of groundwater monitoring indicate that the combined remedial actions listed below have effectively reduced the potential for horizontal migration of chromium-impacted groundwater within the Lower Aquifer, and reduced the potential for downward migration of chromium-impacted groundwater from the Upper Aquifer into the Lower Aquifer. For example, the concentration of chromium in four of the five Lower Aquifer monitoring wells with current chromium concentrations above 3.1/3.2 micrograms per liter (µg/L) was lower during the Third Quarter of 2014 than the historical maximum concentrations at these wells. Reduced lateral and vertical migration of chromium-impacted groundwater in the Lower Aquifer is

Scott.Seyfried@arcadis-us.com

Isaac.Wood@CH2M.com

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achieved by the following measures, which are focused near MW-23C and MW-92C, where chromium has been detected at the highest concentrations in the Lower Aquifer:

· Focused groundwater extraction in Upper Aquifer wells EX-29 and EX-30 (shown on Figure 1). The Upper Aquifer chromium is believed to have entered the Lower Aquifer in this general area when the Lower Aquifer supply wells (Ryken-8 and Ryken-9) (Figure 1) were in operation until August 2011.

· Upper Aquifer groundwater extraction for irrigation supply at the Agricultural Treatment Units (ATUs) and Northwest Extraction Area (EX-16, EX-20, and EX-21). This creates a large area of drawdown in Upper Aquifer as shown on Figures 3-1 and 3-2 of the Third Quarter GMP Report, attached here for reference (CH2M Hill, 2014). Drawdown of the Upper Aquifer has enhanced upward vertical gradients from the Lower Aquifer toward the Upper Aquifer.

· Providing alternative water supply source from supply wells PGE-14, FW-01, and FW-02 (upgradient of the chromium plume) to remove the need for pumping Lower Aquifer supply wells (Ryken-8 and Ryken-9, shown on Figure 1) on an ongoing basis. Pumping from the Lower Aquifer supply wells Ryken-8 and Ryken-9 appears to have been the primary driving force drawing Upper Aquifer chromium into the Lower Aquifer.

Figure 5-6 excerpted from the September 30, 2014 Semiannual Remediation Status and Final Cleanup Effectiveness Report (CH2M Hill and ARCADIS, 2014), and attached here for reference, shows hydrographs for selected Upper and Lower Aquifer well pairs demonstrating that the vertical hydraulic gradient has been reversed in response to the remedial actions listed above and is primarily upward from the Lower Aquifer toward the Upper Aquifer. This hydraulic reversal is shown by higher groundwater elevations in Lower Aquifer wells (MW-21C, MW-23C, MW-34, and MW-55C) compared with groundwater elevations in Upper Aquifer wells (MW-21A, MW-21B, MW-23B, MW-55A, and MW-55B).

The extent of Cr(VI) in the Lower Aquifer remains contained with limited horizontal movement of existing Cr(VI), as evidenced by steady to decreasing concentration trends in the majority of the Lower Aquifer groundwater monitoring wells. Groundwater elevation data collected from the Lower Aquifer are consistent with these concentration trends (see Lower Aquifer groundwater elevation map, Figure 3-4 in the Third Quarter GMP report, included here for reference).

Recently, Cr(VI) concentrations increased at monitoring wells MW-92C and MW-100C, located within the area of elevated Cr(VI) concentrations. The current concentration at MW-92C (24.0 µg/L) is more than 50 percent less than the historical maximum concentration from August 2011 (41.8 µg/L), measured shortly after pumping from the Lower Aquifer supply wells was significantly reduced. The Cr(VI) concentration at MW-100C during Second and Third Quarter of 2014 (19 µg/L) were the highest reported to date at that well.

The recent increases in Cr(VI) concentrations at MW-100C may have been influenced by potential hydraulic impacts resulting from extraction from nearby Upper Aquifer extraction well EX-26 on Lower Aquifer groundwater elevations. Analysis of groundwater elevations in the Lower Aquifer near EX-26

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indicates that extraction from EX-26 results in drawdown within the Lower Aquifer toward that well, which may have resulted in migration of Cr(VI) to the vicinity of well MW-100C (Figure 3-4 from the Third Quarter GMP report).

A hydrograph of two Upper Aquifer/Lower Aquifer well pairs is shown on Figure 2 before and after a period with no extraction at EX-26. The top hydrograph shows pressure transducer data for the MW-23B/MW-23C well pair. Consistent upward gradients from Lower Aquifer well MW-23C towards Upper Aquifer well MW-23B (MW-23C higher in elevation than MW-23B) are seen with limited response to changes in Upper Aquifer extraction at EX-26. However, as shown on the bottom hydrograph of Figure 2, groundwater extraction from EX-26 results in a hydraulic response in the Lower Aquifer at MW-100C, while also drawing down Upper Aquifer monitoring well PZ-02. Drawing down Lower Aquifer water levels at MW-100C with Upper Aquifer extraction in this area could potentially be inducing flow from an area of higher concentration (south near MW-92C), towards well MW-100C. As such, extraction from EX-26 may have resulted in localized migration of Cr(VI)-affected Lower Aquifer groundwater to the north, resulting in the increase in Cr(VI) concentrations in MW-100C. Given that the well EX-26 is screened above the Blue Clay, these data indicate that the Blue Clay in the vicinity of EX-26 is not sufficiently thick and/or continuous to function as a hydraulic aquitard that separates the Upper from the Lower Aquifer. Rather, in the vicinity of EX-26, extraction from above the Blue Clay has a direct hydraulic expression in the Lower Aquifer. This observation is consistent with lithologic data in this portion of the site, which indicates that the Blue Clay is encountered only intermittently and when encountered, is found to be relatively thin (less than a few feet thick).

3.0 Recommendation for New Extraction Well EX-37

Based on these observations, extraction of groundwater from both the Upper Aquifer and Lower Aquifer is recommended near MW-92C, where Cr(VI) has been detected at the highest concentrations within the Lower Aquifer. Lithologic data collected from borings in the vicinity of the proposed location and groundwater levels measured with pressure transducers, indicate that the Blue Clay is either not present, or is thin where present. Under these conditions, the Blue Clay does not function as an effective aquitard separating the Lower and Upper Aquifers, and extraction across both units is recommended to remove Cr(VI) affected groundwater without inducing downward gradients toward the Lower Aquifer.

New groundwater extraction well, EX-37 (Figure 1) is planned for installation during in the second half of November to enhance the existing remedial actions for the Lower Aquifer. EX-37 will be screened across the saturated alluvium forming the Upper Aquifer, through any Blue Clay that is present at this location, and across the weathered bedrock sediments comprising the thin (generally less than 10 feet) Lower Aquifer in this area. This southerly location and screening into the weathered bedrock is designed to enhance capture of Cr(VI) in the Lower Aquifer where concentrations are highest near MW-92C. The MW-92C location was also selected, rather than near MW-100C and EX-26 further to the north, so that the potential undesired effect of drawing existing Lower Aquifer chromium further north towards MW-100C would not occur. In addition, the extraction rate at EX-26 has been reduced and will continue to operate at a reduced rate to improve horizontal hydraulic gradients in the Lower Aquifer to further reduce northward movement of Cr(VI).

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EX-37 will be installed using a sonic drill rig. It is anticipated that a 10-inch diameter borehole will be advanced to the weathered bedrock/bedrock interface. Soil cores will be collected near-continuously. EX-37 will be constructed of 6-inch Schedule 80 PVC casing and 6-inch stainless steel screen. The specific screened interval will be determined during the installation process based on lithologic information collected from soil cores. The well screen will be surrounded by a silica sand pack to two feet above the top of the screen interval, followed by 3 feet of fine-grained silica transition sand, and then overlain by approximately 100 feet of Portland cement grout. Actual screen depths, lengths, slot sizes, and backfill materials may vary based on field findings and lithology during construction. Upon completion of well installation, Well Completion Reports will be prepared and submitted to the California Department of Water Resources.

Water extracted from EX-37 may be applied to Agricultural Treatment Units (ATUs), such as the Ranch or Desert View Dairy (DVD) ATUs, or sent south to the South Central Re-injection Area In Situ Reactive Zone. The plans for piping that will connect EX-37 with the piping network that extends to these remedial systems is in progress and will be shared with the RWQCB prior to installation.

Pumping from Lower Aquifer supply wells Ryken-8 and Ryken-9 will continue to be reduced (or cease altogether) by supplying freshwater to the DVD from extraction wells PGE-14, FW-01, and/or FW-02 and eventually new wells FW-03 and FW-04 (south of the compressor station). In addition to adding a new extraction well, groundwater extraction at Upper Aquifer wells EX-29 and EX-30 and other wells in the area will continue. These efforts, combined with additional Upper Aquifer groundwater extraction in the greater area, are expected to continue to generate upward hydraulic gradients near the DVD and MW-23C to prevent further migration of Upper Aquifer chromium into the Lower Aquifer and continue to reduce chromium mass in the Lower Aquifer.

References

CH2M Hill. 2014. Third Quarter 2014 Groundwater Monitoring Report and Domestic Well Sampling Results, Site-wide Groundwater Monitoring Program. Pacific Gas and Electric Company. Hinkley Compressor Station. Hinkley, California. October 30.

CH2M Hill and ARCADIS. 2014. Semiannual Remediation Status and Final Cleanup Effectiveness Report (January through June 2014), PG&E Compressor Station, Hinkley, California. September 30.

Figures

Figure 1 Extent of Chromium in Lower Aquifer and Proposed Location of EX-37

Figure 2 Hydrographs for Upper/Lower Aquifer Well Pairs

Attachments

Figure 5-3 Chromium Results for Lower Aquifer Groundwater Monitoring and Domestic wells, Third Quarter 2014 (CH2M Hill, 2014)

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Figure 3-1 Groundwater Elevations in the Shallow Zone of the Upper Aquifer, South Hinkley Valley, Third Quarter 2014 (CH2M Hill, 2014)

Figure 3-2 Groundwater Elevations in the Deep Zone of the Upper Aquifer, South Hinkley Valley,

Third Quarter 2014 (CH2M Hill, 2014) Figure 5-6 Lower/Upper Aquifer Groundwater Elevations and Pumping Rates, January 2010 to June

30, 2014 (CH2M Hill and ARCADIS, 2014) Figure 3-4 Groundwater Elevations in the Lower Aquifer and Bedrock, Third Quarter 2014 (CH2M

Hill, 2014)

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EXTENT OF CHROMIUM IN LOWER AQUIFER AND PROPOSED LOCATION OF EX-37

FIGURE1

PACIFIC GAS AND ELECTRIC COMPANYHINKLEY, CALIFORNIA

Note:µg/L = micrograms per literCr(VI) = hexavalent chromiumCr(T) = total dissolved chromium

LegendMonitoring WellExtraction WellProposed Extraction WellInactive Supply Wells Ryken-8 and 9Piezometer

Approximate outline of Cr(VI) and Cr(T)in Lower Aquifer exceeding 3.1 and 3.2 µg/LApproximate 10 µg/L outline of Cr(VI) or Cr(T) concentrations in Lower Aquifer, Third Quarter 2014Approximate extent of blue clay layer forming lower aquifer. The blue clay layer is thin and leaky in portions of the western extent

FIGURE 2HYDROGRAPHS FORUPPER/LOWER AQUIFER WELL PAIRSPACIFIC GAS AND ELECTRIC COMPANYHINKLEY, CALIFORNIA

Notes1) ft. ASML: Feet Above Mean Sea-Level2) Groundwater levels measured with pressure transducers

recording data at 30 minute intervals.

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Upper Aquifer Extraction Well EX-26turned off during this period

Upper Aquifer Extraction Well EX-26turned off during this period

FIGURE 5-3CHROMIUM RESULTS FOR LOWER AQUIFER GROUNDWATER MONITORING AND DOMESTIC WELLS,THIRD QUARTER 2014T HIRD QU ART ER 2014 GROU NDWAT ER MONIT ORING REPORT AND DOMEST IC WEL L RESU L T SSIT E-WIDE GROU NDWAT ER MONIT ORING PROGRAMPACIFIC GAS AND EL ECT RIC COMPANY HINKL EY COMPRESSOR STAT IONHINKL EY, CAL IFORNIA

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Approxim ate 10-µ g/L outline of Cr(VI) or Cr(T ) concentrations in L owerAquifer, T hird Quarter 2014

Approxim ate outline of Cr(VI) or Cr(T ) in L ower Aquifer exceeding values of 3.1 and 3.2 µ g/L , respectively, T hird Quarter 2014

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Approxim ate location of L ockhart Fault; fault trace is inferred, and there is no surface expression (Stam os et al., 2001)PG&E-owned propertyPG&E Com pressor Station

±NOTE:1. Chrom ium concentration contours are based on July through Septem ber 2014 sam pling of groundwater m onitoring wells com pleted in the L ower Aquifer (saturated zone below the blue clay aquitard). Where the blue clay is not present, all saturated deposits above bedrock are part of the U pper Aquifer.2. Pursuant to the L ahontan Regional Water Quality Control Board’s letter Review of Chromium Plume Maps, Third Quarter 2013 Groundwater Monitoring Report and Agreement with Northern Investigation Concept dated Decem ber 12, 2013, groundwater m onitoring wells are not used for chrom ium contouring if they are located in the areas southwest of the L ockhart Fault and on or east of Dixie Road.

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MW-121S*2,094.50

MW-147S*2,092.50

MW-158S*2,099.66

MW-169S2*2,094.53

MW-170S*2,083.52

MW-201S*2,093.72

MW-202S*2,094.72

MW-21A*2,075.35

MW-22A2*2,082.13

MW-29*2,087.59

MW-32S*(2,085.08)

MW-41S*2,089.11

MW-45A*2,087.67

MW-47A*2,088.63

MW-50S*2,087.50

MW-54*2,093.47

MW-55S*2,081.89

MW-58*2,093.94

MW-63*2,084.87

MW-66A*2,090.78

MW-68S*2,082.49

MW-69S*2,081.80

MW-70S*2,080.64

MW-71S*2,078.01

MW-72S*2,079.10

MW-76S*2,089.09

MW-77S*2,124.67

MW-79S*2,079.89

MW-80S*2,080.19

MW-82S*2,089.87

MW-83S*2,082.43

MW-84S*2,078.70

MW-86S*2,082.53

MW-87S*2,086.23

MW-88S*2,089.18

MW-89S*2,080.04

PZ-01A*2,097.00

PZ-04*2,079.25

PZ-05*2,078.76PZ-06*2,077.96

PZ-08*2,082.70

MW-109*2,083.28

MW-143S2,111.41

MW-144S2,114.75

MW-145S2,106.31

MW-146S2,112.51

MW-148S2,091.84

BW-01S2,119.65

CA-MW-107S2,101.08

CA-MW-3012,094.34

CA-MW-302S2,096.60

CA-MW-303S2,097.01

CA-MW-3042,097.16

CA-MW-3052,098.46

CA-MW-3082,098.79

CA-MW-310S2,099.27

CA-MW-4012,091.95

CA-MW-405S2,095.75

CA-MW-409S2,097.46

CA-MW-501S2,089.98

CA-MW-5052,092.55 CA-MW-508S

2,093.46CA-MW-510S2,095.02

CA-MW-6012,087.34

CA-MW-6022,087.70

CA-MW-6032,088.36

DW-012,081.19

EX-102,090.52

MW-101S2,085.07

MW-103S2,111.43

MW-107S2,078.95

MW-108S2,085.22

MW-110S2,095.24

MW-112S2,084.35

MW-114S2,092.30

MW-115S2,107.06

MW-116S2,102.47

MW-117S12,075.64

MW-117S22,075.82

MW-127S12,077.68

MW-128S12,078.03

MW-128S22,078.32

MW-129S2,078.04

MW-149S2,118.06

MW-14A2,088.87

MW-150S12,123.83

MW-155S2,097.46

MW-159S2,131.90 MW-16

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MW-160D2,130.11

MW-163S2,149.05

MW-164S2,094.75

MW-165S2,096.26

MW-167S12,122.37

MW-168S2,093.11

MW-169S12,094.28

MW-172,121.16

MW-171S2,076.88

MW-172S12,074.79

MW-177S2,126.28

MW-178S2,102.71

MW-180RS2,104.00

MW-181S2,126.47

MW-187S12,108.38

MW-190S12,112.90

MW-192S2,110.71

MW-199S12,108.52

MW-203S2,100.53

MW-392,119.32

MW-44A2,089.32

MW-49S2,094.37

MW-512,123.41

MW-532,126.96

MW-592,091.10

MW-612,090.19

MW-67A2,113.09

MW-73S2,112.95

MW-74D2,097.39

MW-78S(2,119.31)

MW-81S2,088.68

MW-85S2,079.44

MW-94S2,078.95

MW-96S2,085.54

MW-97S2,079.84

SA-MW-10S2,110.32

SA-MW-11S2,109.88

SA-MW-16S2,114.54

SA-MW-18S2,111.08

SA-MW-20S2,110.65

SA-MW-24S2,112.26

SA-MW-25S2,112.19

SA-SM-01S2,111.09

SA-SM-08S2,119.33

SA-SM-11S2,114.40

SC-MW-02S2,108.47

SC-MW-03S2,106.84

SC-MW-04S2,105.74

SC-MW-05S2,104.02

SC-MW-06S2,103.10

SC-MW-08S2,100.67

SC-MW-09S2,099.89

SC-MW-12S2,106.74

SC-MW-13S2,104.48

SC-MW-15S2,108.10

SC-MW-16S2,106.92

SC-MW-23S2,107.27

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eb

lo R

d

Se

rra

Rd

Pe

tra

Rd

Bla

nca

Rd

Santa Fe Ave

Dix

ie R

d

Flo

we

r R

d Su

mm

ers

et

Rd

Su

mm

ers

et

Rd

Acacia St

Se

rra

Rd

Aquarius Rd

Highcrest Rd

Mo

un

tain

Vie

w R

d

Alcudia Rd

Community Blvd

Valle

yWell

sRd

Coon Canyon Rd

Co

on

Ca

ny

on

Rd

Riv

erv

iew

Rd

UV58

Va

lle

y W

ell

s R

d

Pa rk Ave

Min or Rd

He

rve

y R

d

IN-01

IN-02

IN-03R

IN-04

IN-05

Area of 1-foot

Contours

Mountain General Fault

Lockhart Fault

2092

20942096

2089

2100

2095

2099

2130

2095

20902085

2098

2093

2120

2090

2080

2105

2145

2080

2085

2125

2125

2115

2110

2091 2088

2105

2110

2135

2140

2115

2097

2098

2075

2096

2097

2145

2087

2096

2125

2088

2089

2140

20942093

2091

2135

2092

2130

2100

2080

2120

2080

2075

2087

2080

2125

2080

GormanNorth

GormanSouth

Cottrell

Ranch

Yang

FIGURE 3-1GROUNDWATER ELEVATIONS IN THE SHALLOW ZONE OF THE UPPER AQUIFER, SOUTH HINKLEY VALLEY, THIRD QUARTER 2014THIRD QUARTER 2014 GROUNDWATER MONITORING REPORT AND DOMESTIC WELL RESULTSSITE-WIDE GROUNDWATER MONITORING PROGRAMPACIFIC GAS AND ELECTRIC COMPANYHINKLEY COMPRESSOR STATIONHINKLEY, CALIFORNIA

BAO R:\PGEHINKLEY20000353\MAPFILES\2014\GMP_REPORT\Q3\FIG3-1_GWE_UUA_C_SIZED.MXD GMOON 10/21/2014

LEGEND:! Monitoring well"/ Active groundwater extraction well "/ Inactive groundwater extraction well @"!A Freshwater injection well

Potentiometric elevation contours (dashed where inferred) General groundwater flow directionAverage Groundwater GradientApproximate limit of saturated alluvium Estimated capture zone in shallow zone of Upper Aquifer based on July/August 2014 groundwater level measurementsIn Situ Reactive ZoneAgricultural Treatment Units

! ! !

Approximate location of fault trace is inferred and there is no surface expression (Stamos et al., 2001)County parcels

0 500 1,000

Feet

±NOTES:1. Groundwater elevation contours represent the hydraulic gradient in the shallow zone of the Upper Aquifer. The shallow wells of nested completions (wells designated “A” or “S”) were preferentially used for contouring. In all cases, the screened interval of the well was taken into account.2. Groundwater level measurements for wells without an asterisk“*” are manual water level measurements collected between July 1 and August 7, 2014. Groundwater elevations marked with an asterisk “*” are the averages of pressure transducer data collected at 30-minute intervals from July 1 through 31, 2014.

WORKS CITED:Stamos, C.L., P. Martin, T. Nishikawa, and B.F. Cox. 2001. Simulation of Ground-Water Flow in the Mojave River Basin, California. U.S. Geological Survey Water-Resources Investigations Report 01-4002, Version 3. Prepared in cooperation with the Mojave Water Agency.

West Hinkley Valley Average Groundwater Gradient: 0.0071 feet/footGroundwater Velocity Estimate Range: 0.02 to 0.96 feet/dayAverage Groundwater Velocity Estimate: 0.29 feet/day or 107 feet per year

East Hinkley Valley Average Groundwater Gradient: 0.0030 feet/footGroundwater Velocity Estimate Range: 0.02 to 5.34 feet/dayAverage Groundwater Velocity Estimate: 1.64 feet/day or 600 feet per year

MW-163S(2149.08)

Well IDGroundwater elevation not used for contouring

BAO R:\PGEHINKLEY20000353\MAPFILES\2014\GMP_REPORT\Q3\FIG3-2_GWE_LUA_C_SIZED.MXD GMOON 10/21/2014

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C-01

C-02C-03

C-04

EX-01

EX-03

EX-05

EX-09

EX-15

EX-16EX-20

EX-21EX-22

EX-23

EX-24 EX-25

EX-26

EX-29

EX-30

EX-31

EX-32

EX-33

EX-34

EX-35

G-1R

G-2R

G-5R

IW-01 IW-02

IW-03

Y-01

Y-02Y-03EX-04

EX-36

MW-143D12,109.38

MW-144D12,113.19

MW-145D12,106.02

MW-146D12,108.74

CA-MW-302D2,093.98

CA-MW-306D2,098.47

CA-MW-310D2,099.21

CA-MW-317D2,096.31

CA-MW-412D2,092.49

CA-MW-510D2,092.58

MW-092,089.51

MW-102,085.33

MW-101D2,085.27

MW-103D2,107.30

MW-107D2,075.25

MW-108D2,085.10

MW-110D2,094.01

MW-112D2,074.38

MW-114D12,098.84

MW-115D2,100.32

MW-116D12,098.03

MW-117D2,066.98

MW-124D2,068.22

MW-14B2,088.32

MW-150S22,135.46

MW-153S2,092.95

MW-155D2,109.70

MW-164D2,093.72

MW-168D2,092.13

MW-171D12,074.36

MW-177D2,126.30

MW-178D2,102.22

MW-179D2,114.39

MW-17D2,121.47

MW-181D2,126.35

MW-187D12,108.35

MW-189D12,108.15MW-189D2

2,108.18

MW-190D12,105.25

MW-190D22,105.67

MW-191D12,109.62 MW-191D2

2,109.21

MW-192D2,106.56

MW-199D12,100.80

MW-201D2,093.32

MW-202D2,094.56

MW-203D2,098.98

MW-21B12,069.65

MW-312,073.10

MW-32B22,066.47

MW-39D2,122.09

MW-432,068.17

PZ-022,079.41

MW-45B2,087.98

MW-522,111.50

MW-67B2,113.46

MW-73D2,113.09

MW-75D2,090.55

MW-77D2,127.38 MW-78D

2,124.86

MW-84D2,065.17

MW-85D2,055.91

MW-96D2,073.16

MW-97D2,078.92

SA-MW-01D2,113.07

SA-MW-06D2,113.15

SA-MW-22D2,111.56

SA-MW-24D2,112.37

SA-MW-25D2,112.96

SA-MW-26D2,123.08 SA-SM-08D

2,120.06SA-SM-11D2,119.19

SC-MW-01D2,110.36

SC-MW-02D2,107.77

SC-MW-03D2,106.41

SC-MW-05D2,102.88

SC-MW-06D2,102.02

SC-MW-07D2,101.26

SC-MW-10D2,096.60

SC-MW-11D2,113.07

SC-MW-13D2,111.74 SC-MW-15D

2,108.55

SC-MW-22D2,112.79

SC-MW-26D2,106.69

SC-MW-32D2,107.25

SC-MW-38D2,103.02

PZ-102,092.61

BW-01D*2,119.89

MW-109*2,083.28

MW-121D*2,092.54

MW-122D*2,094.68

MW-147D*2,092.19

MW-169D*2,092.47

MW-23B*2,081.81

MW-28B*2,084.13

MW-30B2*2,077.99

MW-41B*2,084.26

MW-42B2*2,080.41

MW-47*2,088.44

MW-50B*2,081.50

MW-55A*2,055.92

MW-62A*2,052.25

MW-68D*2,047.53

MW-69D*2,061.91 MW-70D*

2,053.55MW-71D*2,041.40

MW-72D*2,057.44

MW-76D*2,090.65

MW-79D*2,062.09

MW-80D*2,069.46MW-83D*

2,082.48

MW-86D*2,070.99

MW-87D*2,071.90

MW-88D*2,082.21

MW-89D*2,059.79

PZ-01B*2,092.17

Groundwater west of the brown dashed line

is within weathered and/or fractured bedrock

2086

2135

Area of 1-foot Contours

Ale

me

da

St Alcudia Rd

Park 0

Fa

irv

iew

Rd

Ho

pe

St

Pi on eer Rd

Catskill Rd

Bla

nca

Rd

Pa rk Ave

Aca cia St

Sy

cam

ore

St

Mu

lbe

rry

Av

e

Com mun ity Blv d

Lo

cu

st R

d

Carson R d

Pera Rd

Man acor RdThompson Rd

Pa lma Rd

Grana da Rd

Wi llow Sprin gs Rd

Kin ski Rd

Dix

ie R

d

Pu

eb

lo R

d Se

rra

Rd

Pe

tra

Rd

Bla

nca

Rd

Frontier Rd

Rain bow Rd

Santa Fe Ave

Mo

un

tain

Vie

w R

d

He

r ve

yR

d

Su

mm

ers

et

Rd

Riv

erv

iew

Rd

Flo

we

r R

d

Fl o

we

rR

d

Co

on

Canyon

Rd

Su

mm

ers

et

Rd

Frontier Rd

Aca cia St

Salina s Rd

Se

rra

Rd

Aqua ri us Rd

Hi ghc rest Rd

Alcudia Rd

Hin

kle

y R

d

Com mun ity Blv d

Va

lle

yW

ell

sR

d

Coon Can yon Rd

Dix

ieR

dD

ixie

Rd

Mu

lin

ax

Rd

Ca

min

o R

d

UV58

IN-01

IN-02

IN-03IN-03R

IN-04

IN-05

IN-06

2092

2105

21352130

2095

2125

2091

2093

2115

2087

2075

2070 2055

2110

2050

2089

2086

2065

2100

2075

2120

2080

2060

2075

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2085

208520

80

2087

2045

2130

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2105

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2090

2115

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2125

2095

2093

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2100

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2120

2110

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2070

2075

2094

2090

2070

2070

2065

GormanNorth

GormanSouth

Cottrell

Ranch

Mount General Fault

Lockhart Fault

Yang

FIGURE 3-2GROUNDWATER ELEVATIONS IN THE DEEP ZONE OF THE UPPER AQUIFER, SOUTH HINKLEY VALLEY, THIRD QUARTER 2014THIRD QUARTER 2014 GROUNDWATER MONITORINGREPORT AND DOMESTIC WELL RESULTSSITE-WIDE GROUNDWATER MONITORING PROGRAMPACIFIC GAS AND ELECTRIC COMPANYHINKLEY COMPRESSOR STATIONHINKLEY, CALIFORNIA

0 500 1,000

Feet

±LEGEND:! Monitoring well"/ Active groundwater extraction well "/ Inactive groundwater extraction well @"!A Freshwater injection well

Potentiometric elevation contours (dashed where inferred) General groundwater flow directionAverage Groundwater GradientApproximate limit of saturated alluvium in deep zone of Upper Aquifer

! ! !

Approximate location of fault trace is inferred and there is no surface expression (Stamos et al., 2001)Estimated capture zone in deep zone of Upper Aquifer based on July/August 2014 groundwater level measurementsIn Situ Reactive ZoneAgricultural Treatment UnitsCounty parcels

NOTES:1. Groundwater elevation contours represent the hydraulic gradient in the deep zone of the Upper Aquifer. The deep wells of nested completions (wells designated “B” or “D”) were preferentially used for contouring. In all cases, the screened elevation of the well was taken into account.2. Groundwater level measurements for wells without an asterisk“*” are manual water level measurements collected between July 1 and August 7, 2014. Groundwater elevations marked with an asterisk “*” are the averages of pressure transducer data collected at 30-minute intervals from July 1 through 31, 2014.

WORKS CITED:Stamos, C.L., P. Martin, T. Nishikawa, and B.F. Cox. 2001. Simulation of Ground-Water Flow in the Mojave River Basin, California. U.S. Geological Survey Water-Resources Investigations Report 01-4002, Version 3. Prepared in cooperation with the Mojave Water Agency.

West Hinkley Valley Average Groundwater Gradient: 0.0049 feet/footGroundwater Velocity Estimate Range: 0.01 to 2.47 feet/dayAverage Groundwater Velocity Estimate: 0.96 feet/day or 349 feet per year

East Hinkley Valley Average Groundwater Gradient: 0.0031 feet/footGroundwater Velocity Estimate Range: 0.02 to 4.35 feet/dayAverage Groundwater Velocity Estimate: 1.72 feet/day or 628 feet per year

MW-55A2,066.24

Well IDGroundwater elevation

MW-55B(2,077.83)

Well IDGroundwater elevation not used for contouring

FIGURE 5-6LOWER/UPPER AQUIFER GOUNDWATER ELEVATIONS AND PUMPING RATES,JANUARY 2010 TO JUNE 30, 2014SEMIANNUAL REMEDIATION STATUS AND FINAL CLEANUP EFFECTIVENESS REPORT(JANUARY THROUGH JUNE 2014)PACIFIC GAS & ELECTRIC COMPANY,HINKLEY COMPRESSOR STATION,HINKLEY CALIFORNIA

Notes:1. Flow data are weekly averages from June 2010 through February 2012, and

daily averages from February 12, 2012 to June 30, 2014.2. Pressure transducer data was collected in 30-minute intervals.

Abbreviations:ft AMSL = Feet Above Mean Sea Levelgpm = Gallons per minuteLA = Lower Aquifer

0

200

400

600

800

Ext

ract

ion

Rat

e (g

pm)

Jan-10

Apr-10

Jul-10

Oct-10

Jan-11

Apr-11

Jul-11

Oct-11

Jan-12

Apr-12

Jul-12

Oct-12

Jan-13

Apr-13

Jul-13

Oct-13

Jan-14

Apr-14

Jul-14

Average Extraction Rates2030

2035

2040

2045

2050

2055

2060

2065

2070

2075

2080

2085

2090

2095

2100

Gro

undw

ater

Ele

vatio

n (ft

AS

ML)

2030

2035

2040

2045

2050

2055

2060

2065

2070

2075

2080

2085

2090

2095

2100

Gro

undw

ater

Ele

vatio

n (ft

AS

ML)

2030

2035

2040

2045

2050

2055

2060

2065

2070

2075

2080

2085

2090

2095G

roun

dwat

er E

leva

tion

(ft A

SM

L)Pressure Transucer Data

EX-29 and EX-30 operationsbegan on 5/18/12 and 5/9/12,respectively.

FW-01 began operationon 7/25/11, pumpingfrom Ryken 8/9 significantlyreduced

FW-02 beganoperationon 2/2/12

\\zinfandel\proj\PacificGasElectricCo\HinkleyRemediationProject\Monitoring Program\Reports\2014 Reports\SASR\SASR 30Sept2014\Figures\GrapherFiles donotprint\Fig5-6 Vertical Gradients .grf,9/19/14,14:33

FIGURE 3-4GROUNDWATER ELEVATIONS IN THE LOWER AQUIFER AND BEDROCK, THIRD QUARTER 2014T HIRD QU ART ER 2014 GROU NDW AT ER MONIT ORING REPORT AND DOMES T IC W ELL RES U LT SS IT E-W IDE GROU NDW AT ER MONIT ORING PROGRAMPACIFIC GAS & ELECT RIC COMPANY HINK LEY COMPRES S OR S TAT IONHINK LEY , CALIFORNIA

BAO \\MNU S T RICT GFS 01\PROJECT S \PGEHINK LEY 20000353\MAPFILES \2014\GMP_REPORT \Q3\GW E_LA_BEDROCK .MX D MCLAY 9/22/2014

!

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MW -100C*2,082.03

MW -21C*2,080.83

MW -23C*2,082.98

MW -28C*2,084.02

MW -42C*2,082.16

MW -55C*2,081.64

MW -90C*2,081.88

MW -91C*2,083.85

MW -92C*2,082.71

MW -99C*2,081.79

PZ -01BR*2,092.28

MW -11C2,126.44

MW -14C2,097.51

MW -159C2,126.89

MW -160C2,133.00

MW -31C2,080.83

MW -342,080.70MW -47BR

2,088.70

MW -62C2,081.54

MW -65BR2,090.21

MW -66BR2,090.98

MW -68C2,080.12

MW -93C2,085.76

MW -98C2,085.20

S C-MW -16C2,118.74

Alcudia Rd

Hope

St

Blan

ca R

d

Acac ia St

Carson Rd

Pera Rd

Manacor Rd

Palma Rd

Granada Rd

Pueb

lo R

d

Serr

a Rd

Petra

Rd

Blan

ca R

d

Thompson Rd

Frontier Rd

Sum

mer

set R

d

Acac ia St

Sa linas Rd

Serr

a Rd

Aquarius Rd

Highcrest Rd

Moun

tain

Vie

w Rd

CoonCanyon

Rd

Alcudia Rd

Community B lvd

Santa Fe Ave

Coon Canyon Rd

Hink

ley

Rd

UV58

Groundwater Gradient: 0.0060 feet/footGroundwater Velocity Estim ate Range: 0.07 feet/day or 0.66 feet/y earAverage Groundwater Velocity Estim ate: 0.31 feet/day or 111 feet/y ear

2081

2130

2081

2082

2085

2095

2100

209020

83

2105

2084

2087

2088208

6

2089

2110

2115

2125

21202130

2082

2085

20952100

2090

2083

2105

208420872088

20862089

21102115

2125

2120

LEGEND:! Monitoring W ell

Interpreted Groundwater Flow DirectionBedrock exposed at ground surfaceApproxim ate western lim its of blue clay form ing the Lower Aquifer. T he blue clay aquitard is interm ittently absent, thin, and sandy in portions of its western extent. Not all wells posted on the m ap in this area are screened below the blue clay aquitard.

! ! !Approxim ate location of fault trace is inferred and there is no surface expression (S tam os et al., 2001)Potentiom etric elevation contours (dashed where inferred) PG&E-owned propertyPG&E Compressor S tationCounty Parcels

±0 2,0001,000

Feet

PG&E = Pacific Gas & Electric CompanyABBREVIATIONS:

NOTES:1. Groundwater level m easurem ents for wells without an asterisk “*” are m anual water level m easurem ents collected between July 7 through 23, 2014. Groundwater elevations m arked with an asterisk “*” are the averages of pressure transducer data collected at 30-m inute intervals from July 1 through 31, 2014.2. Groundwater contours are based on m easurem ents from groundwater monitoring wells com pleted in the Lower Aquifer (saturated zone below the blue clay aquitard) or weathered bedrock where the blue clay is absent. W here the blue clay is not present, all saturated deposits are in hy draulic com m unication with the U pper Aquifer.

Lockhart Fault

Area of 1-foot Contours

MW -160C2,133.31

W ell IDGroundwater elevation used for contouring