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LIMITS OF CAPPING AREA
CLAY-MEMBRANE CAPPING OPTION ESTIMATED AREAS OF TCE CONTAMINATION AREA COVERED BY EXISTING ASPHALT OR CONCRETE PAVING

R D D 6 3 6 0 5 . R A " MAY 1989

200

400 FE6T

FIGURE 5-4 CAPPING ALTERNATIVE AREA DELINEATED BY SOIL SAMPLING ANALYSES AT PHOENIX GOODYEAR AIRPORT AND FORMER GAG FACILITIES

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PHOENIX GOODYEAR AIRPORT ROD

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-a

LIMITS OF CAPPING AREA CLAY-MEMBRANE CAPPING OPTION AREA COVERED ASPHALT OR

«oo FEET

FIGURE 5-5

Soil Vapor Extraction. Three alternative areas are presented for implementation of a soil vapor extraction system at the airport and former GAG facilities:
o The area delineated by analyses of samples that quantify VOCs in soil in excess of Arizona Department of Health Services (ADHS) cleanup levels for soils. This area corresponds to Target Area 1.
The area delineated by analyses of soil samples indicating VOC levels in soils greater than background. This area corresponds to Target Area 2.

o

o

The area delineated by analyses of soil gas samples that indicate VOCs in soil gas greater than 1 ug/1. This is the concentration considered to be indicative of vadose zone contamination above background levels. This area corresponds to Target Area 3.

Experience at other sites where soil vapor extraction has been applied for removal of VOCs from contaminated soils has shown that a phased or staged approach has been effective. An extraction and treatment system is installed in the area considered to be the most heavily contaminated, such as Target Area 1, and the elements of the system are expanded as required to achieve the desired level of cleanup.
For purposes of evaluation, both immediate full-scale implementation and phased installation are included as alternatives. The full-scale system includes operation of all wells for a period of 2 years. The phased approach includes operation of only one-quarter of the wells at any one time, but extends treatment over an 8-year period.

Table 5-2 presents estimated surface areas for the alternative target areas and the estimated number of vapor extraction wells required for VOC removal from soils. No Action. The no action alternative is presented as a basis for comparison with other alternatives for VOC contamination in vadose soils. A no action alternative may include administrative actions such as restrictions on access and deeds and monitoring of VOCs in the vadose zone at the airport and former GAG facility.

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Table 5-2 ESTIMATED SURFACE AREAS AND NUMBER OF WELLS S AM FOR SOIL VAPOR EXTRACTION I

Total Area Considered for Implementation of Soil Vapor Extraction System (square yards)
Soils Target Area 1 Soils Target Area 2 138,100 284,100

Estimated Number of Wells Required to Provide Coverage
40

· ·
·

«
82 *

Soils Target Area 3

636,000

183

·

I
The screening summary for the remedial action alternatives for VOC soils contamination in the vadose zone is presented in Table 5-3. Evaluation of Alternatives ·

|

The alternatives surviving the screening process are summarized in Table 5-4. The no action alternative does not attain the remedial action objectives. Capping or soil vapor extraction or some combination of capping and soil vapor extraction is feasible for Target Areas 2 and 3. Only soil vapor extraction is feasible for Target Area 1. While capping alone does reduce the rate of infiltration of water through contaminated vadose zone soils, it does not reduce or eliminate the VOC levels in soils and is not a permanent remedy. Combined with capping, soil vapor extraction removes the VOCs from the soil and achieves the remedial action objectives.

I I ·

· · · · jj « ·
_ ·

While some combination of capping and SVE is feasible, an alternative considering both technologies was not evaluated in the Feasibility Study. The most reasonable combination that could have been considered is capping over the most contaminated areas with SVE implemented over a larger area. The reasons that this type of alternative was not evaluated are that (1) capping over the most contaminated areas

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Table 5-3
SOILS REMEDIAL ACTIOS SCREENING SUMttKX

Alternative 1. 2. No action. Soil vapor extraction in area defined by toil sample analyses greater than ADEQ-suggested aoil action lira It*. Soil vapor extraction in area defined by soil sample analyse* greater than background. Soil vapor extraction in area defined by aoil gas analyses that quantify VOCs greater than 1 pg/1. Capping of area defined by analyses of soil aample8 that quantify VOCs greater than ADEQ-suggested action limits. Capping of area defined by analyses of aoil samples that quantify VOCs greater than background.
O1 I
N/A

ImplementabilltT

Effectiveness
N/A

Relative Cost
H/A

Regain

Conclusions Drop No action la retained as a baseline case.

Relatively easy to install, can be staged to allow minimum disruption of surface activities. Relatively easy to install, can be staged to allow minimum disruption of surface activities. Relatively easy to install, can be staged to allow minimum disruption of sur face activities. Relatively easy to Install* can be staged.

Significantly reduces VOCs in contaminated soils. Significantly reduces VOCs In contarainatsd soils. Significantly reduces VOCs in contaminated soils. Questionable. Existing structures and paving have not affected VOC migration through soil In the past. Could be effective in retarding infiltration of vater through VOCcontmnlnated soils.

Medium for target area Medium for target area Medium for target area
Questionable

3.

effectiveness.

Relatively easy to install* can be staged.

Low

Difficult to determine the quantity of VOCs in soils; therefore* the effectiveness of a cap is difficult to ascertain. See note above.

Capping of area defined by analyses of soil gas that Quantify VOCs greater than t 1lg/l.

Relatively easy to install* can be staged.

Most effective of capping options.

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Table 5-3 {Continued) Relative Coat
Excavation and treatment of contaminated soil* In urea defined by soil asraple analyaes that quantify VOC* in ooila at concentrations greater than ADKQ-auggeatod action limit*. Excavation and treatment of contaminated *oil* in area defined by soil cample analyaaa that quantify VOC* in aoil at concentrationa greater than background. Excavation and treatment of contaminated soil* in area defined by aoil ga« analyaen that quantify VOCa in aoil at concentrations greater than 1 pg/1.

Retain

Conclusion* prop Comnants

Very difficult to implement.

Eliminate* VOC cont« ination in ioila.

High

High coat and difficulty in Implementation*

Very difficult to Implement.

Bliminattta VOC contamination in aoil*.

High

High coat and difficulty in implementation.

Very difficult to implement.

Eliminate* VOC contamination in soil.

High

High cost and
difficulty in implementation.

Ul 1

H* 00

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Table 5-4 SUMMARY OF SOILS REMEDIAL ACTION ALTERNATIVES
Reduces Toxicity, Mobility, or Volume of Contaminants

Soils Remedial Action Alternative

Technical Feasibility

Environmental Impacts Increased surface runoff.

Institutional Requirements

Public Health ___Impacts_____
Reduces potential

Capping

Technically feasible--some permanent O&M requirements.

Complies with
ARARs; does not reduce,

for inadvertent exposure; reduces
airborne exposure.

No. Capping does reduce the rate of infiltration through contaminated

immobilize, or
remove contaminants .

soils.

Soil Vapor Extraction

Technically feasible-no permanent

Air discharge of trace offgasses.

Complies with

requirements.

Reduces or eliminates VOC levels
in soils.

Reduces or eliminates

VOC levels in soils.

O&M requirements .
No Action N/A

N/A

Existing

Existing

N/A

conditions do not meet requirements.

potential for airborne and groundwater impacts.

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(Target Area 1 or some portion of it) is not feasible due to existing structures, and (2) results of the pilot study indicate that SVE is effective without capping. Therefore, it was concluded that a combination capping/SVE alternative would not offer any advantages above SVE alone.

Table 5-5 summarizes the costs for the soil remedial actions.
GROUNDWATER

Listing of Alternatives
A wide range of alternatives was identified for the PGA site. These alternatives were separated into three groups; groundwater extraction, water treatment, and water end use (see Figure 5-6). The potential remedial alternatives for groundwater were identified to allow the EPA to select the most cost-effective alternative. Groundwater alternatives were evaluated to compare the relative merits of containing or pumping different areas of groundwater contamination at different rates. Water end use alternatives were selected based on the feasibility of delivering water and the distance to sites capable of accepting the estimated flows.

·
w p I
I ·

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Two target areas were defined for the PGA site based on the levels of TCE detected in Subunit B/C. Target Area 1 included the area of Subunit B/C where analyses of groundwater samples indicate VOCs including trichloroethylene (TCE) are above ARAR values. Target Area 2 is the area of Subunit B/C where analyses of groundwater samples indicate VOCs are above detection limits.

·

The potential remedial actions for groundwater, based on the target areas identified above and the remedial action alternatives, are:
o No action--no active remediation of groundwater. This was evaluated by considering the existing groundwater withdrawals with respect to the contaminated areas.

· B
m || ··

o

Containment using either a soil-bentonite slurry wall or cement-bentonite slurry wall for each of the two target areas. Containment using wells to control the hydraulic gradient and reduce further migration of the

· It

o

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Table 5-5
SOILS REMEDIAL ACTIONS--COST SUMMARY

Alternative
Technology All asphaltic concrete cap

Target
Area Target Area 2
Target Area 3

Capital Cost
____($) 2,081,000
3,301,000

Annual O&M
Cost ($) 62,500
102,200

_________Present Worth_________
3 Percent 4,164,000
6,707,000

5 Percent 3,331,000
5,341,000

10 Percent 2,706,000
4,323,000

Combined

Target

2,226,000
4,555,000

83,000
277,200

4,992,000
13,794,000

3,886,000
10,099,000

3,056,000
7,327,000

asphaltic concrete and
RCRA multi-

Area 2
Target

layer cap

Area 3

Soil vapor

Target

1,700,000
3,325,000

750,000
1,100,000

3,135,000
5,430,000

3,095,000
5,370,000

3,002,000
5,234,000

extractionFull Scale

Area 1
Target

Area 2
Target Area 3 7,248,000 1,950,000 10,979,000 10,874,000 10,632,000

Soil vapor extractionPhased installation

Target Area 1
Target Area 2
Target

650,000
1,293,000
2,841,000

287,000
404,000
677,000

2,665,000
4,129,000
7,593,000

2,505,000
3,904,000
7,217,000

2,181,000
3,448,000
6,453,000

Area 3

No action

N/A

N/A

N/A

N/A

N/A

N/A

Note:

1. Capital cost presented in 1988 dollars. 2. Present worth based on infinite life for capping alternatives, a 2-year life for full-scale SVE, and an 8-year life for phased SVE.

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contaminants. This alternative would be applied to both target areas. o Removal of the contamination by pumping the Subunit B/C aquifers until the contamination is reduced to an acceptable level. This alternative would be applied to both target areas.

Groundwater Extraction Alternatives. A range of alternatives was developed for addressing the contaminated groundwater within the above target areas. Each groundwater extraction alternative is an array of groundwater pumping wells. Existing wells are included, but all alternatives require construction of additional wells to effectively achieve hydraulic capture of the groundwater.
Two rates of removal were considered in the evaluation of groundwater extraction alternatives. The slower rate would use as many existing wells as possible and add only the wells needed to achieve a capture zone equal to the target area. The faster rate would add wells to extract the groundwater at as high a rate as practicable to accelerate the cleanup and achieve a permanent solution as soon as possible. Consequently, the range of extraction alternatives chosen for detailed analysis listed below includes increasing numbers of additional extraction wells, which affects the rate of cleanup.

| M ·

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The extraction alternatives chosen for detailed analyses

are:
o No action--continued use of 20 existing wells to extract and contain contaminated groundwater (Groundwater Alternative 1) Reduction of contamination to meet ARARs--continued use of existing wells and one additional extraction well (Groundwater Alternative 3) Accelerated reduction of contamination to meet ARARs-- continued use of existing wells and three additional extraction wells (Groundwater Alternative 4) Reduction of contamination to exceed ARARs--continued use of existing wells and four additional extraction wells (Groundwater Alternative 5)

·
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o

o

o

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GROUNDWATER AQUIFER ALTERNATIVES NO ACTION CONTAINMENTNO AQUIFER
RESTORATION

WATER TREATMENT ALTERNATIVES
NO TREATMENT

WATER TREATMENT LEVELS

GROUNDWATER END USE ALTERNATIVES
CURRENT WATER

USES

MEET ARARs

PUMP ALL GROUNDWATER

CONCENTRATIONS

CARBON ADSORPTION/ AIR STRIPPING, WITH OR WITHOUT EMISSION CONTROLS

MCLs FOR VOCs

MUNICIPAL

EXCEED ARARs

PUMP ALL GROUNDWATER .ABOVE BACKGROUND
CONCENTRATIONS

BELOW DETECTION FOR VOCs

AGRICULTURAL

MCLs FOR ALL

SURFACE

CONSTITUENTS

DISCHARGE

REINJECTION

RDD63605.RA JULY 1989 REVISED AUGUST 1989 Case 2:03-cv-02226-ROS

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FIGURE 5-6 GROUNDWATER REMEDIAL ACTION ALTERNATIVES