ltr: transmits final ri rpt & response to epa comments on ... · project manager project manager...

SFUND RECORDS CTR

AR002Z C D ^ A ^^^^ DRESSER & McKEE ING. environmental engineers, scientists. One Walnut Creek Center planners, & management consultants 100 Pringle Avenue, Suite 300

Walnut Creek, California 94596 510933-2900, Fax: 510 933-4174

May 20, 1994

SFUND RECORDS CTR

88111950

Mr. Bret Moxley U.S. Environmental Protection Agency H-6-2 75 Hawthome Street San Francisco, California 94105

Subject: Fresno Sanitary Landfill (FSL) Final Remedial Investigation Report

Dear Mr. Moxley:

Camp Dresser & McKee Inc. (CDM), on behalf of the City of Fresno, is pleased to submit five copies of the Final Remedial Investigation (RI) Report prepared in accordance with the requirements of Administrative Consent Order No. 90-22 dated September 21, 1990. This report incorporates the comments received on April 5, 1994 from the U.S. Envirorunental Protection Agency (EPA) on the Draft RI Report dated September 14, 1993. The comment package included the following:

• EPA Comments to Draft Remedial Investigation Report, Fresno Sanitary Landfill - April 5, 1994.

• Fresno Sanitary Landfill, Review of the RI Report, ICF Technology Incorporated - October 26, 1993.

• Report Review - Assessment of the Vertical and Lateral Extent of Surface and Ground Water Contamination, Fresno Sanitary Landfill, Fresno County, Califomia Regional Water Quality Control Board, Central Valley Region -December 17, 1993.

• Evaluation of Remedial Investigation Report, Fresno Sanitary Landfill, Fresno, California, Department of Toxic Substance Control - October 27, 1993.

Responses to all the comments provided by the regulatory agencies have been prepared and are included in this transmittal of the Final RI Report.

Also included with this package are CDM's review comments on the Revised Draft, Human Health Risk Assessment for the Fresno Sanitary Landfill Superfund Site, dated April 1994, prepared by ICF Technology, Inc. The comments attached reflect CDM's identification of the major issues associated with the document which should be addressed prior to the issuance of the final report. However, because the document

Printed on recycled paper

CAMP DRESSER & McKEE INC.

Mr. Bret Moxley May 20, 1994 Page 2

was not available until the last week of April 1994, we were unable to perform a detailed review of the risk assessment prior to the submission of this RI Report.

Please do not hesitate to contact us if you have any questions or require additional information.

Very truly yours,

CAMP DRESSER & McKEE INC.

Wayne Pickus Gordon McCurry Project Manager Project Manager

cc: Larry Allred Ron Anderson John Mitchell Jim Sanchez George Slater

2416#4.062

Printed on recycled paper

EPA Comments

Comment 1

Response

Comment 2

Response

Comment 3

Response

Fresno Rl Comments/Responses

Comment responses include specific text changes. For longer text changes, the report section number of the revised redlined RI text are referenced.

Comments from Mr. Bret Moxley of EPA

Page ES-2 second paragraph. The statement that groundwater and soils ap-pear to have been impacted by the FSL is confusing. After the investigations at this site, the report should be able to state definitively whether or not the landfill has impacted the surrounding media. In the conclusion section of the report, page 5-1, CDM states that soil gas and groundwater are found to be contaminated and that the FSL is the source of this contamination.

The text on page ES-2 has been changed to read: "Groundwater and soil gas appear to have been impacted by the FSL."

Table 1-3 is in error. The shading suggests that CDM conducted the sampling from 9/89 to 10/90. The Executive Summary states that the Administrative Order was signed on September 21, 1990. CDM would not have conducted any work prior to this date.

The footnote references given in Table 1-3 were meant to provide where the data was reported, not the source of the samples. The footnotes in this table have been clarified.

Page 2-5, third paragraph, fourth sentence. EPA, CDM and the City of Fresno have had several conversations about the validity of this statement. While cigarette smoke may contain trace quantities of VC, the levels are not sufficient to contribute a detectable level in in-home air. EPA regards this statement, in its present form, to be misleading. If CDM wishes to retain this statement in cigarettes required to produce a detectable level of VC in a given room size must be included along with the VC in cigarette smoke literature reference which can not presently be found in the reference section of this report.

The paragraph in question has been changed to read; "In-home sources of vinyl chloride may include cigarette smoke and polyvinyl chloride products potentially containing residues of vinyl chloride. CDM agrees with the EPA regarding the relative vinyl chloride concentrations in homes due to cigarette smoke.

2416-1 i2yi*RiR7\RiwL\coMMENTs FN CDM Camp DresscT &. McKee

EPA Comments

Comments 4

Response

Comment 5

Response

Comment 6

Response

Comment 7

Response

Comment 8

Response

Comment 9

Response


Page 2-7, fourth paragraph. The report should state that the soil gas probes were stainless steel (see also page 2-9, first bullet). Also the tubing type used for sample collection should be confirmed.

The first sentence has been changed to read ".. diameter hollow stainless steel.." The first bullet on page 2-9 has been revised to indicate that stainless steel probes were used. The type of tubing used (polyethylene) has been confirmed, however the final sentence in this paragraph has been changed to read: " ..each sampling probe was fitted with a steel an aluminum reducer and silicon tubing followed by a length of polyethylene tubing leading to a vacuum pump.

Page 2-8, first paragraph. The sample syririge was never inserted into the sample probe!

The sentence in question has been changed to read: "During the soil gas evacu-ation, samples were collected in a glass syringe by inserting a syringe needle through a silicon rubber segment in the evacuation line, and down into the steel probe. "

Page 2-11, first paragraph. There are ten Calderon analytes not nine.

The sentence in question has been changed to read: "...in Summa canisters and adsorbent tubes for the nine ten Calderon compounds..."

Table 2-2, pages 21 and 22 of 22. These studies were conducted by Lockheed, not CDM and were not part of the RI. The inclusion of these results in this way is inconsistent with other portions of the report.

The table in question has been changed with the addition of a footnote to emphasize that the "L-" series and "W-" series samples were not collected under the RI and therefore were not collected or analyzed under EPA supervi-sion. These data were included in sections 2.0 and 3.0 to facilitate data review.

Table 2-3. TCE is nussing from this analyte list.

TCE has been added to Table 2-3, along with the analytical method.

Page 3-1, last paragraph. EPA believes that station 3 was 1000 feet downwind from the landfill fence line. This fact should be checked.

The locations of air sample stations have been corrected in this text (Section 3.1.1) to read: "Stations 1, 2 and 3 were located at an approximate midpoint on the east side of the landfill; Station 1 approximately 100 feet within the pcrimc • ter adjacent to the perimeter fence line, Station 2 about 300 feet outside the perimeter 100 feet east and 100 feet south of Station 1, and Station 3 about 599

2416-112\lM\RlR̂ F̂lNAL\coMMÊ •̂s Fwf C D M Camp Dresser &. McKee

EPA Comments

Comment 10

Response

Comment 11

Response

Comment 12

Response

Comment 13


feet outside 900 feet east of Station 2. Locations have also been corrected in Figure 2-1. Revised sample locations are based on field notes taken at the time of air sampling.

Page 3-2, first paragraph. CDM has never made mention of agricultural spray-ing prior to this statement. Further irvformation is required. Some analysis to support the possible conclusion that the analytes detected would possibly be present in agriculture sprays must be included. In addition, the data such as distance from the sample station to the spraying operation, the time spraying was observed, who observed the spraying and how this was recorded should be included with this reference.

The reference to agricultural spraying has been removed since the effects of agricultural spraying could not be substantiated. The TCA value from this sample (220 ppbv) is thought to be anomalous since the sample was collected at a location over 1300 feet east of the landfill, and because all other TCA ambient air results were less than 1 ppbv. In addition, the analytical result for TCA in Sample 2416-AIR-003 has been added to Table 3-2.

Page 3-3, third paragraph. Frequency of detection (FOD) analysis for soil gas is meaningless because the method detection limit for the various analytes changed dramatically as a function of the gas chromatograph injection volume. FOD analysis for soil gas is therefore misleading and should be removed from the report.

Additional text has been added to Section 3.2.2.

Page 3-6. The RI should include some analysis to correlate the subsurface stratigraphy with the perimeter subsurface methane monitoring well screen zones to determine if these wells which were installed at prescriptive depths are screened in zones of high soil gas permeability.

Additional text has been added to Section 2.3.2, and Section 3.2.2 clarifying the relationship between soil gas monitoring well completion zones, subsurface lithologies, and gas analytical results.

Page 3-21, first paragraph on natural infiltration. This paragraph has no ap-parent bearing on the RI report. If the relevance of this paragraph can not be made clear, then the paragraph should be removed.

In addition, further discussion of subsequent HELP models using an uncompacted, unvegetated silty loam soil cover is not clear. Is this soil type similar to the present cover? If so, the report should state that definitively. There is very little natural vegetation on the landfill presently, and the City of Fresno grades the surface occasionally thereby removing any sparse vegetation, consequently the use of a so called "fair grass" scenario is confusing.

2416-1 iz\iM\RiRT«=iNAL\coMMENTs FW C D M Camp DresscT &. McKcc

EPA Comments

Response

Comment 14

Response

Comment 15

Response


It is not clear what conclusions the report makes with regard to the amount or origin of leachate at the landfill. This should be made clear since the report concludes that leachate is not contributing to groundwater contamination while it also states that soil gas contamination is not sufficient to account for the groundwater contaminant levels presently found.

The report is also not clear about the inconsistency between observed leachate seeps and the purported dry quality of trash found during a previous, non CDM investigation.

The section on Natural Infiltration starting on page 3-21 of the draft RI (Section 3.3.4.1) has been revised. Additional text has been added to clarify that the HELP model runs conducted during the RI were targeted to be representative of existing conditions, in order to model potential infiltration of water through the landfill. In addition, text has been added to clarify the distinction between "municipal refuse leachate" and "waste liquid leachate" at the landfill. The term "municipal refuse leachate" is used to designate those waters that have through infiltration and contact with municipal refuse become contaminated. The term "waste liquid leachate" is used to designate non-aqueous and aque-ous phase liquids that potentially have been disposed of at the landfill, and contain the site contaminants of concem. The discussion of the landfill seep has been expanded to include discussion of the current conceptual model that this seep represents flow between landfill daily cover layers, and that the refuse prism as a whole is not saturated.

Page 3-23, fifth paragraph. Ponding in the low area at the center of the landfill has been much deeper than six inches. EPA has observed a bath tub ring in this area of up to several feet in depth on several different site visits. In addi-tion, the use of this area as an equipment storage area has been practiced since at least 1989.

Section 3.3.4.1 been modified to include discussion of site visits and site obser-vations regarding ponding on the landfill surface. This includes an expanded discussion of the vehicle storage area, which is a relatively recent feature (starting approximately the close of landfUl operations in 1989).

Page 3-23, last paragraph. If aerial photographs are being used to suggest that ponding has not been a consistent occurrence, then the dates and seasons of these photographs must be included. Without this information the validity of this statement is very questionable. Local residents and numerous newspaper articles suggest a different conclusion.

The reference to aerial photographs reviewed has been removed since suffi-cient documentation of this review is not available at present.

2416-1 i2MMwiR7\FiNAL\coMMENTs FW C D M Camp Dresscr & McKee

EPA Comments

Comment 16

Response

Comment 17

Response

Comment 18

Response


Page 3-26, last paragraph. Well 19H2 has never been mentioned in any previ-ous CDM report. More data is needed on this well. The existence of a possi-bly improperly abandoned well undemeath the existing trash is a significant finding. The report must provide more investigation of this well and its possi-ble function as a conduit of contaminants to groundwater and deep aquifers.

Well 19H2 was completed to a depth of 128 feet and is probably the open bottom type of construction commonly used for supply wells in the Fresno area. The pump from this well was recently removed by City personnel, and the well has not yet been abandoned. Groundwater from this well (and from the current landfill supply well 19H1) was sampled during the May 1994 sampling rourid. Evaluation of this well as a potential conduit of contaminants to groundwater and deeper aquifers will be undertaken after the sampling results are reviewed. Additional text has been added to the Section 3.3.4.3 regarding the available information on this former landfill supply well.

Page 3-30, third paragraph. Poor data quality is not an adequate rationale for limited characterization of the aquifer. This section should include some discussion about the possible causes of the poor quality of the collected data, problem solving efforts which were applied in the field and a rationale for not attempting to collect the data a second time or with some modification to the protocol.

Additional text has been added to Section 3.6.2 clarifying data useability and hydrogeologic data quality objectives. The data collected is considered ade-quate to characterize the hydrogeology of the site to meet the objectives of the RI.

Page 3-35, last paragraph. The description of metals analysis for soil samples is unclear. The results and rationale for analysis for silver and mercury should be clarified.

The paragraph in question has been rewritten as follows to clarify the sam-pling protocols and results for metals in soils: "Table 3-10 presents results of metals analysis of soils. Analysis of twenty-three metals, the Target Analyte List (TAL) of EPA's Contract Laboratory Program, was conducted on surface soil samples from the eleven locations mentioned above. Subsurface soil samples collected at the same location as the surface soil samples were not analyzed for TAL metals that were below detection limits in the surface soil samples. Two exceptions to this protocol included soil samples from CDM-1, which had several TAL metals detected in a surface soil sample but no subsur-face samples analyzed for metals due to a field sampling oversight. The sec-ond exception to the protocol for metals analysis of soils was mercury, which

2416-1 i2\iMmifrnFiNAL\coMMENTs FW C D M Camp Dresser & McKee

EPA Comments

Comment 19

Response

Comment 20

Response

Comment 21

Response

Comment 22

Response

Comment 23


was not detected in surface soils, but was analyzed in subsurface soil samples from CMW-2, CMW-3, and CMW-5 due to a laboratory error."

Page 3-45, Field Duplicates. A rationale for the RFD of 20% should be given. Also, there is no explanation for the claim that the third duplicate sample taken at station 2 was not representative of the sampling event. This must be included.

Text describing the basis for the RPD control limit of 20 percent has been clarified in Section 3.6.2. Additional text has also been added clarifying the effect of the result for the sample collected at Station 2 in September 1991 that exceeded control limits for three chlorinated parameters.

Page 3-46, section paragraph. The RPD values must include a rationale and an explanation for exceedences.

Text describing the basis for RPD control limits has been added to Section 3.6.2, as well as explanations for exceedences.

Page 3-46, fifth paragraph. The frequent occurrence of lab contamination should be further discussed as the present data bring the analytical lab and the results into question. In addition, the City of Fresno was previously advised that subsequent groundwater sampling rounds must address this issue in detail and eliminate this lab contaminant problem because conclusions regard-ing the possible contamination of the deep aquifer will hinge directly on the upcoming analytical results.

Additional text has been added in Sections 3.6.2.4 and 4.1 to clarify how labo-ratory contamination affects sampling results. Unfortunately, laboratory con-tamination of samples is a common occurrence at present, and no way has been found to guarantee that a laboratory will not have such problems. Addi-tional groundwater data (August 1993) have been added to the report in Section 3.5. This data did not have blank contamination problems. (See also response to RWQCB Comments 1 and 2).

Page 3-47, third paragraph. Some discussion for the exceedence of the RPD for VC should be included.

Discussion has been added regarding the exceedence of the RPD control limit for VC in duplicate samples collected from well CDM4A in March 1993.

Figure 3-9. A legend should be provided for this figure.

24i6-ii2UMWiRmFiNAL\coMMENTs FW CDM Camp Drcsser &. McKee

EPA Comments

Response

Comment 24

Response

Comment 25

Response

Comment 26

Response

Comment 27

Response

Comment 28

Response

Comment 29

Fresno Rt Comments/Responses

A legend has been added to Figure 3-9, clarifying the difference between well water and canal water usage.

Table 3-3d. This table should note that this data was not collected by CDM and is not data collected pursuant to the RI/FS nor was it collected under EPA oversight.

A footnote has been added to Table 3-3d stating "These samples were not collected or analyzed pursuant to the RI/FS nor under EPA oversight."

Page 3-4d. This data was not collected by CDM pursuant to the RI/FS and this should be noted. Furthermore, these samples are not soil gas wells as the author has erroneously suggested. These samples were collected with tempo-rary soil gas probes.

A footnote has been added to Table 3-4d stating "These samples were not collected or analyzed pursuant to the RI/FS nor under EPA oversight." In addition, the title has been corrected as follows: "..Results for VOCs in Soil Gas (L Series Wells Temporary Probes)

Table 3-4e. The identity of these wells is not sufficiently described on this table. Also the samples taken March, 1993 do not appear to have been ana-lyzed, with the exception of carbon tetrachloride, which may be a typographi-cal error.

This table has been corrected with the well ID "SGW" replaced with "W". The footnote in the response to Comment 25 has been added. The data in this table has been checked, and corrected as appropriate, removing the erroneous reference to samples collected in March 1993.

Table 3-5, SG-series. There is no maximum value for VC given even though some of these samples were collected with Summa canisters.

The maximum value for VC has been added to Table 3-5.

Table 3-6. This table should be omitted per comment #11.

Table 3-6 has been omitted.

Page 4-2, paragraph beginning "The remaining three compounds... from subsequent evaluation in this section." This paragraph is indecipherable. Furthermore, benzene, 1,2-dichloroethane and 1,2-dichloropropane should be included in the analysis.

2416-1 i2MM\RiRT\FiNAL\coMMENTs FW C D M Camp Drcsscr & McKec

EPA Comments

Response

Comment 30


This paragraph has been rewritten as follows: "The remaining three com-pounds with federal MCL exceedances were benzene, 1,2-dichloroethane, and 1,2-dichloropropane. These compounds were found to be present in groundwa-ter at low levels and only when other contaminants of concern were found at higher levels, as follows:

Anatytical Detection

Benzene

1,2-Dlcliloropropane

1,2-Dlchloroettiane

1,1-Dichloroethane

Federal

Maximum

Contaminant

Level

None given

CaHfomia

Maximum

Contaminant

Level

0.5

Level and Location of

Detection During the Rl

0.55 u g ^ CDM4A (3/93)

6.10 ugO, W-3 (3/93)

0.S0 ug'U UW2B (8/93)

4.80 ug/L, CDM4A (7/92)

3.10 ug/U CDM4A (3/93)

6.20 ug/U CDM4A (8/93)

6.20 ug/L, W-3 (3/93)

0.53 ugTL, 2121J (7/92)

1.80 ug/L, DWIB (8/93)

6.60 ug/L, W3 (8/93)

2.10 ug/L, W-3 (3/93)

6.50 ug/L, CDM4A (7/92)

10ug/UCDM4A (12/92)

4.90 ug/U CDM4A (8/93)

1.60 ug/L, CDM5A (7/92)

1.70ugn.,DW1B (3/93)

11 ug/L, MWl (3/93)

13 ug/U OWl (7/92)

4.10 ug/U DW1B (8/93)

c o c Compounds Mso Pres-

ent(PCE, TCE, VC)

PCE 44 ug/U TCE 43 ug/L

PCE 5.1 ug/U TCE 9.7 ug/U

VC 140 ugO.

PCE 82 ug/U TCE 74 ug/U VC

12 ug/L



PCE 5.1 ug/U TCE 9.7 ugO,

VC 140 uglL


9.4 ug/L

TCE 8.9 ug/U VC 120 ug/L

PCE 5.1 ug/U TCE 9.7 ug/U

VC 140 ug/L


12 ug/L


26ugn.


PCE 16 ug/U TCE 8.4 ug/U VC

1.4 ug/L

PCE 28 ugO, TCE 12 ug/U VC

2.3 ug/L

PCE 110 ug/U TCE 40 ug/U

VC 29 ug/L


23 ug/L

PCE 45 ug/U TCE23 ug/U VC

9.40 ug/L

— No COC detected.

As these compounds are present at low levels (less than 10 ug/ L) and are always associated with site contaminants of concern (PCE and TCE), no additional evaluations of the nature and extent of contamination by these compounds is considered warranted."

Page 4-26, section 4.3.4 Groundwater. Sampling results from the May/June 1989 should be used with caution in this report. Every reference to data in the

2416-1 i2MM\RiRT\FiNAL\coMMENTs FW C D M Camp Drcsser & McKee

EPA Comments

Response

Comment 31

Response

Comment 32

Response

Fresno Rt Comments/Responses

text and in figures and tables, not collected without EPA oversight or review of the quality of the data. In addition, the sampling protocols and quality assurance/quality control measures for this sampling episode have never been presented.

A footnote has been added to all figures with the May 1989 groundwater data stating: "These samples were not collected or analyzed pursuant to the RI/ FS nor under EPA oversight." In addition this statement has been reiterated in Section 4.3.4, along with the statement: "Sampling protocols and quality assur-ance/ quality control measures for this sampling episode were not evaluated during the RI. The May 1989 data are included to evaluate gross temporal trends, and are not meant to be used for risk assessment or remedial design purposes."

Page 4-50, section 4.4.2.4 contaminant transport model. The second bullet states that the model was used to characterize contaminant fate and transport in the shallow aquifer system. There is no rationale provide for restricting the fate and transport analysis to only the shallow aquifer. Clearly the intermedi-ate and very possibly the deep aquifers have been impacted by the landfill and consequently fate and tiansport analysis for these aquifers could be very valu-able in the eventual design of a groundwater remediation system.

The shallow aquifer system used in the model includes the "A", "B", and "C" aquifers discussed in the report. The bullet in question has been changed to read: "Characterizing the fate and transport in the shallow "A", "B", and "C" aquifer systems.

Table 4-3. The PEL levels must be removed from this table because PEL is an occupational exposure, there is no basis for comparison of occupational and residential exposures and this comparison is misleading.

PEL values in Table 4-3 have been removed, along with the associated discus-sion on pages 4-9 and 4-10.

2416-1 i2\iMwirrnFiNAL\coMMENTs FW C D M Camp Dresser &. McKee

DTSC Comments

Comment 1

Response

Comment 2

Response

Comment 3

Response

Comments 4

2416-112\IM\RIR7\FINAL\C0MMENTS FW


Comments from Mr. Keith Egan of ICF, on behalf of Mr. Bret Moxley of EPA

[Section 3.1.1, Ambient Air] Please discuss the reasons that agricultural spray-ing would contaminate air samples with compounds on the analyte list. It does not appear that the compounds in the analyte list would be present in agricultural sprays.

The reference to possible agricultural spraying contamination has been re-moved from the text.

[Table 3-la] The reason for the potential contanunation in sample 2416-AIR-003 should be stated or the section discussing the contamination referenced.

References to contamination of Sample 2416-AIR-003 have been removed and the analytical results of this sample have been added to Table 3-2.

[Section 3.3, Geology and Hydrogeology Investigative Results] What is the estimated dip of the strata in the general location of the site?

The cross sections do show flat-lying to very gently dipping beds. As pointed out in the text, (Section 3.3.1.3, second paragraph), the units appear to be more continuous in a north-south direction than in the east to west direction. The discontinuous nature of the lithologic units in the east to west direction makes it difficult to determine the actual dip of the units. Using the elevation of the base of the "Correlation Unit", in geophysical logs from CDMl, CDM7, and CDM4 and a trigonometric three-point solution; the dip of the beds is approximately .0039 feet per foot with a bearing of approximately south 56 degrees west. Section 3.3.1.3 has been revised to discuss this.

[Section 3.6.3, Soil Gas QA Results, and 4.4.2.4, Contaminant Transport Model] The use of both field and fixed laboratory data proved in this case to have been a good idea. ICF KE concurs with the use in the fate and transport model of whichever data point is higher to obtain a conservative "worst case" result. ICF KE suggests that this approach be carried through during the feasibihty study to ensure that, for example, a false negative field result is not misinterpreted as a false positive laboratory result.

CDM Camp Dresser & McKee 10

DTSC Comments Fresno Rt Comments/Responses

Response

Comment 5

Response

2416-112MM\RIFmFINAL\C0MMENTS FW

The referenced approach to using field and fixed laboratory soil gas results will be carried through the FS.

[Section 4.2.1.2, Leachate] This section states that there is "limited potential to cause contamination" by leachate at the site. It also indicates that there is no real evidence of leachate. Other sections state that inorganic indicator com-pounds do not demonstrate a leachate problem. However, this is contradicted in other areas of the report.

The first contradiction is in this section when surface seeps are discussed. Although, they try to discount this evidence by stating that none of the com-pounds that were found in the seeps are chemicals of concem. Since the chemicals of concem are highly volatile and have a short half life in open air, this is not surprising.

The second contradiction is in Section 5. One of the conclusions is that tians-port of soil gas to groundwater can not explain the concentrations in the groundwater. Therefore, leachate must be involved.

In addition, use of inorganic compounds as indicators of leachate seems ques-tionable given the proxunity of the Wastewater Treatment Plant (WWTP) recharge basins. On page 4-49, it is stated the WWTP recharge basins exhibit a significant influence on groundwater flow rate and directions near the FSL site. The treated wastewater may also be a significant source of the inorganic com-pounds.

From the experience of ICF, we believe that obtaining direct evidence of leachate is difficult and often involves a degree of luck. ICF does not believe that the lack of direct evidence should rule out the existence of leachate. ICF also believes that the direct evidence of the seep and the fact that groundwater concentiations exceed levels that soil gas could contribute is sufficient to con-clude that leachate exists. The results of the RI seem to confirm the likelihood of leachate as an important transport mechanism, making the absence of leachate in the conceptual model seem illogical.

Paragraph 1 - The section on leachate has been expanded, with a discussion on municipal refuse leachate and waste liquid leachate being provided to clarify the difference between these two potential source types. A reference for typi-cal municipal refuse leachate contanunant signatures have been added to Section 4.3.4.1.

Paragraph 2 - The surface seep discussed in this section is considered a dis-charge of near surface liquids which migrated laterally on top of shallow, low-permeability layers. The landfill daily cover material consisted of clay-rich soils which provided layers on which infiltiated water would flow laterally.

CDM Camp Dresser &. McKee 11

DTSC Comments Fresno Rl Comments/Responses

Comment 6

2416-112\IM«IR-r\FINAL\C0MMENTS FW

and thus not infiltiate vertically into the refuse prism. Additional discussion has been added to Section 3.3.4.1 to support this conclusion.

Paragraph 3 - The discussion of Waste Liquids (now Waste Liquid Leachate) in Section 4.2.1.3 gives a third alternative for a source of VOCs in groundwater other than soil gas or municipal refuse leachate. That a soil gas source does not explain all of the VOC concentrations in groundwater requires that an additional mechanism exists to provide more VOC mass to the shallow aqui-fer. Liquids containing VOC compounds are considered to be the additional source. These liquids could be in the form of diffuse municipal refuse leachate, or more concentrated sources such as waste organic liquids. The downgradient aquifer data do not show large increases in common ions, associated with municipal refuse leachate. Therefore, municipal refuse leachate is not considered to be a significant source, which leaves waste liquids leachate as the most probable source of contamination.

Paragraph 4 - As shown in Figure 3-5, the wastewater treatment plant is hy-drauUcally downgradient of the FSL site. Groundwater modeUng and the site potentiometric surface maps indicate that the wastewater treatment plant has always been downgradient of the FSL site regardless of groundwater pumping at the FSL site. The treatment plant does, however, influence groundwater flow rates and direction downgradient of the FSL due to mounding of the water table associated with recharge operations.

Paragraph 5 - CDM asserts that if municipal refuse leachate were a significant source of the VOCs found in groundwater, then a municipal refuse leachate signature, characterized by conservative (highly mobile) parameters (such as chloride, TDS, and sulfate) would be evident. Additional discussion in Section 4.3.4.1 clarifies the use of the chemical signature of municipal refuse leachate parameters to reach the conclusion that municipal refuse leachate is not a significant source of VOCs in groundwater. The text has also been clarified to indicate that municipal refuse leachate could be a minor contributor to ground-water VOC concentrations downgradient of the FSL.

[Section 4.2.1.3, Waste Liquids] The final paragraph of page 4-7 states that the presence of DNAPLs in groundwater at the site is very unlikely. However, DNAPLs would be most likely be found directiy beneath the landfill, an area that is not monitored by groundwater wells. Concentrations of VOCs in groundwater at the nearest off-site monitoring wells may be lower than would be found directiy beneath the landfill due to dilution or dispersion.

The last sentence of this section states that DNAPLs are unlikely because soil gas concentrations are only a fraction of the vapor saturation concentrations.



Response

Comment 7

Response

Comment 8

Response

Comment 9

Response

2416-112\1M\R1RT\FINA1.\C0MMENTS FW

A table should be provided that has the vapor saturation concentiation and the fraction found in the soil gas for each chemical analyzed in soil gas.

Paragraph 1 - The last sentence in paragraph two of section 4.2.1.3 has been modified to read "No nonaqueous phase liquids have been directly encoun-tered in groundwater at the site, and it does not appear likely that DNAPLs would be present." The last sentence of the third paragraph of section 4.2.1.3 has been modified to read "Based on these percentages, the presence of DNAPLs in groundwater at the site monitoring wells is very unlikely. The possible presence of DNAPLs undemeath the landfill at a distance from the site monitoring wells cannot be absolutely discounted, however."

Paragraph 2 - A table containing the vapor saturations for the DNAPL com-pounds found in soil gas, the highest observed concentrations of these com-pounds in soil gas and the fraction of the saturation concentrations these highest levels represent has been added.

[Section 4.2.2.5, Sorption] The last sentence on page 4-13 referenced Kd values in Section 4.4.2. These Kd values could not be found.

A discussion of Kd values has been added to Section 4.4.2.4.

[Section 4.3.1, Air] Rather than compare the air values to PELs, compare them to the 10"* risk concentiations. These have been published by the EPA.

The text in Section 4.3.1, and Table 4-3 have been modified to have PEL values removed, since PEL values are for occupational and not residential exposures.

[Section 4.3.2.1, Areal Extent of Soil Gas Contamination, PCE, p 4-22] The last paragraph of the PCE discussion speculates that the relatively higher PCE concentrations to the north and south sides of the landfill may be due to lower soil permeability and/or higher methane generation in the north and south ends of the landfill. This is contradicted by the relatively higher methane concentration on the east side of the landfill as described on the next page. ICF suggests deleting the last paragraph of the PCE discussion.

The referenced paragraph has been modified to clarify possible reasons for the higher soil gas concentrations.



Comment 10

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Comment 11

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Comment 12

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Comment 13

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[Section 4.3.2.1, Areal Extent of Soil Gas Contamination, TCE, p 4-23] The reference to the TCE false negative should be to Section 3.6.3 rather than Section 3.6.2.

The referenced section number has been corrected.

[Section 4.3.4, Groundwater] A reference should be provided for the last sentence of the third paragraph. The same reference should be supplied for the first sentence of the first complete paragraph on page 4-30.

A reference to the added discussion in Section 4.2.1.2 on municipal refuse leachate signatures has been added to Section 4.3.4.

[Section 4.3.4.1, Areal Extent of Groundwater Contamination] This section states that PCE and TCE were not found in an west cential wells. The data seems to indicate otherwise. In addition, the affect of U-16 on groundwater concentiations in this area should be discussed.

The third sentence in the PCE paragraph on page 4-28 has been changed to read "PCE was not detected in groundwater wells along the west-cential edge of the landfill, except in well U-16 at 1.5 ug/ L during the July/ August 1992 sampling event." A discussion on the potential affect of well U-16 on VOC concentrations in groundwater has been added to Section 4.3.4.1.

[Section 4.3.4.1, Areal Extent of Groundwater Contamination, Inorganic Param-eters, p 4-30] The decrease in inorganic ion concentiation with increasing well depths is attributed to infiltrating irrigation water which enriches the upper aquifer with anions and cations. TDS concentiations in groundwater well samples are reported to range from 91 to 1,590 mg/L. A comparison of these results to the irrigation pipeline TDS sample results of 61 to 66 mg/L as re-ported in Table 3-20 renders this conclusion unlikely.

The irrigation pipeline is not expected to cause increased TDS concentiations due to the minimal evaporative water loss associated with canals. Irrigation water, however, would get evaporative water loss whether through spraying or flooding techniques and cause increased TDS concentiations in infiltrating water. Text has been added to Section 4.3.4.1 to clarify the role of agricultural irrigation associated evaporative water loss causing TDS enrichment in the upper aquifer.



Comment 14

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Comment 15

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[Section 4.3.4.3, Temporal Trends in Groundwater] The fourth paragraph discusses factors limiting biodegradation. ICF does not vmderstand the correla-tion between the elevated results and limiting rates. It appears that elevated results do not indicate limiting factors. Please clarify this statement.

The following text has been added to clarify this point: "Subsurface conditions favorable for anaerobic biodegradation (primarily the absence of oxygen, the presence of nutrients, and the presence of a sufficient population of anaerobic bacteria) may explain higher concentrations of the anaerobic biodegradation products 1,2-DCE and vinyl chloride."

[Section 4.4.2.4, Contaminant Transport Model, p 4-53] An explanation on how source stiength, as shown in Table 4-9, was developed should be provided.

The model used two separate sources at each end of the site rather than the entire site as a source. This was done because of the lack of "hits" from the west cential wells. ICF believes that the groundwater contamination in the area of the west cential wells has been influenced be well U-16. While this well effectively eliminates the center of the site as a source, if well U-16 was not in operation, the entire site would have to be considered a source. ICF also believes that groundwater remediation should involve the closure of this irrigation well to prevent contamination of the lower aquifers. If this occurs, the entire site would be a source and the groundwater modeling should reflect this. ICF requests that a second tiansport simulation be performed using the entire site as a source. Data for the west cential wells could be interpolated from nearby wells.

In addition, it is noted at the end of page 4-53 that two simulated sources estimated to be approximately 1 acre in size and discharging less than 0.01 gallons of pure product per year were used to satisfactorily model the ob-served distribution of the dissolved PCE and TCE. This should not be inter-preted as proof that the actual VOCs sources fit the description of the simulat-ed sources.

An additional discussion of how source stiength was developed will be in-cluded in the revised text in Section 4.4.2.4. The site data do not suggest a source of contamination in the vicinity of well U-16. If a VOC source near well U-16 existed, then VOC concentiations in well W-5 (screened in the shal-low aquifer) would be relatively high. When pumping, well U-16 will cause contaminated groundwater to flow towards it, if such contamination exists in the area. As stated in the comment, the size, shape, and source stiength of the simulated VOC source could be different than the actual source.



Comment 16

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Comment 17

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Comment 18

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[Section 4.4.2.4, Contaminant Transport Model, p 4-54] The results of the possible soil gas contamination of the groundwater were not incorporated into the contaminant transport model. This data should be included in the ground-water model.

The soil gas contiibution was incorporated into the groundwater contaminant transport model, since the simulated ground water VOC sources adequately match the observed VOC ground water plume distiibutions. The text has been revised to discuss this aspect of the simulated VOC sources.

[Section 4.4.2.4, Contaminant Transport Model] This model assumes that the active sources of these contaminants no longer exist. While ICF KE under-stands the need to make simple assumptions during modeling, the conclusions drawn from the results of this model are flawed. The model seems to assume that some time during the past, quantities of "liquids" were released from two areas at the landfill directly into the groundwater, and that no continual sourc-es exist. In this view of the site, the concentiations dissolved in groundwater will decline with time. But what seems to actually happen based on other sites, is that residual DNAPL in soils continue to act as a source via partition-ing both into the vapor phase, and into the aqueous phase via water percolat-ing down through the vadose zone. This concept should be incorporated into the final report, as should its implications regarding remediation.

The concept of DNAPL's within the vadose zone continuing to serve as a source of contamination to the underlying groundwater system is a valid scenario for many sites. While this scenario cannot be ruled out at the FSL site, the trend of decreasing VOC concentiations over time makes this less likely. Modeling scenarios which simulated an ongoing source produced simulated plumes that were an extiemely poor match with the observed data. A simulated inactive source resulted in a very good match with the observed data. Section 4.4.2.4 has been revised to include additional discussion on the modeled contaminant source.

[Section 4.4.2.4, Contaminant Transport Model, Future Scenarios p 4-55] The request by EPA to model the future tiansport of contamination was not per-formed. EPA's request was made after being shown information that showed the cone of depression (zone of influence) from the Fresno drinking water wells would extend under the site in the future. The requested modeling was to help evaluate if the site would contaminate the Fresno drinking water. This section claims that the modeling was not performed because of uncertainties in regional hydraulic influences.



Response

Comment 19

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The importance of this modeling can not be overstated. If the local irrigation wells are shut down as part of the groundwater remediation, the pumping from the City of Fresno will have an even greater influence. EPA must be presented with some evidence that the City of Fresno drinking water supply is not going to be endangered before writing a Groundwater Operable Unit Re-cord of Decision.

As stated before, the modeling should be conducted. The variables of the model related to pumping by Fresno can be estimated based on the projected pumping rate (which was to be based by interpolating the historical growth in the pumping rate). If the City of Fresno will be increasing recharge in the area, estimates based on the projected recharge rate can be used. Because of the possibility of closing the local irrigation wells to prevent contamination of the lower aquifers, the influence of these wells should be eliminated in the model.

If CDM believes that this approach to the irrigation wells would be too conser-vative, a second model could be performed using the influence of these wells. The EPA understands the uncertainties involved in this model and suggests that CDM try to establish the degree of uncertainty and state it in the text of the report.

As discussed on pages 4-55 and 4-56 of the draft RI report, the areal extent of the plume is limited due to plume capture by irrigation wells located west of the landfill, a declining VOC source and biodegradation of the existing dis-solved phase plume. These factors will cause the plume to decrease in size and concentration, down to approximately 6 percent of the 1992 mass within 20 years. In addition, there is uncertainty in both future local and regional pumping and recharge rates. This includes future pumping of local agricultur-al irrigation wells in the vicinity of the landfill as well as operation of future remediation wells. For these reasons, modeling of future scenarios seems unwarranted at this time.

[Figures 4-13a-d, 4-14a-d, 4-15a-d, 4-16a-d] Why were the maps showing concentiations of VOCs in groundwater contoured using the MCL or 1/2 the MCL as the lowest contour interval not presented? The maps presented showed the concentiations but they were not contoured.

Isoconcentiation contours have been added to figures from all RI sampling events (Figures 4-13b-i through 4-16b-i) for PCE, TCE, trans-l,2-DCE, and vinyl chloride in the "A" and "B" aquifers. In past experience, CDM has found that individuals often take isoconcentiation maps as the actual areal distribution of contaminants, and not as the interpretive tool they are intended to be. Given



Comment 20

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Comment 21

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Comment 22

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Comment 23

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Comment 24

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the nature of a heterogeneous aquifer system, there is always some uncertainty regarding the exact location of individual concentiation contour lines. For this reason, the analytical data were presented in such a way to allow the reader to delineate their own interpretation of the areal distiibution of contaminants. EPA has directed CDM to generate isoconcentiation maps for the chemicals of concem in groundwater. CDM has complied with this directive, and the isoconcentiation maps are included in Section 4.0 of the revised RI. In addi-tion, text has been added to Section 4.3.4.1 clarifying how the isoconcentration maps were generated.

[Figures 4-29, 4-30, 4-31, 4-32] The elevation units should be included in the legend.

The elevation units have been added to these figures.

[Figure 4-30] Label more of the contour elevations and correct the overwriting.

More contour elevation labels have been added to Figure 4-30, and the over-writing has been corrected.

[Figure 4-31 and 4-32] The overwriting should be corrected.

The overwriting in Figures 4-31 and 4-32 have been corrected.

[Table 4-5] All other values for soil gas have been ppbv while this table uses mg/m^. The equivalent ppbv should be included in this table.

Table 4-5 has been corrected to present results in ppbv (ug/m3).

[Section 5, Conclusions] The fourth bullet on page 5-2 states that leakage from the "A" aquifer to the underlying "B" aquifer may be by way of agricultural wells completed within the aquitard. Agricultural wells can be a significant migration pathway between aquifers, especially during periods when they are not being pumped. ICF recommends further work to verify the hazard of these wells and to replace them if investigation demonstiates that it is warrant-ed.



Response

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Given the complex nature of the tiansport of VOCs in groundwater at the FSL, it is not recommended that these wells be immediately abandoned without first determining whether their continued operation presents an unacceptable risk. Based on data collected during the RI, including sampling of agricultural well U-16 (where contaminant detections are below the MCL) and results obtained from the solute tiansport modeling, we feel at this time that contin-ued operation of the irrigation wells will not pose an immediate unacceptable health risk. Additional activities to determine the effect of agricultural wells on the groundwater system will be conducted during the FS, based on infor-mation presented in the RI and the Risk Assessment. Recommendations regarding the long-term operation of the irrigation wells located near the landfill will be made during the feasibility study.



Recommendation 1

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Recommendation 2

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Comments from Ms. Mary Scruggs on behalf of Mr. Frank Lopez of DTSC

GSU recommends that this report be signed by a California licensed Registered Geologist or Professional Engineer (Civil) before formal comments are released. In the future, submittals of a geologic or hydrogeologic nature that contain conclusions, recommendations, and/or technical interpretations need to be signed by a Califomia Registered Geologist who accepts responsibility for technical content.

The signature of a California registered Professional Geologist has been added to the signature page of the report.

GSU recommends that the attached guidance "Recommended Content and Presentation for Reporting Hydrogeologic Data During Site Investigations" be reviewed and applicable sections applied to presenting data in the Report. At a minimum, site-specific potentiometiic surface maps should be constructed for sampling events for which data are available. Potentiometiic maps should be constiucted from data collected on the same day, not over an extended period of time (for example, the summer 1992 data extends over a 5-week period). The summary table of well constiuction details should include filter pack thicknesses and elevations, well screen elevations, aquifer monitored, and bentonite seal thickness and elevations. Cross-section and map scales should be consistent. References to figures and tables should be corrected to be con-sistent.

The referenced report "Recommended Content and Presentation for reporting Hydrogeologic Data During Site Investigations" was prepared for military base closure sites. CDM considers EPA CERCLA guidance documents to be more applicable to the FSL RI/FS site, including the document "Conducting Remedi-al Investigations /Feasibility Studies for CERCLA Municipal Landfill Sites (OSWER Directive 9355.3-11), and the EPA Fact Sheet "Stieamlining the RI/FS for CERCLA Municipal Landfill Sites" (OSWER Directive 9355.3-llFS).

Site-specific potentiometiic surface maps have been generated for each of the sampling events that accessed a wide distiibution of monitoring wells. A sentence has been added to the text in Section 3.3.3 to clarify this point. A potentiometric surface map for August 1993 has been added to the report, along with discussion in the text. A footnote has been added to the potentio-metric surface map for July 1992 (Figure 3-6b) to indicate the time period over which water levels were measured. The water level data were generally



Recommendation 3

Response


collected over as short a time period as was possible, given site access con-stiaints.

The top of the filter pack depth, and the top of the bentonite seal depth have been added to Table 2-4a, as requested. Elevations can be obtained by sub-tracting the depths from the ground surface elevations. The designation of the aquifer monitored are not included in Table 2-4, since these aquifer units are defined later in the report in Section 3.3.

Cross sections and map scales have varied between sets of figures, in an effort to provide the maximum amount of information in each figure. Map scales are contained in each figure to allow the reader to measure distances between points of interest. Any incorrect reference to figures or tables that have been identified have been corrected.

It is recommended that field soil gas data be deleted as input for modeling efforts. In addition, conclusions for mass transport of contaminants from soil gas to groundwater need to be reassessed using orUy data of appropriate quality (level III or higher). In addition, the use of field soil gas data for anything other than field screening is not appropriate and the Report should be revised in all applicable sections to reflect this change. Also, the use of "ND" values for field soil gas data, even as screening data, should be re-evalu-ated because the range of reporting limits can vary be 6 orders of magnitude. If field soil gas data are still used despite the very large range or reporting limits, full justification for use of data should be included in the Report.

According to the EPA Document entitled "Data Quality Objectives for Remedi-al Response Activities (EPA 520/G-87/003A), level II data may be used for site characterization activities but not for risk assessment. The RI Document does not contain a Risk Assessment, and field soil gas analyses have not been used for this purpose in the RI. Field data of level II quality are appropriate for delineation of soil gas and groundwater contamination and assessing the potential for mass tiansport of contaminants from soil gas to groundwater.

The large variation in detection limits in field analysis of soil gas is due pri-marily to two factors. First, many samples collected next to the landfill con-tained very high concentrations of one or two analytes. The gas chromato-graph method necessary to obtain accurate concentiations of the highest con-centration compounds results in high detection limits for the compounds at lower concentrations. Secondly, the main objective of the field soil gas survey was to delineate the extent of soil gas contamination. At the sample locations farthest from the landfill the detection limits are much lower and more uni-form due to low concentiations of all VOCs in these regions. As a result, the



Recommendation 4

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Recommendation 5

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data are adequate for defining the extent of soil gas contamination because "ND" values are very low in samples located farthest from the landfill.

It is recommended that the Report address all COCs and not just the four preliminary COCs. If a particular contaminant is not addressed in the Report (including isoconcentration maps), then justification for excluding the COC should be provided.

Data for all potential COCs has been presented in the report in Section 3.0, and therefore the RI report does address all COCs. The purpose of section 4.0, (the nature and extent of contamination), is to develop a conceptual model for the distiibution of contamination at the site which provides the basis for selecting a remedial altemative during the FS. As discussed in Section 4.1, Chemicals of Concern, the four preliminary COCs were identified by EPA. Other potential COCs were examined, and with the exception of 1,2-Dichloroethene, no addi-tional evaluations beyond those provided in Section 3.0 of the RI were found to be warranted. This is due to the lower concentiations and more limited extent of the compounds not designated by EPA as COCs as discussed in the revised Section 4.1. The data for all sampled compounds is available in Section 3.0, including tables for all organic analytical detections in groundwa-ter (Table 3-14), and frequency of detection data for organic analytes in groundwater (Table 3-15). In addition. Table 4-1 lists the maximum value of all compounds detected historically and during the RI, the Federal and State MCLs, and the number of times each detected compound exceeded Federal and State MCLs during the RI sampling events.

It is recommended that graphic depictions of data be presented in the same section as tabulated data and accompanying text. It is appropriate to present the interpretation and compilation of different sets of data separately, which in this case should be Section 4. It is recommended that the Report be revised to keep all data presentation together rather than separating it.

The RI report text, tables, and graphic depictions have been presented in a manner which conveys the large amount of data and complex interactions as clearly and as concisely as possible. The tables in Section 3.0 pertain to pre-sentation of the results of investigations. The graphic presentations of data in Section 4.0 pertain to evaluating the nature and extent of contamination. The graphic depictions are presented to facilitate interpretation, and so are not considered appropriate in Section 3.0.



Recommendation 6

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Recommendation 7

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It is recommended that the Report be revised so that data from different WBZ are differentiated. Groundwater elevation maps should be revised as neces-sary to reflect contoured data collected from the same aquifer for the same measurement date. Data that do not meet these criteria cannot be used to con-stiuct groundwater elevation maps. In addition, groundwater gradient(s), including direction of flow, should be calculated and shown on maps for each water level measuring event. Any increase or decrease in gradient between measurement event and changes in flow direction should also be noted and included in the discussion of groundwater flow in the Report. Also, any changes made in aquifer designations and/or groundwater elevations should be carried over to other applicable sections of the Report. In future field activities, groundwater levels should be measured on the same day and irriga-tion wells locally pumping during collection of water level measurements should be noted.

The RI has been conducted as efficiently as possible to provide the information needed to complete the feasibility study. This meant that, in some cases, groundwater levels were measured over several days. It also means that cer-tain maps in the RI contain multiple items of data. Several of the potentiomet-ric surface maps fit this latter category. The potentiometiic surface map for February 1993 (Figure 3-6a) shows a generally negligible difference in water levels between the "WBZs" and so the average of the nested completions is deemed adequate for contouring purposes, although data from each WBZ is shown. Due to a decline in groundwater levels which occurred during the RI, many of the shallow wells went dry and maps for this WBZ would have been far less detailed. Groundwater gradients were calculated and are discussed on page 3-16, along with descriptions of the locations from which the gradients were obtained. Discussion of the gradient from the August 1993 potentiomet-ric surface map has been added. Seasonal changes in flow directions and hydraulic gradients were discussed in Section 3.3.3. Time tiend plots of water levels in all of the nest wells has also been discussed in Section 3.3.3, and the plots are contained in Appendix B-3. Water level measurements were taken all on the same day during the May 1994 sampluig round.

It is recommended that the Report provide recommendations for future activi-ties at the site, including remedial actions. A conceptual model that addresses all potential receptor pathways should also be completed. A schedule that provides a description of activities and time frame for completing activities should also be generated. Also, conclusions in the Report should be revised to address issues presented in these comments.

Recommendations for future remedial actions will be addressed in the Feasi-bility Study (FS). A conceptual model that addresses all potential receptor



Comment 8


pathways is within the scope of the Risk Assessment conducted by EPA. The RI provides a conceptual model of all potential contaminant fate and transport pathways in Section 4.0 of the report. This addresses the requirement for the RI to characterize the nature and extent of contamination for the Risk Assess-ment and for the purpose of identifjdng appropriate remedial alternatives dur-ing the FS. A schedule that provides a description of activities and the time frame for completing activities is not within the scope of the RI. Conclusions in the RI report will be revised as needed to address issues presented in these comments.

Miscellaneous Missing or Inadequately Addressed Items in the Remedial Investigation Report

A listing of several nuscellaneous items that should be addressed throughout the Report is provided. This listing is not intended to be all inclusive; rather, it is to illustiate that many discrepancies and shortcomings have been identi-fied during Report review.

• Vertical gradients are mentioned in the Report however calculations and tabulations of vertical gradients are not provided.

• Equations for calculating the mass of contaminants used in the modeling is not provided (Table 4-5).

• Rationale for selection of which wells are to be measured for groundwater levels and which wells are to be sampled for chemical analyses is not provided.

• The monitoring frequency and schedule for both groundwater monitoring wells and soil gas wells is not provided.

• A clear description of how soil gas samples not associated with the 194 soil probes installed in September to December 1991 were collected and analyzed in the field is not discussed in the Report.

• Rationale for evaluating correlation coefficient for field versus fixed labo-ratory soil gas analyses for only three of the eleven chemicals is not pro-vided. Only the correlation coefficient for PCE results was acceptable. The TCE and vinyl chloride correlation coefficients were not acceptable and therefore, field soil gas analyses for TCE and vinyl chloride were not used. It is not know if field and fixed laboratory analyses for other chemi-cals show agreement using linear regression analysis.



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It is not clear in the Report which data were used for linear regression analyses. The Report implies that all fixed laboratory analyses were com-pared to field analyses. However, validity of this is questionable because several sampling events occurred over several years. The text (Section 3.6.3) and figures (Figures 3-13 through 3-15) do not include the total number of samples or data set parameters.

Some cross-sections (Figures 3-3c and 3-4c) do not include all wells shown on the cross-section index map (Figure 3-2).

Methane results from the fixed laboratory for September through Decem-ber 1991 soil gas sampling are not included in the data table (Table 3-3a).

Sample collection procedures for collecting soil gas samples in summa canisters selected from approximately 42 of the 194 temporary sample locations for analysis at the fixed laboratory is not described in the Report.

Text of the report refers to depths below ground surface (Section 3), but the cross-sections use elevations above mean seal level as the point of references.

Some cross-sections show correlations of units across great distances, including across the entire cross-section in one case (Figure 3-3c).

Horizontal distances along the same cross-section are not consistent be-tween figures using horizontal scales provided on figures (Figures 3-3a and 3-3b).

Stratigraphy for individual wells is not the same in all cross-sections (CDM-4 in Figures 3-3a and 3-3b).

Approximate boundaries between aquifer units are not shown on cross-sections (Figures 3-3a through 3-3c).

The lateral extent of PCE, TCE, vinyl chloride, and methane in soil gas outside the landfill boundary is shown on maps (Figures 4-4 through 4-7) with a dashed line labelled "approximate limit of analytical detections." The meaning of the line is not addressed in Report text and it is not clear what it represents. The Hne is sometimes located between the landfill boundary and non-detect sample locations and sometimes located outside non-detect sample locations.

Several figures do not include complete explanations, labels, or scales to identify items on figures (Figures 1-4, 3-9, 3-11, 3-11 through 3-13).



Recommendation 8

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It is recommended that inconsistencies in the Report and missing information and explanations cited above be revised and the Report be revised to address these comments.

Bullet 1 - Data on vertical hydraulic gradients are provided in three locations; Table 3-7, in figures 3-6a-f, and in Section 3.3.3.

Bullet 2 - A footnote has been added to Table 4-5 giving the equation used for calculating the masses of contaminants.

Bullet 3 - The rationale for selection of wells measured for water levels and sampled for chemical analysis was provided in the site Sampling and Analysis Plan (SAP), (CDM 1991), as referenced in Section 2.0.

Bullet 4 - Table 2-2 provides the sampling frequency and schedule for soil gas, and Table 2-7 provides the sampling frequency and schedule for groundwater.

Bullet 5 - The text in Section 2.3 has been modified to state the EPA Method TO-14 was used to collect soil gas VOC samples for fixed base lab analysis.

Bullet 6 - The correlation between fixed base lab and field lab results was undertaken to asses the impact of Freon compounds on the field lab vinyl chloride results. The results demonstiate graphically that the field analysis method for soil gas resulted in incorrect vinyl chloride concentiations due to interference from Freon compounds. Similar correlation plots for TCE and PCE were included to serve as points of reference to compare with the vinyl chloride plot. The PCE plot demonstiates the unbiased variability typically associated with analyzing VOCs in soil gas. The TCE plot shows poor agreement between field and fixed base results but no bias. The vinyl chloride plot clearly shows a bias towards high field based analyses, which reflects the Freon interference.

As stated in the RI, a conservative approach to utilizing the field and fixed base soil gas data has been used in which the higher of the two concentrations for a given sample time and location was selected for presentation and analy-sis.

Bullet 7 - The text in Section 3.6.3 has been modified to clarify that the data that were used to generate the linear regression plots were from sample times and locations which had samples analyzed both by the field lab and the fixed base lab.



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Bullet 8 - The wells shown on the cross-section location map (Figure 3-2) are for reference only. Only wells used to generate the cross-sections were includ-ed on the cross-section figures. A sentence has been added to the text in Section 3.3.1.3 to clarify this point.

Bullet 9 - Methane results from the fixed-base laboratory for the temporary SG wells have been added in Table 3-3d.

Bullet 10 - The text in Section 2.3 has been modified to state that the Summa canister sampling methods followed the procedures set out in the EPA and ASTM methods listed in Table 2-3.

Bullet 11 - The depth below ground surface was used in discussions in Section 3.0 since depths can more easily be conceptualized than elevations. Depths below ground surface can be readily obtained from the geological cross-section maps, which were plotted with a vertical scale of one inch equals fifty feet.

Bullet 12 - As noted in Section 3.3.1.3, the lithologic units appear to be more continuous in the north-south direction than in the east-west direction. The lengthy correlation at depth in Cross-Section C-C (Figure 3-3c) is based on two borings (CDM6 and CDM2) and is interpretive; however, the hypothesized alluvial fan/fluvial depositional environment, and the geophysical similarities between these two borings support lithologic correlation across this distance.

Bullet 13 - The geological cross-sections were plotted at different horizontal scales in order to show the maximum amount of detail on each cross-section. The horizontal scale provided on each cross-section is correct for the informa-tion contained on that cross-section.

Bullet 14 - The inconsistency in geological cross-sections A-A' and B-B' at well CDM-4 has been corrected.

Bullet 15 - Aquifer units are not designated in the geological cross-sections (Figures 3-3a through 3-:3c), but are given in the hydrostiatigraphic cross-sections (Figures 3-4a through 3-4c) because the geological cross-sections are in support of subsurface geology discussions, and the hydrostiatigraphic cross-sections were in support of hydrogeology discussions. The locations of the aquifer units on the geological cross-sections can be determined by measuring the elevations of the aquifer unit contacts at each well location on the hydrostiatigraphic cross-sections.

Bullet 16 - The "approximate limit of analytical detections" contours indicated on Figures 4-4 through 4-7 were located based on interpretation of the results from many sampling locations in a given vicinity. The contours indicate



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approximate boundaries of PCE, TCE, VC and methane at the detection limit of analysis. These limits were approximately 0.14, 0.17, 0.20 ppbv for PCE, TCE, and VC, respectively and 0.70% for methane. Since detection limits varied between points in many cases, the limit of analytical detections was conservatively placed fiirther away from the landfill if there was uncertainty as to direct interpolation between adjacent points. The text has been modified to clarify the definition of these "limits of analytical detections".

Bullet 17 - The referenced figures have been modified to clarify their purpose and better explain their components.



Comment 1

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Comment 2

Response


Comments from Mr. Scott More on behalf of Mr. Dane Johnson, California Regional Water Quality Control Board

The City attiibutes the presence of methylene chloride in groundwater samples from each aquifer zone to laboratory contamination since methylene chloride has also been detected in trip and field blanks. The City needs to provide conclusive information demonstiating the source(s) of methylene chloride in order to determine its vertical and lateral extent in groundwater at the site.

Though it carmot be conclusively proven that all methylene chloride detected in samples collected during the three sampling episodes discussed in the draft RI is due to laboratory contamination, the distribution of methylene chloride detections at low levels throughout all aquifer zones plus the high frequency of methylene chloride being detected in the laboratory blanks makes the pres-ence of this compound highly suspect. If methylene chloride was a contami-nant which migrated into groundwater from the landfill, and if methylene chloride detections in the C aquifer were real, then much higher concentiations would be expected in samples from the A and B aquifers. Furthermore, none of the 19 wells sampled in August 1993 had detections of methylene chloride. Thirteen of these wells had methylene chloride detections in previous sampling episodes. In addition, none of the blanks showed detections of methylene chloride in August 1993. These results support the arguments presented in the RI. Additional text has been added to Sections 3.6.2.4 and 4.1 to address the issue of methylene chloride detections in ground water. The final sampling round, scheduled for April 1994, should further confirm the absence of methylene chloride.

Toluene has been detected in the deep aquifer zone at 3 separate locations. Toluene can result from laboratory contamination. The City needs to provide conclusive information demonstrating the source of toluene in the deep aquifer zone in order to determine the vertical and lateral extent of organic compound migration at the site.

If toluene was a contaminant which migrated into groundwater from the landfill, and if the three toluene detections in the C aquifer were real, then detections of toluene would be expected in samples from the A and B aquifers. Toluene was not detected in any samples from the A or B aquifers. The final groundwater sampling round should further confirm the absence of toluene. Additional text has been added to Section 3.6.2.4 discussing this issue.



Comment 3

Response

Comment 4

Response

Comment 5

2416-112\IM\RIRT\FINAL\C0MMENrrS FW

In accordance with Section 2550.4(a)(1) of Chapter 15, the City needs to deter-mine where in groundwater and/or surface water the concentiation limit of each organic constituent of concem is equal to its background concentiation (nondetect for organic compounds). This is necessary for the City to be able to determine the vertical and lateral extent of organic compound migration in groundwater and/or surface water.

The purpose of the Remedial Investigation Report is characterize the nature and extent of contamination in order to allow the selection of appropriate remedial altematives during the Feasibility Study. The limit of analytical detections has been characterized for each of the organic compounds detected in groundwater at the site, based on the wells in which analytical detections have occurred. Table 3-13 lists all of the site wells and all of the organic com-pounds that have been detected in them. Figures 4-13b-i through 4-6b-i show the lateral extent of PCE, TCE, tians-l,2-DCE, and vinyl chloride in the "A" and "B" aquifers. As presented in Section 4.4.2 of the RI, groundwater flow and solute transport modeling was undertaken to assess the extent of contamination of the two primary site contaminants, PCE and TCE. The modehng results agreed with measured results regarding the downgradient extent of contamination. The temporary (Temp-series) samples established a maximum potential downgradient extent of contamination. A statistical evaluation of the inorganics data was conducted to evaluate the difference between upgradient and downgradient concentiations of inorganics analytes in groundwater. Discussion on this statistical analysis has been added to Section 4.3.4.1.

The lateral extent of organic compound migration in the shallow, intermediate, and deep aquifer zones has not been determined. Section 2550.9(b) of Chapter 15 requires that the City determine the spacial distiibution (vertical and lateral extent) and concentiation of each constituent of concem throughout the zone(s) affected by the release.

The lateral and vertical extent of contamination has been determined to the extent needed for the purpose of the RI, as discussed in the response to Comment 3.

In organic compound migration modehng, the City needs to consider all or-ganic compounds detected in groundwater at the site since Section 2550.4(a)(1) of Chapter 15 requires the discharger to determine where in groundwater the concentration limit of each organic constituent of concem is equal to its back-ground concentiation (nondetect for organic compounds).



Response

Comment 6

Response

Comment 7

Response

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By modeUng the contaminants that are the highest in concentiation, the most prevalent, and the most extensive, the model provides a worst-case (maximum concentration and extent) scenario output for the modeled extent of contamina-tion. Data presented in the RI report and discussed in Section 4.1 show that except for methylene chloride and toluene, detections of organic compounds which exceed their respective federal or state MCLs are located within the zone where the COC compounds are present. The remedial actions chosen for the COCs will therefore also have a remediating effect on the other organic compounds. It is thus not necessary nor useful, for the purposes of an RI conducted under CERCLA to delineate the extent of contamination of com-pounds that are within the area defined as contaminated by the site COCs.

The City has determined that the intermediate aquifer zone has been impacted by organic compounds from the landfill, but has not determined whether organic compounds have impacted the deep aquifer zone. Section 2550.9(b) of Chapter 15 requires that the City determine the spacial distiibution (vertical and lateral extent) and concentiation of each organic constituents of concem throughout the zone(s) affected by the release.

Section 4.3.4.2 discusses the vertical extent of contamination in groundwater. This section includes the statement "...that the VOC concentiations...decrease to below the detection limit in the C aquifer." Table 3-14 shows that none of the site COCs were detected in the C aquifer. These compounds are the most extensive and prevalent, and therefore should be present if organic contamina-tion is present. Methylene chloride and toluene were detected at low con-centrations in the C aquifer; these compounds are common laboratory contam-inants, and any detections in the C aquifer are highly suspect for the reasons discussed in response to comments 1 and 2. The extent of contamination is therefore considered to be limited to the A and B aquifers, as discussed in Section 4.3.4.2. Analytical results from April 1994 should further confirm these conclusions.

In accordance with Section 2550.2 of Chapter 15, the City needs to submit a proposed water quality protection standard that includes a list of the proposed constituents of concem (inorganic and organic), the concentiation limits, the point of compliance, and all monitoring points. This information is needed to evaluate whether there has been an inorganic release from the landfill.

Since remediation of the site is being addressed under CERCLA, the contami-nants of concem are determined by the EPA Risk Assessment. The feasibility study will identify potential water quality protection standards, concentiation limits, points of compliance, and monitoring points for the chemicals of



Comment 8

Response

Comment 9

Response

Comment 10

Response

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concem. Based on information collected in the RI, we feel the MCLs are the appropriate cleanup levels for ground water at the site. This position will be further substantiated in the feasibility study.

In accordance with Section 2550.7(e)(7) of Chapter 15, the City needs to submit the proposed statistical methods for each constituent of concem and monitor-ing parameter to be used in determining statistically significant evidence of any release from the waste management unit.

As indicated in response to Comment 3, a statistical evaluation of inorganic analytes in groundwater was performed, to assess whether downgradient contamination has occurred. Discussion on this statistical analysis has been added to Section 4.3.4.1.

The City needs to continue monitoring upgradient and downgradient pipeline water for potential impacts by the landfill on the organic and inorganic quafity of the pipeline water.

The pipeline sample results discussed in the RI and summarized on Table 3-20 provide sufficient water quality information for the purposes of the RI. As discussed in the RI, no VOCs were detected in either sample. Most inorganic results were within ten percent of each other, or showed a decrease in concen-tiation in the downgradient sample. Only calcium and ammonia showed significant increases, downgradient, each analyte being about 50 percent high-er. Neither analyte is considered to be a potential site contaminant of concem.

No surface water sampling was conducted as a part of the investigation to produce this report. The possibility exists for contaminated landfill gas along with landfill mnoff water during heavy precipitation periods, to migrate to and pollute the water in the Fresno Colony Canal which passes within 50 feet of the landfill's eastem margin. Section 2550.7(c) of Chapter 15 requires that the discharger to establish a surface water monitoring system to monitor each surface water body that could be affected by a release from the waste manage-ment unit. The City needs to establish a surface water monitoring system.

The City's Surface Water Monitoring Program is presented in the March 1994 draft report, NPDES Stormwater Permit Monitoring Program.



Comment 11

Response


The potential exists for the operation of the existing percolation/evaporation basin and possibly future percolation/evaporation basins at the site, to exacer-bate the existing groundwater contamination at the site due to soil gas VOCs being tiansported to groundwater by downward percolating basin water. The City needs to submit a plan to mitigate this potential noncompliance.

Future operation of the existing percolation/evaporation basin and its potential impacts are not within the scope of the RI. Once the source operable unit has been implemented, soil gas concentiations should decline to the extent that is does not appear that the operation of these basins would have a significant impact on the underlying ground water. This issue, however, will be addressed in the FS.


Comment 1

4112*1.005


Camp Dresser & McKee Inc. (CDM) has performed an initial review of the Revised Draft, Human Health Risk Assessment for the Fresno Sanitary Landfill Superfund Site, dated April 1994, prepared by ICF Technology, Inc. The following comments are the major issues which should be addressed prior to the finalization of the Risk Assessment. A detailed review of the document is currently under way.

Comments on the Risk Assessment

Current Land Use Adult Receptor

Carcinogenic risk for current land use scenarios is summarized on Table 6-10 of the risk assessment. For adult receptors, the exposure route which causes the overall risk to exceed EPA's acceptable risk range (10-4 to 10-6) (EPA 1991) is ingestion of potable water for the reasonable maximum exposure (RME) case. As illustiated in Table 6-6, the chemical which accounts for nearly 100 percent of the risk from ingestion of potable water is arsenic. Table 2-5 summarizes the data for arsenic. To calculate exposure point concentrations for arsenic in residential wells, 13 samples from residential wells were used. These 13 samples had an average value of 4.1 ug/L for arsenic with a maximum detected value of 8.0 ug/L.

The problem with this evaluation is the lack of consideration of background concentiations of arsenic upgradient of the site. An examination of background wells (CDM 1A,B,C; CDM 2A,B,C; CDM 7A,C; UW 1B,C) shows that arsenic was detected at three out of the four background well locations with a range of detected concentiations from 5-8 ug/L and an average value of 6 ug/L. As discussed in EPA's Risk Assessment Guidance for Superfund (RAGS) (Section 5.7) (EPA 1989), comparison of backgroimd chemical concentiations, especially for inorganics, to site concentiations is part of the screening process for selecting site-related chemicals of potential concem (COPCs). Given the existing data for the site, as well as regional background data for arsenic in groundwater, arsenic should have been eliminated from the risk assessment as a site-related COPC. It may be desirable to calculate a background risk from arsenic for the Fresno Landfill site, however, it is not appropriate or acceptable to present risks from arsenic in groundwater as a site-related risk.


Fresno Landfill RA Comments

Comment 2

4112*1.00S

Removing consideration of arsenic from the current land use scenario would result in the reduction of RME risk for the adult to within a range considered acceptable by EPA.

Child Receptor

For the child receptor, the exposure route which causes the overall risk to exceed EPA's acceptable risk range is inhalation of outdoor air. As illustiated in Table 6-3, the chemical which accounts for nearly 100 percent of the risk from inhalation of outdoor air is vinyl chloride. Table 2-3 summarizes the data for vinyl chloride in outdoor air. The frequency of detection is 3/40 (7.5 percent) with a range of values from 0.18 to 2.56 ug/m3 and a 95% UCL (RME) concentiation of 0.36 ug/m3. An examination of the outdoor air data in Appendix A-2 show that two of the three detected values were at or below the detection limit for the other 37 samples and only one sample (2416-air-002) showed a significant

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