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Comments were received from one commenter, as follows:

1. Review of the CD on file at the Petaluma City Library did not appear to contain a document for the 

Site Conceptual Model. Please provide an electronic copy or link to this document. If it is contained on 

the CD, please provide the name and date of the report. 

RESPONSE: The Site Conceptual Model (SCM) has been documented in the following three reports: (1) 

“Remedial Investigation Report, Sola Optical USA, Inc., Petaluma, California” (Levine Fricke, 1990); (2) 

“Public Health Risk Assessment, Sola Optical USA, Inc. Site” (CH2M Hill, 1991); and (3) “Evaluation of

Monitored Natural Attenuation as a Remedy to Meet Remedial Action Objectives, Sola Optical USA, Inc., 

Site Petaluma, California” (Levine Fricke, 2001).

The site’s hydrogeologic setting, and the nature, extent, fate and transport of chemicals of concern 

(COCs) are described in Sections 2.0 through 5.0 of the Remedial Investigation report. The fate and 

transport of chemicals of concern is also discussed in the Public Health Risk Assessment (Section 2.5).

Key components of the site conceptual model also are depicted in the Evaluation of Monitored Natural 

Attenuation report (Figure 4, “Site Conceptual Model Showing Natural Attenuation Processes”). These 

reports have been uploaded to the EPA website.

2. It did not appear that vinyl chloride was reported in the tables of the ground water monitoring 

reports, but was probably reported (as ND?) in laboratory data. Was vinyl chloride ever reported above 

laboratory minimum detection levels at the site? Can you provide the document that would contain all 

historical vinyl chloride analytical data, table preferred? Also, final degradation of TCE and TCA would 

produce ethene and hydro chloride. What are the results for those chemicals?

RESPONSE: Vinyl chloride was never detected above the laboratory minimum detection levels. Ethene 

and hydro chloride were not reported by the lab analyses used in the site investigations. 

The August 31, 2012, groundwater monitoring report (Arcadis, 2012), included in the deletion docket, 

shows all the detected constituents from 1997 through 2012. Constituents detected but not shown in 

separate columns are presented in the Notes section at the end of the table. The April 4, 2001,

Evaluation of Monitored Natural Attenuation report (Levine Fricke, 2001), posted on the site webpage, 

shows all the detected constituents from the beginning of site response activities through the date of 

the report. This report also presents the detected constituents that are not shown in separate columns, 

in the Notes section at the end of the table. 

3. It is my understanding that ground water extraction and treatment combined with monitored 

natural attenuation (MNA) were the only remediation techniques used at the site. However, MNA is 

used to observe the degradation of a chemical of concern over time, not the possible migration of the 

chemical away from an observation point and usually not just one monitoring point. I believe well W-27 

was the last water sampling monitoring point remaining on the site. It is screened at 9 to 20 feet. So, it 

appears that the first encountered ground water zone for a product in its free state that is heavier or 

more dense than water is the only location for MNA. The final location for MNA at one solitary well does 

not seem adequate. Please comment. 

RESPONSE: The lateral and vertical extent of COCs was delineated through the RI process that included 

several phases of soil-gas, soil and groundwater investigations, as presented in the RI Report (Levine 

Fricke, 1990). Ground water quality was monitored using a total of 46 monitoring wells that were 
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installed at depths of up 240 feet bgs (Levine Fricke, 1992a). Through the course of remediation and 

monitoring, several wells that were historically below detection limits, or demonstrated results below 

detection for at least two years, were abandoned in order to streamline the monitoring process. 

After the natural attenuation monitoring plan was implemented in 2002, the monitoring well network 

consisted of three wells monitored semi-annually and an additional four wells monitored annually (total 

of 7 wells) (Levine Fricke, 2002b). Based on historical data collected across the entire network of 45 

wells, this network of wells was sufficient to monitor the groundwater remediation at all depths. The 

monitoring network continued to scale back over time as wells achieved and sustained the clean-up 

level. During the latter years of the clean-up, only one monitoring well remained above the clean-up 

level. That last well has now demonstrated consistent achievement of the clean-up level for over two 

years. EPA has determined that the clean-up levels have been achieved and maintained throughout the 

formerly contaminated area.

It is also important to note that non-aqueous phase liquid (NAPL) was not encountered at this site. 

Rather, COCs entered into the groundwater in the dissolved phase. In the dissolved phase, VOCs do not 

exhibit density driven vertical migration apart from the aqueous solution. Rather, the vertical extent of 

VOCs in groundwater at this site was driven by natural and pumping-induced vertical gradients in the 

groundwater. 

Finally, MNA was selected as a remedy at the site based on its protectiveness of human health and the 

environment. Potential migration of COCs away from monitoring points was considered in selection of 

the remedy. Data from the network of downgradient wells showed, however, that concentrations 

decreased to below MCLs, even after the pump and treat system was turned off. That data presented 

compelling evidence that MNA was potentially effective. The fact that the downgradient wells showed a 

lack of migration while the source area wells were showing decreasing trends, supported selection and 

approval of MNA as the remedy. 

4. The concentration trends presented in the Final Closure document dated April 2013 show that 

ground water extraction and treatment did not affect 1,1-DCA concentrations in well W-27. In fact, 

concentrations went up during treatment and stayed above MCL when the treatment system was shut 

down. If MNA was occurring, would you not expect for additional DCA/DCE daughter products to be 

produced? What are the concentrations for all the potential daughter products during the MNA period? 

Were the daughter products routinely analyzed and reported in all the zones of the well network during 

the historical record of these wells? Are ambient bacterial quantities and type sufficient for breakdown 

of these solvents? 

RESPONSE: As described in the Evaluation of Monitored Natural Attenuation Report (Levine Fricke, 

2001), there are several mechanisms that contributed to natural attenuation of COCs in groundwater at 

this site, including mixing, sorption, dispersion, volatilization, and abiotic and biotic degradation. Only 

these last two processes would be expected to produce degradation by-products, including 

chloroethane, acetate, vinyl chloride and ethene. As mentioned above, vinyl chloride was not detected 

above reporting limits, and the other potential breakdown products were not monitored. Rather, the 

steady decline in contaminant concentrations over time, combined with data from a large well network 

that confirmed a stable to decreasing extent of COCs, was taken as a primary line of evidence to 

evaluate the effectiveness of MNA as a remedy. The concentrations of both 1,1-DCA and 1,1-DCE 

declined to below the clean-up level with the data displaying clear trends. 
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Biological assessments (bacterial counts, etc.) were not conducted in groundwater at the site, based on 

the following:

 The primary line of evidence (decreasing concentration trends and reduced plume extent) 

indicated that natural attenuation was occurring

 The mechanisms for natural attenuation were mostly abiotic

The concentrations of VOCs were sufficiently low that, even if some of the attenuation mechanisms 

were biologically mediated, one would not expect to see the influence of the VOCs on the aquifer 

bacteria populations.

5. The concentrations for 1,1-DCE for well W-27 also has an interesting trend. The concentrations rise 

during treatment and reach a near peak when the system is shut off. Then, the concentrations decrease 

when the treatment system was turned off, almost as if the treatment system was causing the increased 

concentrations. Well W-27 is screened at 9 to 20 feet. Where did the dissolved 1,1-DCE and 1,-DCA go? 

Did they degrade? Then to what? Did they migrate? Where? Vertically or laterally? Could the remedial 

pumping caused the deeper dissolved constituents to be ‘pushed’ away from the pumping zones? 

RESPONSE: Well W-27, like other shallow wells in that portion of the site, was screened within a very 

fine-grained clay interval of the formation. As a result, groundwater extraction did not have a direct 

influence on the water level or COC concentration in that well. Rather, groundwater extraction focused 

on pumping from more permeable intervals to contain VOC migration.

As discussed above, several processes likely contributed to the natural attenuation of COCs beneath the 

site including mixing, sorption, dispersion, volatilization, and abiotic and biotic degradation. Based on 

the very low COC concentrations detected, it is unlikely that biodegradation was a significant contributor 

to the overall attenuation of the COCs. 

6. Where exactly was the discharge point in Adobe Creek for the ground water treatment system? 

Was there any violations of their discharge? 

RESPONSE: The as-built drawings show that the effluent from the groundwater treatment system went 

directly into the storm drain at the edge of the former Sola facility property (Levine Fricke, 1992b). We 

could not locate further detail regarding the location where the storm drain enters Adobe Creek. 

The annual monitoring reports contain no indication that the discharge limits were ever violated. 

7. What is the mass of the contaminants removed? What is the estimated mass of contaminants 

remaining? 

RESPONSE: The mass of contaminants removed was estimated as part of an evaluation conducted in 

1996 pursuant to a request for a technical impracticability waiver for the site (Levine Fricke, 1996). In 

that evaluation, the flow rate and concentration of COCs in the influent to the treatment system was 

used to calculate that 11 pounds of COCs had been removed by the treatment system. 

No estimate was made of the total mass removed through the end of the monitored natural attenuation 

phase. It should be noted that EPA did not place any importance on the mass removed calculation 

performed in 1996, nor did EPA see any need to estimate mass removed through the end of the 

cleanup. EPA relied upon monitoring of the groundwater to determine when the clean-up levels had 

been achieved.
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8. What is the historical record, including current status of the Stero well; City well and Sola well? 

What was the pathway for the contaminants to reach these wells?

RESPONSE: The historical records of the Stero well, Crandell well, City Station 5 well, and Sola-City well 

can be summarized as follows: 

(1) Stero well. Sola and Stero reached an agreement for Stero to use city water instead of well 

water in April 1990. The pumping system was removed from the well on May 8, 1990 (Levine 

Fricke, 1990, Section 1.3.2.4).

(2) Crandell well. Sola and the owner reached an agreement for the property to use city water

instead of well water. Sola arranged for well abandonment, which was conducted on October 5, 

1990, by Weeks Drilling and Pump of Sebastapol, CA, under the oversight of a geologist from 

Levin-Fricke and under permit by Sonoma County (Levine Fricke, 1990, Section 1.3.2.4).

(3) City Station 5 well. In October 1989, Sola and the City entered an agreement to keep the well 

closed until the City was satisfied that no further investigation was needed and there was no 

threat of drawing contamination into the well. The agreement stipulated that the City could

operate the well for specifically defined periods of time for sampling or during natural disasters 

(CH2M Hill, 1991, p.2-4; EPA, 2005, Table 2-1). In June 1988, the City ceased operation of the 

Station 5 well (EPA, 2005, Table 2-1). Later, Sola and the City established an agreement to 

replace the Station 5 well with a comparable water supply well and to abandon the well (Levine 

Fricke, 2001, Section 3.5.2).

(4) Sola-City well. Sola and the City entered an agreement to keep the well closed until the City is 

satisfied that no further investigation was needed and there was no threat of drawing 

contamination into the well. The agreement stipulated that the City could operate the well for 

specifically defined periods of time for sampling or during natural disasters (CH2M Hill, 1991, 

p.2-4). Later, the City abandoned the well (Levine Fricke, 2001, Section 3.5.2).

During early investigations, pump tests were performed on the City Station 5 well in order to investigate 

potential contaminant migration pathways were the well to be operated. Groundwater elevations in 

several monitoring wells throughout the COC plume were measured using pressure transducers. It was 

observed that the pumping from the City Station 5 well resulted in inducing downward gradients and 

pulling dissolved contaminants downward and over to the well, even though the Station 5 well is crossgradient from the contamination (Levine Fricke, 1990, Section 1.3.3.2 and Appendix B; Levine Fricke, 

1988). 

The Sola-City well is upgradient of the groundwater contamination but still on the former Sola facility 

property. The Stero well is down and slightly cross-gradient from the groundwater contamination, 

approximately 1000 feet from the Sola facility. The Crandell well is downgradient from the groundwater 

contamination, approximately 1500 feet from the Sola facility. 

9. There appears to be no record of the screen depth of the Stero well. Was this information 

obtained? 

RESPONSE: This information was not obtained. Based on the administrative control enacted on that 

well, and the lack of VOC detections in the vicinity of that well, this information was not a necessary 

component of the site conceptual model.
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10. I believe it was reported that the minor concentrations of contaminants found in the City well were 

not recurring. If the contaminants actually reached the City well, what was the exact pathway 

attributed? If the cone of depression of the active City well was the cause as was reported, where are 

the ground water elevation maps to support this theory? 

RESPONSE: The response to comment #8 describes how pump tests were used to determine the 

hydraulic pathway that the contamination took to reach the Station 5 well. The pathway caused by the 

influence of the pumping is depicted in the pump test report cited in the response. 

11. The City well has a very large screen interval (340 feet from 180 to 520 feet), which cause a dilution 

factor if the contaminant plume entered the screens of the well. Was this considered? 

RESPONSE: The location, depth, screened interval and pumping rates for the City well were all 

considered in developing the site conceptual model and the potential pathway for COCs to migrate from 

the site to the well. 1,1-DCE was detected at concentrations up to 23 ppb at a depth of approximately 

160 feet bgs at well LF-13, located between the plume and the Sola City well. Groundwater elevation 

data collected during pumping of the City well (described above) confirmed that groundwater flow was 

from the site toward the Sola City well in deep groundwater while the City well was pumping. The low 

and intermittent detections of 1,1-DCE at the Sola City well reflect the long screen and dilution effects of

the Sola city well on concentrations at the well head. 

12. I recall reading that an upward vertical gradient was reported in the middle and upper zones, while 

a downward vertical gradient was reported in the deep zone. Since TCA and DCE are DNAPLs in their 

free product state, wouldn’t downward gradients in the deep zone increase the level of concern that 

there may be a diving plume at the site? 

RESPONSE: As described above, non-aqueous phase liquid (NAPL) was not encountered at this site. 

Rather, COCs entered into groundwater in dissolved phase. In dissolved phase, VOCs do not exhibit 

density driven vertical migration apart from the aqueous solution. Rather, the vertical extent of VOCs in 

groundwater at this site was driven by natural and pumping-induced vertical gradients in the 

groundwater. The vertical extent of COCs resulting from these downward gradients was delineated 

with installation of deep (up to 230 feet bgs) wells.

13. It does not appear that there was lateral assessment beyond the City, Stero or Sola well? Is that 

correct? 

RESPONSE: The lateral and vertical extent of COCs in groundwater was established with an extensive 

well network as presented in the RI Report. As shown on that report, the extent of groundwater with 

COCs above MCLs was delineated to be within the footprint of the Sola property. As a result, there was 

no need to extend the investigation beyond the City, Stero or Sola wells. 

14. There does not appear to be a deep well network of three or more wells to provide a ground water 

gradient flow estimate. Deep wells LF-15 and LF-27 did not share any part of their screen depth, while 

LF-12 and LF-15 share only three feet. Were these wells screened in the same lithological strata? 

RESPONSE: The three deep wells are screened in similar strata, and are screened at a sufficiently similar 

depth to allow for characterization of groundwater flow direction. As described in the RI Report, site 

lithology is does not consist of discrete, laterally continuous strata. Rather, sediments below 
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approximately 100 feet beneath the surface of the former Sola facility property consist primarily of clay, 

with intermittent intervals of coarser-grained materials. Each of these wells was screened across these 

more permeable materials at similar elevations. The elevations of the screened intervals for these wells 

(180-200 LF-12, 180-190 LF-15, and 194-214 LF-27) are sufficiently similar to allow for grouping the 

resulting elevations into the same depth interval. 

15. Will the Institutional Control (IC) established with the County PRMD remain on file for future well 

permitting on these parcels after the site is de-listed? 

RESPONSE: Upon deletion of the site from the National Priorities List, EPA will inform the County PRMD 

that EPA considers the groundwater to have achieved all cleanup goals, and that EPA would not consider 

it necessary to continue maintaining institutional controls at the site. It would be up the County whether 

they want to dispense with the control. 
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REFERENCES

1988. Levine Fricke. Results of Hydraulic Testing of Sediments in the Vicinity of the Sola Optical USA Inc. 

Facility, Petaluma, California. January. 

1990. Levine Fricke. Remedial Investigation Report, Sola Optical USA, Inc., Petaluma, California.

December 3. 

1991. CH2M Hill. Public Health Risk Assessment, Sola Optical USA, Inc. Site. April 1. 

1991. Combined Monthly Status Reports of RI/FS Activities During April 1991 and Annual Ground-Water 

Monitoring Report, Sola Optical USA, Inc. Site, Petaluma, California. May 15. 

1991. Levine Fricke. Feasibility Study Report, Sola Optical USA, Inc. Site. June 10. 

1992a. Levine Fricke. Draft Remedial Design Remedial Action Workplan, Sola Optical USA, Inc., 

Petaluma, California. February 10.

1992b. Levine Fricke. Plans, Ground-Water Extraction System Expansion. April. 

1996. Levine Fricke. Request for A Technical Impracticability Waiver, Sola Optical USA, Inc. Site, 

Petaluma, California. November 22. 

2000. Levine Fricke. Letter from Scott Seyfried, Levine Fricke, to Holly Hadlock, EPA. Sola will provide 

EPA a report documenting technical rationale for MNA remedy. October 11. 

2001. Levine Fricke. Evaluation of Monitored Natural Attenuation as a Remedy to Meet Remedial Action 

Objectives, Sola Optical USA, Inc., Site, Petaluma, California. April 4.

2001. U.S. Environmental Protection Agency (EPA). Letter from Holly Hadlock, EPA, to Roman Starno,

Sola. Response to report entitled “Evaluation of Monitored Natural Attenuation as a Remedy to Meet 

Remedial Action Objectives, Sola Optical USA, Inc. Site, Petaluma, California.” November 5.

2002a. Levine Fricke. Letter from Scott Seyfried, Levine Fricke, to Holly Hadlock, EPA. Response to 

Comments and Addendum to the Monitored Natural Attenuation Evaluation Report, Sola Optical USA 

Inc. Site, Petaluma, California. April 16.

2002. U.S. Environmental Protection Agency (EPA). Letter from Holly Hadlock, EPA, to Roman Starno,

Sola. Reviewed Sola’s Response to Comments and Addendum to MNA Evaluation Report, approves 

request. September 20.

2002b. Levine Fricke. Letter from Larry Lapuyade, Levine Fricke, to Holly Hadlock, EPA. Work Plan to 

Implement Monitored Natural Attenuation as a Remedial Measure at the Former Sola Optical U.S.A. 

Facility, 1500 Cader Lane, Petaluma, California. October 22.

2005. U.S. Environmental Protection Agency (EPA). Second Five-Year Review Report for the Sola Optical 

USA, Inc. Superfund Site, Sonoma County, California. September. 
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2012. Arcadis. Letter from Scott Seyfried, Arcadis, to Dante Rodriguez, EPA. Groundwater Monitoring 

Report, July through December 2012, Former Sola Optical U.S.A, Inc., Facility, 1500 Cader Lane, 

Petaluma, California. August 31.