
 Introduction

EPA published a Notice of Intent to Delete the Jasco Chemical Corporation Superfund Site ("Jasco Site") in the Federal Register on May 26, 2020 (85 FR 31427). EPA published the notice to inform the public that EPA planned to delete the Jasco Site from the National Priorities List (NPL) and to provide a 30-day public comment period on the proposed deletion, which ended on June 25, 2020. 

EPA received eight submissions each containing multiple comments opposing the deletion. These comments were carefully considered in EPA's final decision to delete the Jasco Site from the NPL. 

One email contained several comments that are outside the scope of this deletion, including opinions about the U.S. President, EPA's Administrator, and fossil fuels. We do not consider these comments to be relevant or germane to this action and therefore we do not consider these comments as being against this action. Also, these comments do not address a specific regulation or provision in question or recommend a different action on the proposed deletion. 
We are finalizing our action to delete as originally proposed, addressing all relevant comments contained within the eight submissions in the Responsiveness Summary below.
Thank you, commenters, for submitting comments and sharing your concerns with the agency. 

 Responsiveness Summary

This Responsiveness Summary provides a response to all relevant comments submitted to EPA during a 30-day public comment period regarding the Notice of Intent to Delete the Jasco Site from the NPL (85 FR 31427). Original comments are available at http://www.regulations.gov, Docket ID No. EPA-HQ-SFUND-1989-0011, with the supporting materials under document type "Public Submissions." Comments have been summarized and paraphrased below and grouped with similar comments. 

 Summary of Comments

Comment 1: 
Why does the Jasco Superfund site need to be removed from the National Priorities List? Would it not be wise to leave the site under Superfund, allowing more oversight and funding?

Response 1:
EPA is proposing to delete the Jasco Site because it meets the official criteria for site deletion. The National Oil and Hazardous Substances Pollution Contingency Plan establishes criteria that EPA uses to delete sites from the NPL, at 40 CFR 300.425(e). To delete a site from the NPL, EPA must determine, in consultation with the state, that one of those criteria has been met. In consultation with the California Department of Toxic Substances Control (DTSC), EPA determined that the following criterion for delisting the Jasco Site has been met: the responsible party, Jasco Chemical Corporation (or "Jasco"), has implemented all appropriate response actions required for the Jasco Site. 

This means that no further response action is necessary, and the Jasco Site is eligible for deletion. 

EPA identified site deletions as a priority in its 2017 Superfund Task Force Recommendations. The Jasco Site was a clear candidate for delisting, as its 2012 Five-Year Review found that the remedy was protective of human health and the environment, concluding that the remedy had been successfully implemented and no waste was left in place at the Jasco Site.

Once a site is deleted from the NPL, the Comprehensive Environmental Response, Compensation, and Liability Act ("CERCLA" or Superfund) allows EPA to take future actions, as appropriate, to protect human health and the environment if future conditions require action. 42 USC 9605(e); 40 CFR § 300.425(e)(3). In addition:

 Deletion of the site from the NPL does not allow responsible parties to escape legal liability for future response actions at the Jasco Site that may become necessary to protect human health and the environment. 40 CFR § 300.425(b)(4). 
 All releases of contamination from deleted NPL sites are eligible for further remedial actions if warranted. 40 CFR § 300.425(e)(3).
 In the event there is a significant release from the Jasco Site, EPA can restore it to the NPL without application of the hazard ranking system. 40 CFR § 300.425(e)(3).

In summary, deleting the Jasco Site from the NPL does not preclude regulatory oversight or cut off access to funding if additional response actions are needed at the Jasco Site in the future to protect human health and the environment. 

Useful Documents
 EPA's 2011 Office of Solid Waste and Emergency Response Close Out Procedures for National Priorities List Sites guidance document. 
 US EPA 2019 Final Close Out Report for the Jasco Chemical Company Superfund Site 
 Remedial Action Completion Report
 US EPA 2012 Five-Year Review for the Jasco Chemical Corporation Superfund Site

Comment 2:
The site is still contaminated with perchloroethylene (PCE), which likely causes cancer in humans. Is EPA risking the health of future residents at the apartment complex being built at the Jasco Site by deleting the site from the NPL? 

Response 2:
The Jasco Site, which is defined by the contamination that originated from the JASCO Chemical Corporation does not have any PCE contamination. However, an offsite PCE plume was discovered at the JASCO site around 1995. After rigorous study, EPA concluded that the plume did not originate from Jasco and was therefore not a part of the Jasco site or the Superfund cleanup process. This PCE plume is referred to as the Villa Street PCE plume.

Potential risks to future residents from the Villa Street PCE plume at the Jasco Site are being managed independently of the CERCLA or Superfund cleanup process.  A "Covenant and Environmental Restriction on Property" (or "deed restriction") on the Jasco property requires the California Regional Water Quality Control Board (RWQCB) and EPA to oversee the Jasco Site's future reuse and ensure soil and groundwater is managed according to a soil management plan that prevents any human exposure to PCE and other contaminants of concern. 

Under the deed restriction, EPA and the RWQCB will:
 Ensure no wells are drilled at the site except for purposes of investigating or cleaning up contamination.
 Approve a soil management plan to ensure that people do not contact potentially contaminated soil, groundwater or dust at the site. 
 Continue to sample site soil and groundwater, as it is transported offsite, to assure protection of human health and environment.
 Approve plans to install a vapor mitigation system under the building; and 
 Oversee confirmatory pre-occupancy indoor air sampling to verify the efficacy of the system.
 The deed restriction's requirement to involve EPA and the RWQCB also applies to any future soil or groundwater disturbance.

Discussion of Potential Risks
When evaluating potential risks posed to human health by chemicals in the environment, it is important to understand the exposure pathway, or the way in which a chemical enters the human body from the environment. Exposure can come from breathing chemical vapors, accidental eating of contaminated soil, drinking contaminated water, or when a chemical passes through skin and reaches the blood stream.
There is no risk of drinking contaminated water originating from the Jasco Site or in the surrounding neighborhood because there are no groundwater supply wells near the Jasco Site. The City of Mountain View provides drinking water to homes in the Shoreline West neighborhood; most of this water comes from snowmelt in the Sierra Nevada Mountains and less than 2% is sourced from local groundwater wells not near the Jasco site.
There is also no risk of exposure from accidentally eating or breathing in dust generated from PCE-contaminated soil to PCE-contaminated soil at the Jasco Site because PCE was detected in only one isolated area in relatively low concentrations up to 16 mg/kg, or parts per million. Out of hundreds of soil samples collected between 1988 and 2000, only eight had results slightly above the Jasco Site's cleanup level of 7 mg/kg. The area where PCE was present in soil was excavated and treated onsite using bioremediation, a cleanup method that uses bacteria to break down harmful contaminants into less harmful ones. Sampling conducted after bioremediation confirmed that soil cleanup levels for the Jasco Site were reached. Additionally, excavation of the Jasco Site's soil for residential development is subject to a RWQCB-approved soil management plan, and only clean fill soil will be used near the surface.
Vapor intrusion occurs when chemicals in groundwater or soil vapor, or soil gas release gases that travel through the ground and enter homes through utility pathways or cracks and gaps in the building's foundation. Soil vapors may contain a mixture of gases that come from chemicals in groundwater and soil and remain in a gaseous state in between particles of soil. A human health risk assessment was conducted in 2003 using groundwater and soil vapor sampling data to assess the risks posed by the Villa Street PCE plume through the vapor intrusion exposure pathway to construction workers and future residents at the Jasco Site. The report concluded that risks posed were minimal and resulted in an increased cancer risk of less than one in one million using the best available science at the time. Nevertheless, EPA and the RWQCB required Jasco to record a deed restriction to ensure future construction workers and occupants of the property would not be harmed by vapor intrusion or by contact with contaminated groundwater. Due to the limits imposed by the deed restriction, the new apartment complex will have a waterproofing and vapor barrier installed beneath areas of the building that are in contact with soil and groundwater. This will protect the occupants of the building against vapor intrusion. The two-story garage under the building will be equipped with a ventilation system to prevent buildup of harmful gases inside the building and will serve as an added buffer. Confirmation samples of soil vapor, groundwater, and indoor air will be collected prior to the apartment complex being occupied to ensure future residents are protected.
The deed restriction includes a requirement that the developer must create and maintain an operations, maintenance, and monitoring plan as one of the vapor intrusion controls approved by the RWQCB and EPA under the deed restriction. This plan is based on an action level for PCE. If samples collected under the plan exceed the action level, the developer must take actions to reduce the level of PCE in indoor air, until PCE is reduced below the action level. 
It is likely that the potential risks posed by the Villa Street PCE plume will be further reduced by construction currently underway at the Jasco Site. Construction plans, which were submitted under the deed restriction, call for the expected extraction and treatment of 200 million gallons of groundwater as well as the removal of around 62,000 cubic yards of soil (equal to about 6,200 dump trucks). These actions will likely reduce concentrations of PCE in soil vapor and groundwater at the Jasco Site. 
Since construction began at the new apartment complex at 1710 Villa Street, additional sampling under the soil management plan required by the deed restriction has been done. Eleven soil boring profiles were drilled in October 2019, and soil samples were collected at depths of 1, 2, 5, 10, and 20 feet below grade from each boring and analyzed for a variety of different contaminants, including PCE.  Sampling results were well below the Regional Water Quality Control Board's Residential Environmental Screening Level of 80 ppb (parts per billion). Sampling of surface water runoff during stormwater events has taken place under a Stormwater Pollution Prevention Plan administered by the RWQCB. So far, all results have shown that no toxic chemicals are entering storm drains on the perimeter of the site and that the owner and developer, Prometheus Group is in compliance with the requirements of its Stormwater Pollution Prevention Plan. Additionally, groundwater that is pumped to the surface and treated with a water treatment system is sampled before it is discharged into the nearby Permanente Creek under a National Pollutant Discharge Elimination System permit administered by the RWQCB. To date, sampling results for the effluent discharged into Permanente Creek have shown that the treatment system is properly functioning and groundwater is being treated to levels safe to discharge into the environment. 
Useful Documents
 2010 Covenant and Environmental Restriction on Property (or "deed restriction")
 2003 Human Health Risk Assessment
 For more information about the redevelopment of the Jasco Site and the protection of future residents, please see the Regional Water Quality Control Board's GeoTracker database: https://geotracker.waterboards.ca.gov/profile_report?global_id=T0608592706
 City of Mountain View Water Quality Report 2019 https://www.mountainview.gov/depts/pw/services/water/water_quality_report.asp
Comment 3: 
Does the PCE plume threaten the health of other residents in the surrounding neighborhood?

Response 3:
As discussed in Response 2, there is no risk of drinking water contamination at the Jasco Site or in the neighborhood. There is also no risk of contact with contaminated soil from the Jasco Site, because there was limited soil contamination to begin with and it has been cleaned up. EPA has been unable to locate the source of the Villa Street PCE plume, so it is possible that some PCE-contaminated soil exists outside of the Jasco Site. EPA's investigations concluded that the most likely sources of the PCE contamination were in areas that have since been redeveloped.
The soil that is currently being excavated due to construction of the new apartment complex is being managed under a soil management plan required by the deed restriction, which ensures that people do not come into contact with contaminated soil. This includes preventive measures such as sampling soil prior to excavation to characterize it for proper disposal offsite and covering trucks carrying soil offsite. An environmental field representative with hazardous waste training is onsite to monitor conditions at the Jasco Site. A perimeter air monitoring program is in place to ensure that dust or toxic chemicals, including PCE, do not leave the Jasco Site through the air and impact the surrounding community. 
More groundwater and soil vapor sampling is needed to better understand the current boundaries of the Villa Street PCE plume and the potential for PCE to move through the vapor intrusion exposure pathway. While EPA is confident that potential risks to future residents of redevelopment at the Jasco Site are being appropriately managed, EPA lacks information about the potential risk from the Villa Street PCE plume to residents on surrounding properties. The RWQCB has agreed to lead the investigation and oversight of the Villa Street PCE plume. EPA formally referred the Villa Street PCE plume to the RWQCB in a letter dated September 16[th], 2020. RWQCB will evaluate groundwater and soil vapor quality data to be collected after the construction activities are completed at the Jasco Site to better understand current site conditions. The RWQCB will direct a potentially responsible party (a former owner of 1350 Villa Street) to develop a workplan to investigate soil vapor and groundwater quality in the vicinity of 1350 Villa Street. This data will be used to determine if additional investigation or remedial actions are needed in respect to the Villa Street PCE plume. The RWQCB will be working on this investigation over the next year (2021) to assess the nature and extent of the Villa Street PCE plume. 

Comment 4:
I do not believe deletion should occur until the new apartments, under construction at the site, are verified to have been designed and built to meet vapor intrusion mitigation requirements that would ensure the safety of future building occupants. I have asked the Water Board to a) develop a contingency plan if sampling during construction shows exceedances above remedial objectives; b) provide assurances that the ventilation in the parking garage will be adequate to prevent unacceptable PCE exposure and ensure mitigation systems for elevators and stairwells are designed to prevent preferential migration; and c) require that prospective residents be notified of the property's environmental history and response to date. EPA should not delete the site from the NPL before such actions are taken. Deletion now would be misleading to the public, particularly those who may choose to rent the apartments that are now under construction. 
Response 4: 
EPA and RWQCB agree that a contingency plan, adequate ventilation in the parking garage, blocking preferential vapor migration pathways and public notices to prospective residents are all important and we are using our authority under the deed restriction to ensure that these issues are addressed.  A preferential vapor migration pathway is an opening by which soil vapor can enter the apartment complex such as utility connections, elevator shafts and stairways. 
Response to part a) contingency plan: 
The RWQCB is requiring the owner and developer, Prometheus Group, to develop a contingency plan for remedial action if any indoor air samples are above the action level specified in the vapor intrusion mitigation system operations, maintenance, and monitoring plan. The RWQCB and EPA will review the contingency plan to make sure the proposed mitigation measures adequately address any potential levels of PCE in indoor air found at the new apartment complex. The vapor intrusion mitigation system has been designed so that it can be switched easily from passive to active mode if needed.  
Response to part b) adequate ventilation in the parking garage and preventing preferential migration. 
The deed restriction requires a vapor intrusion mitigation system to be installed. The developer submitted a proposal; EPA and RWQCB provided technical comments on it to address concerns of adequate ventilation in the parking garage and protection against preferential migration pathways such as elevator shafts, utility corridors and stairwells. RWQCB and EPA have not yet received a revised design report for the system but will make sure that these issues are addressed in the final design.
Response to part c) notice to prospective residents: 
The deed restriction requires that the following notice must be contained in all purchase agreements or leases relating to the property:
   The land described herein contains hazardous materials in soils and in the groundwater under the property, and is subject to a Covenant and Environmental Restriction on Property dated as of February 24, 2010, and recorded on March 29, 2010, in the Official Records of Santa Clara County, California, as Document No. 20659469, which Covenant and Environmental Restriction imposes certain covenants, conditions, and restrictions on usage of the property described herein. This statement is not a declaration that a hazard exists.
Additionally, the deed restriction must be incorporated in and attached to all deeds and leases of any portion of the property. The developer and EPA are currently working together to draft additional language to be a part of all leases, which will include:
 A description of the vapor intrusion mitigation system
 Contacts for more information or to report problems with the mitigation system
 Websites where residents can find more information about the Jasco Site, including EPA's website: https://www.epa.gov/superfund/jascottps://cumulis.epa.gov/supercpad/cursites/csitinfo.cfm?id=0901126, and the RWQCB's GeoTracker database, https://geotracker.waterboards.ca.gov/profile_report?global_id=T0608592706. 
Keeping the Jasco Site on the Superfund list because the Villa Street PCE plume exists would imply that EPA is using its Superfund authority to address the contaminated Villa Street PCE plume, which might mislead the public into thinking that EPA will investigate or address the Villa Street PCE plume. That is not the case; EPA is not using its Superfund authority to address the Villa Street PCE plume. Once EPA determined that the source of the plume was offsite, it required Jasco to record the deed restriction to address any potential exposure at the Jasco Site. In addition to the deed restriction, EPA worked with state agencies to determine which agency would be the appropriate regulatory lead to address the Villa Street PCE plume. In 2012, DTSC agreed to take responsibility for the Villa Street PCE plume, but DTSC did not complete any work. In 2020, the RWQCB agreed to take responsibility for investigation and oversight of the Villa Street PCE plume. The RWQCB is planning to review the results for post construction groundwater and soil vapor data that will be collected at the Jasco Site in order to determine if additional investigation or remedial actions are needed with respect to the Villa Street PCE plume. It is anticipated that such actions would be conducted by the current or previous landowners.  
Comment 5:
According to the City of Mountain View, "An environmental deed restriction for the site requires the RWQCB and EPA to oversee its development and re-use. The agencies' oversight will ensure soil or groundwater is managed according to a soil management plan that prevents any human exposure to the chemical." As you know, a 226-unit apartment complex is being developed at this location, and we do not want to see future residents there, as well as current construction workers and nearby residents, put at any health risks that can be avoided through proper and complete application of the Superfund and Regional Water Quality Control Board (RWQCB) program.

Response 5:
This comment has been addressed primarily above, but EPA is concerned that the commenter may be under the impression that the deed restriction will expire with the Jasco Site's deletion. This is not the case. The deed restriction, titled Covenant and Environmental Restriction on Property, recorded March 29, 2010, will remain in place and continue to subject the property at 1710 Villa Street to restrictions on its use. As explained in EPA's 2012 Explanation of Significant Differences (ESD): 
      "The deed restriction, though necessary and protective, is addressing a release that is not part of the site. Therefore, this ESD clarifies that the deed restriction is no longer a component of the CERCLA remedy for the Jasco Site." 
Because the Covenant and Environmental Restriction on Property is not a component of the CERCLA remedy for the Jasco Site, it is not affected by the removal of the Jasco Site from the NPL. The deed restriction's terms apply to the land no matter who owns or occupies it, and the restriction must be incorporated into all deeds and leases of any portion of the property.
Specifically, the deed restriction: 
 prohibits drilling of wells into and/or extraction of groundwater for any use other than remediation or monitoring. 
 requires prior approval by the RWQCB and EPA before any use of the property results in:
 Any excavation of soil that is saturated with groundwater or is part of any aquifer or perched zone for any use other than remediation or monitoring;
 Use, removal, or modification of existing groundwater monitoring or extraction wells;
 Constructing any underground structure without engineering controls to adequately control buildup of vapors in occupied spaces and prevent intrusion of groundwater; 
 Soil disturbance (excavating, grading, removal, trenching, filling, earthmoving, or mining).
The apartment complex being developed at this location is subject to these restrictions, and the RWQCB and EPA have reviewed and approved the developer's plans submitted thus far.
Comment 6:
Why didn't EPA clean up the PCE plume at the site? I do not believe deletion should occur until current sampling shows that the original remedial action objectives have been met. The most recent data shows unacceptable levels of PCE in the soil gas and groundwater. The conclusion that the PCE did not originate on site appears to have been first put forward by consultants for JASCO; it's possible, but I do not find the evidence persuasive. I consider corporate self-reporting unreliable, and in this case my organization received a report in the 1980s that someone from JASCO was conducting "midnight dumping." Regulators should also consider preferential pathways in evaluating potential sources of PCE contamination. No one has explained the extremely high levels of PCE in soil gas; in particular, the reported levels of groundwater contamination are not high enough to explain the presence of PCE in soil gas at 45,000 micrograms per cubic meter. I strongly oppose the claim that the contamination in this site is from an outside source therefore the site can be removed from NPL. This claim must be thoroughly investigated. 

Response 6:
EPA did not address the Villa Street PCE plume because it determined that the plume did not originate at the Jasco Site. Under CERCLA, EPA does not hold parties responsible for contaminated groundwater under their site that originated elsewhere (discussed in more detail in the Response 8 below).
Confirmation sampling indicates that cleanup levels for all contaminants that originated from the Jasco Site in soil and groundwater were reached in 2002. Though Jasco met the cleanup goals for contaminants identified as coming from Jasco's operations, two volatile organic compounds, perchloroethylene (PCE) and trichloroethylene (TCE), remain in groundwater. After significant investigation, PCE and its breakdown compound TCE, were determined to be from an unknown offsite source, not Jasco. EPA completed a rigorous independent evaluation to confirm that the PCE plume under the Jasco Site did not originate from site activities at Jasco. 
EPA's evaluation used the following data to conclude that the Villa Street PCE plume was not from Jasco:
 Jasco's contractor reports (or self-reporting) that PCE was not used at the Jasco Site;
 An analysis of more than 300 soil samples from 100+ different locations, 112 soil borings, 44 Hydropunch samples included in the revised PCE investigation report; and
 a close examination of groundwater quality reports. 
   This data was also used to delineate the boundaries of the PCE plume and assess its origins. 
   In 2011, EPA completed a Final Expert Technical Assistance Report. This report included a comprehensive review of hydrogeological groundwater monitoring, soil sampling data, and soil vapor data at the Jasco Site to confirm that Jasco was not responsible for the Villa Street PCE plume. 
   Multiple lines of evidence support the conclusion that the Villa Street plume is not related to Jasco, including the following:
 Out of hundreds of soil samples and soil boring cores collected over decades, PCE was detected in only eight soil samples at relatively low concentrations, suggesting that no source of PCE existed at the Jasco Site. 
 During the Remedial Investigation of the late 1980s, PCE was found in eight shallow surface soil samples in the drainage swale at the Northwest corner of the Jasco Site, which received runoff waste from several other properties. Concentrations ranged from 0.21 to 16 parts per million. These low concentrations in soil are not consistent with being a source for the much higher concentrations of PCE found in groundwater under other parts of the Jasco Site. 
 Additionally, groundwater at the Jasco Site flows north, meaning that the drainage swale is downgradient of the PCE hotspot near monitoring well V-10A. It is not possible for the low levels of PCE found in soil in the drainage swale to have traveled against the prevailing direction of groundwater flow and have caused a much higher concentration of PCE in groundwater.
 PCE was first identified in groundwater near well V-4. After remediation started and groundwater was being pumped at the Jasco Site, PCE began to appear in high concentrations at well V-10A. 
 Two distinct fingerprints have been observed through the history of groundwater monitoring at the Jasco site: Fingerprint A, with 1,1,1-TCA -- 1,1-DCA -- 1,1-DCE, which was observed primarily during the early remedial history of the site (mainly before 1998), with most contaminant concentrations decreasing through time; and Fingerprint B, with PCE -- TCE -- cis-1,2-DCE, which has been observed almost exclusively after 1995, with contaminant concentrations increasing at most locations over time. The two parent compounds (1,1,1-TCA and PCE) and their daughter products are not related by any degradation scheme, and these parent-daughter combinations of compounds are well established in the technical literature. The composition of each fingerprint, along with the differing temporal and spatial patterns, lends confidence to the idea that the two fingerprints represent separate contamination plumes and separate contamination sources. The PCE plume appears to have arrived later and from a contaminant source not on the Jasco site, based on the very extensive soil sampling performed at all potential on-site source areas. 
 PCE was first detected in the Jasco Site's groundwater in 1995 after the groundwater cleanup was underway. Its distribution at the Jasco Site is not consistent with historic contaminant presence and distribution at the Jasco Site from known source areas.
 City of Mountain View Fire Department and Jasco records and correspondence
         indicate that PCE has not been stored, used, or distributed at the Jasco Site.
 The highest concentrations of PCE detected during the investigation were at locations
         on property to the east of the Jasco Site, and PCE has been detected at elevated
         levels at sampling points upgradient of the Jasco Site.
 The property immediately east of the Jasco facility had been previously occupied
         by companies whose industrial activities typically would have used solvents.
After EPA concluded that Jasco was not responsible for the Villa Street plume in 2012, EPA met with DTSC and the RWQCB to determine which agency should have oversight of the Villa Street PCE plume, and DTSC accepted responsibility for addressing it. See Explanation of Significant Differences at the Jasco Chemical Company Superfund Site, Appendix A (Sept. 26, 2012). 

DTSC did not undertake any sampling or investigation efforts to address the Villa Street PCE plume. The RWQCB has now accepted responsibility for investigating the Villa Street PCE plume and EPA will work with the RWQCB to ensure that the RWQCB's investigation work continues.  See Response 7 below for details on how the RWQCB will address the Villa Street PCE plume in the future. 

The most recent groundwater sampling data is from 2010 and the most recent soil vapor data was collected in 2002. Sampling results from these efforts revealed that PCE levels in groundwater ranged from 0.5-190 parts per billion (ppb), which were above the federal Maximum Contaminant Level of 5 ppb. As discussed in Response 2, groundwater at the Jasco Site is not used as drinking water source. Unlike groundwater, there is no Maximum Contaminant Level for PCE in soil vapor because the vapor intrusion exposure pathway is influenced by several variables that change for different exposure scenarios including the depth to groundwater, concentration of the contaminant in groundwater, the type of building, and indoor air ventilation systems. The highest recorded soil vapor concentration of 45,000 μg/m[3] near well V-10A, is consistent with soil vapor levels observed at other sites with comparable concentrations of PCE in groundwater. Because PCE is a volatile organic compound and has a large Henry's Constant, it is transported more easily from the liquid to the gaseous phase. Henry's Law is a law in chemistry that states that the amount of gas disolved in a liquid is proportional to the partial pressure of the gas above the liquid. A large Henry's Constant implies that a substance is not very soluble in a liquid, which means it is more likely to go into the gaseous phase. Under certain conditions, 1ppb of PCE can create a 500 ug/m[3] in soil vapor. While PCE naturally attenuates in groundwater, it does not degrade as easily in soil vapor, which explains why it is thought to have a 500-1000x multiplier effect in soil vapor as compared to groundwater. This explains the high concentrations of PCE in soil vapor relative to groundwater concentrations at the Jasco Site. 
Useful Documents
 Final Expert Technical Assistance Report (2011)
 Explanation of Significant Differences (2012)
 Revised 2000 PCE Investigation Report
 ATSDR Toxic Substances Portal-Tetrachloroethylene (PCE) 
https://www.atsdr.cdc.gov/phs/phs.asp?id=263&tid=48
 Letter referring Villa Street PCE Plume to DTSC (2012)
 The Jasco Site administrative record is available on EPA's website: https://cumulis.epa.gov/supercpad/SiteProfiles/index.cfm?fuseaction=second.ars&id=0901126&doc=Y&colid=65129&region=09&type=AR

Comment 7: 
The site should continue to be on the NPL list until it meets acceptable health standards, and the source should be identified and appropriately dealt with. Some agency needs to take responsibility for cleaning up the remaining PCE, until this has been done, it should remain on the Superfund's National Priorities List. Nothing has been done by the California Department of Toxic Substances Control to identify an off-site responsible party or address the property as an orphan site.

Response 7:
The determination that the Villa Street PCE plume was from an offsite source not related to Jasco was carefully reviewed over a span of 12 years using data from hundreds of surface soil, soil boring, soil vapor, and groundwater samples and several historical records. Response 6 details why EPA concluded that the Villa Street PCE plume did not originate from activities at the Jasco Site. 
EPA has determined that it is appropriate to proceed with the deletion because all response actions at the Jasco Site are complete and the criteria for deletion have been met. The decision to delete the Jasco Site from the NPL is not determined by the presence or absence of the Villa Street PCE plume, because the Villa Street PCE plume is not part of the Jasco Site. After careful consideration of the facts available to and gathered by the agency, EPA determined that the PCE plume was coming from offsite, and subsequently EPA discussed the situation with DTSC and the RWQCB to identify the most appropriate agency to regulate the offsite PCE plume. DTSC, in consultation with the RWQCB, identified itself as the appropriate regulatory agency, and in 2012, EPA formally referred the Villa Street PCE plume to DTSC for further investigation and oversight. DTSC does not have the resources to address the Villa Street PCE plume as an "orphan site." An orphan site is defined as a site without a responsible party to conduct or pay for the investigation or cleanup of the pollution. 
Additionally, a deed restriction is in place to ensure that the Villa Street PCE plume does not pose a risk to future residents of the apartment complex currently under construction at the Jasco Site. Response 2 gives more details on the deed restriction and how it protects human health and the environment. The RWQCB and EPA are requiring additional sampling of PCE (and other contaminants) in groundwater, soil vapor, and indoor air after construction is completed, and before anyone occupies the new apartment complex. This sampling will inform our understanding of current Jasco Site conditions, the Villa Street PCE plume, and identify any potential risks to future residents. 
EPA acknowledges that the current potential risk from the offsite Villa Street PCE plume to occupants of neighboring properties is unknown. After receiving comments on the proposed deletion of the Jasco Site indicating the public's concern that DTSC was not taking action, EPA met with DTSC to discuss the Villa Street PCE plume. DTSC has not addressed the Villa Street PCE plume since they agreed to take over the investigation in 2012. The RWQCB agreed to take over the investigation and oversight of the PCE plume and this decision was documented in a formal referral letter dated September 16, 2020. The RWQCB will evaluate groundwater and soil vapor quality data to be collected after the construction activities are completed at the Jasco Site to better understand current site conditions. The RWQCB will direct a potentially responsible party (a former owner of 1350 Villa Street) to develop a workplan to investigate soil vapor and groundwater quality in the vicinity of 1350 Villa Street. This data will be used to determine if additional investigation or remedial actions are needed in respect to the Villa Street PCE plume. The RWQCB will be working on its investigation over the next year (2021) to assess potential risks to human health and the environment associated with the Villa Street PCE plume.
Additionally, the State of California, through the appropriate state regulatory agencies including the RWQCB and/or DTSC, could request that US EPA evaluate the Villa Street Plume using the hazard ranking system to see if the Villa Street Plume would score high enough to qualify to be listed on the National Priorities List. The State of California has the discretion to request listing or otherwise seek assistance from EPA under its CERCLA authorities in the future if it determines it to be necessary. At that point, the Villa Street Plume would undergo an evaluation under the Superfund Site Assessment Process to see whether it qualifies to be added to the National Priorities List (Superfund List). 
Useful Documents:
Final Expert Technical Assistance Report (2011)
Superfund Site Assessment Process
https://www.epa.gov/superfund/superfund-site-assessment-process

Comment 8: 
The conclusion that PCE did not originate on site seems inconsistent with the Superfund principle of Strict, Joint, and Several Liability. If a party is responsible for any portion of a site's contamination, it can be held responsible for all of it. In other words, NPL listing is based upon the site and the hazard it poses, not the source. Why would EPA walk away from such a site?

Response 8:
Jasco was the owner and operator of the Jasco Chemical Corporation Superfund Site; this means that Jasco is liable for costs of cleanup of the Jasco Site under CERCLA at 42 USC 9607(a). The Villa Street PCE plume was contaminating the Jasco Site; therefore, the principle of strict, joint, and several liability would ordinarily apply to require Jasco pay for the cleanup of the Villa Street PCE plume. EPA has a longstanding policy, established in 1995, which states EPA's position towards owners of property containing contaminated aquifers. Under the policy, if contamination has spread to a property solely as the result of migration in groundwater from a source outside the property, EPA will not take enforcement action against the owner to require cleanup or payment for cleanup of the contaminated groundwater. Because Jasco's cleanup of its contamination in the groundwater was underway when PCE was first detected, and there was no evidence that Jasco had released PCE, EPA applied the principle behind the policy and did not require Jasco to clean up the Villa Street PCE plume.   
Useful Document
 EPA's Final Policy Toward Owners of Property Containing Contaminated Aquifers (1995) https://www.epa.gov/sites/production/files/2013-09/documents/contamin-aqui-rpt.pdf.
Comment 9:
According to this notice all groundwater and soil monitoring was stopped in 2012. The site is under active development and a large amount of soil is being removed daily for the housing complex. It seems prudent to continue to do further monitoring, especially since the last time monitoring was performed there were indeed high levels of PCE and TCE found. No recent subsurface sampling has been conducted at the site. There needs to be current subsurface sampling at the mentioned site showing acceptable levels of tetrachloroethylene or perchloroethylene (PCE) in the soil gas and groundwater. 

Response 9:
Groundwater was last monitored at the Jasco Site in 2010 and soil vapor was last sampled in 2002. However, the current owner collected subsurface soil samples in 2019, prior to excavation and grading at the construction site of the new apartment complex. Samples were collected at 11 locations at depths of 1, 2, 5, 10, and 20 feet below ground surface. PCE was not detected in any of these recent soil samples at levels above the California Regional Water Quality Control Board's residential environmental screening level. 

It is likely that any potential risks posed by the Villa Street PCE plume will be further reduced by construction underway at the Jasco Site. The construction plans, which were required to be submitted under the deed restriction, call for the expected extraction and treatment of 200 million gallons of groundwater as well as the removal of around 62,000 cubic yards of soil. These actions will likely reduce concentrations of PCE in soil vapor and groundwater at the Jasco Site. 
The deed restriction as outlined in Response 2 requires numerous protections to ensure that people do not contact contaminated soil or groundwater at the Jasco Site. As part of the Jasco Site's current redevelopment, groundwater is being pumped to the surface and treated with a portable water filtration system and discharged into surface waters under a permit issued by EPA (referred to in Response 2). Soil excavated during construction is sampled for proper offsite disposal. A perimeter dust and air monitoring program ensures that no dust or dust that might contain PCE leaves the Jasco Site boundary and impacts the surrounding neighborhood. Prior to the apartment complex being occupied, indoor air samples will be taken to confirm that there are no vapor intrusion issues at the Jasco Site. If the samples exceed the action level specified in the vapor intrusion mitigation system operations, maintenance, and monitoring plan, mitigation measures will be applied until the action level is met. 
As discussed in the Responses 3 and 7, more recent groundwater and soil vapor data would be helpful in determining the current boundaries of the Villa Street PCE plume and its impact to the surrounding neighborhood. The RWQCB is planning to issue a letter requiring a potentially responsible party to submit a work plan to assess the nature and extent of PCE in soil vapor and groundwater associated with the Villa Street plume. However, more recent data is not needed to protect the health of future residents at the Jasco Site. 
Comment 10:
The Notice of Intent to Delete was not written in simple and accessible language in accordance with the Plain Writing Act of 2010. 

Response 10:
Thank you for bringing this matter to our attention. We used EPA's standard Federal Register notice templates for deleting sites from the NPL at https://www.epa.gov/superfund/superfund-npl-deletion-federal-register-templates. The rule-making process for NPL deletions is undergoing substantial changes at the present time and we will review and consider modification of this language in new future rulemakings in consultation with General Counsel and the Federal Register staff in the Office of Policy. 
As a result of your comment, we made several improvements in this responsiveness summary. Specifically, we: 
 Used simpler explanations
 Limited our use of acronyms
 Included a list of acronyms and defined terms used in the responsiveness summary (Appendix A)   
We hope you will see and benefit from these changes in understanding our responses and commit to writing in plainer language in the future.


                                  Appendix A

Acronyms
DTSC 		California Department of Toxic Substances Control
CERCLA 	Comprehensive Environmental Response, Compensation, and Liability Act (Superfund)
EPA 		U.S. Environmental Protection Agency 
NPL		National Priorities List
PCE 		Perchloroethylene
PPB		Parts per billion
RWQCB 	Regional Water Quality Control Board
TCE		trichloroethylene
Terms and Definitions
Aquifer - a body of permeable rock and/or soil that can contain or transport groundwater. Groundwater is not an underground lake, it is stored in between the individual particles of rock, gravel, sand, clay or soil. 
Release -  Defined in CERCLA as "any spilling, leaking, pumping, pouring, emitting, emptying, discharging, injecting, escaping, leaching, dumping, or disposing into the environment (including the abandonment or discarding of barrels, containers, and other closed receptacles containing any hazardous substance or pollutant or contaminant)," subject to some exclusions not relevant for purposes of this responsiveness summary. 42 U.S.C. § 9601(22). 

Remedy  -  Defined in CERCLA as "those actions consistent with permanent remedy taken instead of or in addition to removal actions in the event of a release or threatened release of a hazardous substance into the environment, to prevent or minimize the release of hazardous substances so that they do not migrate to cause substantial danger to present or future public health or welfare or the environment. The term includes, but is not limited to, such actions at the location of the release as storage, confinement, perimeter protection using dikes, trenches, or ditches, clay cover, neutralization, cleanup of released hazardous substances and associated contaminated materials, recycling or reuse, diversion, destruction, segregation of reactive wastes, dredging or excavations, repair or replacement of leaking containers, collection of leachate and runoff, onsite treatment or incineration, provision of alternative water supplies, and any monitoring reasonably required to assure that such actions protect the public health and welfare and the environment. The term includes the costs of permanent relocation of residents and businesses and community facilities where the President determines that, alone or in combination with other measures, such relocation is more cost-effective than and environmentally preferable to the transportation, storage, treatment, destruction, or secure disposition offsite of hazardous substances, or may otherwise be necessary to protect the public health or welfare; the term includes offsite transport and offsite storage, treatment, destruction, or secure disposition of hazardous substances and associated contaminated materials." 42 U.S.C. § 9601(24).

Soil Vapor or Vapor - Soil vapor consists of gases that come from chemicals in groundwater and soil and remain in a gaseous state in between particles of soil.

Vapor Intrusion - chemicals in groundwater or soil vapor release gases that travel through the ground and enter homes through utility corridors or cracks and gaps in the building's foundation.
