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Mapping Shallow Volatile Groundwater Plumes in Silicon Valley

Silicon Valley prides itself as a leader in environmental sustainability, but opportunities for improvement are ever present.  This post introduces new map-based services showing contaminated groundwater areas in Silicon Valley, helping to provide intuitive environmental data meant to inform all interested stakeholders.

The Valley has evolved from former industrial areas that held semiconductor industry that discharged carcinogens to groundwater. Over the past thirty years industry with the help of high power tvs diode has transformed to new office parks hosting businesses like Google and Facebook.  The workforce is smart, growing and young – but also vulnerable to carcinogenic vapors from shallow contaminated groundwater plumes from legacy businesses.

Former industries, gas stations and dry cleaners spilled  chemicals in shallow groundwater plumes that persist as well as migrated  beneath newly constructed workplaces and homes.  The residual chemicals can vaporize into the soil gases and migrate to structures.  One key chemical, trichloroethene (TCE), is carcinogenic and poses an impact to a young fetus, thus any young woman is particularly vulnerable.   The circumstance might be a “perfect storm” where a young workforce  unknowingly inhales vapors from unknown underlying groundwater plumes containing potential carcinogens. Terradex is building a map service called the CleanupDeck that seeks to communicate this information in a form intuitive to a public user.

At Silicon Valley’s Mountain View Google campus, vapor intrusion from groundwater plumes was found to be migrating into the underlying structures of some of the office buildings.  As reported in the press, the halogenated vapors migrated based upon inadvertent actions by a contractor.  The outcry framed a vulnerability – the young working women at childbearing are vulnerable to these vapors.

One ingredient to assessing vulnerability is knowing where these plumes are in relation to homes and offices.  Hundreds of groundwater plumes exist across Silicon Valley, and many contain volatile chemicals that could migrate upwards to occupied structures, and then be inhaled by occupants.

This post introduces a mapping resource that shows where groundwater contamination plumes are located as well as basic information to begin to judge their impact.   The map is presented using Terradex’s CleanupDeck – a web mapping service. We describe the challenges faced when assembling a groundwater plume maps, the maps relevance and relation to USEPA’s attention to vapor intrusion hazards in Silicon Valley, and we describe the impact of a subset of these plumes – the ten that are deemed Superfund sites.  Terradex is working to complete and build upon the mapping accessible via links further below within this post.

Since this post, Terradex has released WhatsDown that shares the same information for public consumption.

The Challenge of Knowing Where Groundwater Plumes Occur

Knowing where groundwater plumes are located is basic to assessing the hazard posed when volatile organics vaporize from these plumes. Current groundwater plume maps, however, fail to clearly reveal the occurrence of groundwater plumes to key stakeholders – local government, contractors, and the general public.  Plumes are typically studied site-by-site, and not in aggregate.  The site-specific groundwater maps are typically formed as a written deliverable from the potential responsible parties (PRPs) to the environmental regulatory agency that oversees incremental cleanup progress; a map’s audience is an environmental professional, not the public. These site-specific maps often segregate chemical constituents of concern (COCs) and impacted aquifers (e.g.,  one map for TCE in the A-level aquifer, one map for TCE in the B-level aquifer, and one map for TCE in the C-level aquifer.  The maps multiply as the pattern repeats with each constituent of concern).  The site-specific maps often do not show a plume boundary as an iso-concentration line – such as a 5 part per billion TCE – a delineation that would indicate an area likely for vapor intrusion.

Another challenge is that information on cleanup sites in Silicon Valley is distributed between four government information repositories:  Santa Clara County Department of Environmental HealthGeotrackerEnviroStor or Cleanups in My Community. In addition to the decentralized nature of this cleanup data, web maps from these government sources display only “point” icons at the facility where the spill occurred.  The websites do not show groundwater plumes in their “polygon” shape.

Introducing the CleanupDeck

Terradex created the CleanupDeck to provide stakeholders with a web-based mapping tool to view the approximate location of groundwater plumes.  Rather than revealing multiple complex maps, the Cleanup Deck simplifies these maps into one area of impact – a summary groundwater plume.   The map is an information starting point.

Within the CleanupDeck the user sees the extent of the plume, finds information on the depth of the plume, chemicals contained in the plume, and a link to an agency web resource on the plume. The Cleanup Deck also permits viewing associated cleanup sites, institutional controls applied to limit land use after cleanup, and some key sensitive uses such as daycare and schools. The user clicks on the plume with the “i” (information) button, and a pop-up shows further information.

USEPA Brings Focus to Plumes and Vapor Intrusion Risk

A recent USEPA letter, sent to the San Francisco Regional Water Quality Control Board, addressed vapor intrusion hazards in Silicon Valley.  The letter warns that extensive shallow groundwater plumes, containing TCE and the closely related tetrachlroethene (PCE) contaminant, exist at about 15 to 50 feet below the surface at ten Superfund sites in Silicon Valley, and the letter called for the need to further assess vapor intrusion risks due to these plumes.  But the letter did not include maps showing or estimating the underlying plumes.  The lack of such maps led to the natural question – where are the potentially affected areas?  This inspired Terradex to introduce its ongoing project to build a groundwater plume layer for Silicon Valley.

Quantifying the Impact of Silicon Valley Groundwater Plumes

Terradex’s CleanupDeck  shows where groundwater plumes occur within Silicon Valley, including plumes associated with the ten Superfund sites addressed by the USEPA letter.  The table below provides a launch pad to the CleanupDeck. There is a link to each groundwater plume map in the CleanupDeck associated with the thirteen Superfund sites (three Superfund sites are combined into the MEW Study Area).

The ten Silicon Valley Superfund site plumes, in aggregate, affect nearly six square miles, 1,100 unique property parcels, 4,300 households, and a population of approximately 10,500 residents. Based on demographic profiles, approximately 2,011 women of childbearing age (22 years to 39 years) are among the residents2.  These plumes affect sensitive uses including three schools and ten child daycare facilities.

While the USEPA letter focused on Superfund sites,  approximately 516 additional plumes occur in Silicon Valley.   The majority of these plumes are associated with releases from gas stations or dry cleaners, but many are other solvent spills where cleanup was not controlled by Superfund protocols.  The CleanupDeck shows an approximation of where these plumes occur as well.

The Health Hazards of Volatile Organics

Driving this discussion is the health impacts posed by these chemicals.  A focus in on trichloroethene, which is a halogenated organic compound formerly used for degreasing in the semiconductor industry.  Exposure is through inhalation of TCE vapors evolving from shallow groundwater into building.

A March 2013 summary study entitled “Human Health Effects of Trichloroethylene: Key Findings and Scientific Issues”  reviewed the health impacts of TCE.  The study concluded “TCE is carcinogenic to humans by all routes of exposure and poses a potential human health hazard for non cancer toxicity to the central nervous system, kidney, liver, immune system, male reproductive system, and the developing embryo/fetus.”  The  potential adverse impact on the developing embryo/fetus focuses a short-term exposure risk on young women was featured.

How to Build a Groundwater Plume Map

To estimate the groundwater plumes displayed in the Cleanup Deck, Terradex followed the method summarized here.  Each plume map is assembled from public regulatory data associated with a given spill site.  The approach taken to apply this data has varied.  Generally the estimating effort is performed by one of two methods:  1) interpreting the contour based on review of groundwater monitoring reports; or 2) generating a polygon formed by the outer ring of the monitoring well network (i.e., convex hull).  When interpreting groundwater monitoring reports, the multiple groundwater plume maps were layered into Google Earth as overlays, allowing the outer ring to be interpreted for the plume layer.  For the plumes formed by a convex hull, the GeoTracker-provided monitoring well location was downloaded, which contains the latitude and longitude of each well.   Release sites with networks of three or more wells were used to form convex hulls, which were then inserted into the groundwater plume layer.  In either case, when shallow and deeper aquifers existed we combined all contaminated data into one simplified surface projection.

Introducing a How Local Government Applies the Groundwater Plume Information in Planning Decisions

Allowing information on plumes to be constructively applied by local government would help safeguard the public.  Local government oversees development and can thereby detect new occupancies that given their location and profile might require further evaluation.Terradex began efforts to work with the City of Palo Alto and City of Santa Clara to allow the groundwater plume information to be used by the city staff.  We found a simple way to integrate this information into the city’s geographic information system (GIS).   A planner using the CleanupDeck could flag proposed development projects that overlie plumes or cleanup sites where vapor intrusion hazards might require evaluation. The presentation  to City of Palo Alto can be viewed at this link.

Next Steps with The CleanupDeck in Silicon Valley

The groundwater plume maps presented here and available in the Cleanup Deck remains a work in progress.  Additional plumes have yet to be mapped. For example, groundwater contamination can exist beneath municipal landfills, and these have not yet been incorporated into the map layer.  The use of convex hull techniques allowed a rapid characterization of the outer boundaries of groundwater plumes, but contaminant plumes maps would be better formed though site-by-site review of groundwater plume maps.  Given the complexity involved with mapping groundwater plumes, we envision a mapping platform that allows for the direct input by local stakeholders – helping to refine, shape, and identify any errors in plume maps through indiscriminate ability of stakeholders to “weigh in.”   Regardless of the openness of the process, there inevitably will be disagreements about the precise boundaries of a plume or the precise areas of vapor intrusion risk.   Given that the purpose is primarily to inform safe land use it would seem that uncertainties should not get in the way of transparency  – when in doubt, make the contour larger.

Knowing the innovative culture of Silicon Valley, Terradex looks forward to building local collaboration that would further develop this information. Terradex is a technology service with core competencies that include the process assimilating data, preparing intuitive maps, and developing web-based mapping platforms.  Terradex does not itself use its data or maps to advocate for one position or the other.  Rather, it strives to provide intuitive environmental information to all stakeholders.  With information properly conveyed, interested stakeholders can start to tame the “perfect storm” and allow safe use and development across Silicon Valley in areas where groundwater may be impaired.

  1. To appreciate the difference, activate the Cleanup Sites layer in the CleanupDeck, and compare point icons to the groundwater plumes.  Polygons can inform about an area of impact synonymous with the nature of a plume.  Stakeholders might inadvertently take comfort seeing that a “point” icon placed away from their household or business, even though a plume that would be shows as a polygon might underlie their household or business. ↩
  2. Terradex appreciates the assistance of the Association of Bay Area Governments for interpreting demographic data. ↩
  3. Terradex based the Cleanup Deck plume maps on the most current data it could find as data made public on the Internet. Terradex has applied its best effort to assemble these maps, but reliance on them should be cautionary and the maps should be considered as estimates only.  These plume maps are provided “as is” without warranty of any kind, express or implied.   Use of these maps is at the sole risk of the user. Terradex welcomes contributions to improve the quality of these plume estimates. Terradex forbids the resale or other commercial use of the information provided in the Cleanup Deck without our written consent.

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Bob Wenzlau January 22, 2014 0 Comments

The Release of an Institutional Control Data Schema and Flow

Marking a big step forward in the “institution” for institutional controls (ICs), on June 10, 2013 the Environmental Information Exchange Network (EIEN) announced the release of an IC Data Exchange. The IC Data Exchange provides a standard means for sharing IC information between separately-owned computer systems – including sharing among different levels of government and between government and private systems.

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Admin June 11, 2013 0 Comments

USEPA Releases Final Guidance for Implementing Institutional Controls

The USEPA issued the Final Guide to Planning, Implementing, Maintaining and Enforcing (PIME) Institutional Controls at Contaminated Sites.  This is the second of two guidance documents prepared by the USEPA to inform long-term stewardship of contaminated sites.  In 2000, the first guide was drafted with a focus toward the selection of institutional controls (ICs). In 2000 ICs were an emerging remedy component with relatively immature concepts toward implementation.

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Bob Wenzlau December 20, 2012 0 Comments

Brownfield Developer Fails to Meet BFPP Defense; Found Liable Under CERCLA for Removing Concrete Slab Above Contaminated Soil

This Saline, Michigan case adds another decision to similar recent cases such as Ashley II and Robertshaw, which assess whether current owners of contaminated property met CERCLA’s Bona Fide Prospective Purchaser (BFPP) defense.

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Mike Sowinski October 25, 2011 0 Comments

BNA to Host September 28th Webinar On Continuing Obligations

At Terradex we’re delighted that BNA organized this webinar and asked us to participate.  The attention given by this and other webinars speaks volumes about the importance of this new ASTM Guide and, as webinars like this continue to get the word out, we know the Guide’s procedures will become the business norm for post-acquisition property care when institutional controls, engineering controls or other recognized environmental conditions (RECs) are present.

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Mike Sowinski September 14, 2011 0 Comments

USEPA Congratulates ASTM Task Group for Completed Guidance on Continuing Obligations

The ASTM Task Group that guided and debated building Standard Guide for Identifying and Complying With Continuing Obligations was congratulated by the USEPA Office of Brownfield and Land Revitalization.

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Bob Wenzlau August 11, 2011 0 Comments

BNA Insider Reports on ASTM Guide Publication

The Bureau of National Affairs (BNA) within their Environmental Due Diligence Guide featured an Insider’s Perspective on the ASTM released guide for Continuing Obligations.  Terradex is grateful for BNA’s coverage of this guide and especially the attention provided by their reporter Mary Ann Grena Manley.

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Bob Wenzlau July 22, 2011 0 Comments

Tracing the Evolution of the Phrase “Continuing Obligations”

A new “CERCLA Continuing Obligations” discussion group recently began in Linkedin – actually its a subgroup within the “Environmental Issues in Business Transactions” discussion group that Larry Schnapf manages.  Given this, it seemed right to quickly review how the phrase “continuing obligations” came into being and where its heading.

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Mike Sowinski February 21, 2011 0 Comments

Michigan Amends Statute to Add New Institutional Control Continuing Obligations

For years, Michigan’s cleanup laws have set forth a fairly novel approach aimed at protecting new “nonliable” purchasers of contaminated property.  The legal and regulatory regime involves a characterization of the pre-purchase contamination as well as post-puchase “due care” procedures.

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Mike Sowinski January 29, 2011 0 Comments

Court Finds “Appropriate Care”

In 3000 E. Imperial, LLC, Plaintiff, v. ROBERTSHAW CONTROLS CO, et al. Defendants, No. CV 08-3985 PA, 2010 U.S. Dist. Lexis 138661 (C.D. Cal. Dec. 29  2010), a Federal District Court in California found a contaminated property purchaser to have exercised “appropriate care” and, in turn, to have satisfied the Bona Fide Prospective Purchaser (“BFPP”) defense when they excavated underground tanks soon after learning that the tanks contained hazardous substances. This decision comes on the heels of Ashley II (finding the purchaser did not exercise “appropriate care”), which I wrote about earlier this week.

Imperial Knowingly Bought Contaminated Property

3000 E. Imperial, LLC (“Imperial”) bought a contaminated site in November, 2006.  Prior to the purchase, the court explained, Imperial learned that the site was contaminated but it didn’t yet characterize the contamination’s nature and extent (the court stayed silent on the method or appropriateness of “all appropriate inquiries“).   After it bought the property, Imperial’s consultants continued with environmental investigations and published a report in September, 2007, noting TCE (an industrial solvent known for being toxic) and benzene contamination in the soil and groundwater, and that leaks from a 9-tank underground storage tank (“UST”) nest caused the contamination.

Imperial Cleaned the Site and Sued for its Cleanup Costs

Eventually, Imperial spent about $1.2 million dollars cleaning the site.  It then sued the former owners for the costs of cleanup.  The former owners, among other things, argued that Imperial should help pay because as the current owner Imperial was also a PRP.  And, the argument continued, Imperial did not take “appropriate care” because it left the USTs in place for 2 years after it purchased the site.

The Court Found Imperial Took Appropriate Care After the Purchase

The court disagreed with the former owner’s argument, noting (1) Imperial’s compliance with the state agency’s environmental cleanup program as well as (2) Imperial’s actions soon after learning of the UST contamination.  On the first point, the court noted that Imperial was complying with the California Department of Toxic Substances Control’s voluntary cleanup program by performing cleanup as directed by DTSC.  And that California had found Imperial to qualify for the state version of “appropriate care” – a different standard than set in CERCLA’s 42 U.S.C. sec. 9601(40)(D).  The court turned to the CERCLA “appropriate care” standard, which requires Imperial to take reasonable steps to (1) stop any continuing release; (2) prevent any threatened future release; (3) prevent or limit exposure to previously released hazardous substances.  Under this standard, the court found Imperial to have taken “appropriate care” by sampling the USTs about six months after purchase and emptying the USTs soon after they gained knowledge (through sampling) of their contents, even though Imperial didn’t actually excavate the tanks for about a year afterwards.  The court reasoned as follows:

Plaintiff had the contents of the USTs sampled in May 2007.  In September 2007 Plaintiff’s environmental consultant reported that the TCE was detected in those samples.  In October 2007 Plaintiff had the contents of the USTs removed and placed into twenty 55-gallon drums, which were then removed from the Property. TCE was later found to be present in an oily layer that floated on top of the liquid withdrawn from the USTs.  Since Plaintiff had the USTs emptied soon after learning that they contained a hazardous substance, the Court finds that the Plaintiff took reasonable steps to stop any continuing leak or to prevent any future leaks of TCE from the USTs. It was not unreasonable for Plaintiff to leave the USTs in the ground at that time, given that they were empty. Defendant contends that Plaintiff should have also excavated the USTs in 2007 to prevent the possibility of surface water infiltration, which could mix with any TCE left in the USTs and then leak into the ground. However, Defendant has not provided any evidence suggesting why Plaintiff would have had reason to believe that the USTs were not emptied  of TCE in 2007. In fact, when the nine USTs were excavated in 2009 only one of them was observed to have an oily layer on top. Although some TCE was later detected inside that UST its contents consisted almost entirely of water, which suggests that very little TCE had been left inside since 2007. The Court finds that Plaintiff took reasonable steps to prevent further release of hazardous substances, thus entitling it to bona fide prospective purchaser status.

Other Articles (Providing a Link to the Case) and Additional References

Another article briefly summarizes the case, focusing on other points it addressed. Namely, whether the leaking from the UST occurred during the time when the prior owner held the property and, in turn, whether the leaking was a “disposal” and whether the harm it caused could be divisible.  See Dispute as to When and Underground Storage Tank Began Leaking.

See EPA’s “Common Elements” Guide for, among other things, an introduction to and further citations related to the BFPP Defense.

My short article on the Ashley II decision, which addressed the BFPP defense and the forthcoming ASTM Guide on Continuing Obligations.

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Mike Sowinski January 25, 2011 0 Comments
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