Thomas Mohr, Santa Clara Valley Water District

Groundwater Protection in the Santa Clara Valley - the Role of Geology

  • DINNER MEETING - Tuesday, September 14, 2004
  • Location: Stanford University

  • 5:30 PM-Wine Tasting: . . . Mitchell Bldg., first floor
  • 6:15 PM-Dinner: . . . Mitchell Bldg., first floor
  • 7:30 PM-Meeting: . . . Bloch Lecture Hall (Hewlett201)

    see Map showing Mitchell
    Map showing Bloch

    Anyone wishing to attend the lecture only is welcome at no cost.

    This will be the 364th meeting since 1954.

    (Two presentations: Geology and Case Study, with time for discussion)

    map of US showing plume sites


    The Santa Clara Valley groundwater basin supplies about half of the water supply demand to Silicon Valley's residents, businesses, agriculture, and industry. The highly successful technology industries that have made Silicon Valley a world-class economic center have also been associated with groundwater contamination that resulted when fire safety rules led to underground storage of chlorinated solvents. Santa Clara County leads the nation in number of Superfund sites on a county-wide basis, and yet, groundwater in the drinking water aquifers remains free of contamination with very few exceptions. Extensive efforts by dedicated professionals in several state, federal, and local agencies have been instrumental in ensuring the safety of the groundwater supply. The fortuitous juxtaposition of the geography of Silicon Valley's industry and the geologic features of the Santa Clara Valley also play a critical role in providing natural protection to drinking water aquifers.

    This lecture will focus upon the nature of groundwater contamination in the Santa Clara Valley, and the history of the discovery and aggressive investigation and remediation of contaminated sites. The geologic features contributing to varying degrees of groundwater vulnerability to surficial contamination will also be discussed. The evolution of investigation techniques, remedial technologies, and regulatory policy will be profiled. Examples of where the inescapable virtues of basic geologic thinking have been applied to groundwater cleanup investigations will also be presented. Finally, a brief case study of the San Martin perchlorate plume will be given.

    rocket launching
    Perchlorate is the explosive ingredient of rocket fuel

    CASE STUDY: Perchlorate Impacts to Domestic Well Users in San Martin, California

    Thomas K.G. Mohr will present the Santa Clara Valley Water District's work on the highly publicized San Martin perchlorate plume. The groundwater contamination was first discovered in 2000 and subsequent investigations have indicated that a 10-mile-long perchlorate plume has impacted at least 500 water supply wells, mostly private domestic wells and agricultural wells. As a result, there has been a high level of public concern and the problem has received significant media attention. This presentation will discuss both technical and community relations aspects associated with this high-profile case, and the integral role the District has played in providing technical support to the California Regional Water Quality Control Boards direction of the case. The San Martin perchlorate problem illustrates the critical value of groundwater in the daily lives of citizens and how a single contamination impact can affect every corner of a community. The vulnerability of domestic wells to contamination will be reviewed.

    About the Speaker

    Mr. Thomas Mohr, R.G., C.E.G., C.H. is the Solvents and Toxics Cleanup Liaison for the Santa Clara Valley Water District, where he provides stakeholder oversight for more than 100 solvents and other groundwater contamination plumes. He has been instrumental in identifying risks to from 1,4-dioxane at chlorinated solvent release sites, and is the author of the District's Solvent Stabilizers White Paper. Mr. Mohr is the Vice President of the Groundwater Resources Association of California where he serves as Seminar Chair. He has organized numerous symposia in GRA's Series on Groundwater Contaminants.

    drawing of molicule
    Not a photo of Tom (smile)

    Reservations: The preferred way to make reservations is simply to email Janice Sellers at by Sept. 10, tell her you will attend, commit to pay, and bring your payment to the meeting. Janice always emails a confirmation; if you don't get one, assume email crashed yet again and email her a second time. A check made to "PGS" is preferred, payable at the meeting.

    If you want to pay in advance:

    Stanford faculty and students: Please make dinner reservations by Sept. 10. Contact Dr. Juhn Liou via his mailbox (and leave check), Geological and Environmental Sciences Office, Geocorner - Bldg. 320 (Rm. 118). Make checks out to "PGS."

    All others, including faculty and students from other Bay Area universities and colleges and USGS: Please make dinner reservations by Sept. 10. Contact Janice Sellers, at Seismological Society of America, 201 Plaza Professional Building, El Cerrito, CA 94530, phone (510) 559-1780. Send check made out to "PGS" to Janice.

    Dinner is $30.00. Includes wine (5:30 to 6:15 PM.), dinner (6:15-7:30 PM.), tax, and tip.

    For students from all universities and colleges, the dinner, including the social 3/4-hour, is $5.00 and is partially subsidized thanks to the School of Earth Sciences, Stanford University (Note, no-show reservations owe the full price).

    Doris, whose wonderful crew prepares our meals, asked that we let you know that people who are late RSVP'ing and people who show up without a reservation will be welcome but that they will be eating on paper plates with plastic utensils (food supply permitting).

    Dues for Academic Year 2004-2005 ($10.00) should be sent to Janice Sellers, Seismological Society of America, 201 Plaza Professional Building, El Cerrito, CA 94530. Janice's phone: (510) 559-1780.

    Officers: Cheryl Smith, President; Mike Diggles, Vice President; Vicki Langenheim, Secretary; Janice Sellers, Treasurer; Adina Paytan, Field-Trip Czarina

    Campus map

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    Date created: 09/03/2004
    Last modified: 09/03/2004
    Created by: Mike Diggles, Vice President, PGS.

    c/o U.S. Geological Survey, MS-951, 345 Middlefield Road, Menlo Park, CA 94025. (650) 329-5404. email Mike Diggles at

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