10    STRATEGY FOR MITIGATION OF DBCP
CONTAMINATION OF A GROUNDWATER BASIN
George P. Hanna, Jr., Professor Emeritus
California State University, Fresno
Fresno, California 93720-3005
Kenneth K. Tanji, Professor
Hydrologic Science
University of California at Davis
Davis, California 95616
INTRODUCTION
The economy of the San Joaquin Valley of Central California is strongly agricultural with two
of its counties, Fresno and Kern ranking 1 and 2, respectively, among all counties in the nation
for gross dollar value of farm produce. Over the years a host of fertilizers and pesticides have
been utilized to increase farm production, and now some of these are threatening the quality of
the underlying groundwater which for many communities and nearly all rural homes is the sole
source of water supply. One of these major contaminants is l,2-dibromo-3-chloropropane
(DBCP) which was used extensively as a fumigant to control nematodes attacking the roots of
grape vines and deciduous fruit trees from the mid-fifties to the late seventies. Use of DBCP was
banned by the State of California in 1977 and nationally (except Hawaii) in 1979 due to potential
carcinogenic and infertility risks to production workers in the chemical plants and to agricultural
workers in the fields where the product was applied.' This, along with the discovery of DBCP
residues on food crops, and its implication as a carcinogen, also prompted the suspension of the
use of DBCP on selected agricultural crops by the U.S. Environmental Protection Agency
(USEPA) and the Occupational Safety and Health Administration (OSHA).2
DBCP is a persistent chemical that does not degrade readily. With continued irrigation, the
residual DBCP in the soils is driven deeper into the vadose zone until it reaches, and then migrates, with the groundwater.
The first report of DBCP contamination of a water well in the San Joaquin Valley was in 1977.
By April 1984, over 2,500 wells in California (mostly in the Central Valley) were reported to
have detectable levels of DBCP, with over half containing concentrations of one part per billion
(ppb) or greater.3 In 1989 a maximum contaminant level (MCL) of 0.2 ppb was adopted pursuant
to the amended Safe Drinking Water Act. Currently a number of wells in Valley communities
cannot meet this standard, and have either been removed from service, replaced with deeper
wells, or have been equipped with wellhead treatment systems in order to comply. The California
Department of Health Services (DOHS) has recently proposed a draft Recommended Public
Health Level (RPHL) for DBCP of 0.002 ppb. If adopted, communities will have to assess the
costs of compliance, and if unable to comply, must advise customers of noncompliance.
An example of the DBCP impact can be demonstrated with the City of Fresno which provides
its domestic water supply from some 260 individual wells. More than 20 city wells are now
closed due to DBCP concentrations exceeding the MCL. Six wells have been equipped with
granular activated carbon (GAC) wellhead treatment. It is expected that by the end of the year an
additional three to four wells will be similarly equipped. Cost of the wellhead treatment installation in accordance with city criteria is about $900,000 per well, with estimated annual operation
and maintenance costs approaching some $96,000. The capital costs amortized over 20 years at
6% interest plus operation and maintenance result in an estimated increased cost of $0.46 per
1,000 gallons of water delivered to the consumer.
50th Purdue Industrial Waste Conference Proceedings, 1995, Ann Arbor Press. Inc.. Chelsea. Michigan 48118.
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