}
EXECUTIVE SUMMARY
SANTA CLARA VALLEY
INTEGRATED ENVIRONMENTAL MANAGEMENT PROJECT
- REVISED STAGE ONE REPORT -
MAY 30, 1986
Office of Policy Analysis
Office of Policy, Planning and Evaluation
Environmental Protection Agency
Washington, DC 20460
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234R860O1A
SANTA CLARA VATT.RV
INTEGRATED ENVIRONMENTAL MANAGEMENT PROJECT
REVISED STAGE I REPORT
May 30, 1986
Keith Hinman
Don Schwartz
Eileen Soffer
Regulatory Integration Division
Office of Policy Analysis
Office of Policy, Planning, and Evaluation
U.S. Environmental Protection Agency
Washington, D.C. 20460
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ACKNOWLEDGEMENTS
The authors give special credit and thanks to Forest Reinhardt and David
Morel! for their crucial role in designing the Santa Clara Valley IEMP study
and their significant contribution to the October 1985 draft of this report.
We would also like to thank John Wise, Sam Napolitano, Bob Currie, and Dan
Beardsley for their managerial support. For their substantial technical assistance,
the authors thank Greg Browder, Rod lorang, Andy Manale, Palma Risler, Sue
Perlin, Gary Silverman, Tim Sniith, and David Sullivan.
While we have benefitted greatly fron the generous assistance of people
too numerous to name, we would especially like to thank the following individuals
and organizations for their valuable help throughout the first Stage of the
Santa Clara Valley Integrated Environmental Management Project:
Members of the Intergovernmental Coordinating Committee:
Nancy lanni, City of San Jose (Conmittee Chair)
Thomas Ferrito, Town of Los Gatos (Vice-Chair)
Sharon Albert, City of Gilroy
Lynn Briody, City of Sunnyvale
Rod Diridon, Bay Area Air Quality Management District
Patrick Ferraro, Santa Clara Valley Water District
Homer Hyde, Regional Water Quality Control Board (former)
Dianne McKenna, Association of Bay Area Governments
Peter Snyder, Regional Water Quality Control Board
Susanne Wilson, Santa Clara County
Members of the Public Advisory Committee:
Kenneth Manaster, Santa Clara University (Committee Chair)
Eugene Leong, Association of Bay Area Governments (Vice-Chair)
Delia Alvarez, Santa Clara County Health Department
Cliff Bast, Hewlett-Packard, Industry Environmental Coordinating Council
George Adrian, Santa Clara County Water Retailers (former)
Mike Belliveau, Citizens for a Better Environment
E. H. Braatelein, Jr., Water Pollution Control Plants
Patrick Kwok, Water Pollution Control Plants
Peter Cervantes-Gautschi, Central Labor Council
Ann Coombs, League of Women Voters
Greg Cummings, San Jose Chamber of Commerce/Cummings Environmental
Will Danker, Western Oil and Gas Association/Chevron
Jim Dufour, Semiconductor Industry Association (former)
Don Fast, Industry Environmental Coordinating Committee (former)
Milton Feldstein, Bay Area Air Quality Management District
Roxanne Fynboh, Cal-OSHA
Bernice Giansiracusa, County Health Department (former)
Roger James, Regional Water Quality Control Board
Peter Jones, Fire Marshalls1 Association
Ed Miller, Bay Area Air Quality Management District
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Can Kriege, Santa Clara Valley Water District
June Oberdorfer, San Jose State University
Elisabeth Pate-Cornell, Stanford University
Steve Pederson, Semiconductor Industry Association
David Roe, Environmental Defense Fund
William Sanborn, Santa Clara Chamber of Commerce
Ted Smith, Silicon Valley Toxics Coalition
Greg van Wassenhove, County Agriculture Commission
Jercme Wesolowski, California Department of Health Services
Kirk Willard, Industry Environmental Coordinating Committee
Scott Yoo, San Jose Water Company
Bay Area Air Quality Management District:
Dario LeVaggi
Lew Robinson
Steve Hill
Tom Perardi
Tom Umeda
Toch Mangat
California Department of Health Services:
Cliff Bowen
Dick McMillan
Jim Stratton
Regional Water Quality Control Board:
Don Eisenberg (former)
Adam Olivieri (former)
Peter Johnson
Santa Clara Valley Water District:
David Chesterman
John Sutcliffe
Rich Pardini
Tom Iwamura
County Health Department:
Steve Brooks (former)
Glenn Hildebrand
Lee Esguibel
While this report would not exist without the support of these people
and organizations, EPA and the authors are responsible for the content.
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EXECUTIVE SUMMARY
-------
EXECUTIVE SUMMARY
SANTA CLARA VALLEY
INTEGRATED ENVIRONMENTAL MANAGEMENT PROJECT:
STAGE ONE REPORT
This report presents the results of the first phase of the Santa
Clara Valley Integrated Environmental Management Project (IEMP), an
innovative project designed to address the environmental and public
health problems posed by toxic chemicals in California's Santa Clara Valley.
The IEMP, sponsored by the U.S. Environmental Protection Agency, is an
effort to improve public health protection and environmental management
by applying the best scientific knowledge and management skills available
to the problems found in the Santa Clara Valley. The project's goals
are:
0 to evaluate and compare the health risks - of cancer and other
chronic, toxic effects - from toxic pollutants in the environment;
0 to use this evaluation to set priorities for further analysis
and possible control;
0 to work closely with government agencies and the ccnraunity to
manage environmental public health problems.
Traditionally, EPA has developed regulations aimed at controlling
the health and environmental effects of a single industry, or a single
pollutant in a single environmental medium (such as air or water). While
substantial environmental improvement has been achieved with this approach,
sane drawbacks have also become apparent: often pollution controls merely
shift the problem from one medium to another; little attention is paid to
whether Agency programs, taken as a whole, reduce health risks in the
most efficient or cost-effective way; and rarely do national standards
account for the site-specific nature of a problem.
In contrast, the integrated environmental management approach takes
account of the transfer of toxics across media - in land, air, surface
water, and groundwater. In addition, the integrated approach is founded
on the concepts of risk assessment and risk management in which estimates
of risk to public health are used as a canton currency for comparing a
variety of pollution problems. Finally, by focusing on one conraunity, in
this case the Santa Clara Valley, the approach can assist communities in
developing environmental management strategies tailored to their unique
problems and characteristics.
Integrated environmental management is intended to be a practical
tool for controlling pollution that threatens public health. EPA, in
partnership with state and local leaders, can use estimates of the public
health impacts of a wide range of environmental problems to compare
those problems and set priorities for risk management. Setting priorities
provides a way of working through an environmental agenda by targeting
the worst problems first in order to get the most risk reduction (and
thus public health benefit) for any given level of resources.
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-2-
The Santa Clara Valley IEMP
The Santa Clara Valley IEMP is one of EPA's early efforts to gain
field experience with this alternative approach. Similar integrated
environmental management projects have analyzed the health risks from
environmental toxic chemicals in Philadelphia and Baltimore.
EPA chose to conduct an IEMP in the Santa Clara Valley in part
because the industrial base and environmental concerns were substantially
different from those of other areas under study. In the last three to
four decades, the area's population has grown rapidly to its current
level of about 1.4 million. In addition, the local economy has shifted
increasingly from agriculture to industry. In the 1970's, the area exper-
ienced a rapid growth in electronics and other high-tech, computer-
related industry, becoming a world leader in this field.
Currently, the northern Santa Clara Valley is well populated and has
an industrial economic base. The southern part of the Valley, by contrast,
remains more sparsely populated, with an economy based on agriculture.
The southern Santa Clara Valley, however, is expected to experience
significant population and industrial growth in the coming decades. The
IEMP study area, which roughly corresponds to the Santa Clara Valley, is
shown in Figure 1.
Some of the Santa Clara Valley's environmental concerns are at
least partly a result of its unique industrial base. In recent years,
the discovery of groundwater contamination caused by leaks and spills
from underground tanks and other waste storage areas has generated widespread
public concern; many of these leaks occurred on the grounds of electronics
firms. Other sources of toxics in the local environment are common to
most urban areas, and include automobiles, dry cleaners, sewered industrial
liquid wastes, and disinfection of drinking water supplies. The southern
Santa Clara Valley has high nitrate levels in its groundwater from past
agricultural activity.
The decision to conduct an IEMP in the Santa Clara Valley followed
extensive discussions by EPA with state and local officials, industry
representatives, and public interest groups. EPA was especially impressed
by the local response to groundwater problems associated with underground
storage tanks. In 1982-83, a coalition of local elected and regulatory
officials, industry representatives, and environmental leaders responded
effectively to the discovery of groundwater contamination in the Santa
Clara Valley. Working together, these local leaders drafted a new model
Hazardous Materials Management Ordinance (HMMO) to regulate the storage
and handling of industrial chemicals; most of the cities and the county
then enacted these ordinances within their respective jurisdictions. The
IEMP could thus build upon an unusually active coalition of local interests
committed to effective management of environmental risks.
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-3-
Figure 1
" Area (Shown by -J
•rS\c-;-.-'sv:"-Y.V. .••>:-:.
/• ««i* i• • * ..•••'•• . , ;
m^w-m-
^-.STANISLAUS /
"^'•COUNTY--'
SANTA CLARA
.v;;-:;;COUNTY /-.v:••
;"•' ' ••' ;-':J,-v-v^.-.'->;.^-^! -"v ./'•.V'-'l; '•V-.\:-.t/: "•'.'.-: • ' :'•'*' " • •' •'•'' - •
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-4-
Public Participation
In conducting the Santa Clara Valley IEMP, the EPA has put a great
deal of emphasis on public participation and cooperation with other
agencies. At the project's outset, EPA established two advisory cormittees:
an Intergovernmental Coordinating Ccmnittee (ICC), consisting of local
elected officials and board members of regulatory agencies; and a Public
Advisory Committee (PAC), including staff of regulatory agencies, industry
and public interest groups, and others.
The committees have provided a public forum in which to discuss
complex environmental problems and sensitive issues of public health,
and a process by which to build understanding and consensus within the
conmunity. In addition, the committees have provided a vehicle for
fostering cooperation among the regulatory agencies and local leaders
who need to work together to manage environmental risk effectively.
Local participation through the advisory committees has substantially
improved both the quality of the IEMP analysis and the opportunities for
the project to make useful contributions.
METHODOLOGY
The IEMP applies the techniques of risk assessment and risk manage-
ment to environmental problems. Risk assessment is a means of evaluating
the potential health impact of exposure to chemicals in the environment.
Risk assessment allows decision-makers to compare the potential effects
of different pollutants (such as trichloroethane and benzene), exposure
pathways (such as air and drinking water) and sources (such as underground
tanks and automobiles), using a common denominator of human health risk.
By providing estimates of the comparative impacts of different toxic
chemicals and sources, risk assessement can be used to identify the most
serious problems.
Risk management is the process of controlling the health risks
identified through risk assessment. Risk management considers not only
the level of risk posed by a particular pollutant or source but also the
feasibility and cost of control, public preferences, and institutional
capabilities. Setting priorities for research and risk reduction is a key
aspect of risk management.
This report presents the results of the first phase of the IEMP,
which emphasized risk assessment of a broad set of toxic pollutants and
sources. The project's second stage, now beginning, will emphasize risk
management of a selected set of priority problems.
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- 5 -
Risk Assessment
This study uses risk assessment to evaluate and compare the potential
health risks from toxic pollutants in the air, land and water. Several
measures of risk are used in this report, including estimated risk to
particular individuals and projected risk for an entire population.
Risk to an individual is defined as the increased probability that
an individual exposed to one or more chemicals will experience a particular
adverse health effect during the course of his or her lifetime. It is
important to realize that the risk estimated for a particular type of
exposure is the incremental risk beyond that which a person faces from
exposure to other environmental or hereditary causes of disease, sometimes
referred to as the background rate of disease. In this report, we present
two types of estimated individual cancer risks: (1) average individual
risk, for the typical individual, and (2) risk to the most-exposed individual
(MEI), who may be particularly close to a source or is highly exposed
for some other reason. As explained below, for non-cancer effects, this
study estimates whether or not exposures appear to be high enough to
place a person at increased risk of an adverse health effect.
Risk to the population is the expected increased incidence (number
of cases), above the background rate, of an adverse health effect in an
exposed population. In this report, we present potential increased
numbers of cases of cancer resulting from estimated exposure to particular
chemicals and pollution sources. For health effects other than cancer,
estimates of the number of people exposed at levels high enough to pose
some increased risk are presented.
The two key elements in estimating risk are a chemical's estimated
potency, or toxicity, and human exposure to that chemical. EPA estimates
a chemical's toxicological potency on the basis of available scientific
evidence. Scientific data typically consist of laboratory studies of
animals exposed to a chemical under controlled conditions, or epidemiologic
studies of human exposure to a chemical, usually in an occupational
setting. Exposure to a chemical is estimated by measuring or estimating
the concentration at which a chemical is present in the air or water,
and then making assumptions about how much air a person breathes or
water he or she drinks. Finally, potency and exposure estimates are
combined to estimate individual and population risks. This methodology
is illustrated in Figure 2.
This project examined cancer and a number of other toxic effects,
such as birth defects, neurobehavioral effects, and effects of the immune
system, blood, liver, and kidney, that might result from long-term exposure
to environmental pollutants. Since methods of estimating cancer risks
are fairly well developed and accepted, it was possible to develop
estimates of the potential individual risks and aggregate incidence
(number of cases) for exposure to carcinogens.
EPA's Carcinogen Assessment Group (GAG) has established a method for
evaluating the potential cancer risk from a substance. First, CAG evaluates
the weight of evidence that a substance poses a cancer risk to humans.
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-6-
FIGURE 2 IEMP RISK ASSESSMENT METHODOLOGY
EXPOSURE
ASSESSMENT
Modeling of
Fate and
Transport
Monitoring
Ambient
Pollution
Concentrations
PATHWAY
TO EXPOSURE
nnnnnnnn
illinium ii
iEPIDEMIOLOGICAL!
POTENCY
ASSESSMENT
Hazard
Identification
Quantitative
Potency
Estimates
ESTIMATED HEALTH RISK
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- 7 -
For those substances that may pose some risk, GAG provides a quantitative
ef^unate of their potency, or toxicity. The IEMP used the CAG evaluations
and, in a few cases, developed additional evaluations for substances not
yet studied by CAG.
^^No equivalent and accepted techniques exist for estimating the
probability or incidence of non-cancer effects (an experimental technique
tor making such estimates is now being evaluated by scientists within and
outside EPA). Therefore, in evaluating the potential health risks for
ettects other than cancer, this study relied on "no-effect" thresholds,
also referred to as EPA Reference Doses (RfDs) or Acceptable Daily Intake
levels (ADIs). Thresholds, or RfDs, represent an estimated dose below
which adverse health effects are assumed not to occur in roost people.
In evaluating non-cancer effects, the IEMP estimated the number of people
who might be exposed at levels above an estimated no-effect threshold,
and therefore might be at risk of a toxic effect. However, the IEMP
could not estimate the possible number of cases that might occur as a
result of such exposures.
The IEMP performed an initial screening exercise to identify, fron a
master list of about 1800 pollutants, those chemicals most likely to pose
an environmental health risk in the Santa Clara Valley. Using a combination
of exposure and toxicity criteria, the project initially identified
about 50 chemicals that might pose such risks. For this report, exposure
and health risks were estimated for 41 pollutants - all those for which
sufficient exposure evidence and toxicological data could be found.
These chemicals, an indication of their suspected toxic effects, and
their likely routes of exposure are shown in Table One.
In estimating the possible toxic health effects of such a diverse set
of pollutants, sources and exposure routes, the IEMP encountered a number
of very significant uncertainties and data gaps. In general, the IEMP
approach to this problem was to use conservative, or pessimistic,
assumptions likely to overstate possible health impacts. In addition,
the study made extensive use of sensitivity analysis of key issues, in
which health risks are estimated under several different assumptions.
Sensitivity analysis is useful in showing whether important results are
"robust," i.e., whether they hold up under a variety of different
assumptions. In pinpointing the importance of alternative assumptions in
affecting estimates of health risk, such analysis also can help to identify
those areas where research to provide better information is most important.
It is important to remember that the estimates of individual health
risk and aggregate incidence from exposure to toxics presented in this
report should not be interpreted as precise or absolute estimates of
future health effects. The simplifying assumptions and uncertainties in
both the toxicology and the exposure components of this study are simply
too great to justify a high level of confidence in the predictive value
of the results. (The important limitations and uncertainties are summarized
below.) The value of these estimates lies in their usefulness for com-
paring problems to one another, developing a rough notion of the magnitude
of possible effects, and setting priorities for risk management.
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TABLE ONE
TOXICS IN SANTA CLARA VALLEY
SUMMARY OF HEALTH EFFECT AND EXPOSURE DATA
TOXIC SUBSTANCE
METALS AND MINERALS
ARSENIC
BARIUM
BERYLLIUM
CADMIUM
CHROMIUM
FLUORIDE
LEAD
MERCURY
NICKEL
NITRATES
SELENIUM
SILVER
ZINC
ORGANIC CHEMICALS
BENZO(A)PYRENE (BAP)
BENZENE
BROMOFORM
CARBON TETRACHLORIDE
CHLOROFLUORCCARBON
(CFC-113)
CHLOROFORM
CHLORODIBROMOMETHANE
CHLORAMINES
POTENTIAL
ADVERSE HEALTH EFFECTS
Type of Effect Considered in IEMP 2
CANCER
X*
X
X 5
X5
X
X
X
X
X
X
X
NON-CANCER
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
EXPOSURE PATHWAYS *
Sources of Information on Presence
of Toxics in Santa Clara Valley 3
OUTDOOR AIR
MONITORED
MONITORED
MONITORED
MONITORED
MONITORED
-
MONITORED
^_
MONITORED
-
_
-
MONITORED
ESTIMATED
MODELED
-
SHORT-TERM
MONITORING
MODELED 6
MODELED
-
-
DRINKING WATER
MONITORED
MONITORED
-
MONITORED
MONITORED
MONITORED
MONITORED
MONITORED
-
MONITORED
MONITORED
MONITORED
MONITORED
_
MODELED
MONITORED
MONITORED
MONITORED
MONITORED/
MODELED '
MONITORED
MONITORED
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-9-
TABLE ONE (cont.)
TOXICS IN SANTA CLARA VALLEY
SUMMARY OF HEALTH RISK AND EXPOSURE DATA
TOXIC SUBSTANCE
DICHLOROBENZENE
DICHLOROBROMO-
METHANE
1,2 DICHLOROETHANE
1,1 DICHLORO-
ETHYLENE (DCE)
1,2 DCE
DBCFCP
ETHYLENE DIBROMIDE
ETHYLENE OXIDE
GASOLINE VAPORS
GLYOOL ETHERS
ISOPROPYL ALCOHOL
METHYLENE CHLORIDE
METHYL ETHYL
KETONE (MEK)
PERCHLOROETHYLENE
(PCE)
PESTICIDES*
PHENOL
TOLUENE
1,1,1-TRICHLORO-
ETHANE (TCA)
TRJCHLOROETHYLENE
VINYL CHLORIDE
XYLENE
POTENTIAL
ADVERSE HEALTH EFFECTS
Type of Effect Considered in IEMP 2
CANCER
X
X
X
X
X
X
X
X
X
(8)
X
X
NON-CANCER
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
EXPOSURE PATHWAYS *
Sources of Information on Presence
of Toxics in Santa Clara Valley 3
OUTDOOR AIR
MODELED 6
-
MODELED 6
MODELED 6
-
-
ESTIMATED
MODELED
MODELED
MODELED 6
MODELED 6
MODELED
-
MODELED
-
MODELED 6
MODELED
MODELED
MODELED
-
MODELED
DRINKING WATER
-
MONITORED
-
MONITORED/
MODELED 7
MONITORED
MONITORED
MODELED
-
-
-
-
MODELED
MODELED
MONITORED/
MODELED 7
MONITORED*
-
MODELED
MONITORED/
MODELED 7
MODELED
MODELED
MODELED
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-10-
FOOTNOTES TO TABLE ONE:
1 The IEMP also performed limited analysis of the possible risks
to a hypothetical individual regularly consuming contaminated fish
caught from the South Bay; see text and Table Six. The South Bay was
not thought to be an exposure pathway by which toxics affected many
people, and thus is not included on this table.
2 "X" indicates evidence of adverse, chronic health effect in animals or
humans. This table summarizes the type of potential adverse health
effect (cancer or non-cancer) considered for purposes of the IEMP
report. For a more complete discussion on pollutant selection and
toxicological evaluation of adverse health effects from pollutants
see chapter 2 - General Methodology.
3 The IEMP used different types of information to estimate the potential
exposure of Santa Clara Valley residents to some level of a toxic
substance. Monitored data are obtained by collecting and analyzing
samples frcm the air or water in Santa Clara Valley. Modeling is a
way of estimating the ambient environmental concentration of a pollutant
by calculating the estimated dispersion pattern from sources known to
emit the substance. Estimated exposure is done in different ways
depending on available data as described more completely in the full
report.
4 There is some dispute as to the carcinogenicity of low levels of
arsenic in drinking water. See text.
5 Cadmium and (hexavalent) chromium are assumed to be carcinogenic
through inhalation only, not ingestion.
6 These pollutants were modeled only to estimate exposures to most-
exposed individuals (MEIs) near certain sources.
7 Current exposure to this chemical was derived frcm monitoring data.
Possible future exposure was modeled.
8 In accordance with current EPA policy, the IEMP does not consider TCA
to be a carcinogen in its base case. For sensitivity analyses, however,
the IEMP does examine the impact of TCA as if it were a carcinogen.
* Drinking water sources have been monitored for a number of pesticides.
However, little evidence of pesticide contamination was found. See
chapter 4.
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- 11 -
AIR ANALYSIS
In California, the regulation of sources of air pollution is the
responsibility of the state Air Resources Board (ARE) and local Air
Duality Management Districts. Ihe ARB establishes emissions requirements
for motor vehicles and has oversite responsibilities for control of
other sources of air pollution in the state. The local Bay Area Air
Quality Management District is directly responsible for regulating non-
vehicular sources of air pollution in the Santa Clara Valley.
Vtiile the historical emphasis of air pollution control efforts has
been on criteria pollutants, such as those causing smog, this study examines
toxic pollutants, which may pose health risks at comparatively low
environmental levels. The IEMP Stage I analysis of risk from exposure
to toxics present in outdoor air involved the study of three classes of
toxic air contaminants: organic gases, heavy metals, and organic particulates.
Organic gases. The IEMP analysis of exposure to organic gases
focused on eleven specific organic compounds plus gasoline vapors, a
mixture of compounds. This broad class of chemicals comes from many
sources. Some gases, such as benzene and ethylene dibromide, are emitted
to the atmosphere from fuel combustion or evaporation. Motor vehicles
are a major source. Emissions of other organic gases, such as 1,1,1-
trichloroethane and methylene chloride, result (generally through evaporation)
from the use of solvents by electronics firms, other industrial and
commercial establishments, and households.
To analyze exposure to and risk from organic gases in outdoor air,
the IEMP and the Bay Area Air Quality Management District (AQMD) developed
estimates of toxic gas emissions from various sources, and then modeled
pollutant dispersion to arrive at estimated pollutant concentrations in
the ambient air. The analysis examined 25 major point sources, such as
semiconductor facilities and other industrial plants; and a variety of
small, dispersed area sources, including motor vehicles, industrial
solvent applications, fuel combustion for home heating and dry cleaners.
The organic gases emissions inventory and the dispersion model were used
to estimate human exposure and risk from different sources and pollutants.
The IEMP also estimated toxic organic releases and risks from three
sources not included in the AQMD inventories: sewage treatment plants,
municipal landfills, and groundwater aeration facilities.
Metals. Analysis included eight toxic metals, such as arsenic,
chromium and cadmium. These metals are released to the air primarily as
a result of various forms of combustion (metals are present in trace
quantities in most fuels). Airborne metals may also be present as a result
of windblown dust, which may contain the settled particles fron past emissions.
EPA relied on long-term monitoring data from downtown San Jose to
estimate the concentrations of metals throughout the Valley and to project
risks from exposures to toxic metals. No emissions inventory for metals
has yet been developed. Vtiile the monitoring data are fairly reliable,
countywide projection of these concentrations is problematic. Since it
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- 12 -
is likely that most metals sources are dispersed area sources (likely to
result in a more even distribution pattern than pollution dominated by
point sources), and that downtown San Jose metals concentrations are
probably somewhat higher than average for the Valley (as is the pattern
with most other pollutants), EPA judged that an appropriately conservative
assumption for this screening analysis was to estimate risks as if the
single site's monitoring data were representative of the Valley.
Organic particulates. Organic particulates, such as benzo(a)pyrene,
are toxic organic chemicals present in the air primarily in particulate,
rather than gaseous, form. Sometimes called products of incomplete
combustion (PICs), they are the result of fuel combustion from motor
vehicles, home heating sources (such as fireplaces and wood stoves) and
other sources.
No local monitoring or emissions data exist for organic particulates.
EPA made rough estimates of local levels of these chemicals by scaling
national and other data to local levels based on known sources of organic
particulates (such as residential heating and gasoline combustion) and
on local monitoring data for total suspended particulates, the best
available proxy for organic particulates. These estimates are adequate
for identifying the general magnitude of the problem, but better local
data would be needed to support regulatory actions.
DRINKING WATER ANALYSIS
Drinking water in the Santa Clara Valley cones fron three sources:
local groundwater, surface water imported through the South Bay and
Hetch Hetchy Aqueducts, and local surface water. About half the drinking
water in the Valley is groundwater, and about half is surface water.
Large volumes of imported and local surface water are used to recharge
the groundwater basin artificially, both to prevent the depletion of the
aquifer and to store water supplies at relatively low cost.
Nineteen water retailers - seme municipal and some private - deliver
water to the Valley's consumers, under regulation by the California
Department of Health Services. The Santa Clara Valley Water District
(SCVWD) imports and treats surface water (some imported water is purchased
directly from the City of San Francisco via the Hetch Hetchy Aqueduct)
and is responsible for overall management of the Valley's groundwater
resources. The San Francisco Bay Regional Water Quality Control Board
(BWQCB) has primary responsibility for protecting groundwater quality
(although the SCVWD and municipal authorities are also involved in pro-
tecting groundwater quality). The state Department of Health Services
(DOHS) has primary responsibility for ensuring the quality of drinking
water delivered by major public systems.
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- 13 -
Toxic contamination problems, as well as available data, differ
tor surface water and groundwater. The issues studied in the Stage 1
analysis in^inrto.
analysis include:
By-products of water treatment (disinfection). Disinfection
of water by chlorination and related processes results in the
creation of chloroform and other "trihalcroethanes." Disinfection
of drinking water is necessary to protect people fron diseases
that might otherwise result from microbial contamination.
Since most groundwater is not disinfected (microbial contamination
is not usually a problem with groundwater in the Santa Clara
Valley), this is primarily a concern with surface water.
Metals and minerals. A number of inorganic substances,
including metals that may cause toxic effects, are found in
drinking water in the Santa Clara Valley. Most of these substances
are probably from natural background sources (e.g., substances
naturally present in the soil), although some may be from past
or present man-made contamination. Metals and minerals are
present in both imported surface water and in groundwater.
Pesticides. Runoff from agricultural areas through which
imported surface water travels may contaminate the water with
pesticides. Groundwater may be contaminated through local
pesticide use.
Industrial chemicals from tanks, pipes and spills. The
contamination of local groundwater through leaks of underground
storage tanks, piping or simply through sloppy handling has
became a significant local concern since the discovery of a
leak at Fairchild Camera & Instrument in 1981. About 100
sites involving industrial contamination of soil or groundwater
have since been discovered in the Valley; EPA has added six
of these sites to its Superfund National Priority List, and has
proposed adding an additional twelve. Many sites involve
contamination by industrial solvents, such as trichloroethylene
and perchloroethylene.
Fuels from tanks, pipes and spills. Santa Clara Valley has
about ten tiroes as many fuel storage tanks as industrial chemical
storage tanks. The San Francisco Bay Regional Water Quality
Control Board has documented over 400 leaks and spills from fuel
tanks. Toxic contaminants in fuels include ethylene dibrcmide
and benzene.
Organic chemicals from other sources. Organic chemicals may
contaminate groundwater by leaking from sewer lines that contain
industrial wastewater. While toxic wastes are formally barred
from Class III sanitary landfills (the only landfills sited in
Santa Clara Valley), such wastes may be present in household and
cannercial waste. According to the RWCCB, there is evidence of
historical disposal of organic chemicals in municipal landfills.
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Other potential sources of organic chemical contamination of
groundwater include above-ground chemical tanks and storage areas;
residential use of chemicals such as pesticides and cleaning
agents; leakage from septic tanks; illegal dumping; and dry
wells.
o Nitrates. Nitrates, which can cause methemoglobinemia, or "blue
baby syndrome," may be present in groundwater as a result of
fertilizer use, animal waste, and leakage from septic tanks and
sewered wastes. Parts of southern Santa Clara Valley have high
nitrate levels, and the City of Morgan Hill is under order from
the state Department of Health Services to come into compliance
with state and federal standards for nitrates in drinking water
by 1988.
Different methods were used to assess exposure and risks from these
different sources and pollutants. Historical monitoring data were used
to estimate exposure to metals and minerals. To estimate exposure to
trihalomethanes, the IEWP obtained monitoring data that reflect recent
changes in treatment practices and water quality. Direct monitoring was
also used to assess exposure to pesticides, but these data are less
complete. Risks from nitrates in the groundwater of the south County
were estimated by calculating the number of infants who might be exposed
to nitrate levels high enough to be of concern, based on monitoring
data. Current risks from contamination of drinking water by industrial
chemicals were estimated based on recently collected monitoring data for
public systems. (No comparable data were available for private wells used
as sources of drinking water.)
Estimating the extent of possible future exposure to groundwater
contamination from leaking fuel and industrial tanks and other sources
was the most complex part of the drinking water analysis. Current groundwater
contamination, as well as future leaks and spills, may affect drinking
water wells that are currently unaffected, or worsen contamination at
already affected wells. At the same time, recently instituted programs
to improve tank construction, monitor groundwater near potential sources,
clean up contamination sites and monitor drinking water wells will signifi-
cantly reduce risks from what they might have been in an unregulated
world. Ib estimate possible risks over time, the IEMP modeled possible
future contaminant releases, movement and impact on drinking water wells.
Ihis effort took into account variations in hydrogeology; voluntary
replacement of old tanks; and regulatory programs to prevent and clean
up contamination, and to monitor drinking water wells.
In general, the drinking water analysis based on monitoring data is
more reliable than that based on modeling. The analysis of future risks
from groundwater contains the greatest uncertainties. Because of this,
the modeling effort was consistently conservative, so as not to underestimate
potential risks. In addition, extensive sensitivity analysis was performed
to examine alternative assumptions for key factors such as the size of
tank leaks and the effectiveness of regulatory actions.
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SOUTH SAN FRANCISCO BAY SURFACE WATERS
Surface water contamination in the South San Francisco Bay and its
tributary streams occurs as a result of "non-point source" runoff from
Doth urban and rural areas, and through releases fron identifiable "point"
sources, including sewage treatnrent plants and industrial facilities.
Fairly high levels of metals exist in the water and in the sediment of
tne Bay, and both metals and organic chemicals (mostly pesticides) have
been found in fish and shellfish tissue.
, toxic (and conventional) pollutants are of concern because
of their potential impact on the health of the aquatic ecosystem, their
likely uipact on human health appears to be small by comparison to the
other exposure routes examined. The IEMP was unable to estimate the number
of people exposed to toxics through South Bay surface waters, but it
seems unlikely that such exposure is widespread. South Bay water is not
a drinking water source. In addition, relatively little swimming occurs,
because of limited access. The main exposure route of concern appears
to be possible consumption of contaminated fish or shellfish. Since it
is possible that some persons consume such fish regularly, the IEMP
calculated possible individual risks for a hypothetical individual
consuming significant quantities of contaminated local fish.
LIMITATIONS AND UNCERTAINTIES
An understanding of the uncertainties and limitations that underlie
the IEMP analysis is critical to a proper interpretation of its results.
Limitations in the scope of what was studied, and uncertainties in both
the exposure and toxicological data, argue against taking the estimates too
literally. Nevertheless, decision-makers must often act now to protect
against health threats from toxic chemicals and cannot afford to wait for
scientific certainty. The IEMP analysis uses the best information
available today to estimate health risks from toxics so that decisions
that cannot wait will be as informed as possible.
Limitations in Scope
The reader should recall that this analysis does not directly
examine disease incidence in the local population and attempt to link it
with environmental exposure. Because the analysis is not an epidemiologic
study, it is not intended to and does not answer questions such as what
may have caused a statistically higher rate of birth defects in the Los
Paseos area. Instead, the IEMP attempts to evaluate what health effects
might result from current and future environmental exposures.
This analysis does not attempt to estimate the health risks from
all chemicals that individuals may be exposed to in their daily lives.
The IEMP did not estimate risks from indoor air contaminants, nor those
from occupational exposures. (The IEMP has commissioned a scoping study
on occupational exposures, which is now in progress.) Similarly, risks
from contaminants in food are not estimated, emitting analysis of these
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- 16 -
routes of exposure does not imply that they are unimportant; indeed, it
is quite possible that risks from any of these exposure pathways could
exceed risks from the exposures that we did examine. The IEMP decided
not to assess these exposure routes because of resource limitations and
because they are outside EPA's traditional purview and area of expertise.
The IEMP chose not to analyze exposure to and risks from conventional
pollutants in air and water (such as ozone and oxides of nitrogen and
sulfur in air, and oxygen-depleting substances and oil and grease in
water) because EPA believed it could make a more significant contribution
by concentrating on less well understood and less regulated toxic chemicals
(largely organic chemicals and heavy metals thought to be potentially
hazardous at low levels).
Finally, the IEMP did not estimate risks from possible infrequent,
accidental releases of toxic chemicals, such as a major release of a
toxic gas. (The study did estimate risks from more frequent and predic-
table accidental releases, such as tank leaks and chemical spills.) The
probability and magnitude of such an accident is very difficult to estimate,
and the likely risk from such an event is therefore difficult to quantify.
The omission of such events from this analysis does not imply that possible
accidents are not an important environmental and public health concern.
In sun, it should be clearly understood that this report is not an
analysis of health risks from all possible exposures to potentially
dangerous chemicals in the Santa Clara Valley.
Limitations in Exposure Data
Beyond these intentional limitations in scope, the study's exposure
and toxicological estimates are uncertain in a number of potentially
important ways. On the exposure assessment side, one limitation of the
analysis is that it did not exhaustively examine all sources and pollutants.
While the IEMP has tried to identify and assess risks from the most
significant sources and pollutants, it was unable to estimate exposure
to some chemicals, such as arsine and phosphine, because of a lack of
data. In reality, of course, chemicals not included in the study may
also pose some health risk.
Even where exposure data were available, those data varied significantly
in their quality. Thus, the resulting exposure estimates vary in their
reliability. Those based on extensive monitoring, such as for trihalome-
thanes and inorganic substances in water, are probably fairly good.
Those based on less extensive monitoring, such as for metals in air
(based on a single long-term monitoring station) are somewhat less
reliable.
Exposure estimates derived from modeling also vary in their reliability.
Estimates of exposure to toxic organic chemicals in air, calculated using
a dispersion model, are dependent primarily on the quality of the emissions
estimates and other factors such as meteorological data. The range
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- 17 -
of possible error for most pollutants is probably well under an order
of magnitude. The analysis of the future risks fron groundwater con-
tamination, which relies heavily on engineering assumptions and modeling
of future events, is more uncertain. Where there are significant uncer-
tainties, such as in the groundwater exposure analysis, we have attempted
to make assumptions that are likely to err on the side of overestimating
possible health impacts. In addition, we have performed sensitivity
analysis of particularly important variables, such as possible chemical
reactions and the effectiveness of regulatory actions.
Limitations in lexicological Data
Estimates of the potential health effects of particular chemicals are
designed to be conservative (i.e., more likely to overestimate toxic
health effects than to underestimate them) in several ways. Health
effects observed in laboratory animals are assumed to be a reasonable
indicator of potential effects in humans. In converting the animal data
to predicted human responses, and in extrapolating from high doses to
low doses, EPA uses models that yield a plausible upper-bound estimate
of potency rather than a "best guess" estimate.
On the other hand, many substances of potential concern have never
been evaluated scientifically, or have not been evaluated in sufficient
detail to allow estimation of effects on humans. For example, lead
(present in air, water, and dust) is thought to pose a health risk to
children at ambient levels; currently, however, EPA has no established
way of estimating individual risks or numbers of possible cases. EPA is
likely to be aware of the dangers from many of the most potent chemicals,
since the evidence for their toxicity will typically be the most obvious;
however, it is possible that some chemicals about which we currently
know little may someday be demonstrated to be toxic.
Because of the many uncertainties and potential omissions, it is
impossible to say whether the total risk estimates presented here are
over- or underestimates of total toxic health risks from pollutants in
air and drinking water. For those chemicals for which the IEMP was able
to make quantitative estimates of exposures and risks, it is more likely
that risks are overestimated than underestimated. Tb the extent that
toxic chenicals about which we currently know little have been left out,
risks may be underestimated. The value of the IEMP methodology is that
it allows an evaluation and comparison of the health risk from chemicals
and pollution sources about which we know something. Management of
these risks, based on the best current information, can proceed, while
research continues on the effects of chemicals about which little is
currently known.
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RESULTS OF STftGE I RISK ASSESSMENT
A brief suranary of estimated environmental exposures is presented
below, followed by a presentation of estimated health risks from
environmental toxics.
Exposure
Detailed estimates of exposure to toxic chemicals are too lengthy to
present in this sutranary; the interested reader is referred to the full
report. In air, dispersion modeling of toxic organic substances indicates
that pollutant concentrations are generally highest in the northern part
of the study area, which is more industrialized and more heavily populated.
Monitoring data for toxic metals indicates that they are present in the
Santa Clara Valley's outdoor air at low levels - in some cases, the lower
end of the range of concentrations is below the detection limit for the
analytic equipment used.
Overall, concentrations of air toxics modeled or monitored in the
Santa Clara Valley appear to be similar to or lower than pollutant con-
centrations typical of urban areas. Estimated average concentration
levels for most chemicals examined were below 5 micrograms per cubic
meter (ug/tn3).
Estimated exposures to most-exposed individuals (MEIs) near
sources of air toxics (such as semiconductor facilities, dry cleaners and
traffic intersections) were typically five to one hundred times higher
than the average concentration levels. The difference between average
and MEI exposures was greater for chemicals such as ethylene oxide and
chloroform whose emissions were dominated by a few point sources, and
less for chemicals such as xylene and toluene, which are emitted by
many dispersed sources.
About half the population in the Santa Clara Valley is exposed to
trihalcmethanes in treated drinking water, at levels that are fairly
typical for disinfected water (about 20-80 micrograms per liter (ug/1)).
Highly exposed individuals are estimated to be exposed to THM levels at
the high end of this range but below the 100 ug/1 standard.
Thirty-six public wells and about 56 known private wells have been
affected by industrial chemicals. In the majority of cases where a
source has been identified, the pollution has resulted from leaking
underground tanks or associated chemical spills. Some operating public
wells are serving water containing 1,1,1-trichloroethane, perchloroethylene,
l,l,2-tricnloro-l,2,2-trifluoroethane, carbon tetrachloride, and a few
other chemicals in the low parts per billion, well below current state
drinking water standards. (The highest concentration level recorded at
an operating public well is seven parts per billion, or ug/1). About
129,000 people are currently drinking water from public wells with low
levels of contamination.
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- 19 -
Recent testing by the County Health Department of 171 private wells
found that about 8% of the wells were affected by detectable contamination
by synthetic organic chemicals, and that almost 40% were affected by
bacteriological contamination (i.e., they were unsanitary). Wells were
not selected by randan sampling, so these figures are not necessarily
representative of other private wells in the Valley.
Modeling of possible future drinking water contamination under
conservative (pessimistic) assumptions yielded estimated exposures signifi-
cantly higher than current levels, and included some pollutants (such as
gasoline constituents) not yet seen in drinking water wells. Concentration
levels were estimated to be significantly higher at private wells than
at public wells, because public wells benefit from greater regulatory
and natural hydrogeologic protection. The IEMP estimated that future
exposure to contaminated groundwater sources of drinking water could
affect 10% of the population, in addition to those already affected.
In the southern part of the county, several public wells and an
unknown number of private wells contain levels of nitrates that are above
state and federal standards. Large systems exceeding standards are
under order to comply by 1988. Little evidence was found of pesticide
contamination of drinking water, either in local groundwater or in imported
surface water.
Health Risks
1. Overall Cancer Risk; EPA's findings suggest that the estimated
cancer risks from the toxic chemicals and sources studied are apparently
a small proportion (well below one percent) of total cancer cases in the
Valley. Since any level of exposure to a carcinogen is assumed to pose
sane risk, all 1.4 million residents of the Santa Clara Valley are projected
to face some level of increased cancer risk as a result of environmental
exposure. EPA estimated that exposure to the pollutants and sources
examined may be responsible for about four cases of cancer per year; an
estimated 3,600 cases of cancer occur annually in Santa Clara County.1
This finding, although tentative, provides an important perspective on
health risks from toxic chemicals in the outdoor air and drinking water
in the Santa Clara Valley as compared to other possible means of exposure
to toxic substances, such as smoking, diet, occupation, and indoor air.
However, it is important to keep in mind that this study examined a
relatively small number of known toxic chemicals; exposure to many thousands
of chemicals in the air and drinking water about which we know little
may also be a source of significant, although currently unknown, health
risk.
1 Ratio of estimated cancer cases to estimated cancer deaths, from 1983
national data from the American Cancer Society: 1.93. Cancer deaths in
Santa Clara County, 1984: 1,879. 1,879 cancer deaths X 1.93 cases/jeath
= 3,626 estimated cancer cases in Santa Clara County.
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-20-
Average individual cancer risk estimates for typical individuals
exposed to toxics in both air and drinking water indicate a potential
increase in cancer probability of about 200 in a million over a lifetime.
This estimate of increased risk is the projected cumulative risk for
exposure to all sources and pollutants examined. Projected individual
cancer risk is a small proportion of the total lifetime cancer risk for
an average person of about one in four (250,000 in a million). Of course,
individuals who are particularly highly exposed to chemicals, by virtue
of their proximity to a source or for sane other reason, may face
significantly higher-than-average cancer risk. (Risks to such highly-
exposed individuals are discussed below.)
2. Non-cancer Risks; EPA estimated that about 10% of the population
in the Santa Clara Valley may be exposed to chemicals at levels high enough
to pose a risk of effects other than cancer. Populations estimated to be
at risk of non-cancer health effects due to exposures above no-effect
thresholds are shown in Table Two.l
The IEMP estimated that exposure to benzene in the air could pose an
increased risk of lowered blood cell counts to about 100,000 people in
the Santa Clara Valley. This exposure is the most widespread exposure, at
a level above an estimated no-effect threshold, of any chemical examined.
Benzene is released primarily by vehicles.
1 TCA has not demonstrated any teratogenic potential in published
studies conducted using rodent species. Therefore, the IEMP base-case
analysis assumes that exposure to TCA poses no risk of fetal effects. An
unpublished study, which has not undergone scientific peer review, reports
fetotoxic effects (cardiac malformations) in rat pups exposed in uteto to
TCA (Dapson et al., 1984). In order to assess the importance to Santa
Clara Valley residents of further research on this issue, the IEMP uses
the Dapson study to examine the possible impact of TCA under the alternative
assumption that exposures above an estimated threshold based on that
study's results could pose the risk of fetal effects. THE SENSITIVITY
RESULTS SHOULD NOT BE INTERPRETED AS INDICATING WHETHER OR NOT A RISK IN
FACT EXISTS; EPA RECOMMENDS AGAINST USING THIS INFORMATION FOR RISK MANAGEMENT
DECISION-MAKING OR REGULATORY ACTION. Under this alternative assumption,
the IEMP projects that about 3,000 people, mostly those using private
wells, could be exposed to levels of TCA in their drinking water that
exceed the estimated threshold. In addition, most-exposed individuals
downwind of an industrial facility are projected to be exposed at levels
above the estimated threshold in the air. These findings suggest that
more research is appropriate, both on actual levels of exposure and on
TCA's potential adverse effects. The National Toxicology Program has
commissioned a project to repeat the limited Dapson study; results are
expected in Fall of 1986.
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TABLE TMD
POPULATIONS ESTIMATED TO BE AT RISK OF NON-CANCER HEALTH EFFECTS
IN SANTA CLARA VALLEY, BY POLLUTANT
POLLUTANT
EXPOSURE POTENTIAL
PATHWAY HEALTH EFFECTS
POPULATION
EXPOSED ABOVE
NO-EFFECT
THRESHOLD
PRIMARY
SOURCE(S)
VOLATILE ORGANIC
CHEMICALS
Benzene
1,1 Dichloro-
ethylene
Methylene
Chloride
1,1,1 Trichloro-
ethane 2
Trichloro-
ethylene
Vinyl
Chloride
Air Blood 100,000 Motor Vehicles
Water Liver, kidney 20 - 340 Underground Tanks
Water Liver, fetal
Water Liver, neuro-
behavioral
Water Liver, neuro-
behavioral
Water Liver, kidney,
cardiovascular
0-50 Underground Tanks
10 - 100 Underground Tanks
0-10 Underground Tanks
0-10 Underground Tanks
METALS AND
INORGANIC SUBSTANCES
Nitrates
Water
Blue baby
syndrome
50 - 100 Fertilizer, Septic
Tanks
NOTE; BECAUSE OF SIGNIFICANT UNCERTAINTIES IN THE UNDERLYING DATA AND ASSUMPTIONS,
THESE ESTIMATES OF THE POPULATIONS POTENTIALLY AT RISK OF DISEASE ARE ONLY ROUGH
APPROXIMATIONS. THEY ARE BASED ON CONSERVATIVE ESTIMATES OF EXPOSURE AND CHEMICAL
TOXICITY. See Text. UNLIKE CANCER RISK ESTIMATES IN THIS REPORT, THESE ARE
ESTIMATES OF POPULATIONS EXPOSED AT LEVELS THAT MAY POSE HEALTH RISK; THEY ARE
NOT ESTIMATES OF POSSIBLE NUMBERS OF CASES OR PROBABILITY OF DISEASE.
1 in many cases, risks for most-exposed individuals (MEIs) were estimated
without estimating populations involved. Such risk estimates are presented
in table six.
2 The IEMP conducted sensitivity analysis on TCA for possible fetal effects.
footnote to text.
See
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In the southern part of the Santa Clara Valley, nitrate contamination
of groundwater supplies of drinking water is above threshold levels
estimated to pose an increased risk to infants of methemoglobinemia, or
blue baby syndrome. The IEMP estimates that up to 50 or 100 babies may,
at any one time, be exposed to nitrate levels high enough to pose risk.
In addition, under sane assumptions about the way groundwater
contamination may affect drinking water supplies, the IEMP projects
that several hundred people who drink from private wells could be at
increased risk of a variety of effects - including birth defects and
neurobehavioral, cardiovascular, liver, blood and kidney effects - from
industrial contaninants fron tank leaks and spills. Concentration levels
in public well water are projected to remain below no-effect thresholds,
even under conservative assumptions.
Substantial evidence exists that lead may cause toxic effects,
including blood effects and decreased IQ, particularly in children, who
are most sensitive to it. Lead is present in air, dust and water, as a
result of combustion of leaded gasoline, use of lead solder in pipes,
and other sources. The IEMP was unable to calculate risks from lead
exposure in this analysis because of a lack of an accepted EPA method
for doing so. The IEMP hopes to estimate health risks from lead in the
Santa Clara Valley as a part of follow-on work in Stage II.
It is important to note that exposure to toxic chemicals in the air
or drinking water may pose some health risk at levels below estimated
thresholds if exposures from other sources - such as diet or occupation -
are significant. Even in this instance, comparisons with estimated
thresholds provide a useful indication of the significance of the portion
of exposure due to outdoor air or drinking water. Envirormental exposures
at or near estimated thresholds are likely to pose a more significant
added risk than exposures well below a threshold.
3. Risks by Exposure Route: outdoor air and imported surface
supplies of drinking water appear to be the major exposure routes by
which toxic contaminants in the ambient environment are likely to affect
most people. The estimated breakdown of cancer risk by exposure route
is shown in Table Three.
Estimated toxic health risk through different exposure routes (e.g.,
air or drinking water) generally reflects the extent of exposure to toxic
chemicals through those routes. Exposure to air toxics is the most
widespread; everyone breathes the air and all 1.4 million Santa Clara
Valley residents are estimated to be at some increased health risk from
toxic air pollutants. Not surprisingly, toxic chemicals in the air are
estimated to pose the most significant health risks among the exposure
routes studied, over two estimated additional cancer cases per year.
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TABLE THREE
ESTIMATED INCREASE IN CANCER INCIDENCE
IN SANTA CLARA VALLEY, BY EXPOSURE PATHWAY
POINT ESTIMATE
OF ANNUAL
INCREASE IN CANCER WEIGHT OF EVIDENCE
EXPOSURE PATHWAY INCIDENCE (Range) FOR CARCINOGENICITY
Mr 2.2 (0.8 - 7.8) A-B2
Drinking Water
Surface Water 1.3 (1.3 - 8.3) A-B2
Groundwater 0.06 (0.04 - 0.3) A-C
TOTAL 3.6 (2.1 - 16.4) A-C
NOTE; BECAUSE OF SIGNIFICANT UNCERTAINTIES IN THE UNDERLYING DATA AND
ASSUMPTIONS, THESE ESTIMATES OF DISEASE INCIDENCE ARE ONLY ROUGH APPROXIMATIONS
OF ACTUAL RISK. THEY ARE BASED ON CONSERVATIVE ESTIMATES OF EXPOSURE AND
POTENCY, AND ARE THEREFORE MORE LIKELY TO OVERESTIMATE RISKS THAN UNDERESTIMATE
THEM. See text.
1. The weight of evidence of carcinogenicity for the compounds included in
the analysis varies greatly, from very limited to very substantial. According
to EPA's categorization of levels of evidence of carcinogenicity, A = proven
human carcinogen; Bl = probable human carcinogen (limited human evidence);
B2 = probable human carcinogen (insufficient human evidence but sufficient
animal evidence); C = possible human carcinogen D = not classifiable; E= no
evidence.
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Cancer risks from imported drinking water supplies are estimated to
be somewhat lower than those from air sources - slightly over one
additional case per year. This estimated risk results primarily from
exposure to disinfection by-products, to which half the Valley's population
is exposed. (See Conclusion 5 for more details).
One of the more striking findings of this study is that overall
risks from consumption of contaminated groundwater are estimated to be
low (about 1-2% of the cancer risk anong the sources examined in this
study, or about one additional cancer case every 15 to 30 years).
Estimated cancer risks from current levels of exposure at public wells
are lower: one estimated additional cancer case every 800 years. The
primary reasons for this finding of relatively low risk from groundwater
are that natural hydrogeologic protection and a number of regulatory
programs and voluntary actions in effect or soon to go into effect are
expected to limit most people's exposure. The IEMP estimates that no
more than about 20% of the people in the Santa Clara Valley are likely to
be exposed to groundwater contamination, compared to about 100% to air
contaminants and about 50% to trihalcroethanes in surface water. It is
important to note that while our analysis of future groundwater contamination
involves substantial uncertainties, this conclusion of relatively low health
risks holds up under a wide range of alternative assumptions and appears
fairly solid.
The key hydrogeologic factor is the presence of an aquitard, or
clay layer, over much of the Valley protecting public drinking water
sources. While this clay layer has, for the most part, prevented
contamination near the surface from reaching deep drinking water supplies,
there is concern that such contamination could occur either through
abandoned wells that may function as conduits, or through faults in the
confining layer itself. The recent discovery of deep groundwater contamination
in Mountain View (which has not yet affected public drinking water wells)
provides the first strong evidence of contaminant transfer through conduit
wells in the Santa Clara Valley. This finding is consistent with the
IEMP analysis, which suggests that conduit well transport is likely to be
more significant than contamination through the major clay confining
layer itself, and that a number of public wells may eventually be affected
in this way.
One important set of regulatory programs estimated to reduce
groundwater contamination and human exposure are the local Hazardous
Materials Management Ordinances, which have become models for hazardous
materials control in other areas. These ordinances reduce contamination
at the source by requiring groundwater monitoring near underground tanks,
improved tank construction standards, and better chemical handling
processes. Other important regulatory and response actions include
clean-up actions at existing contamination sites, public drinking water
well monitoring for a broad range of organic chemicals (to be required
annually), and a policy of closing any public well contaminated above
state action levels. Voluntary actions taken by firms, such as underground
tank replacement and improved handling procedures, are also likely to
reduce future groundwater contamination.
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Analysis of the effectiveness of all of these programs indicates
, in combination, they may reduce health risks by roughly one hundred
times (e.g., risks with these programs in place may be only 1% of what
risks would have been without them). Other programs, including efforts
to seal abandoned wells that may act as contaminant conduits, and efforts
to monitor and protect private wells, are also likely to reduce health
risks from groundwater contamination.
Exposure through the outdoor air and drinking water is direct, as
people take in pollutants through breathing or drinking. Contamination
affecting the San Francisco Bay and local surface streams, by contrast,
was judged to be only indirectly related to human exposure, largely
through body contact or fish consumption. Exposure through these routes
appears to be relatively small by comparison with air and drinking water
exposure.
Most hazardous wastes are exported fron the Santa Clara Valley for
recycling or disposal elsewhere, and thus pose little local risk. Those
local risks we could identify from hazardous waste storage and handling
appear to be primarily through groundwater contamination, and were
analyzed under that exposure pathway. Accidental releases, such as those
resulting from transportation accidents, also have the potential to affect
soil and groundwater.
Although the IEMP explicitly examined a number of potential issues
of pollution transfer from one medium to another, none appeared to be
very significant in terms of public health risk in the Santa Clara Valley.
For example, the study estimated the possible toxic organic chemical air
emissions from sewage treatment plants, groundwater aeration/clean-up
sites, and sanitary landfills. Air emissions from these sources were
estimated to be fairly small in comparison to other sources of toxic
organic gases.
4. The toxic environmental contaminants posing the most significant
health risks in the Santa Clara Valley are, for the most part, the same as
those found in the other urban environments. A relatively small number of
toxic chemicals, including the trihalomethanes (primarily in drinking
water), and benzene, gasoline vapors, carbon tetrachloride, benzo(a)pyrene,
chromium and arsenic (primarily in air), account for about 92% of aggregate
cancer risk estimated in this study. National studies and data from
other areas show that estimated exposure levels in the Santa Clara Valley are
similar to, and in some cases lower than, ambient concentrations found in
other urban areas. It should be noted that the less-developed southern
Santa Clara Valley has a contamination problem typical of many agricultural
areas: high nitrate levels in the groundwater. A summary of estimated
cancer risks by pollutant is presented in Table Pour.
As a class, volatile organic compounds account for the majority
(about 58%) of the cancer risk estimated in this study. Heavier organic
chemicals, such as benzo(a)pyrene, comprise an estimated 20% of aggregate
cancer risk. Metals and inorganic substances account for about 22% of
total estimated cancer risk.
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TABLE
ESTIMATED INCREASE
FOUR
IN CANCER INCIDENCE
IN SANTA CLARA VALLEY, BY POLLUTANT
POLLUTANT
(WEIGHT OF EVIDENCE)1
VOLATILE ORGANIC
CHEMICALS
Trihalomethanes (B2) *
Benzene (A)
Carbon Tetrachloride (B2)
Gasoline Vapor (B2)
1,1, Dichloroethylene
Perchloroethylene (B2)
Ethylene Oxide (Bl)
Other (A-C)
TOTAL, VOCs
ORGANIC PARTICULATES
BENZO(A)PYRENE
GROUP (B2)
METALS AND INORGANICS
Chromium (A)
Arsenic (A) ***
Cadmium (Bl)
Other (A-B2)
TOTAL, METALS
TOTAL, ALL CHEMICALS
STUDIED
All Exposure
Pathways
1.3
0.3 (0.3- 1.2)
0.2
0.1 (0 - 0.4)
0.04
0.04
0.03
0.03
2.1 (1.9- 3.5)
0.7 (0.01-1.3)
0.4 (0 - 4.0)
0.3 (0.2- 7.4)
0.07 (0.04-0.1)
0.03 (0 - 0.07)
0.8 (0.2-11.6)
3.6 (2.1-16.4)
POINT ESTIMATE OF ANNUAL INCREASE
IN CANCER INCIDENCE (Range)
Surface
Air Water Groundwater
<0.01 1.3 <0.01
0.3 (0.3- 1.2) <0.01 <0.01
0.2 <0.0001
0.1 (0 - 0.4)
0.04
0.03 <0.01
0.03
0.02 <0.01 0.01
0.7 (0.6- 1.9) 1.3 0.06
(0.03 - 0.3)
0.7 (0.01-1.3)
0.4 (0 - 4.0) 0 0
0.3 (0.2- 0.4) 0 (0-7) ***
0.07 (0.04-0.1) 0 0
0.03 (0 - 0.07) 0 0
0.8 (0.2- 4.6) 0 (0-7) 0
2.2 (0.8- 7.8) 1.3 0.06
(1.3 - 8.3) (0.03 - 0.3)
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FOOTNOTES TO TABLE POUR
NOTE; BECAUSE OF SIGNIFICANT UNCERTAINTIES IN THE UNDERLYING DATA AND
ASSUMPTIONS, THESE ESTIMATES OF DISEASE INCIDENCE ARE ONLY ROUGH APPROXIMATIONS
OF ACTUAL RISK. THEY ARE BASED ON CONSERVATIVE ESTIMATES OF EXPOSURE AND
POTENCY, AND ARE MORE LIKELY TO OVERESTIMATE RISKS THAN UNDERESTIMATE THEM.
See text.
1 The weight of evidence of careinogenicity for the compounds listed varies
greatly, from very limited to very substantial. According to EPA's categori-
zation of levels of evidence of carcinogenicity, A = proven human carcinogen;
Bl = probable human carcinogen (limited human evidence); B2 = probable human
carcinogen (insufficient human evidence but sufficient animal evidence);
C = possible human carcinogen; D = not classifiable; E = no evidence.
* The weight of evidence identified for trihalcmethanes is that for chloroform
only.
** Neither (hexavalent) chromium nor cadmium is thought to be carcinogenic
in water. See chapter 4.
*** There is seme dispute over the carcinogenicity of arsenic in water. See
text. Arsenic exposure listed under surface water is for combined exposure
to surface water and groundwater.
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Arsenic risk in drinking water is a significant question mark in
this analysis. Arsenic accounts for as little as 0 to as much as 66% of
total estimated cancer risk, depending on assumptions about its toxicity.
Some evidence exists that arsenic in drinking water may cause a form of
skin cancer known as "Blackfoot Disease." Applying EPA's standard risk
estimation techniques, the IEMP would estimate up to seven additional
cancer cases a year from exposure to the levels of arsenic found in Santa
Clara Valley water (these levels are fairly low in comparison to those
found in many areas). Substantial disagreement exists as to the carcino-
genicity of low levels of arsenic in drinking water, however, and EPA's
Office of Drinking Water believes that the levels of arsenic found in
Santa Clara Valley water are well within safe limits. This uncertainty
does not affect the estimate of lung cancer from airborne arsenic; the
evidence for this effect is much stronger.
•t
The cancer risk fron chromium in the air is another significant
uncertainty in this analysis. Monitoring data do not distinguish between
hexavalent chromium (thought to pose a risk of lung cancer) and other
forms (not considered carcinogenic). Depending on assumptions about the
proportion of chromium that is hexavalent, estimated cancer risk ranges
from none to four additional cases per year. Based on studies conducted
elsewhere and a tentative identification of local sources, this
study conservatively assumed that about 10% of airborne chromium was
hexavalent.
5. The pollution sources posing the most significant overall
health risks appear to be similar to high-risk sources identified in
other urban areas. However, the sources of some of the most important
environmental toxics are uncertain. Identifying sources is important for
risk management, since pollution control decisions aimed at reducing risk
must be directed at known sources of risk. Table Five presents a preliminary
breakdown of cancer risk by source type, making some assumptions about
the sources of chemicals whose origin is not well understood.
Most (about 77%) of the estimated risk from air exposure, particularly
for the toxic metals and organic particulates, is frcm sources that are
only tentatively identified. The AQMD does not maintain emissions
inventories for the metals and organic particulates, as it does for toxic
organic gases. Since consideration of control actions requires a knowledge
of the sources of risk, this report has identified the collection of data
on the sources and emissions of these substances as an important research
need. In Stage II, the AQMD, with assistance from EPA, plans to compile
a metals emissions inventory. The IEMP has done some preliminary analysis
of the possible sources of many of the substances of concern. However,
more definitive source identification would be required in most cases
before risk management control actions can be taken.
Preliminary analysis of likely sources suggests that the primary sources
of toxic chemicals in the air may be dispersed area sources, such as residen-
tial heating and motor vehicles. These sources appear to emit the bulk
of the benzene, gasoline vapors, benzo(a)pyrene, and metals that are
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TABLE FIVE
ESTIMATED INCREASE IN CANCER INCIDENCE
IN SANTA CLARA VALLEY, BY SOURCE TYPE
SOURCE TYPE
(EXPOSURE PATHWAY)
[WEIGHT OF EVIDENCE!
ESTIMATE OF ANNUAL
INCREASE IN CANCER
INCIDENCE
PERCENT OF
TOTAL ESTIMATED
CANCER INCIDENCE
Drinking Water
Disinfection
(Surface Water) [B2] *
1.3
36%
Fuel Combustion
for Residential
Heating
(Air) [A-B2]
0.63 - 1.1
18-31%
Motor Vehicles
(Air) [A-B2]
0.63 - 0.67
18-19%
**
Cement Plant
(Air) [A-B2]
0 - 0.5
0-14%
Unknown Sources/Back-
ground Contamination
(Air) (A-B2]
0.2
***
6%
Other Area Sources
(Air) [A-B2]
0.15
4%
Other Point Sources
(Air) [A-B2]
0.1
3%
Underground Industrial
Tanks
(Groundwater) [A-C]
0.05
1%
Underground Fuel Tanks
(Groundwater) [A-B]
TOTAL, ALL SOURCES
STUDIED
<0.01
3.6
100%
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FOOTNOTES TO TABLE FIVE
NOTE; BECAUSE OF SIGNIFICANT UNCERTAINTIES IN THE UNDERLYING DATA AND ASSUMPTIONS,
THESE ESTIMATES OF DISEASE INCIDENCE ARE ONLY ROUGH APPROXIMATIONS OF ACTUAL
RISK. THEY ARE BASED ON CONSERVATIVE ESTIMATES OF EXPOSURE AND POTENCY AND
ARE MORE LIKELY TO OVERESTIMATE RISKS THAN UNDERESTIMATE THEM. See text.
1 The weight of evidence of carcinogenic!ty for the compounds listed varies
greatly, from very limited to very substantial. According to EPA's categori-
zation of levels of evidence of carcinogenicity, A = proven human carcinogen;
Bl= probable human carcinogen (limited human evidence); B2 = probable human
carcinogen (insufficient human evidence but sufficient animal evidence);
C = possible human carcinogen; D = not classifiable; and E = no evidence.
* Chloroform is considered a probable carcinogen. The upper end of this
range reflects the possibility that other THMs are also carcinogenic.
See chapter 4.
** Source identification for residential heating and cement plant is
preliminary and uncertain. See chapter 3.
*** This point estimate derives from an estimated range of 0.2 to 7.4 annual
incidence. The point estimate does not include the potential risk from arsenic
in drinking water. There is substantial disagreement as to the carcinogenicity
of low levels of arsenic in drinking water. Conservative assumptions of
carcinogenicity, developed by EPA's Office of Research and Development, suggest
that the levels found in the drinking water in the Santa Clara Valley could
result in up to 7.2 additional cases per year. However, EPA's Office of Drinking
Water, which is responsible for setting standards, believes that low levels do
not pose risk.
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projected to cause most of the air toxics risk. Industrial point sources
do not appear to be significant contributors to aggregate risk, with the
possible exception of the coal-burning cement plant, ihis pattern of
many small and dispersed sources suggests that it may be difficult to
control major contributing sources so as to reduce risk.
Surface water risks are dominated by hazards posed by trihalcmethanes
resulting from water disinfection. The presence of trihalonethanes in
treated drinking water involves a trade-off of one form of risk for another:
while chlorination introduces chloroform and other potential carcinogens
into drinking water supplies, it protects the population fron the otherwise
much greater risk of infectious diseases such as cholera and typhoid.
Although discontinuing disinfection is not a viable option, there are
other disinfection methods that reduce the formation of trihalonethanes.
The Santa Clara Valley Water District (SCVWD) has recently implemented one
such treatment method, chloramination, at its two major local water treatment
plants. The IEMP projects that this change may reduce potential risks
substantially. In addition, the SCVWD has recently commissioned a study
of still other disinfection techniques, such as ozonation, that might
reduce risks further. Given the apparent importance of these chlorinated
organic chemicals relative to other sources of toxic health risk, such
analysis of alternatives may be appropriate, both in the Santa Clara Valley
and elsewhere.
"Background" contamination is contamination not linked to any known
current source. Such contamination may be fron natural sources, such as
minerals in the soil, or from prior agricultural or industrial activities.
Background contamination, largely from persistent levels of carbon
tetrachloride in the air, is estimated to account for about 5% of total
cancer risk from sources and pollutants studied. However, if pessimistic
assunptions about the carcinogenicity of arsenic in drinking water are
correct, the risk from background contaminants increases to well over
half of all estimated cancer risk in the Santa Clara Valley.
The major groundwater contamination sources examined, underground
fuel and solvent tanks, are estimated to account for about 1-2% of the
total cancer risk among sources examined.
6. Some individuals, who live near pollution sources or are highly
exposed for other reasons, face toxic health risks that appear to be
significantly higher than average. Estimates of potential risk to these
most-exposed individuals (MEIs) are shown in Table 6.
In contrast to the estimates of low overall risks from groundwater
contamination, people drinking from private wells appear to be vulnerable
to potentially significant levels of exposure and risk as a result of
leaks from underground tanksTIndividuals who obtain drinking *eter from
private wells are more vulnerable to risk because these wells are shallow
(and thus not protected from surface contamination by an intervening clay
layer) and are not typically monitored. Risks to individuals who may be
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TABLE SIX
ESTIMATED HEALTH RISK TO MOST-EXPOSED INDIVIDUALS
IN SANTA CLARA VALLEY
EXPOSURE PATHWAY
& SOURCE TYPE
INCREASED
LIFETIME
CANCER RISK
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TABLE SIX (cont.)
ESTIMATED HEALTH RISKS TO MOST-EXPOSED INDIVIDUALS
IN SANTA CLARA VALLEY
EXPOSURE PATHWAY
& SOURCE TYPE
INCREASED
LIFETIME
CANCER RISK
(CHANCES IN
A MILLION)1
POLLUTANT
(WEIGHT OF EVIDENCE)2
POTENTIAL
NON-CANCER
HEALTH EFFECTS3
GROUNDWATER;
UNDERGROUND TANKS 5
(AT PRIVATE WELLS)
FERTILIZER, SEPTIC
TANKS
20,000
1,1 Dichloroethylene (C)
Vinyl Chloride (A)
Perchloroethylene(B2)
Ethylene Dibronide (B2)
Methylene Chloride (B2)
Chloroform (B2)
Benzene (A)
Trichloroethylene (B2)
1,1,1-Trichloroethane
Nitrates
Liver, kidney.
Liver, kidney,
cardiovascular
Liver, fetal
Liver, neurobehavioral
Liver, neurobehavioral
*
Methemoglobinemia
(Blue baby syndrone)
SURFACE WATER;
DRINKING WATER
TREATMENT
BACKGROUND
100
I**
Trihalonethanes (B2)
0 - 7,000*** Arsenic (A)
SOUTH SAN FRANCISCO BAY:
SHRIMP CONSUMPTION 7
MUSSEL CONSUMPTION 7
STRIPED BASS
CONSUMPTION 7
0 - 6,000*** Arsenic (A)
20 - 200 PCB (B2)
Chlordane (B2)
DDT (B2)
80 - 16,000
PCB (B2)
Cadmium
Mercury
Liver, neurobehavioral,
kidney, reproductive
Kidney, reproductive,
liver, birth defects
8
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FOOTNOTES TO TABLE SIX:
NOTE: BECAUSE OF SIGNIFICANT UNCERTAINTIES IN THE UNDERLYING EATA AND
ASSUMPTIONS, THESE ESTIMATES OF INDIVIDUAL RISK AND DISEASE INCIDENCE
ARE ONLY ROUGH APPROXIMATIONS OF ACTUAL RISK. THEY ARE BASED ON CON-
SERVATIVE ESTIMATES OF EXPOSURE AND POTENCY AND ARE MORE LIKELY TO
OVERESTIMATE RISKS THAN UNDERESTIMATE THEM. See text.
1 Except in the case of underground tanks at private wells, estimated cancer
risk is for all pollutants combined from given source. For underground
tanks, estimate is for pollutant posing the greatest cancer risk. In each
case, pollutants for each source are listed in decreasing order of estimated
cancer risk.
2 The weight of evidence of carcinogenicity for the compounds listed varies
greatly, from very limited to very substantial. According to EPA's
categorization of levels of evidence of carcinogenicity, A = proven human
carcinogen; Bl = probable human carcinogen (limited human evidence);
B2 = probable human carcinogen (insufficient human evidence, but sufficient
animal evidence); C = possible human carcinogen; D = not classifiable;
E = no evidence.
3 Non-cancer health effects are reported only if exposures are above estimated
thresholds for such effects.
4 If TCA is assumed to be carcinogenic, total estimated cancer risk is at or
slightly above level presented.
5 Estimated impacts are for "high" release, base case; see chapter 4.
6 Estimated taste and odor threshold is very slightly below the estimated
threshold for blood effects.
7 Estimated risks for fish consumption are for a hypothetical individual
who regularly consumes contaminated fish or shellfish caught in the South
Bay. Assumed consumption is 5 to 52 pounds of fish per year. Note that
the IEMP has no actual data on the number of people eating fish from the
South Bay, although we believe that number is small.
8 Estimated exposure value for mercury in striped bass is just slightly
under the lowest estimated human threshold.
* The IEMP conducted sensitivity analysis on TCA for possible fetal effects.
See footnote to text.
** Risk for system with highest estimated average risk; some individuals
may be exposed to higher risks.
*** Considerable controversy exists as to the carcinogenicity of arsenic by
ingestion. See text.
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highly exposed to industrial chemicals in their private wells were
estimated to be potentially higher than risks fron any other source
examined. The estimated risk to the roost-exposed individual drinking
from a private well is quite uncertain and should not be interpreted
literally. However, the potential vulnerability of this group is clear,
and this is the important conclusion for risk management. Current efforts
by the County Health Department to monitor some private wells appear to
be a useful first step in addressing this problem.
Persons living near a highly congested intersection were estimated
to face the highest individual cancer risk fran exposures to toxic air
contaminants such as benzene. The risk facing individuals living near
hospitals and exposed to the sterilant ethylene oxide (ETO) was estimated
to be nearly as large.These potential risks from high exposures to air
toxics are substantially lower than the estimated risks for highly exposed
individuals at private wells. The comparatively high estimated risk
near intersections reinforces the importance of vehicles as a source of
air toxics risk - both to the general populace and to highly exposed
individuals. Ethylene oxide from hospitals, on the other hand, is not
projected to be a major source of risk for roost people but nevertheless
appears to pose comparatively high risks near the source. Because of
uncertainties about ETO emissions, and the possible reactivity of the
chemical once released, estimated emissions and exposure levels should
be confirmed before control actions are taken. Since use of ETO as a
disinfectant is not unique to the Santa Clara Valley area, this finding,
if confirmed, may have implications for other areas.
Although we lack actual consumption data, estimated risks to a
hypothetical individual regularly consuming significant quantities of
contaminated fish or shellfish caught from the South San Francisco Bay
appear to be fairly high. Concentrations of PCBs, pesticides, mercury,
and other metals in shrimp, mussels, and striped bass may pose a significant
risk. Possible effects include cancer, neurobehavioral, reproductive,
kidney, and liver effects (estimated thresholds for non-cancer effects
are exceeded only under a "high" consumption estimate of one pound per
week of contaminated fish). We stress that these exposure estimates are
conservative, and that we have no data on the number of people consuming
contaminated fish from the South Bay. Nevertheless, these estimates
suggest that regular consumption of fish or shellfish fron the South Bay
may pose significant health risks. This finding is consistent with a
health advisory issued by the state Department of Health Services, warning
pregnant women not to eat striped bass.
7. One of the more important implications of this analysis is
that groundwater contamination may be an economic and natural resource
issue as well as a risk issue!IEMP estimates of future risk depend on
many actions that we assume will be taken in the future. For example,
the study assumes that public drinking water wells will be closed when
contaminated above action levels and replacement supplies obtained; it
also assumes that the Hazardous Materials Management Ordinances will be
implemented, although this has not yet fully occurred. While IEMP projects
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that these actions will be largely successful in controlling risk, they
could be extremely expensive. The direct economic costs of contamination
prevention and response include the costs of tank replacement, clean-up,
monitoring and well closure. In addition, groundwater contamination
causes a potentially significant indirect natural resource cost: the
loss of clean, local groundwater.
The IEMP analysis illustrates the difference between drinking water
health risk and groundwater resource impacts. Under the rather pessimistic
assumptions used in this study, health risks to people drinking groundwater
from public wells are projected to be comparatively small. Yet, about
55 public wells serving 139,000 people are projected to be affected by
fuel or industrial contamination, with one quarter to one half of the
wells contaminated above state action levels.
Contamination above action levels requires well closure or treatment.
In some cases, contamination below action levels has also led to removing
a well from service. Clean-up of contaminant plumes can also have a
significant impact on the groundwater resource, as large quantities of
groundwater are pumped, cleaned and discharged to the Bay. This water
must be replaced with recharge water imported from the Sacramento Delta.
While the IEMP estimates of the number of wells likely to be affected
are intentionally pessimistic, they clearly indicate the importance of
examining the natural and economic resource impacts, as well as the
health effects, of groundwater contamination and programs to address it.
Thus, the low aggregate risk estimates presented in this draft report
do not imply that groundwater contamination is not an important environmental
management issue. Despite the comparatively low estimated aggregate
risks, it may be appropriate to assess groundwater control and treatment
options in terms of their potential risk, cost, and resource impacts.
8. This study identified many scientific uncertainties and data
gaps that may be appropriate research priorities for regulatory agencies
or others. A few of the most important include:
0 Hydrogeology: A better understanding of Santa Clara Valley
hydrogeology - in particular the effectiveness of the major clay
confining layer or aquitard - would improve the ability to protect
the groundwater resource effectively.
0 Pollutant transport and transformation: In particular, better
understanding of the speed with which fuel contaminants degrade
after release into the environment is critical to determining the
importance of leaking fuel tanks as a groundwater contamination
source.
0 Monitoring data: Two of the more critical uncertainties in this
Stage I analysis - levels of organic chemicals in the ambient air
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and in private wells - are being addressed by local agencies.
Local data on organic particulates in air would be valuable also;
the IEMP plans to sponsor the collection of such data as a part
of Stage II.
Source data: Better information on sources of metals and organic
particulates in air is needed to assist in the development of risk
management strategies. The Bay Area Air Quality Management District,
with EPA support, will be compiling a metals emissions inventory
in Stage II.
Non-Cancer effects: Development of a method of estimating possible
disease incidence for effects other than cancer would allow a
more complete analysis of toxic health risks. Some key chemicals
of concern in the Santa Clara Valley have been identified in this
report. These issues are being pursued within EPA and by scientific
peer review groups.
Next Steps
This Stage I Report for the Santa Clara Valley Integrated Environmental
Management Project presents the results of the lEMP's comparative analysis
of toxic environmental health risks. Potential health effects were
analyzed, and exposure pathways, pollutants and sources compared in
terms of health risk. A draft of this report has been reviewed widely
by EPA's two advisory committees, the Intergovernmental Coordinating
Committee and the Public Advisory Committee, and by other interested
agencies, scientists and individuals. It is now undergoing scientific
peer review by a group of scientists at Rutgers University.
The Stage I Report findings are intended to provide the basis for
Stage II of the IEMP, which will focus on managing risks: identifying
priority issues, analyzing control options for dealing with those problems,
and implementing solutions. Stage II will also expand and improve upon
the problem definition developed in Stage I.
EPA, in consultation with its IEMP advisory conmittees, has developed
a Stage II workplan to guide the project's future work. This workplan
identifies risk management priorities, taking into account public concerns
and ongoing programs. It outlines research priorities, analyses of
pollution control options, and a management strategy that EPA and its
local partners hope will lead to discussions and actions that protect
public health and the environment more effectively.
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