Private individual water systems throughout Pennsylvania were sampled
for dissolved lead, nitrate-N and radon to determine the prevalence of
these primary pollutants. Approximately 1,600 sources were tested for
lead and nitrate and 989 were tested for radon. Twenty-eight percent of
sampled homes had lead concentrations above 10 |mu~g/L and 19 percent
were above 15 |mu~g/L. These percentages increased to 60 and 34 percent
respectively when calculated total (digested) lead data were used,
suggesting that total lead analysis may be appropriate even when dealing
with relatively clear, low turbidity samples. Nitrate contamination was
less prevalent and more regional than lead. Nine percent sampled homes
contained nitrate-N above 10 mg/L with nearly all (96 percent) of these
homes located in the agricultural southcentral and southeastern regions
of the state. Nearly 80 percent of the groundwater wells tested
contained radon concentrations above the proposed MCL of 300 pCi/L.
Excessive radon concentrations existed in all regions of the state but
were most prevalent in the eastern regions near the Reading Prong
geologic formation.In Pennsylvania there are approximately one million
private individual water supplies which provide water for about two
million of the state's rural residents. Unlike municipal water
supplies which must meet federal Safe Drinking Water Standards,
management of private water supplies is voluntary. Past studies have
shown that numerous health related (primary) and aesthetic (secondary)
pollutants can occur in these unregulated water supplies (1, 2). Of the
pollutants encountered in private water supplies, lead, nitrate and
radon may present the greatest risk based on their estimated prevalence
and health effects.Although lead is often thought of as an urban
problem, some lead can probably be found in the paint, soil, dust,
housewares or drinking water of many rural homes. Drinking water
contributions to blood lead burdens are typically less than 20 percent,
but have been reported as high as 40 percent depending on the amount
contributed by other sources (3, 4).Recent guidance from the Centers for
Disease Control (CDC) suggests that blood lead concentrations over 10
|mu~g/dL may be indicative of lead poisoning (5). Research has shown
that blood lead concentrations increase by about 1 |mu~g/dL for every 5
|mu~g/L of lead in drinking water (6). At a conversion rate of 5:1, 50
|mu~g/L of lead in water would produce an unacceptable 10 |mu~g/dL of
lead in blood. In order to allow for lead contributions from other
sources (e.g., food, dust, etc.) the maximum allowable concentration of
lead in drinking water should be no more than 10 |mu~g/L.The
overwhelming source of lead in both private and municipal water supplies
is corrosion of plumbing materials. Households typically contain various
mixtures of metal pipes, faucets and solders which each can contain lead
or lead impurities. Research has shown that lead based solders, which
are present in 70 percent of American homes, and brass fixtures are the
most significant sources of lead in tap water (7, 8, 9). Brass fixtures
were found to be especially important contributors in first flush water
samples from homes using plastic pipes (8). Corrosion of lead from metal
plumbing increases as the pH, hardness and alkalinity of the source
water decrease (10). Sharpe et al. (1) determined that corrosive
drinking water was the most common problem in private water supplies of
Pennsylvania, occurring in 60 percent of the homes tested.The prevalence
of leaded plumbing components and corrosive groundwater in Pennsylvania
argue that lead contamination is common in private water systems;
however, few studies have actually documented its occurrence. Francis et
al. (2) reported 16 percent of rural water supplies in the U.S.
contained lead concentrations above 50 |mu~g/L and approximately 50
percent were above 10 |mu~g/L. A lab contamination problem, however,
made these results suspect. Based on the limited available data, the
U.S. Public Health Service estimates that 20 percent of the U.S.
population has tap water lead concentration in excess of 20 |mu~g/L
(11).Amendments were recently added to the National Primary Drinking
Water Regulations to control lead in municipal water supplies through a
complex scheme of regulations rather than the simpler, more direct
maximum contamination level (MCL) approach (12). The U.S. Environmental
Protection Agency (EPA) opted for an "action level" of 15
|mu~g/L which will require municipal water utilities to add corrosion
control chemicals at the water treatment plant and take other actions if
more than 10 percent of the tested homes are above 15 |mu~g/L. This
action level replaces an MCL for lead of 50 |mu~g/L. It's estimated
that these regulations will reduce the lead exposure of 130 million
Americans (13), but they provide little protection for private water
systems. Recent legislation in Pennsylvania and other states has
extended lead regulations to private water systems by banning the sale
of leaded solder, leaded pipe and limiting lead impurities in metal
fixtures (14). Additional federal legislation has been introduced that
has proposed a lead MCL of 10 |mu~g/L to provide a more appropriate
level of safety from lead exposure (15).Unlike lead, nitrates usually
occur in the source water as a result of pollution from animal waste,
human sewage, fertilizers and natural organic matter. Increases in the
use of agricultural fertilizers have been implicated in steady increases
in groundwater nitrates over the past 50 years (16). In Pennsylvania,
nitrogen fertilizer applications increased by 150 percent from 1960 to
1982 (17). Because nitrogen recovery in crops is typically only 50
percent, much of the applied nitrogen ends up in groundwater as nitrate
(18).Health concerns about nitrate in water are usually related to young
infants and methemoglobinemia (19). Two thousand cases of
methemoglobinemia were reported internationally from 1945 to 1970, with
an average fatality rate of eight percent (19). Other less proven
effects from nitrates include hypertension, cardiovascular disease,
impaired growth and central nervous system damage (20). The drinking
water standard for nitrate of 10 mg/L as nitrate-N (45 mg/L as nitrate)
was established primarily to protect young children from
methemoglobinemia.The predominance of agriculture makes some areas of
Pennsylvania susceptible to nitrate contamination, however, surveys of
nitrates in private water supplies have reported diverse results. Sharpe
et al. (1) found six to 14 percent of private water sources in
Pennsylvania contained high nitrates. Francis et al. (2) reported only
0.3 percent of eastern U.S. private water supplies had nitrate-N above
10 mg/L. Some researchers in midwestern agricultural states have
reported nitrate-N contamination rates (|is greater than~ 10 mg/L) as
high as 70 percent (21). A U.S. Geological Survey study of Pennsylvania
groundwater found 30 percent had nitrate-N levels indicative of human
activity (|is greater than~ 3 mg/L) (22).Radon is perhaps the least
understood and potentially most dangerous contaminant in private
individual water supplies. The calculated occurrence of fatal cancers
due to radon exposure from water may be larger than the sum of all other
carcinogens known to exist in water supplies (23). It's estimated
that 137 people die every year in the U.S. from exposure to radon in
water (24).Radon becomes dissolved in groundwater and, to a much lesser
extent, in surface water through radioactive decay of radium in rocks
and soil (25). Once radon is dissolved in water, exposure to radon can
occur through ingestion or, more importantly, through inhalation from
showering and other activities which agitate the water. Research has
shown that 10,000 pCi/L of radon in water will produce about 1 pCi/L of
radon in indoor air (26). Drinking water, however, generally only
represents about one percent of the total exposure from all sources of
environmental radon (23). Based on the proposed radon air standard of 1
pCi/ L and to allow for other more important sources of radon, the EPA
has proposed a radon in water standard of 300 pCi/L (27). It's
estimated that even consumption of water with 300 pCi/L of radon
involves a cancer risk of 1 in 10,000.Although there is an extensive
data base of radon in municipal water supplies, little data on private
water systems is available. Hess et al. (28) reported a mean radon
concentration of 910 pCi/L in 16 private groundwater wells and 380 pCi/L
in 105 public groundwater sources in Pennsylvania. In a nationwide study
of community groundwater wells, Pennsylvania was among the top eight
states for radon occurrence with a mean concentration of 1,570 pCi/L
(29). Dixon and Lee (29) also reported higher radon concentrations in
eastern Pennsylvania wells near the Reading Prong geologic formation and
lower radon values in the sandstones, shales and carbonates of the
Appalachian Plateau in western Pennsylvania. A review of the limited
available data suggests that the radon in water risk is much higher in
low-yield private groundwater systems (30).The objectives of this study
were to provide an extensive and representative survey of the prevalence
of lead, nitrate and radon contamination in private water supplies in
Pennsylvania and to relate contamination from lead or nitrate with
various water supply and land use characteristics.Lead and nitrate-N
samplingWater samples were collected from 1,595 private water systems in
35 of the 67 counties of Pennsylvania from March 1989 to April 1992.
Water sampling was conducted as part of county-sponsored Safe Drinking
Water Clinics which were advertised to the general public. Clinic
attendees interested in lead and nitrate-N testing were given clean, 125
ml plastic sample bottles, sample collection instructions and a survey
form. Participants were instructed to collect first-draw water samples
from the following morning and return the samples and completed surveys
to a pre-designated drop-off point. A survey question was used to verify
that samples were collected properly. Samples not collected from first
flush were excluded from lead analyses. First flush rather than running
water samples were collected because lead concentrations from first
flush samples are more closely correlated with blood lead concentrations
(31, 32, 33, 34).Samples were kept cool and returned to the Water
Laboratory at the Environmental Resources Research Institute at Penn
State University for lead and nitrate analysis within 72 hours of
collection. Samples were filtered using 0.45 |mu~m filters and acidified prior to analysis. Nitrate analysis was performed according to the EPA
Cadmium Reduction methodology 353.2 (35) on a Technicon Autoanalyzer II.
Nitrate results are reported in mg/L of nitrate-N with a detection limit
of 0.005 mg/L. Total dissolved lead was analyzed on a Perkin Elmer
Atomic Adsorption Model 703 using the EPA AA Furnace method 239.2 (35).
Lead results are reported in |mu~g/L of total dissolved lead with a
detection limit of 1 |mu~g/L.Samples were analyzed for total dissolved
lead rather than total lead to control costs. Because virtually all of
the samples contained low turbidities, it was anticipated that little or
no suspended lead would be present. To confirm this, a subset of 126
samples were aliquoted and analyzed for total and dissolved lead. Total
lead samples were digested using Ultrex II Ultrapure Nitric Acid and
filtered through 0.45 |mu~m filters.Data quality assurance and quality
control were measuring using blind split samples and deionized water blanks. Twenty split samples and 42 blanks were randomly arranged among
the actual samples throughout the duration of the study. Blanks had a
median lead concentration of 1 |mu~g/L (range |is less than~1 to 15
|mu~g/L) and a median nitrate-N concentration of 0.015 mg/L (range |is
less than~0.005 to 0.200 mg/L). The median difference between split
samples was 2 |mu~g/L for dissolved lead (range 0 to 22 |mu~g/L) and
0.05 mg/L for nitrate-N (range 0.002 to 1.25 mg/L). Four deionized water
blanks were also digested and analyzed for total lead. The median result
was 2 |mu~g/L (range |is less than~1 to 4 |mu~g/L) implying that no
significant lead contamination resulted from the digestion
process.Survey forms were used to provide basic information on the water
samples such as water supply type, depth of well, age of system and any
previous water testing. Additional questions concerning symptoms of lead
contamination, proximity to agriculture, and family health were also
used for correlation with lead and nitrate-N results. Eighty-nine
percent of the distributed surveys were at least partially completed and
returned. Total response rates for given questions ranged from 65 to 88
percent of the samples tested.Data were analyzed on a statewide and
regional basis. Pennsylvania was divided into six regions along county
lines corresponding to the major physiographic provinces of
Pennsylvania. Regional sample sizes roughly correspond to the land area
occupied by each region. The northcentral region included 81 samples
collected from Cattaraugus and Allegany counties in extreme southern New
York state bordering Pennsylvania. Samples sizes from the 37 counties
varied from one to 180 samples with 26 counties having more than 20
samples.Radon samplingGroundwater radon data were provided by the
Pennsylvania Department of Environmental Resources (PADER), Bureau of
Radiation Protection. Radon samples were collected from 989 private
individual groundwater wells by PADER personnel from 1985 to 1989.
Samples were collected from 48 of the 67 Pennsylvania counties although
only 12 counties had more than 20 samples. The most sampled counties
were located primarily in the southcentral and southeastern regions of
the state where radon in air is most prevalent. Samples were analyzed
using the liquid scintillation counting method (36) at the PADER Bureau
of Laboratories, Harrisburg, Pennsylvania. All samples were analyzed
twice with a median difference of 43 pCi/L (range 0 to 5,542 pCi/L).Data
analysesStatistical analyses were conducted using the SAS statistical
package. Data normality was tested using the Kolomogorov normality test (37). The Tukey multiple means comparison method (38) was used to
statistically compare lead, nitrate-N and radon data among geographic
regions and to correlate survey responses to lead and nitrate-N results.
Pearson correlation coefficients (r) were used for correlation of
nitrate-N results to land use data. All statistical tests were conducted
at the 95 percent confidence level.ResultsThe majority of samples from
the lead and nitrate-N survey originated from drilled wells (86%) with
smaller percentages from springs (9%), hand-dug wells (4%) and cisterns
(0.3%). Thus, 99.7 percent of the homes tested utilized groundwater for
their water source. All of the PADER radon samples originated from
groundwater wells. These results agree with 1980 census figures for
rural Pennsylvania water supplies (39). Virtually all (88%) of the
sources were constructed between 1950 and 1990 with similar numbers from
each decade. Wells were generally shallow (median = 120 ft.) but ranged
from |is less than~ 10 feet to 800 feet deep. Approximately half of the
homes (41%) had never had any water quality testing done prior to this
survey.LeadSurvey respondents indicated that 104 samples were not first
flush samples; consequently, only 1,351 samples were included in the
statistical analyses presented for lead. The distribution of lead
concentrations for these samples is shown in Figure 2. Eighty percent of
the samples had detectable amounts of lead (|is greater than~ 1
|mu~g/L). Approximately 28 percent of the samples were above the
proposed MCL (10 |mu~g/L), 19 percent were above the present action
level (15 |mu~g/L), and seven percent were above the previous MCL (50
|mu~g/L). The highest concentration sampled was 2,800 |mu~g/L with 26
samples above 100 |mu~g/L and nine samples above 200 mug/L.Lead
concentrations were similar among the six regions of Pennsylvania.
Median concentrations in each region ranged from 4 |mu~g/L to 10
|mu~g/L. Lead concentrations were significantly higher in southcentral
and southeastern counties despite previous studies which have reported a
lower incidence of corrosive groundwater in these regions (1). The
percent of samples above 10 |mu~g/L in each region ranged from 16 to 49
percent while four to 38 percent were above 15 |mu~g/L. These
percentages concur with regional median comparisons indicating similar
percentages among regions with slightly higher values in the
southcentral and southeastern regions.Significant differences in lead
concentrations were also observed between the various types of water
supplies. Springs and hand-dug wells had the highest median lead levels,
likely the result of the more acidic, corrosive nature of these
generally shallow water supplies (1). No correlation was observed
between drilled well depth or drilled well age and dissolved lead
concentrations.Corrosive water supplies may produce bluish stains and a
metallic taste as a result of dissolution of copper pipes in the
plumbing system. Since the copper pipes are often joined together with
lead solder, these symptoms may be good indicators of lead
contamination. In this study, homeowners noticing bluish stains had
significantly higher lead concentrations (12.5 |mu~g/L) compared to
those without this symptom (4 |mu~g/L). Homes with a metallic tasting
water also had significantly higher lead concentrations (8 |mu~g/L vs. 5
|mu~g/L). Attempts were also made to correlate high lead concentrations
to the occurrence of high blood pressure but no significant correlation
was observed.Dissolved vs. total leadThe relationship of digested
(total) lead concentrations to dissolved lead values for 126 samples is
shown in Figure 5. The resulting regression equation predicted a
difference between dissolved and total lead of six to 18 |mu~g/L within
the range of measurements (0 to 100 |mu~g/L). Although small, these
differences are significant when compared to the proposed lead MCL of 10
|mu~g/L. Use of dissolved rather than total lead could cause a
significant underestimation of homes at risk from chronic exposure to
low concentrations of lead. For example, 28 percent of the tested homes
had dissolved lead concentrations above 10 |mu~g/L and 19 percent were
above 15 |mu~g/L; however, these values increase to 60 and 34 percent,
respectively, when calculated total lead concentrations are used. These
data suggest that measurement of total lead is preferable to dissolved
lead even for generally clear, low turbidity groundwater
samples.NitratesOf the 1,583 water samples analyzed for nitrate-N, 9.4
percent were above the MCL of 10 mg/L and 30 percent were above 3 mg/L.
The 30 percent above 3 mg/L agrees remarkably well with the earlier USGS study of Pennsylvania groundwater wells (22). Although less prevalent
than lead, nitrates were much more regionally influenced. Median
nitrate-N concentrations were |is less than~ 1 mg/L in every region of
the state except the southcentral and southeast where they were
significantly higher at 2.18 and 11 mg/L, respectively. Regional
comparisons of contamination percentages illustrate that water supplies
above the nitrate-N MCL were nearly nonexistent in all regions except
the southcentral and southeastern. Ninety-six percent of the homes found
to have excessive nitrates were in the southcentral (25%) and southeast
(71%) regions. Not surprisingly, these regions also have the highest
percentage of intensive agricultural land use in Pennsylvania.Nitrate
concentrations were not strongly influenced by water supply type
although hand-dug wells did contain significantly higher concentrations
than other types. Wells with nitrate-N above 10 mg/L were significantly
shallower (100 vs. 125 ft.) and older (23 vs. 19 years) than those with
nitrate-N below 10 mg/L.Observed nitrate-N concentrations were
correlated with several agricultural land use variables. Homeowners were
asked to group their water supply into one of four distance categories
to the nearest cornfield. The distance to the nearest cornfield was used
as an indicator of agricultural impacts on groundwater nitrates since
corn crops typically receive large amounts of nitrogen fertilizer.
Median nitrate-N levels significantly increased as the distance to the
nearest cornfield decreased. Median nitrate-N concentrations for each
county were also positively correlated with percent agricultural land
use (r=0.57, p|is less than~0.0014) and pounds per acre of nitrogen
fertilizer used (r=0.82, p|is less than~0.0001).RadonThe distribution of
radon concentrations from the PADER survey is shown in Figure 8.
Approximately 78 percent of the samples were above the proposed MCL (300
pCi/L), 53 percent were above 1,000 pCi/L, and six percent were above
10,000 pCi/L. The highest concentration sampled was 141,270 pCi/L with
13 samples above 50,000 pCi/L.Although regional comparisons are limited
because of the skewed geographic distribution, the radon data are useful
nonetheless. The median radon concentration for all of the samples was
1,100 pCi/L with regional medians ranging from 187 to 2,555 pCi/L.
Significantly higher radon concentrations generally occurred in the
eastern regions of the state which agrees with the earlier study of
Dixon and Lee (29). The percent of radon samples above the proposed MCL
of 300 pCi/L in each region ranged from 52 to 88 percent for the four
regions with sufficient data. The highest percentages occurred in the
southeastern and southcentral regions which include the Reading Prong
and other radon producing geologic formations.It should be noted that
the skewed nature of the radon data set likely overestimates the
prevalence and magnitude of the problem on a statewide basis. Recent,
more representative data collected by the PADER suggest that the
groundwater radon problem is present in all regions of Pennsylvania but
is most severe in the southeastern portion of the state.Summary and
conclusionsBased on their prevalence and health effects, lead and radon
appear to be serious health threats to private individual water system
users in Pennsylvania. Twenty-eight percent of the tested private water
supplies contained dissolved lead concentrations above acceptable levels
and approximately 78 percent contained radon concentrations above the
proposed MCL. This translates into approximately 600,000 rural
Pennsylvanians exposed to excessive lead and over one million exposed to
dangerous radon concentrations in their drinking water. Lead
concentrations were similar among the six regions of Pennsylvania with
the highest values occurring in the southeastern region of the state.
Radon concentrations tended to be higher in the eastern portion of the
state near the Reading Prong geologic formation. The occurrence of lead
contamination from corrosion of plumbing components should decline in
the future as new lead-free plumbing replaces leaded components and as
water systems with leaded components age. Lead in drinking water,
however, still represents a very clear health threat to rural
Pennsylvanians which needs to be addressed in rural health programs.
Because radon is a naturally occurring problem, it will always be a
problem in groundwater supplies from certain geologic
formations.Digestion and analysis of total lead on 126 samples increased
dissolved lead values by six to 18 |mu~g/L These differences are large
in comparison to the proposed MCL of 10 |mu~g/L, strongly suggesting
that total lead should be analyzed even for relatively clear, low
turbidity groundwater sources.Nitrate-N was a less common problem than
lead or radon with only nine percent of samples above the existing MCL.
However, thousands of rural Pennsylvania children under six months of
age may be exposed to dangerous levels of nitrate in their drinking
water. Virtually all of the samples with high nitrate-N originated from
the agricultural southcentral and southeastern regions of the state. It
is anticipated that the incidence of nitrate contamination of
groundwater in Pennsylvania will decline in the future in response to
reduced use of nitrogen fertilizers and better animal waste management
on farms.References1. Sharpe, W.E., D.W. Mooney and R.S. Adams (1985),
An analysis of groundwater quality data obtained from private individual
water systems in Pennsylvania, Northeast. Environ. Sci.
4(3/4):155-159.2. Francis, J.D., B.L. Brower, W.F. Graham, O.W. Larson
III, J.L. McCaull and H.M. Vigorita (1983), National statistical
assessment of rural water conditions, Dept. of Rural Sociology, Cornell
University, Ithaca, NY, 1900 pp.3. U.S. Environmental Protection Agency
(1986), Air Quality Criteria for Lead, NTIS PB87-142410.4. Ryu, J.E.,
E.E. Ziegler, S.E. Nelson and S.J. Fomon (1983), Dietary intake of lead
and blood lead concentration in early infancy, Amer. J. Diseases of
Children 137(9):886-891.5. Centers for Disease Control (1991), U.S.
Department of Health and Human Services, Public Health Service.
Preventing Lead Poisoning in Young Children, 108 pp.6. U.S.
Environmental Protection Agency (1988), Relationship between infant
blood lead concentration and lead in water or liquid diet (draft
report). Prepared by A. Holtzamn and A. Marcus. Battelle - Columbus
Division. EPA Contract No. 68-02-4246.7. U.S. Environmental Protection
Agency (1986), Safe Drinking Water Act Amendments. EPA-570-986-002.8.
Lee, R.G., W.C. Becker and D.W. Collins (1989), Lead at the tap: Sources
and control. J. AWWA 81(7):52-62.9. Schock, M.R. (1985), Treatment or
water quality adjustment to attain MCLs in metallic potable water
plumbing systems. Plumbing Materials and Drinking Water Quality:
Proceedings of a Seminar. EPA-6-600/9-85/007.10. Moore, M.R. (1973),
Plumbosolvency of waters. Nature 243(5404):222-223.11. U.S. Public
Health Service (1988), Toxicological Profile for Lead. Agency for Toxic
Substances and Disease Registry, Atlanta, GA.12. U.S. Environmental
Protection Agency (1991), Final Lead Rule, National Primary Drinking
Water Regulation. Task Force on Lead in Drinking Water, Office of
Drinking Water, Washington, D.C.13. U.S. Environmental Protection Agency
(1986), Reducing lead in drinking water: A benefit analysis.
EPA-230-09-86-019.14. Pennsylvania Plumbing System Lead Ban and
Notification Act (1989), Act No. 1989-33. 35 P.S. |sec~ 723.1.15.
Environmental Reporter (1991), The Bureau of National Affairs, Inc.,
Washington, D.C. November 1, pp. 1651-1652.16. Hallberg, G.R. (1986),
From hoes to herbicides: agriculture and groundwater quality. J. Soil
and Water Cons. 41 (6):357-364.17. Makuch, J. and J.R. Ward (1986),
Groundwater and Agriculture in Pennsylvania. Circular No. 341.
Pennsylvania State University. College of Agriculture, Cooperative
Extension. 21 pp.18. Hallberg, G.R., R.D. Libra and B.E. Hoyer (1985),
Nonpoint source contamination of groundwater in Karst-carbonate aquifers in Iowa. In: Perspectives on Non-point Source Pollution. EPA 440/5
85-001. Washington, D.C. pp. 109-114.19. Fraser, P. and C. Chilvers
(1981), Health aspects of nitrate in drinking water. Sci. Total.
Environ. 28:103-116.20. Terblanche, A.P.S. (1991), Health hazards of
nitrate in drinking water. Water SA 17(1):77-82.21. Exner, M.E. and R.F.
Spaulding (1974), Groundwater quality of the Central Platte region.
Resource Atlas No. 2. Cons. and Surv. Div., University of Nebraska at
Lincoln. 48 pp.22. U.S. Geological Survey (1984), National water summary
1984: Hydraulic events, selected water-quality trends, and ground-water
trends, and ground-water resources. United States Government Printing
Office, Washington, D.C. pp. 95-97.23. Crawford-Brown, D.J. (1992),
Cancer risk from radon, J. AWWA 84(3):77-81.24. U.S. Environmental
Protection Agency (1991), Proposed Revisions in USEPA Estimates of Radon
Risks and Associated Uncertainties. Unpublished report.25. U.S.
Environmental Protection Agency (1985), Nationwide occurrence of radon
and other natural radioactivity in public water supplies.26. Gesell,
T.F. and H.M. Prichard (1978), The contribution of radon in tap water to
indoor radon concentrations. Proc. Sym. Natural Radiation Envir. III,
U.S. Department of Energy Conference.27. U.S. Environmental Protection
Agency (1991), National Primary Drinking Water Regulations:
Radionuclides; Proposed Rule. Fed. Reg. 56:138.28. Hess, C.T., J.
Michel, T.R. Horton, H.M. Prichard and W.A. Coniglio (1985), The
occurrence of radioactivity in public water supplies in the United
States. Health Physics 48(5):553-586.29. Dixon, K.L. and R.G. Lee
(1988), Occurrence of radon in well supplies, J. AWWA 80(7):65-70.30.
Lowry, J.D. and S.B. Lowry (1988), Radionuclides in drinking water, J.
AWWA 80(7):50-64.31. Bacon, A.P.C., K. Froome, A.E. Gent. T.K. Cooke and
P. Sowerby (1967), Lead poisoning from drinking soft water, Lancet
i:264-266.32: Moore, M.R. (1977), Lead in drinking water in soft water
areas -- Health Hazards, Sci. Total Environ. 7:109-115.33. Worth, D., A.
Matranga, M. Lieberman, E. De Vos, P. Karalekas, C. Ryan. G. Craun
(1981), Lead in drinking water: The contribution of household tap water
to blood lead levels. Environmental Lead, Lynam, D.R., L.G. Piantanida
and J.F. Cole, eds. Academic Press, New York. NY.34. Benson, J.A. and H.
Klein (1983), Lead in drinking water: Investigation of a corrosive water
supply. J. Env. Health 45(4):179-181.35. U.S. Environmental Protection
Agency (1983), Methods for chemical analysis of water and wastes. U.S.
EPA, Environ. Monitor. Support Lab., Cincinnati, OH. EPA
600/4-79-020.36. Lowry, J.D. (1991), Measuring low radon levels in
drinking water supplies, J. AWWA 83(4):149-153.37. SAS Institute Inc.
(1985), SAS User's Guide: Statistics. Version 5 Edition. Cary, NC.
957 pp.38. Neter, J., W. Wasserman and M. H. Kutner (1985), Applied
Linear Statistical Models, Second Edition. Richard D. Irwin. Inc.,
Homewood. IL. 1,127 pp.39. U.S. Census Bureau (1980), Pennsylvania
Housing Census, Table 94: Equipment and Plumbing Facilities for
Counties.Bryan R. Swistock, The Pennsylvania State University, 132 Land
and Water Research Building, University Park, PA 16802.
Printer friendly
Cite/link
Email
Feedback