**Field and laboratory investigations into the transport potential of
*Cryptosporidium parvum* oocysts in karstic limestone of the Biscayne
aquifer at a municipal well field (Northwest Well Field, Miami, FL):
impact on oocyst log unit removal estimations**

[David W. Metge^1^]{.underline}, Ronald W. Harvey, Allen M. Shapiro,
Robert A. Renken, Christina L. Osborn, Joseph N. Ryan, and Kevin J.
Cunningham

> ^1^ U.S. Geological Survey
>
> Boulder, CO

The pathogen, *Cryptosporidium parvum*, and its potential to contaminate
domestic water supplies have come under increasing scrutiny. A
large-scale, forced-gradient injection and recovery test was performed
to assess the fate and transport of oocysts within karst limestone flow
zones and to address vulnerability of the Northwest Well Field (NWWF) to
contamination by *C. parvum* oocysts. The Northwest well field,
Florida's largest, is located east of the Everglades within the Lake
Belt mining district of north-central Miami-Dade County. Municipal
supply wells are more likely to be directly influenced by surface water
if extraction activities continue as proposed.

Field-scale use of pathogenic microorganisms within the prolific
Biscayne aquifer, a sole drinking water source aquifer, was not
considered appropriate; therefore, differentially sized and colored
fluorescent microspheres (FMS) were used as surrogates. The field study
involved introduction to the Biscayne aquifer of a conservative tracer
(SF6 gas) and oocyst-sized (\~ 2-5 μm diameter) carboxylated polystyrene
microspheres. Fractional recoveries for microspheres 100 m downgradient
were inversely related to their diameter; recoveries ranged from 2.8%
for the largest to 5.6% for the smallest size classes. Peak breakthrough
of all microsphere sizes occurred at 6.75 hours after injection,
although the first appearance of the 1.6 µm-sized microspheres preceded
the larger-sized FMS by approximately 2 hours.

A series of flow through column tests were performed using intact
Biscayne aquifer limestone core material obtained from the injected flow
zone. Laboratory results suggest that 2.9-4.9 μm (diameter) microspheres
underestimate the transport potential of 3.1-4.2 μm (diameter) oocysts
by 4-6 fold. This may be because zeta potentials for microspheres are
more negative than *C. parvum* oocysts at equivalent ambient pH (8.4).
Several hundred meters of transport may be required to achieve a 1-log
unit removal of oocysts at the NWWF, depending upon local aquifer
heterogeneity.

Riverbank Filtration of *Cryptosporidium, Giardia*, and other Microbial
Indicators, Platte River, Nebraska

[Jason R. Vogel^1^]{.underline}, Stephanie Harris, Eugene Rice, and
Jerry Obrist

^1^U.S. Geological Survey

Lincoln, NE

Riverbank filtration has been used for centuries to partially purify
riverine drinking source water for safe consumption. However, recent
efforts to protect against such waterborne pathogens as Cryptosporidium
and Giardia mandate quantification of riverbank filtration efficiency so
that drinking-water systems can receive regulatory credit for this
natural removal mechanism. Because Cryptosporidium and Giardia are
commonly present in river water, ineffective removal by riverbank
filtration could result in increased health risks. Methods to detect
Cryptosporidium and Giardia can be unreliable and cost prohibitive
relative to tests for traditional fecal-indicator microbes. Due to the
imprecision and high detection limits in Cryptosporidia and Giardia
methods, failure to detect these protozoa in samples does not ensure
their absence in the relevant water volumes of drinking-water.
Correlation of water-quality indicators to the detectable presence of
Cryptosporidium and Giardia may lead to increased reliability and
decreased cost relative to direct detection of these waterborne
pathogens.

A study was recently completed by the U.S. Geological Survey, in
cooperation with the City of Lincoln and the U.S. Environmental
Protection Agency, to evaluate the potential for transport of
microorganisms of varying sizes through riverbank filtration to a
public-water supply at the Platte River near Ashland, Nebraska, during
different seasons and flow regimes. Representative samples were
collected during surface water base-flow conditions and significant
runoff events from the Platte River near Ashland, one collector well,
treatment plant influent, and treated drinking water. The temperature,
dissolved oxygen concentration, specific conductance, pH, and turbidity
of these samples were measured in the field. Samples were analyzed at
various laboratories for concentrations of *Cryptosporidium* and
*Giardia*, dissolved organic carbon, hydrogen and oxygen isotopes, total
coliform bacteria and *E. coli*, aerobic spores, algae, diatoms, and
male-specific and somatic coliphages, and for total particle counts in
various size ranges.

Initial results indicate no detectable breakthrough of *Cryptosporidium*
or *Giardia* into the collector well during the sampling times. Analysis
of microbial indicator concentrations across the riverbank filtration
zone indicates removal efficiencies of up to four or five logs.
Statistical analysis also indicated that the presence of
*Cryptosporidium* or *Giardia* in the Platte River at the research site
may be predicted from other water quality characteristics using
logistical regression techniques.

**Preliminary Occurrence Study of Algal Toxins in Source and Finished
Waters**

[James Sinclair, PhD]{.underline}, Ben Southwell, and Judy Westrick

Office of Water

U.S. Environmental Protection Agency

The United States Environmental Protection Agency 1998 Contaminant
Candidate List contained freshwater algae and their toxins. Contaminants
on this list must be prioritized according to the human health risk
determined from frequency of occurrence, removal efficiency in
conventional and unconventional drinking water treatment processes, and
health effects. In order to better focus their resources, the USEPA
created a short priority list of algal toxins based on their best
estimates of the frequency in surface waters and toxicity. The priority
list contains five hepatotoxins, four adducts of microcystin (LR, RR,
LA, YR) and cylindrospermopsin, and a neurotoxin, anatoxin-a. The goal
of this project was to design and perform a preliminary occurrence study
focused on the monitoring of source and finished waters for potential
toxin producing cyanobacteria and their toxins at drinking water
utilities with notable summer algae blooms. The two summer (2001 and
2002) studies consisted of weekly source and finished water sampling.
Algal identification/enumeration, quick screening assays and advanced
analytical (HPLC-MS) methods were performed so that data could be
reviewed within the World Health Organization model for monitoring and
management of cyanobacteria in drinking water supplies. In the WHO model
algal identification/enumeration of potential algal toxin producing
genera is used as an early warning surrogate.

In the 2001 study, algal identification/enumeration was performed on ten
source waters; ten source and finished waters were screened for
microcystin by commercially available ELISA kits. All source and
finished water microcystin concentrations were below the detection limit
0.2 μg/L. Fourteen out of 76 source samples had more than 500 algal
units of potential microcystin and anatoxin-a producing genera. These
samples screened negative for anatoxin-a by GC/MS and where below the
LC/MS detection limits of 1μg/L for both microcystins and anatoxin-a. In
the 2002 summer study, algal identification/enumeration and the
microcystin screen were performed on both source and finished waters.
During this study, several source water samples tested positive for
microcystin, but the finished water samples tested negative.
Cyanobacteria algal unit removal was at least 99.9% with conventional
treatment; *Aphanizomenon* was the most frequently reported algae in
finished waters. Archived samples with more than 10 cyanobacteria algal
units per mL are being analyzed for microcystins and cylindorspermopsin
levels.

In summary, after two summers of algal monitoring 7% of the source
waters tested positive for microcystin, however only 1% of these source
waters were above the finished water World Health Organization daily
exposure guidelines. There were no instances where algal toxins where
detected in finished water. These limited results suggest that the
drinking water treatment processes that are currently online are
effective at removing the priority toxins monitored in this study.

Environmental factors and chemical and microbiological constituents
related to the presence of viruses in ground water from small public
water supplies in southeastern Michigan

[Donna S. Francy^1^]{.underline}, Rebecca N. Bushon, Emma J. Luzano, and
G. Shay Fout

^1^U.S. Geological Survey

Columbus, OH

Thirty-eight public ground-water-supply wells serving fewer than 3,300
people were sampled from July 1999 through July 2001 in southeastern
Michigan to determine (1) the occurrence of viral pathogens and
microbiological indicators, (2) the adequacy of indicators as predictors
of the presence of viruses, and (3) the factors that affect the presence
of viruses. Samples were analyzed for enteric viruses by reverse
transcriptase-polymerase chain reaction (RT-PCR), for culturable viruses
by cell culture, and for the following indicators: total coliforms, E.
coli, enterococci, and F-specific and somatic coliphage. Ancillary
environmental and water-quality data also were collected.

A total of 169 regular samples and 32 replicate pairs were collected
from 38 wells. Each well was sampled from one to five times. By use of
RT-PCR, enterovirus was found in four wells (10.5 percent) and hepatitis
A virus (HAV) in five wells (13.2 percent). In two of these wells,
investigators found both enterovirus and HAV, but on different sampling
dates. Analyses for Norwalk virus, reoviruses, and rotaviruses by RT-PCR
in a subset of samples gave negative results. Culturable viruses were
found once in two wells (5.9 percent), but neither of these wells was
positive for viruses by RT-PCR on any sampling date. Of the 38 wells, 9
(23.7 percent) were positive for viruses by either RT-PCR or cell
culture.

One or more indicators were found in 18 of 38 wells. Total coliforms, E.
coli, enterococci, and F-specific and somatic coliphage were found in
34.2, 10.5, 15.8, 5.9, and 5.9 percent, respectively, of the wells
tested. Only three of the indicator-positive wells were positive for an
indicator on more than one date at the same well. Five out of nine (55.6
percent) virus-positive wells were also found to be positive for an
indicator. Two wells with detections of viruses had a detection of total
coliforms, one well had a detection of E. coli, one of enterococci, and
one of F-specific coliphage.

More virus-positive samples were found at sites served by septic systems
than those served by sewerlines. Sampling condition (ground water or a
mixture of tank and ground water), distance to septic system, type of
and distance to nearest surface-water body, well characteristics, or
land use were not related to the presence of viruses or indicators.
Statistically significant relations were found between total coliforms
and dissolved organic carbon, iron, or chloride concentrations. Presence
of nitrate was related to presence of E. coli, enterococci, coliphage,
or enteric viruses but not to total coliforms.

This study provides evidence for fecal contamination of ground water at
small public-supply wells and shows the importance of collecting
multiple samples at each site. The study also suggests that the
collection of site-characteristic data, data on multiple water-quality
parameters and data on microbiological indicators are important for
making better predictions of the presence of enteric viruses in small
public water systems. Future data collection toward this end could
include repeat sampling several times a year for different indicators,
measuring dissolved organic carbon, nitrate plus nitrite, and/or
chloride concentrations.

*Although this work was reviewed by EPA, it may not necessarily reflect
official Agency policy.*