Recommendations
The combination of the two literature searches, field
and laboratory, should provide a reasonable basis for estimation of
changes in microbiota concentrations that may be expected during ASR
storage of treated surface water. The laboratory investigations indicate
a range of attenuation rates for pathogenic bacteria, typically 1 to
30 days per log cycle at temperatures exceeding 20°C, which are
reasonably representative of Florida conditions. Most of the results
suggest that 5 days per log cycle is representative. Exact attenuation
mechanisms and their interrelationships will require further research.
However, it seems clear that natural attenuation of microbiota occurs
during ASR storage, as simulated under laboratory conditions and as
confirmed under field conditions.
Controlled conditions in the laboratory approximate those in the field;
however, they cannot replicate the heterogeneity and complexity of natural
aquifer systems. Natural geochemical processes; seasonal variations
in salinity; ambient, naturally occurring microbiota in the aquifer;
nutrient sources; oxidation-reduction reactions; and other factors that
are difficult to replicate in the laboratory can have a significant
effect upon water quality changes during ASR storage, including microbiota
concentrations. For these reasons, field investigations cannot be controlled
as carefully as those conducted in the laboratory, reflecting varying
climatological conditions, site-specific geology and mineralogy, surrounding
land use effects upon recharge water quality, and other factors. Field
investigations are more costly to perform and come from a broad array
of data sources under widely differing conditions. Nevertheless, they
provide a valuable, independent source of information on this subject.
Further ASR field investigations are needed in Florida to confirm the
results of the laboratory literature search and to supplement the field
investigations for which data are already available. Ideally, these
should be conducted under field conditions matching those proposed for
the Comprehensive Everglades Restoration Program (CERP) in Florida,
and other sites. Until such time as field investigations can be conducted
in ASR wells that are recharging treated surface water containing microbiota,
and data sets can be developed at multiple sites for comparison, we
can only rely upon field and laboratory literature search results such
as those presented above.
The three ASR demonstration projects for the CERP will not be obtaining
these data as currently planned, since they will be recharging water
that has been treated to meet all drinking water standards, including
those for microbiota. Either those projects can be modified to include
testing of recharge with treated surface water containing microbiota,
or new ASR demonstration projects could be authorized that obtain such
data at other sites. Comparable testing is underway for the St. Johns
River Water Management District at selected urban drainage well sites.
A suggested 10-step approach for moving forward with ASR field investigations
is as follows:
1. Identify indicator pathogenic microbiota that are pertinent to proposed
ASR operations in Florida, and associated ranges of temperature and
salinity conditions. Those microbiota considered in the Literature Search
are considered reasonable indicators, based upon input from a technical
advisory committee representing numerous state and federal agencies
and public interest groups. However, it is always possible that other
indicators of interest will become evident in the future.
2. From the literature searches, estimate a reasonable range of attenuation
rates (expressed in days/log cycle) for all of these indicator microbiota,
without biasing the results with obvious outlier data. A suggested approach
would be to select the middle half of the range from all the data sets.
3. Select the upper end of this range and determine the number of days
per log cycle attenuation rate that encompasses all indicator pathogenic
bacteria deemed to be of concern.
4. Select the number of log cycles of microbiota attenuation that is
deemed necessary to adequately protect groundwater quality and public
health, based upon available data for naturally occurring concentrations
of these pathogenic microbiota in source waters during representative
recharge periods. Tentatively, it is suggested that three log cycle
attenuation should be ample. Source water monitoring at ASR sites should
be implemented to prevent recharge at times when severe algal blooms
may overload treatment processes.
5. Calculate the travel time radius around each ASR well by multiplying
the number of log cycles of attenuation by the number of days required
for each log cycle, in steps 3 and 4 above. For example, 30 days per
log cycle times 3 log cycles would suggest the need for a 90-day travel
time radius around an ASR well, within which natural treatment processes
would be deemed to occur. It is pertinent to note that most ASR storage
is for months to years, so the duration between end of recharge and
beginning of recovery will normally be sufficient to achieve the desired
attenuation. A much longer time period would occur between the beginning
of recharge and the end of recovery for a typical operating cycle.
6. Estimate the theoretical radius associated with recharge for the
target travel time, at the recharge flow rate for the well. For example,
a 5-million gallon per day (MGD) well recharging for 90 days would have
a treatment radius associated with a storage volume of 450 million gallons
(MG). If the aquifer is 400 feet thick, and has an estimated bulk porosity
of 20 percent, the theoretical treatment radius would be 489 feet. To
account for aquifer heterogeneity and anisotropy, a buffer zone could
be provided. This distance could be increased by approximately 50 percent,
yielding a compliance zone of about 750 feet.
7. Measure compliance with primary standards for microbiota at a radial
distance of 750 feet from the ASR well. An observation well would be
constructed at or close to this radius for the demonstration program
at each site.
8. Seek Florida Department of Environmental Protection (FDEP) authorization
for proposed testing, and measurement of compliance at the edge of the
compliance zone, within existing regulations and policies. If FDEP is
unwilling to move forward without the benefit of ASR legislation, introduce
legislation during the 2003 legislative session to provide for ASR demonstration
projects at up to nine sites, approximately three in each water management
district.
9. Provide both bank filtration and UV disinfection
treatment for surface water ASR demonstration facilities. At groundwater
and reclaimed water ASR demonstration sites, provide UV disinfection.
At most surface water sites, bank filtration should be technically feasible
and will reduce or eliminate the generation of a residuals flow stream.
At any sites where existing surficial aquifer soils are inappropriate
for bank filtration, consider providing a constructed bank filtration
system, including imported permeable materials, or relocating the site.
Note that bank filtration systems would be designed to achieve pathogenic
microbiota attenuation and may therefore typically operate at lower
unit yields (gallons per minute per foot of horizontal well length)
compared to conventional horizontal well intake systems. The two treatment
processes would be designed in series to achieve overall 3 log cycle
reduction in pathogenic microbiota, or whatever other target log cycle
reduction is selected. At an appropriate point during the test program,
the UV disinfection system at each site would be bypassed, allowing
ASR recharge of treated surface water from the bank filtration system
without subsequent disinfection.
This conservative approach is designed to elicit public
and regulatory agency support. It is a close parallel to the approach
followed by SFWMD, FDEP and EPA to address the same issues at the Lake
Okeechobee ASR Demonstration Test Well at Taylor Creek/Nubbin Slough
in 1991. At that time, substantial additional funds were spent to provide
chlorine disinfection facilities and adequate detention time in a constructed
new reservoir on the site; however, the early data from cycle testing
showed that these facilities were not needed for coliform bacteria attenuation
since that occurred rapidly in the aquifer. Criteria and issues have
changed since then, yet the approach is still valid. This will increase
the cost of the ASR demonstration programs; however, by hopefully regaining
public and regulatory agency support for the data collection program,
it should be possible to gather data that can lead to substantial subsequent
savings.
10. Seek leadership to achieve authorization for the
demonstration testing, whether through legal or regulatory measures,
and to implement whatever subsequent legal, regulatory and policy changes
are then deemed appropriate. This is most likely to come from the regulated
community, working closely with FDEP and the Water Management Districts.
AWWA(FS) support for such an effort would be helpful.
Information is
requested regarding additional sources of information regarding the
fate of microbiota during ASR storage, or related processes in which
water moves through an aquifer from a well or sinkhole. Information
from either field or laboratory investigations would be of value. Such
information should be sent to the following address:
R. David G. Pyne,
P.E.
ASR Systems, LLC
POB 969
Gainesville, Florida 32602, U.S.A.
540 NE 5th Avenue,
Gainesville, Florida 32601, U.S.A.
Phone: 352-336-3820
Cell: 352-215-0319
Fax: 352-373-2381
Email: dpyne@asrsystems.ws
Information provided
will be evaluated by a panel comprised of representatives of several
state and federal agencies. At such time as the peer review is completed
satisfactorily, the information will be added to this web site.
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