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Mercury
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Phase II Reports >> Facilities Loadings
Facilities Loadings
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For more
information, contact David Eppstein by email at
deppstein@masco.harvard.edu,
or by calling 617-632-2860.
3.0 STUDY ASSUMPTIONS AND METHODOLOGY
The members of the Facilities Loadings Subgroup agreed that:
1. Clinical Laboratories
2. Incinerators (medical waste)
3. Laundries (hospital)
4. Other (college laboratories, laboratory suppliers, steam suppliers, pharmaceutical
manufacturers, and various testing laboratories)
5. Research Laboratories (medical and biotech)
We chose these types of facilities for the study because we believed
that their operations and discharges would be similar to those of hospitals. We selected
the facilities manually by reviewing a list of all currently MWRA-permitted industrial
dischargers. The final list of selected facilities consisted of 242 facilities.
We would attempt to accurately estimate wastewater discharge flow at
each sampling location within the 242 selected facilities by using a questionnaire that
would be mailed to the facilities. For any sampling locations having a wastewater flow
meter, we would use averaged metered flow rates as shown in questionnaire responses. For
other sampling locations in clinical, research or other laboratory facilities, we would
use a discharge flow model. To obtain input into this model, we would ask in the
questionnaire for numbers of fixtures (defined as laboratory sinks and fume hood (cup)
sinks), numbers of glass washers and photoprocessors, and estimated flow contributions of
discharges from water treatment systems, non-contact cooling water uses, and sanitary
wastewater sources. We could also use the indicated sizes of final pH adjustment or
limestone chip tanks in our model.
To simplify the questionnaire and the study, we would ask only for
current facility configuration information. As a result, we would assume that our
estimated wastewater discharge flow for each sampling location was fixed over our study
period.
For non-respondents to our questionnaire, we would use the discharge
flow estimates (provided by the facilities) that appeared in MWRA permitting and
inspection records. In addition, we would use the questionnaire responses to help us
allocate each identified sampling location into the proper group: Clinical, Incinerator,
Laundry, "Other," or Research. We found that several larger facilities had
multiple sampling locations belonging to two or more of the five study groups.
- MWRA-collected discharge samples tested by an MWRA-contracted
analytical laboratory or by the MWRA Central Laboratory both of which are certified by the
Massachusetts Department of Environmental Protection (MADEP).
- Self-monitoring discharge samples tested by contract analytical
laboratories certified by the MADEP. (These laboratories electronically report their test
results to the MWRA).
We would use a two-year study period corresponding to MWRA fiscal
years 1995 and 1996, i.e., July 1, 1994 to June 30, 1995 and July 1, 1995 to June
30, 1996, respectively. Fiscal Year 1995 was included in the Phase I study of 29
hospitals. To observe any trends in discharged mercury concentrations from the entire 242
facilities of this study and from the 29 Phase I hospitals, we would break the study
period into four half-year intervals.
For each sampling location, we would calculate average concentrations
of mercury over each half-year interval from available discharge sampling concentration
data. For sample results having non-detect values, we would do two calculations. We would
estimate a minimum average mercury concentration when we set all individual
non-detect values equal to 0.0 micrograms per liter (µg/L). The concentration units of
µg/L are often called "parts per billion" (ppb).
Then, we would estimate a maximum average mercury concentration
when we set all individual non-detect values equal to the stated detection limits
(typically, 0.2 to 1.0 µg/L (ppb)). In this way, we could find a range of possible
discharge mercury concentration averages for each sampling location to provide insight
into expected accuracy of our calculations.
To help show the extent and quality of the analytical test database,
we would examine the numbers of sample test results contributing to the individual
half-year mercury concentration averages in each half-year interval at each sampling
location. We found that the numbers of samples varied from one sample to 28 samples. The
number of samples at a sampling location depended upon specific permit requirements for
self-monitoring and MWRA monitoring schedules. Clearly, for a particular sampling
location, more representative half-year mercury concentration averages would be derived
from larger numbers of sample test results.
For each sampling location, we would calculate two mercury discharge
mass loading averages for each half-year interval by multiplying our fixed wastewater
discharge flow estimate by the corresponding minimum and maximum mercury concentration
averages. Then, we would allocate and sum the individual discharge mass loading averages
to find overall mercury loadings discharged from each of the five groups of facilities.
For sampling locations that had no test data for mercury, we would
calculate "group average" half-year discharge mercury concentrations from all
available data within each study group. Then, to estimate the individual half-year mercury
discharge loadings from sampling locations without specific mercury test data, we would
multiply the proper group average mercury concentrations by the individual discharge flow
estimates.
We would then sum all mercury discharge loadings by study group and
compare the group totals against available MWRA estimates of total industrial and
system-wide mercury loadings.
Lastly, extracting applicable data from the above loadings
calculations, we would review mercury discharge loadings for the 29 Phase I hospitals to
compare our study results with the June 1995 Phase I findings and to observe any
subsequent changes.
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