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For more information,
contact David Eppstein by email at
deppstein@masco.harvard.edu,
or by calling 617-632-2860.
9.0 SAMPLING
The validity of results from any laboratory testing is dependent
upon the sample being representative of the source from which
it was taken. It is the operator's responsibility to see that
all personnel who might participate in the sampling program be
personally instructed as to the appropriate sample techniques.
The two types of samples taken for wastewater laboratory analyses
are known as grab samples and composite samples, and each can
be obtained either manually or automatically.
A grab sample is an individual sample which is taken from a wastestream
on a one-time basis without regard to the flow in the wastestream.
These samples must be collected over a period of time not exceeding
15 minutes. A grab sample shows the wastestream characteristics
at the time the sample is taken.
A composite sample is a combination of individual samples of wastewater
taken at pre-selected intervals to represent the integrated composition
of a wastestream. A composite sample is always to be collected
over the entire process day ( or as close to it as possible).
Although the MWRA's regulations 360 CMR 10.00 requires at least
8 grab samples to make up a composite sample, it does not follow
that 8 samples taken over a time period of 2 hours for an industry
that discharges for 8-24 hours is acceptable. In all cases, even
if it is necessary to overlap calendar days, the composite must
cover the entire process day. The daily average limit, the highest
allowable concentration for any pollutant in a wastestream discharged
during one day by an industrial user, is based upon a representative
composite sample.
A composite sample can be prepared proportionally according to
time or flow. A composite sample based on time can be obtained
if the flow of the wastestream is relatively constant over the
entire time period, even though the wastestream characteristics
may change. In this case, equal amounts of each individual sample
can be combined into one composite sample. To prepare a flow-weighted
composite sample, each individual sample is combined with the
others in proportion to the volume of flow at the time the sample
was collected.
Permit sampling shall be representative of the typical volume
and nature of the permittee's discharge. The sample must be taken
at a location, permitted by the MWRA, that is free of any uncontaminated
water, sanitary waste or other non-process water. These samples
shall be collected, preserved and handled in accordance with the
procedures established in 40 CFR Part 136 and amendments. When
performing permit sampling, it is important to review your discharge
permit for the correct sample type. Each individual pollutant/parameter
requires either a grab or composite sample. A mercury sample
obtained via composite sampling at an MWRA permitted discharge
location during a representative discharge event at a location
free of any uncontaminated water, sanitary waste or other non-process
water is an example of a reportable sample under the MWRA's SMART
program (See Section 9.3 for SMART definition).
The results of analysis of representative samples obtained beyond
the requirements of an institution's discharge permit, for any
pollutant/parameter being discharged, using test procedures prescribed
in 40 CFR Part 136 or other United States Environmental Protection
Agency (EPA) approved methods, are required to be submitted to
the MWRA.
Samples obtained outside of these requirements are not representative
and should not be submitted to the MWRA as SMART data. Mercury
results of a grab sample obtained or those from a non-permitted
MWRA sampling location may be an example of a non-SMART reportable
result. The results are non-reportable because the sample was
obtained via a grab sample and at a non-permitted location. Appendix
F contains a copy of a letter from Mr. Eugene B. Benson, Associated
Counsel for MWRA, TRAC to Mr. Robert K. Gingras, Senior Project
Manager for EARTH TECH (formerly HMM Associates) clarifying when
to and when not to submit sampling data.
When performing sampling, it is important to establish a set of
standard operating procedures. This will allow a facility to
obtain representative samples repeatedly. Presented in Appendix
A is a copy of the MWRA's Standard Operating Procedures (SOP)
from their sampling manual. It would be advantageous to develop
a SOP very similar to the MWRA's
It is important to clarify the difference between SMART and NON-SMART
reporting requirements. Self-Monitoring Analytical Report Tracking
(SMART) is a program the MWRA has provided to all DEP Certified
Laboratories. The SMART program generates both a computer diskette
containing the sampling analysis results and a paper copy of the
information on the diskette. The MWRA enters the results from
the diskette into its computer system and retains the paper copy
in the permittee file.
A summary of the MWRA's permit sampling requirements are as follows:
- Sampling must be performed by a DEP certified independent laboratory
unless otherwise approved by the MWRA.
- All analytical testing must be performed at a DEP certified independent
laboratory. A listing of Massachusetts certified independent
laboratories is presented in Appendix B.
- The appropriate sampling technique must be used (i.e. grab or
composite) and the sample field preserved.
- The sample must be analyzed within allowable holding times using
EPA approved methods.
- Samples must be taken at the permit prescribed sampling location,
or at another representative location after pretreatment.
- Samples taken at another representative location for non-permitting
purposes must also be reported using SMART program.
Refer to the copy of Mr. Eugene Benson's letter presented in Appendix
F and your current MWRA permit for additional SMART data reporting
clarification.
The MWRA has developed and published written standard sampling
port guidelines for its permitted Industrial Sewer Users. Figure
9.1 and 9.2 illustrates a detailed cross section and elevation
view of a standard sampling port developed by Flow-Tech Associates,
Inc., on behalf of the MWRA Infrastructure Subcommittee, and presented
to the MWRA for approval. The MWRA has approved and prefers this
"Typical" design set-up, but this is not the only type
of sampling port that is approved by the MWRA.
The sampling port, in most instances and especially during low
flow situation, is only designed for a single sampler. Sampling
locations that are equipped with single sampling port are to be
used on a first come first serve basis. Example:
Self-monitoring sampling has begun and the MWRA shows up to perform
their required unannounced sampling. If an institution has
already begun sampling, prior to the MWRA's arrival, the MWRA
would be obligated to reschedule their sampling. The MWRA would
not force an institution to terminate its sampling to fulfill
their own sampling requirements. Although it is possible to have
a dual sampling port at the same location it is strongly discouraged
for the following reasons:
- During low flow situations, composite samplers would be competing
with each other for wastewater samples.
- During moderate to high flow conditions, there may be sufficient
flow for dual sampling but, when using automated composite sampling
equipment, there is a back flushing step that the sampler goes
through before and after a discrete sample is obtained. A potential
problem would result when one sampler is backwashing while the
other sampler is drawing a sample. The net effect would be one
sampler sampling the other sampler's backwash.
Both of these issues are variables which will effect the quality
of the sample and produce non-representative data. These are
sampling conditions that should be avoided.
Figure 9.1 Standard MWRA Sampling Port (Cross Section View)
Source: Flow Tech Associates, Inc., Detail 1A
Figure 9.2 Standard MWRA Sampling Port (Elevation View)
Source: Flow Tech Associates, Inc., Detail 2B
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