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This page is continued from Steps 9 & 10 of Phase III. This page includes Step 11-sections A & B.
A. Chain of Custody Procedures
B. Collection of Surface Water Samples
C.
Collection of Ground Water Samples
D.
Measuring Total Alkalinity, Bicarbonate and Carbonate
E.
Handling Samples for Water-Quality Analysis
Collecting water-quality samples involves not only the process of physically acquiring the best possible sample for the intended analysis, but also characterizing the environment from which the sample was drawn, and handling the sample so as to protect its value for its intended purpose. The goal of sample collection and field measurements is to accurately represent the water resource being sampled at that time. This means obtaining a series of measurements (field parameters or in situ measurements) in a prescribed manner, preserving and maintaining water-quality and QA/QC samples according to established guidelines, and observing chain of custody requirements.
Obtaining a representative sample means being careful in your choice of equipment. If you are sampling for the presence of heavy metals, do not use samplers with metal components. When sampling for organics, avoid using samplers with plastic components, as the plastic may adsorb and contaminate the samples. Most importantly, always decontaminate equipment before use. Once the equipment is decontaminated, wrap inorganic equipment in plastic and organic equipment in aluminum foil for transport to the site.
The proper handling of water quality samples also includes wearing gloves. Gloves not only protect field personnel, but also prevent potential contamination to the water sample. Always wear powderless, disposable gloves. When sampling for inorganics, wear latex gloves. Nitrile gloves are appropriate for organics.
The following sections provide a field reference for chain of custody procedures, sampling surface water and ground water, and further provide procedures for measuring field parameters and handling water-quality samples.
A. Chain of Custody Procedures
Because a sample is physical evidence, chain of custody procedures are used to maintain and document sample possession from the time the sample is collected until it is introduced as evidence. Chain of custody requirements will vary from agency to agency. However, these procedures are similar and the chain of custody outlined in this manual is only a guideline. Consult your project manager for specific requirements.
If you have physical possession of a sample, have it in view, or have physically secured it to prevent tampering then it is defined as being in custody." A chain of custody record, therefore, begins when the sample containers are obtained from the laboratory. From this point on, a chain of custody record will accompany the sample containers.
Handle the samples as little as possible in the field. Each custody sample requires a chain of custody record and may require a seal. If you do not seal individual samples, then seal the containers in which the samples are shipped.
When the samples transfer possession, both parties involved in the transfer must sign, date and note the time on the chain of custody record. If a shipper refuses to sign, seal the samples and chain of custody documents inside a box or cooler with bottle seals or evidence tape. The recipient will then attach the shipping invoices showing the transfer dates and times to the custody sheets. If the samples are split and sent to more than one laboratory, prepare a separate chain of custody record for each sample. If the samples are delivered to after hours night drop-off boxes, the custody record should note such a transfer and be locked with the sealed samples inside sealed boxes.
B. Collection of Surface Water Samples
1. River and Stream Sampling
2. Pond and Lake Sampling
Representative samples may be collected from rivers, streams and lakes if certain rules are followed:
Collection of samples from rivers and stream involves transporting all
necessary items to the water-quality station (see checklist in STEP
5), and setting up field notes, instrumentation, filtration equipment
(if not performed elsewhere as with microbiologicals), sample containers
and decontamination washes near the channel. The first step is to measure
all field parameters and then measure streamflow. After collecting and
preserving the samples, equipment storage and decontamination will follow.
Avoid spills when decontaminating equipment. For remote sites, extra collections
equipment may be used to eliminate the need for field decontamination.
The USGS and ADEQ have written procedures covering all aspects of surface-water
characterization and sampling.
a. Field Parameters
Measure and record the field parameters of temperature, electrical conductivity, pH and dissolved oxygen in an undisturbed section of streamflow. Other parameters may be measured, if desired.
b. Streamflow Measurement
Before collecting water quality samples, record the stream's flow rate at the selected station. The flow rate measurement is important for estimating contaminant loading and other impacts.
The first step in streamflow measurement is selecting a cross-section (Rantz, 1982). Select a straight reach where the stream bed is uniform and relatively free of boulders and aquatic growth. Be certain that the flow is uniform and free of eddies, slack water and excessive turbulence.
After the cross-section has been selected, determine the width of the
stream by stringing a measuring tape from bank-to-bank at right angles
to the direction of flow. Next, determine the spacing of the verticals.
Space the verticals so that no partial section has more than 5 per cent
of the total discharge within it.
At the first vertical, face upstream and lower the velocity meter to the channel bottom, record its depth, then raise the meter to 0.8 and 0.2 of the distance from the stream surface, measure the water velocities at each level, and average them. Move to the next vertical and repeat the procedure until you reach the opposite bank.
Once the velocity, depth and distance of the cross-section have been determined, the mid-section method can be used for determining discharge. Calculate the discharge in each increment by multiplying the averaged velocity in each increment by the increment width and averaged depth. (Note that the first and last stations are located at the edge of the waterway and have a depth and velocity of zero.) Add up the discharges for each increment to calculate total stream discharge. Record the flow in liters (or cubic feet) per second in your field book.
c. Composite Sampling
Composite sampling is intended to produce a water quality sample representative
of the total stream discharge at the sampling station. If your sampling
plan calls for composite sampling, use a DH-81 depth-integrating sampler.
However, the DH-81 uses different nozzle sizes depending on the velocity
and the size of the container. Consult the DH-81 documentation or your
project manager for the appropriate size to use in your sampling program.
The equal-width-increment (EWI) method is used to obtain a series of sub-samples. Each sub-sample represents a volume of water taken at equal widths apart from each other at different intervals across the channel.
To employ the EWI method, use a tape to measure the bank-to-bank width
of flowing water in the channel. Divide the width into equal increments,
using a minimum of ten increments for streams as much as 1.5 meters (5
feet) wide, to a maximum of twenty increments in extremely wide channels
(Ward and Harr, 1990, p. 8). This will assure enough spacing to allow
for discrete sampling at each vertical.
Next, determine the appropriate Ętransit rate': go to the deepest part of the channel, face upstream, and slowly lower the sampler to the streambed at a constant rate; then immediately raise it back to the surface at a constant transit rate. At the correct transit rate the quart jar is about 3/4 full when it returns to the surface. If the jar becomes completely full while lowering the sampler, you must empty it and start over until you find the best transit rate. This may require some practice.
Once you have determined the transit rate, empty the sampler and return to the first vertical. Using the appropriate transit rate, lower and raise the sampler at successive verticals until the jar is filled. Hand the jar to your co-worker (who is wearing clean, disposable gloves). The co-worker will then pour the sample into the sample containers or a churn splitter. The churn splitter is a polyethylene vessel that slowly stirs the composited sample with a polypropylene disk. Sample additional verticals until enough sample has been collected for your needs, and add all the required preservatives (see STEP 11.E.2). Because the churn splitter requires from 3 to 8 liters of composited water, verticals in a narrow stream may have to be sampled more than once. It is important, however, that all verticals be sampled the same number of times. It is also important to churn while drawing samples from the splitter.
Do not use a churn splitter to composite samples collected for volatile organics, organic carbon, oil and grease, pesticides, herbicides or bacteria, because its plastic components have the potential for adsorbing and contaminating the samples. Instead, use glass containers for sampling these parameters with the grab sampling method.
d. Grab Sampling
Grab sampling is performed when uniform mixing in the river or stream channel makes composite sampling unnecessary, when point samples are desired, when sample degassing may occur, or when the water is too shallow for composite sampling. Record any decision to use grab sampling in the sampling plan.
For streams at least 4 inches (10 cm) deep, collect grab samples in the middle of the channel using a laboratory cleaned or decontaminated glass or plastic container, and add the required preservatives (see STEP 11.E.2).
Determining the representative water quality of large bodies of impounded water sometimes will require samples obtained from more than one location. These locations will depend on the objectives of the sampling program, the impact of local contamination sources, and the size of the water body. Obtain quality control samples according to the procedures described in STEP 12.
a. Field Parameters
As in river and stream sampling, measure temperature, electrical conductivity,
pH, and dissolved oxygen to assess the three-dimensional variability and
stratification of water quality in ponds, lakes and large springs. If
a boat is available, measure the change of these parameters throughout
the lake with depth by slowly lowering and raising the probes at specified
locations. Note the depth and location of the readings as accurately as
possible. If the lake or pond is stratified, record the depth and thickness
of the upper layer (epilimnion), transition zone (metalimnion), and lower
layer (hypolimnion). If no boat is available, non-representative measurements
can be made as a last resort at several accessible locations along the
shore.
b. Onshore Sampling
If no boat is available, collect a surface sample using a one-quart mason
jar cleaned using decontamination procedures. (STEP
6). Record the sampling depth and distance from shore in the field
log book.
c. Offshore Sampling
Water samples from lakes and ponds may be obtained with Kemmerer or Van Dorn (Alpha Bottle) samplers. Peristaltic pumps with weighted hoses also may be used. Use containers and pumps made of materials compatible with the parameters to be analyzed and carefully decontaminated before use. In general, rinse the samplers with lake water before collection, and obtain samples with the lowest concentrations (e.g., top before bottom) first. If samples are to be taken for chlorophyll, do not acid wash the sampler as the acid quickly destroys chlorophyll. Chlorophyll can be analyzed according to Merker et al (1980).
In shallow lakes (those with fairly uniform dissolved oxygen concentrations with depth), take a sample near the center of the lake at 30 cm (1 foot) depth. In deep lakes that are stratified, obtain samples at a minimum of three depths: 30 cm below the surface, at the top of the hypolimnion, and another at the base of the hypolimnion, approximately 1 meter or 3 feet above the lake bottom. Be sure not to mix the sample with bottom sediments. (EPA, August 1990, Monitoring Lake and Reservoir Restoration: EPA Office of Water, Washington, DC 20460, EPA 440/4-90-007)
Record the physical parameter measurements, location and depth of each sample taken. Carefully decontaminate the sampler before reuse.
IMPORTANT: Phase III continues to Step 11-section
C.
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