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SECTION 5

COST ANALYSIS

In addition to the technical capability of a specific sampling method to monitor the medium in question, the potential cost of using any type of sampling method is a significant consideration when devising a sampling strategy. Accordingly, one of the objectives of this demonstration is to evaluate and compare the costs of each different sampling method demonstrated.

Due to the nature of the demonstration performed at McClellan (i.e., deployment and retrieval of multiple sampler types in the same well concurrently), some elements of the cost analysis such as labor costs are difficult to determine based on the actual dollars and hours expended for the demonstration, and must be estimated using professional judgment. To compare the costs of the eight sampling techniques used in this demonstration, the annual cost per well sampled for a given LTM scenario was estimated for each technique. Because other factors in addition to cost are considered in selecting an appropriate groundwater sampling method, it is assumed that each method is technically appropriate and can collect the necessary volume of water required for the target analyses. The following assumptions and expenses were considered in the development of a cost analysis for each different sampling method:

• Only one sample depth per well was assumed for LTM as opposed to the three sample depths scoped in the McClellan demonstration.
• Some of the diffusion and grab sampling devices require more time than others to deploy and retrieve. For LTM using these samplers, it is assumed that new samplers are deployed at the time of sample collection so that only one mobilization is required. A combination of field notes from the McClellan sampling events and professional judgment were used to estimate labor requirements for each of the different sampling methods.
• Each sampling method evaluated requires varying lengths of time at the outset of the LTM program for initial setup (e.g., installing dedicated systems and building sampler strings). This cost analysis does not include those initial setup costs for any of the evaluated methods.
• Some of the sampling methods require a one-time capital expenditure for equipment that is re-used throughout LTM (e.g., dedicated pump, Snap Sampler™ equipment, stainless steel weights). For the cost analysis, the one-time expenditures are amortized over the assumed 20-year duration of the LTM program.
• Rev. Donald W. Sandmann The LTM program was assumed to be comprised of 20 4-inch-diameter wells sampled semi-annually. Each well was assumed to be 50 feet deep, and the bottom 10 feet of each well was assumed to comprise the screened interval. Depth to groundwater at all wells was assumed to be 15 feet.
• All sampling was assumed to be performed by a two-person field crew.
• Since water level measurements would be made regardless of which sampling method was used, costs for this task were not included in the cost analysis.
• Although field filtration of samples was performed in some instances during the McClellan demonstration, this task was not built into the cost analysis.
• Conventional sampling was assumed to be performed in a manner consistent with current practices at McClellan. The low-flow method was assumed to be performed using pumps and tubing that are dedicated to each well. The threevolume purge method was assumed to be performed using non-dedicated pumps and tubing and disposable bailers.
• In order to estimate the labor requirements for conventional sampling, the following assumptions were made:
• Average low-flow and three-volume purge rates used during this demonstration (summarized in Table 3.3) were used to develop the cost estimates for these methods.
• For the low-flow method, the average purge volume used during this demonstration (Table 3.3) was assumed.
• For the three-volume purge method, a per-well purge volume of approximately 69 gallons was assumed, which is approximately three times the volume of water contained in a 4-inch well casing with 35 feet of water.
• Costs associated with disposal and/or management of investigation-derived waste (IDW) at some sites can vary widely depending on the approach used. For this cost analysis, no additional costs were assumed for treatment of IDW since McClellan uses an on-base treatment plant. However, labor and equipment costs to collect and transfer the IDW to the treatment plant were included in the cost analysis. As a qualitative consideration not captured in this cost analysis, IDW disposal and treatment can be significant at some sites where waste water generated must be disposed of off-site. The three-volume purge method would typically be expected to have the highest IDW disposal costs.
• Field mobilization/demobilization costs were assumed to be equal for all methods and therefore were not included in the cost analysis.
• Prices for commercially available products were obtained from product distributors or vendors.
• Three Snap Samplers™ were assumed to be used per well for LTM due to the relatively small volume of a single sampler (40 ml). Depending on the specific sample volume needs, use of a lesser number of Snap Samplers™ may be possible, resulting in a lower cost per sample than calculated for this cost analysis.
• For the RPPS, PsMS, and RCS, which are not commercially available, a retail price was estimated. This price was derived by summing the purchase cost of each individual component of the samplers used for the McClellan demonstration and factoring in a profit of 400 percent (i.e., multiplying the materials cost by a factor of 4).
• Many of the common sampling supplies (e.g., nitrile gloves, plastic sheeting, sample containers) were assumed to be equal in cost regardless of the sampling method and were not included.
• Sales taxes were not included in the cost analysis.
• Labor is broken out by task in the cost analysis. Estimates of labor required for each task are based on field experience and professional judgment.
• A labor rate of $60 per hour was assumed for a field scientist.
• Laboratory analytical expenses were assumed to be equal regardless of sampling method and therefore are not included in the analysis.

Table 5.1 is a detailed account of the various costs that were considered in this analysis. Table 5.2 is a summary of the calculated per-well-per-event sampling costs using each of the eight methods. The results of this analysis indicate that conventional sampling is more expensive than any of the diffusion and grab sampling techniques. The PDBS and HydraSleeve® were the least expensive sampling methods, with the primary cost difference between the two being the time required to refill a new PDBS that is not necessary when using the HydraSleeve®.

The Snap Sampler™ was more expensive than the other no-purge samplers, but it still was substantially less then the purge methods. The initial purchase of the device and the recurring costs for the specialized sample bottles make the Snap Samplers™ more expensive than the other no-purge sampling devices. However, the Snap Sampler™ is less expensive than both conventional sampling methods. Because the Snap Sampler™ is untested in long-term use, it is difficult to estimate a realistic life expectancy for the device. The manufacturer of the Snap Sampler™ (ProHydro, Inc.) states that the Snap Sampler™ itself seems likely to have an extended life, and that replacing trigger linkage parts or other maintenance may be needed rather than full replacement of the samplers. For the cost calculation we assumed replacement parts and maintenance would be equivalent to replacing 1/3 of the sampler cost over the course of the program. It should be noted that the cost analysis assumed a three-vial configuration as was used at McClellan. In some applications, use of a two-vial configuration would be sufficient, which would reduce the cost of using the Snap Sampler method™ from that shown in Tables 5.1 and 5.2.

The cost for use of the RPPS was relatively high compared to other diffusion samplers and the HydraSleeve® primarily due to the labor required to prepare new samplers for deployment. Specifically, a significant amount of time was taken in purging the samplers of residual air. If the sampler is ever developed commercially, it is reasonable to expect that the degassing could be done more cheaply and efficiently prior to delivery.

If so, the cost to use the RPPS would be significantly reduced, potentially to the point where is would be comparable to the PDBS and RCS costs.

Similar to the RPPS, although to lesser degrees, the PsMS and RCS also were relatively time consuming to construct. Although this resulted in higher costs for the McClellan cost analysis, optimized designs and commercial availability would likely

TABLE 5.1
COST ANALYSISa/
NO-PURGE SAMPLER DEMONSTRATION
McCLELLAN AFB, CALIFORNIA
View TABLE 5.1

TABLE 5.2
SUMMARY OF COST ANALYSIS RESULTS
NO-PURGE SAMPLER DEMONSTRATION
McCLELLAN AFB, CALIFORNIA

a/ Assumes use of 3 samplers per well per sampling event.

reduce the construction time needed for both devices and would therefore reduce the overall cost of using them.

Of important note is that this cost analysis did not consider various more subtle aspects of using each of the sampling methods evaluated. For example, fewer QA/QC samples are typically necessary for the diffusion and grab sampling devices compared to conventional methods. This is due in part to the fact that it generally takes longer to sample a given number of wells using conventional methods than using diffusion and grab methods, and that conventional methods may require equipment decontamination. For these reasons, it is presumed that more trip blank and equipment rinseate blank samples would be required for conventional sampling compared to the alternate approaches. In addition, collection of MS/MSD samples may not be required using diffusion sampling given that turbidity would not migrate through the walls of these samplers. Snap Samplers™ are sealed shut while still in the well; therefore, collection of ambient field blanks should not be necessary when using this device (compared to other methods where the sample is transferred into sample bottles above-ground).

Additionally, this cost analysis does not consider the costs required to actually convert from one sampling method to another. Switching from one sampling method to another would probably require approval from one or more regulatory agencies, which could be simple or more complicated, depending on the specific circumstances (e.g., federal or state regulatory requirements, degree of technology “acceptance”). Converting from one sampling method to another also would probably require modification of some sitespecific documents (e.g., QAPP, Record of Decision, Sampling and Analysis Plan). In some instances, additional field demonstrations may also be required in which side-byside comparisons of the results of the proposed sampling method to contemporaneous or historical results of the current sampling method would be performed.

In summary, the cost analysis described above provides a general comparison of the per-well-per-event costs of each of the eight sampling methods demonstrated at McClellan; these costs can be used as an initial screening tool when trying to identify a candidate alternative sampling technology. Accordingly, prior to conversion from one sampling method to another, a more complete cost analysis that takes into account all site-specific cost factors should be performed

Report Cover   Table of Contents   Sec. 1   Sec. 2   Sec. 3   Sec. 4   Sec. 5   Sec. 6   Sec. 7   Sec. 8

HydraSleeve No-Purge Sampling  •  Passive Ground Water Sampling
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