Passive Sampling Costs

Cost Model for Implementing Passive Sampling

Download Cost Model (Excel file) Excel file Analytical testing dotsThe potential cost savings of implementing passive sampling in place of other conventional sampling methods is a driving force in the deployment of passive sampling devices. This cost model was originally developed by the ITRC Diffusion Sampler Workgroup to allow cost implications to be evaluated in the assessment of Polyethylene Diffusion Bag samplers (PDBs) deployment on a site-specific basis. The same information can be used to assess the deployment of other passive samplers, like the Rigid Porous Polyethylene (RPP) sampler.

The cost comparison technique used by the spreadsheet is a standard "present value" calculation to represent the total, present day cost of future sample collection expenses. The spreadsheet model sometimes uses default values based on data collected during previous field demonstrations of passive diffusion samplers, but the user is encouraged to use site-specific cost data so that the cost comparison is more accurate. Certain site-specific conditions, such as whether well purge water is treated on-site without cost or is transported off-site and treated at an additional cost, can impact the cost analysis.

The intent of the cost model is to allow the user to compare sampling costs for the use of:

  • Passive samplers
  • Current sampling methods
  • User alternatives

The alternate scenario can be used to compare costs with a third sampling technique or to allow the modification of certain parameters previously defined in one of the other two scenarios (something akin to a sensitivity analysis for selected parameters). An example would be to evaluate the impact of reducing the sampling frequency.

The cost model is an Excel spreadsheet with defined formulas to calculate Net Present Value (NPV) of up to three sampling scenarios. The cells in the spreadsheet are color coded: a blue font indicates user input is required, and a red font indicates a calculated value. When an override value is entered by the user the cell background changes to blue.

The "economic evaluation" spreadsheet requires the user to enter costs by category (discussed further below), that are used to calculate a "cost per event". This value is multiplied by the number of events per year for up to 30 years to calculate a total annual cost. Using a provided discount rate, the NPV for up to three sampling alternatives is calculated, providing a comparison over a time interval of up to 30 years. These results are presented in the spreadsheet titled "Year by Year NPV."

The user input fields are described in the following table. Each category of costs has extra fields to allow costs not included in the defined cost fields to be included on a site-specific basis.

 

Cost Model for Implementing Polyethylene Diffusion Bag (PDB) Sampling
User Input Description
No. of Field Personnel Field personnel required for sampling
Sampling Days (per event) The number of days required to sample all wells in the sampling event. As a rule of thumb, you can reasonably expect sampling at least 20 wells per day when each well has a single passive sampler and is less than 50 feet in depth. If vertical profiling is conducted, 2 or more passive samples are used for additional sample, or if passive samplers will not be deployed in every well, the number of days for the sampling event will vary.
Length of sampling day (hours) Hours of sampling activity per day from 1 to 16.
Labor Cost (hourly per person) Hourly labor rate for field personnel. This may be an average blended rate if sampling personnel change throughout a project,
Per Diem (daily per person) The daily cost per person for food and lodging.
Travel and Transportation Costs
(per event)
Travel for field personnel and transportation of equipment,
per event.
Equipment Rental / Disposables Costs associated with equipment rental and disposable items. Specify all sampling equipment costs here (whether rented or owned). If equipment or pumps can be re-deployed to another location you may enter a negative dollar amount. The cost of all passive sampling equipment needs to be included here. Detailed site specific costs are preferred, but for guidance see Table 1.
Miscellaneous Sampling Cost 1 User identified supplemental cost. Credits may be entered as negative values.
Miscellaneous Sampling Cost 2 User identified supplemental cost. Credits may be entered as negative values.
One-Time Cost for passive sampling (first year only) Additional costs experienced during the initial year of passive sampling.
VOA analysis cost The cost of laboratory VOC analyses.
No. of Wells The number of wells sampled.
No. of Samples per well The number of samples collected per well. This is generally one unless vertical profiling is being done.
Shipping The cost of shipping samples to the analytical laboratory. A default value is $50 per day (assuming one cooler per day).
No. of Duplicate Samples The default value is 10% of the total number of samples taken, but it may be user defined.
No. of Equipment/Field Blanks The default value is one per day of sampling, but it may be user defined.
No. of matrix spike and matrix spike duplicate samples The default value is 10% of the total number of samples taken, but it may be user defined.
No. of Trip Blanks The default value is 10% of the total number of samples taken, but it may be user defined.
Miscellaneous Analytical Cost 1 User identified supplemental cost. Credits may be entered as negative values.
Miscellaneous Analytical Cost 2 User identified supplemental cost. Credits may be entered as negative values.
Waste Treatment Cost (per event) Cost to treat waste produced by sampling.
Waste Disposal Cost (per event) Cost to dispose of waste produced by sampling.
Waste Transportation Cost (per event) Cost to transport waste produced by sampling.
Miscellaneous Waste Disposal Cost 1 User identified supplemental cost. Credits may be entered as negative values.
Miscellaneous Waste Disposal Cost 2 User identified supplemental cost. Credits may be entered as negative values.
No. Events (annually) Number of sampling events scheduled per year
Inflation Rate Assumed rate of inflation, percent (default value is 3%)
Discount Rate Assumed discount rate, percent (default value is 7%)
No. of Years to Run Model User defined for up to 30 years (default is 30)
Tax Rate Assumed tax rate, percent (default value zero)
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Table 1: Direct costs (other than labor) that may be associated with passive sampling

Item Estimated Cost
Stainless steel weight (~ ½ lb)1 $15
Hanging Assemblies
0 to 50 ft
50-100 ft
100 to 150 ft
150 to 200 ft
200 to 250 ft
$62
$74
$90
$120
$141
Diffusion Samplers
Passive Diffusion Bag Samplers (PDBs), each2
Rigid Porous Polyethylene Samplers (RPPs) , each2
$28.50
$65.00
Plastic sheeting (per roll) $6
Nitrile gloves (box) $11.50
Water level meter rental (per day) $20
Vehicle rental and gas $65
Photoionization detector (PID) $60
Photoionization detector calibration gas $35
Zip ties (each) $0.03
Laboratory analysis for analytes of interest Will vary
Shipping field equipment, disposal costs3 and supplies $50
Sample Shipment (overnight per cooler on average)4 $100

1. If you are deploying multiple samplers on the same line or if your well screen is over 150 feet deep, you may need an additional weight to counteract buoyancy.
2. Volume/project discounts are available.
3. Disposal costs for gloves, spent passive sampler, used zip ties, etc.
4. This is based on a standard 48 quart cooler weighing about 40 lbs and shipping a distance of about 1000 miles.
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One-Time/First Year Costs for Passive Sampling

It may be that you or your regulator wants to perform an evaluation of passive sampling on your site prior to conversion to it. Please note this is not required by any regulation, either state or federal, or any current guidance. The cost of this evaluation can be rather high when compared to the cost of performing your current sampling event costs, but the return on investment may be substantial over time. The costs depend entirely on site-specific conditions and regulatory requirements. The majority of evaluations that ALS Environmental has seen in the past number of years have consisted of a pilot demonstration using a few wells at the site and either comparing the data results to previous quarter results or performing a side-by-side study. Choice of the wells is usually based on typical historical data from those wells. There are usually site-specific low concentration, middle concentration and high concentration wells included in the pilot demonstration. Results from the passive sampling are compared to those from historical sampling methods used at the site.

If performing a side-by-side comparison, the passive samples are retrieved first, then the conventional sampling method is used to gather a sample. The majority of the time the results from passive sampling are not statistically different from the data obtained from conventional sampling techniques. Where there are differences, they can usually be resolved by reviewing the hydrology of the area surrounding the well in question. For instance, because passive sampling is representative of the aquifer immediately adjacent to the well screen, influxes from different aquifers either above or below the well screen, which may affect samples taken with conventional methods, do not influence the passively gathered sample.

If a more rigorous evaluation will be more expensive and may involve the following:

  • Work Plan Development: the objectives and scope of PDB evaluation can be formally written. This can cost a few hundred to several thousands of dollars depending on the type developed.
  • Field and laboratory investigations: Examples of these costs are detailed in Table 1. Costs in this area are heavily dependent on whether you will be vertically profiling your wells as part of your work plan.
  • Analysis of the data and evaluation
  • Recommendations development
  • Regulatory interaction: These are the costs incurred with the interaction with your regulators to gain the regulatory approval to switch to passive sampling.
  • Document revision: The costs with changing sampling instructions, permits, etc. to reflect the move to passive sampling

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