A cost comparison of ISM to discrete sampling approaches is difficult. Cost-effective sampling is important, but it is more critical that the sampling approach(es) meet the sampling objectives.
The cost of collecting and processing an individual ISM sample is nearly always more than that for a single discrete sample. In general, the number of analytical samples to be analyzed for ISM is less than for discrete samples, so ISM analytical cost may be lower. However, costs differences are based on various issues, including specific analytical costs (e.g., metal vs. dioxin), availability and quality of screening technologies, and ease of collecting samples. Costs should be evaluated on a case-by-case basis.
It is also important to remember that ISM generally yields more precise and unbiased estimates of the mean (for example, three 30-increment ISM samples as compared to three discrete samples). This difference is important because, from a decision-making standpoint, investigations based on limited discrete sample data are in many cases more likely to result in a decision error. In those instances where an ISM investigation costs more than discrete sample investigation, the cost-benefit ratio might still favor the ISM investigation because it may result in fewer decision errors.
When ISM and discrete sampling costs are similar, variability in the ISM data can be significantly less. This decreased data variability might allow for less uncertainty in decision making, especially when estimates of the mean are close to an action level. Ultimately, making a correct decision at a site reduces overall project costs by eliminating costly and unnecessary remediation of DUs incorrectly identified as dirty or dealing with the consequences of mistakenly walking away from a DU that is actually contaminated.
Although the survey did not query the question of cost vs. benefit, this section discusses general costs for ISM. It should be noted that the Florida field study presented in Case Study 3 did not have a detailed cost-benefit analysis as a project objective, and for this reason costs analysis for the Florida field study are not presented.
Challenge: How do costs for ISM compare to discrete sampling approaches?
Recommendation: The recommendations below discuss four areas of cost differences between ISM and discrete sampling approaches: systematic planning, sampling plan review, field costs, and laboratory costs.
Systematic Planning. Systematic planning, including the designation of DUs and associated decision statements that guide evaluation of the data collected, while being key components of ISM investigations, are not unique to ISM. ISM requires the up-front consideration of DUs and associated decision statements. Although this should be done prior any project involving soil sample collection, traditionally, systematic planning is often omitted completely or only partially conducted prior to many site investigations. This omission often results in multiple sample collection events purely for site characterization purposes, followed by the designation of what are essentially DUs using already-collected data on which final decision making is based. This process often leads to the need for additional site investigations to fill data gaps or, especially at small sites with limited budgets, final decisions based on low-quality data that may or may not reflect the actual risks posed by contamination at the site.
Very little data exist on how much systematic planning for ISM costs vs. more traditional discrete sample approaches. The reason is likely that the ISM approach is new and that conditions vary so greatly from site to site. Systematic planning costs should be roughly equivalent regardless of the sampling design. Developing DUs, discussing hot spots, including additional staff to participate in planning meetings, and stakeholder agreement may increase front-end costs but can significantly reduce costs and the need for lengthy discussions following completion of the field investigation. The intent of systematic planning is to minimize the need for remobilization to collect additional data or situations where parties disagree on the size of a hot spot. Eliminating both would result in lower overall costs in the project life cycle.
Sampling Plan Review. A common concern of both regulators and the regulated community is ISM sampling plan review. For regulators not trained in ISM investigation approaches, the sampling plan review can be labor-intensive. Many regulators stated that they currently do not have time to review standard sampling plans and reports, let alone a more labor-intensive ISM plan. For consultants, the time required for regulatory approval of ISM projects from agencies that lack adequate training and guidance documents also increases costs to their clients and at least perceived risk of rejection. Many consultants find it much easier to submit standard sampling plans and assessment/remediation reports to regulators in an attempt to get a quicker turnaround time for their clients even if they know that this approach will ultimately result in a more drawn out and costly investigation over the life of the project. While this statement may be true currently, the publication of this ISM document and subsequent training should allow practitioners to develop ISM work plans with less risk of rejection and regulators to review sampling plans more quickly.
Field Costs. Many factors can affect the cost for ISM field sampling. Only limited data on ISM sampling costs were available at the time this ITRC document was developed. All of the costs are highly dependent on DQOs. The discussion of costs presented below is only for surface soil sampling. Generally, field costs for ISM and the equivalent number of discrete samples (e.g., three ISM or 30 discrete samples) are approximately equivalent. Cost considerations include the number of increments in an ISM sample, replicate collection, and field processing.
Based on experience reported by the State of Hawaii, the average time needed to lay out up to a 1‑acre DU in the field and collect a single 30–50 point ISM sample is approximately 45 minutes for a three-person field team (two to collect samples and one to manage samples, decontaminate, manage paperwork, etc.). For the same number of discrete sample or increment points (e.g., 30 points within a targeted area), the collection of a single ISM sample will be faster than the collection of 30 discrete samples due to the need to label, pack, and document a much larger number of the discrete samples. In cases where a relatively low number of discrete samples are required for characterization of a targeted area (e.g., 10 discrete samples), the field time required to collect the discrete samples is likely to be significantly shorter than the time required to collect and process an ISM sample, especially if replicate ISM samples are to be collected.
The real cost saving is in the analysis effort needed to produce equivalent precision, where, for example, instead of analyzing 30 discrete samples from a targeted area, the lab analyzes three ISM samples (one incremental sample and two replicates). An example presented at the 2010 Environment, Energy Security and Sustainability Conference (Penfold 2010), indicated that the total field and lab costs for one ISM sample and two replicates from a single DU was $3,150 vs. $6,975 for 30 discrete samples. The ISM samples contained 100 increments each. The total field and lab cost for 10 DUs was $20,700 for ISM vs. $62,725 for discrete samples. The samples were analyzed by USEPA SW-846 Method 8330B for explosives.
The 2009 Environmental Security Technology Certification Program (ESTCP) Cost and Performance Report (Hewitt et al. 2009) prepared for characterization of energetic residues provides an excellent discussion on the cost issues associated with ISM sampling for USEPA SW-846 Method 8330B. According to the report, extra costs could include ISM sample shipment and disposal (due to extra weight) as well as QA/QC costs associated with batch samples. In addition, the report noted that ISM was not projected to be cost-competitive on smaller scale due to the relative increased processing (e.g., sieving and handling) and analysis; however, the report concluded that there is a cost saving of 50%–80% using ISM (Hewitt et al. 2009).
Laboratory. ISM increases the amount of sample handling in the laboratory. There is a wide variety of ISM laboratory sample processing and subsampling options. The price of ISM processing depends on the specific options selected, the amount of soil to be processed, analytes of concern, and other general business concerns (e.g., number of samples, turnaround time). As of mid-2010, the additional cost of ISM sample processing ranged from $50–$250 for a 1 kg soil sample. Normal sample preparation and analysis charges depend on the contaminant(s) of interest and are not included in this price range estimate. Processing equipment blanks, LCSs, and MS/MSDs through the ISM laboratory steps is recommended, but the lack of readily available and suitable reference materials makes it challenging to estimate potential costs. Depending on QA/QC samples necessary to meet DQOs, per batch cost could increase significantly. Despite increased costs, the added value of processing known QA/QC samples may be worthwhile. Discuss batch QA/QC options with the laboratory during project planning to get specific cost estimates.
The ISM approach might not be the most cost-effective option when low-cost field screening tests provide acceptable accuracy and sensitivity (such as XRF for selected metals) and can be used inexpensively on large numbers of discrete samples.
Challenge: Are there cases where ISM is not cost-effective or when is ISM most cost-effective?
Cost considerations for ISM include individual analyte costs, availability of field analytical methods, type of sample processing necessary (drying, particle size reduction, sieving, subsampling), difficulty in sieving, whether the lab has an ISM SOP, shipping and disposal costs associated with larger ISM sample mass, and need for additional laboratory QC samples.
Recommendation: Costs need to be evaluated on a site-by-site basis as DQOs and other site-specific factors make it very difficult to predict which sample method will be the most cost-effective. The following issues related to costs should be considered:
- What are individual analyte costs?
- Are there field analytical methods that can be used for specific contaminants?
- What type of sample processing has to be done (drying, particle size reduction, sieving, subsampling)?
- If sieving in the field, does the soil contain clay, roots, or very wet soil? These will likely increase overall field processing time and increase costs.
- Will the laboratory charge be based on how difficult is it to sieve the soil (clay, roots, very wet)?
- Does the lab have an ISM SOP, and if not, will it charge to develop one?
- What are the costs for extra QC samples (i.e., batch samples) often needed with ISM?
- Are there added costs for shipping and disposing the large volumes of soil collected with ISM?
Note, however, that cost should not be the most important issue. The priority should be whether the sampling design meets the sampling objectives.