Fact Sheet 10: Compliance with Remediation Objectives

Groundwater

To determine if a site meets the groundwater remediation objectives, the contaminant concentrations of discrete samples are compared to the applicable groundwater remediation objective(s). A discrete sample is a sample collected from only one point.

You will have achieved compliance if the analytical results from each sample do not exceed the applicable remediation objective(s).

Soil

When determining whether a site meets the soil remediation objectives, you may choose among three methods of compliance, depending on the type of contaminant and the potential human receptors.

You may reach compliance with soil remediation objectives in three ways:

  1. Compare the contaminant concentrations of discrete samples to the applicable soil remediation objective(s),

  2. Composite the soil samples by physically mixing the soil from more than one location prior to laboratory analysis. Next, compare the composite analytical result to the applicable soil remediation objective(s), and

  3. Mathematically average individual analytical sample results in accordance with the procedures in 35 Adm. Code 742.225(c), (d) and (e) and then compare the average to the applicable soil remediation objectives(s).

Whichever method or combination of methods you choose to use, you will have achieved compliance if the analytical results of the samples do not exceed the applicable remediation objective(s). There are, however, guidelines to follow when compositing and averaging.

Guidelines for soil compositing and averaging

You can neither composite nor average soil samples for determining compliance with ingestion and inhalation objectives for the construction worker population. This is because construction workers are normally exposed to a specific location and not to the site as a whole. Construction worker exposure must be evaluated at all sites that depend on an industrial/commercial land use for remediation objectives. The term "construction worker population" means people engaged on a temporary basis to perform work involving invasive construction activities such as earth-moving, building, and utility installation and repair during post remediation land use.

You may not composite soil samples if your contaminants of concern are volatile organic compounds (VOCs). Compositing of VOCs is prohibited because the compositing process itself provides a mechanism for the contaminants to escape into the atmosphere. Consequently, composite samples submitted for laboratory analysis underestimate the amount of VOCs actually present at the site.

How do I average the soil samples?

  1. For migration to groundwater exposure route, the arithmetic average of the data collected at each boring should be calculated and then compared to the remediation objective.
  2. For the soil ingestion and inhalation routes, the 95% upper confidence limit of the mean of the concentration of the contaminant should be calculated for the contaminated area and that value should be compared to the remediation objective. To calculate the 95% UCL, it is first necessary to determine the statistical distribution of the data in question. The procedures for calculating the 95% UCL are described in USEPA document titled "Calculating Upper Confidence Limits for Exposure Point Concentrations at Hazardous Waste Sites", USEPA Office of Emergency and Remedial Response, OSWER 9285.6-10 (December, 2002).

How many samples do I need to collect at my site to determine compliance with the remediation objectives?

The number of samples you collect depends on the specific program requirements under which the remediation is performed (Leaking UST, Site Remediation Program, RCRA Closure and Corrective Action).

If any of my laboratory sample results come back as "non-detect" or "below detection limits" how do I average my soil samples?

If more than 15% of the laboratory sample results are reported as "non-detect" or "below detection limits" the results should be included in the averaging calculation at a value equal to one-half the reported detection limit for that contaminant. If more than 15% of  the samples are "non-detect", then the procedures in "Guidance for Data Quality Assessment, Practical Methods for Data Analysis, EPA QA/G-9, AQ00 Update", EPA/600/R-96/084 (July, 2000), should be used.

When does the mixture rule apply?

Depending on your contaminants, the mixture rule may or may not apply as the table below demonstrates. The mixture rule is designed to protect against harmful effects from multiple contaminants which attack the same target organ or have similar modes of action. Tables E and F of Part 742, Appendix A provide a list of chemicals which have noncarcinogenic effects (Table E) and carcinogenic effects (Table F). For example, at a typical gasoline Leaking UST site, the multiple contaminants of concern would be ethylbenzene and toluene which both attack the kidney with noncarcinogenic effects.

The table below, when used in conjunction with Tables E and F, will show you when the rule applies to either groundwater or soil or both.

Application of the Mixture Rule
 Tier 1Tier 2Tier 3
CarcinogensGroundwaterGroundwaterGroundwater
Soil
NoncarcinogensGroundwaterGroundwater
Soil
Groundwater
Soil

 

 General Summary of Soil Compositing and Averaging
Migration to Groundwater Route1

Sample Type

Number of Samples

Sample Compositing

Sample Averaging2

Comments

Sampling for non-VOCs

At a minimum, 2 borings per 0.5 acre. The samples are to be collected every 2 feet, beginning from 6 inches below the ground surface.

Yes

Yes

All compositing or averaging must be done within the same borehole. At least one sample must be collected from the zone of contamination, and samples are to be collected through the zone of contamination. Samples obtained at or below the water table cannot be used for compositing or averaging.

Sampling for VOCs

No

Yes

 

 


Inhalation and Ingestion Routes1

Sample Type

Number of Samples

Sample Compositing

Sample Averaging2

Comments

Sampling for non-VOCs

Program and site specific

Yes3

Program and site specific

Samples must be collected within the contaminated area.

Sampling for VOCs

No

  1. These guidelines are not intended to prescribe a sampling protocol for a site investigation.
  2. Laboratory sample results reported as "non-detect" or "below detection limits" must be included in the averaging calculation at a value equal to one-half of the reported analytical detection limit for the contaminant.
  3. Neither sample compositing nor averaging are allowed under the construction worker scenario.