(1) General considerations.
(a) Presumed exposure scenario soil cleanup levels shall be based on estimates of the reasonable maximum exposure expected to occur under both current and future site use conditions. The department has determined that residential land use is generally the site use requiring the most protective cleanup levels and that exposure to hazardous substances under residential land use conditions represents the reasonable maximum exposure scenario. Unless a site qualifies for use of an industrial soil cleanup level under WAC 173-340-745, soil cleanup levels shall use this presumed exposure scenario and be established in accordance with this section.
(b) In the event of a release of a hazardous substance to the soil at a site, a cleanup action complying with this chapter shall be conducted to address all areas where the concentration of hazardous substances in the soil exceeds cleanup levels at the relevant point of compliance.
(c) The department may require more stringent soil cleanup standards than required by this section where, based on a site-specific evaluation, the department determines that this is necessary to protect human health and the environment. Any imposition of more stringent requirements under this provision shall comply with WAC 173-340-702 and 173-340-708. The following are examples of situations that may require more stringent cleanup levels.
(i) Concentrations that eliminate or substantially reduce the potential for food chain contamination;
(ii) Concentrations that eliminate or substantially reduce the potential for damage to soils or biota in the soils which could impair the use of soils for agricultural or silvicultural purposes;
(iii) Concentrations necessary to address the potential health risk posed by dust at a site;
(iv) Concentrations necessary to protect the groundwater at a particular site;
(v) Concentrations necessary to protect nearby surface waters from hazardous substances in runoff from the site; and
(vi) Concentrations that eliminate or minimize the potential for the accumulation of vapors in buildings or other structures.
(d) Relationship between soil cleanup levels and other cleanup standards. Soil cleanup levels shall be established at concentrations that do not directly or indirectly cause violations of groundwater, surface water, sediment, or air cleanup standards established under this chapter or applicable state and federal laws. A property that qualifies for a Method C soil cleanup level under WAC 173-340-745 does not necessarily qualify for a Method C cleanup level in other media. Each medium must be evaluated separately using the criteria applicable to that medium.
(2) Method A soil cleanup levels for unrestricted land use.
(a) Applicability. Method A soil cleanup levels may only be used at sites qualifying under WAC 173-340-704(1).
(b) General requirements. Method A soil cleanup levels shall be at least as stringent as all of the following:
(i) Concentrations in Table 740-1 and compliance with the corresponding footnotes;
(ii) Concentrations established under applicable state and federal laws;
(iii) Concentrations that result in no significant adverse effects on the protection and propagation of terrestrial ecological receptors using the procedures specified in WAC 173-340-7490 through 173-340-7493, unless it is demonstrated under those sections that establishing a soil concentration is unnecessary; and
(iv) For a hazardous substance that is deemed an indicator hazardous substance under WAC 173-340-708(2) and for which there is no value in Table 740-1 or applicable state and federal laws, a concentration that does not exceed the natural background concentration or the practical quantification limit, subject to the limitations in this chapter.
(3) Method B soil cleanup levels for unrestricted land use.
(a) Applicability. Method B soil cleanup levels consist of standard and modified cleanup levels determined using the procedures in this subsection. Either standard or modified Method B soil cleanup levels may be used at any site.
(b) Standard Method B soil cleanup levels. Standard Method B cleanup levels for soils shall be at least as stringent as all of the following:
(i) Applicable state and federal laws. Concentrations established under applicable state and federal laws;
(ii) Environmental protection. Concentrations that result in no significant adverse effects on the protection and propagation of terrestrial ecological receptors established using the procedures specified in WAC 173-340-7490 through 173-340-7494 unless it is demonstrated under those sections that establishing a soil concentration is unnecessary.
(iii) Human health protection. For hazardous substances for which sufficiently protective, health-based criteria or standards have not been established under applicable state and federal laws, those concentrations that protect human health as determined by evaluating the following exposure pathways:
(A) Groundwater protection. Concentrations that will not cause contamination of groundwater at levels which exceed groundwater cleanup levels established under WAC 173-340-720 as determined using the methods described in WAC 173-340-747.
(B) Soil direct contact. Concentrations that, due to direct contact with contaminated soil, are estimated to result in no acute or chronic noncarcinogenic toxic effects on human health using a hazard quotient of one and concentrations for which the upper bound on the estimated excess cancer risk is less than or equal to one in 1,000,000 (1 x 10-6). Equations 740-1 and 740-2 and the associated default assumptions shall be used to calculate the concentration for direct contact with contaminated soil.
(I) Noncarcinogens. For noncarcinogenic toxic effects of hazardous substances due to soil ingestion, concentrations shall be determined using Equation 740-1. For petroleum mixtures and components of such mixtures, see (b)(iii)(B)(III) of this subsection.
[Equation 740-1] | |||||
Soil Cleanup Level (mg/kg) | = | RfD x ABW x UCF x HQ x AT | |||
SIR x AB1 x EF x ED | |||||
Where: | |||||
RfD | = | Reference dose as defined in WAC 173-340-708(7) (mg/kg-day) | |||
ABW | = | Average body weight over the exposure duration (16 kg) | |||
UCF | = | Unit conversion factor (1,000,000 mg/kg) | |||
SIR | = | Soil ingestion rate (200 mg/day) | |||
AB1 | = | Gastrointestinal absorption fraction (1.0) (unitless) | |||
EF | = | Exposure frequency (1.0) (unitless) | |||
HQ | = | Hazard quotient (1) (unitless) | |||
AT | = | Averaging time (6 years) | |||
ED | = | Exposure duration (6 years) | |||
(II) Carcinogens. For carcinogenic effects of hazardous substances due to soil ingestion, concentrations shall be determined using Equation 740-2. For petroleum mixtures and components of such mixtures, see (b)(iii)(B)(III) of this subsection.
[Equation 740-2] | |||||
Soil Cleanup Level (mg/kg) | = | RISK x ABW x AT x UCF | |||
CPF x SIR x AB1 x ED x EF | |||||
Where: | |||||
RISK | = | Acceptable cancer risk level (1 in 1,000,000) (unitless) | |||
ABW | = | Average body weight over the exposure duration (16 kg) | |||
AT | = | Averaging time (75 years) | |||
UCF | = | Unit conversion factor (1,000,000 mg/kg) | |||
CPF | = | Carcinogenic potency factor as defined in WAC 173-340-708(8) (kg-day/mg) | |||
SIR | = | Soil ingestion rate (200 mg/day) | |||
AB1 | = | Gastrointestinal absorption fraction (1.0) (unitless). May use 0.6 for mixtures of dioxins and/or furans | |||
ED | = | Exposure duration (6 years) | |||
EF | = | Exposure frequency (1.0) (unitless) | |||
(III) Petroleum mixtures. For noncarcinogenic effects of petroleum mixtures, a total petroleum hydrocarbon cleanup level shall be calculated taking into account the additive effects of the petroleum fractions and volatile organic compounds substances present in the petroleum mixture. Equation 740-3 shall be used for this calculation. This equation takes into account concurrent exposure due to ingestion and dermal contact with petroleum contaminated soils. Cleanup levels for other noncarcinogens and known or suspected carcinogens within the petroleum mixture shall be calculated using Equations 740-4 and 740-5. See Table 830-1 for the analyses required for various petroleum products to use this method.
[Equation 740-3]
 |
Where: | ||
Csoil | = | TPH soil cleanup level (mg/kg) |
HI | = | Hazard index (1) (unitless) |
ABW | = | Average body weight over the exposure duration (16 kg) |
AT | = | Averaging time (6 years) |
EF | = | Exposure frequency (1.0) (unitless) |
ED | = | Exposure duration (6 years) |
SIR | = | Soil ingestion rate (200 mg/day) |
AB1 | = | Gastrointestinal absorption fraction (1.0) (unitless) |
F(i) | = | Fraction (by weight) of petroleum component (i) (unitless) |
SA | = | Dermal surface area (2,200 cm2) |
AF | = | Adherence factor (0.2 mg/cm2-day) |
ABS | = | Dermal absorption fraction for petroleum component (i) (unitless). May use chemical-specific values or the following defaults: |
• | 0.0005 for volatile petroleum components with vapor pressure ˃ = benzene | |
• | 0.03 for volatile petroleum components with vapor pressure < benzene | |
• | 0.1 for other petroleum components | |
RfDo(i) | = | Oral reference dose of petroleum component (i) as defined in WAC 173-340-708(7) (mg/kg-day) |
RfDd(i) | = | Dermal reference dose for petroleum component (i) (mg/kg-day) derived by RfDo x GI |
GI | = | Gastrointestinal absorption conversion factor (unitless). May use chemical-specific values or the following defaults: |
• | 0.8 for volatile petroleum components | |
• | 0.5 for other petroleum components | |
n | = | The number of petroleum components (petroleum fractions plus volatile organic compounds with an RfD) present in the petroleum mixture. (See Table 830-1.) |
(C) Soil vapors. The soil to vapor pathway shall be evaluated for volatile organic compounds whenever any of the following conditions exist:
(I) For gasoline range organics, whenever the total petroleum hydrocarbon (TPH) concentration is significantly higher than a concentration derived for protection of groundwater for drinking water beneficial use under WAC 173-340-747(6) using the default assumptions;
(II) For diesel range organics, whenever the total petroleum hydrocarbon (TPH) concentration is greater than 10,000 mg/kg;
(III) For other volatile organic compounds, including petroleum components, whenever the concentration is significantly higher than a concentration derived for protection of groundwater for drinking water beneficial use under WAC 173-340-747(4).
See subsection (3)(c)(iv)(B) of this section for methods that may be used to evaluate the soil to vapor pathway.
(c) Modified Method B soil cleanup levels.
(i) General. Modified Method B soil cleanup levels are standard Method B soil cleanup levels, modified with chemical-specific or site-specific data. When making these modifications, the resultant cleanup levels shall meet applicable state and federal laws, meet health risk levels for standard Method B soil cleanup levels, and be demonstrated to be environmentally protective using the procedures specified in WAC 173-340-7490 through 173-340-7494. Changes to exposure assumptions must comply with WAC 173-340-708(10).
(ii) Allowable modifications. The following modifications can be made to the default assumptions in the standard Method B equations to derive modified Method B soil cleanup levels:
(A) For the protection of groundwater, see WAC 173-340-747;
(B) For soil ingestion, the gastrointestinal absorption fraction, may be modified if the requirements of WAC 173-340-702 (14), (15), (16), and 173-340-708(10) are met;
(C) For dermal contact, the adherence factor, dermal absorption fraction and gastrointestinal absorption conversion factor may be modified if the requirements of WAC 173-340-702 (14), (15), (16), and 173-340-708(10) are met;
(D) The toxicity equivalent factors provided in WAC 173-340-708 (8)(d), (e), and (f), may be modified if the requirements of WAC 173-340-708 (8)(g) and (h) are met;
(E) The reference dose and cancer potency factor may be modified if the requirements in WAC 173-340-708 (7) and (8) are met; and
(F) Other modifications incorporating new science as provided for in WAC 173-340-702 (14), (15) and (16).
(iii) Dermal contact. For hazardous substances other than petroleum mixtures, dermal contact with the soil shall be evaluated whenever the proposed changes to Equations 740-1 or 740-2 would result in a significantly higher soil cleanup level than would be calculated without the proposed changes. When conducting this evaluation, the following equations and default assumptions shall be used.
(A) For noncarcinogens use Equation 740-4. This equation takes into account concurrent exposure due to ingestion and dermal contact with soil.
[Equation 740-4]
 |
Where: | ||
Csoil | = | Soil cleanup level (mg/kg) |
HQ | = | Hazard quotient (unitless) |
ABW | = | Average body weight over the exposure duration (16 kg) |
AT | = | Averaging time (6 years) |
EF | = | Exposure frequency (1.0) (unitless) |
ED | = | Exposure duration (6 years) |
SIR | = | Soil ingestion rate (200 mg/day) |
AB1 | = | Gastrointestinal absorption fraction (1.0) (unitless) |
SA | = | Dermal surface area (2,200 cm2) |
AF | = | Adherence factor (0.2 mg/cm2-day) |
ABS | = | Dermal absorption fraction (unitless). |
May use chemical-specific values or the following defaults: | ||
• | 0.01 for inorganic hazardous substances | |
• | 0.0005 for volatile organic compounds with vapor pressure ˃ = benzene | |
• | 0.03 for volatile organic compounds with vapor pressure < benzene | |
• | 0.1 for other organic hazardous substances | |
RfDo | = | Oral reference dose as defined in WAC 173-340-708(7) (mg/kg-day) |
RfDd | = | Dermal reference dose (mg/kg-day) derived by RfDo x GI |
GI | = | Gastrointestinal absorption conversion factor (unitless). |
May use chemical specific values or the following defaults: | ||
• | 0.2 for inorganic hazardous substances | |
• | 0.8 for volatile organic compounds | |
• | 0.5 for other organic hazardous substances | |
(B) For carcinogens use Equation 740-5. This equation takes into account concurrent exposure due to ingestion and dermal contact with soil.
[Equation 740-5]
 |
Where: | ||
Csoil | = | Soil cleanup level (mg/kg) |
RISK | = | Acceptable cancer risk (1 in 1,000,000) (unitless) |
ABW | = | Average body weight over the exposure duration (16 kg) |
AT | = | Averaging time (75 years) |
EF | = | Exposure frequency (1.0) (unitless) |
ED | = | Exposure duration (6 years) |
SIR | = | Soil ingestion rate (200 mg/day) |
AB1 | = | Gastrointestinal absorption fraction (1.0) (unitless). May use 0.6 for mixtures of dioxins and/or furans |
CPFo | = | Oral cancer potency factor as defined in WAC 173-340-708(8) (kg-day/mg) |
CPFd | = | Dermal cancer potency factor (kg-day/mg) derived by CPFo/GI |
GI | = | Gastrointestinal absorption conversion factor (unitless). |
May use chemical-specific values or the following defaults: | ||
• | 0.2 for inorganic hazardous substances | |
• | 0.8 for volatile organic compounds and for mixtures of dioxins and/or furans | |
• | 0.5 for other organic hazardous substances | |
SA | = | Dermal surface area (2,200 cm2) |
AF | = | Adherence factor (0.2 mg/cm2-day) |
ABS | = | Dermal absorption fraction (unitless). May use chemical-specific values or the following defaults: |
• | 0.01 for inorganic hazardous substances | |
• | 0.0005 for volatile organic compounds with vapor pressure ˃ = benzene | |
• | 0.03 for volatile organic compounds with vapor pressure < benzene and for mixtures of dioxins and/or furans | |
• | 0.1 for other organic hazardous substances | |
(C) Modifications may be made to Equations 740-4 and 740-5 as provided for in subsection (3)(c)(ii) of this section.
(iv) Soil vapors.
(A) Applicability. The soil to vapor pathway shall be evaluated for volatile organic compounds whenever any of the following conditions exist:
(I) For other than petroleum hydrocarbon mixtures, the proposed changes to the standard Method B equations (Equations 740-1 and 740-2) or default values would result in a significantly higher soil cleanup level than would be calculated without the proposed changes;
(II) For petroleum hydrocarbon mixtures, the proposed changes to the standard Method B equations (Equations 740-3, 740-4 and 740-5) or default values would result in a significantly higher soil cleanup level than would be calculated without the proposed changes;
(III) For gasoline range organics, whenever the total petroleum hydrocarbon (TPH) concentration is significantly higher than a concentration derived for protection of groundwater for drinking water beneficial use under WAC 173-340-747(6) using the default assumptions;
(IV) For diesel range organics, whenever the total petroleum hydrocarbon (TPH) concentration is greater than 10,000 mg/kg;
(V) For other volatile organic compounds, including petroleum components, whenever the concentration is significantly higher than a concentration derived for protection of groundwater for drinking water beneficial use under WAC 173-340-747(4).
(B) Evaluation methods. Soil cleanup levels that are protective of the indoor and ambient air shall be determined on a site-specific basis. Soil cleanup levels may be evaluated as being protective of air pathways using any of the following methods:
(I) Measurements of the soil vapor concentrations, using methods approved by the department, demonstrating vapors in the soil would not exceed air cleanup levels established under WAC 173-340-750.
(II) Measurements of ambient air concentrations and/or indoor air vapor concentrations throughout buildings, using methods approved by the department, demonstrating air does not exceed cleanup levels established under WAC 173-340-750. Such measurements must be representative of current and future site conditions when vapors are likely to enter and accumulate in structures. Measurement of ambient air may be excluded if it can be shown that indoor air is the most protective point of exposure.
(III) Use of modeling methods approved by the department to demonstrate the air cleanup standards established under WAC 173-340-750 will not be exceeded. When this method is used, the department may require soil vapor and/or air monitoring to be conducted to verify the calculations and compliance with air cleanup standards.
(IV) Other methods as approved by the department demonstrating the air cleanup standards established under WAC 173-340-750 will not be exceeded.
(d) Using modified Method B to evaluate soil remediation levels. In addition to the adjustments allowed under subsection (3)(c) of this section, adjustments to the reasonable maximum exposure scenario or default exposure assumptions are allowed when using a quantitative site-specific risk assessment to evaluate the protectiveness of a remedy. See WAC 173-340-355, 173-340-357, and 173-340-708 (3)(d) and (10)(b).
(4) Method C soil cleanup levels. This section does not provide procedures for establishing Method C soil cleanup levels. Except for qualifying industrial properties, Method A and Method B, as described in this section, are the only methods available for establishing soil cleanup levels at sites. See WAC 173-340-745 for use of Method C soil cleanup levels at qualifying industrial properties. See also WAC 173-340-357 and 173-340-708 (3)(d) for how land use may be considered when selecting a cleanup action at a site.
(5) Adjustments to cleanup levels.
(a) Total site risk adjustments. Soil cleanup levels for individual hazardous substances developed in accordance with subsection (3) of this section, including cleanup levels based on applicable state and federal laws, shall be adjusted downward to take into account exposure to multiple hazardous substances and/or exposure resulting from more than one pathway of exposure. These adjustments need to be made only if, without these adjustments, the hazard index would exceed one or the total excess cancer risk would exceed one in 100,000 (1 x 10-5). These adjustments shall be made in accordance with the procedures specified in WAC 173-340-708 (5) and (6). In making these adjustments, the hazard index shall not exceed one and the total excess cancer risk shall not exceed one in 100,000 (1 x 10-5).
(b) Adjustments to applicable state and federal laws. Where a cleanup level developed under subsection (2) or (3) of this section is based on an applicable state or federal law and the level of risk upon which the standard is based exceeds an excess cancer risk of one in 100,000 (1 x 10-5) or a hazard index of one, the cleanup level must be adjusted downward so that the total excess cancer risk does not exceed one in 100,000 (1 x 10-5) and the hazard index does not exceed one at the site.
(c) Natural background and PQL considerations. Cleanup levels determined under subsection (2) or (3) of this section, including cleanup levels adjusted under subsection (5)(a) and (b) of this section, shall not be set at levels below the practical quantitation limit or natural background, whichever is higher. See WAC 173-340-707 and 173-340-709 for additional requirements pertaining to practical quantitation limits and natural background.
(6) Point of compliance.
(a) The point of compliance is the point or points where the soil cleanup levels established under subsection (2) or (3) of this section shall be attained.
(b) For soil cleanup levels based on the protection of groundwater, the point of compliance shall be established in the soils throughout the site.
(c) For soil cleanup levels based on protection from vapors, the point of compliance shall be established in the soils throughout the site from the ground surface to the uppermost groundwater saturated zone (e.g., from the ground surface to the uppermost water table).
(d) For soil cleanup levels based on human exposure via direct contact or other exposure pathways where contact with the soil is required to complete the pathway, the point of compliance shall be established in the soils throughout the site from the ground surface to 15 feet below the ground surface. This represents a reasonable estimate of the depth of soil that could be excavated and distributed at the soil surface as a result of site development activities.
(e) For soil cleanup levels based on ecological considerations, see WAC 173-340-7490 for the point of compliance.
(f) The department recognizes that, for those cleanup actions selected under this chapter that involve containment of hazardous substances, the soil cleanup levels will typically not be met at the points of compliance specified in (b) through (e) of this subsection. In these cases, the cleanup action may be determined to comply with cleanup standards, provided:
(i) The selected remedy is permanent to the maximum extent practicable using the procedures in WAC 173-340-360;
(ii) The cleanup action is protective of human health. The department may require a site-specific human health risk assessment conforming to the requirements of this chapter to demonstrate that the cleanup action is protective of human health;
(iii) The cleanup action is demonstrated to be protective of terrestrial ecological receptors under WAC 173-340-7490 through 173-340-7494;
(iv) Institutional controls are put in place under WAC 173-340-440 that prohibit or limit activities that could interfere with the long-term integrity of the containment system;
(v) Compliance monitoring under WAC 173-340-410 and periodic reviews under WAC 173-340-430 are designed to ensure the long-term integrity of the containment system; and
(vi) The types, levels and amount of hazardous substances remaining on-site and the measures that will be used to prevent migration and contact with those substances are specified in the draft cleanup action plan.
(7) Compliance monitoring.
(a) Compliance with soil cleanup levels shall be based on total analyses of the soil fraction less than two millimeters in size. When it is reasonable to expect that larger soil particles could be reduced to two millimeters or less during current or future site use and this reduction could cause an increase in the concentrations of hazardous substances in the soil, soil cleanup levels shall also apply to these larger soil particles. Compliance with soil cleanup levels shall be based on dry weight concentrations. The department may approve the use of alternate procedures for stabilized soils.
(b) When soil levels have been established at a site, sampling of the soil shall be conducted to determine if compliance with the soil cleanup levels has been achieved. Sampling and analytical procedures shall be defined in a compliance monitoring plan prepared under WAC 173-340-410. The sample design shall provide data that are representative of the area where exposure to hazardous substances may occur.
(c) The data analysis and evaluation procedures used to evaluate compliance with soil cleanup levels shall be defined in a compliance monitoring plan prepared under WAC 173-340-410. These procedures shall meet the following general requirements:
(i) Methods of data analysis shall be consistent with the sampling design. Separate methods may be specified for surface soils and deeper soils;
(ii) When cleanup levels are based on requirements specified in applicable state and federal laws, the procedures for evaluating compliance that are specified in those requirements shall be used to evaluate compliance with cleanup levels unless those procedures conflict with the intent of this section;
(iii) Where procedures for evaluating compliance are not specified in an applicable state and federal law, statistical methods shall be appropriate for the distribution of sampling data for each hazardous substance. If the distributions for hazardous substances differ, more than one statistical method may be required; and
(iv) The data analysis plan shall specify which parameters are to be used to determine compliance with soil cleanup levels.
(A) For cleanup levels based on short-term or acute toxic effects on human health or the environment, an upper percentile soil concentration shall be used to evaluate compliance with cleanup levels.
(B) For cleanup levels based on chronic or carcinogenic threats, the true mean soil concentration shall be used to evaluate compliance with cleanup levels.
(d) When data analysis procedures for evaluating compliance are not specified in an applicable state or federal law the following procedures shall be used:
(i) A confidence interval approach that meets the following requirements:
(A) The upper one sided 95 percent confidence limit on the true mean soil concentration shall be less than the soil cleanup level. For lognormally distributed data, the upper one-sided 95 percent confidence limit shall be calculated using Land's method; and
(B) Data shall be assumed to be lognormally distributed unless this assumption is rejected by a statistical test. If a lognormal distribution is inappropriate, data shall be assumed to be normally distributed unless this assumption is rejected by a statistical test. The W test, D'Agostino's test, or, censored probability plots, as appropriate for the data, shall be the statistical methods used to determine whether the data are lognormally or normally distributed;
(ii) For an evaluation conducted under (c)(iv)(A) of this subsection, a parametric test for percentiles based on tolerance intervals to test the proportion of soil samples having concentrations less than the soil cleanup level. When using this method, the true proportion of samples that do not exceed the soil cleanup level shall not be less than 90 percent. Statistical tests shall be performed with a Type I error level of 0.05;
(iii) Direct comparison of soil sample concentrations with cleanup levels may be used to evaluate compliance with cleanup levels where selective sampling of soil can be reliably expected to find suspected soil contamination. There must be documented, reliable information that the soil samples have been taken from the appropriate locations. Persons using this method must demonstrate that the basis used for selecting the soil sample locations provides a high probability that any existing areas of soil contamination have been found; or
(iv) Other statistical methods approved by the department.
(e) All data analysis methods used, including those specified in state and federal law, must meet the following requirements:
(i) No single sample concentration shall be greater than two times the soil cleanup level. Higher exceedances to control false positive error rates at five percent may be approved by the department when the cleanup level is based on background concentrations; and
(ii) Less than 10 percent of the sample concentrations shall exceed the soil cleanup level. Higher exceedances to control false positive error rates at five percent may be approved by the department when the cleanup level is based on background concentrations.
(f) When using statistical methods to demonstrate compliance with soil cleanup levels, the following procedures shall be used for measurements below the practical quantitation limit:
(i) Measurements below the method detection limit shall be assigned a value equal to one-half the method detection limit when not more than 15 percent of the measurements are below the practical quantitation limit.
(ii) Measurements above the method detection limit but below the practical quantitation limit shall be assigned a value equal to the method detection limit when not more than 15 percent of the measurements are below the practical quantitation limit.
(iii) When between 15 and 50 percent of the measurements are below the practical quantitation limit and the data are assumed to be lognormally or normally distributed, Cohen's method shall be used to calculate a corrected mean and standard deviation for use in calculating an upper confidence limit on the true mean soil concentration.
(iv) If more than 50 percent of the measurements are below the practical quantitation limit, the largest value in the data set shall be used in place of an upper confidence limit on the true mean soil concentration.
(v) The department may approve alternate statistical procedures for handling nondetected values or values below the practical quantitation limit.
(vi) If a hazardous substance or petroleum fraction has never been detected in any sample at a site and these substances are not suspected of being present at the site based on site history and other knowledge, that hazardous substance or petroleum fraction may be excluded from the statistical analysis.