SECTION 350.51. Affected Property Assessment

(a) The person shall conduct an affected property assessment in a manner appropriate for the affected property considering the hydrogeology, physical and chemical properties of the COCs, location of human and ecological receptors, and the complete or reasonably anticipated to be completed exposure pathways identified in §350.71 of this title (relating to General Requirements). The assessment shall be designed to collect information necessary to support notification of affected landowners and remedy selection, determine whether or not water resources have been affected or are threatened, and may also evaluate the effectiveness of existing physical controls. Additionally, when existing physical controls will be used as part of the response action in accordance with Remedy Standard B, then the assessment may be conducted such that the primary focus is placed beyond the limits of the existing physical control in order to reduce the degree of assessment within the limits of the physical control. The assessment shall be conducted in a manner most likely to detect the presence and distribution of COCs above the concentration levels defined in subsections (b) - (e) of this section considering the nature of the release and subsequent modifications to the affected property (e.g., judgmental samples in hot spots, stratified random sampling, systematic grid, etc.), and shall use appropriate quality assurance/quality control. The geology and hydrogeology of the affected property shall be adequately characterized, such that COC fate and transport can be reliably predicted in order to confidently locate existing environmental media containing COCs above the concentration levels defined in subsections (b) - (e) of this section and an appropriate response action can be designed. The person shall use sample collection techniques that meet the data quality needs and are acceptable to the executive director. The results of the assessment shall be documented in an Affected Property Assessment Report in accordance with §350.91 of this title (relating to Affected Property Assessment Report). The person shall conduct an assessment in a manner which is timely considering the size and complexity of the situation, and shall comply with an assessment schedule established in any commission rule, order, or permit, or any assessment schedule approved by the executive director.

(b) The person shall perform an affected property assessment through the collection and analysis of a sufficient number of samples from environmental media to reliably characterize the nature and degree of COCs in the source area(s), as well as the horizontal and vertical extent of COCs in soil and groundwater, which equals or exceeds the applicable concentration of COCs as specified in subsections (c), (d) and (e) of this section, unless the executive director determines on a site-specific basis that additional assessment of the extent of COCs is necessary to evaluate a potential threat to human health and the environment. Information obtained from attempts to attain Remedy Standard A may be submitted for this purpose. The person shall characterize the nature, degree and extent of COCs in other environmental media as required by the executive director in consideration of property-specific factors. The executive director may require the person to determine the concentrations of COCs in outdoor or indoor air on a property-specific basis.

(c) The person shall demonstrate that all COCs in environmental media (except for on-site soils as noted below) which exceed the residential assessment level have been characterized horizontally in all directions. If the assessment level is based upon background concentrations, then the assessment shall only extend to the background concentration level. For soils only, the person can focus the horizontal on-site assessment to define the area exceeding the applicable critical PCL (i.e., residential or commercial/industrial). However, the person shall investigate environmental media, including soils, using adequate on-site or off-site data to determine whether off-site properties have been affected with concentrations of COCs which exceed the residential assessment levels. The requirement to use an assessment level based upon a residential receptor (i.e., residential assessment level) pertains to all off-site properties (i.e., both residential and commercial/industrial land use).

(d) For the vertical soil assessment to adequately determine if groundwater has been or will be affected, the person shall complete the requirements of paragraph (1), (2), (3) or (4) of this subsection.

(1) The person shall demonstrate that the vertical limit of COCs in soil which exceed the higher of the method quantitation limit or background concentrations has been characterized. If the person satisfactorily demonstrates that all reasonably available analytical technology has been used to show that the COC cannot be measured to the method quantitation limit due to sample specific interferences, then the sample detection limit may be used in lieu of the method quantitation limit.

(2) If an adequate groundwater assessment has been conducted (i.e., COC concentrations in groundwater have been measured from appropriate locations), then the person shall characterize the vertical limits of COCs in soil which exceed the residential assessment level. The ^GW Soil PCL may not be applicable in the determination of the residential assessment level if the person has conducted an adequate groundwater assessment and can meet the requirements of §350.75(i)(7)(C) of this title (relating to Tiered Human Health Protective Concentration Level Evaluation). The executive director may omit or modify the requirement for a groundwater assessment under this paragraph for use of §350.75(i)(7)(C) of this title on a site-specific determination based upon a combination of supporting evidence including, but not necessarily limited to, probable depth to groundwater, presence of soils or bedrock that prohibit or impede vertical migration of COCs, and physical and chemical properties of the COCs.

(3) If the uppermost groundwater-bearing unit is encountered before the vertical limit of COCs is determined to the higher of the method quantitation limit or background concentrations, then representative groundwater samples (i.e., a groundwater sample does not have to be collected from each boring) must be collected to evaluate potential groundwater impacts. The vertical extent of the soil assessment shall continue beyond the uppermost groundwater-bearing unit as appropriate based on the likelihood that COCs have migrated deeper considering the chemical and physical properties of the COCs (e.g., dense non-aqueous phase liquids) and the hydrogeology of the affected property. The executive director may omit or modify this requirement on a site-specific basis if the vertical assessment would exacerbate the vertical migration of COCs.

(4) If a person has already determined that the groundwater is impacted, then they may satisfy the requirements of this subsection by declaring the entire soil column to the top of the lowest impacted groundwater bearing unit as a soil PCLE zone.

(e) The person shall define the vertical extent of COCs in groundwater to below the residential assessment level by collecting a representative sample from a deeper groundwater-bearing unit with concentrations less than the residential assessment levels, unless the person demonstrates that vertical migration to a lower groundwater-bearing unit is not possible. The person shall base such demonstration on the hydrogeology and the chemical and physical properties of the COCs. The person shall take proper precautions to prevent cross-contamination when collecting a sample from a deeper groundwater-bearing unit. The executive director may omit or modify this requirement on a site-specific basis if the vertical assessment would exacerbate the vertical migration of COCs.

(f) The person shall use concentrations measured in groundwater at or immediately upgradient of the zone of groundwater discharge to surface water to determine if COCs in groundwater have discharged to surface waters.

(g) For affected properties with response actions which are designed and approved under Remedy Standard B for the use of a plume management zone, the person shall characterize the geology and hydrogeology throughout all areas of the plume management zone (i.e., including those areas of the plume management zone which are currently beyond the limits of the groundwater which contains COCs in excess of the assessment level).

(h) The person shall attempt to identify all surface and subsurface structures at the affected property which may influence COC migration, including subsurface utilities.

(i) The person shall conduct a field survey to locate potential receptors, including water wells and surface waters to at least 500 feet beyond the boundary of the affected property; and conduct a records survey to identify all water wells and surface water bodies within 1/2 mile of the limits of groundwater which contains COCs in excess of the residential assessment level. The person shall also attempt to identify any off-site properties within 1/4 mile of the affected property that have environmental information (e.g., soil boring logs, analytical results from samples of environmental media, etc.) collected for submission to the agency which may be useful in fulfilling the requirements of this section, although collection and submittal of this information by the person is not required.

(j) When determining concentrations of COCs in an environmental medium, the person shall collect and handle samples in accordance with sampling methodologies which will yield representative concentrations of COCs present in the sampled medium.

(k) When determining concentrations of COCs in surface water and sediment, the person shall collect and handle samples in accordance with the requirements in the agency's Surface Water Quality Monitoring Procedures, Volume I, as amended, or shall use an alternative methodology approved by the executive director.

(l) The person shall determine concentrations of COCs within the environmental media at the affected property. The executive director may approve the use of statistical or geostatistical methods to determine representative concentrations of COCs at the affected property or within areas representative of site-specific background conditions as long as the following conditions are satisfied.

(1) The person shall ensure that all assumptions for the selected statistical or geostatistical method are met or critically examined and explained if the assumptions cannot be met (e.g., random sampling design, normal or log-normal distribution, etc.). Judgmental samples may be used, as long as it can be demonstrated that the resulting estimated representative concentration is not biased low.

(2) An appropriate number of samples for the statistical method shall be used. If site-specific background is determined using the upper confidence limit or similar statistical method, then a minimum of eight samples shall be used. If the person uses an arithmetic average to determine the background concentration, then a minimum of five samples shall be used.

(3) The soil exposure area for existing residential yards or platted residential properties shall not exceed 1/8th acre or the size of the front or back yard of the affected residential lot, unless it is demonstrated that a larger area, not to exceed 1/2 acre, is appropriate based upon the activity patterns of residents at a specific affected property. For other properties classified as residential (e.g., parks, hospitals), the executive director may approve a larger exposure area if justified based on site-specific conditions. If an area larger than 1/8th acre or the size of the front or back yard of the existing affected residential lot is approved by the executive director, then the person shall comply with the applicable institutional control in requirements §350.111(b), (b)(8) or (10) of this title (relating to Use of Institutional Controls). If COCs are relatively homogeneous over an area larger than the residential default size, the executive director may allow concentrations to be averaged over this larger area, in which case the institutional control would not be required.

(4) The soil exposure area for commercial/industrial properties shall not exceed 1/2 acre, unless it is demonstrated that a larger area is appropriate based upon documented activity patterns for commercial/industrial workers at an active commercial/industrial facility (the assumed exposure area should represent the smallest area over which an individual can be expected to move randomly). In approving an exposure area for an active commercial/industrial facility, the executive director may consider any appropriate site-specific information which documents typical worker activity patterns. If an area larger than 1/2 acre is approved by the executive director, then the person shall comply with the institutional control requirements in §350.111(b), (b)(9) or (11) of this title (relating to Use of Institutional Controls), as applicable. If COCs are relatively homogeneous over an area larger than 1/2 acre, the executive director may allow concentrations to be averaged over this larger area, in which case the institutional control provision would not be required.

(5) The executive director may require a separate assessment of smaller but notable areas of soil contamination (i.e., "hot spots") at sites where site-specific features are present such that there is likely to be preferential exposure to this smaller area (e.g., worker exposures around the physical infrastructure of a work space, soils within a child's play area). The presence of hot spots with respect to ecological risk shall be determined on a site-specific basis.

(m) If a person does not desire to determine a site-specific soil background concentration, then they may use the Texas-specific median background concentrations for metals provided in the following figure. The Texas-specific background concentrations may be used to determine the critical PCL and then used in comparisons to individual measurements of COCs or representative concentrations of COCs in accordance with §350.79(1) or (2)(A) of this title (relating to Comparison of Chemical of Concern Concentrations to Protective Concentration Levels), respectively.

Attached Graphic

(n) Analytical results, including non-detected analytical results, should be considered whether doing direct comparisons of individual measurements or when using statistical or geostatistical approaches. In cases where there is reason to believe, based on available analytical data, that the COC could be present at that sampling location and that the concentration of the COC is suspected to be near but below the sample detection limit, the full value of the sample detection limit should be used as a proxy for the non-detected result. If there is reason to believe, based on available analytical data, that the COC could be present at that sampling location and that the concentration of the COC is suspected to be below, but not near to, the sample detection limit, then 1/2 the sample detection limit should be used as a proxy for the non-detected result. Other statistically-based approaches for handling non-detected results or assigning proxy values may be appropriate and approved if there is sufficient technical basis. If greater than 15 percent non-detected results are reported for a particular medium, and the exposure area cannot be definitively identified based on documented and verifiable site-specific information, the executive director may require persons to utilize alternative statistical methods for calculating the concentration term.

(o) When required by the executive director, the person shall classify an affected property in accordance with a risk-based system established by the executive director. The classification shall consider all information collected during the affected property assessment, any historical knowledge concerning the conditions at the affected property, and the short-term or long-term potential for human or ecological receptors to be exposed to COCs.

Source Note: The provisions of this §350.51 adopted to be effective September 23, 1999, 24 TexReg 7436; amended to be effective March 19, 2007, 32 TexReg 1526