SWMU B-20 Remedial Investigation Report Section 7 - Closure Options and Recommendations

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B-20 Remedial Investigation Report for Former Open Burn/Open Detonation Area

Section 7 - Closure Options and Recommendations

As described in Section 3, there are three closure standards under which CSSA may close the site. The requirements for these standards are described in the Texas Risk Reduction Rules (30 TAC 335 Subchapter S).

Risk Reduction Standards 1, 2, and 3 represent three alternate levels of site closure, ranging from complete removal of contaminants under RRS1 to in-place containment of contaminated media under RRS3. Recommended actions at the B-20 site to meet each of these standards are described below. An approach to achieve a combination of standards at the site is also described.

7.1 - Standard 1

7.1.1 Requirements

Closure under RRS1 provides a permanent remedy with a great degree of risk reduction. RRS1 requires that all waste, waste residues, leachate, and contaminated media be removed to background levels unaffected by waste management activities. The facility must submit a report to the TNRCC documenting compliance with the requirements of RRS1. This report must include descriptions of procedures and conclusions of the investigation to characterize the nature and extent of contamination, descriptions of removal actions performed, and summaries of sampling methodology and analytical results which demonstrate that contaminants have been removed or decontaminated to applicable levels. There are no requirements for post-closure care or deed recordation at site closed under RRS1.

7.1.2 Recommendations

As described in Section 6, contaminants (UXO and chemical contaminants) in surface soil, subsurface soil, sediment, and surface water exceed background levels at B-20. The following recommended actions would remove contaminants to background levels and provide analytical data to confirm that background conditions have been met.

7.1.2.1   Surface Soil

Due to chemical contamination of surface soil in four areas of the site and the possibility of UXO still remaining on the surface, the site does not meet RRS1 requirements. The following actions are recommended for surface soil:

Clear vegetation on site and around the perimeter are to facilitate sweeping for surface UXO. Although a sweep for UXO was conducted in November 1994, vegetation at the site may have visually obstructed other remaining UXO. Vegetation should be cleared by a controlled burn carried out by UXO professionals. For safety reasons, the explosion range for the types of UXO found at B-20 should be considered in preparing for this controlled burn.

The site should be reswept visually for UXO after the controlled burn has been conducted to ensure that no UXO remains.

Since the screening of the area outside the boundary was not done as systematically as the site UXO sweep, additional screening of this area is recommended. Additional screening should begin with a 300-foot boundary around the site. Screening should continue in 300-foot sections until no UXO is found. This 300-foot interval was selected based on information from the UXO professionals and the distance at which UXO was found from the site during this investigation (550 feet). Since some areas around B-20 are heavily vegetation with dense cedar and underbrush, this action will require prior vegetation clearing with the help of CSSA and UXO professionals.

While the site is being swept for UXO, all surface scrap metal should be removed for disposal. Costs for disposal of the scrap metal could be minimized if a recycling facility accepts this material.

Contaminants in surface soils covering approximately 10 acres exceed background metals levels. This surface soil must be removed and disposed of to meet RRS1 requirements. These soils should be removed to a depth of 2 feet, or to bedrock, whichever comes first. Samples should be collected from the excavated material to determine disposal options.

Explosives-contaminated surface soil in the immediate vicinity of sample location SS19 must be removed to meet RRS1.

Soils at SS20 should be sampled and analyzed for explosive compounds. If explosives are detected at concentrations exceeding PQLs, the soil should be removed and disposed.

Three small ammunition disposal areas and associated metals-contaminated soil must be removed to meet RRS1 requirements. It is estimated that approximately 200 cubic yards of soil and small ammunition need to be removed and transported off site for disposal. The estimated amount is based on the surface area of the disposal sites and 2 feet of subsurface excavation.

All UXO found at the site must be detonated. Of the 193 items found at the site, one item had to be left in place for safety reasons. The remaining items are still on site but, according to UXO professionals from UXB International, additional movement of these items is not recommended. For these reasons, on-site detonation of all of the UXO items is recommended. The BLU series anitpersonnel bomblet should be disposed of using the blow-in-place (BIP) method (EPA, 1993). A previously disturbed area at the B-20 site should be selected for disposal of the remaining UXO, thereby limiting unnecessary environmental impact to other areas.

Confirmation sampling and analysis must be conducted at all areas at which soil was removed or BIP disposal took place to verify that the site meets RRS1 requirements.

7.1.2.2   Subsurface Soil

Metals concentrations in subsurface soil and rock at three borings (SB2, SB9, and SB10) exceeded background levels. In addition, subsurface magnetic anomalies at the site may be caused by buried UXO, especially in the crater areas. The following actions are recommended to address subsurface soil/rock contamination:

To determine if metals levels in borings SB2, SB9, and SB10 could leach, it is recommended that borings be drilled near these locations and that two samples be collected from each new boring and analyzed by the toxicity characteristic leaching procedure (TCLP) and the synthetic precipitation leaching procedure (SPLP) for arsenic and mercury. If data shows that the metals do not leach, it may be recommended to close these areas under RRS1.

Magnetic anomalies were identified at ten of the fifteen craters. Since it is possible that these anomalies are caused by unexploded ordnance, the soil in the craters should be excavated and the anomalies should be identified and removed. If the anomalies are caused by UXO, it can be detonated with the UXO found during the investigation.

Based on the analytical results of this investigation, the soil in the craters is not contaminated so excavated soil can be backfilled. Clean fill can be brought in to fill all of the craters to grade.

Due to the limited amount of information regarding historic EOD activities at the site, it is recommended that a magnetometer survey be conducted in the entire northern portion of the site where a number of craters were found. Historical aerial photographs indicate that this was the portion of the site used in the 1960s, and possibly earlier. Any anomalies identified in this portion of the site should be excavated and disposed of appropriately.

7.1.2.3   Sediment

Sediments at crater 8 exceeded background metals concentrations. Therefore, to meet RRS1 requirements these soils must be removed. The following actions are recommended:

Sediments within crater 8 should be removed to a depth of 2 feet, transported off-site, and disposed of appropriately. A sample of excavated material should be analyzed by the TCLP for cadmium, lead, and mercury to determine disposal options.

Confirmation sampling and analysis should be conducted to determine if RRS1 requirements have been met.

7.1.2.4   Surface Water

Surface water samples collected from craters 8, 12, and 13 contained metals concentrations exceeding freshwater criteria. The following actions are recommended:

To determine if metals levels in sediments at craters 12 and 13 are contributing to the elevated metals levels observed in surface water, sediment samples should be collected from these craters and analyzed by the TCLP for cadmium and lead. Crater 8 was not included in this TCLP sampling because sediments there must be removed to closure under RRS1 (Section 7.1.2.3).

If the TCLP analysis indicates significant leaching potential, sediments in these craters should be excavated and disposed of at an appropriate disposal facility. TCLP analyses should be used to determine disposal options.

7.2 - Standard 2

7.2.1 Requirements

Closure under risk reduction standard 2 provides a permanent remedy with a high degree of risk reduction. RRS2 requires that all waste, waste residues, leachate, and contaminated media be removed to risk-based levels specified at 335.556 through 335.559. The facility must submit a report to the TNRCC documenting compliance with the requirements of RRS2. This report must include descriptions of procedures and conclusions of the investigation to characterize the nature and extent of contamination, descriptions of removal actions performed, and summaries of sampling methodology and analytical results which demonstrate that contaminants have been removed or decontaminated to applicable levels. A requirement for post-closure care is possible under RRS2. Deed recordation is required.

7.2.2 Recommendations

As described in Section 6, contaminants (UXO and chemical contaminants) in surface soil, subsurface soil, and surface water exceed risk-based levels. The following recommended actions would remove contaminants to risk-based levels and provide analytical data to confirm that RRS2 conditions have been met.

7.2.2.1   Surface Soil

Due to chemical contamination of surface soil in four areas of the site and the possibility of UXO still remaining on the surface, the site does not meet RRS2 requirements. The following actions are recommended for surface soil (actions are described in detail in Section 7.1.2.1):

Clear vegetation on site and around perimeter area to facilitate sweeping for surface UXO.

Resweep site for UXO after the controlled burn.

Sweep boundary of B-20 site in 300-foot sections.

Remove explosives-contaminated surface soil near SS19.

Sample soils at SS20 and analyze for explosive compounds. Dispose of soils, if necessary.

Remove soils and small ammunition in three disposal areas on site (approximately 200 cubic yards).

Detonate all UXO found on site.

Confirmation sampling.

7.2.2.2   Subsurface Soil

Subsurface magnetic anomalies at the site may be caused by buried UXO, especially in the crater areas. The following actions are recommended to address subsurface soil/rock contamination (actions are described in detail in Section 7.1.2.2):

Excavate magnetic anomalies identified at ten of the fifteen craters.

Backfill craters.

Conduct a magnetometer survey in the entire northern portion of the site. Remove any identified magnetic anomalies.

7.2.2.3   Surface Water

Surface water samples collected from craters 8, 12, and 13 contained metals concentrations exceeding freshwater criteria. The following actions are recommended (actions are detailed in Section 7.1.2.4):

Collect sediment samples at craters 8, 12, and 13 and analyze them using the TCLP for cadmium and lead.

If the TCLP analysis indicates significant leaching potential, excavate sediments. TCLP analyses should be used to determine disposal options.

7.3 - Standard 3

7.3.1 Requirements

Closure under risk reduction standard 3 requires that all waste and waste residues be removed to the maximum extent possible. Under the third standard, removal or decontamination processes are used where feasible to remove the principal threats at the site. TNRCC approval is required when closure under RRS3 is desired. Submittal of a remedial investigation report, baseline risk assessment, and corrective measures study is considered notification of intent to perform closure under RRS3. If the risk assessment concludes that no further action is required to achieve RRS3, the site must be deed recorded and post-closure care must be conducted. If the site does not meet RRS3 requirements, a closure/remedy must be implemented. After the cleanup levels are achieved, the site must be deed recorded and posts-closure care must be conducted.

7.3.2 Recommendations

Removal of UXO and chemical contaminants at the B-20 site is feasible, therefore the levels of these contaminants do not meet RRS3 requirements. Contaminants (UXO and chemical contaminants) in surface soil, subsurface soil, and surface water have not been removed to the maximum extent possible. The following recommended actions would remove contaminants to the maximum extent possible:

7.3.2.1   Surface Soil

Due to chemical contamination of surface soil in four areas of the site and the possibility of UXO still remaining on the surface, and because removal of this contamination is feasible, the site does not meet RRS3 requirements. The following actions are recommended for surface soil (actions are described in detail in Section 7.1.2.1):

Clear vegetation on site and around the perimeter area to facilitate sweeping for surface UXO.

Resweep the site for UXO after the controlled burn has been conducted to ensure that no UXO remains.

Sweep the boundary in 300-foot sections until no more UXO is found.

Remove explosives contaminated soil at SS19.

Sample soil at SS20 and analyze for explosives compounds. Dispose of soil if necessary.

Remove and disposal of soil and small ammunition at three disposal areas at B-20.

Detonate all UXO found at the site.

Confirmation sampling.

7.3.2.2   Subsurface Soil

Metals concentrations in subsurface soil and rock at three borings (SB2, SB9, and SB10) have not been removed to the maximum extent possible. In addition, subsurface magnetic anomalies at the site may be caused by buried UXO, especially in the crater areas. The following actions are recommended to address subsurface soil/rock contamination (actions are detailed in Section 7.1.2.2):

Metals concentrations in subsurface soil/rock should be evaluated in the risk assessment.

Remove magnetic anomalies identified at ten of the fifteen craters.

Backfill excavated areas.

Conduct a magnetometer survey in the entire northern portion of the site. Remove any identified magnetic anomalies.

7.3.2.3   Surface Water

Surface water samples collected from craters 8, 12, and 13 contained metals concentrations exceeding freshwater criteria. However, since these craters only contain water after intense periods of precipitation, removal of this contamination may not be feasible. Therefore, these sediments would be evaluated in a risk assessment for closure under RRS3.

7.3.2.4   Other Requirements

The Texas risk reduction rules require a risk assessment and corrective measures study for closure under RRS3.

7.4 - Combination of Standards

7.4.1 Requirements

Since contamination at the site is limited to several distinct areas, closure of a portion of the site under RRS2 and a portion under RRS1 is possible. All the requirements for closure under these standards are still necessary. If a portion of the site is closed under RRS2, that portion would be deed recorded and post-closure care would be required for that area. Use of a combination of standards would limit the area that must be deed recorded and limit the amount of work to be done at the site.

7.4.2 Recommendations

The portions of the site which seem to be most suitable for closure under RRS2 are the craters and the central portion of the site where metals levels were detected above background. The following recommended actions are for closure of the majority of the site under RRS1, and a portion under RRS2.

7.4.2.1   Surface Soil

Due to chemical contamination of surface soil in four areas of the site and the possibility of UXO still remaining on the surface, the site does not meet RRS1 requirements. The following actions are recommended for surface soil:

Clear vegetation on site and around the perimeter area to facilitate sweeping for surface UXO.

Resweep site for UXO after the controlled burn has been conducted to ensure that no UXO remains.

Sweep the boundary in 300-foot section until no more UXO is found.

Remove explosives-contaminated soil near SS19.

Sample soils at SS20 and analyze them for explosive compounds. If explosives are detected there at concentrations exceeding PQLs, the soil should be removed and disposed.

Remove and dispose of soil and small ammunition from three disposal areas at B-20 (approximately 200 cubic yards).

Detonate all UXO found on site.

Collect confirmation samples.

7.4.2.2   Subsurface Soil

Metals concentrations in subsurface soil and rock at three borings (SB2, SB9, and SB10) exceeded background levels. In addition, subsurface magnetic anomalies at the site may be caused by buried UXO, especially in the crater areas. The following actions are recommended to address subsurface soil/rock contamination (actions are described in detail in Section 7.1.2.2):

Metals concentrations in subsurface soil/rock should be evaluated in the risk assessment.

Excavate and remove magnetic anomalies identified in ten of fifteen craters.

Backfill craters.

Conduct a magnetometer survey in entire northern portion of the B-20 site. Excavate and remove any magnetic anomalies identified there.

7.4.2.3   Other Requirements

The Texas risk reduction rules require areas meeting RRS2 to be deed recorded. Post-closure care may be required for areas being closed under RRS2.

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	Clear vegetation on site and around the perimeter are to facilitate sweeping for surface UXO. Although a sweep for UXO was conducted in November 1994, vegetation at the site may have visually obstructed other remaining UXO. Vegetation should be cleared by a controlled burn carried out by UXO professionals. For safety reasons, the explosion range for the types of UXO found at B-20 should be considered in preparing for this controlled burn.
	The site should be reswept visually for UXO after the controlled burn has been conducted to ensure that no UXO remains.
	Since the screening of the area outside the boundary was not done as systematically as the site UXO sweep, additional screening of this area is recommended. Additional screening should begin with a 300-foot boundary around the site. Screening should continue in 300-foot sections until no UXO is found. This 300-foot interval was selected based on information from the UXO professionals and the distance at which UXO was found from the site during this investigation (550 feet). Since some areas around B-20 are heavily vegetation with dense cedar and underbrush, this action will require prior vegetation clearing with the help of CSSA and UXO professionals.
	While the site is being swept for UXO, all surface scrap metal should be removed for disposal. Costs for disposal of the scrap metal could be minimized if a recycling facility accepts this material.
	Contaminants in surface soils covering approximately 10 acres exceed background metals levels. This surface soil must be removed and disposed of to meet RRS1 requirements. These soils should be removed to a depth of 2 feet, or to bedrock, whichever comes first. Samples should be collected from the excavated material to determine disposal options.
	Explosives-contaminated surface soil in the immediate vicinity of sample location SS19 must be removed to meet RRS1.
	Soils at SS20 should be sampled and analyzed for explosive compounds. If explosives are detected at concentrations exceeding PQLs, the soil should be removed and disposed.
	Three small ammunition disposal areas and associated metals-contaminated soil must be removed to meet RRS1 requirements. It is estimated that approximately 200 cubic yards of soil and small ammunition need to be removed and transported off site for disposal. The estimated amount is based on the surface area of the disposal sites and 2 feet of subsurface excavation.
	All UXO found at the site must be detonated. Of the 193 items found at the site, one item had to be left in place for safety reasons. The remaining items are still on site but, according to UXO professionals from UXB International, additional movement of these items is not recommended. For these reasons, on-site detonation of all of the UXO items is recommended. The BLU series anitpersonnel bomblet should be disposed of using the blow-in-place (BIP) method (EPA, 1993). A previously disturbed area at the B-20 site should be selected for disposal of the remaining UXO, thereby limiting unnecessary environmental impact to other areas.
	Confirmation sampling and analysis must be conducted at all areas at which soil was removed or BIP disposal took place to verify that the site meets RRS1 requirements.

	To determine if metals levels in borings SB2, SB9, and SB10 could leach, it is recommended that borings be drilled near these locations and that two samples be collected from each new boring and analyzed by the toxicity characteristic leaching procedure (TCLP) and the synthetic precipitation leaching procedure (SPLP) for arsenic and mercury. If data shows that the metals do not leach, it may be recommended to close these areas under RRS1.
	Magnetic anomalies were identified at ten of the fifteen craters. Since it is possible that these anomalies are caused by unexploded ordnance, the soil in the craters should be excavated and the anomalies should be identified and removed. If the anomalies are caused by UXO, it can be detonated with the UXO found during the investigation.
	Based on the analytical results of this investigation, the soil in the craters is not contaminated so excavated soil can be backfilled. Clean fill can be brought in to fill all of the craters to grade.
	Due to the limited amount of information regarding historic EOD activities at the site, it is recommended that a magnetometer survey be conducted in the entire northern portion of the site where a number of craters were found. Historical aerial photographs indicate that this was the portion of the site used in the 1960s, and possibly earlier. Any anomalies identified in this portion of the site should be excavated and disposed of appropriately.

	Sediments within crater 8 should be removed to a depth of 2 feet, transported off-site, and disposed of appropriately. A sample of excavated material should be analyzed by the TCLP for cadmium, lead, and mercury to determine disposal options.
	Confirmation sampling and analysis should be conducted to determine if RRS1 requirements have been met.

	To determine if metals levels in sediments at craters 12 and 13 are contributing to the elevated metals levels observed in surface water, sediment samples should be collected from these craters and analyzed by the TCLP for cadmium and lead. Crater 8 was not included in this TCLP sampling because sediments there must be removed to closure under RRS1 (Section 7.1.2.3).
	If the TCLP analysis indicates significant leaching potential, sediments in these craters should be excavated and disposed of at an appropriate disposal facility. TCLP analyses should be used to determine disposal options.

	Clear vegetation on site and around perimeter area to facilitate sweeping for surface UXO.
	Resweep site for UXO after the controlled burn.
	Sweep boundary of B-20 site in 300-foot sections.
	Remove explosives-contaminated surface soil near SS19.
	Sample soils at SS20 and analyze for explosive compounds. Dispose of soils, if necessary.
	Remove soils and small ammunition in three disposal areas on site (approximately 200 cubic yards).
	Detonate all UXO found on site.
	Confirmation sampling.

	Excavate magnetic anomalies identified at ten of the fifteen craters.
	Backfill craters.
	Conduct a magnetometer survey in the entire northern portion of the site. Remove any identified magnetic anomalies.

	Collect sediment samples at craters 8, 12, and 13 and analyze them using the TCLP for cadmium and lead.
	If the TCLP analysis indicates significant leaching potential, excavate sediments. TCLP analyses should be used to determine disposal options.

	Clear vegetation on site and around the perimeter area to facilitate sweeping for surface UXO.
	Resweep the site for UXO after the controlled burn has been conducted to ensure that no UXO remains.
	Sweep the boundary in 300-foot sections until no more UXO is found.
	Remove explosives contaminated soil at SS19.
	Sample soil at SS20 and analyze for explosives compounds. Dispose of soil if necessary.
	Remove and disposal of soil and small ammunition at three disposal areas at B-20.
	Detonate all UXO found at the site.
	Confirmation sampling.

	Metals concentrations in subsurface soil/rock should be evaluated in the risk assessment.
	Remove magnetic anomalies identified at ten of the fifteen craters.
	Backfill excavated areas.
	Conduct a magnetometer survey in the entire northern portion of the site. Remove any identified magnetic anomalies.

	Clear vegetation on site and around the perimeter area to facilitate sweeping for surface UXO.
	Resweep site for UXO after the controlled burn has been conducted to ensure that no UXO remains.
	Sweep the boundary in 300-foot section until no more UXO is found.
	Remove explosives-contaminated soil near SS19.
	Sample soils at SS20 and analyze them for explosive compounds. If explosives are detected there at concentrations exceeding PQLs, the soil should be removed and disposed.
	Remove and dispose of soil and small ammunition from three disposal areas at B-20 (approximately 200 cubic yards).
	Detonate all UXO found on site.
	Collect confirmation samples.

	Metals concentrations in subsurface soil/rock should be evaluated in the risk assessment.
	Excavate and remove magnetic anomalies identified in ten of fifteen craters.
	Backfill craters.
	Conduct a magnetometer survey in entire northern portion of the B-20 site. Excavate and remove any magnetic anomalies identified there.