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Aspects of Weston Village and Hcbd Problems

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The ICI chemical plant at Runcorn has been landfilling its unwanted waste by products in the disused quarries in the village of Weston in Cheshire. These by products were the result of the production of a variety of chemical products including polyvinyl chemicals, chlorinated alkanes, chlorinated naphthalene, and many more solvents. However, over the last decade high concentrations of hexachloro-1,3-butadiene (HCBD) have been measured close to and inside a number of residences within close proximity to the site. A major concern is that this chemical is not manufactured commercially, meaning that that the presence must be from the landfill. Further investigation into several boreholes revealed that HCBD vapour concentrations were high. The use of these quarries stopped in the mid 1970’s, thus meaning the site was capped and landscaped to fit back in with the environment around it.

HCBD

HCBD is a man made chemical, which is colourless, oily and does not dissolve in water. This chemical is toxic to aquatic organism and plants, and tends to accumulate and persist in soils and water. This means that it could have global scale environmental effects.

Hexachlorobutadiene occur as a by-product during the chlorinolysis of butane in the production of tetrachloride and tetrachloroethene (Berndt and Mehendale, 1979). These two commodities are manufactured on such a large scale that the amount of HCBD can be produced on industrial demand.

Toxicity

According to the EPA IRIS report the oral slope factor is 7.8 x10 -2 per mg/kg-day (EPA IRIS, 2002). An oral slope factor is used to estimate the risk of cancer with exposure to a carcinogenic, in this case HCBD was tested. It uses a 95% confidence limit for the increased cancer risk from a lifetime of exposure to HCBD via ingestion or inhalation. This estimation uses the units of mg per substance, kg of body weight, per day. The drinking water unit risk is 2.2 x10 -6 per µg/L, this means level of HCBD in drinking water where the level is dangerous to consume (EPA IRIS, 2018). The quantitative estimation of the carcinogenic risk from inhalation exposure is 2.2 x10 -5 per µg/m3.

Concerns over HCBD relate to limited toxicological studies that show that this chemical is a probable human carcinogen as well as a systemic toxin, being probable to cause liver damage if exposed to humans. Studies on rats have shown high levels of HCBD to cause kidney cancer, although this has yet to be proven within humans. Kociba et al. (1997) found from studies on the rats, the tumour’s to be located in the urinary, this does not differ for either oral exposure or inhalation. Fish species and crustaceans have been found to be the most sensitive, 96-h LC50 values ranging from 0.032 to 1.2 and 0.09 to approximately 1.7 mg l -1 for crustaceans and fish respectively (Toxic substance profile, 2018).

Exposure assessment:

CalTOX

The purpose of this assessment is to undertake a risk assessment on HCBD through relevant toxicological information and applying a multi-media, fate and toxic assessment model (CalTOX) to the Weston site. This model was developed for the Californian EPA for specific use in assessing the human risk through exposure to organic chemicals in environmental media from contaminated landfill sites (McKone, 1993). This model was created using both Excel/Visual Basic and incorporates a dynamic Level III fugacity model to distribute the chemical into 8 environmental compartments and to determine concentrations in soil, air, water (surface and groundwater) as well as plants/crops. A human risk characterisation pathways model is also incorporated within CalTOX to determine human doses for the various pathways of exposure (McKone, 1993).

Pathways

The exact quantities of HCBD are unknown, however as part of ICI “Project Pathway” an assessment into the industrial activity around Weston village. This used borehole data and over 2000 indoor air measurements. This occurred in 1993 and was a voluntary assessment of the legacy of almost 200 years of industry. The aim of the project pathway was to explore whether the industrial activity posed an unacceptable risk to people or the environment (Barnes et al., 2002).

The Western Quarries are located on a Triassic sandstone, with a depth of 30m below the surface. The ground water level at the quarry 70m. The last quarrying action stopped in the 1900’s but since then it has been for dispersal of industrial and chemical waste. The data provided from the initial assessment, such as geology, contaminants, migration pathway and sources, helped to review the site. This review found that subsurface vapour transport of volatile chlorinated hydrocarbons through the relative air-permeable vadose zone in the sandstone as a potentially significant contaminant mitigation pathway (Moss, 2004). Due to this finding, a plan was implemented to assess the significance of this potential contaminant migration pathway.

This plan involved installing a network of vapour monitoring wells around the North and South Quarry between the source area and the potentially affected houses. These monitoring stations found hexachlorobutadiene concentrations, these have raised concern over the potential to affect indoor air in the surrounding properties.

Dose Data

In the following years, a more comprehensive study was undertaken by the Building Research Establishment (BRE), this involved screening 390 properties over 15 months (Moss, 2004). They indoor air value has a guideline if 0.6 ppbv (Parts per billion by volume) for HCBD levels (Barnes et al., 2002). The tests found a total of 29 properties that exceeded this level. All of these houses were adjacent to the quarry. From these findings, the release of HCBD from the quarry is at a dangerous level, action must be taken to prevent human life being put at risk.

Risk Assessment:

Cancer

HCBD has been found to be a carcinogen, studies on rats have proven that the chemical does cause cancer in high doses (Berndt and Mehendale, 1979). This has yet to be proven on humans. Using the cancer potency information taken from the EPA IRIS database, the probability for the additional cancer risk through exposure to HCBD has been calculated at 6.0E-4 (6.0×10-4). The equation to calculate this reads:

P(d) = q * d

The P(d) is the lifetime probability of developing cancer, d is the dose (mg/kg per day), q is the slope potency factor (mg/kg per day)-1.

The odds of gaining cancer through exposure to any chemical need to be below one in a million. As proven by this equation the conservative low-dose cancer probability is 6.0E-4. This is way above the one in a million, meaning exposure to this chemical is too high of a risk of causing cancer. From this it shows that something must be done to more humans away from the site. As HCBD was found at the quarry and within the air in and around the houses, some action must be taken as it is not safe to live there.

Hazard

From the CalTOX model a hazard index can be produced. This uses the Exposure dose over the tolerable daily intake. If this value is greater than one, there is an unacceptable risk. From this a hazard index number is calculated, for this exposure it is 7.4 E (7.4×10). The value of 7.4 E is very high, proving some action needs to be taken.

What could be done?

As proven by the results the hazard and cancer risk is too high to have no intervention at this site. Something must be done to either stop the outbreak and/or remove residents from living near the quarry. The ICI have many options to try and resolve this problem, however some have concerns over effectiveness and expensiveness of the methods.

The first method is to remove the source of the HCBD. This would involve excavating the site, pulling up all the landfill and removing it to a secure location where it can be destroyed or dealt with. This method would ensure no more HCBD and other dangerous chemicals would be released around the quarry (Poblete et al., 2011). This method is useful as the source has been removed, so there would be no new production. However, this will be a large-scale project, that will take months to years to complete. This would cause major disruption to the town with heavy traffic and noisy work. On top of this, it would be the most expensive method.

Another method that could be considered is trying to contain the site. This method would involve re-capping the site, by removing what is already there and putting a new layer on. There are three steps to this, a top layer of soil and vegetation, the second is a drainage layer and the third is a low permeable layer (Rittmann et al., 1996; Raghab et al., 2013). This is typically made of synthetic material covering a few feet of compacted clay. The main benefit of this is that no more chemicals would be allowed to escape into the surrounding area. This would also make the local properties livable again after the HCBD has been removed from the air. A problem with this method is that it could become quite expensive and has the potential to cause minor disruption. The effectiveness of this is also questioned, as typically when landfill sites are capped they should be contained and as proven at Weston it does not always work.

A method that should be considered is to capture the HCBD released. Siwajek et al. (1998) studied the recovery of gas at landfill sites. This was done for both methane and carbon dioxide, however it’s still unsure if this could be done for HCBD. As stated by Siwajek et al. (1998) this method would require the installation of pipe work all around the site and has the potential to be expensive. A third option is to relocate and rehouse the local residents and demolish the houses. This would mean that residents would not be at risk. However, this would not be favorable to local residents.

Management of HCBD risk in Weston

The recommendations going forward would be to prevent the further release of HCBD and any other chemicals. This would best be done via containment, if plausible at this site. This would mean that local residents would be able to stay. However, it could be for the best if the house that recorded unsafe levels of HCBD be demolished or evacuated until safe to return. On top of this, a plan should be put in place for healthcare to local residents that were/could have been at risk of ingestion of HCBD. The uncertainties within this approach is the effectiveness of the containment and the potential for future leakage as the source is still nearby. To counter these a safe radius around the site should be erected with any houses within this demolished and the residents rehomed. When resealing the site, an alternative cover type could be used such as asphalt or a bioengineered management cover, however the most effective for preventing further release should be used.

Model suitability and validation

Like any model, the results are not always accurate, however they are very useful. This is especially true when predicting future outcome. They are also valuable when testing something potentially dangerous, such as the exposure of chemicals. The CalTOX model used was useful as many parameters can be inputted into the model. This is especially true for the landscape as biological, aquatic and soils based properties can be altered (Bonnard, 2006). One advantage of the model is the speed, the model can be changed and run in minutes (Hurtwich, 2000). To make any alteration, the whole model does not have to be run again, this is the advantage of the model being simulated in Excels.

However, there are some disadvantages with using the CalTOX model. This includes the uncertainty and sensitivity to the parameters, this also raises questions over the accurate meaning given to the parameters concerning their actual use in the equations (Bonnard, 2006). As much of an advantage having lots of parameters is, it can also be a problem. This is shown if there is a lack of scientific data for many of the limits, the model cannot be run to full potential. To complete the spreadsheet a lot of data collection would be needed.

What did happen at Weston village?

As the results from the Building Research Establishment were over 0.6 ppbv in 29 houses adjacent to the quarry, it was determined the best course of action was to demolish the houses. This meant there would be no future risk as the land is uninhabitable, and the quickest solution (Barnes et al., 2005).

Conclusion

The quarry site around Weston village has leaked the carcinogenic chemical HCBD. From inputting the details of this exposure into the CalTOX model, it assessed the human risk to HCBD. From this it was determined the chemical was unsafe and too much of a hazard to allow it to be inhaled. To prevent future incidents, a recommendation to re-contain the site to prevent the further release of HCBD and other chemicals. This method would cause disruption to the local community and force some residents out of their homes, however this seems the best method going forward. Comparing this to the actual outcome, less houses would be demolished and the continued leakage of chemicals out of the quarry would be stopped. However, this would be more expensive and potentially time consuming.

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Aspects of Weston village and HCBD problems. (2018, November 19). GradesFixer. Retrieved May 21, 2022, from https://gradesfixer.com/free-essay-examples/aspects-of-weston-village-and-hcbd-problems/
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