10.3 Consultancy database
Using consultancy data, various factors were found to give rise to different causes and severity of LNAPL product loss to ground. These factors are presented in the following sections.
10.3.1 Causes of contamination
The following factors were identified as causes of contamination at commercial and retail LNAPL storage sites.
10.3.1.1 Line leaks
The results indicated that, with an increasing age of product lines, particularly mild steel pipework, the likelihood of contamination risk also increased considering a positive coefficient a of the best fit regression line. The mean age of line failure was calculated as 19.5 years and the probability of failure was greater than a modelled constant probability after the age of 22 years.
Single containment pipe replacement, particularly mild steel, should therefore be considered as best practice at a maximum age of 22 years until more comprehensive failure data are available.
10.3.1.2 Unknown Causes of Contamination
The causes of contamination at retail and commercial fuel facilities should be further investigated to determine whether those presented in this dissertation are exhaustive and complete.
10.3.1.3 Tank failures
Although the mean age of tank failure was calculated as 23.2 years, the likelihood of failure was not observed to increase with increasing age, as demonstrated by a negative coefficient a for observed data.
The standard deviation of tank failures was calculated as 11.18, indicating a wide distribution of failure ages.
A higher failure rate was noted for tanks between the ages of 21 and 48 years, when compared with hypothetical constant failure rate data.
Management of tank failures should therefore be performed according to detailed risk assessment consistent with international best practise.
10.3.1.4 Other
Other causes of contamination can be differentiated as follows:
Site Infrastructure. Permeable forecourts, dispensing areas, fill areas and tank manholes were found to increase the likelihood of contamination. Ensuring that these infrastructural elements are impermeable would therefore reduce the likelihood of sub-surface contamination.
Operational Practises. Contamination of the sub-surface was noted to occur as a result of operational practises, such as tank overfilling. Overfill protection devices within the tanks, as well as operator training would serve to reduce the incidents thereof.
Table 10.1 summarises causes of contamination and possible mitigation.
Table 10.1. Methods to reduce contamination risk Factors Increasing Contamination
Risk
Recommendation to Reduce Risk SANS 10089-3:2010 Requirement (new
installations) Unprotected mild steel pipework. Replace pipework with non-ferrous. Yes
Permeable tank manholes. Seal manholes. Yes
Tank manholes where dispensing lines were not sealed correctly.
Seal manhole. Yes
Dispensing pumps where
impermeable pump sumps are absent.
Install pump sumps where possible. No
Remote fillers where spill containment was absent or insufficient.
Refurbish filler area. Yes
Dispensing areas that were not paved with impermeable hard surfacing, for example g-block paving.
Pave dispensing area with
impermeable material where possible.
No
Sites where leak detectors were absent or malfunctioned on submersible pumps.
Ensure leak detectors installed and correctly functioning, where possible.
Yes
Inspect and check leak detectors on a routine basis, where possible.
No
Sites where tank overfill protection devices were absent or
malfunctioned.
Install correctly functioning overfill protectors, where possible.
Yes
Sites where pipework has not been buried to the mandatory 300 mm below ground level.
Re-pipe site in affected area. Yes
Sites where pipework junctions were not housed within containment chambers.
Install pipework junctions in manholes.
Yes
Sites where tanks are not installed on specified material, as per SANS 089- 3: 2010, Section 5.2.
Inspect tank bedding on future installations prior to backfilling to ensure material meets SANS specification.
Yes
Sites where product reconciliation is Ensure product reconciliation is No
Factors Increasing Contamination Risk
Recommendation to Reduce Risk SANS 10089-3:2010 Requirement (new
installations) not performed or is performed poorly. performed according to established
procedure.
A draft template for Pollution Control Officers has been developed and attached as Appendix K. This template could be used to assist in data collection of infrastructure characteristics; integrity of equipment;
occurrence of product on site; and recent incidents.
10.3.2 Severity of an incident
Various factors were found to increase the severity of an incident, as per the following sections.
10.3.2.1 Causes
The severity of an incident was determined by calculating the mean volume lost per cause. Results indicated that the maximum mean was associated with line leaks, followed by filler related incidents and tank holes.
The severity of an incident did not correlate with the age of the infrastructure. Consistent maintenance and management of infrastructure is therefore essential throughout the lifespan of an LNAPL storage facility.
10.3.2.2 Pump type
Pump type was found to significantly influence contamination risk and the severity of an incident. In the event of failure, sites serviced with submersible pumps were found to have a greater mean volume lost compared with sites serviced with suction pumps. The mean volume lost for incident sites serviced with submersible pumps was calculated as 7 134 L while the mean for sites serviced with suction pumps was 1 040 L.
Based on the above findings, it is recommended that sites with submersible pumps are:
Not serviced with unprotected mild steel single containment pipework, as a minimum; and
Functionality of leak detectors on the submersible pumps should be checked according to a routine schedule.
10.4 Logistic regression model
The above findings are supported by the results of the logistic regression whereby a relatively higher risk is posed by retail sites serviced by mild steel USTs and submersible pumps, as compared with commercial sites where the installation is generally above-ground and serviced by a suction pump. The
model would suggest that in order to reduce contamination risk, tanks should be placed above-ground where feasible, or serviced by suction pumps, not submersible pumps. This would however be subject to product types, site specifics and requirements of the respective oil companies.
10.5 Municipal governance and regulations
LNAPL storage and distribution should be managed by a newly created department within the eThekwini Municipality. This would require the adoption of the eThekwini Fire and Emergency Services database, or the establishment of a new database. An example questionnaire has been attached as Appendix L that could be used for data capture.
This data could be entered into GIS and used to manage and as well as prevent incidents within the Municipality if used in conjunction with other GIS data such as hydrology, geology, presence of nearby receptors, proximity of conduits for migration etc. Nobre et al (2007) demonstrated this in his paper Groundwater vulnerability and risk mapping using GIS, modelling and a fuzzy logic tool, as supported by Dixon (2005) in his work Groundwater vulnerability mapping: a GIS and fuzzy rule based integrated tool.
Preventative measures are imperative to ensure the protection of groundwater resources. The New Hampshire Department of Environmental Services has demonstrated this by the implemented a number of measures. The Environmental Fact Sheet: Preventing groundwater contamination at gas stations – what municipalities and water suppliers can do, includes the following items:
Siting restrictions whereby new installations are required to be situated beyond a minimum distance from certain receptors, termed setback requirements;
Spill containment regulating filling areas and dispensing areas;
Stormwater management where drainage separation is mandatory; and
Environmental Management Plans where sites are required to submit documentation demonstrating the methodology that will be employed to manage the site.
In addition to the above, the Department recommends the routine inspection and servicing of release prevention and detection systems (New Hampshire Department of Environmental Services, 2007).
The Maine Department of Environmental Protection provide a framework for owners and operators of USTs to submit an ‘Annual Inspection Report and an Annual Summary Report’ (Maine Department of Environmental Protection. 2007). This system could similarly be implemented in the eThekwini region.
10.6 Loss reporting
The eThekwini Municipality could implement a by-law whereby reconciliation figures for all service stations and commercial installations are required to be submitted to the Municipality on a monthly basis.
This could be established for sites handling greater and a specified volume throughput per month. A database could be established whereby losses greater than a threshold are flagged and investigated.
10.7 National governance and regulations
A regulatory framework was proposed by Pretorius and Usher in their unpublished and undated paper where they identify the need for additional guidelines to ensure the protection of groundwater resources;
and to further regulate LNAPL storage facilities, including the closure thereof. The authors propose a UST program whereby all tanks are identified and managed, and when incidents occur, these are managed according to risk assessment protocol. It is recommended that this proposal is undertaken by means of a work-shop, and implemented in a phased approach. A literature review and consultation with regulations of other countries would assist in aligning the framework with internationally accepted norms.
The guidelines should be prescribed within a framework of the current and future use of underground storage, as described by Evans et al (2009) in his paper investigating use of ‘land below ground’ in the United Kingdom.
In addition, contaminated sites in South Africa should be documented in a centrally held database that is within the public domain.
The effectiveness of the Environmental Impact Assessment process in preventing soil and groundwater contamination and in addressing soil and groundwater contamination in the event of an incident for new sites should determined by the assessment of these same sites following a set period of time whereby incidents are analysed to determined whether sufficient mitigatory measures were specified in the EIA documentation. In this manner a feedback loop could be introduced into EIA documentation to prevent re-occurrence of similar incident types.
Similarly, the effectiveness of the EIA process required prior to remediation should be determined by the assessment of a number of sample sites. This assessment would incorporate determining whether the EIA process was effective in preventing environmental damage or whether the process facilitated contaminant spreading and migration.
10.8 Probabilistic model and competencies
Due to a lack of suitable data, a probabilistic model could not be constructed. Hall and Strutt (2003) however demonstrate the methodology to develop a model that can be used to predict physical failure of components of a system as a result of processes such as corrosion, wear, fatigue and mechanical overload.
The results provide a distribution of time to failure that can then be fitted to a Weibull distribution with parameters to describe failure types characteristic life parameters.
Breton et al (2010) demonstrate how the likelihood of pipeline failure can successfully be determined by utilizing a Bayesian probabilistic approach whereby the probability and type (rupture or leakage) of failure is modelled.
It is therefore recommended that a probabilistic model be constructed by one of the above two methodologies in order to determine the likely failure rate of commercial and retail LNAPL
infrastructure, particularly GRP tanks and non-ferrous pipework. It is recommended that this is performed by observation of failures over a set period of time. In this manner, the risk of failure can be determined for a specific site characteristics (age etc) and corrective actions implemented prior to failure occurring. Alternatively, an ‘accelerated life test’ could be developed whereby failure is observed under conditions likely to increase failure.
The probabilistic model should be based on a non-biased data set from a cross section of oil companies, such as that prepared by the United States Environmental Protection Agency for the State of South Carolina. The study assessed the ‘Frequency and extent of dispenser releases at underground storage tank facilities in South Carolina’ (United States Environmental Protection Agency, 2004).
The results of the probabilistic model can be fed back into design of the various components of USTs and dispensing infrastructure in order to allow for more accurate failure prediction.
The dependability of components is also dictated by the competency of the design consultants and the contractors; and the quality of the installation. These three components require competency certification and management to ensure installations are built to minimum requirement specification.
10.9 Non-uniform risk based approach
Metzger (1989) recommends the implementation of a risk based approach for the management of USTs whereby multiple variables are accounted for in determining risk, including and not limited to infrastructure characteristics; the vulnerability of potential receptors; and the nature of the subsurface soils and bedrock. The approach considers the cost of prevention versus the cost of correction and indicates that by risk profiling, non-uniform standards are the most cost effective in preventing LNAPL contamination.
10.10 Investigation of new technologies
Global research into zero discharge of LNAPLs to the environment and limiting contamination impacts is being performed, as demonstrated by Sacile (2006) where a study site in Italy was subjected to remote real-time monitoring, and in the event of an incident, remote remedial works were undertaken.