Methods - how we monitor
Where and how we collect the data
Waikato Regional Council monitors concentrations of benzene in Hamilton and has monitored benzene in Tokoroa.
Waikato Regional Council monitors benzene in Hamilton because this is the area where the greatest number of people are exposed and is the area where concentrations are likely to be the highest.
There are six benzene monitoring sites in Hamilton, including the Peachgrove Road air monitoring site and a site in the high-density traffic area around Bridge Street. The monitoring sites are marked in blue on the map below.
The Peachgrove Road monitoring site was originally used to determine average exposure to benzene, whereas the high-density traffic site on Bridge Street was selected to investigate likely peak concentrations.
(Map source: LAWA)
The monitoring frequency was consecutive sampling of three-month passive absorption badges.
Benzene concentrations were first monitored in Hamilton in 1995/96 as part of a national benzene monitoring programme carried out by the Ministry of Health. Results of that study indicated benzene concentrations in Hamilton met national air quality guidelines of the time. More information on that study can be found here,on the Ministry for the Environment's website.
Waikato Regional Council started monitoring for benzene in Hamilton at two sites in Hamilton (Peachgrove Road and Bridge Street) in February 2003 and has continued through until January 2019. The sites on Peachgrove Road and Bridge Street are now permanent monitoring sites for benzene. Another site near Claudelands Bridge was added in 2004 and three further sites (Hamilton Intermediate, Greenwood St, and Tristram St) were added in 2006. In Tokoroa monitoring commenced in May 2003 and concluded in February 2004.
Passive sampling for benzene was carried out using BTEX passive absorption badges. The method used is as described in the survey carried out by Stevenson et al.,(1999)1 with duplicate badges being deployed for periods of three months. The analysis is carried out by Hill's Laboratories in Hamilton.
How this indicator is compiled
Monitoring results are reported in relation to the National Ambient Air Quality Guideline for benzene, which is the same as the Regional Ambient Air Quality Guideline (section 6.3 of the Waikato Regional Plan).
Guidelines and standards
National and Regional ambient air guidelines for benzene (specified as annual averages) were 10 µg/m3 until 2010 and 3.6 µg/m3 from 2010.
The passive sampling technique used to monitor benzene concentrations in the Waikato region does not comply with the monitoring method specifications outlined in the Ministry for the Environment’s ambient air quality guidelines. While this type of passive sampling is recommended as a screening method only, it is the most common approach to benzene monitoring in New Zealand and is significantly more cost effective than compliant methods.
Another minor limitation is the duration of monitoring carried out in Tokoroa (May 2003 to February 2004), which was less than the annual monitoring requirement by the guideline. Notwithstanding this, results from this monitoring are of value in assessing a likely annual average concentration. No further monitoring of benzene has taken place in Tokoroa.
Quality control procedures
Waikato Regional Council, 1999: Environmental Monitoring Technical Manual. Waikato Regional Council, Hamilton. (unpublished)
Waikato Regional Council, 2003: Quality Assurance Procedures Manual for Ambient Air Quality Monitoring at Environment Waikato. Waikato Regional Council, Hamilton. (unpublished)