In recent years we’ve seen an increase in frequency of wildfires occurring along wildland-urban interfaces across the western United States. Because of the increased incidence of wildfire causing large-scale loss of structures, more efforts by universities, water districts, and state regulators have been made to study the effects on drinking water infrastructure and the resulting water quality. When large-scale structure loss occurs, the type of chemical contamination that results is found primarily in the distribution system. Traditionally, most wildfire water quality concerns relate to source water contamination, especially when the wildfire primarily affects the watershed. However in recent years, contamination in distribution systems has also been observed. The distribution system chemical contamination being detected in some cases is made up of primarily volatile organic compounds (VOCs) such as benzene. Short term exposure to high concentrations of such chemicals is a public health concern.
By observing trends from the recent fires in California, Oregon, and Colorado, we have been able to determine factors that appear to lead to higher levels of VOC contamination. These factors include:
- A loss of pressure combined with burned structures and service connections
- Entry of smoke into broken or damaged water lines
- Plastic piping or other distribution system materials that have been exposed to high temperatures
In addition to observing factors that lead to contamination, there have also been important lessons learned that can help prevent or minimize contamination:
- Isolating damaged portions of the distribution system and service connections as soon as safely possible can prevent the spread of contamination
- Use unidirectional flushing when bringing damaged areas back on line and avoid flushing contaminated water through uncontaminated areas
- Contamination appears to be more severe in areas that experienced depressurization as well as damage. So extra caution should be taken when bringing these areas back on line. For example, issuing a drinking water advisory and completing additional sampling should be considered.
In areas where depressurization occurs typical follow up sampling (coliform bacteria and disinfectant residual) should take place, as well as additional testing for VOCs. Water systems should work with CDPHE and their local public health agency to create a sampling plan that identifies target contaminants, sample collection protocols, sampling locations (in the distribution system and surviving buildings), and data quality and management.
In recent fires we have observed that contamination tends to absorb into distribution system piping and can leach out over time. Because of this, it is important to let the water stagnate, with no movement or flow in the line before sampling. Ideally, the stagnation period should be 72 hours but if that is not feasible shorter times are acceptable.
Remediating VOC contamination can be a long term process. Flushing is the primary method of removal but at times, infrastructure replacement may be necessary.
Don’t hesitate to reach out to us if you have any questions, would like more information on this topic, or would like any input on activities such as emergency planning and tabletop exercises. For additional information see the EPA’s guidance on Addressing Contamination of Drinking Water Distribution Systems from Volatile Organic Compounds (VOCs) After Wildfires
➽ Chelsea Cotton, P.E. Source Water and Emerging Contaminants Engineer
