Updated: Jan 27
Of concern, HDPE pipes and contamination by volatile organic compounds (VOCs).
HDPE pipe is a type of flexible plastic pipe used for fluid and gas transfer and is often used to replace ageing concrete or steel mains pipelines. Made from the thermoplastic HDPE (high-density polyethylene), its high level of impermeability and strong molecular bond make it suitable for high pressure pipelines.
The following is information provided by District Manager, Rick Rogers, at the emergency meeting of the SLVWD Board of Directors on Friday Aug 28 on above-ground plastic pipes and possible contamination from melted pipes :
• The above-ground HDPE pipes at the three tanks that drained and the 5-mile long stretch of pipe that transfers water from the creek intakes above Boulder Creek that were destroyed were all installed more than 20 years ago. That was and has been the standard for rural water districts like ours.
• The reason for using HDPE is not solely cost. It is more flexible, making it more earthquake-resistant and better for avoiding obstacles. Putting the pipes above ground avoided environmental issues that arise when pipes are buried. In particular, the environmental effects of trenching, tree removal, and going up and down ravines along the 5-mile line would have been great and would have met regulatory hurdles. As built, the pipeline traced a crooked path, avoiding trees.
• In replacing the melted pipes adjacent to the 3 tanks, steel will be used and it will be buried, so there is no opportunity for a future catastrophic loss of water. The materials for this work are already beginning to arrive, and contracts have been let to do the work. The hope is that the tanks will be on-line within a few weeks.
• A pipe that will be built from the inlet at Foreman Creek to the water treatment plant, which must be kept operating for the integrity of the plant, will be plastic and is considered temporary.
• Because volatile organic compounds (VOCs) produced by melting of the HDPE pipes could have been back-siphoned into the three tanks when they drained, the tanks will be cleaned before being put back into use.
• Water samples will be taken throughout the system to test for more than 80 organic compounds. The turnaround on these tests is 48 hours, so we should know more about the extent of the contamination soon. It will also reveal which VOCs are present. This matters because different ones have different toxicities and mechanisms for cleanup (e.g., some can be removed by home carbon filtration units, whereas others can only be removed by complex processes at a water treatment facility.
• The District's water quality manager was still in discussions with the State about the details of what a "Do not drink. Do not boil" entails (e.g., whether it is safe to take short, lukewarm showers). These will be clarified in detail before the affected areas are repopulated, and this information will be made available to residents on-line and in local signage (so fire fighters, emergency workers, and visitors will also know). If testing finds areas that have high levels of contamination, this could trigger a "Do not drink. Do not use." warning.
• The southern boundary of the "Do not drink. Do not boil." zone is at the intersection of Alba Road and Hwy 9. It affects both sides of Hwy 9. To the east, water could have contamination from District tanks; to the west, there is the additional potential source from burned plumbing in homes.
• The District Manager, Rick Rogers, was hopeful that contamination of the downtown areas in SLV will be minimal because the District kept this area pressurized to provide water for firefighting. Any VOC contamination is likely to be worse in outlying areas where pressure was lost.
• There is no way to know how long this order will last until the testing reveals the extent of the contamination. The District will be engaged in a testing program at least through Spring, because Winter run-off could mobilize VOCs in soil contaminated by burned pipes on the east flank of Ben Lomond Mountain. In the case of the Tubbs and Camp fires, it was about a year before advisories were lifted.
Photo by Julie Horner above Davidson Way, Boulder Creek taken August 28, 2020.