Parachute Creek spill: Day 170

The area of the underground hydrocarbon plume is outlined in yellow. This map is dated April 30, 2013

The area of the underground hydrocarbon plume is outlined in yellow. This map is dated April 30, 2013

August 23, 2013 – CDPHE Update

Upgrades to the original air sparge system (Phase I) are in operation, including three new vertical air sparge wells installed on the east side of Parachute Creek to ensure benzene in groundwater does not migrate any further south. The second air sparge system (Phase II A), installed to treat benzene in groundwater closer to the original source, is in operation and effectively reducing benzene concentrations in groundwater.

There was an increase in the benzene concentration at sample point CS-6 up to 9.2 ppb for about a one-week period, around the time the upgrades to the original air sparge system were activated. The concentrations of benzene in surface water at CS-6 have since dropped slowly and were non-detect for the samples collected August 8, August 12 and August 15, 2013.

Date                        CS-6 Reading (parts per billion – ppb)
Thursday, July 11          5.5
Monday, July 15            9.2
Thursday, July 18          4.4
Monday, July 22            4.1
Monday, July 29            2.2
Monday, August 5        1.5
Thursday, August 8      Non-Detect
Monday, August 12      Non-Detect
Thursday, August 15    Non-Detect

Parachute Creek is not used as a drinking water source and the actual surface water standard for benzene in the creek is 5300 ppb based on protection of aquatic life. Minor fluctuations in the concentration of benzene in the surface water in Parachute Creek may occur as new groundwater treatment systems are brought on-line.

All waste soil generated during investigation and cleanup of the pipeline release has been removed from the site and shipped to an industrial waste landfill in Utah for disposal.

As of August 13, all the contaminated groundwater generated during remediation activities that had been in storage was treated in the newly-operational groundwater treatment system (also known as the Hydrocarbon Recovery System or HRS). The sample results from the effluent of the HRS during the first week of stored water treatment demonstrated that the concentration of all parameters was within the limits specified in the state-issued water discharge permit.

Pumping equipment capable of enhancing the recovery of liquid hydrocarbon by drawing down the groundwater table in the recovery well has been installed in all recovery wells. The recovery wells should be in operation by the last week in August. The groundwater will be treated in the HRS prior to discharge back into the Parachute Creek alluvium. The recovered liquid hydrocarbon will be temporarily stored prior to recycling.
[end of update]

Williams Testing Results

**********

CDPHE Parachute Creek

Amount of hydrocarbons extracted as of August 1:
7,664 gallons (approximately 182.5 barrels)

Amount of contaminated water brought up with the hydrocarbons as of June 20:
Approximately 369,000 gallons

More than 1,700 tons of contaminated soil have been disposed off-site.

Plume size:
The maximum estimated size of the plume is approximately 1,500 feet long, 308 feet wide and 10 feet thick. This equals an area of approximately 462,000 square feet or 10.6 acres in area; roughly 34,595,000 gallons.

Chemical composition of plume:
Benzene; toluene; ethylbenzene; all three xylenes (M, O and P); cyclohexane; hexane;
methylcyclohexane; isopropylbenzene; acetone; bromoform; heptanes; 1, 2 , 3-trimethylbenzene; 1, 2, 4-trimethylbenzene; 1, 3, 5-trimethylbenzene and tetrachloroethene.

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