Contamination of Parachute Creek worsened this week, more than six months after an oil and gas industry spill, with levels of cancer-causing benzene exceeding the federal safe drinking water limit.
Water samples drawn near the spill at a Williams Co. gas-processing plant near Parachute showed benzene levels at 5.5 parts per billion on July 11 and 9.2 ppb on July 15, according to data provided Thursday by the Colorado Department of Public Health and Environment …
CDPHE Update July 18, 2013
Creek and ground water samples continue to be recorded regularly. All creek surface water sample points have remained non-detect for benzene contamination with the exception of CS-6.
Date CS-6 Reading (parts per billion – ppb)
Friday, July 5 2.8
Monday, July 8 3.9
Thursday, July 11 5.5
Monday, July 15 9.2
The sample result for CS-6 from Thursday, July 11 is the first time since the single detection on May 1, 2013 that the concentration of benzene at CS-6 has exceeded the drinking water standard of 5 ppb. However, the surface water from Parachute Creek is not used as a drinking water source and the actual surface water standard for benzene in the creek is 5,300 ppb based on protection of aquatic life. The sampling results do not represent a risk to public health.
It also is important to note that contamination found at CS-6 is isolated and does not appear to be traveling. All other sample points remain non-detect for contamination, including the Town of Parachute’s diversion point for irrigation water.
On Saturday, July 13, Williams began operation of new vertical air sparge wells installed to upgrade the existing air sparge/vapor extraction system. The new sparge wells were placed to stop the flow of benzene-contaminated ground water around the east end of the existing system that may be the cause of the increased benzene concentrations at sample point CS-6. As noted in the July 12 update, a new air sparge/vapor extraction system located farther upstream of CS-6 will be activated the week of July 22. The intent of this system will be to treat contaminated ground water closer to the original source area and speed up the overall cleanup process.
[end of update]
On June 28, 2013, Williams submitted a 45-page Water Management Plan to the CDPHE, which was approved on July 18: Williams Water Management Plan
[If this link doesn’t work go to CDPHE Parachute Creek, click on Documents in the drop-down menus then click on Water Management Plan]
Williams Testing Results
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.
(The Glenwood Springs Hot Springs Pool is 405 feet long and 100 feet wide at the widest point, and contains 1,071,000 gallons of water.)
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.
Amount of hydrocarbons extracted as of July 17:
7,602 gallons (approximately 181 barrels)
Amount of contaminated water brought up with the hydrocarbons as of June 20:
Approximately 369,000 gallons
Groundwater benzene levels in mid-May from selected monitoring wells:
“Williams has draft groundwater results that show a significant decrease in benzene concentration in groundwater down-gradient of the aeration trench. The concentration of benzene in monitoring point TMP-48 dropped from 670 ppb on April 29 to 100 ppb on May 13 to 4 ppb on May 15. The benzene concentration in monitoring point TMP-52 dropped from 360 ppb on April 29 to 170 ppb on May 12 (the last sample collection date for TMP-52). Furthermore, the
benzene concentration in the down-gradient air sparge trench and vertical well points efficacy monitoring location, SPT1-4, has decreased from 760 ppb on May 12 to 140 ug/L on May 15, 2013.”