No update from the CDPHE since July 18.
From July 22 to July 29, benzene levels continued to fluctuate at sampling site CS-6, where benzene contamination has persisted for several months.
July 22 4.1 ppb
July 24 4.7 ppb
July 26 1.2 ppb
July 29 2.2 ppb
Williams August 1 update:
Benzene Concentration at Surface Water Point CS-6 Lowers; Company Response Continuing to Show Progress in Protecting Parachute Creek; Additional Remediation Still in Progress
[excerpts below — click thru to read full update]
“After an increase last week in benzene concentration of surface water samples at a single testing site (CS-6), the concentration has reduced considerably at that location over the past several days. The latest sample from July 29 was 2.2 ppb. All other surface water sampling points, including the downstream Orona and Town of Parachute diversion points, have been consistently non-detect since testing began.
“Because of all the remediation activity occurring at the original spill site, Williams had already anticipated and planned for the possibility of increased concentrations at that detection point. As a result, we have been working ahead to expand the remediation systems:
- Six additional air sparge wells were added to the existing sparging system and three additional points are being installed.
- Williams has installed and activated an additional sparging trench on the northeast side of the creek to remove benzene from another area at the site. This new system, consisting of additional air sparge wells and vapor extraction trench, will focus additional remediation work on an area of higher concentration of benzene in groundwater.
“… Williams has installed a liquid hydrocarbon recovery system as part of its long-term remediation plan. The system is expected to start operation on Aug. 1. It was constructed to remove liquid hydrocarbons and groundwater from the aquifer using recovery wells, and subsequently treat the recovered water to remove hydrocarbons so that the water can be safely returned to the aquifer. Treated water will be discharged back to an infiltration gallery, where it will infiltrate by gravity into the same aquifer. Samples will be collected continuously throughout the process to monitor water quality and the performance of the system.”
While it is important to keep track of the benzene levels at CS-6, there is perhaps an over-emphasis on Parachute Creek at this point. As you can see from the dated (4/30) map above, the groundwater contamination surrounding the creek is widespread. High benzene levels persist in the groundwater surrounding the creek, especially northeast of the creek, and have remained consistently high, and as a result Williams has expanded their remediation system.
To get a sense of the benzene contamination in the groundwater, scroll through Data Summary Tables – July 26, 2013 (look for yellow for benzene), you will see that groundwater contamination levels of benzene, and other BTEXs, at several monitoring wells remain very high (Groundwater data begins on page 145).
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.
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.