The results indicate the plume appears to be more widespread than previous graphics have shown and the groundwater and well sampling results from 2016 still show levels of TCE above the EPA's maximum contaminant levels.
The company retained by the city of Camdenton to determine a final solution for the contaminated Mulberry Well has delivered new findings to the Missouri Department of Natural Resources (MDNR) related to the Trichloroethylene (TCE) plume caused by former manufacturing industrial waste influent to the city’s former Hulett Lagoon.
Golder Associates Inc. of St. Charles submitted a Supplemental Remedial Investigation Report Addendum to MDNR on August 10. It describes actions characterizing the Mulberry Well to determine intervals within the well borehole that contribute to the water production of the well which was pulled offline in 1999, but turned back on several times afterward when other wells experienced mechanical issues.
The results of this investigation, conducted in 2015 and 2016, concluded the pumping method being used to contain the plume of the Mulberry Well production zone is currently working as designed, which “essentially functions as a blanket drain beneath low hydraulic conductivity strata which contains majority of the TCE plume.”
However, the results also indicate the plume appears to be more widespread than previous graphics have shown and the groundwater and well sampling results from 2016 still show levels of TCE above the Environmental Protection Agency’s (EPA) maximum contaminant levels.
The Supplemental Remedial Investigation was conducted within the scope of work identified in the Administrative Settlement and Abatement Order on Consent for Supplemental RI/Feasibility Study for the site agreed to by Camdenton and MDNR on March 21, 2016.
According to MDNR, “The volume of water produced within each production interval was determined to calculate the optimum pumping rate to maintain hydrological control of the tricholorethylene contaminant plume.”
The EPA’s value of 5.0 ug/L for TCE was exceeded in all of the samples collected during the pumping test, which included the following monitor wells in Camdenton, MWPT-1, MWPT-3, and MWPT-4, as well as the samples collected during the pre-design interval testing of Mulberry Well at various depths which showed values of 58, 59, 60, 240, 140, 30, 58, and 52 ug/L, respectively, according to the report.
“The Deep Aquifer observation wells completed approximately 200 to 300 feet above the mid-point of the Mulberry Well Production Zone (500 feet btoc), at radial distances between 600 and 1,400 feet from the Mulberry Well, yet show no distinct lateral variation in drawdown over these distances,” according to the report’s conclusions. “This suggests that the cone of depression in the underlying acquire is relatively “flat” and broad versus steep and aerially constrained, consistent with high transmissivity and low storativity for the Mulberry Well Production Zone.”
Pumping from the Mulberry Well, according to Golder Associates Inc., induces horizontal flow from the Mulberry Well Production Zone in high permeability bedding plane fractures between 400 and 600 feet. This zone is expected to be aerially extensive as no boundaries were detected in the pumping test response for a computed radius of influence of 2 to 9 miles, according to the report.
During the pumping tests, the Mulberry Well Production Zone was indicated as the shallowest groundwater production zone encountered, but “pumping is expected to prevent migration of contaminant mass deeper than the Mulberry Well Production Zone,” according to the report.
Pending MRND approval of the report, a feasibility report will be developed to analyze potential options for “implementation and operation of pumping systems for the Mulberry Well,” according to Golder Associates Inc.
“The results of the Supplemental Remedial Investigation indicate that a continuous pumping rate of approximately 105 gallons per minute is capable of inducing downward vertical flow to the Mulberry Well Production Zone over the extent of the Deep Aquifer plume,” the report concluded.
Golder Associates Inc. also recommended that additional numerical modeling be conducted during the Remedial Design phase to optimize pumping rates for Remedial Action implementation.
WHAT IS TCE:
TCE is a non-flammable, colorless liquid with a “somewhat sweet odor and a sweet, burning taste.”
The volatile organic compound, classified by the EPA as carcinogenic to humans, meaning there is evidence for cancer based on kidney cancer, limited evidence for non-Hodgkin lymphoma and liver cancer.
The chemical is mainly used as an industrial solvent to remove grease from metal parts, but is also found in adhesives and spot removers. TCE is thought to occur naturally in the environment; however, it has been found in underground water sources and many surface waters as a result of the manufacture, use and disposal of the chemical, according to the U.S Department of Health and Human Services ATSDR.
According to the Center for Disease Control, exposure routes include inhalation, skin absorption, ingestion as well as skin or eye contact. Symptoms include irritated eyes and skin, headache, visual disturbance, weakness or exhaustion, nausea, vomiting and other more serious complications.