Groundwater investigations and monitoring are ongoing. The department continues to review and comment on groundwater and other monitoring results to determine next steps in investigation and cleanup. Investigation of groundwater conditions on- and off-site is continuing in the Ozark and Springfield aquifers, including installing additional monitoring/ extraction wells and testing existing monitoring wells. For additional information, please review the information under Future Activities.
Regular private drinking water well testing is ongoing. To date, Northrop Grumman and the department have collectively sampled more than 400 domestic-use wells near the former Litton facility. The cumulative number of sampled domestic wells continues to increase, as previously unknown wells are discovered and permission is granted by property owners to sample those wells.
During the 2023 third and fourth quarter domestic well sampling events, Northrop Grumman collected samples at 51 private well locations. Forty-eight additional wells were scheduled for sampling during this period; however, these wells were not sampled due to the lack of response from homeowners, homeowners declining to be sampled, house renovations underway, or lack of contact information for new homeowners. Of the 51 wells sampled, TCE was not detected above the reporting limit of 1 microgram per liter, or 1 part per billion (ppb) in 37 wells. Samples from 7 of 51 wells contained detectable concentrations of TCE or TCE breakdown products. However, all detections for these seven wells were below the respective TCE maximum contaminant level (MCL) of 5 ppb for drinking water use. Seven wells showed a TCE concentration above the MCL. Home water treatment systems were installed at those residences. Groundwater entering and exiting the treatment systems was tested and neither TCE nor TCE breakdown products were reported above the MCL in the samples collected following treatment.
The most recent domestic well sampling event that the department has final, validated results was conducted between mid-January 2024 and mid-March 2024. During this event, Northrop Grumman collected samples at 11 private wells. Fifteen wells in the program were not sampled because the property was vacant, or there was no response from homeowners to voicemails and door hangers after three or more attempts in the past year. Five other wells were not sampled due to no response from homeowners, lack of contact information for new homeowners, or the well was not functional. In 8 of 11 wells sampled during the first quarter of 2024, TCE and TCE degradation products were either not detected or were detected below 1 ppb. One well location had detections greater than 2 ppb, but less than 5 ppb. Two locations had detections greater than 5 ppb; however, no detections of TCE or TCE degradation products were reported in water samples taken at these locations after treatment using the home water treatment systems.
Multiple sampling events have provided a comprehensive data set for private wells in the area and the basis for periodic adjustment of the sampling frequency for those wells. A modified sampling scheme for private wells was developed based on this data and approved by the department in September 2021:
- Wells with TCE concentrations less than 2 ppb are sampled yearly, except that any wells demonstrating an “increasing” or “probably increasing” contamination trend are sampled twice a year, regardless of TCE concentration.
- Wells with TCE concentrations greater than 2 ppb are sampled twice a year.
- Wells with detections of only TCE breakdown products are sampled yearly.
- Wells with no TCE or TCE breakdown products are sampled on a quarterly or semi-annual rotating basis for a total of one sample per each of the wells every two years. The rotating sampling effort is designed to ensure that non-detect wells within one-quarter mile of wells with positive detections are sampled during each rotational sampling event.
- Any new wells where detections of TCE or TCE breakdown products are present during the initial sampling event are sampled every three months for the first year. This is done in order to have a full year of data to determine potential concentration variations and to properly place these wells in the correct sampling tier.
- Any new wells without detections during the initial sampling event are placed in the two-year sampling rotation, unless circumstances indicate that more frequent sampling is necessary in specific instances.
