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Site Report: Six Mile Richardson Highway Groundwater Investigation

Site Name: Six Mile Richardson Highway Groundwater Investigation
Address: 6 Mile Richardson Highway, North Pole, AK 99705
File Number: 100.38.112
Hazard ID: 25660
Status: Informational
Staff: Janice Wiegers, 9074512127
Latitude: 64.802615
Longitude: -147.559203
Horizontal Datum:WGS84

We make every effort to ensure the data presented here is accurate based on the best available information currently on file with DEC. It is therefore subject to change as new information becomes available. We recommend contacting the assigned project staff prior to making decisions based on this information.


In 1995/1996, an area-wide trichloroethylene (TCE) groundwater plume was discovered in the Six-Mile Richardson Highway area. The plume is over a mile in length, up to 1,200 feet wide, and up to 100 feet in depth. It extends in a northwesterly direction from south of the New Richardson Highway to the Six-Mile Village Subdivision area. The plume impacted fifteen residential drinking water wells and the homeowners were provided financial assistance to install water treatment systems (e.g., carbon filters) to remove the TCE from their drinking water. In 1996, DEC initiated an annual long-term groundwater program that includes sampling from permanent monitoring wells and a selected number of residential wells. The data indicates a decreasing trend in contaminant concentrations over time. Individual site investigations were conducted concurrently with the initial phases of the area wide groundwater investigation. Site investigations at the McCall, Holder, Walsky, and 6-Mile Truck Shop properties concluded that there are multiple source areas where TCE was discharged to the ground. The individual source areas are creating groundwater plumes that eventually merge together to form the area-wide plume. The source areas appear to be located on the Holder and Walsky properties. Potentially responsible parties have been notified of the contamination, but DEC has continued to lead investigation and treatment of the areawide plume. Most of the early work on the Six-Mile Richardson Highway area was documented in the database entry for hte Walsky property. That and other associated contaminated sites include: (Site Name; Hazard ID; File Number; Address) Walsky Property; 2479; 100.38.110; 1491 New Richardson Hwy. North Pole Six-Mile Truck Shop; 329; 100.38.078; 1455 Richardson Highway North Pole McCall Property; 718; 100.23.025; Bethany St. & Frontage Rd Fairbanks Holder Property; 2477; 100.38.109; 1569 Davison Street North Pole

Action Information

Action Date Action Description DEC Staff
5/27/2011 Site Added to Database A new site has been added to the database. See Actions for the Walsky Property (File ID 100.38.110; Hazard ID 2479) for earlier action history). Mitzi Read
7/15/2011 Report or Workplan Review - Other Reviewed and approved workplan for groundwater monitoring, private well sampling, and treatment system maintenance. DEC will send letter to well owners to notify them of upcoming sampling event. Two residential wells have fallen below the sampling threshold and will be phased out of the sampling/maintenance program. Janice Wiegers
8/31/2011 Update or Other Action Met with real estate appraiser regarding property near or on Henry Street. Discussed delineation of the six-mile plume, possible sources, and regulatory status. Provided copies of database reports for the areawide groundwater investigation and sites that may be related. Janice Wiegers
9/10/2011 Update or Other Action DEC staff and S&W conducted site visit to several properties to discuss upcoming soil gas investigation and identify sampling points. Discovered owner off Eskimo Musuem Lane is installing two additional sand points into the aquifer. Janice Wiegers
12/30/2011 Update or Other Action 2011 Long-Term Groundwater Monitoring Report submitted by Shannon & Wilson. Nineteen monitoring wells were sampled with 5 exceeding the groundwater cleanup levels for TCE. The highest TCE concentration was present in MW-32 at 27 ug/L. Eleven private drinking water wells were sampled for TCE; all results were below the threshold criteria of 3.5 ug/L established by DEC for water treatment system maintenance. No other contaminants were detected above groundwater cleanup levels. The carbon filter on four water treatment systems were maintained through Ecowater or by an independent contractor chosen by the homeowner. Mann-Kendall and regression analysis indicate that most monitoring and drinking water wells show a decreasing trend. Wells that are not decreasing showed no trend. Janice Wiegers
2/10/2012 Update or Other Action Phone call to owner of 1430 Richardson Highway. Most recent well water results have been below the treament cutoff of 3.5 ppm TCE. DEC will discontinue filter maintenance. If owner wishes to continue using the treatment system, the system must be maintained. Janice Wiegers
3/9/2012 Update or Other Action DEC met with Shannon & Wilson to discuss soil gas data obtained in fall 2011 and drinking water well results. Developed plans for additional vapor intrusion investigation. Janice Wiegers
3/13/2012 Update or Other Action Shannon & Wilson submitted a draft data report for soil gas results collected in September 2011. Soil gas was collected from 25 soil gas sampling points at 9 properties. The soil gas probes were installed at depths between 3 and 6 feet below ground surface. Results indicated that soil gas is present above DEC's soil gas target levels on at least 7 properties. Janice Wiegers
4/9/2012 Update or Other Action Sent letters to landowners that allowed access for sampling soil gas on their properties. Letters included preliminary report from Shannon & Wilson with sample results. Some soil gas results were above ADEC target levels, so further investigation will be focused on subslab sampling. Shannon & Wilson will not complete full characterization report until further sampling is completed. Janice Wiegers
4/18/2012 Update or Other Action Sent letter to landowners where soil gas samples were collected in the fall of 2011 providing the testing results and information about further sampling plans. Janice Wiegers
4/27/2012 Site Characterization Workplan Approved Received and approved workplan addendum for soil gas investigation from Shannon & Wilson. S&W will select three buildings and sample subslab soil gas and indoor air. The buildings will be selected based on the soil gas samples collected last fall and knowledge of the potential source areas. Janice Wiegers
11/26/2012 Report or Workplan Review - Other Received 2012 Long-term Groundwater Monitoring Report from Shannon & Wilson, Inc. The report documents sampling of 5 drinking water wells, three groundwater monitoring wells, and maintenance of water treatment systems by replacing carbon media in four systems. Janice Wiegers
2/28/2013 Report or Workplan Review - Other Received Vapor Intrusion Assessment Report from Shannon & Wilson, Inc. The report summarized vapor intrusion investigations conducted over the six mile groundwater plume between 2011 and 2013. The investigation included installation of 25 temporary soil gas probes on 9 properties where occupied buildings may be affected by vapors migrating from the groundwater plume. Based on the results of the initial soil gas sampling, three building were selected for indoor air and subslab soil gas testing. Of these buildings, S&W were able to coordinate sampling with two (1410 Richardson Highway and 1540 Eskimo Musuem Lane). Subslab soil gas sampling indicated low levels of TCE were present beneath the two buildings. Indoor air samples did not exceed the ADEC's residential indoor air target levels, with the exception on one sample at 1540 Eskimo Musuem Lane. Indoor air at 1540 Eskimo Musuem Lane exceeded the ADEC residential indoor air target level, but uncertainty exists regarding the source of this TCE. Janice Wiegers
4/15/2013 Update or Other Action Contacted owners of 1540 Eskimo Musuem Lane about resampling indoor and subslab soil gas. Owners did not want to participate in sampling. Janice Wiegers
6/28/2013 Report or Workplan Review - Other Received and reviewed report on subslab soil gas and indoor air sampling at 1511 Richardson Highway. TCE, PCE, and 1,1,1-TCA were detected in subslab soil gas below DEC target levels. PCE was detected in indoor air, but TCE was not detected. Janice Wiegers
7/5/2013 Update or Other Action DEC received letter report from Shannon & Wilson dated 6/25/13. The report describes the results of indoor air and subslab soil gas sampling conducted in May 2013. On subslab soil gas and one indoor air sample were collected from the basement at 1511 Richardson Highway. TCE was detected in the subslab soil gas, but not in indoor air. Subslab soil gas did not exceed DEC's vapor intrusion target levels. DEC also sent letters to the property owners that allowed indoor air and subslab soil gas testing. The letters described the sampling results. Janice Wiegers
9/19/2013 Update or Other Action Met with Shannon & Wilson to discuss 2013 monitoring program and vapor intrusion investigation. Janice Wiegers
9/19/2013 Report or Workplan Review - Other Workplans from Shannon & Wilson for groundwater sampling, drinking water well sampling, drinking water treatment maintenance, and additional vapor intrusion investigation in 2013/2014 reviewed and approved. Janice Wiegers
9/20/2013 Update or Other Action DEC sent letters to 6-mile landowners with impacted drinking water wells to notify them of upcoming water well sampling and treatment maintenance. A fact sheet about 1,4-dioxane was included. This compound has been identified nationally as a concern at locations where 1,1,1-trichloroethane was spilled. Additional samples will be collected this year to allow detection of this compound in the groundwater at lower levels. Janice Wiegers
10/3/2013 Update or Other Action DEC was contacted by the owner of 1357 Sloan and 1357 Leslie. This owner has been involved in several of the 6-mile properties, but has recently acquired 1357 Leslie again. He requested informtion on past sampling at 1357 Leslie and asked about the possibility of having a treatment system installed. Janice Wiegers
10/7/2013 Update or Other Action Sampling notification letter to 1366 Sloan Street returned undelivered - no mail receptabe and unable to forward. Also sent notification to owners of 1540 and 1542 Eskimo Museum Lane requesting access for vapor intrusion sampling and stating that tenants should be made aware of the groundwater plume and potential for vapor intrusion. This letter was later returned unclaimed. Janice Wiegers
1/27/2014 Report or Workplan Review - Other Received report titled Soil-Gas and Inoor-Air Sample Results from Shannon & Wilson. This report summarized the first set of vapor intrusion sampling for FY2014. Samples were collected at 1410 Richardson Highway and 1530 Eskimo Musuem Lane. The owner of 1540 Eskimo Musuem Lane declined sampling, and scheduling conflicts prevented sampling at 1511 and 1531 Richardson HIghway. No contaminants of concern were detected above the indoor air or subslab soil gas target levels. Janice Wiegers
6/30/2014 Update or Other Action 2013 Long term groundwater monitoring report submitted by Shannon & Wilson. VOCs and 1,4-dioxane sampled in 10 monitoring wells and 5 private drinking water wells. 1,4-dioxane was added to this sampling round because it can be a byproduct of TCE production. No contaminants were detected above DEC groundwater cleanup levels in the private drinking water wells. However, 4 private wells remained above the threshold concentration of 2.6 µg/L, recently chosen by the DEC for continued sampling and treatment. TCE exceeded the groundwater cleanup level in 5 monitoring wells, with the highest concentration (14.8 µg/L) in MW-17. Most of the sampled monitoring wells sampled showed a decreasing concentration trend, except MW-13, MW-15A, and MW-38, which showed no statistically significant trend. MW-39 appeared to be increasing in concentration. Janice Wiegers
9/25/2014 Update or Other Action Notified by Shannon & Wilson that a new drinking water well had been installed at 1357 Leslie Street. DEC plans to sample this well too. Janice Wiegers
10/3/2014 Report or Workplan Review - Other Additional vapor intrusion data submitted by Shannon & Wilson for 1511 Richardson Highway, 1531 Richardson Highway, and 1410 Richardson Highway. Subslab soil gas and indoor air samples were collected from each building. TCE was detected in subslab soil gas and indoor air but not above DEC's vapor intrusion target levels. Indoor air collected at 1531 Richardson Highway contained trans-1,2-dichloroethene above residential target levels, but this data appears to be associated with use or storage of chemicals within the building. Janice Wiegers
2/6/2015 Update or Other Action Letters sent to residents describing 2014 drinking water sampling results and treatment system maintenance. Janice Wiegers
3/23/2015 Report or Workplan Review - Other Well search results report submitted by Shannon & Wilson. Drinking water wells were confirmed at 29 properties within the plume, 14 of which have not been sampled. An additional 11 properties were identified that may have a well, but this could not be confirmed. Janice Wiegers
4/21/2015 Report or Workplan Review - Other Report titled "Compilation of Residential Well Results" submitted by Shannon & Wilson. Report summarizes drinking water well data collected since 1995 on over 100 wells. Because groundwater cleanup levels for TCE are being re-evaluated, the drinking water well data were compared to the proposed cleanup level of 2.6 ug/L. Twenty five wells contained TCE concentrations above this level at some time. Janice Wiegers
4/28/2015 Update or Other Action Contacted by property owner of several properties on Smithson Street regarding TCE concentrations in drinking water wells. The owner is planning to sell the properties. These properties were tested in 1995. TCE was detected in one well below the cleanup level of 5 ug/L. Janice Wiegers
6/4/2015 Report or Workplan Review - Other Reviewed report for 2014 long-term monitoring. Groundwater samples were collected from 5 monitoring wells and 5 residential drinking water wells. All TCE sample results were below the Maximum Contaminant Level (5 ug/L). TCE was present in one drinking water sample at a concentration equivalent to the risk-based threshold (2.8 ug/L). Trend analysis indicates that concentrations are increasing in one monitoring well (MW-16A) near the end of the plume. Concentrations are stable, decreasing, or no trend is apparent in the other monitoring wells and residential drinking water wells that were tested. Residential water treatment systems were also maintained at 4 properties. Janice Wiegers
6/17/2016 Update or Other Action Letters sent to 5 private well owners regarding 2015 sampling results and treatment maintenance. Janice Wiegers
6/22/2016 Update or Other Action Letters sent to 24 private well owners regarding 2016 sampling results and qualification for treatment system maintenance. Janice Wiegers
7/14/2016 Update or Other Action Six additional letters sent to private well owners regarding 2016 sampling results and qualification for treatment system maintenance. Janice Wiegers
10/28/2016 Update or Other Action Contacted by a real estate agent about property on Warner Street. Project maps indicate that this area is not within the groundwater contaminant plume associate with the Six Mile site. Janice Wiegers
11/6/2016 Update or Other Action DEC groundwater cleanup level for TCE revised from 5.0 ug/L to 2.8 ug/L. This regulatory change effects cleanup levels in use for both private drinking water wells and monitoring wells in the Six Mile area. Janice Wiegers
6/1/2017 Report or Workplan Review - Other Shannon & Wilson submitted a Private Water-Well Report for samples collected in 2015, 2016, and 2017. An additional 23 private wells were sampled in 2016 to re-evaluate wells previously ruled out for continued sampling when the DEC groundwater cleanup levels was higher. In 2016, the DEC groundwater cleanup levels for TCE went from 5 ug/L to 2.8 ug/L. No wells sampled in 2015, 2016, or 2017 exceeded the new DEC TCE groundwater cleanup level of 2.8 ug/L. Cumulative risk was also calculated for 22 wells where multiple contaminants were present. Cumulative risk did not exceed DEC criteria. Trend analysis indicate decreasing trends except at two locations. Because wells of concern all have three sampling events where TCE was less than the DEC groundwater cleanup level, Shannon & Wilson recommended no additional private well sampling. Janice Wiegers
7/1/2017 Report or Workplan Review - Other Shannon & Wilson submitted the 2017 Monitoring Well Report. Nine monitoring wells were sampled in 2017. MW-19 and MW-34 contained TCE at concentrations above the DEC groundwater cleanup level of 2.8 ug/L. These wells contained 3.43 and 3.55 ug/L, respectively. Decreasing trends were noted at each of the 9 wells sampled. In 2016, 9 monitoring wells were repaired. Currently, 31 monitoring wells remain in the Six Mile area. Janice Wiegers
3/23/2018 Report or Workplan Review - Other Shannon & Wilson submitted the Soil Gas Sampling Report for soil gas sampling completed in 2015. Soil gas samples were collected on selected properties on October 6th through the 8th to evaluate the need for additional vapor intrusion evaluation in the downgradient plume. The properties included 1357 Sloan Street, 1366 Sloan Street, 1369 Sloan Street, 891 Conley Avenue, and 1438 Richardson Highway. All properties were located on the north side of the Richardson Highway. Due to a high groundwater table at the time (measured at 3.02 to 3.17 ft bgs), soil gas samples were collected at 2.5 to 2.9 ft bgs. No contaminants were detected in any of the soil gas samples. Janice Wiegers

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