The URL can be used to link to this page

Home My WebLink AboutWS-9571_44769_G_C_20170823_RSPNSNOV 1818 Perimeter Road • Dawsonville, GA 30534 706-579-1607 PHONE • 1-706-265-4916 FAX • www.millcreekenvironmental.com August 23, 2017 North Carolina Department of Environment Quality UST Section, Division of Waste Management 450 West Hanes Mill Road, Suite 300 Winston-Salem, North Carolina 17105 Attn: Ms. Karen J. Hall, Environmental Senior Technician karen.j.hall@ncdenr.gov Subject: Response to NOV, Limited Site Assessment (LSA) Nick’s Motor Cars 3384 West US Highway 421 Wilkesboro, Wilkes County, North Carolina 28697 Incident Number: 44769 Dear Ms. Hall, Mill Creek Environmental, LLC (MCE) has received your letter dated June 15, 2017 concerning the subject property. The purpose of this letter is to respond to your comments (italics) and provide additional information for the site. The following are our responses to your comments: 1) Comment: Water Supply Well Survey (we need this to rank the site). Response: The Expanded Well Survey map is attached as Figure 1 and Table 1. Based on the results of the Expanded Well Survey, MCE has identified nine (9) water supply wells within 1,500 feet of the subject property. Seven (7) of the wells are unused and two (2) are used. The following is a summary of the two used wells identified on the attached map: Well #2 This well is located approximately 957 feet southwest of the tank basin on the subject property. Well #2 serves a residence and was reported by the homeowner to be used on an as- needed basis. The homeowner reported the well as being turbid during our site visit. They switch a valve to the municipal water system as-needed. This well is located cross-gradient and across a topographic divide from the subject property. Construction details and depth of this well are unknown. Well #8 This well is located approximately 650 feet southwest of the tank basin on the subject property. Well #8 serves a small appliance repair and sales operations and was in use at the time of our site visit. The well is located on the west side of a topographic divide that separates the subject property from the well. This well is drilled into bedrock and constructed with 6-inch PVC surface casing. Ms. Karen J. Hall August 23, 2017 Page 2 of 2 P:\Nicks Auto Cars Wilkesboro NC UST LSA\Report\Response Letter to NC Env Quality .docx Much is known about the geology and hydrogeology of the region and generalizations can be made to predict the fate and transport of contaminants in this geologic setting. The generalizations are from “A Master Conceptual Model for Hydrogeological Site Characterization in the Piedmont and Mountain Region of North Carolina” (Harry E. LeGrand, Sr., North Carolina Department of Environment and Natural Resources Division of Water Quality, Groundwater Section, 2004). The generalizations were compiled from large amounts of data and were used to develop a conceptual model to assist in evaluating the potential risk associated with this site. The following are key generalizations from LeGrand, 2004, that were useful in conducting a risk evaluation for this site:  Groundwater occurs in two separate media in the Piedmont and Mountain Regions: 1) clayey granular soil and saprolite, and; 2) fractures and linear openings in the bedrock. The soil and saprolite have a relatively large groundwater storage capacity, but transmits it slowly. The bedrock fracture system has a relatively low storage capacity, but can transmit water readily where fractures interconnect.  Groundwater generally flows toward streams and discharges at seeps and springs in lowland areas.  Streams are linear lows in the water table. Topography of the water table generally mimics that of the ground surface, but with less relief.  The behavior of groundwater can be estimated using a slope aquifer model where natural conditions prevail. This is a general concept which states that groundwater recharge occurs in upland areas and discharge occurs in local perennial streams. Only under rare conditions does groundwater pass beneath a perennial stream to a more distant stream or cross a topographic high point. Based on the aquifer slope model, it is inferred that groundwater flow in the surficial and bedrock aquifers at the subject property mimic topography, and flow to the east towards the nearest down slope stream. Under static conditions, groundwater would not typically cross a hydraulic boundary such as a topographic high point or a stream. Due to the anticipated low pumping volume of the 6-inch drilled wells at residences and small businesses, it would not be expected that there is sufficient pumping rate or volume to overcome the large storage volume of the aquifers and the natural flow gradients towards the east from the subject property. Based on the slope aquifer model and the anticipated pumping rate of the two used wells, it is our opinion that the potential for the used wells to be impacted by the release from the subject property is low. 2) Comment: Soil samples at the pump island that were missed during the closure. I had asked that they be taken as part of the LSA. Response: MCE was not copied on correspondence concerning pump island sampling and was unaware of this request when the site was drilled for the LSA. Ms. Karen J. Hall August 23, 2017 Page 3 of 2 P:\Nicks Auto Cars Wilkesboro NC UST LSA\Report\Response Letter to NC Env Quality .docx Based on the data collected during the LSA, it does not appear that additional testing is warranted at this time. The bases for this determination is as follows:  Soil boring SB-1 was drilled to 50 feet below ground surface (BGS) without encountering groundwater.  Benzene was detected in soil sample SB-1, 48-50’ at a concentration that exceeds the Soil-to-Water Maximum Contaminant Concentration (MSCC) by 0.0001 milligram per kilogram. No other regulated compounds exceeded their respective MSCC, Industrial/Commercials CL, or Residential CL values.  The large unsaturated soil zone above groundwater serves to provide treatment of residual petroleum through natural attenuation processes such as biodegradation, dispersion, volatilization, and absorption.  The former pump islands are located sufficiently close to the former UST basin that the soil samples from the UST basin, collected at depths of approximately 25, 40, and 50 feet BGS are sufficient to evaluate potential soil contamination from the pump island locations. This evaluation is sufficient due to the increased dispersion of petroleum in soil with depth, allowing a near surface release to be evaluated for risk by collecting a deep soil sample in the general vicinity.  The petroleum release does not pose a threat of explosion due the accumulation of vapors in a confined space nor does the release pose a risk to public health or the environment. Based on the data collected during the LSA and our additional evaluation described above, MCE recommends a “No Further Action Required” (NFAR) status for this site. If you have any questions, or if MCE can be of assistance in any other capacity, please don’t hesitate to call the undersigned at 706-579-1607. Sincerely, MILL CREEK ENVIRONMENTAL, LLC Dan Centofanti, PG, EP Steven Van Johnson, PG Technical Director Senior Geologist Table 1 Well Survey Key Well ID Property Information 1 421 Motor Sales 3290 U.S. 421 Wilkesboro, NC 28697 6 inch Drilled Well - Unused 2 Residence 2462 County Road 1313 Wilkesboro, NC 28697 6 inch Drilled Well - Used 3 Residence 2154 Congo Road Wilkesboro, NC 28697 Well - Unused 4 Jester's Auto 2462 Congo Road Wilkesboro, NC 28697 Block Well - Unused 5 Residence 586 Buck Road Wilkesboro, NC 28697 24 inch Concrete Casing Well - Unused 6 Residence 260 Buck Road Wilkesboro, NC 28697 Well - Unused 7 Residence 161 Laurelwood Drive Wilkesboro, NC 28697 Suspected Well - Unused 8 Bob Young Appliances 3481 U.S. 421 Wilkesboro, NC 28697 Well - Used 9 Residence 3481 U.S. 421 Wilkesboro, NC 28697 Well - Unused