ARCHIVED REPORTS_XR0012223 - Laserfiche WebLink

Home Browse Search

Mr. Nuel Henderson Page 2 of 4 • above the top of the screened intervals in monitoring wells MW4 through MW13B, MW15B, MW15C, MW16B and vapor wells VW1 and VW4. Vapor well VW5 was dry. During this event an upward vertical gradient component was present across the site. Wells screened deeper than 60 feet had higher potentiometric surface elevations than shallower wells in close proximity. Examples are well pairs MWI/MW6, MW3/MW7, MW15A/MW15B and MW16A/MW16B. A potentiometric surface map generated using the May 24, 2005 groundwater elevation data for most groundwater monitoring wells, regardless of screen depth, is shown on Figure 2. The gradient across the site according to this interpretation was approximately 0.001- 0.002 feet per foot in an easterly to northeasterly direction. Figure 3 is a gradient map utilizing data from the shallower wells only (screened above 60 feet). Gradient is approximately 0.002 ft/ft in a southeasterly direction. The gradient computed from the deeper wells only (screened below 60 feet) ranges from approximately 0.001 - 0.003 ft/ft. Flow direction in the deeper zone ranges from southeasterly to northeasterly (Figure 4). Groundwater monitoring data are summarized in Table 1. Monitoring data sheets and well construction details are included in Attachment A. On May 25, 2005, a Ground Zero technician collected groundwater samples from monitoring wells MWS, MW11, MW12, MW15A, MW15B and MW15C. A minimum of three well casing volumes was purged from each well prior to sampling. During the purging process, physical parameters (pH, electrical conductivity, and temperature) were monitored. Subsequent to parameter stabilization, and 100% recovery of initial depth to • groundwater measurements, groundwater samples were collected and placed in an iced cooler for transport to Argon Laboratories (FLAP#2359) under chain of custody protocol. Analysis consisted of gasoline oxygenates, EDB and 1,2-DCA by EPA Method 8260B, TPHg by EPA Method 8015B and BTEX by EPA Method 8021B. Purge water was transferred into labeled 55-gallon drums approved by the Department of Transportation (DOT). The waste is stored onsite within a secured area. Purge logs are included in Attachment A. GROUNDWATER ANALYTICAL RESULTS Groundwater Monitoring Wells TPHg and benzene was not detected in wells MW11, MW12, MW15A, MW15B and MW15C. TPHg and benzene was detected in well MW8 at concentrations of 230 parts per billion (ppb) and 15 ppb, respectively. Dissolved TPHg and BTEX levels were within historical ranges, and appear to be stable to decreasing. TPHg and BTEX concentration data are summarized in Table 2. Attachment B contains laboratory reports and chain of custody documentation. Attachment C contains graphs of contaminant concentrations over time. MTBE was not detected in well MW15C. MTBE was detected in wells MW8 (0.6 ppb), MW 11 (120 ppb), MW12 (97 ppb), MW15A (4.9 ppb), and MW15B (1,100 ppb). These wells are affected by MTBE releases originating at 101 S. Wilson Way and/or 130 S. Wilson Way. • G:\GROUNDZE\ROEKkQMR\2005\2qm2OO5.doc