SITE INFORMATION AND CORRESPONDENCE FILE 1

Home Browse Search

West Clay Properties Page 2 of 3 639 (revised 655) West Clay Street April 3, 2015 Stockton, California 95206 • Advance additional soil borings if petroleum hydrocarbon contamination is detected during advancement of the northern-most proposed soil boring; • Install three monitoring wells using hollow-stem auger drill technology while collecting soil samples in selected borings at five-foot intervals, beginning at thirty-five feet bsg to total depths of approximately sixty feet bsg for lithologic evaluation, chemical analysis and field screening for the presence of volatile organic compounds (VOCs) using a photo-ionization detector (PID); • Install the one off-site and two on-site monitoring wells, screened approximately forty to sixty feet bsg, based on hydrogeologic conditions encountered while drilling, at locations illustrated on Figure 2 of the Work Plan; • Monitor and collect groundwater samples quarterly for chemical analysis for a minimum of one year following the installation, development and surveying of the three wells; • Analyze groundwater samples from the newly-installed wells for TPH-g, TPH-d, BTEX, MTBE, ETBE, TAME, DIPE, TBA, EDB and 1,2-DCA; and • Submit a report of findings following the advancement of the three or four soil borings and installation of the three monitoring wells. Although AGE proposes to advance three, four, or possibly more soil borings and install three monitoring wells, it is unclear in which order the fieldwork will take place. AGE proposes to collect soil samples in selected borings during installation of the three monitoring wells but the exact location for collecting soil samples is not specified. AGE has indicated that discrete soil samples will not be collected from the three or four initially-proposed soil borings since "the site geology framework and sampling depth have been established". However, AGE indicated that if the EHD required collection of soil samples, then AGE proposes to collect soil samples at five- foot intervals between forty and fifty feet bsg for lithologic evaluation, chemical analysis of constituents listed in previous bullets, and field screening for VOCs using a PID. Because the proposed soil borings are more than 150 feet from previously-advanced soil borings associated with this site, the EHD believes that soil samples should be collected from at least one soil boring advanced to a depth of approximately sixty feet instead of the proposed fifty feet bsg to verify the hydrogeologic model at this distance from the site. Review of screen intervals of impacted versus un-impacted wells in the plume area suggests that the interval fifty to sixty feet bsg, possibly fifty to seventy feet bsg, is where the dissolved contaminants reside. Soil data collected preferably from the soil boring advanced near the home at 1217 Harrison Street may help determine the best depths from which to collect grab groundwater samples, targeting the silt/clay interval of HU2 while avoiding the deeper un-impacted or minimally impacted sand unit, and assist in determining where best to set the screen interval for the one off-site monitoring well.