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f <br /> i <br /> A R and M E Glover +' <br /> Re: 7675 W. Eleventh Street <br /> Page 2 of 2 <br /> example samples 133-9.0 with 2,400 mg/kg TPH-g and B3-26.5 with less than 1 <br /> mg/kg TPH-g). The EHD interprets the data for your site to indicate that <br /> contaminants present in the shallow fine-grained soil desorb into groundwater in <br /> the underlying sand unit where the dissolved contaminants migrate laterally under <br /> the influence of groundwater flow. The EHD believes this mechanism reduces the <br /> potential for contaminants to impact the fine-grained soil underlying the sand unit, <br /> i.e. at 25 feet bsg. <br /> • The models for shallow soil should be utilized for the risk assessments as the <br /> analytical results for sample B3-9.0 and other shallow soil. samples demonstrate, <br /> and it has not been shown that shallower impacted soil is not present on the site. <br /> Additionally, the depth to groundwater has always been measured as less than 3 <br /> meters on the site, hence the deeper impacted soil is in the saturated zone. <br /> To move your site toward closure, the EHD recommends the following: <br /> • Acquire current soil data in the known impacted soil areas, addressing those areas <br /> thought to be most impacted; <br /> • Obtain soil gas data to address the vapor intrusion issue; and <br /> • Propose and conduct localized . remediation of soil and groundwater in the <br /> impacted area, such as limited excavation and/or batch groundwater extraction. <br /> The EHD directs the following: <br /> Reinitiate quarterly groundwater monitoring —the EHD will consider modification of <br /> the sampling schedule and frequency if proposed and justified for each well by <br /> your consultant; and <br /> • Resubmit the risk assessment and vapor intrusion evaluation utilizing technically <br /> appropriate models and data. <br /> Submit work plans as appropriate to enact the above recommendations and directives. If <br /> you have any questions or comments, or if you would like to have a meeting with the EHD <br /> to discuss your site in more detail, please contact Nuel Henderson at (209) 468-3436. <br /> Donna Heran, RENS, Director <br /> Environmental Health Division <br /> Nuel C. Henderson, Jr., PG Margaret agorio, REHS <br /> Engineering Geologist Program Coordinator <br /> LOP/Site Mitigation Unit IV LOP/Site Mitigation Unit IV <br /> cc: James L.L. Barton, PG, CVRWQCB <br /> Jeanne Homsey, PE, ATC <br />