SITE INFORMATION AND CORRESPONDENCE FILE 2

Home Browse Search

r ; SR/ I Steve & Gene's Service Page 2 of 3 2315 N. EI Dorado Street May 21, 2013 Stockton, CA gradient from MW-108 is either from wells screened at shallower depths than MW-108 or are grab water samples from borings at such a distance that it is arguable as to which site the contaminants in those grab samples came from. The EHD is satisfied, if not fully convinced, that the plume of impacted groundwater, if not less than 250 feet in length, is not significantly larger than that and will accept GTI's interpretation. GTI applies the active service station exemption to the site with respect to the vapor intrusion issue; the site is not an active service station at this time and the exemption does not apply. While there appears to be at least a 10-foot bioattenuation zone beneath the site that may favorably address the issue, the LTCP does not provide a scenario to discount the vapor intrusion risk when the benzene concentration exceeds 1000 lag/l. Please provide a demonstration that the potential risks associated with vapor intrusion are at acceptable levels. • The sparse shallow soil data also indicates a low direct contact or out-door air exposure risk, and this review by the EHD found no data that shows or suggests that significant shallow soil contamination exists on the site that would elevate the exposure risks. The EHD has discussed your site with a representative of the Central Valley Regional Water Quality Control Board (CVRWQCB) on several occasions, the latest being 27 April 2013, 06 May 2013 and 20 May 2013; both agencies request you to provide an estimate of when groundwater on your site will achieve water quality objectives (WQOs); the CVRWQCB uses the maximum contaminant levels (MCLs) instead of the WQOs. The time estimate and vapor intrusion evaluation need not be in report form; an email with the information will suffice and advance this site to closure faster. The EHD and the CVRWQB are both of the opinion that your site can be closed with the additional requested information. The EHD also reviewed Well Destruction (WDWP), dated 10 December 2012, and Well Destruction Addendum (WDWPA), dated 30 April 2013, and an email addendum dated 14 May 2013 for destroying the continuous multichannel tubing (CMT) wells. It was proposed in WDWP to destroy all the wells by overdrilling except CMT-9 and MW-201. The EHD approves destruction of all the wells proposed for overdrilling as proposed. MW-201 has a steel conductor casing grouted into place from near surface grade to 46 feet below surface grade (bsg); this portion of the well may be destroyed in place by pressure grouting, but the PVC casing from 46 feet bsg to total depth 155 feet bsg passes through contaminant-impacted soil and must be destroyed by removal of the well contents by overdrilling. Destruction of the CMT wells as detailed in WDWPA was superseded by the email proposal dated 14 May 2013. GZA's proposal was as follows: 1. Explosive -- per SJCEHD specifications—to be obtained from the County 2. Drill out using stinger and auger equipment 3. Possible Alternative—after using explosive, wrap the casing in the auger and pull it out in a spaghetti style, then go to#4 4. Pressure grout to 8 inches below grade 5. Concrete cap the last 8 inches This was approved by the EHD with conditions as follows: Comment Letter 0513