SITE INFORMATION AND CORRESPONDENCE_FILE 1

Home Browse Search

Page 2 of 4 changed the concentration of hydrocarbons in the soil. CAA fr Shell is getting ready to spend a large amount oniony to perform remediation at this site. Therefore, it is prudent to collect additional data to ensure that this money is spent wisely and will achieve the most cleanup possible for this site. Relying on old and incomplete data will result in guessing where ISCO should be applied at the site and may result in a longer cleanup time and more money being spent. Proposed wells MW-16 and MW-17 will allow collection of current soil data in the area of the site where ISCO will most likely be applied. Installing these wells will fill in gaps in the groundwater monitoring data in the most impacted area of the site. Groundwater data for proposed wells MW-16 and MW-17 will help determine the depths at which ISCO needs to be applied. We agree with EHD that soil and groundwater samples from these borings (MW-16 and MW-17) can be used for performing the ISCO Bench Scale Testing. In addition, these wells can potentially be used as ISCO injection points or as monitoring points to evaluate the progress of ISCO treatment. We feel strongly that wells MW-16 and MW-17 are a vital component of the plan for implementing ISCO as the remedial alternative for this site. 3. We proposed a CPT boring near VEW-7 to help delineate deep contamination in this area. • This CPT boring was not specifically discussed in the EHD letter,but none of the CPT borings were approved by EHD. • Well boring VEW-7 was drilled to 45 fbg. The deepest soil sample analyzed from this boring was at 34 fbg and was relatively clean. However PID readings from this boring at 35 and 40 fbg were at 538 and 100 ppm,respectively. • Soil data from nearby SB-4 indicates there is hydrocarbon impact to a depth of 56.5 fbg in this area of the site. • Groundwater monitoring data from VEW-7 indicates moderate levels of hydrocarbons. • VEW-7 is screened from 27.5 to 42.5 fbg. • Based on the data from upgradient VEW-4 (screened from 45 to 65 fbg),it is unknown if the relatively high levels of hydrocarbons present in VEW-4 extend downgradient to the VEW-7 area. • The reason we proposed a CPT boring in the vicinity of VEW-7 was to determine soil and groundwater conditions in the 45-65 fbg depth zone and to determine if ISCO would need to be applied in this area of the site. 4. We proposed 3 CPT borings between the dispenser islands and MW-4 to investigate the increased concentration trend in MW-4 groundwater samples. • EHD did not approve these borings. EHD requested additional explanation regarding how these borings would provide information that would explain the increased concentration trend in MW- 4. Our additional explanation is as follows: • No prior investigation has been performed between the southern dispenser islands and MW-4. • There is no upgradient data to explain why MW-4 groundwater samples show an increasing concentration trend. • We are proposing CPT borings for collection of soil and groundwater samples in this portion of the site to determine if there are hydrocarbons upgradient of MW-4 that could be causing the upward trend in concentration in MW-4. • If hydrocarbons are present upgradient of MW-4,then remediation may be required in that area of the site as well. 4/12/2010