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• • 1990's, but the detection limit was 100 micrograms per liter of water (ug/L). Additional di-WET analysis with a lower detection limit will be warranted for the DLM. The additional samples should be analyzed for total lead and di-WET for lead. The total lead detection limit should be 10 milligrams per kilogram of soil and the di-WET detection limit should be 5 ug/L. As stated in section 8 in the RAW, the CCVWQCB use of a di-WET value of 0.5 mg/L as a screening level for lead to determine if lead is a threat to the groundwater is incorrect. The CCVWQCB uses the DLM as a screening level. Information on the DLM can be downloaded at: http://www.swrcb.ca.gov/rwqcb5/available documents/guidance/dim pdf#search=%22 designated%201evel%20methodologv%22. 5) There are three monitoring wells and one domestic well on the property. Groundwater samples should be collected and analyzed for lead to support the DLM conclusions, as discussed in comment 4. The detection limit for lead should be 2 ug/L. When collecting the groundwater samples, the depth to the groundwater should be measure from each well to determine flow direction. 6') The RAW must contain an evaluation of the risks posed by onsite contamination to current and future users. This evaluation is necessary to provide criteria for identifying the contaminants of concern that require remediation and the appropriate uses for the property given contaminants that remain onsite as part of the final remedy. The risk evaluation must show that public health and the environment are protected with the final remedy. For lead, the risk assessment should use the most current Lead Spread model in evaluating risk and estimated cleanup levels. The Lead Spread Excel model can be downloaded at www.dtsc.ca.gov. 7) In Section 3.3, the RAW states that total petroleum hydrocarbons (TPH) as oil in the stockpiles was detected in twenty samples at concentrations ranging from 81 to 2,000 milligram per kilogram. Also TPH as gasoline and diesel were detected in some stockpiles samples. The RAW should discuss if the TPH will pose a threat to the groundwater if placed back in the excavation area. The RAW should use the DLM or the CCVWQCB screening levels for TPH. 8) Once the stockpiled soil is removed, confirmation sampling is required in all area where stockpiled soil was located. Confirmation sampling must indicate that all chemicals of concern have been removed to cleanup levels safe for public health and the environmental and protecting the groundwater. 9) The FLAW should include a discussion on methods or controls that may be implemented during excavation to monitor and control noise, storm water runoff, dust generation, erosion control, and ensuring soil stockpiles are properly maintained. 10) Section 9 and 10 in the RAW should define the evaluation criteria of effectiveness, implementability, cost effectiveness and overall protectiveness and identify how each alternative (e.g., no action, stabilization, offsite disposal, and replacement of stockpiled soil in the open excavation, etc) meets the criteria. Page 2 of 5