SITE INFORMATION AND CORRESPONDENCE

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� s W.T.Nickerson July 14, 1997 Page 3 We thank the Board for this comprehensive summary ofpast investigative work at this site, much of which was not in our possession. In future, all ten chemicals indicated as being present at or above their respective levels of concern will be evaluated. "4.2 Physical and Chemical Properties The document states that the chemical concentration in the vapor phase will increase with an increase in temperature. This has been shown to occur at the site when 1,2-DCP has volatilized when stored in an open 500-gallon poly tank. Therefore,another remedial alternative may be to pump the water,heat it, and volatilize the 1,2-DCP. Depending on the pounds volatilized, it could then either be vented to air or captured in a carbon drum." In evaluating the feasibility of various alternatives for remediation, several viable methods for removing 1,2- DCP from retrieved groundwater were recognized. The greatest concern is how to achieve effective ground- water There are two leaky aquifers identified on the site and in the near vicinity. The lower aquifer appears to be free of contamination at present, based upon data from MW-7. A gravel horizon is present at approximately 50 feet below ground, within the impacted upper aquifer, known in the regional literature as the 'fifty foot gravel", which is a conduit for rapid lateral flow from beneath the site. We recognize, therefore, that there are problems associated with the effective capture and retrieval.of a reasonable portion of the affected ground water, in order that the considerable expense of construction of a treatment system, a recovery and re-injection well array, and a pumped water storage and conveyance system is economically justified. These problems will be addressed as the investigation proceeds. "4.3 Toxicity_and Health Risks Outdated water quality criteria are given for 1,2-DCP. (See comment#3 for the Executive Summary for the most recent criteria). I don't understand why 1,2-DCP is compared to 1,3-DCP, since 1,3-DCP isn't a breakdown product and hasn't been found at this site." Our response to comment#3 is repeated here. With regard to 1,3-DCP, it was not our intention to compare this compound with 1,2-DCP. The reason it is mentioned at all is that 1,3-DCP was the active compound dispensed for agricultural use, with 1,2-DCP merely present as a manufacturing by-product All the literature we reviewed, and quoted from, addressed the two compounds together. It was merely expedient to provide the whole quoted paragraphs, rather than chopping them up to delete all reference to 1,3-DCP. "4.4 Establishment of Action Levels The Basin Plan described the method the Board is to use in setting groundwater cleanup levels. Groundwater cleanup levels are "equal to background concentrations if background levels are technologically and economically feasible to achieve. If background levels are infeasible to achieve,cleanup levels are set between background concentrations and concentrations that"protect beneficial uses of the waterbody and do not pose a significant risk to human health or the environment. " Within this concentration range, cleanup levels must be set at the lowest concentrations that are technologically and economically achievable."