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File Number: 21-069 <br />performed by the contractor revealed that pesticides were present in some locations and <br />consequently the original disposal site would no longer accept the dirt. The contract for hauling <br />was cancelled and the City began to investigate methods for remediating the entire stockpile so <br />that it could be removed from the site. <br />Subsequent to cancelation of the 2017 dirt removal contract, the City received a grant to prepare <br />a design for conversion of the former polishing ponds to a wetland treatment area for WPCP <br />effluent. The project will require dirt to fill the polishing ponds and the stockpiled soil could <br />constitute a portion of this fill if desired. <br />While there is currently no regulatory requirement to remediate dirt that remains on site, staff <br />investigated options so that costs and benefits of remediating the dirt could be evaluated. <br />Cement or lime is commonly used to remediate soil containing metals but is ineffective on <br />pesticides. Traditional pesticide remediation uses specific plants to absorb the chemicals which <br />requires both an area to lay the dirt out in a thin layer and time for plants to grow. The area <br />required for treatment of the soil in this method is 24 acres, and the treatment could take 2 years <br />to complete. Unfortunately, there is no land available on site in the required size for the treatment <br />period. This method also only treats pesticides, metals would still require treatment with cement, <br />making this more expensive than other options, even if land was available. The City contacted <br />several consulting firms that specialize in soil remediation and while they were all familiar with the <br />traditional methods for pesticide mitigation only Leland had a solution that could work with the <br />WPCP’s space constraints. Leland proposes using biochar (charcoal prepared from organic <br />material) to not only remediate the soil for metals but also to bind the pesticides via adsorption, <br />and thus prevent them from leaching out of the soil. <br />The biochar method seemed promising and the City solicited bids in 2019 from construction <br />teams to test the dirt, specify, and supply the biochar, mix the material, and move it to the <br />polishing ponds. Unfortunately, this process is not common, and no bids were received. The only <br />way to remediate the dirt with biochar is to hire Leland for the design and supply of materials and <br />then hire a contractor to process and move the dirt. <br />Analysis <br />Staff considered the following options for this work: <br />1) reuse dirt without treatment; <br />2) treat the dirt with cement and reuse it; <br />3) treat the dirt with the proprietary biochar offered by Leland and reuse it on site; or <br />4) treat the dirt with cement, haul it to a regulated dump site, and import make up soil for <br />the wetland treatment project. <br />Reusing the dirt without treatment is currently permitted but the City would remain liable for the <br />future cost of cleanup, if and when regulations change. Future clean up would be more expensive <br />than current clean up; consequently, this option was discarded. <br />Reusing the dirt on site with cement treatment relies on a common process that many contractors <br />can perform. However, the amount of cement required is significant and is predicted to transform <br />the soil into solid chunks that are not suitable for the proposed re-use; consequently, this option <br />Page 2 City of San Leandro Printed on 2/24/2021