455 W Fir Avenue
Clovis, CA 93611-0242
Tel: (559) 449-2700
Fax: (559) 449-2715
www.provostandpritchard.com
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Engineering Surveying Planning Environmental GIS Construction Services Hydrogeology Consulting Clovis Bakersfield Visalia Modesto Los Banos Chico • Sacramento Merced Successor Agency
Project Update Memorandum
To: Sierra Omlin, Frank Quintero, Joy Otsuki, Leibold (McClendon & Mann) From: David Norman
Subject: Status Update - Merced DLA site – Former Exxon and Pacific Pride UST Site at 1415 and 1455 R Street, Merced, CA
Date: December 15, 2023
Merced DLA Site
Merced R Street
The R Street project has been a leaky gasoline tank (UST) project since the mid-1990s. Several consultants have attempted to clean up and close the two sites (Former Texaco and Pacific Pride Card Lock). The former Merced RDA took responsibility for cleanup in a complex set of circumstances. Since 2014, the DLA and Provost & Pritchard has been working towards site closure. To date there are still two groundwater monitoring wells left (out of more than 75 monitoring points) that contain MTBE near the closure criteria. At the request of the RWQCB, P&P has re-sampling these two wells (MW-6C and MW-10C) several times. Concentrations of MTBE increased after long groundwater purging events as reported in the 1st Quarter Groundwater Monitoring Report (July 2020). In addition, in February, March and early April 2020 Provost & Pritchard conducted biweekly sampling of Monitoring well MW- 6. During this event we increase purge volumes in an attempt to qualitatively evaluate the volume of MTBE mass near MW-6. As the sampling events continued concentrations increase to more than 6,000 parts per billion. After the three sampling events approved by the RWQCB sampling was ceased.
Since it has previously been demonstrated that there is no connectivity between the saturated zones affected by MTBE and the deep water used for residential potable water by the City (Assessment of Aquifer Hydraulic Connectivity City well 5B Pump Test P&P 2008). If there is no potential impact to human receptors it is reasonable to grant site closure. Therefore, despite concentrations at higher than closure criteria of residual MTBE in monitoring well MW-6C, Provost & Pritchard has requested site closure in the 1st quarter report.
In 2021, groundwater sampling of the remaining wells was conducted as required by the RWQCB. In later 2021, a new RWQCB project manager contacted P&P after he reviewed the most current reporting and closure request. He requested additional information. After his review of the data 2 conference calls with P&P, DLA and the RWQCB were held. As a result, the RWQCB responded in writing on October 15, 2021, with a letter reviewing the project history and requirements for remedial work near monitoring well 6C to elevate the RWQCB concern that MTBE could affect City well 5, regardless of previous findings. In addition, some soil sampling was requested to document a previous removal of a water oil underground tank.
Mark explained to the RWQCB the ROPS funding process and that there would be no funding for the required work until July 2022 if the DLA proved the work scope and the Department of Finance approved the funding.
To: Merced Successor Agency: Sierra Omiln December 15, 2023 Subject: Status Update - Merced DLA Site Page 2 of 3
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Although the DLA and P&P expressed professional differences of opinion with the RWQCB it was agreed that the DLA would request funding for the next ROPS period for P&P to install and operate 2 air only sparge points and system near (up gradient of) monitoring well 6C in R Street.
The system would be installed and operated for a pilot period of 6 months. At the end of the 6- month period an evaluation would be conducted by the RWQCB in order to grant closure or require further treatment. It was furthered agreed that the sparge system was the best and only acceptable system for limited use with in the east bound lanes of R Street. R street is a difficult location to install any system due to high traffic and the high number of utilities.
At Kosmont’s request, P&P prepared a response letter agreeing to the conditions of the November RWQCB letter, including a workplan and installation of a limited air only sparge system near well 6C, operation and maintenance costs and groundwater sampling and reporting for the 6-month. This will require the owner of the adjacent to agree to placement of the system on their property and agreement by the City to issue permits to install the sparge point in R street.
As of July 1, 2022, the RWQCB has approve our air sparge system for remediation I the 6c area. In addition, access agreement has been secured from the landowner, and details are being worked out with the triple net lessee (Mr. Ed Colson) and agreed from the property lease (Victoria’s restaurant) of the placement of the remedial shed to house a compressor, distribution manifold and various electronic parts. Traffic plans and encroachments for drilling and trenching in R Street are in progress. The scope of the work includes a 6-month pilot study remediate the residual MTBE to a concentration that allows site closure.
The drilling of the sparge points in R Street and the soil borings at the two stations in October 2022 and technical memo will be provided to the RWQCB in February 2023. The sparge points were installed in R Street in mid- December 2022. After several months of negotiating with the City Engineering Department and the tenant (Victoria’s Mexican Restaurant) the treatment system installation was completed in August of 2023. During the initial and second groundwater sampling, required by the RWQCB related to startup of the sparge system, free product gasoline was detected floating on groundwater with dissolved concentrations of gasoline exceeding 100,000 parts per billion were detected in sampling collected from well MW-6AR.
This information was reported to the RWQCB on August 16 th. The Board followed up on the
August 29th, 2023 with a letter requesting the assessment of the extent of free product and plans to remove said product (attached). The initial request included the submittal of the workplan and delayed start-up of the sparge system.
To meet the requirements for the Board request P&P will produce a work plan including two (2) rounds of drilling and sampling by CTP that will identify the presence of free-floating product on groundwater and allow for the design of appropriate remedies to remove the product prior to start up of the sparge MTBE treatment system.
The estimated cost to conduct the tasks required including work plans, permits, traffic control, property access, drilling, waste disposal, monitoring and reporting and recommendations for product removal for the ROPS period 2023-2024 ending June 30, 2024, will be $486,500. Much of this cost is allocated to drilling and laboratory sub consultants.
During the recent switchover from Kosmont to the Merced Successor Agency (MSA) some budgetary confusion and $120,000 was deducted from the $486,500 RPOS request by the To: Merced Successor Agency: Sierra Omiln December 15, 2023 Subject: Status Update - Merced DLA Site Page 3 of 3
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MSA. This amount was intended for Operation & Maintenance of the sparge system and will be re-requested post product removal. The workplan for the CTP free produce assessment is being prepared and will be submitted in early January 2024 to the RWQCB for review and approval. CTP filed work is anticipated to be conducted in February 2024 with the report submitted to the RWQCB in April. The Sparge system will sit idle until the free product removal is completed.
Product removal will include specialized floating product skimmer pumps designed to remove only the floating gasoline and not groundwater. These pumps are powered by compressed air or nitrogen, and solar or batteries. Each system will need to be housed in a small shed within a chain link fence on private property, which access will need to be secured, and utilize 55-gallon drums to store the recovered gasoline and filter off gases These systems, including the parts, new recovery groundwater wells and associated monitoring wells, construction permit, weekly disposal and operation and maintenance. We are not yet able to estimate the volume of free product to remove so, the ROPS request for the next ROPS period includes capitol costs for two product recovery systems and 6 months of O&M, and labor. If additional product recovery is necessary additional costs will be requested in subsequent ROPS requests.
This ROPS request for 24- 25a is intended to include installation of the two free product removal systems (exact locations to be determined during the CTP task described above) and six months of operation and weekly disposal of recovered gasoline as described above. The systems are anticipated to be installed in late April and May of 2024 and operated through November 2024. The ROPS request to cover this work is estimated at $393,000.
A Proposal for this ROPS request, is submitted separately.