Subject: Aquifer Test Observation Well Installation Work Plan Hilmar Cheese Company, Hilmar, Merced County, CA

Transcription

1 October 1, 2009 Mr. Jan Alfson California Regional Water Quality Control Board Fresno Branch Office 1685 E Street Fresno, CA Subject: Aquifer Test Observation Well Installation Work Plan Hilmar Cheese Company, Hilmar, Merced County, CA Dear Mr. Alfson: On behalf of Hilmar Cheese Company (HCC), Jacobson James & Associates, Inc. (JJ&A) is submitting this Aquifer Test Observation Well Installation Work Plan (Work Plan). This Work Plan details procedures for the installation, development and destruction of one temporary observation well (OBS-1) in the area downgradient of the Turlock Irrigation District (TID) well IW-21 at the property located on APN# and in Hilmar, California (Figure 1). The aquifer pump test will be conducted using TID well IW-21 as described in the June 8, 2009 Aquifer Pumping Test Approach Technical Memorandum prepared by JJ&A. An observation well (OBS-1) is proposed to be installed within 200 feet of the pumping well as shown on Figure 2. Observation well OBS-1 will have a similar screened interval to that of IW-21. Existing wells in the vicinity of IW-21 will also be used as observation wells for distance draw down calculations. Well installation activities will include the following: Field work preparation including utility clearance and permitting. Installation of the temporary Observation Well OBS-1 using Mud Rotary Technology. Continuous Core Logging. Well development using surge and purge techniques. Complete a land survey of OBS-1, IW-21 and DW-53 wells. Destruction of temporary observation well OBS-1. HCCAquiferTestObservationWellInstallationWorkPlanfinal

2 AquiferTestObservationWellInstallationWorkPlan,HilmarCheeseCompany October1,2009 Page2of3 Observation Well OBS-1 Installation One observation well OBS-1 will be constructed in the upper supply well zone. The boring will be advanced to a total depth of approximately 115 feet using mud rotary technology. Continuous core will be collected and logged under the direction of a California Registered Geologist to allow for a detailed lithological characterization. The boring will be converted to an observation well by installing 2-inch diameter Schedule 40 PVC well casing and factory-slotted well screen from 38 to 115 feet. The observation well screen has been designed to closely match the screened interval of the pumping well. The lithologies encountered during drilling will be evaluated to confirm that the long screen interval is appropriate. If field conditions indicate a different well construction is warranted, JJ&A will be prepared to modify the well construction in the field. A sand pack will be placed in the annular space adjacent to the well screen, extending at least 2 feet above the top of the screened interval, followed by a 2-foot (minimum) interval of hydrated bentonite and a neat cement seal extending to the ground surface. All annular materials will be tremied from the bottom up. The filter pack will be lightly surged to ensure proper placement prior to installing the bentonite seal. A locking cap and traffic-rated vault box or steel surface monument will be installed to secure the well. The observation well design is presented as Figure 3. Well Development The observation well will be properly developed following installation of the well seal. Initially, the monitoring well will be surged across discreet 10-foot sections of screen using a surge block. Following surging at each interval, the well will be purged to remove sediment. Surging and purging will continue (from the bottom up) until the entire screened interval has been properly surged. Groundwater will be extracted from the well (minimum of 10 well volumes) using a submersible pump until the turbidity of the water stabilizes and the discharged water is visibly free of sediment. Standard groundwater parameters will be measured during the development to calculate stabilization of each parameter. Parameters to be measured include: ph, Temperature (ºC), turbidity, conductivity, and oxygen reduction potential (ORP). The groundwater parameters will be collected and recorded at the beginning of purging and after each well volume is removed. A JJ&A representative will be on-site during the well development activities. Purging equipment will be properly decontaminated. Well development water will be transported to the HCC facility and disposed of in the on-site treatment system.

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4 AquiferTestObservationWellInstallationWorkPlan,HilmarCheeseCompany October1,2009 Attachments Figure 1 Site Plan Figure 2 Proposed OBS-1 Observation Well Location Figure 3 Observation Well Design

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