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1.0 Objective of the Preliminary Site Assessment
A Preliminary Site Assessment (PSA) is required when it has been confirmed that an unauthorized release has occurred. The scope of the PSA is to collect detailed background information and determine whether groundwater beneath the site has been or could be impacted. The PSA, at a minimum, requires soil sample collection in the over-excavation pit and installation of a groundwater monitoring well within ten (10) feet of the original tank pit in the verified down-gradient location. When on-site groundwater gradient cannot be confirmed, at a minimum, three groundwater monitoring wells (at least one well must be on-site), are needed in order to determine the range of groundwater flow direction. Guidance for this work is contained in the "Tri-Regional Board Staff Recommendations for Preliminary Evaluation and Investigation of Underground Tank Sites" dated August 10, 1990, the SWRCB's "Leaking Underground Fuel Tanks (LUFT) Field Manual" dated April 5, 1989 (or future revisions), and the Department of Water Resources "California Well Standards, Bulletin 74-90".
2.0 Conditions Which Require a Preliminary Site Assessment
2.1 The Source of an Unauthorized Release is an Underground Fuel Tank System. Preliminary site assessment is required if any of the following conditions exist.
2.1.1 Soil concentrations exceed 100 parts per million (ppm) of total petroleum hydrocarbons (TPH) or total Oil and Grease (TOG) within two feet of native soil beneath an underground fuel tank system.
2.1.2 Detectable concentrations of any contaminant above laboratory detection limits are found in soil at or below the seasonal high groundwater level.
2.1.3 Detectable concentrations of any contaminant are found in soil below a tank where the soil contains layers of sand, gravel or other highly permeable material.
2.1.4 Groundwater in the tank pit has detectable concentrations of any contaminant. The pit may be pumped once and allowed to recharge before sampling.
2.1.5 The site has a history of leaks or spills or the tank is in poor condition upon removal.
2.1.6 Recommendation from an inspector, based upon observation and experience, that further investigation is warranted despite contradicting analytical results.
2.2 The Source of an Unauthorized Release is Other than a Leaking Underground Fuel Tank System. Preliminary site assessments are required if any of the following conditions exist.
2.2.1 Documentation of unauthorized release of hazardous materials/waste.
2.2.2 Evidence of a past spill or mishandling and storage of hazardous materials/waste.
2.2.3 The sum of volatile organic compound concentrations of all soil samples collected from any borehole exceeds 1 ppm.
2.2.4 The sum of volatile organic compound concentrations of a grab soil sample exceeds 1 ppm.
2.2.5 The sum of DDD, DDE and DDT concentrations of a grab soil sample exceeds 1 ppm.
2.2.6 A grab soil sample contains metals concentrations above published California or USEPA Preliminary Remediation Goals (PRG).
2.2.7 Groundwater analytical results exceed the established maximum primary or secondary drinking water standards.
2.2.8 Any conditions exist that may jeopardize designated beneficial uses identified in the RWQCB Basin Plan.
2.2.9 Conditions exist which may present a potential or existing threat to human health or the environment.
2.2.10 Recommendation from an inspector, based upon observation and experience, that further investigation is warranted despite contradicting analytical results.
3.0 Preliminary Site Assessment Workplan
The Preliminary Site Assessment Workplan must be prepared in accordance with the following format and scope.
3.1 Site Information
3.1.1 Name and address of the site and the Responsible Party
3.1.2 Site description
3.1.3 Current and past business activities on the site
3.1.4 History of spills and unauthorized release(s) at the site and adjacent properties
3.1.5 Summary of the environmental assessment activities and associated dates performed at the site
3.2. Scale Maps
3.2.1 Site boundaries and adjacent streets
3.2.2 Locations of all current and historic tanks, associated piping, chemicals and waste storage areas, processing, manufacturing and loading areas
3.2.3 Locations and concentrations of tank pit soil samples and any other over-excavation confirmation samples
3.2.4 Locations of borings and wells, measured at right angles to the nearest center of streets
3.2.5 Sewer and utility maps
3.2.6 Location of nearby surface water
3.2.7 Actual or potential subsurface conduits
3.2.8 Locations for the proposed soil borings and/or monitoring wells
3.2.9 North arrow and scale
3.3 Sampling and Analysis Plan
3.3.1 Identification of chemicals of concern
3.2.2 Name of the certified laboratory and chain of custody procedures
3.3.3 Sampling procedures and sample management
3.3.4 Analytical detection limits/preservation protocol
3.3.5 Identification of field screening instruments and calibration protocol
3.4 Soil Boring and Monitoring Well Installation
3.4.1 Soil boring or groundwater monitoring well drilling method, well construction design, and well development method (use the DWR's California Well Standards and the guidance manual published by the State of California Environmental Protection Agency, Monitoring Well Design and Construction for Hydrogeologic Characterization as reference for the construction of monitoring wells and soil borings).
3.4.2 Prevention plan for avoiding cross-contamination when installing monitoring wells in the second or deeper water bearing zones.
3.4.3 Top-of-casing elevation of all monitoring wells must be surveyed to Mean Sea Level datum
3.4.4 Variances from the above standards (e.g., selected screened interval for confined conditions, shallow water conditions for well seals, less than 2-inch diameter annular space) must be proposed in workplans.
3.4.5 Proposed drill cutting and purge water containment, storage, and disposal.
3.5 Geology and Hydrogeology
3.5.1 Description of geologic characteristics of all the aquifers which could be impacted
3.5.2 Regional and site-specific verified groundwater flow directions
3.5.3 Description of soil lithology
3.5.4 Detailed description of proposed aquifer tests (if applicable):
3.5.4.1 Type of test proposed
3.5.4.2 Installation of observation wells
3.5.4.3 Duration of test and equipment selection
3.5.4.4 Proposed test/data analysis method
3.6 Extent of Soil Pollution
3.6.1 Objective and rationale for boring locations
3.6.2 The number, location, and depth of proposed borings
3.6.3 At least one soil boring on-site, in or near the source are, shall be continuously cored and logged
3.6.4 For vertical definition, soil samples shall be collected at five (5) foot intervals, at significant changes in lithology, or detection of contamination
3.6.5 For horizontal definition, borings shall be designed to fully define the limits of contamination in the vadose zone
3.7 Extent of Groundwater Pollution
3.7.1 Objective and rationale for monitoring well/boring locations
3.7.2 The number, location, and specific design of monitoring wells (e.g., proposed screened interval, proposed filter pack design)
3.7.3 For vertical definition, proposed monitoring well design for targeted compounds
3.7.3.1 For petroleum hydrocarbons or other light non-aqueous phase liquids (LNAPL), the screened interval should be designed with the top of screens 5 feet above the seasonal high groundwater table, and should allow for seasonal or historic low groundwater conditions as well. For confined water-bearing zones, only the water-bearing zone should be screened.
3.7.3.2 For chlorinated solvents, halogenated hydrocarbons, and other dense non-aqueous phase liquids (DNAPL), the screened interval should be set at the bottom ten feet of the targeted water bearing zone.
3.7.4 For horizontal definition, monitoring wells should be designed to fully define the limits of groundwater contamination to below the practical quantitation limit for all constituents of concern.
3.8 Beneficial Uses
3.8.1 Description of the existing and potential beneficial water uses is provided in the RWQCB Basin Plan.
3.8.2 Determination of beneficial uses of groundwater must be investigated by evaluating the results of well surveys (see Policies and Procedures) of active and inactive municipal, agricultural, industrial, and domestic water wells.
4.0 Preliminary Site Assessment Report
Within sixty (60) calendar days following completion of a preliminary site assessment, a Preliminary Site Assessment Report must be submitted to GPP for review. If the extent of soil and groundwater contamination has been defined, proceed with the feasibility study phase (see Feasibility Study). Otherwise, proceed with the remedial investigation phase (see Remedial Investigation). The Preliminary Site Assessment Report must be prepared in accordance with the following format and scope.
4.1 Site Information
4.1.1 Executive summary
4.1.2 Name and address of the site and the Responsible Party
4.1.3 Site description
4.1.4 Current and past business activities on the site
4.1.5 History of spills and unauthorized releases at the site and adjacent properties
4.1.6 Summary of the environmental assessment activities and dates performed at the site
4.2 Scale Maps
4.2.1 Site boundaries and adjacent streets
4.2.2 Locations of all current and historic tanks, associated piping, chemicals and waste storage areas, processing, manufacturing and loading areas
4.2.3 Locations and concentrations of tank pit soil samples and any other over-excavation confirmation samples
4.2.4 Locations of borings and soil sampling analytical results
4.2.5 Locations of monitoring wells, measured at right angles to the nearest center of streets
4.2.6 Sewer and utility maps
4.2.7 Iso-concentration contours of dissolved constituents in groundwater, including date of sample collection
4.2.8 Groundwater elevation contours with flow direction and calculated gradient
4.2.9 Contours of free-product thickness
4.2.10 North arrow and scale
4.3 Geology and Hydrogeology
4.3.1 Discussion of the lithology encountered during drilling operations
4.3.2 Discussion of chemical properties of contaminants (e.g., adsorption, degradation)
4.3.3 Discussion of physical properties of contaminants (e.g. density, solubility, diffusion, dispersion, advection) which may affect transport
4.3.4 Discussion of chemical and physical characteristics of the water-bearing zone (e.g. organic carbon content, Eh, pH, conductance, permeability, storativity, hydraulic gradient, hydraulic conductivity, transmissivity, total and effective porosity)
4.3.5 Detailed discussion of contaminant migration based on cross-sections, groundwater flow direction and gradient, and potential subsurface conduits
4.3.6 Discussion of aquitard/aquiclude occurrence and permeability
4.3.7 Identification of pathways to the aquifer
4.3.8 Identification of pathways within the aquifer
4.3.9 Identification of any unique site features which may create preferential pathways for the contaminants to move through soil or groundwater
4.3.9.1 Naturally occurring pathways such as faults, animal burrows, buried stream channels, buried stream banks, and tree roots
4.3.9.2 Artificial pathways such as sewer and other utility lines
4.3.10 Elevation of all monitoring wells surveyed by a licensed land surveyor to Mean Sea Level datum, not an arbitrary or site-specific datum.
4.3.11 Calculation of groundwater gradient and discussion of historical flow direction and gradient information should be documented and reported as number of degrees from North.
4.3.12 Discussion of potential influences on local groundwater flow (e.g., construction dewatering, dewatering wells, pumping stations, sump pumps, dry wells)
4.3.13 Identification of nearby domestic, industrial, or agricultural wells
4.3.14 Complete and legible boring logs, including the following
4.3.14.1 Appropriate lithologic description (USCS for soils, GSA for rock)
4.3.14.2 Percentage of sample recovery
4.3.14.3 Identification of samples collected
4.3.14.4 Field-screening data (e.g., PID/FID readings, immunoassay data)
4.4 Sampling
4.4.1 Description of procedures used to obtain samples (See Site-Specific Sampling Plans, Appendix B)
4.4.2 Copies of field notes and field data sheets
4.4.3 Description of field screening procedures, including calibration and quality control for field screening methods and equipment
4.5 Soil Boring and Monitoring Well Installation
4.5.1 Detailed drilling method of soil borings and monitoring wells
4.5.2 Construction details of monitoring wells
4.5.3 Depth to groundwater and groundwater elevation, including both first-encountered and stabilized water levels
4.5.4 Documentation of drill-cutting disposal or proposed treatment
4.6 Laboratory Results
4.6.1 Tables
4.6.1.1 Summary of soil and groundwater analytical results
4.6.1.2 Historical soil and groundwater analytical results
4.6.1.3 Sample identification such as boring number and depth
4.6.1.4 Analytical detection/reporting limits
4.6.1.5 Date of collection
4.6.2 Date samples arrived at the laboratory, temperature upon arrival, holding times, and date of extraction
4.6.3 Any unusual events in the laboratory or in the field
4.6.4 Copy of complete, signed laboratory report, including complete chain-of-custody documentation
4.7 Conclusion and Recommendations
4.7.1 Data evaluation and interpretation - Mere data summary is not acceptable.
4.7.2 Discussion of the distribution and concentration of contaminants in soil, capillary fringe, and saturated zone
4.7.3 Calculation of the quantity of impacted soil, in cubic yards
4.7.4 Calculation of the quantity of impacted groundwater and surface water
4.7.5 Justification of the completion of site characterization
4.7.6 Final recommendations: additional site characterization or proceed with the next phase of corrective action (either feasibility study or remediation).
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