Sacramento Modesto Roseville Pleasanton. Jeff Black, PE Blackwater Consulting Engineers, Inc. 605 Standiford Ave., Suite N Modesto, CA 95350

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1 Sacramento Modesto Roseville Pleasanton December, 01 File Number: Jeff Black, PE Blackwater Consulting Engineers, Inc. 605 Standiford Ave., Suite N Modesto, CA 9550 Subject: Mr. Black, GEOTECHNICAL MEMORANDUM Waste Water Treatment Plant Evaluation Thornton, CA Crawford & Associates, Inc. (CAInc) completed this Geotechnical Memorandum for the Waste Water Treatment Plant (WWTP) Evaluation Project in Thornton, California. We understand that the existing effluent pond will be re- graded, divided into smaller ponds, and improved to minimize future erosion. This memorandum includes a description of subsurface conditions, and geotechnical recommendations for design and reconstruction of the Thornton WWTP effluent ponds. CAInc prepared this memorandum in accordance with our September, 01 agreement. Existing Facilities The existing Thornton WWTP consists of an Imhoff Tank, where raw sewage is initially collected, and ponds where effluent evaporates and/or infiltrates. The Imhoff Tank is located east of Interstate 5 and the effluent pond is located west of Interstate 5 along Koontz Road. We understand that the effluent pond originally contained interior dikes that divided the pond into seven smaller ponds, however the interior dikes have been eroded and no longer exist. The perimeter dike has also been diminished and is currently about 7 to 9 ft wide at the crest with steep and/or near vertical interior slopes. The housing authority placed plastic sheeting, sandbags, and wooden stakes in an attempt to minimize further erosion of the perimeter dikes, however continued slumping and erosion was noticeable during our site visits. Scope of Services To prepare this memo, CAInc: 1. Discussed the project with the design team,. Measured the basin sludge depth at various locations on October 16, 01.. Excavated and sampled two exploratory borings ranging from 16.5 to 1.5 ft below ground surface (bgs) on October, 01. 1

2 Thornton WWTP December, 01 Geotechnical Memorandum CAInc # Performed four infiltration rate tests near the bottom of the basin elevation on October, Performed geotechnical engineering calculations and analysis to develop our recommendations. Subsurface Soil and Groundwater Conditions To characterize the subsurface conditions at the site, CAInc observed two exploratory borings to depths ranging from 16.5 to 1.5 ft below ground surface (bgs) on October, 01. The locations of our borings are shown on Figure 1. In general, our borings indicate that the upper ft of the site consists of medium dense silty sand, underlain by medium stiff to stiff lean clay and sandy lean clay to the depths explored. During our fieldwork we encountered groundwater about 9 ft bgs. Historical groundwater depths in the area vary from about to 1 ft below ground surface. Ground water levels will fluctuate due to changes in precipitation, creek levels, irrigation, pumping of wells, and other factors. Subsurface soil and groundwater information is shown on our attached boring logs. Infiltration Rate Testing To determine infiltration rates in the lagoon vicinity we used the United States Bureau of Reclamation falling head test method. We performed our infiltration rate testing outside the pond at the approximate bottom of pond elevation. In general, the tests consist of the following: Drill a 6- inch diameter hole to test depth. Clean the borehole. Place a two- inch layer of fine gravel at the bottom of the hole, and set an observation pipe. Secure the perforated pipe with gravel to prevent movement during testing. Saturate the bottom of the hole with water a minimum of 1 inches of water overnight. Begin measuring water levels from a fixed reference point. Infiltration rates are considered stable after four consecutive readings show a consistent water level drop rate. Infiltration test locations are shown on Figure 1. We present the results of our infiltration tests in Table 1.

3 Thornton WWTP December, 01 Geotechnical Memorandum CAInc # Test Number Table 1: Infiltration Test Data Test Depth (bgs) Field Infiltration Rate (inches/hr) Soil Classification P1 5 ft 1.5 silty sand to lean clay P 5 ft silty sand to lean clay P 5 ft 0.7 lean clay P 5 ft 0.7 lean clay In general, our field tests show moderate to low infiltration rates ranging from approximately 0.7 to inches per hour, at the depths tested. USDA Web Soil Survey data indicates that the upper five feet of the site should yield infiltration rates of about 0.6 inches, which correlate well with our results in the lean clay layer. Based on our experience, the falling head test method can yield results that can vary by as much as 90% between locations. Due to the variability of the test method CAInc recommends that the designer apply a factor of safety to the field results above for design of the effluent ponds. CAInc also recommends the designer assume the pond is founded within the slower infiltrating lean clay soil stratification and discount the above infiltration rates within the silty sand to lean clay layers. Conclusions and Recommendations Grading The lagoon dike shall be graded as described below to minimize settlement, slumping, erosion and to provide sufficient support for liners and maintenance vehicles. Where referenced in this report, use the most current ASTM D 1557 test methods to determine relative compaction and optimum moisture. Compacted soil should not be considered suitable (even if it meets relative compaction requirements) if it is unstable and pumps or flexes excessively under construction equipment loads, as determined by CAInc. Soil Excavatability Based on the conditions observed in our subsurface explorations and our experience, the on- site soil should be excavatable with typical grading equipment such as scrapers, dozers, backhoes and excavators.

4 Thornton WWTP December, 01 Geotechnical Memorandum CAInc # Clearing and Degrade Prior to site grading, dewater the pond and excavate the existing sludge to firm native material. Properly dispose of the existing sludge off- site as required by local and state regulations. Based on our fieldwork we estimate the sludge to be approximately 1 to ft thick and that native material will be encountered at elevations between.0 to 5.5 ft. Degrade the existing perimeter dike to firm native material. We expect the perimeter dike will be excavated to an elevation equal to the landside toe (elevations ranging from 6.6 to 8.06 ft). See the survey information provided by O Dell Engineering for the actual landside toe elevations. CAInc must observe the bottom of the clearing and degrade effort within the pond and below the existing perimeter dike. Scarification and Compaction Process and compact the exposed subgrade below proposed dike areas as follows: 1. Scarify the subgrade to a depth of approximately 6- inches.. Moisture condition subgrade soil to within % of optimum moisture content and compact it to a minimum 90% of ASTM D1557 test procedure. The on- site clayey soils will likely be difficult to compact due to high moisture content. The on- site clayey soils will likely need to be disced and dried back during prolonged periods of dry weather or over- excavated and replaced with drier material.. Minimize compaction, and construction traffic along the bottom of the ponds. Fill Placement On- site perimeter dike soil may be used for fill provided it contains no rock fragments larger than / in maximum dimension and is free of concentrations of debris and vegetation. If import material is required, it should meet the following criteria: Contain no concentration of organics, debris or deleterious materials, Maximum particle size of 1 with at least 0% passing the No. Sieve and 5% to 0% passing the No. 00 sieve, Expansion Index 5, per ASTM D89. R- value > 0. Import fill must be observed and tested by CAInc prior to its approval. Place fill in maximum 8 loose lifts, moisture condition to within % of optimum and compact to a minimum 90% relative compaction. Increase relative compaction to 95% in final lift. Fill placed on slopes should be benched into the slope a minimum of ft (horizontal) for each 1 ft (vertical) of fill placed, or as necessary to remove loose material and allow access for compaction equipment.

5 Thornton WWTP December, 01 Geotechnical Memorandum CAInc # Pond Slopes Construct interior and exterior pond dike side slopes at.5h:1v (horizontal: vertical) or flatter. Slope dike crest to prevent slope erosion due to surface runoff. To prevent erosion and minimize maintenance, CAInc recommends lining all interior slopes with Mirafi 180NC Geotextile (or equivalent) and rock slope protection (RSP). Install Geotextile per manufactures recommendations; overlap edges a minimum of 1 inches with anchor pins. Temporarily anchor the Geotextile, particularly at the top of the slope to minimize movement during RSP placement. Rock slope protection (RSP) should consist of large, heavy, angular, well- graded rock. RSP grading should consist of 50-0 percent larger than 75lb rock. Place RSP a minimum of 1.8 ft. thick as shown on detail 1. Limit maximum height of rockfall during placement to less than ft. End dumping of rock down embankment slopes is not recommend. Geotextile should be protected from puncture or tearing during placement of RSP. Replace/repair fabric damaged during rock placement with new fabric with a minimum overlap of 1 inches. Check RSP annually for damage and presence of vegetation. Repair RSP as needed and remove vegetation to prevent damage to Geotextile and RSP. Pond slope recommendations are shown in Detail 1 below. Limitations CAInc prepared this geotechnical memorandum in accordance with generally accepted geotechnical engineering principles and practices currently used in this area. This report is intended for Blackwater Consulting Engineers, Inc., the design team, and the HACSJ to use during design and construction. Do not use this information for different locations or projects without the written consent of CAInc. Logs of our exploratory borings are attached. The lines designating the interface between soil types are approximate. The transition between soil types may be abrupt or gradual. Our recommendations are based on the final logs, which represent our interpretation of the field logs and general knowledge of the site and geological conditions. 5

6 Thornton WWTP December, 01 Geotechnical Memorandum CAInc # Modern design and construction are complex, with many regulatory sources/restrictions, involved parties, construction alternatives, etc. It is common to experience changes and delays. The owner should set aside a reasonable contingency fund based on complexities and cost estimates to cover changes and delays. We appreciate the opportunity to work on this project. Please call if you have questions. Sincerely, Crawford & Associates, Inc., David P. Castro, P.E. Associate Project Manager Benjamin D. Crawford, P.E., G.E. Principal Attachments: Figure 1 Boring and Infiltration Rate Test Locations Boring Legend and Logs 6

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8 MATERIAL TYPES COARSE- GRAINED SOILS >50% RETAINED ON NO. 00 SIEVE PLASTICITY INDEX (PI) FINE- GRAINED SOILS >50% PASSING NO. 00 SIEVE UNIFIED SOIL CLASSIFICATION (ASTM D 87-06) CRITERIA FOR ASSIGNING SOIL GROUP NAMES GRAVELS >50% OF COARSE FRACTION RETAINED ON NO. SIEVE SANDS <50% OF COARSE FRACTION RETAINED ON NO. SIEVE SILTS AND CLAYS LIQUID LIMIT <50 SILTS AND CLAYS LIQUID LIMIT >50 HIGHLY ORGANIC SOILS NOTE: Cu=D 60/D Cc=(D ) / D xd CL-ML 0 60 CLEAN GRAVELS <5% FINES GRAVELS WITH FINES >1% FINES CLEAN SANDS <5% FINES SANDS WITH FINES >1% FINES INORGANIC ORGANIC INORGANIC ORGANIC Cu > AND 1 < Cc < Cu < AND/OR 1 > Cc > FINES CLASSIFY AS ML OR MH FINES CLASSIFY AS CL OR CH Cu > 6 AND 1 < Cc < Cu < 6 AND/OR 1 > Cc > FINES CLASSIFY AS ML OR MH FINES CLASSIFY AS CL OR CH LL (oven dried)<0.75/ll (not dried) PI PLOTS ON OR ABOVE "A" LINE PI PLOTS BELOW "A" LINE LL (oven dried)<0.75/ll (not dried) PRIMARILY ORGANIC MATTER, DARK COLOR, ORGANIC ODOR BLOW COUNT The number of blows of a -lb. hammer falling 0-inches required to drive the sampler the last 1-inches of an 18-inch drive. The notation 50/0. indicates -inches of penetration achieved in 50 blows. For classification of fine-grained soils and fine-grained fraction of coarse-grained soils. Equation of "A"-line Horizontal at PI= to LL=5.5, then PI=0.7 (LL - 0) Equation of "U"-line Vertical at LL=16 to PI=7, then PI=0.9 (LL - 8) PLASTICITY CHART CL or OL ML or OL "U" LINE CH or OH "A" LINE MH or OH LIQUID LIMIT (LL) GROUP SYMBOL GW SOIL GROUP NAMES BORING LOG / TEST PIT LEGEND AND SOIL DESCRIPTIONS GP GM GC SW SP SM SC CL ML OL CH MH OH PT SAMPLE TYPES Auger or backhoe cuttings Shelby tube Standard Penetration (SPT) Bulk Sample GRAPHIC SYMBOL C CP CR CU DS EI P PA PI PP R SE SG SL SW TV UC UU WELL-GRADED GRAVEL POORLY-GRADED GRAVEL SILTY GRAVEL CLAYEY GRAVEL WELL-GRADED SAND POORLY-GRADED SAND SILTY SAND CLAYEY SAND LEAN CLAY SILT ORGANIC CLAY OR SILT FAT CLAY ELASTIC SILT ORGANIC CLAY OR SILT PEAT Modified California " California Standard.5" Rock core ADDITIONAL TESTS - Consolidation - Compaction Curve - Corrosivity Testing - Consolidated Undrained Triaxial - Direct Shear - Expansion Index - Permeability - Partical Size Analysis - Plasticity Index - Pocket Penetrometer - R-Value - Sand Equivalent - Specific Gravity - Shrinkage Limit - Swell Potential - Pocket Torvane Shear Test - Unconfined Compression - Unconsolidated Undrained Triaxial GROUND WATER LEVELS Later water level after drilling Water level at time of drilling

9 LOGGED BY JJW DRILLING CONTRACTOR GeoEX DRILLING METHOD Solid-Stem Auger BEGIN DATE --1 SAMPLER TYPE(S) AND SIZE(S) (ID) SPT (1.") BOREHOLE BACKFILL AND COMPLETION Cement Grout COMPLETION DATE --1 BOREHOLE LOCATION (Lat/Long or North/East and Datum) BOREHOLE LOCATION (Offset, Station, Line) DRILL RIG CME 750. SPT HAMMER TYPE Automatic Trip, lb, 0 inch GROUNDWATER READINGS DURING DRILLING 9.0 ft AFTER DRILLING (DATE) HOLE ID B1 SURFACE ELEVATION BOREHOLE DIAMETER 6 in HAMMER EFFICIENCY, ERi TOTAL DEPTH OF BORING 16.5 ft ELEVATION (ft) DEPTH (ft) 0 1 Material Graphics DESCRIPTION SILTY SAND (SM); medium dense; grayish brown; dry; about 5 to 0% fines. Sample Location Sample Number Blows per 6 in. Blows per foot Recovery (%) RQD (%) Moisture Content (%) Dry Unit Weight (pcf) Shear Strength (tsf) Drilling Method Casing Depth Remarks Lean CLAY (CL); medium stiff to stiff; brown; moist; about 5 to % fine SAND; medium plasticity fines SANDY lean CLAY (CL); medium stiff to stiff; brown; moist; about 0 to 5% fine SAND; medium plasticity fines Lean CLAY (CL); medium stiff to stiff; brown; moist; about 5 to % fine SAND; medium plasticity fines Bottom of borehole at 16.5 ft bgs REPORT TITLE BORING RECORD DIST. COUNTY STA PROJECT OR BRIDGE NAME Thornton WWTP BRIDGE NUMBER ROUTE PREPARED BY DPC POSTMILE D HOLE ID B1 EA DATE SHEET 1 of 1

10 LOGGED BY JJW DRILLING CONTRACTOR GeoEX DRILLING METHOD Solid-Stem Auger BEGIN DATE --1 SAMPLER TYPE(S) AND SIZE(S) (ID) SPT (1.") BOREHOLE BACKFILL AND COMPLETION Cement Grout COMPLETION DATE --1 BOREHOLE LOCATION (Lat/Long or North/East and Datum) BOREHOLE LOCATION (Offset, Station, Line) DRILL RIG CME 750. SPT HAMMER TYPE Automatic Trip, lb, 0 inch GROUNDWATER READINGS DURING DRILLING 9.0 ft AFTER DRILLING (DATE) HOLE ID B SURFACE ELEVATION BOREHOLE DIAMETER 6 in HAMMER EFFICIENCY, ERi TOTAL DEPTH OF BORING 1.5 ft ELEVATION (ft) DEPTH (ft) 0 1 Material Graphics DESCRIPTION SILTY SAND (SM); medium dense; grayish brown; dry; about 5 to 0% fines. Sample Location Sample Number Blows per 6 in. Blows per foot Recovery (%) RQD (%) Moisture Content (%) Dry Unit Weight (pcf) Shear Strength (tsf) Drilling Method Casing Depth Remarks Lean CLAY (CL); medium stiff to stiff; brown; moist; about 5 to % fine SAND; medium plasticity fines; oxidation SANDY lean CLAY (CL); medium stiff to stiff; brown; moist; about 0 to 5% fine SAND; medium plasticity fines Lean CLAY (CL); medium stiff to stiff; brown; moist; about 15% medium to fine SAND; medium plasticity fines. 0 1 Bottom of borehole at 1.5 ft bgs REPORT TITLE BORING RECORD DIST. COUNTY STA PROJECT OR BRIDGE NAME Thornton WWTP BRIDGE NUMBER ROUTE PREPARED BY DPC POSTMILE D HOLE ID B EA DATE SHEET 1 of 1