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Home My WebLink AboutMONTAVA - PHASE D CORE - BDR240006 - SUBMITTAL DOCUMENTS - ROUND 1 - Supporting Documentation (12) SUBSURFACE EXPLORATION REPORT MONTAVA DEVELOPMENT – TRACT E – DETENTION POND EVALUATION OF GROUNDWATER AND SUBSURFACE CONDITIONS FORT COLLINS, COLORADO EEC PROJECT NO. 1172058 Prepared for: Montava Development, LLC 430 N College Avenue, Suite 410 Fort Collins, Colorado 80524 Attn: Mr. Max Moss (Max@hf2m.com), and Mr. Forrest Hancock (forrest@montava.com) - Development Director Prepared by: Earth Engineering Consultants, LLC 4396 Greenfield Drive Windsor, Colorado 80550 4396 GREENFIELD D RIVE W INDSOR, C OLORADO 80550 (970) 545-3908 FAX (970) 6 63-0 282 www.earth-engineering.com July 26, 2023 (Revised from December 6, 2022) Montava Development, LLC 430 N College Avenue, Suite 410 Fort Collins, Colorado 80524 Attn: Mr. Max Moss (Max@hf2m.com), and Mr. Forrest Hancock (forrest@montava.com) - Development Director Re: Supplemental Subsurface Exploration and Geotechnical Engineering Services Montava Development – Tract E – Detention/Irrigation Pond Installation of 4 Monitoring Wells and Liner Recommendations Fort Collins, Larimer County, Colorado EEC Project No. 1172058 Mr. Moss and Mr. Hancock: Enclosed, herewith, are the results of the subsurface exploration completed by Earth Engineering Consultants, LLC (EEC) personnel for the referenced project. The results presented herein are from the evaluation of the field observation and laboratory testing procedures obtained from four (4) soil borings which were then converted to long-term groundwater monitoring wells (MWs) positioned around the perimeter of the proposed detention pond currently in the design phase for Tract E at the Montava Development project, (please refer to the site plans included herein), which were drilled to depths of approximately 15 to 20 feet below current site grades. This study was completed in general accordance with our proposal dated July 12, 2022. EEC initially provided a “DRAFT” report to the project design . Based on review of the “DRAFT” report, it was determined the development group elected to utilize a hybrid liner approach as further discussed herein. We understand the proposed detention pond will have a top of embankment elevation of approximately 5002 as presented on the topographic map provided to us by the project’s civil engineering consultant, TST, Inc.- Consulting Engineers, along with a bottom or floor elevation of approximately 4987 (normal bottom of the pond) and 4982 (bottom of the pond at the intake). The normal high-water level within the pond is planned at approximately 4998.75 and at a 100-year elevation of 5001, which would create an approximate pond volume of 53 acre-feet (AF) or approximately 85,506 cubic yard (CY). As presented on the enclosed site plan and TST’s civil drawing/grading plan Sheet 6 of 10 around the perimeter of the pond will be an approximate 4.75 foot “stacked stone wall” from elevation 4999.75 to elevation 4995.0. At the base of the stone Earth Engineering Consultants, LLC EEC Project No. 1172058 Montava Development – Tract E – Detention Pond Fort Collins, Colorado July 26, 2023 (Revised from December 6, 2022) Page 2 stack wall the bottom of the pond will be sloped at a 4:1 ratio (horizontal to vertical) toward the intake, which has an elevation of 4984 at the intake and an elevation of 4982 along the bottom of the pond. The side walls/embankments of the pond are anticipated to be constructed with approximate 4:1 slope (horizontal to vertical) or flatter with a hybrid “enhanced cohesive” earthen liner over an approved PVC synthetic membrane liner placed along the wetted perimeter to minimize seepage and/or groundwater intrusion. To evaluate and analyze the existing subsurface conditions around the outer perimeter of the proposed pond configuration, and to assist the civil engineering consultants in the design of either an earthen liner or synthetic liner for pond, EEC personnel were requested to perform a subsurface exploration which consisted of drilling and sampling the subsurface conditions around the perimeter of the proposed pond configuration, (please refer to Figure Nos. 1 and 2 in the Appendix of this report), with a total of four (4) test borings drilled to approximate depths of 15 to 20 feet below existing site grades, and upon completion of the drilling operations, convert the bore holes to long-term registered PVC cased piezometers/monitoring wells. The purpose of this report is to describe the subsurface conditions encountered within the four (4) borings/piezometers/MWs, analyze and evaluate the test data, and provide geotechnical recommendations concerning the design and construction of the new synthetic liner for the water storage pond. EXPLORATION AND TESTING PROCEDURES The four (4) boring locations were established in the field by EEC personnel using a hand-held GPS unit referencing approximate horizontal coordinates from a “Google Earth” image of the site, and by estimating locations from identifiable site features. The approximate locations for the four (4) borings/piezometers/MWs, identified herein as MW-1 through MW-4, are presented on Figure Nos. 1 and 2 in Appendix A of this report. Ground surface elevations were obtained by using linear interpolation of contours as presented on the topographic map prepared by the civil engineer. The topographic map was also used to create the groundwater contour map as further discussed herein. The estimated ground surface and top of casing elevations are recorded on each respective boring log. The locations of the test borings/piezometers and ground surface elevations should be considered accurate only to the degree implied by the methods used to make the field measurements. Earth Engineering Consultants, LLC EEC Project No. 1172058 Montava Development – Tract E – Detention Pond Fort Collins, Colorado July 26, 2023 (Revised from December 6, 2022) Page 3 The four (4) test borings/MWs were completed using a truck mounted, CME-75 drill rig equipped with a hydraulic head employed in drilling and sampling operations and were advanced using 4-1/2-inch nominal inside diameter hollow stem augers. After completing the drilling and sampling, and prior to removal of the hollow stem augers, PVC cased piezometers were installed in the open boreholes through the hollow stem augers. The piezometers/monitoring wells were constructed with 2-inch nominal diameter schedule 40 manufactured well screen and riser pipe. In general, the piezometers consisted of an approximate 10-foot section of flush threaded slotted well screen at the bottom of the boreholes with flush threaded solid riser pipe, as required, to extend the piezometers above ground level. The screen portion of the piezometers were backfilled with 10/20 silica sand, with an approximate 2-foot bentonite plug/seal placed above the sand layer, and then backfilled with a blend of the auger cuttings generated and bentonite to the existing ground surface elevations. A 4-inch by 4-inch by 4-foot in length steel proactive casing encased in concrete was installed at the surface of MW. Cross-sectional schematics of the piezometer/MW installations are indicated on the attached boring logs. Photographs taken during our field exploration are included in the appendix of this report. The State of Colorado Division of Water Resources was notified of intent to construct monitoring holes prior to beginning the field exploration. Copies of those notices with acknowledgement from the State Engineer’s Office are attached with this report. The well construction and test reports will be provided to the Division of Water Resources including copies of the boring logs provided with this report. If the monitoring wells will remain in place longer than 18 months, it will be necessary to notify the Division of Water Resources and complete registration of those wells. Piezometer installation was completed by a licensed water well driller and was completed in accordance with the water well construction rules from the Division of Water Resources. Samples of the subsurface materials encountered were obtained using split barrel (Standard Penetration Test / SPT) sampling procedures. In the split barrel/SPT sampling procedures, standard sampling spoons are advanced into the ground by means of a 140-pound hammer falling a distance of 30 inches. The number of blows required to advance the split barrel sampler is recorded and is used to estimate the in-situ relative density of cohesionless soils and, to a lesser degree of accuracy, the consistency of cohesive soils and hardness of weathered bedrock. In conjunction with the split spoon samples, two (2) composite samples of the overburden subsoil materials were also collected from the test borings for further laboratory analyses. All samples Earth Engineering Consultants, LLC EEC Project No. 1172058 Montava Development – Tract E – Detention Pond Fort Collins, Colorado July 26, 2023 (Revised from December 6, 2022) Page 4 obtained in the field were sealed and returned to the laboratory for further examination, classification, and testing. Laboratory moisture content tests were completed on each of the recovered split-spoon samples. In addition, the unconfined strength of select samples was estimated using a calibrated hand penetrometer. Atterberg limits and washed sieve analysis tests were completed to evaluate the quantity and plasticity of fines in selected subsurface samples. Additional laboratory testing procedures included moisture-density relationship/standard Proctor density (ASTM Specification D698) and falling head permeability characteristics (ASTM Specification D5856) on the bulk/composite samples collected during the drilling operations. Results of the outlined tests are indicated on the attached boring logs and summary sheets. As part of the testing program, all samples were examined in the laboratory by an engineer and classified in accordance with the attached General Notes and the Unified Soil Classification System, based on the soil’s texture and plasticity. The estimated group symbol for the Unified Soil Classification System is indicated on the boring logs and a brief description of that classification system is included with this report. SUBSURFACE CONDITIONS An EEC field engineer was on site during the drilling operations to evaluate the subsurface conditions encountered and direct the drilling activities. Field logs prepared by EEC site personnel were based on visual and tactual observation of disturbed samples and auger cuttings. The final boring logs included with this report may contain modifications to the field logs based on the results of laboratory testing and evaluation. Based on the results of the field borings and laboratory evaluation, subsurface conditions can be generalized as follows. Sparse vegetation/weed growth/agricultural growth, as evident in the site photographs in the Appendix of this report was encountered at the surface of each test boring/piezometer. The subsurface materials encountered beneath the surficial layer generally consisted of sandy lean clay transitioning to a poorly graded sand with gravel with depth, which extended to the depths explored, approximately 15 to 20 feet. The overburden cohesive subsoils were generally soft to medium stiff in-situ, and when properly moisture conditioned and compacted, appeared to exhibit permeability characteristics conducive for earthen liner material; however, due to the Earth Engineering Consultants, LLC EEC Project No. 1172058 Montava Development – Tract E – Detention Pond Fort Collins, Colorado July 26, 2023 (Revised from December 6, 2022) Page 5 groundwater conditions and the proposed design of the pond, consideration should be given to the use of synthetic liner with a sufficient amount of cover to minimize the potential for groundwater seepage/intrusion into the pond, as well as a slurry wall. As further discussed herein, the development group has elected to utilize a hybrid system consisting of an approved synthetic liner with a minimum 3-foot zone of cohesive material placed and compacted along the wetted perimeter of the pond. The stratification boundaries indicated on the boring logs represent the approximate locations of changes in soil and rock types. In-situ, the transition of materials may be gradual and indistinct. GROUNDWATER CONDITIONS Observations were made while drilling, shortly thereafter and again on December 1, 2022, to detect the presence and depth to hydrostatic groundwater within the completed borings. At the time of our subsequent groundwater measurement episode on December 1, 2022, groundwater was measured at depths ranging from approximately 8 to 12 feet below existing site grades. The recorded measurements are listed on the upper right-hand corner of each boring log/piezometer included in the Appendix of this report. Fluctuations in groundwater levels can occur over time depending on variations in hydrologic conditions, fluctuations in the proposed water storage pond elevations, irrigation demands, and other conditions not apparent at the time of this report. Monitoring in cased borings, such as those installed for this project and protected from the infiltration of surface water, can more accurately evaluate the depth and fluctuation in groundwater levels. EEC anticipates performing periodic groundwater measurements over the next several months, especially after the installation of either the earthen liner of the synthetic liner, to evaluate the groundwater fluctuations and to evaluate the effectiveness of the liner, (i.e., an evaluation of the equilibrium of water levels inside and outside of the pond configuration). The observations provided in this report represent groundwater conditions at the time of the field exploration, and may not be indicative of other times, or at other locations. As part of our geotechnical engineering assessment, we prepared a groundwater contour map, included in the Appendix of this report, based on the approximate groundwater level reading measurements obtained on December 1, 2022. The contour elevations were based on the Earth Engineering Consultants, LLC EEC Project No. 1172058 Montava Development – Tract E – Detention Pond Fort Collins, Colorado July 26, 2023 (Revised from December 6, 2022) Page 6 approximate ground surface elevations at each boring location, and the approximate depth at which groundwater was encountered. As shown on the Groundwater Contour Map, the hydrologic gradient/piezometric surface flow of the measurable amount of water is in the south to southeast direction. The groundwater contour map presented herein on approximate 1-foot intervals, is for illustration purposes only; variations may exist between boring locations across the site and at different times of the year. It should be noted that the measured groundwater contour elevation of the proposed pond configuration on December 1, 2022, was at an approximate elevation of 4992; whereas the proposed bottom of the pond is currently designed at elevations of 4987 and 4982, which is approximately 5 to 10 feet into the groundwater surface; thus requiring dewatering significant dewatering measures to construct the pond. ANALYSIS AND RECOMMENDATIONS Moisture Density Relationship-Standard Proctor Density EEC personnel performed standard Proctor density (ASTM Specification D698) tests on the two (2) composite samples of overburden cohesive materials collected during our field exploration. For each composite sample, soil classification/Atterberg limits and minus No. 200 sieve wash gradations in conjunction with the standard Proctor density tests were performed. The results of the soil classification and standard Proctor density testing on the two (2) composite samples collected during our subsurface exploration are presented in the Table below with curves provided in the Appendix of this report. Table I – Summary of Laboratory Compaction Characteristics and Classification of Soils Sample ID Standard Proctor Density Soil Classification Optimum Moisture Content, % Maximum Dry Density, PCF Liquid Limit Plastic Index % (-) No. 200 Sieve Description Upper 5’ – 10’ 18.5 109.0 32 18 66.8 Sandy Lean Clay (CL) Lower 10’ – 15’ 17.0 110.0 32 18 75.4 Lean Clay with Sand (CL) It is our understanding the pond’s embankment modifications/improvements, and the earthen liner and wetted perimeter will be constructed with the excavated on-site overburden cohesive soils obtained during the excavation phases. As further mentioned in this report the primary focus is to create a uniform/consistent cohesive material having falling head permeability characteristics of 1 x 10-7 cm/sec or slower. Earth Engineering Consultants, LLC EEC Project No. 1172058 Montava Development – Tract E – Detention Pond Fort Collins, Colorado July 26, 2023 (Revised from December 6, 2022) Page 7 Laboratory Falling Head Permeability Tests EEC conducted a falling head permeability test (ASTM Specification D5856) on a remolded overburden sample obtained from the soil borings as described herein. The sample was remolded to near optimum moisture content and was compacted to approximately 95% of the material’s standard Proctor maximum dry density (ASTM Specification D698) test results. The results from this test indicated a coefficient of permeability (k-value) of 6.6 x 10-8 cm/sec. This measured k- value indicates the overburden cohesive soils have permeability and/or seepage characteristics suitable for reuse in constructing the earthen liner. The laboratory test results for the falling head permeability sample are presented in the Appendix of this report. General Geotechnical Considerations Field and laboratory test results indicate the cohesive soils encountered in the piezometers are soft to medium stiff in consistency and when properly placed and compacted, would be suitable for use as an earthen liner material. However due to the current groundwater levels above the bottom the designed pond elevation, consideration should be given to the use of a synthetic liner in conjunction with a minimum 3-foot zone or more of placed and compacted cohesive earthen liner material to minimize groundwater intrusion, as well as a perimeter slurry wall. The design concept for the liner and slurry wall will be to reduce the potential for seepage and groundwater intrusion, as well as to enhance the holding capacity of the pond. As evident on the Log of Borings/Piezometer Logs, and the groundwater contour map, the groundwater levels ranged from approximately 5 to 10 feet above the current pond bottom elevations. After the installation of the liner, readings of the piezometers/monitoring wells should be performed to verify the effectiveness of the liner, (i.e., the equilibrium of water levels inside and outside of the pond). If after construction of the pond, the groundwater readings in the “equilibrium piezometers” in comparison to the pond level, indicates the groundwater intrusion, consideration should be given to installing a slurry wall around the perimeter of the pond. With use of an earthen liner and/or a PVC membrane liner, it is typically suggested that the bottom of any pond be at least 3-feet above maximum anticipated groundwater level, or the construction a deepened core trench into the underlying bedrock formation be installed to Earth Engineering Consultants, LLC EEC Project No. 1172058 Montava Development – Tract E – Detention Pond Fort Collins, Colorado July 26, 2023 (Revised from December 6, 2022) Page 8 minimize groundwater intrusion. It should be noted that the monitoring wells were only completed to depths of approximately 15 to 20 feet below existing site grades and bedrock was not encountered. A minimum/permanent operating level of water is also necessary to minimize the amount of groundwater intrusion by maintaining a constant head as well as to reduce the buoyancy effects on a PVC synthetic liner. The pond’s embankments/wetted perimeter should consist of a homogeneous cohesive material constructed with relatively impervious clay material having a coefficient of permeability, (k-value) of 1x10-7 cm/sec or slower when compacted to at least 95% of standard Proctor density (ASTM Specification D698). We suggest the improvements of the existing embankments be cut to an approximate 1:1 slope and the proposed/enhanced liner be constructed on a minimum 4:1 (horizontal: vertical) or flatter slopes around the perimeter. The design of wave and slope protection for the pond is beyond the scope of this subsurface exploration study and should be reviewed during the final design stages. It is recommended any vegetation within the limits of the pond configuration be stripped and removed. It is anticipated that excavation of the pond could be accomplished by conventional type excavation equipment; however specialized or rubber-tired equipment may be necessary when approaching the bottom of the pond due to the presence of groundwater and soft compressible subsoils. Special precautions may be required to maintain a working platform at the bottom of pond due to the potential for soft/compressible conditions at or near the groundwater and/or perched surface interface. For any proposed intake and/or outlet pipes, or any other intrusions penetrating the cohesive embankments and/or the synthetic liner, the pipes should be properly bedded and backfilled with approved, relatively impervious cohesive soils. The intrusions/pipes should be surrounded by a minimum of 2-feet of relatively impervious cohesive materials having a coefficient of permeability of 1x10-7 cm/sec. or slower when properly compacted as described herein. The backfill should be compacted to a minimum of 95% of the material’s standard Proctor density as determined by ASTM D698. Anti-seep collars should be placed around all inlet and outlet pipes. Earth Engineering Consultants, LLC EEC Project No. 1172058 Montava Development – Tract E – Detention Pond Fort Collins, Colorado July 26, 2023 (Revised from December 6, 2022) Page 9 Earthen Liner/Wetted Perimeter Improvements Groundwater and/or the initial presence of a water surface as previously discussed was encountered within the piezometers/monitoring wells at approximate depths of 8 to 12 feet below existing site grades. To minimize the potential for groundwater fluctuations to impact and/or enter the pond, we suggest the bottom of the pond have a minimum separation of 3-feet above the maximum anticipated rise in groundwater. For this project, this concept will not be applicable, and the development group has elected to utilize a hybrid liner system consisting of an approved synthetic liner with a minimum 3-foot cover of placed and compacted earthen liner material. Dewatering will be required to achieve the hybrid synthetic/earthen liner improvements along the bottom portion of the pond as the current design elevations are into the groundwater table. Consideration could be given to installing a slurry wall around the perimeter of the pond to further reduce the potential for groundwater intrusion. A slurry wall subcontractor should review the contents of this report and provide supplemental recommendations accordingly. A 90-day water balance/seepage analysis may not be required for the proposed Montava Tract E Pond improvements. However due to the groundwater conditions a 90-day water balance/seepage analysis should be considered to evaluate the effectiveness of the hybrid synthetic/earthen liner approach. Included below are typical guidelines for developing a water storage pond. The performance of the raw water storage pond may be required to conform to the “Colorado State Engineer Guidelines for Lining Criteria for Gravel Pits” dated August 1999. The general guidelines state the following: “1.0 Design Standard: The intent of the reservoir lining design is to achieve groundwater inflow (leakage rate) into the reservoir that is not greater than 0.03 ft3/day/ft2 (1x10-5 cm3/cm2/sec) multiplied by the length of the perimeter wall in feet, multiplied by the average vertical depth of the perimeter wall as measured from the ground surface to the pit bottom along the toe of the pit side slope, plus 0.0015 ft3/day/ft2 (5x10-7 cm3/cm2/sec) multiplied by the area of the bottom of the liner system or natural bedrock bounded by the perimeter wall. 2.0 Construction Standards: The applicant must demonstrate the constructed liner meets the requirements of the design by performing appropriate quality control Earth Engineering Consultants, LLC EEC Project No. 1172058 Montava Development – Tract E – Detention Pond Fort Collins, Colorado July 26, 2023 (Revised from December 6, 2022) Page 10 observations and tests. The applicant shall provide written documentation of the work performed and results of the quality control field and laboratory tests. 3.0 Performance Standards: The Performance Standard shall be three times the Design Standard as described above. The performance Standard shall be applied to an initial test of competency of the liner, as well as to the on-going operation of the reservoir. 3.1 Initial Liner Test For Mined Pits: The unregulated groundwater inflow to the reservoir will be tested by evacuating the contents of the reservoir and observing the inflow of water over a period of 90 days. The start of the test will be under essentially dry conditions. If the Montava Tract E Pond is to conform, a water balance must be performed to demonstrate the balance of the inflows (i.e. precipitation and groundwater) and outflows (i.e. evaporation) equals the change in storage volume by a minimum of a 90-day test. Ongoing monitoring of the water balance may also be required as determined by the Division Engineer.” The berms/embankments surrounding the pond should be lined as part of the wetted perimeter with an approved earthen liner material. Approved materials used in the earthen liner/embankment should be placed in maximum 9-inch-thick loose lifts, adjusted in moisture content, and compacted to at least 95% of the materials’ maximum dry density as determined in accordance with ASTM Specification D698. The moisture of the liner materials should be adjusted to be within the range of ±2% of standard Proctor optimum moisture at the time of compaction. All earthwork/compaction activities should be field verified/approved by means of field density testing procedures and visual observations. The approved liner material, when compacted to at least 95% of the materials’ maximum dry density should have a coefficient of permeability of 1 x 10-7 cm/sec or slower. The liner thickness is a function of the material used to construct the earthen embankments, the material’s in-situ permeability characteristics, as well as the piezometric head or volume of water planned for short and/or long-term purposes. Based on our understanding of the proposed pond and our experience with materials with similar properties, we expect the majority of on-site overburden cohesive soils, excluding the fine Earth Engineering Consultants, LLC EEC Project No. 1172058 Montava Development – Tract E – Detention Pond Fort Collins, Colorado July 26, 2023 (Revised from December 6, 2022) Page 11 granular silty sand without some sort of enhancement provided, would be suitable for use as a low permeability earthen embankment material as intended. Care should be taken to provide a consistent, uniform low permeability cohesive material for use as the earthen liner. The materials’ permeability should continually be evaluated during construction to verify acceptance, and upon completion of the pond, in-situ flex-wall permeability tests (ASTM Specification D5084) should be performed for final compliance purposes. Other Considerations and Recommendations Groundwater was observed at depths of approximately 8 to 12 feet below present site grades. Excavations extending to the wetter soils could create difficulties for backfilling of the utility/pipe trenches with drying of the subgrade soils required to use those materials as backfill. In general, the subgrade soils could be used as backfill soils although care will be necessary to maintain sufficient moisture to reduce potential for post-construction movement. Excavations into the on-site soils will encounter a variety of conditions. Excavations into the clays can be expected to stand on relatively steep temporary slopes during construction; however, caving soils may also be encountered especially in close proximity to the groundwater table. Groundwater seepage should also be anticipated for utility excavations. Pumping from sumps may be utilized to control water within the excavations. Well points may be required for significant groundwater flow, or where excavations penetrate groundwater to a significant depth. The individual contractor(s) should be made responsible for designing and constructing stable, temporary excavations as required to maintain stability of both the excavation sides and bottom. All excavations should be sloped or shored in the interest of safety following local and federal regulations, including current OSHA excavation and trench safety standards. GENERAL COMMENTS The analysis and recommendations presented in this report are based upon the data obtained from the soil borings performed at the indicated locations and from any other information discussed in this report. This report does not reflect any variations which may occur between borings or across the site. The nature and extent of such variations may not become evident until Earth Engineering Consultants, LLC DRILLING AND EXPLORATION DRILLING & SAMPLING SYMBOLS: SS: Split Spoon ‐ 13/8" I.D., 2" O.D., unless otherwise noted PS: Piston Sample ST: Thin‐Walled Tube ‐ 2" O.D., unless otherwise noted WS: Wash Sample R: Ring Barrel Sampler ‐ 2.42" I.D., 3" O.D. unless otherwise noted PA: Power Auger FT: Fish Tail Bit HA: Hand Auger RB: Rock Bit DB: Diamond Bit = 4", N, B BS: Bulk Sample AS: Auger Sample PM: Pressure Meter HS: Hollow Stem Auger WB: Wash Bore Standard "N" Penetration: Blows per foot of a 140 pound hammer falling 30 inches on a 2‐inch O.D. split spoon, except where noted. WATER LEVEL MEASUREMENT SYMBOLS: WL : Water Level WS : While Sampling WCI: Wet Cave in WD : While Drilling DCI: Dry Cave in BCR: Before Casing Removal AB : After Boring ACR: After Casting Removal Water levels indicated on the boring logs are the levels measured in the borings at the time indicated. In pervious soils, the indicated levels may reflect the location of ground water. In low permeability soils, the accurate determination of ground water levels is not possible with only short term observations. DESCRIPTIVE SOIL CLASSIFICATION Soil Classification is based on the Unified Soil Classification system and the ASTM Designations D‐2488. Coarse Grained Soils have move than 50% of their dry weight retained on a #200 sieve; they are described as: boulders, cobbles, gravel or sand. Fine Grained Soils have less than 50% of their dry weight retained on a #200 sieve; they are described as : clays, if they are plastic, and silts if they are slightly plastic or non‐plastic. Major constituents may be added as modifiers and minor constituents may be added according to the relative proportions based on grain size. In addition to gradation, coarse grained soils are defined on the basis of their relative in‐ place density and fine grained soils on the basis of their consistency. Example: Lean clay with sand, trace gravel, stiff (CL); silty sand, trace gravel, medium dense (SM). CONSISTENCY OF FINE‐GRAINED SOILS Unconfined Compressive Strength, Qu, psf Consistency < 500 Very Soft 500 ‐ 1,000 Soft 1,001 ‐ 2,000 Medium 2,001 ‐ 4,000 Stiff 4,001 ‐ 8,000 Very Stiff 8,001 ‐ 16,000 Very Hard RELATIVE DENSITY OF COARSE‐GRAINED SOILS: N‐Blows/ft Relative Density 0‐3 Very Loose 4‐9 Loose 10‐29 Medium Dense 30‐49 Dense 50‐80 Very Dense 80 + Extremely Dense PHYSICAL PROPERTIES OF BEDROCK DEGREE OF WEATHERING: Slight Slight decomposition of parent material on joints. May be color change. Moderate Some decomposition and color change throughout. High Rock highly decomposed, may be extremely broken. HARDNESS AND DEGREE OF CEMENTATION: Limestone and Dolomite: Hard Difficult to scratch with knife. Moderately Can be scratched easily with knife. Hard Cannot be scratched with fingernail. Soft Can be scratched with fingernail. Shale, Siltstone and Claystone: Hard Can be scratched easily with knife, cannot be scratched with fingernail. Moderately Can be scratched with fingernail. Hard Soft Can be easily dented but not molded with fingers. Sandstone and Conglomerate: Well Capable of scratching a knife blade. Cemented Cemented Can be scratched with knife. Poorly Can be broken apart easily with fingers. Cemented Group Symbol Group Name Cu≥4 and 1<Cc≤3E GW Well-graded gravel F Cu<4 and/or 1>Cc>3E GP Poorly-graded gravel F Fines classify as ML or MH GM Silty gravel G,H Fines Classify as CL or CH GC Clayey Gravel F,G,H Cu≥6 and 1<Cc≤3E SW Well-graded sand I Cu<6 and/or 1>Cc>3E SP Poorly-graded sand I Fines classify as ML or MH SM Silty sand G,H,I Fines classify as CL or CH SC Clayey sand G,H,I inorganic PI>7 and plots on or above "A" Line CL Lean clay K,L,M PI<4 or plots below "A" Line ML Silt K,L,M organic Liquid Limit - oven dried Organic clay K,L,M,N Liquid Limit - not dried Organic silt K,L,M,O inorganic PI plots on or above "A" Line CH Fat clay K,L,M PI plots below "A" Line MH Elastic Silt K,L,M organic Liquid Limit - oven dried Organic clay K,L,M,P Liquid Limit - not dried Organic silt K,L,M,O Highly organic soils PT Peat (D30)2 D10 x D60 GW-GM well graded gravel with silt NPI≥4 and plots on or above "A" line. GW-GC well-graded gravel with clay OPI≤4 or plots below "A" line. GP-GM poorly-graded gravel with silt PPI plots on or above "A" line. GP-GC poorly-graded gravel with clay QPI plots below "A" line. SW-SM well-graded sand with silt SW-SC well-graded sand with clay SP-SM poorly graded sand with silt SP-SC poorly graded sand with clay Earth Engineering Consultants, LLC IIf soil contains >15% gravel, add "with gravel" to group name JIf Atterberg limits plots shaded area, soil is a CL- ML, Silty clay Unified Soil Classification System Soil Classification Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests Sands 50% or more coarse fraction passes No. 4 sieve Fine-Grained Soils 50% or more passes the No. 200 sieve <0.75 OL Gravels with Fines more than 12% fines Clean Sands Less than 5% fines Sands with Fines more than 12% fines Clean Gravels Less than 5% fines Gravels more than 50% of coarse fraction retained on No. 4 sieve Coarse - Grained Soils more than 50% retained on No. 200 sieve CGravels with 5 to 12% fines required dual symbols: Kif soil contains 15 to 29% plus No. 200, add "with sand" or "with gravel", whichever is predominant. <0.75 OH Primarily organic matter, dark in color, and organic odor ABased on the material passing the 3-in. (75-mm) sieve ECu=D60/D10 Cc= HIf fines are organic, add "with organic fines" to group name LIf soil contains ≥ 30% plus No. 200 predominantly sand, add "sandy" to group name. MIf soil contains ≥30% plus No. 200 predominantly gravel, add "gravelly" to group name. DSands with 5 to 12% fines require dual symbols: BIf field sample contained cobbles or boulders, or both, add "with cobbles or boulders, or both" to group name.FIf soil contains ≥15% sand, add "with sand" to GIf fines classify as CL-ML, use dual symbol GC- CM, or SC-SM. Silts and Clays Liquid Limit less than 50 Silts and Clays Liquid Limit 50 or more 0 10 20 30 40 50 60 0 10 20 30 40 50 60 70 80 90 100 110 PL A S T I C I T Y I N D E X ( P I ) LIQUID LIMIT (LL) ML OR OL MH OR OH For Classification of fine-grained soils and fine-grained fraction of coarse-grained soils. Equation of "A"-line Horizontal at PI=4 to LL=25.5 then PI-0.73 (LL-20) Equation of "U"-line Vertical at LL=16 to PI-7, then PI=0.9 (LL-8) CL-ML MW-1 MW-3 MW-2 MW-4 Figure 1: Monitoring Well Location Diagram Montava Irrigation Storm Water Pond Fort Collins, Colorado EEC Project #: 1172058 Date: December 2022 EARTH ENGINEERING CONSULTANTS, LLC ASSro[imate Locations Ior GroundZater Monitoring Wells, 20 25 Legend MW-1 MW-3 MW-2 4993 4992 MW-4 4991 (5005) (5001.5) (5003) (5002.5) [4993.5] [4993] [4992] [4991] Figure 2: Groundwater Contour Diagram Montava Irrigation Storm Water Pond Fort Collins, Colorado EEC Project #: 1172058 Date: December 2022 EARTH ENGINEERING CONSULTANTS, LLC ASSro[ Locations Ior Groundwater Monitoring Wells, 20 25 Legend ASSro[imate Ground SurIace Elevations ASSro[imate Groundwater Elevations ASSro[imate Groundwater Contours Estimated Directional Flow (5005) [4992] DATE: RIG TYPE: CME55 FOREMAN: AK AUGER TYPE: 4 1/4" HSA SPT HAMMER: AUTOMATIC SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % SWELL AGRICULTURAL / CORN STUBBLE FIELD _ _ 1 _ _ 2 _ _ 3 SANDY LEAN CLAY (CL) _ _ brown 4 moist, stiff to medium stiff _ _ SS 5 13 18.2 _ _ 6 _ _ 7 _ _ 8 _ _32 18 66.8 18.5 109.0 9 _ _ SS 10 9 20.0 36 23 62.2 _ _ *transitioning to LEAN CLAY with SAND (CL) 11 _ _ 12 _ _ 13 _ _32 18 75.4 17.0 110.0 14 _ _ SS 15 9 18.9 _ _ 16 _ _ 17 _ _ 18 SAND & GRAVEL _ _ brown / red 19 mist to wet, medium dense _ _ SS 20 9 13.6 _ _ 21 _ _ 22 BOTTOM OF BORING DEPTH 22' _ _ 23 _ _ 24 _ _2-Inch Dia. Flush Threaded- Schedule 40 PVC Slotted screen pipe 25 Silica Sand _ _ Earth Engineering Consultants, LLC Note: a 4-inch by 4-inch - 4-foot in length steel protective cover encased in concrete was positioned at the surface FINISH DATE APPROX. SURFACE ELEV WATER DEPTH PIEZOMETER / MONITORING WELL LEGEND Flush Threaded Riser Pipe Grout Bentonite Seal 10/28/2022 Checked 12-1-22 11' 5" Composite Sample MW-1 thru MW-4 - Upper 5 to 10 Feet: SANDY LEAN CLAY (CL) Standard Proctor ASTM D698 Results Optimum Moisture Content, % Maximum Dry Density, PCF Composite Sample MW-1 thru MW-4 - Upper 10 to 15-Feet: LEAN CLAY with SAND (CL) WELL DETAIL Standard Proctor ASTM D698 Results Optimum Moisture Content, % Maximum Dry Density, PCF MONTAVA DEVELOPMENT - TRACT E - DETENTION POND NOVEMBER 2022PROJECT NO: 1172058 LOG OF BORING MW-1 FORT COLLINS, COLORADO 10/28/2022 WHILE DRILLING 16' SHEET 1 OF 1 START DATE 5005 A-LIMITS SWELL DATE: RIG TYPE: CME55 FOREMAN: AK AUGER TYPE: 4 1/4" HSA SPT HAMMER: AUTOMATIC SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % SWELL AGRICULTURAL / CORN STUBBLE FIELD _ _ 1 _ _ 2 _ _ 3 LEAN CLAY with SAND (CL) _ _ brown, moist 4 soft to medium stiff _ _ SS 5 4 27.5 36 21 84.2 _ _ 6 _ _ 7 _ _ 8 _ _32 18 66.8 18.5 109.0 9 _ _ SS 10 5 20.1 _ _ *transitioning to LEAN CLAY with SAND (CL) 11 _ _ 12 _ _ SAND & GRAVEL 13 brown / red _ _32 18 75.4 17.0 110.0 moist to wet, loose to medium dense 14 _ _ SS 15 9 _ _ 16 _ _ 17 _ _ 18 _ _ 19 *with interbedded clay seams _ _ SS 20 22 9.3 _ _ 21 _ _ 22 BOTTOM OF BORING DEPTH 22' _ _ 23 _ _ 24 _ _2-Inch Dia. Flush Threaded- Schedule 40 PVC Slotted screen pipe 25 Silica Sand _ _ Earth Engineering Consultants, LLC Composite Sample MW-1 thru MW-4 - Upper 5 to 10 Feet: SANDY LEAN CLAY (CL) Standard Proctor ASTM D698 Results Optimum Moisture Content, % Maximum Dry Density, PCF Composite Sample MW-1 thru MW-4 - Upper 10 to 15-Feet: LEAN CLAY with SAND (CL) Standard Proctor ASTM D698 Results Optimum Moisture Content, % Maximum Dry Density, PCF Note: a 4-inch by 4-inch - 4-foot in length steel protective cover encased in concrete was positioned at the surface MONTAVA DEVELOPMENT - TRACT E - DETENTION POND FORT COLLINS, COLORADO PROJECT NO: 1172058 LOG OF BORING MW-2 NOVEMBER 2022 APPROX. SURFACE ELEV 5001.5 SHEET 1 OF 1 WATER DEPTH FINISH DATE 10/28/2022 Checked 12-1-22 8' 5" START DATE 10/28/2022 WHILE DRILLING 14' WELL A-LIMITS SWELL PIEZOMETER / MONITORING WELL LEGEND Flush Threaded Riser Pipe Grout Bentonite Seal DETAIL DATE: RIG TYPE: CME55 FOREMAN: AK AUGER TYPE: 4 1/4" HSA SPT HAMMER: AUTOMATIC SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % SWELL AGRICULTURAL / CORN STUBBLE FIELD _ _ 1 _ _ 2 _ _ 3 SANDY LEAN CLAY (CL) _ _ brown, rust 4 soft to medium stiff to stiff _ _ SS 5 3 31.6 _ _ 6 _ _ 7 _ _ 8 _ _32 18 66.8 18.5 109.0 9 _ _ SS 10 4 31.5 _ _ *transitioning to LEAN CLAY with SAND (CL) 11 _ _ 12 _ _ 13 _ _32 18 75.4 17.0 110.0 14 _ _ *classified as LEAN CLAY (CL) SS 15 12 26.1 36 17 94.7 _ _ 16 _ _ 17 _ _ 18 _ _ 19 _ _ SS 20 20 _ _ 21 _ _ 22 BOTTOM OF BORING DEPTH 22' _ _ 23 _ _ 24 _ _2-Inch Dia. Flush Threaded- Schedule 40 PVC Slotted screen pipe 25 Silica Sand _ _ Earth Engineering Consultants, LLC Composite Sample MW-1 thru MW-4 - Upper 5 to 10 Feet: SANDY LEAN CLAY (CL) Standard Proctor ASTM D698 Results Optimum Moisture Content, % Maximum Dry Density, PCF Composite Sample MW-1 thru MW-4 - Upper 10 to 15-Feet: LEAN CLAY with SAND (CL) Standard Proctor ASTM D698 Results Optimum Moisture Content, % Maximum Dry Density, PCF Note: a 4-inch by 4-inch - 4-foot in length steel protective cover encased in concrete was positioned at the surface MONTAVA DEVELOPMENT - TRACT E - DETENTION POND FORT COLLINS, COLORADO PROJECT NO: 1172058 LOG OF BORING MW-3 NOVEMBER 2022 APPROX. SURFACE ELEV 5000 SHEET 1 OF 1 WATER DEPTH FINISH DATE 10/28/2022 Checked 12-1-22 7' 10" START DATE 10/28/2022 WHILE DRILLING 16' WELL A-LIMITS SWELL PIEZOMETER / MONITORING WELL LEGEND Flush Threaded Riser Pipe Grout Bentonite Seal DETAIL DATE: RIG TYPE: CME55 FOREMAN: AK AUGER TYPE: 4 1/4" HSA SPT HAMMER: AUTOMATIC SOIL DESCRIPTION D N QU MC DD -200 TYPE (FEET) (BLOWS/FT) (PSF) (%) (PCF) LL PI (%) PRESSURE % SWELL AGRICULTURAL / CORN STUBBLE FIELD _ _ 1 _ _ SANDY LEAN CLAY (CL) 2 brown _ _ moist, stiff to medium stiff 3 _ _ 4 _ _ SS 5 6 17.6 _ _ 6 _ _ 7 _ _ 8 _ _32 18 66.8 18.5 109.0 9 _ _ SS 10 7 20.7 _ _ *transitioning to LEAN CLAY with SAND (CL) 11 _ _ 12 _ _ 13 _ _32 18 75.4 17.0 110.0 14 _ _ SS 15 9 21.7 _ _ 16 _ _ 17 _ _ SILTY SAND with trace GRAVEL 18 tan, gray, moist to wet _ _ medium dense 19 _ _ SS 20 18 22.3 _ _ 21 _ _ 22 BOTTOM OF BORING DEPTH 22' _ _ 23 _ _ 24 _ _2-Inch Dia. Flush Threaded- Schedule 40 PVC Slotted screen pipe 25 Silica Sand _ _ Earth Engineering Consultants, LLC Composite Sample MW-1 thru MW-4 - Upper 5 to 10 Feet: SANDY LEAN CLAY (CL) Standard Proctor ASTM D698 Results Optimum Moisture Content, % Maximum Dry Density, PCF Composite Sample MW-1 thru MW-4 - Upper 10 to 15-Feet: LEAN CLAY with SAND (CL) Standard Proctor ASTM D698 Results Optimum Moisture Content, % Maximum Dry Density, PCF Note: a 4-inch by 4-inch - 4-foot in length steel protective cover encased in concrete was positioned at the surface MONTAVA DEVELOPMENT - TRACT E - DETENTION POND FORT COLLINS, COLORADO PROJECT NO: 1172058 LOG OF BORING MW-4 NOVEMBER 2022 APPROX. SURFACE ELEV 5002.5 SHEET 1 OF 1 WATER DEPTH FINISH DATE 10/28/2022 Checked 12-1-22 11.5' START DATE 10/28/2022 WHILE DRILLING 16' WELL A-LIMITS SWELL PIEZOMETER / MONITORING WELL LEGEND Flush Threaded Riser Pipe Grout Bentonite Seal DETAIL 0% 10% 20% 30% Project: Montava Subdivision - Tract E Detention Pond Fort Collins, Colorado Project No: 1172058 Date November O-20 128.8 6.4 O-30 Proctor Designation Rock Correction (AASHTO T 224) Maximum Dry Density (pcf)Optimum Moisture Content (%) Retained 3/4" 7.2 O 125.0 O-10 126.9 8.0 130.9 5.6 90 95 100 105 110 115 120 125 130 135 140 145 0 5 10 15 20 25 30 35 Dr y D e n s i t y ( P o u n d s p e r C u b i c F o o t ) Percent Moisture Curves for 100% Saturation For Specific Gravity Equal to: 2.80 2.70 2.60 Material Designation: Sample Location: Description: Lower 10 to 15 feet of Overburden Comp. Sample - MW-1 thru MW-4 Lean Clay with Sand (CL) Atterberg Limits (ASTM D-4318) Liquid Limit: Plastic Limit: Plasticity Index: 32 18 14 Passing No. 200 Sieve (AASHTO T 11/ASTM C 117): 75.4% Standard Proctor (ASTM D-698) Maximum Dry Density: Optimum Moisture Content: 110.0 pcf 17.0% EARTH ENGINEERING CONSULTANTS, LLC SUMMARY OF LABORATORY CLASSIFICATION/MOISTURE-DENSITY RELATIONSHIP Material Designation: Lower 10 to 15 feet of Overburden Sample Location: Comp. Sample - MW-1 thru MW-4 Material Description: Lean Clay with Sand (CL) Project No: Date EARTH ENGINEERING CONSULTANTS, LLC SUMMARY OF LABORATORY CLASSIFICATION / MOISTURE-DENSITY RELATIONSHIP Sieve Size Percent Passing No. 4 100% 75.4% 99% 98%No. 40 No. 10 No. 200 Montava Subdivision - Tract E Detention Pond Fort Collins, Colorado 1172058 November Project: 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.0010.010.1110100 Pe r c e n t F i n e r b y W e i g h t Grain Size in Millimeters 2 1/2" (63 mm) 2" (50 mm) 1 1/2" (37.5 mm) 1" (25 mm) 3/4" (19 mm) 1/2" (12.5 mm) 3/8" (9.5 mm) No. 4 (4.75 mm) No. 8 (2.36 mm) No. 10 (2 mm) No. 16 (1.18 mm) No. 30 (0.6 mm) No. 40 (0.425 mm) No. 50 (0.3 mm) No. 100 (0.15 mm) No. 200 (0.075 mm) Project: Montova - Detention Pond Monitoring Wells Location: Broomfield, Colorado Project No: 1172058B Sample ID: MW1 S4 19 Sample Desc.: Well Graded Sand with Gravel (SW) Date: December 2022 EARTH ENGINEERING CONSULTANTS, LLC SUMMARY OF LABORATORY TEST RESULTS Sieve Analysis (AASHTO T 11 & T 27 / ASTM C 117 & C 136) 100 Sieve Size Percent Passing 100 100 100 100 100 98 79 51 8 4.8 45 30 19 14 11 1.18 0.26 Fine 12.28 1.72 D30 D10 Cu CC December 2022 12.50 3.15 2.32 Montova - Detention Pond Monitoring Wells Broomfield, Colorado 1172058B MW1 S4 19 Well Graded Sand with Gravel (SW) D100 D60 D50 EARTH ENGINEERING CONSULTANTS, LLC Summary of Washed Sieve Analysis Tests (ASTM C117 & C136) Date: Project: Location: Project No: Sample ID: Sample Desc.: Cobble Silt or ClayGravel Coarse Fine Sand Coarse Medium 6" 5" 4" 3" 2.5" 2" 1.5" 1" 3/4" 1/2" 3/8" No. 4 No. 8 No. 10 No. 16 No. 30 No. 40 No. 50 No. 100 No. 200 0 10 20 30 40 50 60 70 80 90 100 0.010.11101001000 Fi n e r b y W e i g h t ( % ) Grain Size (mm) Standard Sieve Size Liquid Limit: 32 Plasticity Index: 18 % Passing #200: 66.8% Initial Moisture: 18.5% Dry Density: 104.0 pcf 95.4% Project Name: Montava Development - Tract E - Detention Pond Location: Fort Collins, Colorado Project Number: Date: Percent Compaction: November 2022 1172058 EARTH ENGINEERING CONSULTANTS, LLC Material Description: Permeability Test Results (ASTM D5856) Montava Development - Tract E - Detention Pond - Fort Collins, Colorado brown Sandy Lean Clay (CL) Coefficient of Permeability, k = 6.6 x 10 -8 cm/s Sample: Composite Sample - Upper 5-Feet of Cohesive Soils MW-1 thru MW-4 0.0E+00 1.0E-08 2.0E-08 3.0E-08 4.0E-08 5.0E-08 6.0E-08 7.0E-08 8.0E-08 9.0E-08 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Co e f f i c i e n t o f P e r m e a b i l i t y , k ( c m / s e c ) Elapsed Time (min)