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HomeMy WebLinkAboutGeotechnical Investigation and OWTS Design 08.25.2020Huddleston -Berry Engineering & Testing, LLC Mountain Ridge Construction Services, LLC 109 Creekside Drive Rifle, Colorado 81650 Attention: Mr. Jerry Caves Subject: Geotechnical Investigation and OWTS Design 2693 County Road 301 Parachute, Colorado Dear Mr. Caves, 2789 Riverside Parkway Grand Junction, Colorado 81501 Phone: 970-255-8005 Info@huddlestonberry.com August 25, 2020 Project#01273-0018 This letter presents the results of a geotechnical investigation conducted by Huddleston -Berry Engineering & Testing, LLC (HBET) at 2693 County Road 301 near Parachute, Colorado. The site location is shown on Figure 1. The proposed construction is anticipated to consist of a new single family residence. The scope of our investigation included evaluating the subsurface conditions at the site to aid in developing foundation recommendations for the proposed construction and to permit design of the Onsite Wastewater Treatment System (OWTS). Site Conditions At the time of the investigation, the site was open. The general site grade was down to the north. Site topography is shown on Figure 2. Battlement Creek ran through the southwestern portion of the site. Vegetation consisted primarily of grasses, weeds, and brush. The site was bordered to the north by open land, to the south by County Road 301, and to the west and east by existing rural residential properties. Subsurface Investigation The subsurface investigation included three test pits as shown on Figure 2. The test pits were excavated to depths of between 4.0 and 10.0 feet below the existing ground surface. Typed test pit logs are included in Appendix A. As indicated on the logs, the subsurface conditions at the site were slightly variable. However, the test pits generally encountered 1.5 feet of topsoil at the ground surface. In TP -1 and TP -2, the topsoil was underlain by brown, moist, stiff lean clay (clay loam) with trace gravel to depths of between 3.0 and 4.0 feet. Below the clay in TP -1 and TP -2, and below the topsoil in TP -3, white, moist, dense sandy silt (silt loam) with cobbles and boulders extended to the bottoms of the excavations. Groundwater was not encountered in the subsurface at the time of the investigation. 2693 County Road 301 #01273-0018 08/25/20 Huddleston -Berry Engineering & Testing, LLC Laboratory Testing Laboratory testing was conducted on samples of the native soils encountered in the test pits. The testing included grain size analysis, Atterberg limits determination, natural moisture content determination, and maximum dry density and optimum moisture content (Proctor) determination. The laboratory testing results are included in Appendix B. The laboratory testing results indicate that the native clay soils are slightly plastic. In general, based upon our experience with similar soil in the vicinity of the subject site, the native clay soils are anticipated to be slightly collapsible. The fines in the cobble and boulder soils were indicated to be moderately plastic. Based upon the Atterberg limits of the material, the fine grained portion of these soils may be slightly expansive. Foundation Recommendations Based upon the results of the subsurface investigation and nature of the proposed construction, shallow foundations are recommended. Spread footings and monolithic (turndown) structural slabs are both appropriate foundation alternatives. However, as discussed previously, the shallow native soils are anticipated to be slightly collapsible and the deeper soils may be slightly expansive. Therefore, in order to provide a stable bearing stratum and limit the potential for excessive differential movements, it is recommended that the foundations be constructed above structural fill extending to the dense cobble and boulder soils. However, it is recommended that the foundations be constructed above a minimum of 24 -inches of structural fill. The native clay soils, exclusive of topsoil, are suitable for reuse as structural fill. The native cobble and boulder soils are not suitable for reuse as structural fill. Imported structural fill should consist of a granular, non -expansive, non -free draining material approved by HBET. For spread footing foundations, the footing areas may be trenched. However, for monolithic slab foundations, the structural fill should extend across the entire building pad area to a depth of 24 - inches below the turndown edges. Structural fill should extend laterally beyond the edges of the foundation a distance equal to the thickness of structural fill for both foundation types. Prior to placement of structural fill, it is recommended that the bottom of the foundation excavation be scarified to a depth of 6 to 9 inches, moisture conditioned, and proofrolled to HBET's satisfaction. Structural fill should be moisture conditioned, placed in maximum 8 -inch loose lifts, and compacted to a minimum of 95% of the standard Proctor maximum dry density for fine grained soils and modified Proctor maximum dry density for coarse grained soils, within ± 2% of the optimum moisture content as determined in accordance with ASTM D698 and D1557, respectively. Structural fill should be extended to within 0.1 -feet of the bottom of the foundation. No more than 0.1 -feet of gravel should be placed below the footings or turndown edge as a leveling course. C:\HBET\Project Files \2020\01273-0018 2693 CR 301 \200 - Geo \01273-0018 LR082420 doc 2 2693 County Road 301 ■ ■ Huddleston -Berry #01273 0018 � � Ennincc,ina&Tesring,LLC 08/25/20 For structural fill consisting of the native clay soils or imported granular materials and foundation building pad preparation as recommended, a maximum allowable bearing capacity of 2,000 psf may be used. In addition, a modulus of subgrade reaction of 150 pci may be used for structural fill consisting of the native clay soils and a modulus of 200 pci may be used for structural fill consisting of approved imported materials. Foundations subject to frost should be at least 36 -inches below the finished grade. Any stemwalls or retaining walls should be designed to resist lateral earth pressures. For backfill consisting of the native clay soils or imported granular, non -free draining, non -expansive material, we recommend that the walls be designed for an active equivalent fluid unit weight of 50 pcf in areas where no surcharge loads are present. An at -rest equivalent fluid unit weight of 70 pcf is recommended for braced walls. Lateral earth pressures should be increased as necessary to reflect any surcharge loading behind the walls. Water soluble sulfates are common to the soils in Western Colorado. Therefore, at a minimum, Type I-II sulfate resistant cement is recommended for construction at this site. Non -Structural Floor Slab and Exterior Flatwork Recommendations In order to reduce the potential for excessive differential movements, it is recommended that non-structural floating floor slabs be constructed above a minimum of 18 -inches of structural fill with subgrade preparation, structural fill materials, and fill placement be in accordance with the Foundation Recommendations section of this report. It is recommended that exterior flatwork be constructed above a minimum of 12 -inches of structural fill. Drainage Recommendations Grading and drainage are critical for the long-term performance of the structure and grading around the structure should be designed to carry precipitation and runoff away from the structure. It is recommended that the finished ground surface drop at least twelve inches within the first ten feet away from the structure. It is also recommended that landscaping within five feet of the structure include primarily desert plants with low water requirements. In addition, it is recommended that irrigation, including drip lines, within ten feet of foundations be minimized. HBET recommends that downspout extensions be used which discharge a minimum of 15 feet from the structure or beyond the backfill zone, whichever is greater. However, if subsurface downspout drains are utilized, they should be carefully constructed of solid -wall PVC and should daylight a minimum of 15 feet from the structure. In addition, an impermeable membrane is recommended below subsurface downspout drain lines. Dry wells should not be used. As discussed previously, groundwater was not encountered at the time of the investigation. However, a perimeter foundation drain is recommended to limit the potential for surface moisture to impact the structure. In general, the perimeter foundation drain should consist of prefabricated drain materials or perforated pipe and gravel systems with the flowline of the drain at the bottom of the foundation (at the highest point). The perimeter drain should slope at a minimum of 1% to daylight or to a sump with pump. An impermeable membrane is also recommended at the base of the drain to limit the potential for moisture to infiltrate into the subsurface below the foundations. C:\HBET\Project Files\2020\01273-0018 2693 CR 301\200 - Geo\01273-0018 LR082420 doc 3 2693 County Road 301 #01273-0018 08/25/20 Huddleston -Berry Engineering& Tc,.rin6• LLC Onsite Wastewater Treatment System In order to evaluate the site soils for onsite wastewater treatment, percolation testing was conducted in Test Pits TP -1 and TP -2 in accordance with Garfield County regulations. The percolation rate in the native soils ranged from 20 to 60 minutes -per -inch. The percolation testing data are included in Appendix C. In accordance with Garfield County regulations, a percolation rate of between 5 to 60 minutes - per -inch is required for soils to be deemed suitable for onsite wastewater treatment. Therefore, based upon the results of the percolation testing and visual/tactile evaluation, HBET believes that the native soils are suitable for onsite wastewater treatment. In addition to the percolation rate of the subsurface materials, the seasonal high groundwater elevation is an important factor in determining the suitability of the site for Onsite Wastewater Treatment Systems. For OWTS suitability, the seasonal high groundwater elevation should be at least four feet below the bottom of the proposed absorption bed. As discussed previously, groundwater was not encountered at the time of the investigation. In general, based upon the results of the subsurface investigations, HBET believes that the seasonal high groundwater level is deeper than 8.0 feet below the existing grade at this site. Seepage Bed Design The design of the absorption system generally follows the requirements of the Garfield County On -Site Wastewater Treatment System Regulations, adopted June 2018. The proposed construction at the site is anticipated to include a three bedroom home. Based upon the soil percolation rate, a conservative Long Term Acceptance Rate (LTAR) of 0.35 will be utilized for the absorption field design. Infiltrator Systems Quick4 Standard Chambers are proposed in lieu of a conventional gravel absorption bed. The daily flow of the sewage disposal system is calculated below and a plan and profile of the absorption bed are shown on Figure 3. Average Daily Flow = (3 bedrooms)(2 persons/bedroom)(75 GPD/person) = 450 GPD Soil Treatment Area = (450 GPD / 0.35) = 1,286 Square Feet Adjusted Soil Treatment Area = (1,286 SF)(1.2)(0.7) = 1,080 Square Feet # of Quick4 Chambers = (1,080 / 12) = 90; Use 92 Chambers System Installation The installation of the septic tank, plumbing lines, Infiltrators, etc. should be completed in accordance with the Garfield County On -Site Wastewater Treatment System Regulations and Infiltrator Systems, Inc. specifications. In addition, the following construction procedures are recommended: C'\HRFT\Project Files \2020\01273-0018 2693 CR 301 \200 - Geo \01273-0018 LR082420 doc 4 2693 County Road 301 #01273-0018 08/25/20 Huddleston -Berry EIlginccring& Toting, LLC • The septic tank and distribution box should be placed level over native soils that have been scarified to a depth of 8 to 12 inches, moisture conditioned, and recompacted to a minimum of 95% of the standard Proctor maximum dry density, within ±2% of optimum moisture content. However, up to 3 -inches of washed rock or pipe bedding passing the 1 -inch sieve may be used as a leveling course under the septic tank and/or distribution box. • The bottoms of trenches and backfill around the septic tank and distribution box which will support sewer or effluent lines should be compacted to at least 90 percent of the standard Proctor maximum dry density, within ±2% of optimum moisture content. Pipe bedding should have a maximum particle size of 1 -inch. • Vehicular or heavy equipment traffic and placement of structures should not encroach within 10 feet of the septic tank or distribution box. Inspection Schedule Huddleston -Berry Engineering & Testing LLC should be retained to monitor the construction of the OWTS. The following schedule of observation and/or testing should be followed: • Observe the absorption bed excavation prior to placement of Infiltrator chambers. • Observe placement of the septic tank, distribution box, and all connecting sewer and effluent lines prior to backfill. Verify proper fall between inverts. • Observe and verify installation of the absorption bed prior to placement of cover and backfill. In conformance with Garfield County regulations, HBET will be required to provide Garfield County with documentation certifying that the OWTS was placed in conformance to the plan and profile and Garfield County regulations. General Notes The recommendations included above are based upon the results of the subsurface investigation and on our local experience. These conclusions and recommendations are valid only for the proposed construction. As discussed previously, the subsurface conditions encountered in the test pits were slightly variable. However, the precise nature and extent of any subsurface variability may not become evident until construction. As a result, it is recommended that HBET provide construction materials testing and engineering oversight during the entire construction process. 11 is important to note that the recommendations herein are intended to reduce the risk of structural movement and/or damage, to varying degrees, associated with volume change of the native soils. However, HBET cannot predict long-term changes in subsurface moisture conditions and/or the precise magnitude or extent of volume change in the native soils. Where significant increases in subsurface moisture occur due to poor grading, unproper stormwater management, utility line failure, excess irrigation, or other cause, either during construction or the result of actions of the property owner, several inches of movement are possible. In addition, any failure to comply with the recommendations in this report releases Huddleston - Berry Engineering & Testing, LLC of any liability with regard to the structure performance. C:\HBET\Project Files \2020\01273-0018 2693 CR 301 \200 - Geo \01273-0018 LR082420 doc 5 2693 County Road 301 #01273-0018 08/25/20 We are pleased to be of service to your project. Please contact us if you have any questions or comments regarding the contents of this report. Huddleston -Berry Enniveering & Testing, LLC Respectfully Submitted: Huddleston -Berry Engineering and Testing, LLC Michael A. Berry, P.E. Vice President of Engineering C:\IHBET\Project Files\2020\01273-0018 2693 CR 301\200 - Geo\01273-0018 LR082420.doc 6 FIGURES Ci 2020 Google FIGURE 1 Site Location Map 5000 ft APPENDIX A Typed Test Pit Logs GEOTECH BH COLUMNS 01273-0018 2693 COUNTY ROAD 301 GPJ GINT US LAB GDT 8/14/20 -4 cn ru s o DEPTH H o (ft) DATE STARTED 7/23/20 COMPLETED 7/23/20 GROUND ELEVATION TEST PIT SIZE EXCAVATION CONTRACTOR Client GROUND WATER LEVELS: EXCAVATION METHOD Trackh/Backhoe AT TIME OF EXCAVATION dry LOGGED BY CM CHECKED BY MAB AT END OF EXCAVATION dry NOTES 39 27.501' -107 59.480' AFTER EXCAVATION --- �v I-luddleston-Berry Engineering & Testing, LLC TEST PIT NUMBER TP -1 7 :2789 Riverside Parkway PAGE 1 OF 1 m q Grand Junction. CO 81501 970.255-8005 CLIENT Mountain Ridge Construction Services, LLC PROJECT NAME 2693 County Road 301 PROJECT NUMBER 01273-0018 PROJECT LOCATION Parachute, CO ' ! w Sandy SILT with Cobbles and Boulders (ML), white, moist, dense .• i •` *** Lab Classified GB2 • IV, •• 1 1 1•. ■ ■, • 1 • .1 •of X11 \ti , . _ • ^ . . •• • :OG GRAPHIC Bottom of test pit at 8.0 feet. Lean CLAY with trace Gravel (CL), brown. moist, stiff "*" Lab Classified GB1 Lean CLAY with Gravel and Organics (TOPSOIL) MATERIAL DESCRIPTION CA C4-4 co , W SAMPLE TYPE NUMBER RECOVERY % (RQD) BLOW COUNTS (N VALUE) POCKET PEN. (tsf) DRY UNIT WT. (Pcf) 61 a _ MOISTURE CONTENT (%) CO m LIQUID LIMIT D 1 N.) c N o PLASTIC LIMIT r —i a) cnm `"' PLASTICITY INDEX al 0) o co FINES CONTENT (%) GEOTECH BH COLUMNS 01273-0018 2693 COUNTY ROAD 301 GPJ GINT US LAB. GDT 8/14120 ;aa; 0'b;e lid lee; ;o woo rnlk I - v DEPTH (ft) (D D7 7 W 0- m .•< C) 0 0- 6 (D (n D7 0. CO 0 C_ 0 (D N 3 (D 3 0 N Lean CLAY with trace Gravel (cl), brown, moist, stiff Lean CLAY with Gravel and Organics (TOPSOIL) GRAPHIC • LOG NOIld1aOS3a 1Via31Wi SAMPLE TYPE NUMBER RECOVERY % (RQD) BLOW COUNTS (N VALUE) POCKET PEN. (tsf) DRY UNIT WT. (pcf) MOISTURE CONTENT (%) LIQUID LIMIT PLASTIC LIMIT PLASTICITY INDEX FINES CONTENT (%) Z 0 m co ,£917'69 LO1•- ,1 19'LZ 6£ NOIIVAV3X3 a313V NO la a3JJOl 8VW A9 03)103HO NOIIVAVOX3 AO DNB IV EXCAVATION METHOD Trackh/Backhoe NOIIVAVOX3 AO 31NI11V EXCAVATION CONTRACTOR Client :S13A31 a31VM (MOND OZ/£Z/L a311tIVIS 31VO a3131dINOO N W O NOIIVA313 aNfOaO 3ZIS lId 1531 NOIIV3O1 lO3fOad 00 'a;n140eied P1a ufe;unow 011 'saoinlas uol;ona;suo3 a PROJECT NAME 2693 County Road 301 .0 0 N .. O�CF 00 V n 0 cro 0'xa ODS D6 +ice s 66 O6Q r m cn z c -0 03 Dm Fri 73 O TI GEOTECH BH COLUMNS 01273-0018 2693 COUNTY ROAD 301 GPJ GINT US LAB.GDT 8/14/20 1 1 1 1 o o I I I ( -r in f 1 i I w 0 1 7 II to in o DEPTH o (ft) '4 Iluddleston-Berry Engineering & Testing, LLC TEST PIT NUMBER TP -3 Hi, 2789 Riverside Parkway PAGE 1 OF 1 g Grand Junction, CO 81501 970-255-8005 CLIENT Mountain Ridge Construction Services, LLC PROJECT NAME 2693 County Road 301 PROJECT NUMBER 01273-0018 PROJECT LOCATION Parachute, CO w '' ' 'r ' ' '' • 'w ' '� • .■►.'/►-'�►-'/►.'■► '■►an'! �! ►a'1r-'11►..'/►..'/►'►.. :Pr' '�`.rc- .1:' lam ..' ;.: APPENDIX B Laboratory Testing Results 0 co 0 0 q 1- z 0 M 0 0 [Y Z 0 0 0 U N s O N O W N y z_ C7 `" ', , Huddleston -Berry Engineering & Testing, LLC GRAIN SIZE DISTRIBUTION 1 \2789 Riverside Parkway Mg Grand Junction, CO 81501 o' 970-255-8005 CLIENT Mountain Ridge Construction Services, LLC PROJECT NAME 2693 County Road 301 PROJECT NUMBER 01273-0018 PROJECT LOCATION Parachute, CO U.S- SIEVE OPENING 6 4 3 IN NCHES 1.5 1 3/4 1/210 I U.S. SIEVE NUMBERS I HYDROMETER 3 4 6 810 14 16 20 30 40 50 60 100 140 200 100 1\ I 11` 1�F -� jr1-14_,L.04_,1 1 1 -1\1 95 li�i 90 `__ 65 BO �- 75 \ 70 — - 65 o 60 w >- 55 m rr U-1 50 z II 1— 45 z w 40 w a 35 30 25 20 ` 15 10 5 0 100 10 1 GRAIN SIZE 0 1 IN MILLIMETERS 0.01 0.001 GRAVEL SAND — SILT OR CLAY COBBLES coarse fine coarse medium r fine Specimen Identification Classification LL PL PI Cc Cu • TP -1, GB1 7/2020 LEAN CLAY(CL) 29 20 9 x TP -1, GB2 7/2020 SANDY SILT(ML) 38 25 13 Specimen Identification D100 D60 D30 D10 %Gravel %Sand %Silt %Clay • TP -1, GB1 7/2020 9.5 0.8 10.5 88.7 X TP -1, GB2 7/2020 50 0.105 13.0 31.3 55.7 ATTERBERG LIMITS 01273-0018 2693 COUNTY ROAD 301 GPJ GINT US LAB GDT 8/14/20 CLIENT ,s' Mountain Huddleston -Berry Engineering & Testing, LLC ATTERBERG LIMITS' RESULTS 2789 Riverside Parkway Grand Junction, CO 81501 970-255-8005 Ridge Construction Services. LLC PROJECT NAME 2693 County Road 301 PROJECT NUMBER 01273-0018 PROJECT LOCATION Parachute. CO CLI CI1 50 P L A s 40 T I C T 30 Y I N 20 D E X 10 • CL -ML 7 ML MH 0 - - 0 20 40 60 80 100 LIQUID LIMIT Specimen Identification LL PL PI #200 Classification • TP -1, GB1 7/2020 29 20 9 89 LEAN CLAY(CL) m TP -1, GB2 7/2020 38 25 13 56 SANDY SILT(ML) O csi 0 a 3 1- z z_ ci L9 0 0 0 4X CO 2 0 HES inn,2789 r. ss CLIENT PROJECT C Huddleston -Berry Engineering & Testing, LLC Riverside Parkway Grand Junction, CO 81501 970-255-8005 Mountain Ridge Construction Services. LLC PROJECT _ PROJECT Material: of Material Dry Water MOISTURE NAME LOCATION TEST Density -DENSITY 2693 County Parachute, RELATIONSHIP Road 301 NUMBER 01273-0018 CO U 0. F) } 0 0 150 145 140 135 130 125 120 115 110\\\ 105 100 95 900 \ \ Sample Sample Source Description Test Method: Maximum Optimum \ Date: No.: of Content GRADATION #200 7/23/2020 \ GB1 TP -1 LEAN CLAY(CL) \ \ \ ASTM D698A RESULTS ATTERBERG RESULTS Curves for 108.0 PCF % (% LIMITS 100% Gravity 2.80 2.70 2.60 PASSING) PI 3/4" 1 ` \ \ \ \ 15.5 #4 99 \ \ \ 89 100 \ \ LL PL \ \ �\ \\ 29 20 Specific of 9 Saturation Equal to: \� \ \N.\,, \ N S \ N\\ 5 10 15 20 25 30 WATER CONTENT, % APPENDIX C Percolation Testing Results PERCOLATION TESTING Project Name: 2693 CR 301 Testing Conducted By: Pit Dimensions: Length Water Level Depth: SOIL PROFILE C. Miller Location: Parachute, CO Death Description Project No. 01273-0011 8 Test Pit No. TP -1 Date: 7/23/2020 Supervising Engineer: M. Berry ; Width Not Encountered X • Depth 8.0 ft Remarks 0-1.5 ft Clay Loam with Gravel and Organics (TOPSOIL) Change (in.) 1.5-4 ft Clay Loam with trace Gravel (CL), brown, moist, stiff 4-8 ft Silt Loam with Cobbles and Boulders (ML), white, moist, dense 0.125 10 2.875 0.25 15 3 0.125 Test Number: 1 Top of Hole Depth: 4 ft Diameter of Hole: 10 -in. Depth of Hole: 15 -in. Time (min.) Water Depth (in.) Change (in.) 0 2.5 5 2.625 0.125 10 2.875 0.25 15 3 0.125 20 3.125 , 0.125 25 3.25 0.125 30 3.5 0.25 35 3.75 0.25 40 4 0.25 45 4.125 0.125 50 4.25 0.125 55 4.375 0.125 60 4.5 0.125 Rate (min/in): j 30 1 Average Percolation Rate (min/in): Test Number: 2 Top of Hole Depth: 5.5 ft Diameter of Hole: 12 -in. Depth of Hole: 16 -in. Time (min.) Water Depth (in.) Change (in.) 0 0.75 5 0.875 0.125 10 1 0.125 15 1.125 0.125 20 1.125 0 25 1.25 0.125 30 1.375 0.125 35 1.375 0 r 40 1.5 0.125 45 1.5 0 50 1.625 0.125 55 1.625 0 60 1.75 0.125 Rate (min/in):! 60 L Test Number: Top of Hole Depth: Diameter of Hole: Depth of Hole: Time (min.) Water Depth (in.) Change (in.) Rate (min/in): PERCOLATION TESTING Project Name: 2693 CR 301 Location: Parachute, CO Testing Conducted By: Pit Dimensions: Length Water Level Depth: SOIL PROFILE C. Miller Depth Description Project No. 01273-0018 Test Pit No. TP -2 Date: 7/23/2020 Supervising Engineer: M. Berry ; Width Not Encountered X ; Depth 4.0 ft Remarks 0-1.5 ft Clay Loam with Gravel and Organics (TOPSOIL) Change (in.) 1.5-3 ft Clay Loam with trace Gravel (CL), brown, moist, stiff 3-4 ft Silt Loam with Cobbles and Boulders (ml), white, moist, dense 0.25 10 1 0.25 15 1.25 0.25 Test Number: 1 Top of Hole Depth: 4 ft Diameter of Hole: 11 -in. Depth of Hole: 14 -in. Time (min.) Water Depth (in.) Change (in.) 0 0.5 5 0.75 0.25 10 1 0.25 15 1.25 0.25 20 1.5 0.25 25 1.75 0.25 30 2 0.25 35 2.25 0.25 40 2.5 0.25 45 2.75 0.25 50 3 0.25 55 3.25 0.25 60 3.5 0.25 Rate (min/in):20 Average Percolation Rate (min/in) Test Number: Top of Hole Depth: Diameter of Hole: Depth of Hole Time (min.) Water Depth (in.) Change (in.) Rate (min/in): Test Number: Top of Hole Depth Diameter of Hole: Depth of Hole: Time (min.) Water Depth (in.) Change (in.) Rate (min/in):