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Home My WebLink AboutSW4200703_Hawbridge School_SHWT_20200708 Tai and Associates, PLLC P.O. Box 90067 Raleigh, NC 27675 (919) 782-9525 www.taiandassociates.com March 20, 2019 Ms. Mya Ciccotti Geiss Interim Executive Director The Hawbridge School 1735 Saxapahaw-Bethlehem Church Road Saxapahaw, North Carolina 27340 Re: SHWT Determination The Hawbridge School Saxapahaw, North Carolina Tai Job No. 18-196-1 Dear Ms. Ciccotti Geiss: As requested, we are providing the following information regarding seasonal high water table (SHWT) for the proposed stormwater BMP locations. Proposed Stormwater BMP: We understand that four (4) stormwater BMP locations are being assessed, in the general area of soil borings S-1, S-2, S-3, and S-4 (see attached Boring Location Plan). The following information represents our understanding of the proposed elevations: Location Existing Grade Target Investigation Depth (Elevation) S-1 468.0 10.0’ (458.0) S-2 468.0 10.0’ (458.0) S-3 467.0 10.0’ (457.0) S-4 465.0 10.0’ (455.0) Field Exploration: The field exploration program consisted of the drilling of four (4) soil borings: S-1, S-2, S-3 and S-4. The soil borings were advanced to a maximum depth of 10.0 feet below existing ground surface at each location. The drilling was performed utilizing a CME 550 drill rig using 2-1/4” inside diameter hollow stem augers to advance the boring. Standard Penetration Tests (ASTM D-1586) were performed at 2.5-foot intervals. The approximate locations and logs of the soil borings are shown on the attached “Boring Location Plan” and “Boring Logs”. Soil Conditions: Topsoil and natural, residual soils were encountered at the soil boring locations. Soil conditions encountered at boring S-1 consisted of 2.0 inches of topsoil over firm to very stiff, silty clay and clayey silt to a depth of 10.0 below ground surface. At boring S-2, we encountered 1.0 inch of topsoil over 10.0 feet of firm to stiff, silty clay. At boring S-3, we encountered 10.0 feet of stiff to very Ms. Mya Ciccotti Geiss Re: Tai Job No. 18-196-1 March 20, 2019 Page 2 stiff, silty clay and clayey, sandy silt. At boring S-4, we encountered 10.0 feet of firm to stiff, silt and silty clay. No alluvium was encountered. We did not observe groundwater or soil morphology that would indicated the presence of a significant saturated soil zone over portions of the year at the soil boring locations. NRCS: According to the NRCS Soil Survey Map, the test locations belong to the Cullen Clay Loam (CnD2 and CnE2) soil unit. Depth to groundwater is reported to be more than 80 inches. SHWT Evaluation: There may currently exist an insignificant SHWT within the top few feet of the site. However, this does not represent a significant aquifer, and it will be disrupted upon grading of the site. Upon completion of excavation at the proposed BMP locations, we anticipate the excavations will be dry. This study was intended to investigate for the presence of a SHWT within the above-referenced target investigation depth. The SHWT would be evidenced by the presence of groundwater or soil morphology that would indicate a significant saturated soil zone over portions of the year. Based on the results of this study, it appears the SHWT is lower than the target investigation elevation. Ksat: The NRCS Soil Survey Map reports an estimated Ksat of 0.57 to 1.98 in/hr. However, based on our soil samples obtained on the site, and based on published infiltration test data, our best estimate of infiltration rates would be approximately 0.1 to 0.001 in/hr, making the site a poor candidate for infiltration of surface water. If you have any questions, please contact us at your convenience. Very Truly Yours, Tai and Associates, PLLC Firm License No.: P-0370 Matthew T. Ryan, PE Attachments (6p) TAI JOB NO.: 18-196-1 MARCH, 2019 S-1 S-2 S-3 BORING LOCATION PLAN HAWBRIDGE SCHOOL SAXAPAHAW, NORTH CAROLINA S-4 Symbols and Nomenclature Penetration Resistance Results - Sands Undisturbed Sample (UD) ●25 Standard penetration resistance (ASTM D-1586) , with SPT N-Value 50/0.2 Number of blows (50) to drive the spoon a measured distance (0.2 feet) AX,BX,NX Core barrel sizes for rock cores 65% Percentage of rock core recovered RQD Rock quality designation - % of core 4 or more inches long ▼ Water table at least 24 hours after drilling ∇ Water table one hour or less after drilling ∆ Loss of drilling water A Atterberg Limits test performed C Consolidation test performed GS Grain size test performed T Triaxial shear test performed P Proctor compaction test performed M=18 Natural moisture content (percent) Number of blows, N Relative Density 0-4 very loose 5-10 loose 11-20 firm 21-30 very firm 31-50 dense over 50 very dense or weathered rock 50/0.2' Partially weathered rock Penetration Resistance Results - Silts and Clays Number of blows, N Approx. consistency 0-1 very soft 2-4 soft 5-8 firm 9-15 stiff 16-30 very stiff 31-50 hard over 50 very hard or weathered rock 50/0.2' Partially weathered rock DRILLING PROCEDURES Soil sampling and standard penetration testing performed in accordance with ASTM D-1586. The standard penetration resistance is the number of blows of a 140 pound hammer falling 30 inches to drive a 2 inch O.D., 1.4 inch I.D. split spoon sampler one foot. Core drilling performed in accordance with ASTM D-2113. Undisturbed sampling (shelby tube) performed in accordance with ASTM D-1587. Soil classification performed in accordance with ASTM D2487/D-2488. ABBREVIATIONS SOIL MOISTURE - CORRELATION OF TERMS AR - AUGER REFUSAL BOF – BOTTOM OF FOOTING BT - BORING TERMINATED DCP Nc – DYNAMIC CONE PENT. TEST e - VOID RATIO FFE – FINISHED FLOOR ELEVATION HI. – HIGHLY HP – HIGH PLASTICITY INV – INVERT LP – LOW PLASTICITY MP – MEDIUM PLASTICITY MED. - MEDIUM MICA. - MICACEOUS MOD. – MODERATELY N – STANDARD PENETRATION TEST NP. - NON PLASTIC PFG – PROPOSED FINAL GRADE TCR - TRICONE REFUSAL TOF – TOP OF FOOTING w - MOISTURE CONTENT V – VERY γ - UNIT WEIGHT γd - DRY UNIT WEIGHT SAMPLE ABBREVIATIONS S - BULK SS - SPLIT SPOON ST - SHELBY TUBE RS - ROCK RT - RECOMP. TRIAXIAL CBR - CAILFORNIA BEARING RATIO FIELD MOISTURE DESCRIPTION SATURATED - (SAT.) WET - (W) MOIST - (M) DRY - (D) GUIDE-FIELD MOISTURE DESC. USUALLY LIQUID, VERY WET, USUALLY FROM THE BELOW GROUND WATER TABLE SEMISOLID: REQUIRES DRYING TO ATTAIN OPTIMUM MOISTURE SOLID: AT OR NEAR OPTIMUM MOISTURE REQUIRES ADDITIONAL WATER TO ATTAIN OPTIMUM MOISTURE EQUIPMENT USED ON SUBJECT PROJECT DRILL UNITS □ CMESS □ CMESS ATV □ __________ □ __________ CORE SIZE □-B_________ □-N_________ □-H_________ ADVANCING TOOLS: □ CLAY BITS □ 6"CONT. FLIGHT AUGER □ 8" HOLLOW AUGER □ CASING □ W/ADVANCER □ TRICONE___STEEL TEETH □ TRICONE___TUNG.CARB. □ CORE BIT □ ______________________ PERCENTAGE OF MATERIAL ORGANIC MATERIAL GRANULAR SOILS SILT-CLAY SOILS TRACE OF ORGANIC MATTER 2-3% 3-5% LITTLE ORGANIC MATTER 3-5% 5-12% MODERATELY ORGANIC 5-10% 12-20% HIGHLY ORGANIC >10% >20% OTHER MATERIAL TRACE 1-10% LITTLE 10-20% SOME 20-35 % HIGHLY 35% AND ABOVE PLASTICITY HAMMER TYPE: PLASTICITY INDEX (PI) NONPLASTIC 0-5 LOW PLASTICITY 6-15 MEDIUM PLASTICITY 16-25 HIGH PLASTICITY 26 OR MORE DRY STRENGTH VERY LOW SLIGHT MEDIUM HIGH □ AUTOMATIC □ CAT HEAD HAND TOOLS: □ POST HOLE DIGGER □ ______________________ □ HAND AUGER □ ______________________ □ SOUNDING ROD □ ______________________ □ VANE SHEAR TEST Tai and Associates, PLLC P.O. Box 90067 Raleigh, NC 27675 (919) 782-9525 www.taiandassociates.com 0.2 8.0 10.0 TOPSOIL (2'') Red, brown, moist, stiff to very stiff, silty CLAY Gray, tan, orange, moist, firm, gravelly, slightly clayey SILT Boring Terminated at 10.0 Feet 9 14 16 8 468 463 458 453 448 443 438 433 428 423 TAI JOB NO. 18-196-1 B-12 FEBRUARY 14, 2019 THE HAWBRIDGE SCHOOL SAXAPAHAW, NORTH CAROLINA THE HAWBRIDGE SCHOOL PAGE 1 OF 1 DRY CAVED DEPTH DESCRIPTION GW ELEV 10 50 90 TAI and ASSOCIATES, PLLC PO BOX 90067 RALEIGH, NC 27675 919-782-9525 PROJECT: LOCATION: CLIENT: BORING NO. DATE: N-VALUE (ASTM D-1586) S-1 0.1 10.0 TOPSOIL (1'') Red, brown, orange, tan, moist, firm to stiff, silty CLAY Boring Terminated at 10.0 Feet 8 12 9 11 468 463 458 453 448 443 438 433 428 423 TAI JOB NO. 18-196-1 B-13 FEBRUARY 14, 2019 THE HAWBRIDGE SCHOOL SAXAPAHAW, NORTH CAROLINA THE HAWBRIDGE SCHOOL PAGE 1 OF 1 DRY CAVED DEPTH DESCRIPTION GW ELEV 10 50 90 TAI and ASSOCIATES, PLLC PO BOX 90067 RALEIGH, NC 27675 919-782-9525 PROJECT: LOCATION: CLIENT: BORING NO. DATE: N-VALUE (ASTM D-1586) S-2 3.0 10.0 Red, brown, moist, stiff, silty CLAY Orange, brown, black, dry to moist, stiff to very stiff, clayey, fine sandy SILT Boring Terminated at 10.0 Feet 14 13 15 22 467 462 457 452 447 442 437 432 427 422 TAI JOB NO. 18-196-1 B-19 FEBRUARY 12, 2019 THE HAWBRIDGE SCHOOL SAXAPAHAW, NORTH CAROLINA THE HAWBRIDGE SCHOOL PAGE 1 OF 1 DRY CAVED DEPTH DESCRIPTION GW ELEV 10 50 90 TAI and ASSOCIATES, PLLC PO BOX 90067 RALEIGH, NC 27675 919-782-9525 PROJECT: LOCATION: CLIENT: BORING NO. DATE: N-VALUE (ASTM D-1586) S-3 3.0 10.0 Red, brown, moist, stiff, silty CLAY Orange, brown, tan, moist, firm to stiff, SILT, with varying amounts of clay Boring Terminated at 10.0 Feet 9 12 5 7 465 460 455 450 445 440 435 430 425 420 TAI JOB NO. 18-196-1 B-23 FEBRUARY 12, 2019 THE HAWBRIDGE SCHOOL SAXAPAHAW, NORTH CAROLINA THE HAWBRIDGE SCHOOL PAGE 1 OF 1 DRY CAVED DEPTH DESCRIPTION GW ELEV 10 50 90 TAI and ASSOCIATES, PLLC PO BOX 90067 RALEIGH, NC 27675 919-782-9525 PROJECT: LOCATION: CLIENT: BORING NO. DATE: N-VALUE (ASTM D-1586) S-4