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Engineer's Certification Letter - Storm Vault.pdf
Surveying LDC1 Engineering Planning June 19, 2019 City of Edmonds Stormwater Engineering Program Manager 121 51h Avenue N Edmonds, WA 98020 RE: ENGINEER'S CERTIFICATION LETTER IZfj5 : 5T02M VAIAUT PROSPECT LANE CITY OF EDMONDS FILE NUMBER: PLN20160014 LDC PROJECT NO. C19-127 Per Mr. Jake Lyon's request, LDC is pleased to provide the following professional engineering evaluation of the stormwater detention vault for the Prospect Lane project at 8713 - 2361h Street SW. The project is a Category 2 Small Site Project in a Direct Discharge Basin, an underground detention vault was designed for flow control. The project is subject to the recurrence interval maximum peak flows of 0.25, and 0.45 cfs per acre of impervious surface, for the 10-year, and 100-year, respectively. The engineering site plan included a water quality treatment facility (WQHM - BayFilter Manhole Model 545L-72-2) installed downstream of detention. Project Total Impervious Surface Area = 17,781 sf (0.408 acres) Allowed Peak Flow Designed As built cfs) (cfs) (cfs 10- r storm event = 0.25 x 0.408 = 0.1020 0.1006 0.1020 100- r storm event = 0.45 x 0.408 = 0.1836 0.1749 0.1769 The permitted facilities have been built in accordance with the approved plans, permit conditions, and all applicable codes. The footing drain for the vault is discharging to the water quality manhole (WQHM) installed downstream of detention. Some components of the work have not been built in strict conformance to the plans and conditions and, in the engineer's option, these exceptions do not compromise the integrity of the project. A list of the exceptions includes the following: • The detention vault was 0.1' shallower than the designed depth. • The standpipe riser within the flow control structure was 0.12' shallower than the designed height. • Storm drain IEs were installed slightly differently than planned. No slope was less than 0.5% (minimum designed pipe slope). M Qo co N N W Ln N co w co ID O U) N 7 r o_ W z v v a N O N O N Engineering ABOVE the Standard These exceptions do not constitute a material defect, compromise the integrity of the project, or violate any provisions of this code. The WWHM project report (attached) indicated that the detention vault is adequate for flow control. The engineered systems should function as intended. Please give me a call if you have further questions or need additional information. Sincerely, LDC, INC. John Yuen, PE Project Manager HQ Office Attachment: Prospect Lane - WWHM Project Report L9 E 0 u 4 U U U 0 J 3 3 3 m c C c ro n. Engineering ABOVE the Standard WWHM2012 PROJECT REPORT Project Name: 5601-DETENTION_AS-BUILT Site Name: LSA 5601 Site Address: 8713 236th Street SW City : Edmonds Report Date: 6/19/2019 MGS Regoin Puget East Data Start 1901/10/1 Data End : 2058/09/30 DOT Data Number: 03 Version Date: 2018/10/10 Version : 4.2.16 Low Flow Threshold for POC 1 : 50 Percent of the 2 Year High Flow Threshold for POC 1: 50 year PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Mod .552 Pervious Total 0.552 Impervious Land Use acre ROADS MOD 0.214 ROOF TOPS FLAT 0.101 DRIVEWAYS MOD 0.054 Impervious Total 0.369 Basin Total 0.921 Element Flows To: Surface MITIGATED LAND USE Name : Basin Bypass: No Interflow Groundwater GroundWater: No Pervious Land Use acre C, Pasture, Mod .513 Pervious Total 0.513 Impervious Land Use acre ROADS MOD 0.077 ROOF TOPS FLAT 0.235 DRIVEWAYS MOD 0.096 Impervious Total 0.408 Basin Total 0.921 Element Flows To: Surface Interflow Vault 1 Vault 1 Name Vault 1 Width 8 ft. Length 28 ft. Depth: 4.9 ft. Discharge Structure Riser Height: 3.88 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 1.25 in. Elevation: 0 ft. Element Flows To: Outlet 1 Outlet 2 Groundwater Vault Hydraulic Table Stage(feet) Area(ac.) Volume(ac_-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.005 0.000 0.000 0.000 0.0544 0.005 0.000 0.009 0.000 0.1089 0.005 0.000 0.014 0.000 0.1633 0.005 0.000 0.017 0.000 0.2178 0.005 0.001 0.019 0.000 0.2722 0.005 0.001 0.022 0.000 0.3267 0.005 0.001 0.024 0.000 0.3811 0.005 0.002 0.026 0.000 0.4356 0.005 0.002 0.028 0.000 0.4900 0.005 0.002 0.029 0.000 0.5444 0.005 0.002 0.031 0.000 0.5989 0.005 0.003 0.032 0.000 0.6533 0.005 0.003 0.034 0.000 0.7078 0.005 0.003 0.035 0.000 0.7622 0.005 0.003 0.037 0.000 0.8167 0.005 0.004 0.038 0.000 0.8711 0.005 0.004 0.039 0.000 0.9256 0.005 0.004 0.040 0.000 0.9800 0.005 0.005 0.042 0.000 1.0344 0.005 0.005 0.043 0.000 1.0889 0.005 0.005 0.044 0.000 1.1433 0.005 0.005 0.045 0.000 1.1978 0.005 0.006 0.046 0.000 1.2522 0.005 0.006 0.047 0.000 1.3067 0.005 0.006 0.048 0.000 1.3611 0.005 0.007 0.049 0.000 1.4156 0.005 0.007 0.050 0.000 1.4700 0.005 0.007 0.051 0.000 1.5244 0.005 0.007 0.052 0.000 1.5789 0.005 0.008 0.053 0.000 1.6333 0.005 0.008 0.054 0.000 1.6878 0.005 0.008 0.055 0.000 1.7422 0.005 0.009 0.056 0.000 1.7967 0.005 0.009 0.056 0.000 1.8511 0.005 0.009 0.057 0.000 1.9056 0.005 0.009 0.058 0.000 1.9600 0.005 0.010 0.059 0.000 2.0144 0.005 0.010 0.060 0.000 2.0689 0.005 0.010 0.061 0.000 2.1233 0.005 0.010 0.061 0.000 2.1778 0.005 0.011 0.062 0.000 2.2322 0.005 0.011 0.063 0.000 2.2867 0.005 0.011 0.064 0.000 2.3411 0.005 0.012 0.064 0.000 2.3956 0.005 0.012 0.065 0.000 2.4500 0.005 0.012 0.066 0.000 2.5044 0.005 0.012 0.067 0.000 2.5589 0.005 0.013 0.067 0.000 2.6133 0.005 0.013 0.068 0.000 2.6678 0.005 0.013 0.069 0.000 2.7222 0.005 0.014 0.070 0.000 2.7767 0.005 0.014 0.070 0.000 2.8311 0.005 0.014 0.071 0.000 2.8856 0.005 0.014 0.072 0.000 2.9400 0.005 0.015 0.072 0.000 2.9944 0.005 0.015 0.073 0.000 3.0489 0.005 0.015 0.074 0.000 3.1033 0.005 0.016 0.074 0.000 3.1578 0.005 0.016 0.075 0.000 3.2122 0.005 0.016 0.076 0.000 3.2667 0.005 0.016 0.076 0.000 3.3211 0.005 0.017 0.077 0.000 3.3756 0.005 0.017 0.077 0.000 3.4300 0.005 0.017 0.078 0.000 3.4844 0.005 0.017 0.079 0.000 3.5389 0.005 0.018 0.079 0.000 3.5933 0.005 0.018 0.080 0.000 3.6478 0.005 0.018 0.081 0.000 3.7022 0.005 0.019 0.081 0.000 3.7567 0.005 0.019 0.082 0.000 3.8111 0.005 0.019 0.082 0.000 3.8656 0.005 0.019 0.083 0.000 3.9200 0.005 0.020 0.168 0.000 3.9744 0.005 0.020 0.390 0.000 4.0289 0.005 0.020 0.683 0.000 4.0833 0.005 0.021 1.014 0.000 4.1378 0.005 0.021 1.351 0.000 4.1922 0.005 0.021 1.662 0.000 4.2467 0.005 0.021 1.921 0.000 4.3011 0.005 0.022 2.114 0.000 4.3556 0.005 0.022 2.245 0.000 4.4100 0.005 0.022 2.382 0.000 4.4644 0.005 0.023 2.497 0.000 4.5189 0.005 0.023 2.607 0.000 4.5733 0.005 0.023 2.713 0.000 4.6278 0.005 0.023 2.814 0.000 4.6822 0.005 0.024 2.912 0.000 4.7367 0.005 0.024 3.007 0.000 4.7911 0.005 0.024 3.099 0.000 4.8456 0.005 0.024 3.188 0.000 4.9000 0.005 0.025 3.274 0.000 4.9544 0.005 0.025 3.359 0.000 5.0089 0.000 0.000 3.441 0.000 ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.552 Total Impervious Area:0.369 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.513 Total Impervious Area:0.408 Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.119027 5 year 0.167743 10 year 0.205271 25 year 0.259126 50 year 0.304218 100 year 0.353829 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.062363 5 year 0.084303 10 year 0.102012 25 year 0.128359 50 year 0.151138 100 year 0.176863 Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1902 0.112 0.064 1903 0.133 0.059 1904 0.195 0.074 1905 0.076 0.047 1906 0.080 0.051 1907 0.132 0.079 1908 0.104 0.065 1909 0.117 0.060 1910 0.140 0.075 1911 0.112 0.063 1912 0.293 0.206 1913 0.077 0.056 1914 0.362 0.106 1915 0.075 0.049 1916 0.115 0.060 1917 0.071 0.051 1918 0.104 0.051 1919 0.065 0.050 1920 0.101 0.057 1921 0.081 0.051 1922 0.114 0.064 1923 0.116 0.056 1924 0.132 0.053 1925 0.071 0.043 1926 0.127 0.061 1927 0.096 0.056 1928 0.099 0.052 1929 0.172 0.073 1930 0.173 0.064 1931 0.084 0.058 1932 0.100 0.058 1933 0.094 0.056 1934 0.179 0.089 1935 0.079 0.054 1936 0.107 0.057 1937 0.154 0.073 1938 0.088 0.057 1939 0.107 0.054 1940 0.165 0.074 1941 0.133 0.062 1942 0.149 0.073 1943 0.148 0.065 1944 0.233 0.102 1945 0.142 0.073 1946 0.111 0.055 1947 0.083 0.057 1948 0.128 0.095 1949 0.182 0.084 1950 0.073 0.050 1951 0.119 0.054 1952 0.272 0.203 1953 0.248 0.171 1954 0.108 0.063 1955 0.087 0.054 1956 0.068 0.043 1957 0.102 0.054 1958 0.160 0.104 1959 0.142 0.065 1960 0.092 0.049 1961 0.331 0.116 1962 0.105 0.065 1963 0.066 0.043 1964 0.280 0.078 1965 0.147 0.079 1966 0.094 0.045 1967 0.131 0.050 1968 0.094 0.055 1969 0.106 0.059 1970 0.141 0.064 1971 0.145 0.118 1972 0.490 0.171 1973 0.187 0.073 1974 0.163 0.064 1975 0.226 0.155 1976 0.181 0.077 1977 0.068 0.048 1978 0.154 0.091 1979 0.127 0.054 1980 0.135 0.055 1981 0.133 0.060 1982 0.099 0.046 1983 0.149 0.067 1984 0.135 0.066 1985 0.151 0.059 1986 0.082 0.054 1987 0.135 0.070 1988 0.085 0.064 1989 0.078 0.054 1990 0.098 0.056 1991 0.141 0.074 1992 0.150 0.080 1993 0.147 0.065 1994 0.121 0.076 1995 0.068 0.043 1996 0.125 0.067 1997 0.097 0.055 1998 0.129 0.071 1999 0.116 0.052 2000 0.137 0.066 2001 0.110 0.050 2002 0.219 0.077 2003 0.092 0.063 2004 0.150 0.064 2005 0.250 0.077 2006 0.097 0.049 2007 0.148 0.067 2008 0.107 0.056 2009 0.097 0.057 2010 0.120 0.073 2011 0.086 0.046 2012 0.133 0.119 2013 0.108 0.053 2014 0.082 0.052 2015 0.273 0.074 2016 0.085 0.041 2017 0.185 0.084 2018 0.162 0.082 2019 0.221 0.175 2020 0.164 0.064 2021 0.143 0.077 2022 0.175 0.064 2023 0.166 0.062 2024 0.338 0.237 2025 0.098 0.050 2026 0.119 0.066 2027 0.135 0.065 2028 0.052 0.039 2029 0.102 0.060 2030 0.166 0.087 2031 0.060 0.045 2032 0.085 0.046 2033 0.079 0.041 2034 0.084 0.053 2035 0.145 0.124 2036 0.104 0.060 2037 0.109 0.053 2038 0.140 0.069 2039 0.179 0.064 2040 0.102 0.064 2041 0.117 0.062 2042 0.158 0.139 2043 0.136 0.069 2044 0.113 0.061 2045 0.105 0.053 2046 0.096 0.063 2047 0.105 0.061 2048 0.092 0.070 2049 0.150 0.070 2050 0.100 0.056 2051 0.188 0.124 2052 0.098 0.050 2053 0.095 0.056 2054 0.234 0.103 2055 0.098 0.053 2056 0.129 0.060 2057 0.080 0.051 2058 0.128 0.060 Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.4898 0.2370 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 0.3617 0.2061 0.3376 0.2034 0.3305 0.1751 0.2931 0.1714 0.2800 0.1712 0.2726 0.1554 0.2719 0.1390 0.2498 0.1244 0.2482 0.1242 0.2335 0.1190 0.2332 0.1178 0.2258 0.1163 0.2209 0.1059 0.2190 0.1044 0.1953 0.1034 0.1875 0.1019 0.1866 0.0947 0.1848 0.0908 0.1823 0.0886 0.1806 0.0871 0.1791 0.0845 0.1788 0.0837 0.1746 0.0815 0.1733 0.0799 0.1722 0.0794 0.1661 0.0790 0.1659 0.0775 0.1646 0.0769 0.1637 0.0768 0.1631 0.0767 0.1619 0.0767 0.1596 0.0763 0.1583 0.0752 0.1539 0.0743 0.1535 0.0742 0.1514 0.0737 0.1504 0.0735 0.1502 0.0729 0.1497 0.0728 0.1491 0.0727 0.1485 0.0727 0.1481 0.0725 0.1477 0.0725 0.1470 0.0712 0.1468 0.0704 0.1446 0.0700 0.1445 0.0696 0.1429 0.0690 0.1424 0.0690 0.1423 0.0672 0.1410 0.0666 0.1410 0.0665 0.1401 0.0663 0.1397 0.0660 0.1374 0.0658 0.1365 0.0653 0.1353 0.0652 59 0.1353 0.0649 60 0.1353 0.0648 61 0.1349 0.0647 62 0.1334 0.0645 63 0.1330 0.0644 64 0.1329 0.0643 65 0.1326 0.0643 66 0.1324 0.0641 67 0.1318 0.0641 68 0.1309 0.0640 69 0.1294 0.0640 70 0.1293 0.0638 71 0.1278 0.0637 72 0.1275 0.0637 73 0.1273 0.0635 74 0.1267 0.0634 75 0.1247 0.0633 76 0.1209 0.0631 77 0.1196 0.0626 78 0.1194 0.0624 79 0.1192 0.0622 80 0.1170 0.0616 81 0.1168 0.0612 82 0.1165 0.0609 83 0.1158 0.0607 84 0.1149 0.0604 85 0.1145 0.0604 86 0.1135 0.0604 87 0.1118 0.0600 88 0.1117 0.0600 89 0.1109 0.0598 90 0.1103 0.0595 91 0.1091 0.0594 92 0.1083 0.0592 93 0.1078 0.0590 94 0.1069 0.0577 95 0.1068 -0.0576 96 0.1067 0.0574 97 0.1063 0.0571 98 0.1053 0.0571 99 0.1051 0.0571 100 0.1045 0.0567 101 0.1043 0.0564 102 0.1039 0.0563 103 0.1036 0.0562 104 0.1019 0.0561 105 0.1017 0.0558 106 0.1016 0.0557 107 0.1010 0.0556 108 0.1001 0.0556 109 0.0995 0.0553 110 0.0989 0.0553 111 0.0985 0.0552 112 0.0982 0.0551 113 0.0979 0.0545 114 0.0977 0.0541 115 0.0976 0.0541 116 0.0974 0.0541 117 0.0966 0.0541 118 0.0966 0.0540 119 0.0964 0.0536 120 0.0961 0.0535 121 0.0946 0.0533 122 0.0944 0.0531 123 0.0942 0.0529 124 0.0937 0.0527 125 0.0923 0.0527 126 0.0922 0.0526 127 0.0917 0.0521 128 0.0882 0.0519 129 0.0870 0.0519 130 0.0861 0.0513 131 0.0853 0.0512 132 0.0850 0.0511 133 0.0849 0.0509 134 0.0839 0.0506 135 0.0839 0.0505 136 0.0828 0.0504 137 0.0825 0.0503 138 0.0824 0.0503 139 0.0811 0.0498 140 0.0799 0.0497 141 0.0797 0.0494 142 0.0795 0.0494 143 0.0794 0.0489 144 0.0785 0.0476 145 0.0773 0.0466 146 0.0762 0.0457 147 0.0754 0.0457 148 0.0735 0.0455 149 0.0713 0.0451 150 0.0712 0.0445 151 0.0684 0.0434 152 0.0679 0.0432 153 0.0678 0.0429 154 0.0665 0.0426 155 0.0654 0.0415 156 0.0596 0.0410 157 0.0518 0.0387 Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0595 2038 625 30 Pass 0.0620 1763 492 27 Pass 0.0645 1530 384 25 Pass 0.0669 1316 304 23 Pass 0.0694 1162 229 19 Pass 0.0719 1020 187 18 Pass 0.0743 912 133 14 Pass 0.0768 805 108 13 Pass 0.0793 719 89 12 Pass 0.0818 662 76 11 Pass 0.0842 600 66 11 Pass 0.0867 532 60 11 Pass 0.0892 497 54 10 Pass 0.0916 456 51 11 Pass 0.0941 419 50 11 Pass 0.0966 379 46 12 Pass 0.0991 356 46 12 Pass 0.1015 328 43 13 Pass 0.1040 299 40 13 Pass 0.1065 277 36 12 Pass 0.1089 253 35 13 Pass 0.1114 229 33 14 Pass 0.1139 213 32 15 Pass 0.1164 195 29 14 Pass 0.1188 182 27 14 Pass 0.1213 167 24 14 Pass 0.1238 160 23 14 Pass 0.1263 146 20 13 Pass 0.1287 133 20 15 Pass 0.1312 123 19 15 Pass 0.1337 109 18 16 Pass 0.1361 103 16 15 Pass 0.1386 95 15 15 Pass 0.1411 90 14 15 Pass 0.1436 82 13 15 Pass 0.1460 77 13 16 Pass 0.1485 67 13 19 Pass 0.1510 59 13 22 Pass 0.1534 58 13 22 Pass 0.1559 52 12 23 Pass 0.1584 51 11 21 Pass 0.1609 48 11 22 Pass 0.1633 46 11 23 Pass 0.1658 44 11 25 Pass 0.1683 40 10 25 Pass 0.1707 38 9 23 Pass 0.1732 36 7 19 Pass 0.1757 34 5 14 Pass 0.1782 33 5 15 Pass 0.1806 29 5 17 Pass 0.1831 26 5 19 Pass 0.1856 25 5 20 Pass 0.1880 21 5 23 Pass 0.1905 21 5 23 Pass 0.1930 21 5 23 Pass 0.1955 20 4 20 Pass 0.1979 19 4 21 Pass 0.2004 19 4 21 Pass 0.2029 19 4 21 Pass 0.2053 19 3 15 Pass 0.2078 19 2 10 Pass 0.2103 19 2 10 Pass 0.2128 19 2 10 Pass 0.2152 19 2 10 Pass 0.2177 19 2 10 Pass 0.2202 18 2 11 Pass 0.2226 16 1 6 Pass 0.2251 16 1 6 Pass 0.2276 15 1 6 Pass 0.2301 15 1 6 Pass 0.2325 15 1 6 Pass 0.2350 13 1 7 Pass 0.2375 13 0 0 Pass 0.2400 13 0 0 Pass 0.2424 13 0 0 Pass 0.2449 13 0 0 Pass 0.2474 12 0 0 Pass 0.2498 11 0 0 Pass 0.2523 10 0 0 Pass 0.2548 10 0 0 Pass 0.2573 10 0 0 Pass 0.2597 10 0 0 Pass 0.2622 10 0 0 Pass 0.2647 10 0 0 Pass 0.2671 10 0 0 Pass 0.2696 10 0 0 Pass 0.2721 9 0 0 Pass 0.2746 8 0 0 Pass 0.2770 8 0 0 Pass 0.2795 7 0 0 Pass 0.2820 6 0 0 Pass 0.2844 6 0 0 Pass 0.2869 6 0 0 Pass 0.2894 6 0 0 Pass 0.2919 6 0 0 Pass 0.2943 5 0 0 Pass 0.2968 5 0 0 Pass 0.2993 5 0 0 Pass 0.3017 5 0 0 Pass 0.3042 5 0 0 Pass Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.0443 acre-feet On-line facility target flow: 0.04 cfs. Adjusted for 15 min: 0.0424 cfs. Off-line facility target flow: 0.0237 cfs. Adjusted for 15 min: 0.0251 cfs. LID Report LID Technique Used for Total Volume Percent Water Quality Percent Comment Treatment? Needs Volume Water Quality Treatment Infiltrated Treated (ac-ft) Vault 1 POC N 182.63 0.00 Volume Infiltration Cumulative Through Volume Volume Facility (ac-ft.) Infiltration ac-f Credit N Total Volume Infiltrated 182.63 0.00 0.00 0.00 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Passed Perind and Impind Changes No changes have been made. This program and accompanying documentation are provided 'as -is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright 0 by : Clear Creek Solutions, Inc. 2005-2019; All Rights Reserved.