Agenda packet, regular meeting — Laguna Hills City Council, February 10, 2026 (part 5 of 11)

*** AERMOD - VERSION 24142 *** *** C:\HRA\30752430_AERMOD\Model_infant_Unmit\Model_infant_Unmit.isc *** 01/06/26 *** AERMET - VERSION 22112 *** *** *** 15:48:45
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*** MODELOPTs: RegDFAULT CONC ELEV URBAN ADJ_U* *** NETWORK ID: UCART1 ; NETWORK TYPE: GRIDCART *** * ELEVATION HEIGHTS IN METERS * Y-COORD | X-COORD (METERS) (METERS) | 431808.32 431858.32 431908.32 431958.32 432008.32 432058.32 432108.32 432158.32 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3721332.58 | 80.80 80.00 81.10 79.40 79.90 80.30 80.60 80.90 3721282.58 | 80.10 79.80 79.70 78.60 78.40 79.30 79.30 79.30 3721232.58 | 80.10 80.20 78.70 78.20 77.90 79.10 79.10 79.00 3721182.58 | 79.00 79.70 78.50 77.90 77.90 78.60 79.00 79.00 3721132.58 | 78.00 79.00 77.90 77.60 77.90 78.30 78.30 78.60 3721082.58 | 75.40 78.20 77.80 77.40 77.60 77.50 77.70 78.30 3721032.58 | 78.50 76.40 76.40 76.20 75.90 75.60 76.50 75.90 3720982.58 | 82.40 78.70 78.10 79.30 81.60 80.80 81.40 80.10 3720932.58 | 91.70 82.50 77.20 78.10 89.10 88.10 83.30 82.70 3720882.58 | 94.00 86.30 77.90 78.20 87.40 88.00 87.90 87.70 3720832.58 | 96.20 92.60 79.50 84.40 86.30 87.00 89.70 88.90 3720782.58 | 101.70 104.90 86.60 86.20 86.20 86.20 88.40 89.70 3720732.58 | 110.10 105.10 100.30 86.80 86.20 86.20 88.70 88.80 3720682.58 | 110.30 104.70 105.10 98.60 87.30 86.20 86.30 87.80 3720632.58 | 108.10 105.60 104.30 104.90 97.70 86.40 86.20 87.50 3720582.58 | 105.50 105.50 104.20 102.80 103.30 95.80 86.30 86.70 3720532.58 | 104.00 101.80 101.40 102.00 101.40 100.90 87.80 87.70

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*** AERMOD - VERSION 24142 *** *** C:\HRA\30752430_AERMOD\Model_infant_Unmit\Model_infant_Unmit.isc *** 01/06/26 *** AERMET - VERSION 22112 *** *** *** 15:48:45
PAGE 8
*** MODELOPTs: RegDFAULT CONC ELEV URBAN ADJ_U* *** NETWORK ID: UCART1 ; NETWORK TYPE: GRIDCART *** * HILL HEIGHT SCALES IN METERS * Y-COORD | X-COORD (METERS) (METERS) | 431358.32 431408.32 431458.32 431508.32 431558.32 431608.32 431658.32 431708.32 431758.32 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3721332.58 | 74.30 74.60 74.20 74.40 74.20 74.30 74.60 75.30 80.90 3721282.58 | 115.50 109.90 74.00 74.40 74.50 74.60 74.70 75.10 80.40 3721232.58 | 115.50 115.50 115.50 115.50 115.50 74.50 74.80 75.00 80.30 3721182.58 | 159.50 115.50 115.50 115.50 115.50 115.50 115.40 75.50 78.70 3721132.58 | 115.50 115.50 118.20 118.20 118.20 120.40 117.40 96.40 78.60 3721082.58 | 115.50 115.50 115.50 123.90 123.90 123.90 123.90 123.90 123.90 3721032.58 | 115.50 115.50 115.50 123.90 123.90 123.90 123.90 123.90 123.90 3720982.58 | 115.50 115.50 115.50 118.20 123.90 123.90 123.90 109.30 92.60 3720932.58 | 109.90 115.50 115.40 118.20 117.40 120.40 114.60 96.70 114.20 3720882.58 | 115.40 115.50 115.40 118.20 118.20 120.40 117.60 100.50 99.00 3720832.58 | 115.20 115.40 115.40 123.90 118.20 120.40 117.50 117.30 117.50 3720782.58 | 115.30 115.40 123.90 120.60 118.20 120.40 117.40 117.30 109.80 3720732.58 | 115.40 123.90 118.00 118.00 118.10 120.40 116.70 120.10 110.20 3720682.58 | 102.90 123.90 123.90 123.90 120.60 120.30 117.10 123.90 110.30 3720632.58 | 102.80 125.90 125.90 123.90 123.90 123.90 123.90 123.90 109.60 3720582.58 | 125.90 125.90 125.90 125.90 123.50 123.70 126.30 127.10 127.10 3720532.58 | 119.90 126.00 125.90 125.90 125.90 126.30 126.60 127.10 127.10

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*** AERMOD - VERSION 24142 *** *** C:\HRA\30752430_AERMOD\Model_infant_Unmit\Model_infant_Unmit.isc *** 01/06/26 *** AERMET - VERSION 22112 *** *** *** 15:48:45
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*** MODELOPTs: RegDFAULT CONC ELEV URBAN ADJ_U* *** NETWORK ID: UCART1 ; NETWORK TYPE: GRIDCART *** * HILL HEIGHT SCALES IN METERS * Y-COORD | X-COORD (METERS) (METERS) | 431808.32 431858.32 431908.32 431958.32 432008.32 432058.32 432108.32 432158.32 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3721332.58 | 80.80 80.00 81.10 79.40 79.90 80.30 80.60 80.90 3721282.58 | 80.10 79.80 79.70 78.60 78.40 79.30 79.30 79.30 3721232.58 | 80.10 80.20 79.40 78.20 77.90 79.10 79.10 79.00 3721182.58 | 79.00 79.70 78.50 77.90 77.90 78.60 79.00 79.00 3721132.58 | 78.00 79.00 77.90 77.60 77.90 78.30 78.30 78.60 3721082.58 | 120.40 92.50 77.80 77.40 77.60 77.50 77.70 78.30 3721032.58 | 123.90 123.90 110.40 110.40 110.40 90.00 90.00 78.70 3720982.58 | 123.90 123.90 120.10 110.40 109.90 90.00 89.90 87.60 3720932.58 | 110.40 123.90 123.90 117.90 90.00 89.90 89.90 88.20 3720882.58 | 110.60 123.90 126.30 123.90 110.40 88.00 87.90 87.70 3720832.58 | 117.50 117.30 127.10 115.60 110.40 88.50 89.70 88.90 3720782.58 | 110.40 110.40 123.90 110.90 110.90 110.40 89.70 89.90 3720732.58 | 110.10 110.40 110.40 116.40 110.90 110.40 88.70 88.80 3720682.58 | 110.30 110.90 105.10 105.30 110.90 110.60 104.90 87.80 3720632.58 | 110.90 110.80 104.30 104.90 104.90 110.60 104.90 103.40 3720582.58 | 105.50 105.50 104.20 102.80 103.30 103.40 104.90 103.40 3720532.58 | 127.10 127.10 101.40 102.00 103.10 100.90 104.50 103.40

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*** AERMOD - VERSION 24142 *** *** C:\HRA\30752430_AERMOD\Model_infant_Unmit\Model_infant_Unmit.isc *** 01/06/26 *** AERMET - VERSION 22112 *** *** *** 15:48:45
PAGE 10
*** MODELOPTs: RegDFAULT CONC ELEV URBAN ADJ_U* *** DISCRETE CARTESIAN RECEPTORS *** (X-COORD, Y-COORD, ZELEV, ZHILL, ZFLAG) (METERS) ( 431744.4, 3721165.3, 75.8, 78.5, 0.0); ( 431704.3, 3721167.9, 75.8, 77.6, 0.0); ( 431688.2, 3721046.3, 79.9, 123.9, 0.0); ( 431704.3, 3720991.5, 87.8, 120.4, 0.0); ( 431701.0, 3720934.7, 96.7, 96.7, 0.0); ( 431703.6, 3720877.2, 100.9, 100.9, 0.0); ( 431700.3, 3720842.4, 103.8, 103.8, 0.0); ( 431696.9, 3720819.7, 105.5, 114.0, 0.0); ( 431689.6, 3720783.6, 109.1, 109.1, 0.0); ( 431684.2, 3720724.8, 113.9, 113.9, 0.0); ( 431680.9, 3720680.7, 114.2, 121.0, 0.0);

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*** AERMOD - VERSION 24142 *** *** C:\HRA\30752430_AERMOD\Model_infant_Unmit\Model_infant_Unmit.isc *** 01/06/26 *** AERMET - VERSION 22112 *** *** *** 15:48:45
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*** MODELOPTs: RegDFAULT CONC ELEV URBAN ADJ_U* *** METEOROLOGICAL DAYS SELECTED FOR PROCESSING *** (1=YES; 0=NO)
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 NOTE: METEOROLOGICAL DATA ACTUALLY PROCESSED WILL ALSO DEPEND ON WHAT IS INCLUDED IN THE DATA FILE. *** UPPER BOUND OF FIRST THROUGH FIFTH WIND SPEED CATEGORIES *** (METERS/SEC) 1.54, 3.09, 5.14, 8.23, 10.80,

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*** AERMOD - VERSION 24142 *** *** C:\HRA\30752430_AERMOD\Model_infant_Unmit\Model_infant_Unmit.isc *** 01/06/26 *** AERMET - VERSION 22112 *** *** *** 15:48:45
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*** MODELOPTs: RegDFAULT CONC ELEV URBAN ADJ_U* *** UP TO THE FIRST 24 HOURS OF METEOROLOGICAL DATA *** Surface ϐile: O:\3000-3999\30752430\30752430_HRA\HRA_Air Quality Data\msvj_sfc_pϐl (2)\MSVJ_V1 Met Version: 22112 Proϐile ϐile: O:\3000-3999\30752430\30752430_HRA\HRA_Air Quality Data\msvj_sfc_pϐl (2)\MSVJ_V1 Surface format: FREE Proϐile format: FREE Surface station no.: 93184 Upper air station no.: 3190 Name: UNKNOWN Name: UNKNOWN Year: 2017 Year: 2017 First 24 hours of scalar data YR MO DY JDY HR H0 U* W* DT/DZ ZICNV ZIMCH M-O LEN Z0 BOWEN ALBEDO REF WS WD HT REF TA HT - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 17 01 01 1 01 -3.5 0.085 -9.000 -9.000 -999. 59. 15.7 0.20 1.20 1.00 0.86 69. 10.0 280.0 9.0 17 01 01 1 02 -3.7 0.087 -9.000 -9.000 -999. 62. 15.9 0.20 1.20 1.00 0.90 61. 10.0 279.7 9.0 17 01 01 1 03 -8.0 0.126 -9.000 -9.000 -999. 107. 22.3 0.20 1.20 1.00 1.34 69. 10.0 280.4 9.0 17 01 01 1 04 -3.1 0.081 -9.000 -9.000 -999. 56. 15.5 0.20 1.20 1.00 0.80 67. 10.0 279.9 9.0 17 01 01 1 05 -3.0 0.080 -9.000 -9.000 -999. 54. 14.8 0.15 1.20 1.00 0.86 113. 10.0 279.8 9.0 17 01 01 1 06 -6.1 0.109 -9.000 -9.000 -999. 86. 18.7 0.15 1.20 1.00 1.26 92. 10.0 279.9 9.0 17 01 01 1 07 -5.8 0.107 -9.000 -9.000 -999. 84. 18.8 0.20 1.20 1.00 1.14 86. 10.0 279.8 9.0 17 01 01 1 08 -3.2 0.087 -9.000 -9.000 -999. 61. 18.2 0.15 1.20 0.53 1.00 98. 10.0 280.2 9.0 17 01 01 1 09 36.6 0.148 0.553 0.005 163. 136. -7.8 0.15 1.20 0.31 1.12 106. 10.0 283.2 9.0 17 01 01 1 10 89.0 0.203 1.161 0.005 624. 219. -8.3 0.19 1.20 0.24 1.45 159. 10.0 285.0 9.0 17 01 01 1 11 102.2 0.298 1.444 0.005 1044. 390. -22.9 0.25 1.20 0.21 2.23 183. 10.0 285.5 9.0 17 01 01 1 12 116.1 0.262 1.560 0.005 1160. 323. -13.7 0.25 1.20 0.20 1.83 200. 10.0 286.2 9.0 17 01 01 1 13 114.8 0.302 1.599 0.005 1265. 399. -21.4 0.17 1.20 0.20 2.51 225. 10.0 286.6 9.0 17 01 01 1 14 98.2 0.415 1.544 0.005 1330. 641. -64.5 0.25 1.20 0.21 3.44 205. 10.0 286.5 9.0 17 01 01 1 15 79.0 0.324 1.451 0.005 1370. 448. -38.2 0.25 1.20 0.25 2.57 199. 10.0 286.4 9.0 17 01 01 1 16 26.2 0.313 1.007 0.005 1383. 420. -103.7 0.25 1.20 0.33 2.68 195. 10.0 286.5 9.0 17 01 01 1 17 -20.5 0.246 -9.000 -9.000 -999. 295. 66.8 0.25 1.20 0.61 2.33 190. 10.0 285.5 9.0 17 01 01 1 18 -7.1 0.119 -9.000 -9.000 -999. 109. 21.0 0.19 1.20 1.00 1.29 162. 10.0 284.2 9.0 17 01 01 1 19 -6.0 0.108 -9.000 -9.000 -999. 86. 18.7 0.15 1.20 1.00 1.25 117. 10.0 283.5 9.0 17 01 01 1 20 -8.2 0.127 -9.000 -9.000 -999. 108. 22.1 0.15 1.20 1.00 1.46 104. 10.0 283.4 9.0 17 01 01 1 21 -8.0 0.125 -9.000 -9.000 -999. 106. 21.8 0.15 1.20 1.00 1.44 120. 10.0 284.0 9.0 17 01 01 1 22 -7.3 0.120 -9.000 -9.000 -999. 100. 21.1 0.17 1.20 1.00 1.34 127. 10.0 284.3 9.0 17 01 01 1 23 -5.7 0.106 -9.000 -9.000 -999. 83. 18.6 0.17 1.20 1.00 1.19 128. 10.0 284.0 9.0 17 01 01 1 24 -9.5 0.137 -9.000 -9.000 -999. 122. 24.2 0.17 1.20 1.00 1.52 129. 10.0 283.9 9.0

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First hour of proϐile data
YR MO DY HR HEIGHT F WDIR WSPD AMB_TMP sigmaA sigmaW sigmaV 17 01 01 01 9.0 0 -999. -99.00 280.0 99.0 -99.00 -99.00 17 01 01 01 10.0 1 69. 0.86 -999.0 99.0 -99.00 -99.00 F indicates top of proϐile (=1) or below (=0)

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*** AERMOD - VERSION 24142 *** *** C:\HRA\30752430_AERMOD\Model_infant_Unmit\Model_infant_Unmit.isc *** 01/06/26 *** AERMET - VERSION 22112 *** *** *** 15:48:45
PAGE 13
*** MODELOPTs: RegDFAULT CONC ELEV URBAN ADJ_U* *** THE PERIOD ( 43824 HRS) AVERAGE CONCENTRATION VALUES FOR SOURCE GROUP: ALL *** INCLUDING SOURCE(S): PAREA1 , *** NETWORK ID: UCART1 ; NETWORK TYPE: GRIDCART *** ** CONC OF DPM IN MICROGRAMS/M**3 ** Y-COORD | X-COORD (METERS) (METERS) | 431358.32 431408.32 431458.32 431508.32 431558.32 431608.32 431658.32 431708.32 431758.32 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3721332.58 | 0.00039 0.00043 0.00048 0.00054 0.00061 0.00068 0.00075 0.00080 0.00083 3721282.58 | 0.00043 0.00048 0.00055 0.00062 0.00072 0.00082 0.00092 0.00100 0.00103 3721232.58 | 0.00048 0.00054 0.00062 0.00072 0.00084 0.00099 0.00114 0.00127 0.00134 3721182.58 | 0.00053 0.00062 0.00072 0.00085 0.00101 0.00122 0.00147 0.00170 0.00183 3721132.58 | 0.00060 0.00069 0.00082 0.00100 0.00123 0.00154 0.00195 0.00241 0.00272 3721082.58 | 0.00068 0.00080 0.00098 0.00120 0.00152 0.00200 0.00269 0.00356 0.00419 3721032.58 | 0.00072 0.00089 0.00114 0.00146 0.00194 0.00274 0.00423 0.00668 0.00911 3720982.58 | 0.00077 0.00095 0.00121 0.00170 0.00239 0.00367 0.00665 0.01732 0.04820 3720932.58 | 0.00071 0.00088 0.00114 0.00182 0.00256 0.00411 0.00772 0.01887 0.04990 3720882.58 | 0.00071 0.00085 0.00115 0.00186 0.00258 0.00390 0.00628 0.00946 0.01309 3720832.58 | 0.00074 0.00091 0.00122 0.00178 0.00227 0.00301 0.00368 0.00393 0.00418 3720782.58 | 0.00083 0.00102 0.00131 0.00153 0.00176 0.00195 0.00191 0.00171 0.00136 3720732.58 | 0.00088 0.00104 0.00114 0.00119 0.00119 0.00115 0.00099 0.00090 0.00076 3720682.58 | 0.00084 0.00095 0.00098 0.00091 0.00079 0.00068 0.00058 0.00055 0.00052 3720632.58 | 0.00076 0.00082 0.00080 0.00068 0.00054 0.00045 0.00042 0.00039 0.00041 3720582.58 | 0.00066 0.00066 0.00060 0.00050 0.00039 0.00032 0.00030 0.00030 0.00032 3720532.58 | 0.00054 0.00052 0.00045 0.00036 0.00028 0.00023 0.00021 0.00022 0.00025

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*** AERMOD - VERSION 24142 *** *** C:\HRA\30752430_AERMOD\Model_infant_Unmit\Model_infant_Unmit.isc *** 01/06/26 *** AERMET - VERSION 22112 *** *** *** 15:48:45
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*** MODELOPTs: RegDFAULT CONC ELEV URBAN ADJ_U* *** THE PERIOD ( 43824 HRS) AVERAGE CONCENTRATION VALUES FOR SOURCE GROUP: ALL *** INCLUDING SOURCE(S): PAREA1 , *** NETWORK ID: UCART1 ; NETWORK TYPE: GRIDCART *** ** CONC OF DPM IN MICROGRAMS/M**3 ** Y-COORD | X-COORD (METERS) (METERS) | 431808.32 431858.32 431908.32 431958.32 432008.32 432058.32 432108.32 432158.32 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3721332.58 | 0.00082 0.00077 0.00069 0.00059 0.00050 0.00042 0.00035 0.00029 3721282.58 | 0.00103 0.00094 0.00082 0.00069 0.00056 0.00046 0.00037 0.00030 3721232.58 | 0.00133 0.00120 0.00100 0.00081 0.00063 0.00050 0.00039 0.00032 3721182.58 | 0.00180 0.00157 0.00125 0.00095 0.00071 0.00054 0.00041 0.00032 3721132.58 | 0.00259 0.00215 0.00157 0.00111 0.00078 0.00057 0.00042 0.00032 3721082.58 | 0.00400 0.00307 0.00199 0.00126 0.00083 0.00057 0.00042 0.00032 3721032.58 | 0.00778 0.00454 0.00240 0.00134 0.00083 0.00055 0.00040 0.00030 3720982.58 | 0.02417 0.00736 0.00268 0.00135 0.00081 0.00054 0.00038 0.00029 3720932.58 | 0.05471 0.01024 0.00262 0.00128 0.00078 0.00052 0.00037 0.00028 3720882.58 | 0.01770 0.00796 0.00261 0.00132 0.00081 0.00053 0.00037 0.00028 3720832.58 | 0.00450 0.00405 0.00232 0.00138 0.00085 0.00056 0.00039 0.00029 3720782.58 | 0.00182 0.00179 0.00181 0.00126 0.00085 0.00059 0.00042 0.00031 3720732.58 | 0.00085 0.00114 0.00125 0.00105 0.00079 0.00058 0.00043 0.00033 3720682.58 | 0.00058 0.00079 0.00083 0.00085 0.00069 0.00055 0.00043 0.00034 3720632.58 | 0.00045 0.00055 0.00063 0.00062 0.00061 0.00050 0.00041 0.00033 3720582.58 | 0.00036 0.00042 0.00048 0.00051 0.00049 0.00045 0.00038 0.00032 3720532.58 | 0.00030 0.00034 0.00038 0.00041 0.00041 0.00039 0.00034 0.00030

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*** AERMOD - VERSION 24142 *** *** C:\HRA\30752430_AERMOD\Model_infant_Unmit\Model_infant_Unmit.isc *** 01/06/26 *** AERMET - VERSION 22112 *** *** *** 15:48:45
PAGE 15
*** MODELOPTs: RegDFAULT CONC ELEV URBAN ADJ_U* *** THE PERIOD ( 43824 HRS) AVERAGE CONCENTRATION VALUES FOR SOURCE GROUP: ALL *** INCLUDING SOURCE(S): PAREA1 , *** DISCRETE CARTESIAN RECEPTOR POINTS *** ** CONC OF DPM IN MICROGRAMS/M**3 ** X-COORD (M) Y-COORD (M) CONC X-COORD (M) Y-COORD (M) CONC - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 431744.40 3721165.27 0.00203 431704.29 3721167.94 0.00185 431688.25 3721046.30 0.00478 431704.29 3720991.49 0.01365 431700.95 3720934.68 0.01589 431703.63 3720877.19 0.00832 431700.28 3720842.44 0.00445 431696.94 3720819.71 0.00308 431689.59 3720783.62 0.00176 431684.24 3720724.80 0.00082 431680.90 3720680.69 0.00056

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*** AERMOD - VERSION 24142 *** *** C:\HRA\30752430_AERMOD\Model_infant_Unmit\Model_infant_Unmit.isc *** 01/06/26 *** AERMET - VERSION 22112 *** *** *** 15:48:45
PAGE 16
*** MODELOPTs: RegDFAULT CONC ELEV URBAN ADJ_U* *** THE SUMMARY OF MAXIMUM PERIOD ( 43824 HRS) RESULTS *** ** CONC OF DPM IN MICROGRAMS/M**3 **

NETWORK
GROUP ID AVERAGE CONC RECEPTOR (XR, YR, ZELEV, ZHILL, ZFLAG) OF TYPE GRID-ID - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ALL 1ST HIGHEST VALUE IS 0.05471 AT ( 431808.32, 3720932.58, 91.70, 110.40, 0.00) GC UCART1 2ND HIGHEST VALUE IS 0.04990 AT ( 431758.32, 3720932.58, 92.40, 114.20, 0.00) GC UCART1 3RD HIGHEST VALUE IS 0.04820 AT ( 431758.32, 3720982.58, 90.50, 92.60, 0.00) GC UCART1 4TH HIGHEST VALUE IS 0.02417 AT ( 431808.32, 3720982.58, 82.40, 123.90, 0.00) GC UCART1 5TH HIGHEST VALUE IS 0.01887 AT ( 431708.32, 3720932.58, 96.70, 96.70, 0.00) GC UCART1 6TH HIGHEST VALUE IS 0.01770 AT ( 431808.32, 3720882.58, 94.00, 110.60, 0.00) GC UCART1 7TH HIGHEST VALUE IS 0.01732 AT ( 431708.32, 3720982.58, 89.90, 109.30, 0.00) GC UCART1 8TH HIGHEST VALUE IS 0.01589 AT ( 431700.95, 3720934.68, 96.71, 96.71, 0.00) DC 9TH HIGHEST VALUE IS 0.01365 AT ( 431704.29, 3720991.49, 87.82, 120.37, 0.00) DC 10TH HIGHEST VALUE IS 0.01309 AT ( 431758.32, 3720882.58, 99.00, 99.00, 0.00) GC UCART1 *** RECEPTOR TYPES: GC = GRIDCART GP = GRIDPOLR DC = DISCCART DP = DISCPOLR

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*** AERMOD - VERSION 24142 *** *** C:\HRA\30752430_AERMOD\Model_infant_Unmit\Model_infant_Unmit.isc *** 01/06/26 *** AERMET - VERSION 22112 *** *** *** 15:48:45
PAGE 17
*** MODELOPTs: RegDFAULT CONC ELEV URBAN ADJ_U* *** Message Summary : AERMOD Model Execution *** --------- Summary of Total Messages -------- A Total of 0 Fatal Error Message(s) A Total of 2 Warning Message(s) A Total of 471 Informational Message(s) A Total of 43824 Hours Were Processed A Total of 92 Calm Hours Identiϐied A Total of 379 Missing Hours Identiϐied ( 0.86 Percent) ******** FATAL ERROR MESSAGES ******** *** NONE *** ******** WARNING MESSAGES ******** ME W186 71 MEOPEN: THRESH_1MIN 1-min ASOS wind speed threshold used 0.50 ME W187 71 MEOPEN: ADJ_U* Option for Stable Low Winds used in AERMET ************************************ *** AERMOD Finishes Successfully *** ************************************

Page 711 of 1727 ends

Appendix D
Health Risk Calculation Worksheets

Page 712 of 1727 ends

Project: Toll Brothers Laguna Hills Townhome Project Engineer: B. Morrison Date: 1/9/2026 JN: 3075-2025-69
Exposure Frequency
1 : 91.25 days/year
Exposure Duration: 0.25 years
Daily Breathing Rate2
: 361 L/kg BW-day
Age Sensitivity Factor3:10
Fraction of Time at Home (FAH): 1
Averaging Time (Cancer): da 25,550 ys
Averaging Time (Non-Cancer): 91.25 days 1
Exposure frequency is based on the total number of active construction days during the first year of construction. 2 Source: OEHHA Air Toxics Hot Spots Program Guidance Manual , Table 8.3: Age Sensitivity Factors by Age Group for Cancer Risk Assessment. (ug/m3)
(b)
(mg/m3)
(c)
CPF
(mg/kg/day)
(f)
RISK (per
million)
(g)
REL
(ug/m3
)
(h)
RfD
(mg/kg/day)
(i)
Index
(j)
1 0.00302 3.02E-06 1 DPM 1.10E+00 0.01 5.00E+00 1.43E-03 0.0006 2 0.00614 6.14E-06 1 DPM 1.10E+00 0.02 5.00E+00 1.43E-03 0.0012 3 0.01961 1.96E-05 1 DPM 1.10E+00 0.07 5.00E+00 1.43E-03 0.0039 4 0.00554 5.54E-06 1 DPM 1.10E+00 0.02 5.00E+00 1.43E-03 0.0011 5 0.00222 2.22E-06 1 DPM 1.10E+00 0.01 5.00E+00 1.43E-03 0.0004 6 0.00071 7.10E-07 1 DPM 1.10E+00 0.00 5.00E+00 1.43E-03 0.0001 7 0.00257 2.57E-06 1 DPM 1.10E+00 0.01 5.00E+00 1.43E-03 0.0005 8 0.01697 1.70E-05 1 DPM 1.10E+00 0.06 5.00E+00 1.43E-03 0.0034 9 0.01031 1.03E-05 1 DPM 1.10E+00 0.04 5.00E+00 1.43E-03 0.0021 10 0.00385 3.85E-06 1 DPM 1.10E+00 0.01 5.00E+00 1.43E-03 0.0008 11 0.00104 1.04E-06 1 DPM 1.10E+00 0.00 5.00E+00 1.43E-03 0.0002 Construction Carcinogenic and Non-Carcinogenic Risks - 3rd Trimester Exposure Scenario (0.25-Year) Exposure Factors
3 Source: OEHHA Air Toxics Hot Spots Program Guidance Manual , Table 5.6: Point Estimates of Residential Daily Breathing Rates for 3rd Trimester, 0<2, 2<9, 2<16, 16<30, and 16-70 years (L/kg BW-day).

AERMOD
Receptor ID
(a)
Maximum Concentration
Weight
Fraction
(d)
Contaminant
(e)
Carcinogenic Hazards Noncarcinogenic Hazards
𝐶𝑎𝑛𝑐𝑒𝑟 𝑅𝑖𝑠𝑘 ൌ 𝐷𝑃𝑀 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 ൈ 𝐶𝑃𝐹 ൈ 𝐷𝐵𝑅 ൈ 𝐸𝐷 ൈ 𝐸𝐹 ൈ 𝐴𝑆𝐹 ൈ 𝐹𝐴𝐻 ൊ 25550

Page 713 of 1727 ends

AERMOD
Receptor ID
(a)
Maximum Concentration
Weight
Fraction
(d)
Contaminant
(e)
Carcinogenic Hazards Noncarcinogenic Hazards
ͷͷͷͲ ʹൊ ܪܣܨ ൈ ܨܵܣ ൈ ܨܧ ൈ ܦܧ ൈ ܴܤܦ ൈ ܨܲܥ ൈ ݊݋݅ݐܽݎݐ݊ܿ݁݊݋ܥܯܲܦ ൌ ݇ݏܴ݅ݎܽ݊ܿ݁ܥ

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Project: Engineer: B. Morrison Date: 1/9/2026
JN: 3075-2025-69
1 No
1 No
Maximum 0.0039
SCAQMD Threshold

2.6625
10 Exceeds Threshold?

0.0008

0.0032

0.0017

0.0009

0.0034

2.6625
Maximum Non-Cancer Hazard
Index

0.0006

0.0012

0.0039

0.0027

0.5747
Cumulative Cancer Risk
(per one million)

0.3498

0.3308

0.8681

2.3000
Cumulative Risk - Construction
Sensitive Receptor Location
Toll Brothers Laguna Hills Townhome Project
10 AERMOD Receptor ID
1 2
3 4
5 6
7 8

0.1506

1.3925

0.7525
11 0.0972 0.0002
9 0.3306 0.0021

Page 715 of 1727 ends

WQ XX-XXXX
County of Orange/Santa Ana Region
Priority Project
Water Quality Management Plan
(WQMP)
Project Name:
23161 Mill Creek Development
P.M. 147, 43-47
Prepared for:

Toll Brothers
350 Commerce, Suite 200
Irvine, CA 92602
(714) 347-1375
Prepared by:

Wilson Mikami Corporation
9 Corporate Park, Suite 100
Irvine, CA 92606
(949) 679-0090
July 11, 2025

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Road Development

Toll Brothers Owner’s Certification
North OC Priority WQMP Page i
This Water Quality Management Plan (WQMP) has been prepared for Toll Brothers by Wilson Mikami Corporation. The WQMP is intended to comply with the requirements of the County of Orange NPDES Stormwater Program requiring the preparation of the plan.

The undersigned, while it owns the subject property, is responsible for the implementation of the provisions of this plan , including the ongoing operation and maintenance of all best management practices (BMPs), and will ensure that this plan is amended as appropriate to reflect up-to-date conditions on the site consistent with the current Orange County Drainage Area Management Plan (DAMP) and the intent of the non-point source NPDES Permit for Waste Discharge Requirements for the County of Orange, Orange County Flood Control District and the incorporated Cities of Orange County within the Santa Ana Region. Once the undersigned transfers its interest in the property, its successors-in-interest shall bear the aforementioned responsibility to implement and amend the WQMP. An appropriate number of approved and signed copies of this document shall be available on the subject site in perpetuity.

Owner:

Title Kris Campbell, Vice President of Land Development Company Toll Brothers
Address 350 Commerce, Suite 200, Irvine, CA 92602
Email [email protected]
Telephone # (714) 347-1375
I understand my responsibility to implement the provisions of this WQMP including the ongoing operation and maintenance of the best management practices (BMPs) described herein.

Owner
Signature Date
Project Owner’s Certification
Planning Application No.
(If applicable) TBD Grading Permit No. TBD
Tract/Parcel Map and
Lot(s) No. P.M. 147-43-47 Building Permit No. TBD
Address of Project Site and APN
(If no address, specify Tract/Parcel Map and Lot Numbers) 23161 Mill Creek,
Laguna Hills

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Water Quality Management Plan (WQMP)
Toll Brothers

Toll Brothers Owner’s Certification
North OC Priority WQMP Page ii
Preparer (Engineer):

Title Scott Wilson, Principal PE Registration # 49884
Company Wilson Mikami Corporation
Address 9 Corporate Park, Suite 100
Email [email protected]
Telephone # (949) 679-0090
I hereby certify that this Water Quality Management Plan is in compliance with, and meets the requirements set forth in, Order No. R8-2009-0030/NPDES No. CAS618030, of the Santa Ana Regional Water Quality Control Board.

Preparer
Signature Date
Place
Stamp
Here

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Road Development

Toll BrothersTOLL BROTHERS Table of Contents
North OC Priority WQMP Page iii
Contents Page No.

Section I Permit(s) and Water Quality Conditions of Approval or Issuance ........... 1 Section II Project Description .................................................................................. 3 Section III Site Description ....................................................................................... 8 Section IV Best Management Practices (BMPs) ...................................................... 10 Section V Inspection/Maintenance Responsibility for BMPs ................................. 24 Section VI BMP Exhibit (Site Plan) ......................................................................... 25 Section VII Educational Materials ............................................................................ 26 Attachments
Attachment A . ................................................................................. Educational Materials Attachment B . ..................................................................................... Rainfall Zones Map Attachment C . ............................................................................................ WQMP Exhibit Attachment D . .......................................... Hydrologic Conditions of Concern Calculations Attachment E . .................................................... BMP Sizing Calculations and Worksheet Attachment F . ............................................................................ Preliminary Soils Report Attachment G . ......................................................................Preliminary Drainage Report

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section I
North OC Priority WQMP Page 1
Section I Permit(s) and Water Quality Conditions of Approval or Issuance
Provide discretionary or grading/building permit information and water quality conditions of approval, or permit issuance, applied to the project. If conditions are unknown, please request applicable conditions from staff. Refer to Section 2.1 in the Technical Guidance Document (TGD) available on the OC Planning website (ocplanning.net).

Project Infomation
Permit/Application No.
(If applicable) TBD
Grading or Building
Permit No.
(If applicable)
TBD
Address of Project Site (or
Tract Map and Lot
Number if no address)
and APN
23161 Mill Creek, Laguna Hills
Water Quality Conditions of Approval or Issuance
Water Quality
Conditions of Approval
or Issuance applied to
this project.
(Please list verbatim.)
None
Conceptual WQMP
Was a Conceptual Water
Quality Management Plan
previously approved for
this project?
No

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section I
North OC Priority WQMP Page 2
Watershed-Based Plan Conditions
Provide applicable
conditions from watershed -
based plans including
WIHMPs and TMDLS.

N/A

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section II
North OC Priority WQMP Page 3
Section II Project Description
II.1 Project Description
Provide a detailed project description including:
 Project areas;
 Land uses;
 Land cover;
 Design elements;
 A general description not broken down by drainage management areas (DMAs).

Include attributes relevant to determining applicable source controls. Refer to Section 2.2 in the Technical Guidance Document (TGD) for information that must be included in the project description.

Description of Proposed Project
Development Category
(From Model WQMP,
Table 7.11-2; or -3):

Priority Project: New development projects that create 10,000 square feet or more of impervious surface. This category includes commercial, industrial, residential housing subdivisions, mixed-use, and public projects on private or public property that falls under the planning and building authority or the Permittees.

Project Area (ft2): 105,917 Number of Dwelling Units: 36 SIC Code: N/A Project Area
Pervious Impervious
Area
(acres or sq ft)
Percentage
Area
(acres or sq ft)
Percentage
Pre-Project Conditions 0.53 ac 22% 1.87 ac 78%
Post-Project Conditions 0.62 ac 26% 1.78 ac 74%
Drainage
Patterns/Connections
The drainage from the project is collected by a series of area drains and catch basins to collect street flow. The south half of the property drains out to Mill Creek through a proposed parkway culvert near the proposed driveway. The north half of the property drains out to Mill Creek Drive through a second proposed parkway culvert near the northeast corner of the site.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section II
North OC Priority WQMP Page 4
Narrative Project
Description:
(Use as much space as
necessary.)
Re-development of an existing commercial property to a residential development including 36 duplex residential. No off-site drainage is anticipated.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section II
North OC Priority WQMP Page 5
II.2 Potential Stormwater Pollutants
Determine and list expected stormwater pollutants based on land uses and site activities. Refer to Section 2.2.2 and Table 2.1 in the Technical Guidance Document (TGD) for guidance.

Pollutants of Concern
Pollutant
Check One for
each:

E=Expected to
be of concern
N=Not Expected
to be of concern
Attached Residential Development
Suspended-Solid/ Sediment E N
Nutrients E N
Heavy Metals E N
Pathogens (Bacteria/Virus) E N
Pesticides E N
Oil and Grease E N
Toxic Organic Compounds E N
Trash and Debris E N
II.3 Hydrologic Conditions of Concern
Determine if streams located downstream from the project area are potentially susceptible to hydromodification impacts. Refer to Section 2.2.3.1 in the Technical Guidance Document (TGD) for North Orange County or Section 2.2.3.2 for South Orange County.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section II
North OC Priority WQMP Page 6
No – Show map
Yes – Describe applicable hydrologic conditions of concern below. Refer to Section 2.2.3 in the Technical Guidance Document (TGD).

The post development volume for the 2 year storm event does not exceed that of the pre development condition by more than 5%. The time of concentration of the post development runoff is less than the pre development condition. Per Section 5.3-1 of the Technical Guidance, the following calculations are prepared:

1. (V 2 year, post/ V2 year, pre) = < 1.05
( 776 cf / 833 cf) = 0.93 (7% decrease)

1. Tc 2 year, post / Tc 2 year, pre = < 1.05
(6.6 min / 7.1 min = 0.93 (7% decrease) *
* Reference calculations for time of concentration information for the 2 year storm event in Attachment D.

Hydrologic Conditions of Concern will not be considered for this project since the post development time of concentration is less than pre development time of concentration and the post development volume does not exceed pre development volume by more than 5%.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section II
North OC Priority WQMP Page 7
II.4 Post Development Drainage Characteristics
Describe post development drainage characteristics. Refer to Section 2.2.4 in the Technical Guidance Document (TGD).

The drainage from the project is collected by a series of area drains and catch basins to collect street flow.

The south half of the property drains out to Mill Creek through a proposed parkway culvert near the proposed driveway. The north half of the property drains out to Mill Creek Drive through a second proposed parkway culvert near the northeast corner of the site.

The flow continues down Mill Creek to an existing storm drain system tributary to San Diego Creek Channel.

San Diego Creek channel drains to Upper Newport Bay.

II.5 Property Ownership/Management
Describe property ownership/management. Refer to Section 2.2.5 in the Technical Guidance Document (TGD).

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section II
North OC Priority WQMP Page 8
On-site proposed drainage facilities will be privately owned and maintained.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section III
North OC Priority WQMP Page 9
Section III Site Description
III.1 Physical Setting
Fill out table with relevant information. Refer to Section 2.3.1 in the Technical Guidance Document (TGD).

Name of Planned
Community/Planning
Area (if applicable)
Not applicable
Location/Address
23161 Mill Creek Drive
Laguna Hills
General Plan Land Use
Designation MXU
Zoning Mixed use, MXU
Acreage of Project Site 2.4 acres
Predominant Soil Type Hydrological Soil Type “D”
III.2 Site Characteristics
Fill out table with relevant information and include information regarding BMP sizing, suitability, and feasibility, as applicable. Refer to Section 2.3.2 in the Technical Guidance Document (TGD).

Site Characteristics
Precipitation Zone 0.80" (Refer to Figure XVI-1 of the TGD located in Attachment D) Topography
Slopes on the existing and proposed developed portion of the site are relatively flat (<5%) with vegetative slopes at 2:1 (+30 feet) surrounding existing and proposed development

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section III
North OC Priority WQMP Page 10
Drainage
Patterns/Connections
parkway culvert to Mill Creek. Ultimately tributary to San Diego Creek Reach 2, then Reach 1, then Upper Newport Bay
Soil Type, Geology, and
Infiltration Properties
silty fine to coarse sands, clayey to fine sandy silts, silty clay, siltsone/claystone, and sandstone layers; relatively low infiltration rate. percolation test in process
Hydrogeologic
(Groundwater)
Conditions
Greater than 50 ft below ground surface
Geotechnical Conditions
(relevant to infiltration) relatively low infiltration (<0.5 in/hr) expected. Percolation test in process Off-Site Drainage Offsite drainage is not anticipated for this project.

Utility and Infrastructure
Information
There is no existing storm drain system adjacent to the site. Stormwater will be collected by a series of PVC pipes discharging to a proposed bio-treatment BMP and then through a parkway culvert onto Mill Creek.

III.3 Watershed Description
Fill out table with relevant information and include information regarding BMP sizing, suitability, and feasibility, as applicable. Refer to Section 2.3.3 in the Technical Guidance Document (TGD).

Receiving Waters San Diego Creek Reach 1&2/Upper Newport Bay 303(d) Listed Impairments category 5
Applicable TMDLs 5A-TMDL/5B-TMDL being addressed by USEPA approved TMDL Pollutants of Concern for
the Project
San Diego Creek Reach 2 -Indicator Bacteria, Nutrients, Sedimentation/Siltation, Unknown Toxicity
San Diego Creek Reach 1 – Fecal Coliform, Nutrients, Pesticides, Sedimentation/Siltation, Selenium, Toxaphene
Upper Newport Bay – Chlordane, Copper, DDT, Indicator Bacteria, Metals, Nutrients, PCB’s, Pesticides, Sediment Toxicity, Sedimentation/Siltation

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section III
North OC Priority WQMP Page 11
Environmentally Sensitive
and Special Biological
Significant Areas
There are no Environment Sensitive Areas (ESA) or Areas of Special Biological Sign

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 12
Section IV Best Management Practices (BMPs)
IV. 1 Project Performance Criteria
Describe project performance criteria. Several steps must be followed in order to determine what performance criteria will apply to a project. These steps include:
 If the project has an approved WIHMP or equivalent, then any watershed specific criteria must be used and the project can evaluate participation in the approved regional or subregional opportunities. (Please ask your assigned planner or plan checker regarding whether your project is part of an approved WIHMP or equivalent.)  Determine applicable hydromodification control performance criteria. Refer to Section 7.II2.4.2.2 of the Model WQMP.  Determine applicable LID performance criteria. Refer to Section 7.II-2.4.3 of the Model WQMP.  Determine applicable treatment control BMP performance criteria. Refer to Section 7.II-3.2.2 of the Model WQMP.
 Calculate the LID design storm capture volume for the project. Refer to Section 7.II-2.4.3 of the Model WQMP.
(NOC Permit Area only) Is there an approved WIHMP or equivalent for the project area that includes more stringent LID feasibility criteria or if there are opportunities identified for implementing LID on regional or sub-regional basis?
YES NO
If yes, describe WIHMP
feasibility criteria or
regional/sub-regional LID
opportunities.

Newport Bay has a WIHMP. This project will use LID Treatment BMPs to reduce the post development impacts including infiltration, harvest and use, evapotranspire, or biotreat/biofilter, the 85th percentile of a 24 hour storm event. This project specifically proposes a LID Treatment BMP of impervious area dispersion. Biotreatment will be utilized for the remaining volume. Due to the limited available space, this project proposed the use of proprietary media biofiltration units.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 13
Project Performance Criteria
If HCOC exists,
list applicable
hydromodification
control
performance
criteria (Section

7.II-2.4.2.2 in
MWQMP)
Per Section II-3 of this WQMP, HCOC’s do not exist.

List applicable LID
performance
criteria (Section

7.II-2.4.3 from
MWQMP)
Per 7.II 2.4.3 of the Model WQMP, the available LID Treatment BMPs to be utilized in reducing the post development impacts include infiltration, harvest and use, evapotranspire, or biotreat/biofilter, the 85th percentile of a 24 hour storm event.

List applicable
treatment control
BMP performance
criteria (Section

7.II-3.2.2 from
MWQMP)
Per 7.II 3.2.2 of the Model MQMP, if the LID performance criteria is not feasibly met by retention and/or biotreatment, then sizing of onsite treatment control BMPs are required. For this project, a LID BMP of impervious area dispersion (e.g. roof top disconnection) will be implemented. This does not
Calculate LID
design storm
capture volume
for Project.

DMA A, VBMP = 1850 cf*
DMA B, VBMP=2570 cf*
*Refer to Worksheet A and C in Attachment E of this report.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 14
IV.2. Site Design and Drainage
Describe site design and drainage including
 A narrative of site design practices utilized or rationale for not using practices;  A narrative of how site is designed to allow BMPs to be incorporated to the MEP  A table of DMA characteristics and list of LID BMPs proposed in each DMA.  Reference to the WQMP “BMP Exhibit.”
 Calculation of Design Capture Volume (DCV) for each drainage area.  A listing of GIS coordinates for LID and Treatment Control BMPs.

Refer to Section 2.4.2 in the Technical Guidance Document (TGD).

DMA A includes the surface drainage, proposed inlets, and an underground piping system in the south half of the site. The piping discharges to a proposed BMP biofiltration basin with an underdrain. The underdrain connects to a parkway culvert discharging onto Mill Creek near the driveway entrance. DMA B includes the surface drainage, proposed inlets, and an underground piping system in the north half of the site. The piping discharges to a proposed BMP biofiltration basin with an underdrain. The underdrain connects to a proposed parkway culvert further down Mill Creek Drive. The limited surface area necessitates the use of a proprietary biofiltration system with engineered media to reduce the footprint. The use of proprietary biofiltration system will need to treat 150% of the design capture volume. Refer to BMP exhibit in Attachment C.

Drainage Area No.
(DMA)
Area
(ac)
Proposed BMPs Northing Easting DCV
(cf)
150%
DCV (cf)
A 0.96 Bio-7 Proprietary
Biofiltration
2174538 6109626 1,850 2775
B 1.22 Bio-7 Proprietary
Bilfiltration
2174693 6109566 2,570 3855
The sizing calculations and worksheets are in Attachment E.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 15
IV.3 LID BMP Selection and Project Conformance Analysis Each sub-section below documents that the proposed design features conform to the applicable project performance criteria via check boxes, tables, calculations, narratives, and/or references to worksheets. Refer to Section 2.4.2.3 in the Technical Guidance Document (TGD) for selecting LID BMPs and Section 2.4.3 in the Technical Guidance Document (TGD) for conducting conformance analysis with project performance criteria.

IV.3.1 Hydrologic Source Controls (HSCs)
If required HSCs are included, fill out applicable check box forms. If the retention criteria are otherwise met with other LID BMPs, include a statement indicating HSCs not required.

Name Included?
Localized on-lot infiltration
Impervious area dispersion (e.g. roof top
disconnection)
Street trees (canopy interception)
Residential rain barrels (not actively managed)
Green roofs/Brown roofs
Blue roofs
Impervious area reduction (e.g. permeable
pavers, site design)
Other:

Other:

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 16
Hydrologic Source Control (HSCs):

The proposed development and site conditions were evaluated in order to select the most feasible BMP implementation for the project. The HSC BMP Selection process was determined by the following:

HSC-1 Localized On Lot Infiltration: Infiltration is not proposed for this site due to soil type.

HSC- 2 Impervious Area Dispersion: Impervious Area Dispersion will be utilized for the downspout locations of the project buildings. Roof runoff will be collected in a series of roof downspouts and outlet the runoff to splash blocks which will drain into area drains which will discharge to subsurface infiltration galleries. Refer to Worksheet A in Attachment B of this report for additional information.

HSC-3 Street Trees: Street Trees will not be utilized as number and size has not been determined in the preliminary stage.

HSC-4 Residential Rain Barrels: Harvest and Reuse type BMPs are not suitable for a Southern California climate or feasible for this project type and will not be utilized.

HSC 4 Green/ Brown Roofs: Green and Brown Roof BMPs are not feasible for this project type and are not sustainable in Southern California climates.

HSC 5 Blue Roofs: Blue BMPs are not feasible for this project type and are not sustainable in Southern California climates.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 17
IV.3.2 Infiltration BMPs
Identify infiltration BMPs to be used in project. If design volume cannot be met, state why.

Name Included?
Bioretention without underdrains
Rain gardens
Porous landscaping
Infiltration planters
Retention swales
Infiltration trenches
Infiltration basins
Drywells
Subsurface infiltration galleries
French drains
Permeable asphalt
Permeable concrete
Permeable concrete pavers
Other:

Other:

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Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 18
Not applicable because the natural soil has an infiltration rate that is too low to use bioretention without underdrains or other infiltration BMP’s.

IV.3.3 Evapotranspiration, Rainwater Harvesting BMPs
If the full Design Storm Capture Volume cannot be met with infiltration BMPs, describe any evapotranspiration and/or rainwater harvesting BMPs included.

Name Included?
All HSCs; See Section IV.3.1
Surface-based infiltration BMPs
Biotreatment BMPs
Above-ground cisterns and basins
Underground detention
Other:

Other:

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Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 19
IV.3.4 Biotreatment BMPs
If the full Design Storm Capture Volume cannot be met with infiltration BMPs, and/or evapotranspiration and rainwater harvesting BMPs, describe biotreatment BMPs included. Include sections for selection, suitability, sizing, and infeasibility, as applicable.

Name Included?
Bioretention with underdrains
Stormwater planter boxes with underdrains
Rain gardens with underdrains
Constructed wetlands
Vegetated swales
Vegetated filter strips
Proprietary vegetated biotreatment systems
Wet extended detention basin
Dry extended detention basins
Other:

Other:

Proprietary vegetated biotreatment systems will be used to treat 150% of the DCV. See calculations and sizing in Attachment E.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 20
IV.3.5 Hydromodification Control BMPs
Describe hydromodification control BMPs. See Section 5 of the Technical Guidance Document (TGD).

Include sections for selection, suitability, sizing, and infeasibility, as applicable. Detail compliance with Prior Conditions of Approval (if applicable).

Hydromodification Control BMPs
BMP Name BMP Description

N/A N/A

IV.3.6 Regional/Sub-Regional LID BMPs
Describe regional/sub-regional LID BMPs in which the project will participate. Refer to Section 7.II2.4.3.2 of the Model WQMP.

Regional/Sub-Regional LID BMPs
Not Applicable

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Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 21
IV.3.7 Treatment Control BMPs
Treatment control BMPs can only be considered if the project conformance analysis indicates that it is not feasible to retain the full design capture volume with LID BMPs. Describe treatment control BMPs including sections for selection, sizing, and infeasibility, as applicable.

Treatment Control BMPs
BMP Name BMP Description
DMA A – Filterra Model FTPD0809-HC-P
Filterra Bioretention planter (72 sq ft bed area) with 3” of mulch on top of a 18”high flow media layer (measured infiltration rate of 175 in/hr) over 6” of bridging stone on top of a 6” underdrain.

Underdrain outlets to a proposed 18” RCP outlet pipe.

DMA B – Filterra Model FTPD08105-HC-P
Filterra Bioretention planter (84 sq ft bed area) with 3” of mulch on top of a 18”high flow media layer (measured infiltration rate of 175 in/hr) over 6” of bridging stone on top of a 6” underdrain.

Underdrain outlets to a proposed 18” RCP outlet pipe.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 22
IV.3.8 Non-structural Source Control BMPs
Fill out non-structural source control check box forms or provide a brief narrative explaining if nonstructural source controls were not used.

Non-Structural Source Control BMPs
Identifier Name
Check One
If not applicable, state brief
reason Included Not
Applicable
N1 Education for Property Owners,
Tenants and Occupants
N2 Activity Restrictions
N3 Common Area Landscape
Management
N4 BMP Maintenance
N5 Title 22 CCR Compliance (How
development will comply)
N6 Local Industrial Permit Compliance N/A Residential Development N7 Spill Contingency Plan N/A Residential Development
N8 Underground Storage Tank
Compliance N/A Residential Development
N9 Hazardous Materials Disclosure
Compliance
No proposed hazardous
Materials
N10 Uniform Fire Code Implementation
N11 Common Area Litter Control
N12 Employee Training
N13 Housekeeping of Loading Docks
N14 Common Area Catch Basin Inspection
N15 Street Sweeping Private Streets and
Parking Lots

N16 Retail Gasoline Outlets N/A Residential Development

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 23
IV.3.9 Structural Source Control BMPs
Fill out structural source control check box forms or provide a brief narrative explaining if structural source controls were not used.

Structural Source Control BMPs
Identifier Name
Check One
If not applicable, state brief
reason Included Not
Applicable
S1 Provide storm drain system stenciling
and signage
S2
Design and construct outdoor material
storage areas to reduce pollution
introduction
No proposed outdoor storage
areas
S3
Design and construct trash and waste
storage areas to reduce pollution
introduction
Trash and waste will not be
stored in common areas
S4
Use efficient irrigation systems &
landscape design, water conservation,
smart controllers, and source control

S5 Protect slopes and channels and
provide energy dissipation
Incorporate requirements applicable to
individual priority project categories
(from SDRWQCB NPDES Permit)
Not applicable
S6 Dock areas Not applicable
S7 Maintenance bays Not applicable
S8 Vehicle wash areas No proposed vehicle wash areas
S9 Outdoor processing areas Not applicable
S10 Equipment wash areas Not applicable
S11 Fueling areas Not applicable
S12 Hillside landscaping
S13 Wash water control for food
preparation areas Not applicable
S14 Community car wash racks Not applicable

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 24
IV.4 Alternative Compliance Plan (If Applicable)
Describe an alternative compliance plan (if applicable). Include alternative compliance obligations (i.e., gallons, pounds) and describe proposed alternative compliance measures.

Not applicable
IV.4.1 Water Quality Credits
Determine if water quality credits are applicable for the project. Refer to Section 3.1 of the Model WQMP for description of credits and Appendix VI of the Technical Guidance Document (TGD) for calculation methods for applying water quality credits.

Description of Proposed Project
Project Types that Qualify for Water Quality Credits (Select all that apply):

Redevelopment
projects that reduce the
overall impervious
footprint of the project
site.

Brownfield redevelopment, meaning
redevelopment, expansion, or reuse of real
property which may be complicated by the
presence or potential presence of hazardous
substances, pollutants or contaminants, and
which have the potential to contribute to
adverse ground or surface WQ if not
redeveloped.

Higher density development projects which
include two distinct categories (credits can only
be taken for one category): those with more
than seven units per acre of development (lower
credit allowance); vertical density
developments, for example, those with a Floor
to Area Ratio (FAR) of 2 or those having more
than 18 units per acre (greater credit allowance).

Mixed use development, such as a
combination of residential, commercial,
industrial, office, institutional, or other land
uses which incorporate design principles that
can demonstrate environmental benefits that
would not be realized through single use
projects (e.g. reduced vehicle trip traffic with
the potential to reduce sources of water or air
pollution).

Transit-oriented developments, such as a
mixed use residential or commercial area
designed to maximize access to public
transportation; similar to above criterion, but
where the development center is within one
half mile of a mass transit center (e.g. bus, rail,
light rail or commuter train station). Such
projects would not be able to take credit for
both categories, but may have greater credit
assigned
Redevelopment projects
in an established historic
district, historic
preservation area, or similar
significant city area
including core City Center
areas (to be defined through
mapping).

Developments with
dedication of
undeveloped portions to
parks, preservation
areas and other pervious
uses.

Developments
in a city center
area.

Developments
in historic
districts or
historic
preservation
areas.

Live-work
developments, a variety of
developments designed to
support residential and
vocational needs together –
similar to criteria to mixed
use development; would not
be able to take credit for
both categories.

In-fill projects, the
conversion of empty lots
and other underused spaces
into more beneficially used
spaces, such as residential
or commercial areas.

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Mill Creek Development

Toll Brothers Section IV
North OC Priority WQMP Page 25
Calculation of
Water Quality
Credits
(if applicable)
The entire DCV for the project site is being treated by LID BMP’s Water quality credits will not be used.

IV.4.2 Alternative Compliance Plan Information
Describe an alternative compliance plan (if applicable). Include alternative compliance obligations (i.e., gallons, pounds) and describe proposed alternative compliance measures. Refer to Section 7.II

3.0 in the Model WQMP.

Not applicable

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section V
North OC Priority WQMP Page 26
Section V Inspection/Maintenance Responsibility for BMPs Fill out information in table below. Prepare and attach an Operation and Maintenance Plan.

Identify the funding mechanism through which BMPs will be maintained. Inspection and maintenance records must be kept for a minimum of five years for inspection by the regulatory agencies. Refer to Section 7.II 4.0 in the Model WQMP.

BMP Inspection/Maintenance
BMP
Reponsible
Party(s)
Inspection/
Maintenance
Activities
Required
Minimum
Frequency of
Activities
Education of
Property Owners,
Tenants, Occupants
& Employees
Homeowner
Maintenance
Association
Information to be
provided to property
owners, tenants,
occupants and
employees
As needed
Activity restrictions
Homeowner
Maintenance
Association
Employees are to be
notified of activities
that are prohibited by
employees and
tenants
Restrictions identified
in employee manual
and reviewed yearly
by employees
Common Area
Landscape
Management
Homeowner
Maintenance
Association
Hire professional
landscape contractor
to properly maintain
common areas
Landscape
maintenance required
on a weekly basis or
as needed
Uniform Fire Code
Implementation
Homeowner
Maintenance
Association
Provide litter
removal
of site parking lot
and
landscape areas
Once per week

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section V
North OC Priority WQMP Page 27
Parking Lot Street
sweeping
Homeowner
Maintenance
Association
Hire a professional
street sweeping
service
Once per week
Efficient Irrigation
and Landscape
planting
Homeowner
Maintenance
Association
Hire professional
landscape contractor
to properly maintain
landscape and
control
irrigation measures
in
common areas
Landscape
maintenance
required
on a weekly basis or
as needed. All
irrigation services
shall be efficient, any
repairs conducted
immediately.

Irrigation timers
shall
be set according to
County standard and
seasonal conditions.

Filterra Planter
Boxes
Homeowner
Maintenance
Association
Hire professional
contractor to
properly maintain
the biofiltration
planter boxes
Regular maintenance
prior to, during, and
following the rainy
season. Service a
minimum of once per
year and as
necessary.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section VI
North OC Priority WQMP Page 28
Section VI BMP Exhibit (Site Plan)
VI.1 BMP Exhibit (Site Plan)
Include a BMP Exhibit (Site Plan), at a size no less than 24” by 36,” which includes the following minimum information:
 Insert in the title block (lower right hand corner) of BMP Exhibit: the WQMP Number (assigned by staff) and the grading/building or Planning Application permit numbers  Project location (address, tract/lot number(s), etc.)  Site boundary
 Land uses and land covers, as applicable
 Suitability/feasibility constraints
 Structural BMP locations
 Drainage delineations and flow information
 Delineate the area being treated by each structural BMP  GIS coordinates for LID and Treatment Control BMPs
 Drainage connections
 BMP details
 Preparer name and stamp
Please do not include any areas outside of the project area or any information not related to drainage or water quality. The approved BMP Exhibit (Site Plan) shall be submitted as a plan sheet on all grading and building plan sets submitted for plan check review and approval. The BMP Exhibit shall be at the same size as the rest of the plan sheets in the submittal and shall have an approval stamp and signature prior to plan check submittal.

VI.2 Submittal and Recordation of Water Quality Management Plan Following approval of the Final Project-Specific WQMP, three copies of the approved WQMP (including BMP Exhibit, Operations and Maintenance (O&M) Plan, and Appendices) shall be submitted. In addition, these documents shall be submitted in a PDF format.

Each approved WQMP (including BMP Exhibit, Operations and Maintenance (O&M) Plan, and Appendices) shall be recorded in the Orange County Clerk-Recorder’s Office, prior to close-out of grading and/or building permit. Educational Materials are not required to be included.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section VII
North OC Priority WQMP Page 29
Section VII Educational Materials
Refer to the Orange County Stormwater Program (ocwatersheds.com) for a library of materials available. Please only attach the educational materials specifically applicable to this project. Other materials specific to the project may be included as well and must be attached.

Education Materials
Residential Material
(http://www.ocwatersheds.com)
Check If
Applicable
Business Material
(http://www.ocwatersheds.com)
Check If
Applicable
The Ocean Begins at Your Front Door Tips for the Automotive Industry Tips for Car Wash Fund-raisers Tips for Using Concrete and Mortar Tips for the Home Mechanic Tips for the Food Service Industry Homeowners Guide for Sustainable
Water Use
Proper Maintenance Practices for Your
Business
Household Tips
Other Material
Check If
Attached Proper Disposal of Household
Hazardous Waste
Recycle at Your Local Used Oil
Collection Center (North County)
Recycle at Your Local Used Oil
Collection Center (Central County)
Recycle at Your Local Used Oil
Collection Center (South County)
Tips for Maintaining a Septic Tank
System
Responsible Pest Control
Sewer Spill
Tips for the Home Improvement
Projects
Tips for Horse Care
Tips for Landscaping and Gardening
Tips for Pet Care
Tips for Pool Maintenance
Tips for Residential Pool, Landscape
and Hardscape Drains
Tips for Projects Using Paint

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Mill Creek Development

Toll Brothers Section VII
North OC Priority WQMP Page 30
Attachment A
Education Materials

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Before Buying Pest Control Products Think ahead.

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section VII
North OC Priority WQMP Page 31
Attachment B
Rainfall Zones Map

Page 778 of 1727 ends

ORANGE COUNTY RIVERSIDE COUNTY

ORANGE COUNTY SAN BERNARDINO COUNTY

ORANGE COUNTY

LOS ANGELES COUNTY

ORANGE COUNTY ORANGE COUNTY LOS ANGELES COUNTY LOS ANGELES COUNTY

1.05 0.7

0.95 1

0.9 0.85

0.8 0.75

0.7 0.65

0.95 0.7

0.9 0.9

0.75 P:\9526E\6-GIS\Mxds\Reports\InfiltrationFeasability_20110215\9526E_FigureXVI-1_RainfallZones_20110215.mxd FIGURE JOB TITLE SCALE 1" = 1.8 miles DESIGNED

DRAWINGCHECKED
BMP
04/22/10
DATEJOB NO.

THTH9526-E

ORANGE COUNTY

TECHNICAL GUIDANCE

DOCUMENT
ORANGE CO. CA

RAINFALL ZONES

SUBJECT TO FURTHER REVISION
0 3.6 7.2 1.8
Miles
0 6 12 3
Kilometers
LEGEND
Orange County Precipitation Stations
24 Hour, 85th Percentile Rainfall (Inches)
24 Hour, 85th Percentile Rainfall (Inches) - Extrapolated City Boundaries
Rainfall Zones
Design Capture Storm Depth (inches)

0.65"

0.7 0.75

0.80 0.85

0.90 0.95

1.00 1.10"
Note: Events defined as 24-hour periods (calendar days) with greater than 0.1 inches of rainfall.

For areas outside of available data coverage, professional judgment shall be applied.

XVI-1

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section VII
North OC Priority WQMP Page 32
Attachment C
WQMP Exhibit

Page 780 of 1727 ends

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 212223 2526 27 28 29 30 31 32 33 34 35 36
24 CORPORATION WILSON MIKAMI · · ·

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CORPORATION WILSON MIKAMI

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section VII
North OC Priority WQMP Page 33
Attachment D
Hydrologic Conditions of Concern Calculations

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Project: Proposed Mill Creek Development
JN 10501
Storm Event Volume Calculations
Storm Event: 2 Year
Existing Condition
Volume(24 hour) = 1/2 (dQ)*(dTime)
Tc= 7.12 min
dTime = 2 x Tc 14.24 min
dQ = 3.9 cfs
Volume (24 hr)= 833 cf
Proposed Condition
Volume(24 hour) = 1/2 (dQ)*(dTime)
Tc= 6.6 10.6 min
dTime = 2 x Tc 13.3 21.2 min
dQ = 3.9 3.0 cfs
Volume (24 hr)= 776 cf

Page 784 of 1727 ends

____________________________________________________________________________ ****************************************************************************

RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE
(Reference: 1986 ORANGE COUNTY HYDROLOGY CRITERION)
(c) Copyright 1983-2016 Advanced Engineering Software (aes) Ver. 23.0 Release Date: 07/01/2016 License ID 1557
Analysis prepared by:

Wilson Mikami, Inc
9 CORPORATE PARK, SUITE 100
IRVINE, CA 92606
(949) 679-0090
************************** DESCRIPTION OF STUDY ************************** * KHOSHBIN MILL CREEK PROPERTY *
* EXISTING CONDITION 2-YEAR HYDROLOGY *
* BY KAM 071425 *
************************************************************************** FILE NAME: EX_MC2.DAT
TIME/DATE OF STUDY: 13:57 07/14/2025
============================================================================ USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION:
============================================================================ --*TIME-OF-CONCENTRATION MODEL*--
USER SPECIFIED STORM EVENT(YEAR) = 2.00
SPECIFIED MINIMUM PIPE SIZE(INCH) = 18.00
SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE = 0.95 *DATA BANK RAINFALL USED*
*ANTECEDENT MOISTURE CONDITION (AMC) I ASSUMED FOR RATIONAL METHOD* *USER-DEFINED STREET-SECTIONS FOR COUPLED PIPEFLOW AND STREETFLOW MODEL* HALF- CROWN TO STREET-CROSSFALL: CURB GUTTER-GEOMETRIES: MANNING

WIDTH CROSSFALL IN- / OUT-/PARK- HEIGHT WIDTH LIP HIKE FACTOR NO. (FT) (FT) SIDE / SIDE/ WAY (FT) (FT) (FT) (FT) (n)
=== ===== ========= ================= ====== ===== ====== ===== ======= 1 30.0 20.0 0.018/0.018/0.020 0.67 2.00 0.0312 0.167 0.0150 GLOBAL STREET FLOW-DEPTH CONSTRAINTS:

1. Relative Flow-Depth = 0.00 FEET
as (Maximum Allowable Street Flow Depth) - (Top-of-Curb)

2. (Depth)*(Velocity) Constraint = 6.0 (FT*FT/S)
*SIZE PIPE WITH A FLOW CAPACITY GREATER THAN
OR EQUAL TO THE UPSTREAM TRIBUTARY PIPE.*
*USER-SPECIFIED MINIMUM TOPOGRAPHIC SLOPE ADJUSTMENT NOT SELECTED **************************************************************************** FLOW PROCESS FROM NODE 10.00 TO NODE 11.00 IS CODE = 21 ---------------------------------------------------------------------------- >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<<
>>USE TIME-OF-CONCENTRATION NOMOGRAPH FOR INITIAL SUBAREA<< ============================================================================ INITIAL SUBAREA FLOW-LENGTH(FEET) = 203.00
ELEVATION DATA: UPSTREAM(FEET) = 316.50 DOWNSTREAM(FEET) = 304.00 Tc = K*[(LENGTH** 3.00)/(ELEVATION CHANGE)]**0.20
SUBAREA ANALYSIS USED MINIMUM Tc(MIN.) = 5.000
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 2.264
SUBAREA Tc AND LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS Tc
LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN (MIN.)

Page 785 of 1727 ends

COMMERCIAL D 0.18 0.20 0.100 57 5.00
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.100
SUBAREA RUNOFF(CFS) = 0.36
TOTAL AREA(ACRES) = 0.18 PEAK FLOW RATE(CFS) = 0.36
**************************************************************************** FLOW PROCESS FROM NODE 11.00 TO NODE 12.00 IS CODE = 61 ---------------------------------------------------------------------------- >>>>>COMPUTE STREET FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>(STANDARD CURB SECTION USED)<<<<<
============================================================================ UPSTREAM ELEVATION(FEET) = 304.00 DOWNSTREAM ELEVATION(FEET) = 299.70 STREET LENGTH(FEET) = 185.00 CURB HEIGHT(INCHES) = 6.0
STREET HALFWIDTH(FEET) = 10.00
DISTANCE FROM CROWN TO CROSSFALL GRADEBREAK(FEET) = 5.00 INSIDE STREET CROSSFALL(DECIMAL) = 0.020
OUTSIDE STREET CROSSFALL(DECIMAL) = 0.020
SPECIFIED NUMBER OF HALFSTREETS CARRYING RUNOFF = 1
Manning's FRICTION FACTOR for Streetflow Section(curb-to-curb) = 0.0150 **TRAVEL TIME COMPUTED USING ESTIMATED FLOW(CFS) = 0.53 STREETFLOW MODEL RESULTS USING ESTIMATED FLOW:

STREET FLOW DEPTH(FEET) = 0.19
HALFSTREET FLOOD WIDTH(FEET) = 3.19
AVERAGE FLOW VELOCITY(FEET/SEC.) = 2.42
PRODUCT OF DEPTH&VELOCITY(FT*FT/SEC.) = 0.46
STREET FLOW TRAVEL TIME(MIN.) = 1.28 Tc(MIN.) = 6.28
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.987
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN
COMMERCIAL D 0.19 0.20 0.100 57
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.100
SUBAREA AREA(ACRES) = 0.19 SUBAREA RUNOFF(CFS) = 0.34
EFFECTIVE AREA(ACRES) = 0.37 AREA-AVERAGED Fm(INCH/HR) = 0.02 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.10 TOTAL AREA(ACRES) = 0.4 PEAK FLOW RATE(CFS) = 0.65
END OF SUBAREA STREET FLOW HYDRAULICS:

DEPTH(FEET) = 0.20 HALFSTREET FLOOD WIDTH(FEET) = 3.86
FLOW VELOCITY(FEET/SEC.) = 2.45 DEPTH*VELOCITY(FT*FT/SEC.) = 0.50 LONGEST FLOWPATH FROM NODE 10.00 TO NODE 12.00 = 388.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 12.00 TO NODE 12.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 6.28
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.987
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN
COMMERCIAL D 0.96 0.20 0.100 57
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.100
SUBAREA AREA(ACRES) = 0.96 SUBAREA RUNOFF(CFS) = 1.70
EFFECTIVE AREA(ACRES) = 1.33 AREA-AVERAGED Fm(INCH/HR) = 0.02 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.10

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TOTAL AREA(ACRES) = 1.3 PEAK FLOW RATE(CFS) = 2.35
**************************************************************************** FLOW PROCESS FROM NODE 12.00 TO NODE 13.00 IS CODE = 51 ---------------------------------------------------------------------------- >>>>>COMPUTE TRAPEZOIDAL CHANNEL FLOW<<<<<
>>>>>TRAVELTIME THRU SUBAREA (EXISTING ELEMENT)<<<<<
============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 299.70 DOWNSTREAM(FEET) = 296.00 CHANNEL LENGTH THRU SUBAREA(FEET) = 119.00 CHANNEL SLOPE = 0.0311 CHANNEL BASE(FEET) = 0.00 "Z" FACTOR = 7.500
MANNING'S FACTOR = 0.015 MAXIMUM DEPTH(FEET) = 1.00
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.913
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN
COMMERCIAL D 0.55 0.20 0.100 57
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.100
TRAVEL TIME COMPUTED USING ESTIMATED FLOW(CFS) = 2.82
TRAVEL TIME THRU SUBAREA BASED ON VELOCITY(FEET/SEC.) = 4.63 AVERAGE FLOW DEPTH(FEET) = 0.29 TRAVEL TIME(MIN.) = 0.43 Tc(MIN.) = 6.70
SUBAREA AREA(ACRES) = 0.55 SUBAREA RUNOFF(CFS) = 0.94
EFFECTIVE AREA(ACRES) = 1.88 AREA-AVERAGED Fm(INCH/HR) = 0.02 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.10 TOTAL AREA(ACRES) = 1.9 PEAK FLOW RATE(CFS) = 3.20
END OF SUBAREA CHANNEL FLOW HYDRAULICS:

DEPTH(FEET) = 0.29 FLOW VELOCITY(FEET/SEC.) = 4.92
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 13.00 = 507.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 13.00 TO NODE 13.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 6.70
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.913
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN

NATURAL FAIR COVER
"CHAPARRAL,BROADLEAF" D 0.27 0.20 1.000 64
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 1.000
SUBAREA AREA(ACRES) = 0.27 SUBAREA RUNOFF(CFS) = 0.42
EFFECTIVE AREA(ACRES) = 2.15 AREA-AVERAGED Fm(INCH/HR) = 0.04 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.21 TOTAL AREA(ACRES) = 2.1 PEAK FLOW RATE(CFS) = 3.62
**************************************************************************** FLOW PROCESS FROM NODE 13.00 TO NODE 21.00 IS CODE = 31 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 296.00 DOWNSTREAM(FEET) = 272.00 FLOW LENGTH(FEET) = 265.00 MANNING'S N = 0.015
ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 18.000
DEPTH OF FLOW IN 18.0 INCH PIPE IS 4.5 INCHES
PIPE-FLOW VELOCITY(FEET/SEC.) = 10.56
ESTIMATED PIPE DIAMETER(INCH) = 18.00 NUMBER OF PIPES = 1

Page 787 of 1727 ends

PIPE-FLOW(CFS) = 3.62
PIPE TRAVEL TIME(MIN.) = 0.42 Tc(MIN.) = 7.12
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 21.00 = 772.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 21.00 TO NODE 21.00 IS CODE = 1
---------------------------------------------------------------------------- >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<<
============================================================================ TOTAL NUMBER OF STREAMS = 2
CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 1 ARE:

TIME OF CONCENTRATION(MIN.) = 7.12
RAINFALL INTENSITY(INCH/HR) = 1.85
AREA-AVERAGED Fm(INCH/HR) = 0.04
AREA-AVERAGED Fp(INCH/HR) = 0.20
AREA-AVERAGED Ap = 0.21
EFFECTIVE STREAM AREA(ACRES) = 2.15
TOTAL STREAM AREA(ACRES) = 2.15
PEAK FLOW RATE(CFS) AT CONFLUENCE = 3.62
**************************************************************************** FLOW PROCESS FROM NODE 20.00 TO NODE 21.00 IS CODE = 21 ---------------------------------------------------------------------------- >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<<
>>USE TIME-OF-CONCENTRATION NOMOGRAPH FOR INITIAL SUBAREA<< ============================================================================ INITIAL SUBAREA FLOW-LENGTH(FEET) = 70.00
ELEVATION DATA: UPSTREAM(FEET) = 302.00 DOWNSTREAM(FEET) = 272.00 Tc = K*[(LENGTH** 3.00)/(ELEVATION CHANGE)]**0.20
SUBAREA ANALYSIS USED MINIMUM Tc(MIN.) = 5.000
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 2.264
SUBAREA Tc AND LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS Tc
LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN (MIN.)

NATURAL FAIR COVER
"CHAPARRAL,BROADLEAF" D 0.21 0.20 1.000 64 5.00
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 1.000
SUBAREA RUNOFF(CFS) = 0.39
TOTAL AREA(ACRES) = 0.21 PEAK FLOW RATE(CFS) = 0.39
**************************************************************************** FLOW PROCESS FROM NODE 21.00 TO NODE 21.00 IS CODE = 1
---------------------------------------------------------------------------- >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<<
>>>>>AND COMPUTE VARIOUS CONFLUENCED STREAM VALUES<<<<< ============================================================================ TOTAL NUMBER OF STREAMS = 2
CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 2 ARE:

TIME OF CONCENTRATION(MIN.) = 5.00
RAINFALL INTENSITY(INCH/HR) = 2.26
AREA-AVERAGED Fm(INCH/HR) = 0.20
AREA-AVERAGED Fp(INCH/HR) = 0.20
AREA-AVERAGED Ap = 1.00
EFFECTIVE STREAM AREA(ACRES) = 0.21
TOTAL STREAM AREA(ACRES) = 0.21
PEAK FLOW RATE(CFS) AT CONFLUENCE = 0.39
** CONFLUENCE DATA **
STREAM Q Tc Intensity Fp(Fm) Ap Ae HEADWATER
NUMBER (CFS) (MIN.) (INCH/HR) (INCH/HR) (ACRES) NODE
1 3.62 7.12 1.848 0.20( 0.04) 0.21 2.1 10.00

Page 788 of 1727 ends

2 0.39 5.00 2.264 0.20( 0.20) 1.00 0.2 20.00

RAINFALL INTENSITY AND TIME OF CONCENTRATION RATIO
CONFLUENCE FORMULA USED FOR 2 STREAMS.
** PEAK FLOW RATE TABLE **
STREAM Q Tc Intensity Fp(Fm) Ap Ae HEADWATER
NUMBER (CFS) (MIN.) (INCH/HR) (INCH/HR) (ACRES) NODE
1 3.52 5.00 2.264 0.20( 0.06) 0.31 1.7 20.00
2 3.93 7.12 1.848 0.20( 0.06) 0.28 2.4 10.00
COMPUTED CONFLUENCE ESTIMATES ARE AS FOLLOWS:

PEAK FLOW RATE(CFS) = 3.93 Tc(MIN.) = 7.12
EFFECTIVE AREA(ACRES) = 2.36 AREA-AVERAGED Fm(INCH/HR) = 0.06 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.28 TOTAL AREA(ACRES) = 2.4
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 21.00 = 772.00 FEET. ============================================================================ END OF STUDY SUMMARY:

TOTAL AREA(ACRES) = 2.4 TC(MIN.) = 7.12
EFFECTIVE AREA(ACRES) = 2.36 AREA-AVERAGED Fm(INCH/HR)= 0.06 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.283 PEAK FLOW RATE(CFS) = 3.93
** PEAK FLOW RATE TABLE **
STREAM Q Tc Intensity Fp(Fm) Ap Ae HEADWATER
NUMBER (CFS) (MIN.) (INCH/HR) (INCH/HR) (ACRES) NODE
1 3.52 5.00 2.264 0.20( 0.06) 0.31 1.7 20.00
2 3.93 7.12 1.848 0.20( 0.06) 0.28 2.4 10.00
============================================================================ ============================================================================

END OF RATIONAL METHOD ANALYSIS

Page 789 of 1727 ends

____________________________________________________________________________ ****************************************************************************

Wilson Mikami, Inc
9 CORPORATE PARK, SUITE 100
IRVINE, CA 92606
(949) 679-0090
************************** DESCRIPTION OF STUDY ************************** * KHOSHBIN MILL CREEK PROPOSED CONDITION HYDROLOGY *
* 2-YEAR HYDROLOGY *
* BY KAM 071425 *
************************************************************************** FILE NAME: KOSH.DAT
TIME/DATE OF STUDY: 13:48 07/14/2025
============================================================================ USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION:
============================================================================ --*TIME-OF-CONCENTRATION MODEL*--
USER SPECIFIED STORM EVENT(YEAR) = 2.00
SPECIFIED MINIMUM PIPE SIZE(INCH) = 12.00
SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE = 0.95 *DATA BANK RAINFALL USED*
*ANTECEDENT MOISTURE CONDITION (AMC) I ASSUMED FOR RATIONAL METHOD* *USER-DEFINED STREET-SECTIONS FOR COUPLED PIPEFLOW AND STREETFLOW MODEL* HALF- CROWN TO STREET-CROSSFALL: CURB GUTTER-GEOMETRIES: MANNING

1. Relative Flow-Depth = 0.00 FEET
as (Maximum Allowable Street Flow Depth) - (Top-of-Curb)

2. (Depth)*(Velocity) Constraint = 6.0 (FT*FT/S)
*SIZE PIPE WITH A FLOW CAPACITY GREATER THAN
OR EQUAL TO THE UPSTREAM TRIBUTARY PIPE.*
*USER-SPECIFIED MINIMUM TOPOGRAPHIC SLOPE ADJUSTMENT NOT SELECTED **************************************************************************** FLOW PROCESS FROM NODE 10.00 TO NODE 11.00 IS CODE = 21 ---------------------------------------------------------------------------- >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<<
>>USE TIME-OF-CONCENTRATION NOMOGRAPH FOR INITIAL SUBAREA<< ============================================================================ INITIAL SUBAREA FLOW-LENGTH(FEET) = 240.00
ELEVATION DATA: UPSTREAM(FEET) = 312.40 DOWNSTREAM(FEET) = 309.20 Tc = K*[(LENGTH** 3.00)/(ELEVATION CHANGE)]**0.20
SUBAREA ANALYSIS USED MINIMUM Tc(MIN.) = 6.456
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.955
SUBAREA Tc AND LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS Tc
LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN (MIN.)

Page 790 of 1727 ends

COMMERCIAL D 0.10 0.20 0.100 57 6.46
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.100
SUBAREA RUNOFF(CFS) = 0.17
TOTAL AREA(ACRES) = 0.10 PEAK FLOW RATE(CFS) = 0.17
**************************************************************************** FLOW PROCESS FROM NODE 11.00 TO NODE 11.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 6.46
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.955
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN

RESIDENTIAL
"11+ DWELLINGS/ACRE" D 0.24 0.20 0.200 57
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.200
SUBAREA AREA(ACRES) = 0.24 SUBAREA RUNOFF(CFS) = 0.41
EFFECTIVE AREA(ACRES) = 0.34 AREA-AVERAGED Fm(INCH/HR) = 0.03 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.17 TOTAL AREA(ACRES) = 0.3 PEAK FLOW RATE(CFS) = 0.59
**************************************************************************** FLOW PROCESS FROM NODE 11.00 TO NODE 12.00 IS CODE = 31 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 303.20 DOWNSTREAM(FEET) = 302.50 FLOW LENGTH(FEET) = 47.00 MANNING'S N = 0.010
ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 12.000
DEPTH OF FLOW IN 12.0 INCH PIPE IS 2.6 INCHES
PIPE-FLOW VELOCITY(FEET/SEC.) = 4.58
ESTIMATED PIPE DIAMETER(INCH) = 12.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 0.59
PIPE TRAVEL TIME(MIN.) = 0.17 Tc(MIN.) = 6.63
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 12.00 = 287.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 12.00 TO NODE 12.00 IS CODE = 1
---------------------------------------------------------------------------- >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<<
============================================================================ TOTAL NUMBER OF STREAMS = 2
CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 1 ARE:

TIME OF CONCENTRATION(MIN.) = 6.63
RAINFALL INTENSITY(INCH/HR) = 1.93
AREA-AVERAGED Fm(INCH/HR) = 0.03
AREA-AVERAGED Fp(INCH/HR) = 0.20
AREA-AVERAGED Ap = 0.17
EFFECTIVE STREAM AREA(ACRES) = 0.34
TOTAL STREAM AREA(ACRES) = 0.34
PEAK FLOW RATE(CFS) AT CONFLUENCE = 0.59
**************************************************************************** FLOW PROCESS FROM NODE 10.00 TO NODE 13.00 IS CODE = 21 ---------------------------------------------------------------------------- >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<<
>>USE TIME-OF-CONCENTRATION NOMOGRAPH FOR INITIAL SUBAREA<< ============================================================================

Page 791 of 1727 ends

INITIAL SUBAREA FLOW-LENGTH(FEET) = 254.00
ELEVATION DATA: UPSTREAM(FEET) = 312.40 DOWNSTREAM(FEET) = 308.20 Tc = K*[(LENGTH** 3.00)/(ELEVATION CHANGE)]**0.20
SUBAREA ANALYSIS USED MINIMUM Tc(MIN.) = 6.326
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.978
SUBAREA Tc AND LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS Tc
LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN (MIN.)
COMMERCIAL D 0.10 0.20 0.100 57 6.33
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.100
SUBAREA RUNOFF(CFS) = 0.18
TOTAL AREA(ACRES) = 0.10 PEAK FLOW RATE(CFS) = 0.18
**************************************************************************** FLOW PROCESS FROM NODE 13.00 TO NODE 13.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 6.33
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.978
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN

RESIDENTIAL
"11+ DWELLINGS/ACRE" D 0.26 0.20 0.200 57
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.200
SUBAREA AREA(ACRES) = 0.26 SUBAREA RUNOFF(CFS) = 0.45
EFFECTIVE AREA(ACRES) = 0.36 AREA-AVERAGED Fm(INCH/HR) = 0.03 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.17 TOTAL AREA(ACRES) = 0.4 PEAK FLOW RATE(CFS) = 0.63
**************************************************************************** FLOW PROCESS FROM NODE 13.00 TO NODE 12.00 IS CODE = 31 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 302.70 DOWNSTREAM(FEET) = 302.50 FLOW LENGTH(FEET) = 11.00 MANNING'S N = 0.010
ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 12.000
DEPTH OF FLOW IN 12.0 INCH PIPE IS 2.6 INCHES
PIPE-FLOW VELOCITY(FEET/SEC.) = 5.02
ESTIMATED PIPE DIAMETER(INCH) = 12.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 0.63
PIPE TRAVEL TIME(MIN.) = 0.04 Tc(MIN.) = 6.36
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 12.00 = 265.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 12.00 TO NODE 12.00 IS CODE = 1
---------------------------------------------------------------------------- >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<<
>>>>>AND COMPUTE VARIOUS CONFLUENCED STREAM VALUES<<<<< ============================================================================ TOTAL NUMBER OF STREAMS = 2
CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 2 ARE:

TIME OF CONCENTRATION(MIN.) = 6.36
RAINFALL INTENSITY(INCH/HR) = 1.97
AREA-AVERAGED Fm(INCH/HR) = 0.03
AREA-AVERAGED Fp(INCH/HR) = 0.20
AREA-AVERAGED Ap = 0.17

Page 792 of 1727 ends

EFFECTIVE STREAM AREA(ACRES) = 0.36
TOTAL STREAM AREA(ACRES) = 0.36
PEAK FLOW RATE(CFS) AT CONFLUENCE = 0.63
** CONFLUENCE DATA **
STREAM Q Tc Intensity Fp(Fm) Ap Ae HEADWATER
NUMBER (CFS) (MIN.) (INCH/HR) (INCH/HR) (ACRES) NODE
1 0.59 6.63 1.926 0.20( 0.03) 0.17 0.3 10.00
2 0.63 6.36 1.971 0.20( 0.03) 0.17 0.4 10.00

RAINFALL INTENSITY AND TIME OF CONCENTRATION RATIO
CONFLUENCE FORMULA USED FOR 2 STREAMS.
** PEAK FLOW RATE TABLE **
STREAM Q Tc Intensity Fp(Fm) Ap Ae HEADWATER
NUMBER (CFS) (MIN.) (INCH/HR) (INCH/HR) (ACRES) NODE
1 1.21 6.36 1.971 0.20( 0.03) 0.17 0.7 10.00
2 1.20 6.63 1.926 0.20( 0.03) 0.17 0.7 10.00
COMPUTED CONFLUENCE ESTIMATES ARE AS FOLLOWS:

PEAK FLOW RATE(CFS) = 1.21 Tc(MIN.) = 6.36
EFFECTIVE AREA(ACRES) = 0.69 AREA-AVERAGED Fm(INCH/HR) = 0.03 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.17 TOTAL AREA(ACRES) = 0.7
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 12.00 = 287.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 12.00 TO NODE 14.00 IS CODE = 31 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 302.50 DOWNSTREAM(FEET) = 296.20 FLOW LENGTH(FEET) = 103.00 MANNING'S N = 0.010
ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 12.000
DEPTH OF FLOW IN 12.0 INCH PIPE IS 2.7 INCHES
PIPE-FLOW VELOCITY(FEET/SEC.) = 9.29
ESTIMATED PIPE DIAMETER(INCH) = 12.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 1.21
PIPE TRAVEL TIME(MIN.) = 0.18 Tc(MIN.) = 6.55
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 14.00 = 390.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 14.00 TO NODE 14.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 6.55
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.939
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

Page 793 of 1727 ends

>>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 296.20 DOWNSTREAM(FEET) = 294.30 FLOW LENGTH(FEET) = 45.00 MANNING'S N = 0.010
ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 12.000
DEPTH OF FLOW IN 12.0 INCH PIPE IS 3.2 INCHES
PIPE-FLOW VELOCITY(FEET/SEC.) = 8.56
ESTIMATED PIPE DIAMETER(INCH) = 12.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 1.42
PIPE TRAVEL TIME(MIN.) = 0.09 Tc(MIN.) = 6.63
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 15.00 = 435.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 15.00 TO NODE 15.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 6.63
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.924
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN
COMMERCIAL D 0.10 0.20 0.100 57
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.100
SUBAREA AREA(ACRES) = 0.10 SUBAREA RUNOFF(CFS) = 0.17
EFFECTIVE AREA(ACRES) = 0.93 AREA-AVERAGED Fm(INCH/HR) = 0.03 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.15 TOTAL AREA(ACRES) = 0.9 PEAK FLOW RATE(CFS) = 1.58
**************************************************************************** FLOW PROCESS FROM NODE 15.00 TO NODE 16.00 IS CODE = 31 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 294.30 DOWNSTREAM(FEET) = 292.30 FLOW LENGTH(FEET) = 50.00 MANNING'S N = 0.010
ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 12.000
DEPTH OF FLOW IN 12.0 INCH PIPE IS 3.4 INCHES
PIPE-FLOW VELOCITY(FEET/SEC.) = 8.66
ESTIMATED PIPE DIAMETER(INCH) = 12.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 1.58
PIPE TRAVEL TIME(MIN.) = 0.10 Tc(MIN.) = 6.73
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 16.00 = 485.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 16.00 TO NODE 26.00 IS CODE = 31 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 292.30 DOWNSTREAM(FEET) = 272.30 FLOW LENGTH(FEET) = 206.00 MANNING'S N = 0.015
ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 12.000
DEPTH OF FLOW IN 12.0 INCH PIPE IS 3.3 INCHES
PIPE-FLOW VELOCITY(FEET/SEC.) = 8.87
ESTIMATED PIPE DIAMETER(INCH) = 12.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 1.58
PIPE TRAVEL TIME(MIN.) = 0.39 Tc(MIN.) = 7.12
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 26.00 = 691.00 FEET.

Page 794 of 1727 ends

**************************************************************************** FLOW PROCESS FROM NODE 26.00 TO NODE 26.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 7.12
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.848
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN

NATURAL FAIR COVER
"CHAPARRAL,NARROWLEAF" D 0.28 0.20 1.000 72
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 1.000
SUBAREA AREA(ACRES) = 0.28 SUBAREA RUNOFF(CFS) = 0.42
EFFECTIVE AREA(ACRES) = 1.21 AREA-AVERAGED Fm(INCH/HR) = 0.07 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.35 TOTAL AREA(ACRES) = 1.2 PEAK FLOW RATE(CFS) = 1.93
**************************************************************************** FLOW PROCESS FROM NODE 26.00 TO NODE 26.00 IS CODE = 10 ---------------------------------------------------------------------------- >>>>>MAIN-STREAM MEMORY COPIED ONTO MEMORY BANK # 1 <<<<< ============================================================================ **************************************************************************** FLOW PROCESS FROM NODE 20.00 TO NODE 21.00 IS CODE = 21 ---------------------------------------------------------------------------- >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<<
>>USE TIME-OF-CONCENTRATION NOMOGRAPH FOR INITIAL SUBAREA<< ============================================================================ INITIAL SUBAREA FLOW-LENGTH(FEET) = 262.00
ELEVATION DATA: UPSTREAM(FEET) = 306.00 DOWNSTREAM(FEET) = 301.70 Tc = K*[(LENGTH** 3.00)/(ELEVATION CHANGE)]**0.20
SUBAREA ANALYSIS USED MINIMUM Tc(MIN.) = 6.414
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.962
SUBAREA Tc AND LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS Tc
LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN (MIN.)
COMMERCIAL D 0.13 0.20 0.100 57 6.41
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.100
SUBAREA RUNOFF(CFS) = 0.23
TOTAL AREA(ACRES) = 0.13 PEAK FLOW RATE(CFS) = 0.23
**************************************************************************** FLOW PROCESS FROM NODE 21.00 TO NODE 21.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 6.41
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.962
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN
COMMERCIAL D 0.06 0.20 0.100 57
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.100
SUBAREA AREA(ACRES) = 0.06 SUBAREA RUNOFF(CFS) = 0.10
EFFECTIVE AREA(ACRES) = 0.19 AREA-AVERAGED Fm(INCH/HR) = 0.02 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.10 TOTAL AREA(ACRES) = 0.2 PEAK FLOW RATE(CFS) = 0.33

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**************************************************************************** FLOW PROCESS FROM NODE 21.00 TO NODE 21.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 6.41
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.962
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN

RESIDENTIAL
"11+ DWELLINGS/ACRE" D 0.26 0.20 0.200 57
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.200
SUBAREA AREA(ACRES) = 0.26 SUBAREA RUNOFF(CFS) = 0.45
EFFECTIVE AREA(ACRES) = 0.45 AREA-AVERAGED Fm(INCH/HR) = 0.03 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.16 TOTAL AREA(ACRES) = 0.4 PEAK FLOW RATE(CFS) = 0.78
**************************************************************************** FLOW PROCESS FROM NODE 21.00 TO NODE 22.00 IS CODE = 31 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 296.70 DOWNSTREAM(FEET) = 296.50 FLOW LENGTH(FEET) = 21.00 MANNING'S N = 0.010
ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 12.000
DEPTH OF FLOW IN 12.0 INCH PIPE IS 3.4 INCHES
PIPE-FLOW VELOCITY(FEET/SEC.) = 4.22
ESTIMATED PIPE DIAMETER(INCH) = 12.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 0.78
PIPE TRAVEL TIME(MIN.) = 0.08 Tc(MIN.) = 6.50
LONGEST FLOWPATH FROM NODE 20.00 TO NODE 22.00 = 283.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 22.00 TO NODE 22.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 6.50
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.948
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN
COMMERCIAL D 0.14 0.20 0.100 57
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.100
SUBAREA AREA(ACRES) = 0.14 SUBAREA RUNOFF(CFS) = 0.24
EFFECTIVE AREA(ACRES) = 0.59 AREA-AVERAGED Fm(INCH/HR) = 0.03 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.14 TOTAL AREA(ACRES) = 0.6 PEAK FLOW RATE(CFS) = 1.02
**************************************************************************** FLOW PROCESS FROM NODE 22.00 TO NODE 25.00 IS CODE = 31 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 296.50 DOWNSTREAM(FEET) = 296.30 FLOW LENGTH(FEET) = 22.00 MANNING'S N = 0.010
ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 12.000

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DEPTH OF FLOW IN 12.0 INCH PIPE IS 4.0 INCHES
PIPE-FLOW VELOCITY(FEET/SEC.) = 4.50
ESTIMATED PIPE DIAMETER(INCH) = 12.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 1.02
PIPE TRAVEL TIME(MIN.) = 0.08 Tc(MIN.) = 6.58
LONGEST FLOWPATH FROM NODE 20.00 TO NODE 25.00 = 305.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 25.00 TO NODE 25.00 IS CODE = 1
---------------------------------------------------------------------------- >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<<
============================================================================ TOTAL NUMBER OF STREAMS = 2
CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 1 ARE:

TIME OF CONCENTRATION(MIN.) = 6.58
RAINFALL INTENSITY(INCH/HR) = 1.93
AREA-AVERAGED Fm(INCH/HR) = 0.03
AREA-AVERAGED Fp(INCH/HR) = 0.20
AREA-AVERAGED Ap = 0.14
EFFECTIVE STREAM AREA(ACRES) = 0.59
TOTAL STREAM AREA(ACRES) = 0.59
PEAK FLOW RATE(CFS) AT CONFLUENCE = 1.02
**************************************************************************** FLOW PROCESS FROM NODE 20.00 TO NODE 23.00 IS CODE = 21 ---------------------------------------------------------------------------- >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<<
>>USE TIME-OF-CONCENTRATION NOMOGRAPH FOR INITIAL SUBAREA<< ============================================================================ INITIAL SUBAREA FLOW-LENGTH(FEET) = 173.00
ELEVATION DATA: UPSTREAM(FEET) = 306.00 DOWNSTREAM(FEET) = 300.80 Tc = K*[(LENGTH** 3.00)/(ELEVATION CHANGE)]**0.20
SUBAREA ANALYSIS USED MINIMUM Tc(MIN.) = 5.000
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 2.264
SUBAREA Tc AND LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS Tc
LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN (MIN.)
COMMERCIAL D 0.07 0.20 0.100 57 5.00
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.100
SUBAREA RUNOFF(CFS) = 0.14
TOTAL AREA(ACRES) = 0.07 PEAK FLOW RATE(CFS) = 0.14
**************************************************************************** FLOW PROCESS FROM NODE 23.00 TO NODE 23.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 5.00
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 2.264
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN

RESIDENTIAL
"11+ DWELLINGS/ACRE" D 0.18 0.20 0.200 57
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.200
SUBAREA AREA(ACRES) = 0.18 SUBAREA RUNOFF(CFS) = 0.36
EFFECTIVE AREA(ACRES) = 0.25 AREA-AVERAGED Fm(INCH/HR) = 0.03 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.17 TOTAL AREA(ACRES) = 0.2 PEAK FLOW RATE(CFS) = 0.50

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**************************************************************************** FLOW PROCESS FROM NODE 23.00 TO NODE 24.00 IS CODE = 31 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 297.80 DOWNSTREAM(FEET) = 297.60 FLOW LENGTH(FEET) = 21.00 MANNING'S N = 0.010
ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 12.000
DEPTH OF FLOW IN 12.0 INCH PIPE IS 2.7 INCHES
PIPE-FLOW VELOCITY(FEET/SEC.) = 3.73
ESTIMATED PIPE DIAMETER(INCH) = 12.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 0.50
PIPE TRAVEL TIME(MIN.) = 0.09 Tc(MIN.) = 5.09
LONGEST FLOWPATH FROM NODE 20.00 TO NODE 24.00 = 194.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 24.00 TO NODE 24.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 5.09
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 2.240
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN
COMMERCIAL D 0.03 0.20 0.100 57
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.100
SUBAREA AREA(ACRES) = 0.03 SUBAREA RUNOFF(CFS) = 0.06
EFFECTIVE AREA(ACRES) = 0.28 AREA-AVERAGED Fm(INCH/HR) = 0.03 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.16 TOTAL AREA(ACRES) = 0.3 PEAK FLOW RATE(CFS) = 0.56
**************************************************************************** FLOW PROCESS FROM NODE 24.00 TO NODE 25.00 IS CODE = 31 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 297.60 DOWNSTREAM(FEET) = 296.30 FLOW LENGTH(FEET) = 245.00 MANNING'S N = 0.010
ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 12.000
DEPTH OF FLOW IN 12.0 INCH PIPE IS 3.3 INCHES
PIPE-FLOW VELOCITY(FEET/SEC.) = 3.12
ESTIMATED PIPE DIAMETER(INCH) = 12.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 0.56
PIPE TRAVEL TIME(MIN.) = 1.31 Tc(MIN.) = 6.40
LONGEST FLOWPATH FROM NODE 20.00 TO NODE 25.00 = 439.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 25.00 TO NODE 25.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 6.40
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.965
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN

RESIDENTIAL
"11+ DWELLINGS/ACRE" D 0.20 0.20 0.200 57
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20

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SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.200
SUBAREA AREA(ACRES) = 0.20 SUBAREA RUNOFF(CFS) = 0.35
EFFECTIVE AREA(ACRES) = 0.48 AREA-AVERAGED Fm(INCH/HR) = 0.04 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.18 TOTAL AREA(ACRES) = 0.5 PEAK FLOW RATE(CFS) = 0.83
**************************************************************************** FLOW PROCESS FROM NODE 25.00 TO NODE 25.00 IS CODE = 1
---------------------------------------------------------------------------- >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<<
>>>>>AND COMPUTE VARIOUS CONFLUENCED STREAM VALUES<<<<< ============================================================================ TOTAL NUMBER OF STREAMS = 2
CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 2 ARE:

TIME OF CONCENTRATION(MIN.) = 6.40
RAINFALL INTENSITY(INCH/HR) = 1.96
AREA-AVERAGED Fm(INCH/HR) = 0.04
AREA-AVERAGED Fp(INCH/HR) = 0.20
AREA-AVERAGED Ap = 0.18
EFFECTIVE STREAM AREA(ACRES) = 0.48
TOTAL STREAM AREA(ACRES) = 0.48
PEAK FLOW RATE(CFS) AT CONFLUENCE = 0.83
** CONFLUENCE DATA **
STREAM Q Tc Intensity Fp(Fm) Ap Ae HEADWATER
NUMBER (CFS) (MIN.) (INCH/HR) (INCH/HR) (ACRES) NODE
1 1.02 6.58 1.934 0.20( 0.03) 0.14 0.6 20.00
2 0.83 6.40 1.965 0.20( 0.04) 0.18 0.5 20.00

RAINFALL INTENSITY AND TIME OF CONCENTRATION RATIO
CONFLUENCE FORMULA USED FOR 2 STREAMS.
** PEAK FLOW RATE TABLE **
STREAM Q Tc Intensity Fp(Fm) Ap Ae HEADWATER
NUMBER (CFS) (MIN.) (INCH/HR) (INCH/HR) (ACRES) NODE
1 1.84 6.40 1.965 0.20( 0.03) 0.16 1.1 20.00
2 1.84 6.58 1.934 0.20( 0.03) 0.16 1.1 20.00
COMPUTED CONFLUENCE ESTIMATES ARE AS FOLLOWS:

PEAK FLOW RATE(CFS) = 1.84 Tc(MIN.) = 6.40
EFFECTIVE AREA(ACRES) = 1.05 AREA-AVERAGED Fm(INCH/HR) = 0.03 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.16 TOTAL AREA(ACRES) = 1.1
LONGEST FLOWPATH FROM NODE 20.00 TO NODE 25.00 = 439.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 25.00 TO NODE 25.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<<
============================================================================ MAINLINE Tc(MIN.) = 6.40
* 2 YEAR RAINFALL INTENSITY(INCH/HR) = 1.965
SUBAREA LOSS RATE DATA(AMC I ):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS

LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN

RESIDENTIAL
"11+ DWELLINGS/ACRE" D 0.12 0.20 0.200 57
SUBAREA AVERAGE PERVIOUS LOSS RATE, Fp(INCH/HR) = 0.20
SUBAREA AVERAGE PERVIOUS AREA FRACTION, Ap = 0.200
SUBAREA AREA(ACRES) = 0.12 SUBAREA RUNOFF(CFS) = 0.21
EFFECTIVE AREA(ACRES) = 1.17 AREA-AVERAGED Fm(INCH/HR) = 0.03 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.16 TOTAL AREA(ACRES) = 1.2 PEAK FLOW RATE(CFS) = 2.04

Page 799 of 1727 ends

**************************************************************************** FLOW PROCESS FROM NODE 25.00 TO NODE 26.00 IS CODE = 31 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<<
>>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 296.30 DOWNSTREAM(FEET) = 274.00 FLOW LENGTH(FEET) = 60.00 MANNING'S N = 0.010
ESTIMATED PIPE DIAMETER(INCH) INCREASED TO 12.000
DEPTH OF FLOW IN 12.0 INCH PIPE IS 2.2 INCHES
PIPE-FLOW VELOCITY(FEET/SEC.) = 20.50
ESTIMATED PIPE DIAMETER(INCH) = 12.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 2.04
PIPE TRAVEL TIME(MIN.) = 0.05 Tc(MIN.) = 6.45
LONGEST FLOWPATH FROM NODE 20.00 TO NODE 26.00 = 499.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 26.00 TO NODE 26.00 IS CODE = 11 ---------------------------------------------------------------------------- >>>>>CONFLUENCE MEMORY BANK # 1 WITH THE MAIN-STREAM MEMORY<<<<< ============================================================================ ** MAIN STREAM CONFLUENCE DATA **
STREAM Q Tc Intensity Fp(Fm) Ap Ae HEADWATER
NUMBER (CFS) (MIN.) (INCH/HR) (INCH/HR) (ACRES) NODE
1 2.04 6.45 1.956 0.20( 0.03) 0.16 1.2 20.00
2 2.04 6.63 1.926 0.20( 0.03) 0.16 1.2 20.00
LONGEST FLOWPATH FROM NODE 20.00 TO NODE 26.00 = 499.00 FEET. ** MEMORY BANK # 1 CONFLUENCE DATA **
STREAM Q Tc Intensity Fp(Fm) Ap Ae HEADWATER
NUMBER (CFS) (MIN.) (INCH/HR) (INCH/HR) (ACRES) NODE
1 1.93 7.12 1.848 0.20( 0.07) 0.35 1.2 10.00
2 1.91 7.38 1.810 0.20( 0.07) 0.35 1.2 10.00
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 26.00 = 691.00 FEET. ** PEAK FLOW RATE TABLE **
STREAM Q Tc Intensity Fp(Fm) Ap Ae HEADWATER
NUMBER (CFS) (MIN.) (INCH/HR) (INCH/HR) (ACRES) NODE
1 3.90 6.45 1.956 0.20( 0.05) 0.25 2.3 20.00
2 3.91 6.63 1.926 0.20( 0.05) 0.25 2.3 20.00
3 3.88 7.12 1.848 0.20( 0.05) 0.26 2.4 10.00
4 3.82 7.38 1.810 0.20( 0.05) 0.26 2.4 10.00
TOTAL AREA(ACRES) = 2.4
COMPUTED CONFLUENCE ESTIMATES ARE AS FOLLOWS:

PEAK FLOW RATE(CFS) = 3.91 Tc(MIN.) = 6.628
EFFECTIVE AREA(ACRES) = 2.31 AREA-AVERAGED Fm(INCH/HR) = 0.05 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.25 TOTAL AREA(ACRES) = 2.4
LONGEST FLOWPATH FROM NODE 10.00 TO NODE 26.00 = 691.00 FEET. ============================================================================ END OF STUDY SUMMARY:

TOTAL AREA(ACRES) = 2.4 TC(MIN.) = 6.63
EFFECTIVE AREA(ACRES) = 2.31 AREA-AVERAGED Fm(INCH/HR)= 0.05 AREA-AVERAGED Fp(INCH/HR) = 0.20 AREA-AVERAGED Ap = 0.254 PEAK FLOW RATE(CFS) = 3.91
** PEAK FLOW RATE TABLE **
STREAM Q Tc Intensity Fp(Fm) Ap Ae HEADWATER
NUMBER (CFS) (MIN.) (INCH/HR) (INCH/HR) (ACRES) NODE
1 3.90 6.45 1.956 0.20( 0.05) 0.25 2.3 20.00

Page 800 of 1727 ends

2 3.91 6.63 1.926 0.20( 0.05) 0.25 2.3 20.00
3 3.88 7.12 1.848 0.20( 0.05) 0.26 2.4 10.00
4 3.82 7.38 1.810 0.20( 0.05) 0.26 2.4 10.00
============================================================================ ============================================================================

END OF RATIONAL METHOD ANALYSIS

Page 801 of 1727 ends

Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section VII
North OC Priority WQMP Page 34
Attachment E
BMP Sizing Calculations and Worksheets

Page 802 of 1727 ends

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ON-SITE
DMA
AREA

PERVIOUS

AREA (SF)

IMPERVIOUS

AREA (SF)
TOTAL

AREA (AC)
TOTAL
AREA (SF) Aimp (%)

C RUNOFF
COEFF
DCV 1
VOLUME
(CU-FT)
Q(BMP) 2
(CFS)
DCV 3

REQUIRED
(CU-FT)
Q(BMP) 3

REQUIRED
(CFS)

FILTERRA

REQUIRED

SURFACE
AREA (SF) 4

PROVIDED

SURFACE

AREA (SF)

PROPOSED BMP
SIZING
A 8180 33638 0.96 41818 0.80 0.753 1850 0.159 2775 0.239 59 72 FTPD0809-HC-P B 5476 47667 1.22 53143 0.90 0.823 2570 0.221 3855 0.332 82 84 FTPD08105-HC-P 1 SEE WORKSHEETS A AND B
2 SEE WORKSHEETS A AND D
3 APPLY A 1.5x FACTOR TO 85TH PERCENTILE DESIGN CAPTURE DEPTH 4 ASSUMING A 175 IN/HR LOAD RATE, REQUIRED SURFACE AREA = Q(BMP)/175 IN/HR

Page 810 of 1727 ends

Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section VII
North OC Priority WQMP Page 35
Attachment F
Preliminary Soils Report

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9272 Jeronimo Road, Suite 104,  Irvine  CA 92618  (949) 297-3856

PRELIMINARY GEOTECHNICAL INVESTIGATION,

PROPOSED RESIDENTIAL DEVELOPMENT,
23161 MILL CREEK DRIVE,

LAGUNA HILLS, CALIFORNIA
Dated: August 15, 2024
Project No. 244006-01
Prepared For:

Toll Brothers
350 Commerce, Suite 200
Irvine, California 92602

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9272 Jeronimo Road, Suite 104 • Irvine • CA 92618 • (949) 297-3856 August 15, 2024 Project No. 244006-01
Ms. Aylene Chu
Toll Brothers
350 Commerce, Suite 200
Irvine, California 92602
Subject: Preliminary Geotechnical Investigation, Proposed Residential Development, 23161 Mill Creek Drive, Laguna Hills, California
In accordance with your request, LGC Valley, Inc. (LGC) has performed a preliminary geotechnical investigation for the proposed multi-family residential development located at 23161 Mill Creek Drive (Assessor Parcel Number [APN] 588-142-07) in the City of Laguna Hills, California. The purpose of our geotechnical investigation was to evaluate the existing on-site geotechnical conditions relative to the proposed multi-family residential development of the site and to provide geotechnical recommendations applicable to the grading operations and future site construction for the project.

Our geotechnical study included: 1) review of the available geotechnical as-graded documents of the site and adjacent properties, and pertinent geotechnical and geologic reports and maps relative to the general vicinity; 2) a site reconnaissance, geologic mapping, and field exploration consisting of the excavation of six small-diameter borings; 3) laboratory testing of representative on-site soil samples; 4) geotechnical analysis of the collected data; and 5) preparation of this report that includes our findings, conclusions, opinions, and recommendations relative to the grading and development of the site.

Based on the results of our preliminary geotechnical investigation, it is our professional opinion that the proposed site development is feasible from a geotechnical standpoint provided the recommendations included in this report are incorporated into the project plans and specifications and followed during site grading and construction. If you have any questions regarding our report, please contact this office. We appreciate this opportunity to be of service.

Respectfully submitted,
LGC VALLEY, INC.

Randall K. Wagner, CEG 1612 Basil Hattar, GE 2734
Senior Project Geologist Principal Engineer
Distribution: (1) Addressee (via e-mail)

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Project No. 233016-01 Page i August 15, 2024

TABLE OF CONTENTS
Section
Page

1.0 INTRODUCTION..............................................................................................................1

1.1 Purpose and Scope of Services .................................................................................1

1.2 Site and Project Description......................................................................................3

1.3 Proposed Development.............................................................................................3

1.4 Subsurface Investigation and Laboratory Testing......................................................4

1.5 Existing As-Graded Geotechnical Conditions..........................................................4

2.0 GEOTECHNICAL CONDITIONS...................................................................................5

2.1 Site Geology.............................................................................................................5

2.1.1 Artificial Older Fill (Afo)..............................................................................5

2.1.2 Tertiary-Aged Sespe Formation (Ts).............................................................5

2.2 Geologic Structure....................................................................................................6

2.3 Landslides.................................................................................................................6

2.4 Groundwater.............................................................................................................6

2.5 Surface Water and Flooding ....................................................................................6

2.6 Faulting ....................................................................................................................7

2.7 Seismicity and Related Effects ................................................................................7

2.7.1 Seismic Design Criteria ...............................................................................8

2.7.2 Lurching and Shallow Ground Rupture......................................................9

2.7.3 Liquefaction and Dynamic Settlement .........................................................9

2.7.4 Tsunamis and Seiches..................................................................................9

2.8 Slope Stability........................................................................................................10

2.9 Expansion Potential ................................................................................................10

2.10 Soluble Sulfate and Corrosivity of the On-Site Soils ..............................................10

2.11 Excavation Characteristics......................................................................................10

2.12 Earthwork Shrinkage and Bulking ..........................................................................11

2.13 Stormwater Infiltration/Percolation.........................................................................11

3.0 CONCLUSIONS...............................................................................................................13

4.0 RECOMMENDATIONS .................................................................................................16

4.1 Site Earthwork........................................................................................................16

4.1.1 Site Preparation..........................................................................................16

4.1.2 Removal and Recompaction........................................................................16

4.1.3 Cut/Fill Transition Condition ....................................................................17

4.1.4 Shrinkage/Bulking ......................................................................................17

4.1.5 Temporary Excavation Stability ................................................................17

4.1.6 Temporary Shoring ....................................................................................18

4.1.7 Fill Placement and Compaction .................................................................20

4.1.8 Trench Backfill and Compaction ................................................................20

4.2 Foundation Design..................................................................................................20

4.2.1 General Foundation Selection ....................................................................20

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Project No. 233016-01 Page ii August 15, 2024

4.2.2 Bearing Capacity........................................................................................21

4.2.3 Post-Tension Foundation............................................................................21

4.2.4 Mat Foundations........................................................................................23

4.2.5 Foundation Settlement................................................................................24

4.2.6 Building Clearance and Foundation Setbacks ..........................................24

4.3 Lateral Earth Pressures for Retaining Walls..........................................................25

4.4 Segmental Retaining Wall Recommendations.......................................................26

4.5 Soldier Pile Wall Recommendations.....................................................................29

4.6 Preliminary Pavement Recommendations.............................................................30

4.6.1 Asphalt Concrete (AC) Pavement ...............................................................30

4.6.2 Portland Cement Concrete Pavement.........................................................31

4.6.3 Vehicular Concrete Paver Pavement ..........................................................31

4.7 Nonstructural Concrete Flatwork...........................................................................31

4.8 Corrosivity to Concrete and Metal ..........................................................................32

4.9 Freestanding Walls.................................................................................................33

4.10 Control of Surface Water and Drainage Control .....................................................33

4.11 Construction Observation and Testing....................................................................33

5.0 LIMITATIONS..................................................................................................................35

LIST OF TABLES, APPENDICES, AND ILLUSTRATIONS
Tables
Table 1 - California Building Code Seismic Design Parameters (page 8) Table 2 - Earthwork Shrinkage and Bulking Estimates (page 11) Table 3 - Preliminary Geotechnical Parameters for Post-Tension Foundation Design (page 23) Table 4 - Lateral Earth Pressures for Retaining Walls (page 25) Table 5 - Design Soil Strength Parameters for Segmental Retaining Walls (page 27) Table 6 - Preliminary AC Pavement Design Sections (page 30) Table 7 - Nonstructural Concrete Flatwork (page 32)
Figures
Figure 1 - Site Location Map (page 2)
Figure 2 - Geotechnical Map (rear of text)
Figure 3 - Retaining Wall Drainage Detail (rear of text) Appendices
Appendix A - References
Appendix B - Geotechnical Boring Logs (Current Study)
Appendix C - Laboratory Testing Procedures and Test Results (Current Study) Appendix D - Previous Geotechnical Borings Logs (by Others) Appendix E - General Earthwork and Grading Specifications for Rough Grading

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1.0 INTRODUCTION

1.1 Purpose and Scope of Services
The purpose of this preliminary geotechnical investigation was to identify and evaluate the existing geologic and geotechnical conditions at the subject site (Figure 1) and to provide preliminary geotechnical design criteria relative to the proposed multi-family development of the site. Recommendations for site grading, construction, preliminary foundation design for the proposed structures, and other relevant aspects of the proposed development are included herein to address the identified site geotechnical conditions.

Our scope-of-services for preparation of this document included:
 Review of available reports including prior geotechnical investigations, as-graded geotechnical documents, and other geotechnical related documents of the site and adjacent properties; and pertinent published geologic, geotechnical, and seismic reports and maps relative to the general vicinity (Appendix A).  A site reconnaissance and geologic mapping of the site.  A subsurface investigation consisting of the excavation, sampling, and logging of six smalldiameter hollow-stem borings. The locations of the borings are shown on the Geotechnical Map (Figure 2). The logs of the borings are presented in Appendix B. The test borings were sampled and logged under the supervision of a licensed engineering geologist from our firm. The excavations were performed to evaluate the general characteristics of the subsurface conditions of the site including the classification of site soils and the determination of the depth to competent soil.
 Laboratory testing of representative soil samples obtained during our investigation (Appendix C).
 Review of boring logs from the geotechnical studies previously performed on the site and/or adjacent sites. The applicable boring logs are presented in Appendix D.  Determination of seismic design parameters based on current building code requirements. • Geotechnical analyses and evaluation of the data obtained during this study.  Preparation of this report presenting our findings, conclusions, opinions, and recommendations including the General Earthwork and Grading Specifications for Rough Grading (Appendix E) with respect to the evaluated geotechnical conditions at the site and the proposed development.

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Site Location
Basemap: ESRI World Imagery Basemap, Accessed August 13, 2024 Figure 1
Site Location Map
23161 Mill Creek Drive
Laguna Hills, California
244006-01
Toll/23161 Mill Creek

BIH/RKW
Not-to-Scale
August 15, 2024
Project Name
Project No.

Eng. / Geol.

Scale
Date

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1.2 Site and Project Description
The approximately 2.44-acre site is located on the west side of Mill Creek Drive southwest of the intersection of Mill Creek Drive and Lake Forest Drive in the northwestern portion of the City of Laguna Hills, California (Figure 1). The site is bounded by Mill Creek Drive on the east, existing business developments on the north (23091 Mill Creek Drive) and south (23201 Mill Creek Drive), and a residential development on the west. The site currently consists of one three-story commercial building in the northern portion of the site and a large, paved parking lot in the central and southern portions of the site. Additional improvements include underground utility lines, retaining walls along the south and west sides of the parking lot, landscaping, and associated improvements. A north- to east-facing slope up to approximately 40 to 45 feet in height is present on the north and east sides of the property that descends to the parking lot of 23091 Mill Creek Drive on the north and Mill Creek Drive on the east. An approximately 10 to 15-foot-tall north-facing slope is present along the south side of the property.

Review of available aerial photographs, historical Google Earth images, old topography maps, and geotechnical reports of adjacent properties (Appendix A) indicate that the site (and general vicinity) was rough graded in the late 1970’s/early 1980’s and the site was precise graded in 1985/1986. The as-graded geotechnical reports and grading plans specific to 23161 Mill Creek were not available at the City of Laguna Hills; and consequently, were not reviewed by us for the purposes of this study.

Prior to the grading of the site, the property was located along the north side of a northwestsoutheast trending ridgeline. Mill Creek Drive along the east side of the property was the location of a small tributary canyon that was partially in-filled during the grading of the area.

Based on Google Earth images, elevations of the relatively flat portion of the property range from approximately 297 to 301 feet along the north side of the property to 300 to 316 feet along the south side. Based on the original topography, current site grades, and our limited subsurface investigation, we anticipate that the prior grading of the site consisted of a cut-fill condition with shallow fills located across the site (existing parking lot area) and deeper fills along the northern side of the property (and beneath the existing building) with backfill soils behind the on-site retaining walls.

1.3 Proposed Development
We understand that the proposed development will consist of a multi-family townhome residential development consisting of nine 3- to 6-unit structures (totaling 43 units).

Preliminary plans show perimeter retaining walls are being considered around the perimeter of the site consisting of a combination of block walls, pile walls, and segmental (MSE) walls ranging in height from 4 to 17 feet. Anticipated associated improvements will include asphalt concrete (AC) streets and parking areas, a gated entrance, Portland cement concrete (PCC) sidewalks, open‐space areas/landscaping, underground utility lines, a storm water biofiltration system, and associated improvements.

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1.4 Subsurface Investigation and Laboratory Testing
Our subsurface investigation was performed on May 8, 2024, and consisted of the excavation, sampling, and logging of six small diameter hollow-stem borings (designated Borings LGC-B-1 through LGC-B-6) excavated to depths ranging from approximately 10.5 to 20.5 feet. All of the borings were extended into competent formational material. The logs of the borings are presented in Appendix B while the approximate locations of the borings are shown on the Geotechnical Map (Figure 1). At least three days prior to the start of our subsurface investigation, the proposed boring excavation locations were staked, Underground Service Alert (USA) notified, and the applicable information provided to them. The USA Dig Alert Number for this project is A241230333.

During the subsurface investigation, representative bulk samples and relatively undisturbed samples were collected for laboratory testing, and were forwarded to EGLAB, Inc. (EGL) and to LGC Valley, Inc. for classification testing. Laboratory testing was performed on representative soil samples and included moisture/density, Atterberg Limit, sieve analysis, consolidation, expansion index, direct shear, remolded direct shear, maximum density, sulfate content, chloride content, pH, and minimum resistivity testing. A summary of the test procedures and printouts of the laboratory test results are presented in Appendix C. The moisture and density test results were presented on the boring logs included in Appendix B.

1.5 Existing As-Graded Geotechnical Conditions
Based on our review of available PDF copies of public records obtained from the City of Laguna Hills (see References - Appendix A); a number of different preliminary geotechnical investigations and as-grade reports have been prepared for adjacent properties. However, the preliminary geotechnical investigations and as-grade reports for the subject property (23161 Mill Creek Drive) and the property to the south (23201 Mill Creek Drive) were not available for our review. The findings and conclusions of the available geotechnical reports relative to 23091 Mill Creek Drive (located to the north of the subject site) are discussed below.

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2.0 GEOTECHNICAL CONDITIONS

2.1 Site Geology
Based on our subsurface exploration and review of the available previous geotechnical reports for the property and pertinent geologic literature and maps (Appendix A), the bedrock unit at the site is the Tertiary-aged Sespe Formation. The bedrock is overlain by older artificial fills placed during previous development of the site. The approximate extent of the mapped geologic units present on the site is depicted on the Geotechnical Map (Figure 2). A brief description of the geologic units encountered on the site is presented below.

2.1.1 Artificial Older Fill (Afo)
Based on our review of the available geotechnical reports of the site and the general vicinity, it is our understanding that the on-site existing artificial fills (up to approximately 25+ feet in thickness) were placed and documented by Irvine Soils Engineering, Inc. (1980) and G.A. Nicoll and Associates, Inc. (1986); however, these reports were not available for our review.

Existing artificial fills were encountered in our recent geotechnical borings within the existing parking areas across the site and were found to consist of silty to clayey sands that were slightly moist and medium dense. The depths of the encountered fills ranged from approximately 1 to 5 feet in thickness. Based on the available data, the deeper existing fills are located underlying the existing structure and slope located along the northern portion of the site. Due to the existing site improvements and access issues, this deeper fill was not investigated as a part of this study.

Based on our understanding of the placement/documentation of the existing older fills and our observations and testing of the encountered fills on-site, it is our preliminary conclusion that the existing fills are considered suitable for support of the proposed structures, provided remedial removals are performed of any fills disturbed during site demolition. For confirmation purposes, an additional evaluation of the fill soils (after the existing building is demolished and removed) should be performed. This additional evaluation will need to include surface excavation (drilling), sampling, and laboratory testing to determine the competency of the existing fill soils, and suitability for support of the proposed structures. Additional remedial removal or foundation recommendations will be provided at that time, as necessary.

2.1.2 Tertiary-Aged Sespe Formation (Ts)
Based on our review of geologic maps of the site and general vicinity, the site is underlain by massive to thickly bedded non-marine gray to red pebbly sandstones and silty to clayey sandstones with interbedded siltstones and claystones of the Tertiaryaged Sespe Formation (Morton, Hauser, and Ruppert, 1999; and Morton and Miller,

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2006). The results of our subsurface investigation indicated that the Sespe Formation soils encountered consisted of fine to coarse sandstone, silty and clayey fine to medium sandstone, and sandy to clayey siltstone with little to no pebbles.

2.2 Geologic Structure
Based on our review of geotechnical documents relative to the property directly north of the site, it appears that a large-diameter boring was excavated in the northern portion of the 23161 Mill Creek Drive property in 1986 by G. A. Nicoll and Associates Inc. (Lawmaster & Co, Inc., 1989). The location of the boring (Boring N-B-2) and the bedding attitudes obtained in the boring are shown on Figure 2. This information was obtained from a geotechnical investigation map of 23091 Mill Creek Drive (Lawmaster, 1989). As indicated, the bedding observed in the Sespe Formation ranges from N68W to N65E dipping 5 to 33 degrees to the south. As a result, bedding is dipping into-the-slope and is considered favorable in regard to slope stability. It should be noted that the geotechnical investigation report by G.A. Nicoll and Associates in 1986 that includes the boring log and the description of the subsurface investigation was not available for our review.

2.3 Landslides
Based on our review of aerial photographs and available geotechnical reports for the site, (Appendix A), no evidence of landsliding or other slope instability conditions were observed on-site or noted in the literature. Consequently, the potential for the existence of landslides is considered insignificant.

2.4 Groundwater
Review of available groundwater related internet web sites (Appendix A) indicates that groundwater is likely greater than 50 feet below the ground surface at the site. Groundwater is relatively shallow (generally less than 20 feet below the ground surface) in the large alluvial valley north and northeast of the site. As a result, groundwater is not expected to have a significant impact to the proposed development (provided the recommendations of this report are implemented during the design, grading, and construction of the proposed site improvements).

2.5 Surface Water and Flooding
Based on our review of the existing site grading plans and topography map of the site, sheet flow across the site is to the southeast. Surface water runoff relative to project design is the purview of the project civil engineer and should be directed away from planned structures. Due to the elevation of the site relative to drainages, flooding at the site is considered insignificant.

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2.6 Faulting
The southern California region has long been recognized as being seismically active. The seismic activity results from several active faults that cross the region, all of which are related to the San Andreas transform system, a broad zone of right lateral faults that extend from Baja California to Cape Mendocino. The numerous faults in Southern California include Holocene active, pre-Holocene active, and age-undetermined faults. The definitions of fault activity terms used here are based on those developed for the Alquist-Priolo Special Studies Zone/Earthquake Zone Act of 1972 (CGS, 2018).

Holocene active faults are those faults that have had surface displacement within Holocene time (approximately the last 11,700 years) and have been included within an Alquist-Priolo Earthquake Zone. Pre-Holocene faults have not moved in the last 11,700 years but may be considered potentially active. Age-undetermined faults are faults where the recency of fault movement has not been determined and may likely be considered inactive faults.

The site is not within the currently established Alquist-Priolo Earthquake Fault Zone for fault rupture hazard (formerly Special Studies Zones for fault rupture hazard). Based on a review of geologic literature, no active faults are known to occur beneath or in the general vicinity of the project site. Accordingly, it appears that there is little probability of surface rupture due to faulting beneath the site. There are, however, several faults located in sufficiently close proximity that movement associated with them could cause significant ground motion at the site.

Regional active faults that occur within the Laguna Hills and southern California area include the Newport-Inglewood fault zone to the west and the San Joaquin Hills blind thrust fault, Whittier-Elsinore, San Jacinto, and San Andreas faults to the east. The closest known active faults to the site are the San Joaquin blind thrust Hills fault located approximately 1 mile (1.7 kilometers) to the northeast, the Newport-Inglewood fault zone located approximately 7 miles (11.5 kilometers) to the southwest, and the Elsinore fault zone located approximately 16.5 miles (26.5 kilometers) to the northeast.

The main seismic parameters to be considered when discussing the potential for earthquakeinduced damage are the distances to the causative faults, earthquake magnitudes, and expected ground accelerations. Secondary effects of seismic shaking resulting from large earthquakes on the major faults in the southern California region include soil liquefaction and dynamic settlement. Other secondary seismic effects include shallow ground rupture, seiches and tsunamis. In general, these secondary effects of seismic shaking are a possibility throughout the Southern California region and are dependent on the distance between the site and the causative fault and the on-site geology.

2.7 Seismicity and Related Effects
We have performed site-specific analysis based on these seismic parameters for the site and the on-site geologic conditions. The results of our analysis are discussed in terms of the potential seismic events that could be produced by the maximum probable earthquakes. A

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maximum probable earthquake is the maximum earthquake likely to occur given the known tectonic framework.

2.7.1 Seismic Design Criteria
Based on the 2022 California Building Code (CBC) the site seismic characteristics for the project were evaluated per the guidelines set forth in Chapter 16, Section 1613 of the 2022 CBC. Representative site coordinates for the project site of Latitude

33.625942º N and Longitude -117.735614º W were utilized in our analyses. The maximum considered earthquake (MCE) spectral response accelerations (SMS and SM1) and adjusted design spectral response acceleration parameters (SDS and SD1) for Site Class C are provided in the following table.

Table 1
California Building Code Seismic Design Parameters
Selected Parameters from 2022 CBC, Section 1613 -
Earthquake Loads
Seismic Design
Values
Site Class (per Chapter 20 of ASCE 7) C
Risk-Targeted Spectral Acceleration for Short Periods (SS) 1.223g Risk-Targeted Spectral Accelerations for 1-Second Periods (S1) 0.439g Site Coefficient Fa [per CBC Table 1613.2.3(1)] 1.2
Site Coefficient Fv [per CBC Table 1613.2.3(2)] 1.5
Site Modified Spectral Acceleration for Short Periods (SMS) [Note: SMS = FaSS]

1.467g
Site Modified Spectral Acceleration for 1-Second Periods (SM1) [Note: SM1 = FvS1]

0.659g
Design Spectral Acceleration for Short Periods (SDS)
[Note: SDS = (2/3)SMS]

0.978g
Design Spectral Acceleration for 1-Second Periods (SD1) [Note: SD1 = (2/3)SM1]

0.439g
Seismic Design Category (per CBC Section 1613.2.5) D
Section 1803.5.12 of the 2022 CBC (per Section 11.8.3 of ASCE 7) states that the maximum considered earthquake ground motions, Peak Ground Acceleration (PGA) should be used for the geotechnical evaluations. The PGAM for the site is equal to

0.617g (USGS Seismic Design Maps based on ASCE/SEI 7-16 and ASCE/SEI 7-16 Table 1.5-2).

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A deaggregation of the PGA based on a 2,475-year average return period indicates that an earthquake magnitude of 6.89 at approximately 3.33 km (2.07 mi) from the site would contribute the most to this ground motion (USGS, 2014).

2.7.2 Lurching and Shallow Ground Rupture
Soil lurching refers to the rolling motion on the ground surface by the passage of seismic surface waves. Effects of this nature are not likely to be significant where the thickness of soft sediments do not vary appreciably under structures. Although there are several nearby active and potentially active faults, the native soils are dense, and no active faults are known or interpreted to cross the site. Based on this data, it is our opinion that the potential for lurching or shallow rupture at the site is very low to nil.

2.7.3 Liquefaction and Dynamic Settlement
Liquefaction is a seismic phenomenon in which loose, saturated, granular soils behave similarly to a fluid when subject to high-intensity ground shaking.

Liquefaction occurs when three general conditions exist: 1) shallow groundwater; 2) low density non-cohesive (granular) soils; and 3) high-intensity ground motion.

Liquefaction is typified by a buildup of pore-water pressure in the affected soil layer to a point where a total loss of shear strength occurs, causing the soil to behave as a liquid. Studies indicate that saturated, loose to medium dense, near surface cohesionless soils exhibit the highest liquefaction potential, while dry, dense, cohesionless soils and cohesive soils exhibit low to negligible liquefaction potential.

Effects of liquefaction on level ground include settlement, sand boils, and bearing capacity failures below structures.

Based on the anticipated relative density of the on-site soils and the depth to the static groundwater in the area of the proposed development; it is our opinion that the potential for liquefaction impacting the site is nil, and seismically induced settlements are considered to be negligible.

During a strong seismic event, seismically induced settlement can occur within loose to moderately dense, dry, or saturated granular soil. Settlement caused by ground shaking is often non-uniformly distributed, which can result in differential settlement.

Based on in-situ densities, and soil types, dry sand settlement and induced surface manifestations are not considered an issue at the site.

2.7.4 Tsunamis and Seiches
Due to the elevation of the proposed development at the site with respect to sea level and its distance from large open bodies of water, the potential of seiches and/or tsunami is considered to be very low.

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2.8 Slope Stability
Based on the massive to thickly bedded Sespe Formation on the site, favorable (into-theslope) geologic bedding conditions, and the construction of the proposed segmental geogrid retaining walls along the north and east sides of the property and the block and pile retaining walls along the west and south sides of the property, slope stability is not considered an issue with respect to site development. However, as part of our geotechnical review of the proposed segmental geogrid retaining walls and pile walls, a global slope stability analysis will be performed once the segmental wall designs are completed. The results will be presented in a future retaining wall plan review letter.

2.9 Expansion Potential
Expansion potential testing of representative on-site soil samples indicates that the on-site soils have a very low to low expansion potential (Appendix C). Although some of the near surface soils (Sespe Formation claystone layers) may have a medium to high expansion potential, we would anticipate the mixture and redistribution of site soils will result in a low expansion potential for the site. The as-graded soil conditions of the proposed building pads should be verified with confirmatory observation, sampling, and testing after site grading is completed and prior to the construction of the structures.

2.10 Soluble Sulfate and Corrosivity of the On-Site Soils Laboratory testing of representative on-site soils indicated the on-site soils tested had soluble sulfate contents that ranged from 0.005 to 0.007 percent (Appendix C). As a result, the on-site soils should be considered to have a negligible degree of corrosivity to concrete and have an Exposure Class of S0 in accordance with ACI 318R-14 Table 19.3.1.1. The as-graded sulfate content of the finish grade soils on the building pads should be verified upon completion of grading.

Minimum resistivity, pH, and chloride content tests were also performed on two representative soil samples obtained during our subsurface investigation. These corrosion tests resulted in a minimum resistivity of 1,300 to 1,700 ohm-centimeters, a pH of 7.82 to

8.15, and a chloride content of 125 to 140 ppm (Appendix C). Based on these results, the onsite soils should be considered moderately corrosive to buried metals in contact with the onsite soils.

2.11 Excavation Characteristics
The site is underlain by near surface soils consisting of silty fine to coarse sands, clayey to fine sandy silts, silty clay, siltstone/claystone, and sandstone layers. It is anticipated that the on-site materials can be excavated with conventional heavy-duty construction equipment and that difficult excavation and/or blasting is not anticipated. In addition, the anticipated site excavation and the proposed construction will not have an adverse impact on the adjacent properties.

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2.12 Earthwork Shrinkage and Bulking
The volume change of excavated on-site materials upon recompaction as fill is expected to vary with materials and location. Typically, the surficial soils and bedrock materials vary significantly in natural and compacted density, and therefore, accurate earthwork shrinkage/bulking estimate cannot be determined. However, the following factors (based on the results of our subsurface investigation and previous investigations of the site, laboratory testing, geotechnical analysis, and professional experience on nearby sites) are provided in Table 2 as guideline estimates. If possible, we suggest an area where site grades can be adjusted be provided as a balance area.

Table 2
Earthwork Shrinkage and Bulking Estimates
Geologic Unit Estimated
Shrinkage/Bulking
Artificial Fill and upper 1 to 2 feet of the site 3 to 7 percent shrinkage Sespe Formation 0 to 5 percent bulking

2.12 Stormwater Infiltration/Percolation
Based on our understanding of site development, on-site storm water will flow into proprietary underground biofiltration BMP structures that will treat the storm water and then discharge it into the on-site storm drain system that is connected to the storm drain system in Mill Creek Drive. We also understand that site infiltration is not currently proposed.

However, a future percolation/infiltration study may be required to determine the feasibility of storm water subsurface infiltration for the site.

Our limited subsurface investigation of the site that was performed on May 8, 2024 and consisted of the excavation, sampling, and logging of six small diameter hollow-stem borings excavated to depths ranging from approximately 10.5 to 20.5 feet, indicated the near surface soils consist of fill soils and Tertiary-Aged Sespe Formation. As encountered, the Sespe Formation soils consisted of fine to coarse sandstone, silty and clayey fine to medium sandstone, and sandy to clayey siltstone with little to no pebbles. Based on our professional experience with similar soils, infiltration of these sandy soils are likely feasible; however, the results will likely have a relatively low infiltration rate (slightly above the typical minimum required rate of 0.5 inches per hour). Infiltration into the fill soils and along the north, northeast, and east sides of the site are not recommended due to the presence of descending slopes, large retaining walls, and fill soils that will have a reduced factor-of-safety as the result of subsurface groundwater.

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Once the final storm water infiltration design is determined for the site, a percolation/infiltration study (in accordance with the City of Laguna Hills/County of Orange requirements) should be performed to determine the actual percolation/infiltration rate(s) at the proposed storm water infiltration locations and appropriate factor-of-safeties.

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3.0 CONCLUSIONS
Based on the results of our geotechnical investigation, evaluation, and review; it is our professional opinion that the proposed site development is feasible from a geotechnical standpoint, provided the recommendations included in this report are incorporated into the project plans and specifications, and followed during site grading and construction. Our geotechnical conclusions are as follows:
 Review of available aerial photographs, historical Google Earth images, old topography maps, and geotechnical reports of adjacent properties (Appendix A) indicate that the site (and general vicinity) was rough graded in the early 1980’s and the site was precise graded in 1986. The asgraded geotechnical reports and grading plans specific to 23161 Mill Creek were not available at the City of Laguna Hills; and consequently were not reviewed by us.  Based on our subsurface exploration and review of the available previous geotechnical reports for the property and pertinent geologic literature and maps, the bedrock unit at the site is the Tertiaryaged Sespe Formation that is overlain by artificial older fills. The fill soils are a mixture of silty to clayey sands, silty fine to coarse sands, clayey to fine sandy silts, and silty clay. The Sespe Formation generally consisted of massive to thickly bedded fine to coarse sandstone, silty and clayey fine to medium sandstone, and sandy to clayey siltstone with little to no pebbles. The fill soil layers encountered in our current geotechnical investigation were found to be competent and suitable for support of proposed structures, provided the recommendations of this report are followed during site grading and construction.
 After the removal of the existing buried underground utilities has been made, the trench locations should be surveyed, and the excavations should be replaced with fill soils compacted to a minimum 90 percent relative compaction (based on ASTM D1557). Where these trenches are located within the limits of the proposed multi-family building foundation footprints, special consideration should be made as the majority of the site is cut and the trenches will create cut/fill transition conditions.

Mitigation measures may include overexcavation of the upper 5 feet of the pad and replacement with compacted fill or backfilling the trenches with a 2-sack sand/cement slurry.  The existing on-site soils appear to be suitable material for use as fill provided, they are relatively free of rocks (larger than 8 inches in maximum dimension), organic material, and debris.
 The on-site formational material is anticipated to be massive to thickly bedded. The bedding observed in the Sespe Formation ranges from N68W to N65E dipping 5 to 33 degrees to the south (Lawmaster & Co, Inc., 1989). As a result, bedding is dipping into-the-slope and is considered favorable in regard to slope stability.
 There are no known landslides or other slope instability issues impacting the site.  Review of available groundwater related internet web sites (Appendix A) indicates that groundwater is likely greater than 50 feet below the ground surface at the site. Groundwater was not encountered during our recent subsurface investigation. Consequently, groundwater is not expected to have an impact on the proposed development.

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 Based on the topography of the site, surface water is anticipated to flow across the sheet-graded pad from the west to southeast.
 Due to the elevation of the site relative to existing drainages, flooding at the site is not considered an issue for the site.
 Active or potentially active faults are not known to exist on the site.  The site is not located within the Alquist-Priolo Earthquake Fault Zone (CGS, 2018). The closest known Holocene active faults to the site are the San Joaquin blind thrust Hills fault located approximately 1 mile (1.7 kilometers) to the northeast, the Newport-Inglewood fault zone located approximately 7 miles (11.5 kilometers) to the southwest, and the Elsinore fault zone located approximately 16.5 miles (26.5 kilometers) to the northeast.  The main seismic hazard that may affect the site is ground shaking from one of the active regional faults.
 Based on the relatively dense nature of the proposed compacted fill soils and existing formational material and lack of a permanent shallow groundwater condition, liquefaction and/or dynamic settlement at the site is considered very low to nil.
 Due to the elevation of the proposed development at the site with respect to sea level and its distance from large open bodies of water, the potential of seiches and/or tsunami is considered to be nil.
 Based on the massive to thickly bedded Sespe Formation on the site, generally favorable geologic bedding conditions, and the construction of the proposed segmental geogrid retaining walls along the north and west sides of the property, slope stability is not considered an issue with respect to site development. However, as part of our geotechnical review of the proposed geogrid retaining walls and pile walls, a global slope stability analysis will be performed once the wall designs are completed. The results will be presented in a future retaining wall plan review letter.
 Expansion potential testing of representative samples of the on-site soils indicate those soils have a very low to low expansion potential (Appendix C). Although some of the near surface soils may have a medium to high expansion potential, most of the soils on the site have a low expansion potential. The as-graded soil conditions of the proposed building pads should be verified with confirmatory observation, sampling, and testing after site grading is completed and prior to the construction of the structures.
 Laboratory testing of representative on-site soils indicated the on-site soils should be considered to have a negligible degree of corrosivity to concrete and have an Exposure Class of S0 in accordance with ACI 318R-14 Table 19.3.1.1.
 Minimum resistivity, pH, and chloride content tests were also performed on the two representative soil samples obtained during our subsurface investigation and these results indicate the on-site soils should be considered moderately corrosive to buried metals in contact with the on-site soils.

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 It is anticipated that the on-site materials can be excavated with conventional heavy-duty construction equipment and that difficult excavation and/or blasting is not anticipated.  The anticipated site excavation and the proposed construction will not have an adverse impact on the adjacent properties.
 The multi-family residential structures may be designed to be supported by post-tension or mat foundation systems.
 In order to reduce the potential for differential settlement in areas of cut/fill transitions, we recommend the upper 5 feet of the building pad be overexcavated and replaced with properly compacted fill to mitigate the transition condition beneath the proposed structure. This condition is likely along the north and west sides of the property, where existing buried utility lines that are abandoned and the trenches replace with compacted fill, and possibly in the eastern portion of the site along the property boundary.
 Based on our professional experience with similar soils, infiltration of the on-site sandy formational soils are likely feasible; however, a percolation/infiltration study (in accordance with the City of Laguna Hills/County of Orange requirements) should be performed to determine the actual percolation/infiltration rate(s) at the proposed storm water infiltration locations and appropriate factor-of-safeties.

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4.0 RECOMMENDATIONS

4.1 Site Earthwork
We anticipate that earthwork at the site will consist of site preparation and remedial grading and construction of site perimeter retaining walls followed by construction of the proposed slab-on-grade type foundations and associated improvements. We recommend that earthwork on-site be performed in accordance with the recommendations herein, the City of Laguna Hills grading requirements, and the General Earthwork and Grading Specifications for Rough Grading included in Appendix E. In case of conflict, the recommendations in the following sections shall supersede those included as part of Appendix E.

4.1.1 Site Preparation
Prior to grading of the area to receive structural fill or engineered structures, the ground surface should be cleared of obstructions, debris, potentially compressible material (such as undocumented fill soils, dry, disturbed, or desiccated documented fill and formational material and stripped of vegetation). Vegetation and debris should be removed and properly disposed of offsite. Holes resulting from the removal of buried obstructions or utilities, which extend below finished site grades, should be replaced with suitable compacted fill material. Areas to receive fill and/or other surface improvements should be scarified to a minimum depth of 6 inches, brought to a nearoptimum moisture condition, and recompacted to at least 90 percent relative compaction (based on American Standard of Testing and Materials [ASTM] Test Method D1557).

4.1.2 Removal and Recompaction
The upper portion of the site is underlain by potentially compressible/collapsible or unsuitable soils (i.e., desiccated existing fills, and formational material) which may settle under the addition of water, under the surcharge of fill, and/or foundation loads.

Compressible materials not removed by the planned grading should be excavated to competent material (as determined by the geotechnical consultant) and replaced with compacted fill soils. From a geotechnical perspective, soil that is removed may be placed as fill provided the material is relatively free from rocks (greater than 8-inches in maximum dimension), organic material and construction debris; is moistureconditioned or dried (as needed) to obtain above-optimum moisture content; and then recompacted prior to additional fill placement or construction.

All disturbed or desiccated fills underlying or within the influence of the proposed development should be removed to competent soils. The actual depth and extent of the required removals should be determined during grading operations by the geotechnical consultant; however, the estimated remedial removals are as follows:
we anticipate removals of up to 3 feet below existing grades; however, localized, deeper removals should be anticipated where deemed necessary by the geotechnical consultant based on observations during grading.

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4.1.3 Cut/Fill Transition Condition
In order to reduce the potential for differential settlement of proposed buildings located across cut/fill transitions, we recommend the entire cut portion of the transition building pads be overexcavated to a minimum depth of 5 feet and replaced with properly compacted fill to mitigate the transition condition beneath the proposed structure; or the building foundations deepened so that all foundation footings are founded on formational material. Where existing buried utility lines that will be abandoned are located with the limits of the proposed building foundation footprint, special consideration should be made as the majority of the site is likely cut and the trenches will create cut/fill transition conditions. Mitigation measures may include overexcavation of the upper 5 feet of the pad and replacement with compacted fill or backfilling the trenches with a 2-sack sand/cement slurry.

4.1.4 Shrinkage/Bulking
Based on the encountered site soils; the existing fills and upper 1 to 2 feet of the site is anticipated to shrink while the formational materials are anticipated to bulk. The preliminary estimated shrinkage and bulking factors are presented in Table 2 (in Section 2.12 of this report). The value ranges are preliminary rough estimates which will vary with depth of removal, stripping losses, field conditions at the time of grading, etc. In addition, handling losses is not included in the estimates. If possible, we suggest an area where site grades can be adjusted be provided as a balance area.

4.1.5 Temporary Excavation Stability
In general, all excavations should be performed in accordance with project plans, specifications, and all Occupational Safety and Health Administration (OSHA) requirements. Excavations should be laid back or shored in accordance with OSHA requirements before personnel or equipment are allowed to enter. Soil conditions should be mapped and frequently checked by a representative of LGC to verify conditions are as anticipated. The contractor shall be responsible for providing the “competent person” required by OSHA standards to evaluate soil conditions. Close coordination with the geotechnical engineer should be maintained to facilitate construction while providing safe excavations. Excavation safety is the responsibility of the contractor.

Temporary excavations may be cut vertically up to five feet. Excavations over five feet should be slot-cut, shored, or cut no steeper than 1:1 (horizontal to vertical) slope gradient. If a block wall along the western property line adjacent to the existing off -site building is planned, shoring of the western property line will need to be provided to for support of the wall backcut and to maintain lateral support for the off-site structure.

Surface water should be diverted away from any exposed cut, and not be allowed to pond on top of the excavations. Temporary cuts should not be left open for an extended period of time. Planned temporary conditions should be reviewed by the geotechnical consultant of record in order to reduce the potential for sidewall failure. The geotechnical consultant may provide recommendations for controlling the length of sidewall exposed.

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4.1.6 Temporary Shoring
The following preliminary geotechnical parameters may be utilized by the shoring consultant for design of the temporary shoring system along the southern property boundary, as necessary. Temporary shoring is generally considered to have a service life of two years or less. The geotechnical conditions outside of the perimeter of the proposed site have not been investigated as part of this report. The recommendations provided herein with regard to shoring of the proposed excavation are based on assumed conditions, extrapolated from the data gathered from our review of the subject site and adjacent sites. The shoring designer should independently evaluate the parameters provided and conduct an additional investigation if they consider necessary.

Prior to construction, the contractor should verify underground clearance of any existing utility lines or structures that must be removed or protected in place during construction, or may conflict with any proposed shoring system. Any tieback anchors and/or soil nails that extend beyond the site property limits will require permission from the adjacent property owner. Special attention will be required to protect existing settlement sensitive improvement in close proximity to the proposed excavation, such as any adjacent structures or streets located along the boundary of the site.

Typical cantilever temporary shoring, where deflection of the shoring will not impact the performance of adjacent structures or streets, may be designed using the active equivalent fluid pressures of 40 pounds per square foot (psf) per foot of depth (or pcf) for a level condition, and a 50 pcf for a 2:1 (horizontal to vertical) sloping condition.

Braced (i.e. internal bracing -rakers) or tied-back shoring is recommended in areas where the shoring will be located close to existing structures or streets in order to limit shoring defections or required due to the proposed depth of excavation. Braced or tied-back shoring with a level backfill may be designed using an active trapezoidal soil pressure of 24H in pounds per square foot (psf) per foot of depth (or pcf) for level condition and 30 pcf for a 2:1 (horizontal to vertical) sloping condition, where H is equal to the depth in feet of the excavation being shored (shape of the trapezoid should be 0.2H, 0.6H, 0.2H).

Any building, equipment, or traffic loads located within a 1:1 (horizontal to vertical) projection from the base of the shoring should be added to the applicable lateral earth pressure. A minimum additional uniform lateral pressure of 100 psf for the upper 10 feet should be added to the appropriate lateral earth pressures to account for typical vehicle traffic loading. The proposed shoring should be designed for a maximum shoring deflection of up to 1-inch adjacent to the street (non-surcharged condition) and up to a maximum of 0.5-inches adjacent to existing buildings (surcharged condition).

Surcharge loads on basement walls and shoring systems from existing structures located within the 1:1 (h:v) surcharge influence zone of the excavation, shoring, and basement should be determined and considered in the design.

If temporary gravity grouted tie-backs are used anchors may be designed using a preliminary bond stress of 400 pounds per square foot (psf), and if pressure/postgrouted tieback anchors are used, anchors may be designed using a preliminary bond

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stress of up to 2,500 pounds per square foot (psf). However, the tieback designer should make an independent evaluation in order to verify the preliminary bond stress is adequate for site conditions. Tieback bond stress should be verified by field testing.

Tieback anchors should be designed, constructed, and tested in accordance with the requirements of the Post-Tensioning Institute (PTI).

For design purposes, tieback should obtain their load-carrying capacity from the soil behind a plane taken to be 3 horizontal feet from the bottom of the shoring facing and inclined at an angle of 60 degrees measured from the horizontal extending to the top of the excavation. Passive resistance of soldier piles (drilled or driven) may be assumed to be an equivalent fluid pressure of 350 pcf to a maximum value of 3,500 psf. The passive earth pressure may be increased by 100 percent for isolated piles. Piles with spacing greater than 3 times of pile diameter can be considered as isolated piles. In order to develop full lateral resistance, firm contact between the soldier pile and undisturbed soils must be assured. For vertical shoring capacity, an allowable skin friction of 500 psf may be used for the portion of pier below the proposed development excavation.

End bearing should be neglected. Drilling of shafts for solider piles may require casing or drilling mud to prevent caving.

Due to the nature of the site soils, it is expected that continuous lagging between soldier piles will be required. The time between lagging excavation and lagging placement should be as short as possible. Soldier piles should be designed for the full-anticipated pressures. Due to arching in the soils, the pressure on the lagging will be less. However, it is recommended that the lagging be designed for the full design active fluid pressure but be limited to a maximum of 400 psf. Therefore, the design lagging pressure should consider a parabolic earth pressure distribution with an active equivalent fluid pressure of 40 pounds per square foot (psf) per foot of depth (or pcf) up to a maximum of 400 psf. The maximum span for lagging for this project should be 10 feet.

The components of the shoring system should be designed by a California licensed structural and/or civil engineer specializing in the design of shoring systems. Field pullout testing should be performed during construction to verify the estimated pullout resistance used in the design and/or post grout tubes should be used to ensure adequate design capacities are obtained. Ultimately, it is the specialty contractor’s responsibility to obtain the required pullout capacity, which may require design and/or field modifications. LGC should review the shoring plans prior to construction to verify that geotechnical recommendations are properly implemented into the project plans.

It is highly recommended that a program of documentation and monitoring be devised and put into practice before the onset of any groundwork. The contractor should establish survey points on the shoring, adjacent streets, and neighboring buildings within 100 feet of the excavation perimeter prior to any excavation. These survey points should be used to monitor the movement of the shoring and existing improvements during construction excavation.

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The monitoring program should include, but not necessarily be limited to detailed documentation of the existing improvements, buildings and utilities around the excavation, with particular attention to any distress that is already present prior to the start of work. A licensed surveyor should be retained to establish monuments on the shoring and the surrounding ground prior to excavation. Such monuments should be monitored for horizontal and vertical movement during construction. Results of the monitoring program should be provided immediately to the project structural (shoring) engineer and LGC for review and evaluation.

4.1.7 Fill Placement and Compaction
From a geotechnical perspective, the on-site soils are suitable for use as compacted fill, provided they are screened of rocks greater than 8-inches in maximum dimension, organic material, and construction debris. Areas prepared to receive structural fill and/or other surface improvements should be scarified to a minimum depth of 6-inches, brought to at least optimum-moisture content, and recompacted to at least 90 percent relative compaction (based on ASTM Test Method D1557). The optimum lift thickness to produce a uniformly compacted fill will depend on the type and size of compaction equipment used. In general, fill should be placed in uniform lifts generally not exceeding 8-inches in loose thickness. Placement and compaction of fill should be performed in accordance with local grading ordinances under the observation and testing of the geotechnical consultant.

If possible, imported soils should contain no materials over 3- to 8-inches in maximum dimension and have a very low to low expansion potential.

4.1.8 Trench Backfill and Compaction
The on-site soils may generally be suitable as trench backfill provided, they are screened of rocks and other material over 3- to 6-inches in diameter and organic matter.

Trench backfill should be compacted in uniform lifts (generally not exceeding 8-inches in compacted thickness) by mechanical means to at least 90 percent relative compaction (per ASTM Test Method D1557).

If trenches are shallow and the use of conventional equipment may result in damage to the utilities; clean sand, having sand equivalent (SE) of 30 or greater, should be used to bed and shade the utilities. Sand backfill should be densified. The densification may be accomplished by jetting or flooding and then tamping to ensure adequate compaction.

A representative from LGC should observe, probe, and test the backfill to verify compliance with the project specifications.

4.2 Foundation Design

4.2.1 General Foundation Selection
Recommendations for preliminary foundation design and construction are presented

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herein. Based on the results of representative expansion potential laboratory testing of the representative on-site soils, the proposed structures should be designed for a low or medium expansion potential (i.e., a 20 to 90 Expansion Index). The following post-tension and mat slab foundation recommendations are provided.

The information and recommendations presented in this section are not meant to supersede design by the project structural engineer or civil engineer specializing in the structural design nor impede those recommendations by a corrosion consultant. Should conflict arise, modifications to the foundation design provided herein can be provided.

4.2.2 Bearing Capacity
Shallow foundations may be designed for a maximum allowable bearing capacity of 2,000 lb/ft2(gross), for continuous footings a minimum of 18-inches wide and 12- inches deep; and spread footings 24-inches wide and 18-inches deep, into certified compacted fill or competent formational material. A factor of safety greater than 3 was used in evaluating the above bearing capacity value. This value may be increased by 300 psf for each additional foot in depth and 150 psf for each additional foot of width to a maximum value of 4,000 psf.

Lateral forces on footings may be resisted by passive earth resistance and friction at the bottom of the footing. Foundations may be designed for a coefficient of friction of

0.35, and a passive earth pressure of 250 lb/ft2/ft. The passive earth pressure incorporates a factor-of-safety of greater than 1.5.

All footing excavations should be cut square and level as much as possible, and should be free of sloughed materials including sand, rocks and gravel, and trash debris. Subgrade soils should be pre-moistened for the assumed medium or high expansion potential (to be confirmed at the completion of grading). These allowable bearing pressures are applicable for level (ground slope equal to or flatter than 5:1[horizontal to vertical]) conditions only.

Bearing values indicated above are for total dead loads and frequently applied live loads. The above vertical bearing may be increased by one-third for short durations of loading which will include the effect of wind or seismic forces.

4.2.3 Post-Tension Foundation
Based on our review, the site may be considered suitable for the support of the proposed structure using a post-tensioned slab-on-grade foundation system for the anticipated low to medium expansion potential. The following section summaries our recommendations for the foundation system. Table 3 contains the geotechnical recommendations for the construction of a PT slab-on-grade foundation. The structural engineer should design the foundation system based on these parameters including the foundation settlement as indicated in the following section to the allowable deflection criteria determined by the structural engineer/architect.

As indicated above, the underslab vapor/moisture retarder (i.e., an equivalent

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capillary break method) may consist of a minimum 15-mil vapor barrier in conformance with ASTM E 1745 Class A material, placed in general conformance with ASTM E1643, underlain by a minimum 1-inch of sand, as needed. The sand layer requirements above the vapor barrier are the purview of the foundation engineer/structural engineer and should be provided in accordance with ACI Publication 302 “Guide for Concrete Floor and Slab Construction”. These recommendations must be confirmed (and/or altered) by the foundation engineer, based upon the performance expectations of the foundation. Ultimately, the design of the moisture retarder system and recommendations for concrete placement and concrete mix design, which will address bleeding, shrinkage, and curling are the purview of the foundation engineer, in consideration of the project requirements provided by the architect and developer. The underslab vapor/moisture retarder described above is considered a suitable alternative in accordance with the Capillary Break Section 4.505.2.1 of the CAL Green code.

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Table 3
Preliminary Geotechnical Parameters for Post-Tensioned Foundation Design Parameter Value
Expansion Classification (Assumed to be confirmed at
the completion of grading): Low and Medium Expansion
Thornthwaite Moisture Index (from Figure 3.3): -20
Constant Soil Suction (from Figure 3.4): PF 3.6
Center Lift
Edge moisture variation distance (from Figure 3.6), em:

Center lift, ym:

Low

9.0 feet

0.35 inches
Medium

9.0 feet

0.5 inches
Edge Lift
Edge moisture variation distance (from Figure 3.6), em:

Edge lift, ym:

Low

5.2 feet

0.65 inches
Medium

5.0 feet

1.1 inches
Expansion Potential: Low
(21-50)
Medium
(51-90)
Soluble Sulfate Content for Design of Concrete Mix in
Contact with Site Soils in Accordance with American
Concrete Institute Standard 318, Section 4.3:

Negligible Exposure
(Exposure Class S0)
Corrosivity of Earth Materials to Ferrous Metals: Corrosive Modulus of Subgrade Reaction, k (assuming
presaturation as indicated below):
100 pci (low)
85 pci (medium to high)
Additional Recommendations:

1. Presaturate slab subgrade to at least 1.2 times optimum moisture to minimum depth of 12 for low expansion potential and at least 1.2 times optimum moisture to a minimum depth of 18 inches below ground surface for medium expansion potential.

2. Install a 15-mil moisture/vapor barrier in direct contact with the concrete (unless superseded by the Structural/Post-tension Engineer*) with minimum 1 inches of sand below the moisture/vapor barrier.

3. Minimum perimeter foundation embedment below finish grade for moisture cut off should be 12 and 18 inches, respectively for low and medium expansion potentials, respectively.

4. Minimum slab thickness should be 5 inches.
* The above sand and moisture/vapor barrier recommendations are traditionally included with geotechnical foundation recommendations although they are generally not a major factor influencing the geotechnical performance of the foundation. The sand and moisture/vapor barrier requirements are the purview of the foundation engineer/corrosion engineer (in accordance with ACI Publication 302 “Guide for Concrete Floor and Slab Construction”) and the homebuilder to ensure that the concrete cures more evenly than it would otherwise, is protected from corrosive environments, and moisture penetration of through the floor is acceptable to future homeowners. Therefore, the recommendations provided herein may be superseded by the requirements of the previously mentioned parties.

4.2.4 Mat Foundations
A mat foundation can be used for support of proposed residential buildings. An

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allowable soil bearing pressure of 1,500 psf may be used for the design of the mat at the surface under the slab area.
for the design of the mat at the surface under the slab area.

The allowable bearing value is for total dead loads and frequently applied live loads and may be increased by one-third for short durations of loading which will include the effect of wind or seismic forces. A coefficient of vertical subgrade reaction, k, of 85 pounds per cubic inch (pci) may be used to evaluate the pressure distribution beneath the mat foundation.

The magnitude of total and differential settlements of the mat foundation will be a function of the structural design and stiffness of the mat. Based on assumed structural loads, we estimate that total static settlement will be on the order of an inch at the center of the mat foundation. Post construction differential settlement can be taken as one-half of the maximum estimated settlement.

Resistance to lateral loads can be provided by friction acting at the base of foundations and by passive earth pressure. Foundations may be designed for a coefficient of friction of 0.35.

Coordination with the structural engineer will be required in order to ensure structural loads are adequately distributed throughout the mat foundation to avoid localized stress concentrations resulting in potential settlement. The foundation plan should be reviewed by LGC to confirm preliminary estimated total and differential static settlements.

4.2.5 Foundation Settlement
Based on our current understanding of the project, the results of our site investigation and the recommended remedial grading with shallow foundations embedded into compacted fills or competent bedrock, we estimate the post-construction static settlement of the site to be less than 1-inch with a differential settlement of approximately of 0.5-inches in 30 feet.

For buildings located above the proposed segmental wall, with a portion of the building underlain by the geogrid reinforced soils, the proposed foundation should be designed for a minimum of a medium expansion potential and for a differential settlement of up to 2-inches in 30 feet. Recommendations to reduce the potential for differential settlements in the vicinity of the segmental walls are provided herein in Section 4.4.

4.2.6 Building Clearance and Foundation Setbacks
All building foundations located close to slopes should have a minimum setback per Figure 1808.7.1 of the 2022 CBC. The setback distances should be measured from competent materials on the outer slope face, excluding any weathered and loose materials.

Per the 2022 CBC Section 1808.7.1 and Figure 1808.7.1, building clearance from the

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toe of an ascending slope should be equal one-half of the total slope height to a maximum setback of 15 feet. Retaining walls may be constructed at the base of the slope to achieve the required building clearances.

Per the 2022 CBC Section 1808.7.2 and Figure 1808.7.1, the building foundation constructed on or near a descending slope should be setback or deepened to provide a minimum footing setback equal to the total height of slope (H) divided by 3 (H/3).

The footing setback should be a minimum of 5 feet for slopes up to 15 feet in height and vary up to 40 feet for slopes up to 120 feet in height. The footing setbacks should be measured from the edge of the footing to the competent materials on the outer slope face.

4.3 Lateral Earth Pressures for Retaining Walls
The following lateral earth pressures may be used for the design of any future site retaining walls. Due to the expansive nature of some of the on-site clayey formational materials, we recommend site retaining walls be backfilled with either the very low expansive bedrock or sandy soils (with minus 3-inch rock) or approved select soils. Approved select soils should consist of clean, granular soils (less than 15 percent passing the No. 200 sieve) of very low expansion potential (expansion index 20 or less based on UBC. 18-2). The recommended lateral pressures for approved select soils for level or sloping backfill are presented in Table 4.

Table 4
Lateral Earth Pressures for Retaining Walls
Conditions
Equivalent Fluid Weight (pcf)
Level Backfill 2:1 Backfill Sloping
Upwards Dynamic Load
Increment
(pcf) * Approved Select
Material
Approved Select
Material
Active 35 50 Level -10H
2 2H:1V - 17H
2 At Rest 55 80 16H
2 Passive 250 -- --
* For walls with greater than 6-feet in backfill height, the above seismic earth pressure should be added to the static pressures given in the table above. The seismic earth pressure should be considered as a triangular distribution with the resultant acting at 0.4H in relation to the base of the retaining wall footing (where H is the retained height). The incremental seismic load was determined in general accordance with the standard of practice in the industry for determining earth pressures as a result of seismic events.

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For design purposes, the recommended equivalent fluid pressure for each case for walls founded above the static ground water and backfilled with approved select soils is provided in Table 4. The equivalent fluid pressure values assume free-draining conditions. If conditions other than those assumed above are anticipated, the equivalent fluid pressure values should be provided on an individual-case basis by the geotechnical engineer. Surcharge loading effects from the adjacent structures should be evaluated by the geotechnical and structural engineers.

Retaining wall structures should be provided with appropriate drainage and appropriately waterproofed. The outlet pipe should be sloped to drain to a suitable outlet. Typical wall drainage design is illustrated in Figure 3. It should be noted that the recommended subdrain does not provide protection against seepage through the face of the wall and/or efflorescence.

Efflorescence is generally a white crystalline powder (discoloration) that results when water, which contains soluble salts, migrates over a period of time through the face of a retaining wall and evaporates. If such seepage or efflorescence is undesirable, retaining walls should be waterproofed to reduce this potential.

Lateral earth pressures are provided as equivalent fluid unit weights, in psf/ft of depth or pcf.

These values do not contain an appreciable factor of safety. A soil unit weight of 120 pcf may be assumed for calculating the actual weight of soil. For sliding resistance, a friction coefficient of 0.35 may be used at the concrete and soil interface. Wall footings should be designed in accordance with structural considerations. Refer to Section 4.2.2 for passive resistance and allowable soil bearing.

4.4 Segmental Retaining Wall Recommendations
Segmental retaining walls that may be constructed on the site are anticipated to have a level or up to a 2:1 (horizontal to vertical) sloping backfill above the walls. The zone of influence for geogrid-reinforced modular block walls is defined by a 1:1 (horizontal to vertical) projection from the heel of the bottom geogrid to the finished ground surface overlying the wall. Any building or vehicle loads within this zone should be considered in the wall design.

The following geotechnical parameters presented in Table 5 may be utilized by the wall engineer in design of the on-site segmental walls. Design of segmental retaining walls should be per the National Concrete Masonry Association (NCMA) guidelines (or equivalent guidelines).

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Table 5
Design Soil Strength Parameters for Segmental Retaining Walls Cohesion (psf)
Friction Angle
Peak/Ultimate
(Degrees)
Unit Weight (pcf)
Infill (Reinforced) Soil 50 35/30 120
Retained (Backfill) Soil 100 35/30 120
Foundation Soil 100 35/30 120
The design acceleration of 0.411g (or 2/3 PGAm), should be used for the proposed design. A Pseudo-Static Coefficient of 0.28g should be used for Slope Stability Analysis. Once the wall designer designs the wall considering external, internal, and local wall stability, LGC will then check the global slope stability. Where global slope stability is the controlling factor, additional geogrid will be added to the design and/or the geogrid will be lengthened, as needed. Thus, the final design is expected to satisfy both the “conventional method” of modular wall design as well as global slope stability.

All excavations should be made in accordance with Cal OSHA, as a general guideline. The backfill soils (having an expansion index less than 30 per UBC. 18-I-B) should be compacted to at least 90 percent relative compaction (based on ASTM Test Methods D2922 and D3017). The walls should be constructed and backfilled as soon as possible after back-cut excavation.

Prolonged exposure of back-cut slopes may result in some localized slope instability.

Excavation safety is the sole responsibility of the contractor.

The subject walls may be backfilled using the on-site native soils. For closed face walls we recommend a minimum 1-foot-wide drainage gallery be constructed immediately behind the face of the wall using Class II Permeable material and augmented with a perforated 4-inch PVC pipe, or per the wall manufactures specifications. This drainage layer and drain is not a requirement for open faced walls. The remainder of the wall may be backfilled using the onsite native soils. The subject segmental retaining walls should be constructed founded onto competent soils (i.e., compacted fills or competent native soils), or per manufactures specifications. For preliminary purposes, the allowable bearing capacities to be used in the wall design is 1,500 pounds per square foot.

From a geotechnical perspective, the on-site soils are generally suitable for use as compacted fill, provided they are screened of rocks greater than 8 inches in maximum dimension, organic materials, and construction debris. Fill soils should be brought to at least optimum-moisture content, and recompacted to at least 90 percent relative compaction (based on ASTM Test Method D1557). The optimum lift thickness to produce a uniformly compacted fill will depend on the type and size of compaction equipment used. In general, fill should be placed in uniform lifts generally not exceeding 8 inches in compacted thickness. Placement and compaction of fill should be performed in accordance with local grading ordinances under full-time observation

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and testing of the geotechnical consultant. The geotechnical consultant shall review and approve all fill materials, including on-site and import materials.

Prior to placement of the geogrid, the surface of the compacted fill shall be prepared such that it has a maximum variation of 6 vertical inches over a distance of 15 feet. Each geogrid layer shall be pulled taut and secured in-place prior to placing backfill material on the geogrid. The geogrid layers shall be continuous and no splice and/or connection system will be accepted. The contractor shall not operate tracked construction equipment directly upon the geogrid reinforcement but shall use rubber tired equipment. All passes with tracked equipment for the purposes of obtaining compaction shall be done in straight lines and shall minimize the turning movements of the equipment to reduce the potential for displacing and/or damaging the geo-grids.

The manufacturer shall provide the owner with quality control testing for each lot of blocks which are shipped to the site. The contractor shall install the block per the manufacturer’s recommended procedures.

All excavations should be made in accordance with Cal OSHA, as a general guideline. All excavations should be made at 1:1 inclinations or flatter. Once excavation has been initiated, the segmental retaining wall should be constructed as soon as possible after back-cut excavation. Prolonged exposure of back-cut slopes may result in some localized slope instability. Excavations should be planned so that they are not initiated without sufficient time to backfill them prior to weekends, holidays, or forecasted rain. Excavation safety is the sole responsibility of the contractor.

We recommend the contractors proposed plan of operations be reviewed by this office prior to initiation of work and closely monitored by representatives of this office during excavation and construction.

A backdrain should be installed at the heel of the wall back-cut consisting of a 4-inch PVC pipe surrounded by ¾-inch crushed rock and wrapped in a filter fabric and outletted through the wall face or to another suitable outlet. If water seepage is encountered along the wall back-cut, a continuous chimney drain consisting of a one-foot layer Caltrans Class II permeable material shall be placed at the heel along the back-cut behind the geogrid, as necessary. The chimney drains should be outletted through the backdrain at the heel of the cut. The outlet pipes should be constructed at the low points of the subdrains and have a minimum 2 percent fall to the outlet location. Additional subdrains may be needed if seepage and/or areas of potential seepage are encountered during grading operations.

Positive drainage of surface water away from the base and top of the proposed segmental retaining walls are important. A concrete V-ditch shall be constructed behind the top of each of the proposed walls to prevent surface water from infiltrating the backfill soil. The V-ditch shall be designed and placed by the project civil engineer in accordance with the local codes.

Where proposed residential structures are located above the proposed segmental walls, where the proposed reinforced zones will encroach into the proposed buildings, the following recommendations should be considered in the design and site construction. The fill behind the wall within the reinforced zone should be comprised of on-site sandy granular soils with

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a low expansion potential. Sandy/granular soils will interlock with the geogrid layers which is expected to reduce the potential for long-term, creep-type lateral deformation of the segmental wall, beyond the initial elastic deformation. As a result, the long-term differential settlement potential behind/above the segmental wall is expected to be reduced. Further, the backcut for wall construction should be excavated at a gradient no steeper than 2:1 (horizontal to vertical). This will help reduce the differential fill thickness beneath the proposed structures. The fills outside the reinforced zone should also consist of soils with relatively low expansion potentials and should be compacted to a minimum 93 percent relative compaction.

4.5 Soldier Pile Wall Recommendations
The following preliminary geotechnical parameters may be utilized by the soldier pile wall consultant for design of the permanent wall system. The recommendations provided herein with regard to the proposed wall design are based on assumed conditions, extrapolated from the data gathered from our site investigation and geotechnical analysis. The wall designer should independently evaluate the parameters provided and conduct an additional investigation if they consider necessary.
based on assumed conditions, extrapolated from the data gathered from our site investigation and geotechnical analysis. The wall designer should independently evaluate the parameters provided and conduct an additional investigation if they consider necessary.

Typical cantilever soldier pile wall design, where deflection of the wall will not impact the performance of adjacent structures or streets, may be designed using the active equivalent fluid pressures of 40 pounds per square foot (psf) per foot of depth (or pcf). Restrained walls (with soil nails or tied-back) is recommended to limit defections or required due to the proposed wall height. Restrained or tied-back shoring with a level backfill may be designed using an active trapezoidal soil pressure of 38H in pounds per square foot (psf), where H is equal to the depth in feet of the wall (shape of the trapezoid should be 0.2H, 0.6H, 0.2H) or may be designed using an active triangular soil pressure of 60 pounds per square foot (psf).

Any building, equipment, or traffic loads located within a 1:1 (horizontal to vertical) projection from the base of the wall should be added to the applicable lateral earth pressure.

A minimum additional uniform lateral pressure of 100 psf for the upper 10 feet should be added to the appropriate lateral earth pressures to account for typical vehicle traffic loading. the appropriate lateral earth pressures to account for typical vehicle traffic loading. he appropriate lateral earth pressures to account for typical vehicle traffic loading.

A seismic earth pressure of 17 pcf should be added to the static pressures given in Table 4 above. The seismic earth pressure should be considered as an inverted triangular distribution with the resultant acting at 0.6H in relation to the base of the retaining wall footing (where H is the retained height).

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Project No. 244006-01 Page 30 August 15, 2024
Passive resistance of soldier piles may be assumed to be an equivalent fluid pressure of 350 pcf for level and 150 pcf for sloping down conditions to a maximum value of 3,500 psf. The passive earth pressure may be increased by 100 percent for isolated piles. Piles with spacing greater than 3 times of pile diameter can be considered as isolated piles. In order to develop the full lateral resistance, firm contact between the soldier pile and undisturbed soils must be assured. For vertical capacity, an allowable skin friction of 500 psf may be used for the embedded depth. End bearing should be neglected.

4.6 Preliminary Pavement Recommendations
Preliminary pavement sections utilizing asphalt concrete (AC), Portland Cement Concrete Pavement PCCP), and vehicular concrete pavers, are presented in the following sections.

4.6.1 Asphalt Concrete (AC) Pavement
Based on an assumed R-value of 7 (obtained during the preliminary investigation of an adjacent property), we utilized an assumed R-Value of 7 and recommend the following preliminary minimum street sections for Traffic Indices of 5, 6, and 7 (as indicated in Table 6). These recommendations should be confirmed with R-value testing of representative near-surface soils at the completion of grading. Final AC sections should be confirmed by the project civil engineer based upon the projected Traffic Index. In addition, additional sections can be provided based on other traffic indices.

Table 6
Preliminary AC Pavement Design Sections
Assumed Traffic Index 5 6 7
R-Value Subgrade 7 7 7
AC Thickness 4.0 inches 4.0 inches 4.0 inches
Aggregate Base Thickness 7.0 inches 12.0 inches 15.0 inches The aggregate base material should conform to the specifications for Crushed Aggregate Base or Crushed Miscellaneous Base (Standard Specifications for Public Works Construction –SSPWC Section 200-2). The subgrade should achieve a minimum relative compaction of 95 percent. The base material should be compacted to achieve a minimum relative compaction of 95 percent. Aggregate base and subgrade materials should be moisture-conditioned to a relatively uniform moisture content at or slightly over optimum.

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4.6.2 Portland Cement Concrete Pavement
Portland Cement Concrete Pavement (PCCP) may be designed using a minimum of 8- inches of Portland Cement Concrete over 8-inches of compacted aggregate base.

The modulus of rupture of the PCCP should be a minimum of 500 pounds per square inch (psi) at 28 days. Contraction joints should be placed at maximum 15-foot spacing.

Where the outer edge of a concrete pavement connects to an asphalt pavement, the concrete slab should be thickened by 50 percent at a taper not to exceed a slope of 1 in

10. In addition, additional sections can be provided based on other desired anticipated traffic loadings.

The aggregate base material should conform to the specifications for Crushed Aggregate Base or Crushed Miscellaneous Base (Standard Specifications for Public Works Construction - SSPWC Section 200-2). The subgrade should achieve a minimum relative compaction of 95 percent. The base material should be compacted to achieve a minimum relative compaction of 95 percent. Base and subgrade materials should be moisture-conditioned to a relatively uniform moisture content at or slightly over optimum.

4.6.3 Vehicular Concrete Paver Pavement
Typical vehicular pavers are 3-1/8 inches in thickness and the manufacturers usually recommend that the pavers be underlain by a 1-inch-thick sand layer. Based on ASCE 58-10 for interlocking pavers and considering a Traffic Index (TI) of 6 and an R-Value of 7 for the subgrade soils, we recommend that the vehicular pavers and sand layer be underlain by a minimum of 16-inches of aggregate base.

The aggregate base material should conform to the specifications for Crushed Aggregate Base or Crushed Miscellaneous Base (Standard Specifications for Public Works Construction –SSPWC Section 200-2). The subgrade should achieve a minimum relative compaction of 95 percent per ASTM- D1557. The base material should be compacted to achieve a minimum relative compaction of 95 percent. Base and subgrade materials should be moisture-conditioned to a relatively uniform moisture content at or slightly over optimum.

4.7 Nonstructural Concrete Flatwork
Preliminary nonstructural concrete flatwork designs are presented in the following sections.

Portland Cement Concrete (PCC) flatwork (such as sidewalks, walkways, patios, entryways, etc.) have a high potential for cracking due to changes in soil volume related to soil-moisture fluctuations because these slabs are typically much thinner than foundation slabs and are not reinforced with the same dynamics as foundation elements. To reduce the potential for excessive cracking and lifting, concrete may be designed in accordance with the minimum guidelines outlined in Table 7. These guidelines will reduce the potential for irregular cracking and promote cracking along construction joints but will not eliminate all cracking

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Project No. 244006-01 Page 32 August 15, 2024
or lifting. Thickening the concrete and/or adding reinforcement will further reduce cosmetic distress.

Table 7
Nonstructural Concrete Flatwork
Private Sidewalks Patio/Entryways
Minimum Thickness
(in inches) 4 5
Presaturation Presoak to 12-inches prior
to placement
Presoak to 12-inches prior
to placement
Reinforcement --
No. 3 at 24 inches on
centers or 6x6 No. 6 by No.
6 Welded Wire Mesh
Crack Control
Saw cut or deep tool joint
to a minimum of 1/3 the
concrete thickness
Saw cut or deep tool joint
to a minimum of 1/3 the
concrete thickness
Maximum Joint Spacing 5 feet 6 feet
Aggregate Base -- 2 inches

4.8 Corrosivity to Concrete and Metal
The National Association of Corrosion Engineers (NACE) defines corrosion as “a deterioration of a substance or its properties because of a reaction with its environment.” From a geotechnical viewpoint, the “environment” is the prevailing foundation soils and the “substances” are the reinforced concrete foundations or various buried metallic elements such as rebar, piles, pipes, etc., which are in direct contact with or within close vicinity of the foundation soil.

In general, soil environments that are detrimental to concrete have high concentrations of soluble sulfates and/or pH values of less than 5.5. ACI 318R-14 Table 19.3.1.1, provides specific guidelines for the concrete mix design when the soluble sulfate content of the soils exceeds 0.1 percent by weight or 1,000 ppm. The minimum amount of chloride ions in the soil environment that are corrosive to steel, either in the form of reinforcement protected by concrete cover, or plain steel substructures such as steel pipes or piles, is 500 ppm per California Test 532.

Laboratory testing of representative on-site soils indicated that the on-site soils tested are

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Project No. 244006-01 Page 33 August 15, 2024
classified as having a Sulfate Exposure Class of S0 (per Table 19.3.1.2 of the ACI 318-19).

As a preliminary recommendation, concrete in contact with on-site soils should be designed in accordance with ACI 318-19 Table 19.3.2.1 for the S0/negligible or not applicable category. It is also our opinion that on-site soil should be considered moderately corrosive to buried metals. Site grading will redistribute the materials, which may result in soils with different corrosion potentials. Therefore, the as-graded soil conditions should be verified with confirmatory sampling and testing during the grading phase of the project.

Despite the minimum recommendation above, LGC is not a corrosion-engineering firm.

Therefore, we recommend that after site grading, consultation with a competent corrosion engineer be initiated to evaluate the actual corrosion potential of the site and to provide recommendations to reduce the corrosion potential with respect to the proposed improvements, as necessary. The recommendations of the corrosion engineer may supersede the above requirements.

4.9 Freestanding Walls
Freestanding wall footings should be founded a minimum of 24-inches below the lowest adjacent grade. To reduce the potential for unsightly cracks, we recommend inclusion of construction joints at 10- to 20-foot intervals.

Due to the potential creep of soils, where free standing walls are constructed close to a topof-slope, some tilt of the wall should be anticipated. To reduce the amount of tilt, a combination of grade beam and caisson foundations may be used to support the wall. The system should consist of a minimum of 12-inch diameter caissons placed at 8 feet maximum on centers, and each 8 feet long and connected together at top with 12-inch by 12-inch grade beam.

4.10 Control of Surface Water and Drainage Control
Positive drainage of surface water away from structures is very important. No water should be allowed to pond adjacent to buildings. Positive drainage may be accomplished by providing drainage away from the building at a gradient of at least 2-percent for a distance of at least 5 feet, and further maintained by a swale or drainage path at a gradient of at least 1-percent.

Where necessary, drainage paths may be shortened by use of area drains and collector pipes.

Planters with open bottoms adjacent to buildings should be avoided. Planters should not be designed adjacent to buildings unless provisions for drainage, such as catch basins, liners, and/or area drains, are made. Overwatering must be avoided.

4.11 Construction Observation and Testing
The recommendations provided in this report are based on limited subsurface observations and geotechnical analysis. The interpolated subsurface conditions should be checked in the field during construction by a representative of LGC.

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Geotechnical observation and testing should be performed by the geotechnical consultant during site excavations, subgrade for slab/foundation, backfill of utility trenches, preparation of any subgrade and placement of aggregate base, or when any unusual soil conditions are encountered at the site. Grading plans, foundation plans, and final project drawings should be reviewed by this office prior to construction.

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5.0 LIMITATIONS
Our services were performed using the degree of care and skill ordinarily exercised, under similar circumstances, by reputable engineers and geologists practicing in this or similar localities. No other warranty, expressed or implied, is made as to the conclusions and professional advice included in this report. The samples taken and submitted for laboratory testing, the observations made, and the in-situ field testing performed are believed representative of the entire project; however, soil and geologic conditions revealed by excavation may be different than our preliminary findings. If this occurs, the changed conditions must be evaluated by the project soils engineer and geologist and design(s) adjusted as required or alternate design(s) recommended.

This report is issued with the understanding that it is the responsibility of the owner, or of his/her representative, to ensure that the information and recommendations contained herein are brought to the attention of the architect and/or project engineer and incorporated into the plans, and the necessary steps are taken to see that the contractor and/or subcontractor properly implements the recommendations in the field. The contractor and/or subcontractor should notify the owner if they consider any of the recommendations presented herein to be unsafe.

The findings of this report are valid as of the present date. However, changes in the conditions of a property can and do occur with the passage of time, whether they be due to natural processes or the works of man on this or adjacent properties.

In addition, changes in applicable or appropriate standards may occur, whether they result from legislation or the broadening of knowledge. Accordingly, the findings of this report may be invalidated wholly or partially by changes outside our control.

Page 850 of 1727 ends

1 2
3 4
5 7
6 8
91011 28 29 30 31 32 33 34 35 36 37 38 40 41 42 43 16 15 14 13 12 21 20 19 18 39 252627 242322 17 B-4 B-5 B-6 TD=10.5' TD=10.5' TD=10.5' L-B-1 L-B-2 TD=56' N-B-2TD=? B-1 B-3 TD=20.5' TD=20.5' B-2 TD=11.0' ?
?
?
?
? TD=60' Ts Ts Ts Ts Afo Ts Ts N-B-2 30N36W @10.0' 33N68W @13.9' 5N48W @22.5'
5 ?
N65E @53.0'
?
? Afo Afo Ts Ts Ts
?
?
?
?
? Legend Afo Artificial Older Fill Ts Tertiary-aged Sespe Formation, circled where buried Approximate limits of fill, queried where uncertain Approximate Boring Location by LGC Valley (2024)Approximate Boring Location by Lawmaster & Co. (1986)Approximate Boring Location by G. A. Nichol (1986)Approximate Bedding Attitude Base Map: 2024-07-30, Site Plan Laguna Hills Mill Creek 2.4 Acre Site, Sheet 1 of 1, by Wilson Mikami Corporation.

Geotechnical Map 23161 Mill Creek Drive Laguna Hills, California 244006-01 Toll/23161 Mill Creek BIH/RKW 1" = 50' August 15, 2024 Project Name Project No. Eng. / Geol. Scale Figure 2 Date 0 25 50 100
? B-6 TD=10.5' L-B-2 TD=60' N-B-2 TD=? 33N68W

Page 851 of 1727 ends

FENCE

WALL HEIGHT, H

EXTENT OF FREE DRAINING SAND BACKFILL, MINIMUM
HEEL WIDTH OR H/2 WHICH EVER IS GREATER

BACKCUT PER OSHA
1' MINIMUM

WATER PROOFING PER CIVIL ENGINEER

FOOTING/WALL DESIGN PER CIVIL ENGINEER
MINIMUM 1 CUBIC FOOT PER LINEAR FOOT

BURRITO TYPE SUBDRAIN, CONSISTING OF
3/4 INCH CRUSHED ROCK WRAPPED IN
MIRAFI 140N OR APPROVED EQUIVALENT

NATIVE BACKFILL COMPACTED
TO MINIMUM 90% RELATIVE
COMPACTION PER ASTM1557-D

FREE DRAINING SAND BACKFILL
SE 30 OR GREATER
4 INCH DIAMETER, SCHEDULE 40 PERFORATED

PVC PIPE TO FLOW TO DRAINAGE DEVICE
Project Name
Eng. / Geol.

Date
Scale
Project No.

Backfill
Detail, Sand
Retaining Wall
Figure 3:

August 15, 2024
Not-To-Scale

BIH/RKW
244006-01
Toll/Laguna Hills

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Project No. 244006-01 Page A-1 August 15, 2024

APPENDIX A
References
American Concrete Institute (ACI), 1985, Manual of Concrete Practice, Parts 1 and 2.

American Concrete Institute (ACI), 2019, Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary, an ACI Standard, reported by ACI Committee 318.

American Society of Civil Engineers (ASCE), 2017, Minimum Design Loads for Buildings and Other Structures, ASCE/SEI 7-16, with Supplement 1, Effective December 12, 2018.

ASCE 7 Hazard Tool, https://asce7hazardtool.online/, accessed August 2024.

Bock & Clark Corporation, 2022, ALTA/NSPS Land Title Survey Map, Project No. 202201282-005 AAC, dated May 23, 2022.

California Building Standards Commission, 2022, California Building Code, California Code of Regulations Title 24, Volumes 1 and 2, dated July 2022.

California Department of Conservation Geologic Energy Management Division (CalGEM), 2023, Well Finder at https://www.concervation.ca.gov/calgem/Pages/WellFinder.aspx, accessed May 2024.

California Department of Water Resources (CDWR), 2023, Water Data Library (WDL) Station Map, at https://wdl.water.ca.gov, accessed May 2024.

CDWR, 2023, Sustainable Groundwater Management Act (SGMA) Data Viewer, at https://sgma.water.ca.gov/webgis/?appid=SGMADataViewer#gwlevels, accessed May 2024.

California Geological Survey (CGS), 1997, Guidelines for Evaluating and Mitigating Seismic Hazards in California, dated March 13, 1997, SP 117.

CGS, 2001, Earthquake Zones of Required Investigation, San Juan Capistrano Quadrangle, dated December 21, 2001.

CGS, 2006, Seismic Hazard Zone Report for the San Juan Capistrano 7.5-minute Quadrangle, Orange County, California, Seismic Hazard Zone Report 053, dated 2000, revised January 17, 2006.

CGS, 2018, Earthquake Fault Zones; A Guide for Government Agencies, Property Owners/Developers, and Geoscience Practitioners for Assessing Fault Rupture Hazards in California, Special Publication 42, dated January 2018.

CGS, 2023, California Earthquake Hazards Zone Application (EQ Zapp) Online Map at https://maps.conservation.ca.gov/cgs/EQZApp/app/, accessed August 2024.

Page 853 of 1727 ends

Project No. 244006-01 Page A-2 August 15, 2024
References (continued)
California State Water Resources Control Board (CSWRCB), 2023, GeoTracker at https://geotracker.waterboards.ca.gov, accessed August 2024.

EJN & Associates, Inc., 1986, Preliminary Soils Investigation, Tentative Parcel Map No. 85-367, Orange County, California, Job No. 86-155-1, dated March 18, 1986.

EJN Geotechnical, 1988, Final Compaction Report, Landmark Lake Hills, 23422 Mill Creek Drive, Laguna Hills, California, Grading Permit No. 86-146836, Job No. 86-155, dated March 2, 1988.

Google Earth at https://earth.google.com, accessed May 2024.

Google Maps and Street View at https://www.googlemaps.com, accessed May 2024.

Historical Aerials, 2023, Historical Aerial Photographs from 1946 and Historical Topography Maps from 1896, at https://www.historicalaerials.com, accessed May 2024.

Irvine Soils Engineering Inc., 1983a, Geotechnical Investigation, Proposed Two (2) Three-Story Office Buildings, Mill Creek Drive, Lots 9 and 10, Laguna Hills, California, Job No. 2405-00, dated June 10, 1983, revised July 25, 1983.

Irvine Soils Engineering Inc., 1983b, Soils Compaction Report, Rough Grading, Retaining Wall Grading, 23272 Mill Creek Road, Laguna Hills, California, Grading Permit No. 424,854, Job No. 2405-10, dated December 19, 1983.

Ishihara, K., 1985, “Stability of Natural Deposits During Earthquakes”. Proceedings of the Eleventh International Conference on Soil Mechanics and Foundation Engineering. A.A. Bakema Publishers, Rotterdam, Netherlands.

Jennings, C.W., and Bryant, W.A., 2010a, Fault Activity Map of California: California Geological Survey Geologic Data Map No. 6, Scale 1:750,000.

Jennings, C.W., and Bryant, W.A., 2010b, An Explanatory Text to Accompany the 2010 Fault Activity Map of California, 98 p.

Jennings, C.W., Gutierrez, C., Bryant, W., Saucedo, G., and Wills, C., 2010, Geologic Map of California, CGS Geologic Data Map 2, Scale: 1:750,000.

Lawmaster & Co., Inc, 1986, Geotechnical Investigation, Proposed Office Building (Mill Creek Plaza), 23091 Mill Creek Drive, Laguna Hills, California, File No. 86-10789, dated June 24, 1986.

Lawmaster & Co, Inc., 1989, Laguna Hills Office Building, Responses to Orange County Geologic Review Sheet dated July 14, 1989, File No. 89-11524-R, dated July 21, 1989.

Page 854 of 1727 ends

Project No. 244006-01 Page A-3 August 15, 2024
References (continued)
LGC Valley, Inc., 2024a, Preliminary Geotechnical Investigation, Proposed Residential Development, 23272 and 23282 Mill Creek Drive, Laguna Hills, California, Project No. 233016-01, dated November 17, 2023, revised January 16, 2024.

LGC Valley Inc., 2024b, Geotechnical Due Diligence Review of the 23161 Mill Creek Drive, Assessor Parcel Number 588-142-07, Laguna Hills, California, Project No. 244006-01, dated May 28, 2024.

Morton, D.M., Hauser, R.M., and Ruppert, K.R., 1999, Preliminary digital geologic map of the Santa Ana 30' X 60' quadrangle, southern California, U.S. Geological Survey, Open-File Report OF99-172, Scale 1:100,000.

Morton, D.M. and Miller, F.K., 2006, Geologic Map of the San Bernardino and Santa Ana 30’x60’ Quadrangle, USGS OFR-2006-1217, Scale 1:100,000.

Morton, P.K., Miller, R.V., and Evans, J.R., 1976, Environmental Geology of Orange County, California., California Division of Mines and Geology, Open-File Report OFR-79-08, Scale 1:48,000.

National Association of Corrosion Engineers (NACE), 1984, Corrosion Basics: An Introduction, 353 pages.

Post-Tensioning Institute, 2010, Design of Post Tensioned Slabs-on-Ground, Third Addition, Addendum 1 dated May 2007, and Addendum 2 dated May 2008, with Errata February 4, 2010.

Pradel, D., 1998, “Procedure to Evaluate Earthquake Induced Settlements in Dry Sandy Soils”, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 124, No. 4, April 1998.

Sadigh, K., Chang, C.-Y., Egan, J.A., Makdisi, F., and Youngs, R.R. (1997), "Attenuation Relations for Shallow Crustal Earthquakes Based on California Strong Motion Data," Seismological Research Letters, Vol. 68, No. 1, pp. 180-189.

Secor International Inc., 1997, Final Quarterly Groundwater Monitoring, 23552 Moulton Parkway, Laguna Hills, California, 92653, OCHCA Case # 96UT13, 24 p., dated February 20, 1997.

Seed, H.B., Tokimatsu, K., Harder, L.F., and Chungh, R.M., 1985, “Influence of SPT Procedures in Soil Liquefaction Resistance Evaluations,” Journal of Geotechnical Engineering, Vol. 111, No. 12, December 1985.

United States Geological Survey (USGS), 2008, “2008 National Seismic Hazard Maps – Fault Parameters” at https://earthquake.usgs.gov/cfusion/hazfaults_2008_search/query_main.cfm, accessed October 2023.

USGS, 2013, U.S. Seismic Design Maps, at
http://geohazards.usgs.gov/designmaps/us/batch.php#csv, accessed August 2024.

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Project No. 244006-01 Page A-4 August 15, 2024
References (continued)
USGS, 2014, “2008 Interactive Deaggregations (Beta),” at: https://geohazards.usgs.gov/deaggint/2008/, accessed August 2024.

USGS and CGS, 2020, Quaternary Fault and Fold Database of the United States at https://www.usgs.gov/programs/earthquake-hazards/faults, last update September 2, 2020, accessed August 2024.

Wilson Mikami Corporation, 2024, Site Plan, Laguna Hills Mill Creek 2.4 Acre Site, Sheet 1 of 1, dated July 30, 2024.

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Project No. 244006-01 Page B-1 August 15, 2024

APPENDIX B
Geotechnical Boring Logs (Current Study)

Page 857 of 1727 ends

0 5
10 298
293
288Elevation (ft) Depth (ft) Graphic Log Sample Number Blow Count Dry Density (pcf) Moisture (%) USCS Symbol

DESCRIPTION
Logged By: MET
Sampled By: MET Type of Test
Date:

Project Name:

Drilling Company:

Drive Weight:

Elevation of Top of Hole:

Project Number:

Type of Rig:

Drop:

Hole Location:

Hole Dia:

Page:

Geotechnical Boring Log
= Ring Sample
= SPT
THIS SUMMARY APPLIES ONLY AT THE LOCATION OF THIS BORING AND AT THE TIME OF DRILLING. SUBSURFACE CONDITIONS MAY DIFFER AT OTHER LOCATIONS AND MAY CHANGE AT THIS LOCATION WITH THE PASSAGE OF TIME. THE DATA PRESENTED IS A SIMPLIFICATION OF THE ACTUAL CONDITIOND ENCOUNTERED. LGC VALLEY, INC.

B-1
May 8, 2024 1 of 1
Toll/23161 Mill Creek
Martini Drilling
140 pounds
+298 Feet
244006-01
Hollow Stem Auger
30 inches
See Geotechnical Map
8 inches
@ 0' 4.5-inches of asphalt concrete over
8-inches of aggregate base
Sespe Formation (Ts):
@ 5' Silty fine to medium sandy CLAYSTONE
to silty fine to coarse SANDSTONE, very minor
gravel; dark brown to red brown, damp, hard
to very dense
Total Depth = 20.5 Feet
No Ground Water Encountered
Backfilled 5/8/2024
with Native Soil and Concrete Plug
Artificial Fill, Older (Afo):
@ 1' Silty to clayey fine to medium SAND,
very minor gravel; red brown to dark brown,
damp, medium dense
SM
1 2
50/6"
50/6"
B1
@1'-5'
110.9 6.9 CL/SM
15283
20278
3 50/2"
@ 6' Silty fine to medium SANDSTONE, very
minor gravel; red brown, damp, very dense
@ 10' Silty fine to medium SANDSTONE,
minor gravel; pale red brown, slightly damp,
very dense; sample disturbed - rock in
sampler
4 50/6"
5 50/4"
@ 15' Silty fine to medium SANDSTONE,
minor gravel; red brown, damp, very dense
SM
B2
@10'-15'
COR,
AL, EI
DS
110.5 8.2
114.2 2.0
Project No. 244006-01 Figure B - 1 August 15, 2024

Page 858 of 1727 ends

0 5
10 306
301
296Elevation (ft) Depth (ft) Graphic Log Sample Number Blow Count Dry Density (pcf) Moisture (%) USCS Symbol

DESCRIPTION
Logged By: MET
Sampled By: MET Type of Test
Date:

Project Name:

Drilling Company:

Drive Weight:

Elevation of Top of Hole:

Project Number:

Type of Rig:

Drop:

Hole Location:

Hole Dia:

Page:

B-2
May 8, 2024 1 of 1
Toll/23161 Mill Creek
Martini Drilling
140 pounds
+306 Feet
244006-01
Hollow Stem Auger
30 inches
See Geotechnical Map
8 inches
50/6" 111.3 1
@ 0' 5.5-inches of asphalt concrete over
6-inches of aggregate base
@ 5' Becomes a very silty fine to medium

SANDSTONE
Total Depth = 11 Feet
No Ground Water Encountered
Backfilled 5/8/2024
with Native Soil and Concrete Plug
Sespe Formation (Ts):
@ 1' Silty fine to medium SANDSTONE, very
minor gravel; red brown, damp, very dense

14.0 SM
2 3
86/8.5"
88/9" @ 10' Silty fine SANDSTONE to fine sandy
SILTSTONE; red brown to dark red brown,
damp, very dense to hard
SM/ML
B1
@1'-6'
111.7 12.4
116.0 12.2
Project No. 244006-01 Figure B - 2 August 15, 2024

Page 859 of 1727 ends

0 5
10 15
20 297
292
287
282
277Elevation (ft) Depth (ft) Graphic Log Sample Number Blow Count Dry Density (pcf) Moisture (%) USCS Symbol

DESCRIPTION
Logged By: MET
Sampled By: MET Type of Test
Date:

Project Name:

Drilling Company:

Drive Weight:

Elevation of Top of Hole:

Project Number:

Type of Rig:

Drop:

Hole Location:

Hole Dia:

Page:

B-3
May 8, 2024 1 of 1
Toll/23161 Mill Creek
Martini Drilling
140 pounds
+297 Feet
244006-01
Hollow Stem Auger
30 inches
See Geotechnical Map
8 inches
1 69
@ 0' 5.5-inches of asphalt concrete over
8-inches of aggregate base
Total Depth = 20.5 Feet
No Ground Water Encountered
Backfilled 5/8/2024
with Native Soil & Concrete Plug
Artificial Fill, Older (Afo):
@ 1.1' Silty fine to coarse SAND, minor gravel
and minor clay; red brown, damp, medium
dense
SM
2 3
4 5
6 82
50/5"
@ 10' Increase in coarse sand
@ 20' Decrease in coarse sand
@ 5' Silty fine to coarse SANDSTONE, very
minor gravel; red brown, damp, dense
B1
@1'-6'
50/6"
50/6"
50/5"
SM
Sespe Formation (Ts):
@ 2.5' Silty fine to coarse SANDSTONE, very
minor gravel and minor clay; red brown,
damp, dense
119.3 5.7
119.6 4.2
119.1 7.5
110.4 5.7
Project No. 244006-01 Figure B - 3 August 15, 2024

Page 860 of 1727 ends

0 5
10 308
303
298Elevation (ft) Depth (ft) Graphic Log Sample Number Blow Count Dry Density (pcf) Moisture (%) USCS Symbol

DESCRIPTION
Logged By: MET
Sampled By: MET Type of Test
Date:

Project Name:

Drilling Company:

Drive Weight:

Elevation of Top of Hole:

Project Number:

Type of Rig:

Drop:

Hole Location:

Hole Dia:

Page:

B-4
May 8, 2024 1 of 1
Toll/23161 Mill Creek
Martini Drilling
140 pounds
+308 Feet
244006-01
Hollow Stem Auger
30 inches
See Geotechnical Map
8 inches
50/6" 113.4

EI, RDS,
COR
1 @ 0' 3-inches of asphalt concrete over
5-inches of aggregate base
@ 1.5' Clayey fine to coarse SAND, very minor
gravel; dark brown to red brown, damp,
medium dense
Total Depth = 10.5 Feet
No Ground Water Encountered
Backfilled 5/8/2024
with Native Soil and Concrete Plug
Artificial Fill, Older (Afo):
@ 0.8' Silty fine to medium SAND, very minor
gravel; dark red brown, damp, medium dense

12.1 SC/SM
2 3
86/9"
50/6"
@ 10' Becomes a very silty fine to coarse

SANDSTONE
Sespe Formation (Ts):
@ 3' Silty fine to coarse SANDSTONE; pale red
brown, damp, very dense
SM
B1
@1'-3'
113.9 8.8
110.3 9.4
CN
Project No. 244006-01 Figure B - 4 August 15, 2024

Page 861 of 1727 ends

0 5
10 317
312
307Elevation (ft) Depth (ft) Graphic Log Sample Number Blow Count Dry Density (pcf) Moisture (%) USCS Symbol

DESCRIPTION
Logged By: MET
Sampled By: MET Type of Test
Date:

Project Name:

Drilling Company:

Drive Weight:

Elevation of Top of Hole:

Project Number:

Type of Rig:

Drop:

Hole Location:

Hole Dia:

Page:

B-5
May 8, 2024 1 of 1
Toll/23161 Mill Creek
Martini Drilling
140 pounds
+317 Feet
244006-01
Hollow Stem Auger
30 inches
See Geotechnical Map
8 inches
1 52 CN
@ 0' 8-inches of Asphalt over 5-inches of
aggregate base
Sespe Formation (Ts):
@3.5' Silty fine to medium SANDSTONE, very
minor gravel; red brown, damp, very dense
Total Depth = 10.5 Feet
No Ground Water Encountered
Backfilled 5/8/2024
with Native Soil and Concrete Plug
Artificial Fill, Older (Afo):
@ 1.1' Silty fine to medium SAND, very minor
gravel, slightly clayey; red brown, damp,
medium dense
SM
2 4
85/9"
50/6"
SM
3 50/6"
SW
@7.5' Becomes a silty fine to medium

SANDSTONE
@10' Fine to coarse SANDSTONE; red brown
to gray brown, damp, very dense
115.8 13.4
115.6 9.6
111.3 8.4
105.2 6.5
Project No. 244006-01 Figure B - 5 August 15, 2024

Page 862 of 1727 ends

0 5
10 312
307
302Elevation (ft) Depth (ft) Graphic Log Sample Number Blow Count Dry Density (pcf) Moisture (%) USCS Symbol

DESCRIPTION
Logged By: MET
Sampled By: MET Type of Test
Date:

Project Name:

Drilling Company:

Drive Weight:

Elevation of Top of Hole:

Project Number:

Type of Rig:

Drop:

Hole Location:

Hole Dia:

Page:

B-6
May 8, 2024 1 of 1
Toll/23161 Mill Creek
Martini Drilling
140 pounds
+312 Feet
244006-01
Hollow Stem Auger
30 inches
See Geotechnical Map
8 inches
86/11"
SA, SE
1 Total Depth = 10.5 Feet
No Ground Water Encountered
Backfilled 5/8/2024
with Native Soil and Concrete Plug
Sespe Formation (Ts):
@ 2.5' Silty fine to coarse gravelly
SANDSTONE, minor fine cobbles; red brown,
damp, very dense
SW
2 3
80/8.5"
50/6"
B1
@2.5'-5'
SM
@ 5' Silty fine to coarse SANDSTONE, very
minor gravel; red brown, damp, very dense
SW
@ 0' 8-inches of asphalt concrete over
5-inches of aggregate base
Artificial Fill, Older (Afo):
@ 1.1' Silty fine to coarse gravelly SAND,
minor fine cobbles; dark red brown, damp,
medium dense
118.1 6.0
111.9 9.9
105.1 9.8
Project No. 244006-01 Figure B - 6 August 15, 2024

Page 863 of 1727 ends

Symbol Laboratory Test
SA Sieve Analysis
H Hydrometer Anlysis
SHA Sieve & Hydrometer Analysis
-200 Percent Passing #200 Sieve
AL Atterburge Limits
MAX Maximum Density
DS Undisturbed Direct Shear
RDS Remolded Direct Shear
SE Sand Equivalent
EI Expansion Index
P Permeability
CN Consolidation
COL Collapse
UC Unconfined Compression
S Sulfate Content
pHR pH & Resistivity
COR Corrosion Suite (pH, Resistivity, Chloride, Sulfate) RV R-Value
Key to Boring Logs
Approximate Groundwater Level
Aggregate Base Approximate Seepage Location
Asphalt Concrete
GW
GP MH
SW
SP
SM
SC
CL
OH
ML
CH
PT
Gravel Sand Silt Clay
OL
Organics
Project No. 244006-01 Figure B - 7 August 15, 2024

Page 864 of 1727 ends

Project No. 244006-01 Page C-1 August 15, 2024

APPENDIX C
Laboratory Testing Procedures and Test Results (Current Study) The laboratory testing program was directed towards providing quantitative data relating to the relevant engineering properties of the soils. Samples considered representative of site conditions were tested in general accordance with American Society for Testing and Materials (ASTM) procedure and/or California Test Methods (CTM), where applicable. The following summary is a brief outline of the test type, and the results are presented on the following pages. LGC has reviewed the laboratory test data, procedures, and results with respect to the subject site, concurs with, and accepts responsibility as geotechnical engineer of record for their work (laboratory testing).

Soil Classification: Soils were classified according to the Unified Soil Classification System (USCS) in accordance with ASTM Test Methods D2487 and D2488. This system relies on the Atterberg limits and grain size distribution of a soil. The soil classifications (or group symbol) are shown on the laboratory test data and boring logs.

Atterberg Limits: The liquid and plastic limits (“Atterberg limits”) were determined in accordance with ASTM Test Method D4318 for engineering classification of fine-grained material and presented on the following table:

Sample Location Sample Description
Liquid
Limit
(%)
Plastic
Limit
(%)
Plasticity
Index
(%)
B-1 #B1 @ 1-5’ Silty to clayey fine to medium SAND 27 15 12 Chloride Content: Chloride content was tested in accordance with CTM 422. The results are presented below:

Sample Location Sample Description
Chloride
Content
(ppm)
Potential Degree
of Chloride
Attack*
B-1 #B1 @ 1-5’ Silty to clayey fine to medium SAND 125 Negligible B-4 #B1 @ 1-3’ Clayey fine to medium SAND 140 Negligible * Extrapolation from California Test Method 532, Method for Estimating the Time to Corrosion of Reinforced Concrete Substructures and previous experience.

Page 865 of 1727 ends

Project No. 244006-01 Page C-2 August 15, 2024
Laboratory Testing Procedures and Test Results (Current Study) (continued) Consolidation: Consolidation tests were performed on selected, relatively undisturbed ring samples (per Modified ASTM Test Method D2435). Samples (2.42 inches in diameter and 1 inch in height) were placed in a consolidometer and increasing loads were applied. The samples were allowed to consolidate under “double drainage” and total deformation for each loading step was recorded. The percent consolidation for each load step was recorded as the ratio of the amount of vertical compression to the original sample height. The consolidation pressure curves are presented on the attached figures at the end of this appendix.

Direct Shear (Remolded or Undisturbed): Direct shear tests were performed on selected remolded and/or undisturbed samples, which were soaked for a minimum of 24 hours under a surcharge equal to the applied normal force during testing. After transfer of the sample to the shear box, and reloading the sample, pore pressures set up in the sample due to the transfer were allowed to dissipate for a period of approximately 1 hour prior to application of shearing force. The samples were tested under various normal loads, a motor-driven, strain-controlled, direct-shear testing apparatus at a strain rate of less than 0.001 to 0.5 inch per minute (depending upon the soil type). The test results are presented on the following table and/or on the attached figures at the end of this appendix.

Sample
Location Sample Description
Peak/Ultimate
Friction
Angle
(degrees)
Peak/Ultimate
Apparent
Cohesion (psf)
B-1 #4 @15’ Undisturbed 29/29 278/96
B-4 #B1 @ 1-3’ Clayey fine to medium SAND (Remolded) 30/30 227/198 Expansion Index Tests: The expansion potential of selected materials was evaluated by the Expansion Index Test, UBC Standard No. 18-I-B and/or ASTM D4829. Specimens are molded under a given compactive energy to approximately the optimum moisture content and approximately 50 percent saturation or approximately 90 percent relative compaction. The prepared 1-inch thick by 4-inch diameter specimens are loaded to an equivalent 144 psf surcharge and are inundated with tap water until volumetric equilibrium is reached. The results of these tests are presented in the table below:

Sample Location Sample Description Expansion
Index
Expansion
Potential
B-1 #B1 @ 1-5’ Silty to clayey fine to medium SAND 14 Very Low B-4 #B1 @ 1-3’ Clayey fine to medium SAND 38 Low

Page 866 of 1727 ends

Project No. 244006-01 Page C-3 August 15, 2024
Laboratory Testing Procedures and Test Results (Current Study) (continued) Maximum Dry Density Tests: The maximum dry density and optimum moisture content of typical materials were determined in accordance with ASTM Test Method D1557. The results of these tests are presented in the table below:

Sample
Location Sample Description
Maximum
Dry Density
(pcf)
Optimum
Moisture
Content (%)
B-4 #B1 @ 1-3’ Clayey fine to medium SAND 133.5 8.0
Moisture and Density Determination Tests: Moisture content (ASTM D2216) and dry density determinations (ASTM D2937) were performed on relatively undisturbed samples obtained from the test borings. The results of these tests are presented on the boring logs. Where applicable, only moisture content was determined from undisturbed or disturbed samples.

Grain Size Distribution/Sieve Analysis: Representative samples were dried, weighed, and soaked in water until individual soil particles were separated (per ASTM D421) and then washed on a No. 200 sieve. The portion retained on the No. 200 sieve was dried and then sieved on a U.S. Standard brass sieve set in accordance with ASTM D422 (CTM 202). The sieve analysis curve is presented on the attached figure at the end of this appendix. The percent passing the #200 sieve is presented on the following table:

Sample Location Sample Description Percent Passing
#200 Sieve
B-6 #B1 @2.5-5’ Silty fine to coarse gravelly SAND 26.5

Page 867 of 1727 ends

Project No. 244006-01 Page C-4 August 15, 2024
Laboratory Testing Procedures and Test Results (Current Study) (continued) Minimum Resistivity and pH Tests: Minimum resistivity and pH tests were performed in general accordance with CTM 643 and standard geochemical methods. The electrical resistivity of a soil is a measure of its resistance to the flow of electrical current. As a result of soil’s resistivity decreases corrosivity increases. The results are presented in the table below:

Sample Location Sample Description pH
Minimum
Resistivity
(ohms-cm)
Potential
Degree of
Corrosivity*
B-1 #B1 @ 1-5’
Silty to clayey fine to medium
SAND 7.82 1,700 Moderately Corrosive
B-4 #B1 @ 1-3’ Clayey fine to medium SAND 8.15 1,300 Moderately Corrosive
* NACE Corrosion Basics, 1984.

Sand Equivalent: The sand equivalent (SE) of selected samples was determined in accordance with ASTM D2419. The sand equivalent results are used to determine the applicability of material for use as backfill and to assess whether flooding or jetting is a suitable compaction method. The results are presented in the table below:

Sample Location Sample Description Sand Equivalent
Value
B-6 #B1 @2.5-5’ Silty fine to coarse gravelly SAND 14
Soluble Sulfates: The soluble sulfate contents of selected samples were determined by standard geochemical methods (CTM417). The soluble sulfate content is used to determine the appropriate cement type and maximum water-cement ratios. The test results are presented in the table below:

Sample
Location Sample Description
Sulfate
Content
(% by
weight)
Exposure Class
(Exposure
Severity)*
B-1 #B1 @ 1-5’ Silty to clayey fine to medium SAND 0.007 S0 (Not Applicable) B-4 #B1 @ 1-3’ Clayey fine to medium SAND 0.005 S0 (Not Applicable) * Per ACI 318-19 Table 19.3.2.1 (ACI, 2019).

Page 868 of 1727 ends

Project Name:

Toll / Mill Creek 2
Client: LGC Valley, Inc.

Job No.: 244006-01
EGLAB Project No.: 24-059-009
08/24 Figure
Symbol Boring
No.

Sample
No.

Depth
(Ft.)
Soil
Type
Init. Moisture
Content (%)
B-4 1 2.5 SM 12.1
EGLAB, INC.

CONSOLIDATION
(ASTM D2435)
Init. Dry Density
(PCF)
Init. Void
Ratio
115.1 0.463
0 1
2 3
4 5
6 7
8 9
10 11
12 13
14 15
16 17
18 19
20 0.1 1 10 100
DEFORMATION (%)

COMPRESSIVE STRESS (KSF)

SATURATED
Project No. 244006-01 Figure C-1 August 15,

Page 869 of 1727 ends

20024
Project Name:

Toll / Mill Creek 2
Client: LGC Valley, Inc.

Job No.: 244006-01
EGLAB Project No.: 24-059-009
08/24 Figure
Symbol Boring
No.

Sample
No.

Depth
(Ft.)
Soil
Type
Init. Moisture
Content (%)
B-5 1 2.5 CL/SC 13.4
EGLAB, INC.

CONSOLIDATION
(ASTM D2435)
Init. Dry Density
(PCF)
Init. Void
Ratio
118.4 0.423
0 1
2 3
4 5
6 7
8 9
10 11
12 13
14 15
16 17
18 19
20 0.1 1 10 100
DEFORMATION (%)

COMPRESSIVE STRESS (KSF)

SATURATED
Project No. 244006-01 Figure C-2 August 15,

Page 870 of 1727 ends

20024
gd S
(pcf) (%)
1000 102.8 92
2000 103.5 92
4000 104.8 90
Boring No. Sample No. Depth (ft) Sample
Type
Soil Type Symbol Cohesion
(PSF)
Friction
Angle
B-1 4 15.0 Ring SM 227 30
198 30
Project Name:

EGLAB, INC.

Toll / Mill Creek 2

7.9 20.3 DIRECT SHEAR
Normal
Stress (psf)
Initial
Moisture (%)
Final
Moisture (%)
Client: LGC Valley, Inc.

Project No.: 244006-01
08/24 (ASTM D3080) Figure

7.9 21.8 EGLAB Project No.: , California 24-059-009

7.9 21.3
0 500
1000
1500
2000
2500
3000
3500
4000
4500
5000
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

SHEAR STRESS (PSF)

NORMAL PRESSURE (PSF)
Peak Ultimate
Project No. 244006-01 Figure C-3 August 15,

Page 871 of 1727 ends

20024
Note: Sample was remolded to 90 % maximum relative density and optimum moisture Maximum Dry Density: 133.5 pcf Optimum Moisture: 8.0 %
Toll / Mill Creek 2
Client: LGC Valley, Inc.

Project No.: 244006-01
500 EGLAB Project No.: 24-059-009
1000
2000
Normal
Stress
(psf)
B-4 B1 1.0-3.0 SC
EGLAB, INC.

19.0 Cohesion
(PSF) Boring No.

Sample
No.

Symbol
96 Bulk
Depth (ft)
Figure
Initial
Moisture
(%)
Final
Moisture
(%)

18.1 7.8 19.5

7.8 7.8
29 (ASTM D3080)
Sample
Type
08/24
278
Friction
Angle
29 DIRECT SHEAR
Project Address:

Soil Type
0 500
1000
1500
2000
2500
3000
0 500 1000 1500 2000 2500 3000

SHEAR STRESS (PSF)

NORMAL PRESSURE (PSF)
Peak
Ultimate
Project No. 244006-01 Figure C-4 August 15,

Page 872 of 1727 ends

20024

SYMBOL BORING
NO.

SAMPLE
NO.

DEPTH
(FT)
SAMPLE
TYPE
SOIL
TYPE
LIQUID
LIMIT
B-6 B1 2.5-5.0 Bulk SC N/A
Gravel: 23.3%
Sand: 50.2%
Fine: 26.5%
Client Job No.:

Client Name:

EGLAB Project No.:

GRAIN SIZE

DISTRIBUTION CURVE
08/07/24 (ASTM D422) FIGURE
24-059-009
EGLAB, INC.

LGC Valley, Inc.
244006-01

PLASTICITY
INDEX
N/A
Project Name:

Toll / Mill Creek 2
0 10
20 30
40 50
60 70
80 90
100
100 10 1 0.1 0.01

PERCENT FINER BY WEIGHT
GRAIN SIZE (mm)
U.S STANDARD SIEVE OPENING U.S. STANDARD SIEVE NUMBER HYDROMETER

GRAVEL SAND

COARSE FINE COAR MEDIUM FINE

SILT OR CLAY
3" 1.5" 1" 3/4" 1/2" 3/8" #4 #10 #20 #40 #60 #100 #200
Project No. 244006-01 Figure C-5 August 15,

Page 873 of 1727 ends

20024
Boring No: B-4
Sample: B1
(ASTM D1557) Date :

Client Name:
24-059-009
Job No.:

Maximum Dry Density = 133.5
Toll / Mill Creek 2
Figure
LGC Valley, Inc.

Modified Proctor
EGLAB, INC.
pcf
Optimum Moisture Content = 8.0 %
Method "A"
Aug-24
244006-01
Project Name:

Description : Clayey sand (SC), reddish brown,
trace of gravel
Depth : 1.0-3.0 feet
EGLAB Project No.:
90 100
110
120
130
140
150
0 5 10 15 20 25 30 35
Dry Density, pcf
Moisture Content %
Gs=2.95
Gs=2.85
Gs=2.75
Gs=2.65
Project No. 244006-01 Figure C-6 August 15,

Page 874 of 1727 ends

20024
Project No. 244006-01 Page D-1 August 15, 2024

APPENDIX D
Previous Geotechnical Borings Logs (by Others)

Page 875 of 1727 ends

~ ;' .
•
•
•
•
••
•
•
•
•
•
•
s-1 ·soil chani!icHlon.
so· n.:;L
~
. .
.
sr,• p =''·J
~ Dre\1~/reddlsh brown CU11Y.&Y Sl\llll
Br.;·..,ll/tliddish brcl/n SI\IIOV Sll.T,
132/50/lB.I P s•
Liqht ~~ddJ &h bro!ltl 571.'1'\' F:r!I£-'HtDIUI! 511!10 Droun/ruddhh bro~m SII-S't(it;r
130/M/:\.4) 0 25 I .
110 GROUt:oiiATER ·
UO CAVING.
~l:lllll
Q - Undbturb~d· core G~pho .'
(\Sand/\ silt/~ cl'a~•) @ :sample. dnptl:t
ii.S,;C• - llrtifLQd soi1 c1aaUt!c.iUon 5,\filtem Group Sl'lOhoi.

DrY \ J.lointUrtl p.,nn!tt• l!!:r U • .G.c.
sc
tiL
ro l2S
15 ill
111
20 . 112
112
10 l.lS
121
9 ill
1 lti
tiLl: No, •BS,.l07B9
j\, V. \li,',!\W.'liliU co,, 1liC,
Project No. 244006-01 Figure D - 1 August 15, 2024

Page 876 of 1727 ends

•
•
•
•
•
•
•
•
•
••
. · .. / :]
l:""""!"--------~-----'!""""-----....... -------------1--·· _.....,._.., Soil claosiflcAtion
tiTtTUMt.c . Bro•'ll/reddbh bro\m St.IID\' SlLT,
~y ll2/SC/lBI @ IJ!
t.lqht qrayish brown SMlD,STOUt
Ydlowish br""''ll S]tTSTOII£/SIIIIOSTOIIt
UO GROUUDithTtil
liD 'CAVliiC
\ lloJatllra
11 12
10 l.l
12 10
6 '
io
B
11 . .
cry
Danoltt• p.:C
ll!i
112
1U
119
102
. 102.
114
U.l
115
116
.l!.s.c.
sc
,£it£ llo. · BS-10789
,II. v. Lt.,.'>Wi'n:A, t. co. I liiC •
Project No. 244006-01 Figure D - 2 August 15, 2024

Page 877 of 1727 ends

LGC Valley, Inc.

General Earthwork and Grading Specifications

Page 1 of 5 ends

APPENDIX E
General Earthwork and Grading Specifications for Rough Grading

1.0 General

1.1 Intent: These General Earthwork and Grading Specifications are for the grading and earthwork shown on the approved grading plan(s) and/or indicated in the geotechnical report(s). These Specifications are a part of the recommendations contained in the geotechnical report(s). In case of conflict, the specific recommendations in the geotechnical report shall supersede these more general Specifications. Observations of the earthwork by the project Geotechnical Consultant during the course of grading may result in new or revised recommendations that could supersede these specifications or the recommendations in the geotechnical report(s).

1.2 The Geotechnical Consultant of Record: Prior to commencement of work, the owner shall employ a qualified Geotechnical Consultant of Record (Geotechnical Consultant).

The Geotechnical Consultant shall be responsible for reviewing the approved geotechnical report(s) and accepting the adequacy of the preliminary geotechnical findings, conclusions, and recommendations prior to the commencement of the grading.

Prior to commencement of grading, the Geotechnical Consultant shall review the "work plan" prepared by the Earthwork Contractor (Contractor) and schedule sufficient personnel to perform the appropriate level of observation, mapping, and compaction testing.

During the grading and earthwork operations, the Geotechnical Consultant shall observe, map, and document the subsurface exposures to verify the geotechnical design assumptions. If the observed conditions are found to be significantly different than the interpreted assumptions during the design phase, the Geotechnical Consultant shall inform the owner, recommend appropriate changes in design to accommodate the observed conditions, and notify the review agency where required.

The Geotechnical Consultant shall observe the moisture-conditioning and processing of the subgrade and fill materials and perform relative compaction testing of fill to confirm that the attained level of compaction is being accomplished as specified. The Geotechnical Consultant shall provide the test results to the owner and the Contractor on a routine and frequent basis.

1.3 The Earthwork Contractor: The Earthwork Contractor (Contractor) shall be qualified, experienced, and knowledgeable in earthwork logistics, preparation, and processing of ground to receive fill, moisture-conditioning and processing of fill, and compacting fill.

The Contractor shall review and accept the plans, geotechnical report(s), and these Specifications prior to commencement of grading. The Contractor shall be solely responsible for performing the grading in accordance with the project plans and specifications. The Contractor shall prepare and submit to the owner and the Geotechnical Consultant a work plan that indicates the sequence of earthwork grading,

Page 878 of 1727 ends

LGC Valley, Inc.

General Earthwork and Grading Specifications

Page 2 of 5 ends

the number of “equipment” of work and the estimated quantities of daily earthwork contemplated for the site prior to commencement of grading. The Contractor shall inform the owner and the Geotechnical Consultant of changes in work schedules and updates to the work plan at least 24 hours in advance of such changes so that appropriate personnel will be available for observation and testing. The Contractor shall not assume that the Geotechnical Consultant is aware of all grading operations.

The Contractor shall have the sole responsibility to provide adequate equipment and methods to accomplish the earthwork in accordance with the applicable grading codes and agency ordinances, these Specifications, and the recommendations in the approved geotechnical report(s) and grading plan(s). If, in the opinion of the Geotechnical Consultant, unsatisfactory conditions, such as unsuitable soil, improper moisture condition, inadequate compaction, insufficient buttress key size, adverse weather, etc., are resulting in a quality of work less than required in these specifications, the Geotechnical Consultant shall reject the work and may recommend to the owner that construction be stopped until the conditions are rectified. It is the contractor’s sole responsibility to provide proper fill compaction.

2.0 Preparation of Areas to be Filled

2.1 Clearing and Grubbing: Vegetation, such as brush, grass, roots, and other deleterious material shall be sufficiently removed and properly disposed of in a method acceptable to the owner, governing agencies, and the Geotechnical Consultant.

The Geotechnical Consultant shall evaluate the extent of these removals depending on specific site conditions. Earth fill material shall not contain more than 1 percent of organic materials (by volume). No fill lift shall contain more than 10 percent organic matter. Nesting of organic materials shall not be allowed.

If potentially hazardous materials are encountered, the Contractor shall stop work in the affected area, and a hazardous material specialist shall be informed immediately for proper evaluation and handling of these materials prior to continuing to work in that area.

As presently defined by the State of California, most refined petroleum products (gasoline, diesel fuel, motor oil, grease, coolant, etc.) have chemical constituents that are considered to be hazardous waste. As such, the indiscriminate dumping or spillage of these fluids onto the ground may constitute a misdemeanor, punishable by fines and/or imprisonment, and shall not be allowed. The contractor is responsible for all hazardous waste relating to his work. The Geotechnical Consultant does not have expertise in this area. If hazardous waste is a concern, then the Client should acquire the services of a qualified environmental assessor.

2.2 Processing: Existing ground that has been declared satisfactory for support of fill by the Geotechnical Consultant shall be scarified to a minimum depth of 6 inches. Existing ground that is not satisfactory shall be overexcavated as specified in the following section. Scarification shall continue until soils are broken down and free from oversize

Page 879 of 1727 ends

LGC Valley, Inc.

General Earthwork and Grading Specifications

Page 3 of 5 ends

material and the working surface is reasonably uniform, flat, and free from uneven features that would inhibit uniform compaction.

2.3 Overexcavation: In addition to removals and overexcavations recommended in the approved geotechnical report(s) and the grading plan, soft, loose, dry, saturated, spongy, organic-rich, highly fractured, or otherwise unsuitable ground shall be overexcavated to competent ground as evaluated by the Geotechnical Consultant during grading.

2.4 Benching: Where fills are to be placed on ground with slopes steeper than 5:1 (horizontal to vertical units), the ground shall be stepped or benched. Please see the Standard Details for a graphic illustration. The lowest bench or key shall be a minimum of 15 feet wide and at least 2 feet deep, into competent material as evaluated by the Geotechnical Consultant. Other benches shall be excavated a minimum height of 4 feet into competent material or as otherwise recommended by the Geotechnical Consultant.

Fill placed on ground sloping flatter than 5:1 shall also be benched or otherwise overexcavated to provide a flat subgrade for the fill.

2.5 Evaluation/Acceptance of Fill Areas: All areas to receive fill, including removal and processed areas, key bottoms, and benches, shall be observed, mapped, elevations recorded, and/or tested prior to being accepted by the Geotechnical Consultant as suitable to receive fill. The Contractor shall obtain a written acceptance from the Geotechnical Consultant prior to fill placement. A licensed surveyor shall provide the survey control for determining elevations of processed areas, keys, and benches.

3.0 Fill Material

3.1 General: Material to be used as fill shall be essentially free from organic matter and other deleterious substances evaluated and accepted by the Geotechnical Consultant prior to placement. Soils of poor quality, such as those with unacceptable gradation, high expansion potential, or low strength shall be placed in areas acceptable to the Geotechnical Consultant or mixed with other soils to achieve satisfactory fill material.

3.2 Oversize: Oversize material defined as rock, or other irreducible material with a maximum dimension greater than 8 inches, shall not be buried or placed in fill unless location, materials, and placement methods are specifically accepted by the Geotechnical Consultant. Placement operations shall be such that nesting of oversized material does not occur and such that oversized material is completely surrounded by compacted or densified fill. Oversize material shall not be placed within 10 vertical feet of finish grade or within 2 feet of future utilities or underground construction.

3.3 Import: If importing of fill material is required for grading, proposed import material shall meet the requirements of Section 3.1. The potential import source shall be given to the Geotechnical Consultant at least 48 hours (2 working days) before importing begins so that its suitability can be determined, and appropriate tests performed.

Page 880 of 1727 ends

LGC Valley, Inc.

General Earthwork and Grading Specifications

Page 4 of 5 ends

4.0 Fill Placement and Compaction

4.1 Fill Layers: Approved fill material shall be placed in areas prepared to receive fill (per Section 3.0) in near-horizontal layers not exceeding 8 inches in loose thickness. The Geotechnical Consultant may accept thicker layers if testing indicates the grading procedures can adequately compact the thicker layers. Each layer shall be spread evenly and mixed thoroughly to attain relative uniformity of material and moisture throughout.

4.2 Fill Moisture Conditioning: Fill soils shall be watered, dried back, blended, and/or mixed, as necessary to attain a relatively uniform moisture content at or slightly over optimum. Maximum density and optimum soil moisture content tests shall be performed in accordance with the American Society of Testing and Materials (ASTM Test Method D1557-91).

4.3 Compaction of Fill: After each layer has been moisture conditioned, mixed, and evenly spread, it shall be uniformly compacted to not less than 90 percent of maximum dry density (ASTM Test Method D1557-91). Compaction equipment shall be adequately sized and be either specifically designed for soil compaction or of proven reliability to efficiently achieve the specified level of compaction with uniformity.

4.4 Compaction of Fill Slopes: In addition to normal compaction procedures specified above, compaction of slopes shall be accomplished by backrolling of slopes with sheeps-foot rollers at increments of 3 to 4 feet in fill elevation, or by other methods producing satisfactory results acceptable to the Geotechnical Consultant. Upon completion of grading, relative compaction of the fill, out to the slope face, shall be at least 90 percent of maximum density per ASTM Test Method D1557-91.

4.5 Compaction Testing: Field tests for moisture content and relative compaction of the fill soils shall be performed by the Geotechnical Consultant. Location and frequency of tests shall be at the Consultant's discretion based on field conditions encountered.

Compaction test locations will not necessarily be selected on a random basis. Test locations shall be selected to verify adequacy of compaction levels in areas that are judged to be prone to inadequate compaction (such as close to slope faces and at the fill/bedrock benches).

4.6 Frequency of Compaction Testing: Tests shall be taken at intervals not exceeding 2 feet in vertical rise and/or 1,000 cubic yards of compacted fill soils embankment. In addition, as a guideline, at least one test shall be taken on slope faces for each 5,000 square feet of slope face and/or each 10 feet of vertical height of slope. The Contractor shall assure that fill construction is such that the testing schedule can be accomplished by the Geotechnical Consultant. The Contractor shall stop or slow down the earthwork construction if these minimum standards are not met.

4.7 Compaction Test Locations: The Geotechnical Consultant shall document the approximate elevation and horizontal coordinates of each test location. The Contractor shall coordinate with the project surveyor to assure that sufficient grade stakes are established so that the Geotechnical Consultant can determine the test locations with

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LGC Valley, Inc.

General Earthwork and Grading Specifications

Page 5 of 5 ends

sufficient accuracy. At a minimum, two grade stakes within a horizontal distance of 100 feet and vertically less than 5 feet apart from potential test locations shall be provided.

5.0 Subdrain Installation
Subdrain systems shall be installed in accordance with the approved geotechnical report(s), the grading plan, and the Standard Details. The Geotechnical Consultant may recommend additional subdrains and/or changes in subdrain extent, location, grade, or material depending on conditions encountered during grading. All subdrains shall be surveyed by a land surveyor/civil engineer for line and grade after installation and prior to burial. Sufficient time should be allowed by the Contractor for these surveys.

6.0 Excavation
Excavations, as well as over-excavation for remedial purposes, shall be evaluated by the Geotechnical Consultant during grading. Remedial removal depths shown on geotechnical plans are estimates only. The actual extent of removal shall be determined by the Geotechnical Consultant based on the field evaluation of exposed conditions during grading. Where fill-over-cut slopes are to be graded, the cut portion of the slope shall be made, evaluated, and accepted by the Geotechnical Consultant prior to placement of materials for construction of the fill portion of the slope, unless otherwise recommended by the Geotechnical Consultant.

7.0 Trench Backfills

7.1 The Contractor shall follow all OHSA and Cal/OSHA requirements for safety of trench excavations.

7.2 All bedding and backfill of utility trenches shall be done in accordance with the applicable provisions of Standard Specifications of Public Works Construction.

Bedding material shall have a Sand Equivalent greater than 30 (SE>30). The bedding shall be placed to 1 foot over the top of the conduit and densified by jetting. Backfill shall be placed and densified to a minimum of 90 percent of maximum from 1 foot above the top of the conduit to the surface.

7.3 The jetting of the bedding around the conduits shall be observed by the Geotechnical Consultant.

7.4 The Geotechnical Consultant shall test the trench backfill for relative compaction. At least one test should be made for every 300 feet of trench and 2 feet of fill.

7.5 Lift thickness of trench backfill shall not exceed those allowed in the Standard Specifications of Public Works Construction unless the Contractor can demonstrate to the Geotechnical Consultant that the fill lift can be compacted to the minimum relative compaction by his alternative equipment and method.

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Project No. 244006-01 Figure E - 1 August 15, 2024

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Project No. 244006-01 Figure E - 2 August 15, 2024

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Project No. 244006-01 Figure E - 3 August 15, 2024

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Project No. 244006-01 Figure E - 4 August 15, 2024

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Priority Project Water Quality Management Plan (WQMP)
Mill Creek Development

Toll Brothers Section VII
North OC Priority WQMP Page 36
Attachment G
Preliminary Drainage Report

Page 887 of 1727 ends

23161 MILL CREEK PROJECT

CITY OF LAGUNA HILLS

PRELIMINARY HYDROLOGY REPORT
Prepared for:

Toll Brothers
350 Commerce, Suite 200
Irvine, CA 92602
January, 2025
Prepared by:

WILSON•MIKAMI•CORPORATION
9 CORPORATE PARK•SUITE 100•IRVINE•CA•92606
Phone: (949) 679-0090 Fax: (949) 679-0091

Page 888 of 1727 ends

TABLE OF CONTENTS
I. Introduction
Project Description 1
Purpose 1
Methodology 1
Conclusion 2
Project Location Map Fig. 1
Project Soils Map Fig. 2
NOAA Atlas 14 Point Precipitation Values Fig. 3
II. References
III. Appendices
A. Existing Condtion Rational Method Q25 and Q100 Hydrology and Hydrology Map
B. Proposed Condition Rational Method Q25 and Q100 Hydrology and Hydrology Map
C. Existing Condition Unit Hydrograph analysis for a 100 Year -24 Hour Storm Event
D. Proposed Condition Unit Hydrograph analysis for a 100 Year- 24 Hour Storm Event

Page 889 of 1727 ends

I. INTRODUCTION
A. PROJECT DESCRIPTION:

Toll Brothers is proposing the development of a 2.4 acre site within the City of Laguna Hills, at Mill Creek Drive (Refer to Project Location Map, Figure 1). The site will consist of 18 duplex units, 36 residences.

The existing project site is currently a commercial building and parking lot and surface drains through a series of v-gutters down the drive entrance on onto Mill Creek Drive. There are currently no underground storm drain pipes.

The drainage from the project is collected by a series of area drains and catch basins to collect street flow. The south half of the property drains out to Mill Creek through a proposed parkway culvert near the proposed driveway. The north half of the property drains out to Mill Creek Drive through a second proposed parkway culvert near the northeast corner of the site.

B. PURPOSE:

This drainage report is intended to analyze the proposed drainage facilities associated with the project improvements and determine that the receiving facilities are not overburdened.

C. METHODOLOGY:

The existing and proposed conditions were analyzed utilizing the Advanced Engineering Software (AES) package for Orange County (RATSCX) (ref. 2). A rational method hydrology analysis was performed on both the existing pre-development, and proposed post-development condition for the 25 and 100-year storm events. The results are summarized in the table below and included in Appendix A and B of this report.

Existing Condition Area (ac) Q25 (cfs) Q100 (cfs)
Sub-area A 2.2 8.0 10.3
Sub-area B 0.2 0.9 1.1
Total 2.4 8.9 11.4
Proposed Condition
Sub-area A 0.9 3.4 4.4
Sub-area B 1.5 5.4 7.0
Total 2.4 8.8 11.4

Page 890 of 1727 ends

The storm volumes were analyzed using the Civil D unit hydrograph (ref 3) module for Orange County. The point precipitation values were taken from NOAA Atlas 14 for the Laguna Hills area. The unit hydrograph results can be found in Appendix C (existing) and D (proposed) and are summarized below:

Existing Condition-Unit Hydrograph
Storm
Event
Storm
Duration
Total
Tribuary
Area (ac)
Pervious
Percent
Ap
Total
Storm
Volume
(ac-ft)
100-Year 24 Hour 2.4 ac 22% 1.054 ac-ft
Proposed Condition-Unit Hydrograph
Storm
Event
Storm
Duration
Total
Tribuary
Area (ac)
Pervious
Percent
Ap
Total
Storm
Volume
(ac-ft)
00-Year 24 Hour 2.4 ac 26% 1.048 ac-ft
The storm volume and peak flow rates in the existing condition does not exceed the expected storm volume or peak flow rates in the proposed condition and no on-site detention is required.

D. CONCLUSION:

These analyses and calculations confirm that the proposed development does not overburden the downstream drainage facility or increase flow onto Mill Creek Drive and no on-site detention is required. Additionally, protection of onsite structures will be maintained for the 100-year storm event.

II. REFERENCES

1. Orange County Hydrology Manual, 1986/1996 Addendum

2. Advanced Engineering Software (AES) RATSCX, 2016

3. Civil Design Software (CIVILD), 2018

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PROJECT LOCATION
FIGURE MAP 1

PROJECT LOCATION

MILL CREEK DR

LAKE FOREST DR

RIDGE ROUTE DR

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Hydrologic Soil Group—Orange County and Part of Riverside County, California Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/16/2024

Page 1 of 4 ends

3720860 3720880 3720900 3720920 3720940 3720960 3720980 3721000 3721020 3720860 3720880 3720900 3720920 3720940 3720960 3720980 3721000 3721020 431650 431670 431690 431710 431730 431750 431770 431790 431810 431830 431850 431870 431890 431650 431670 431690 431710 431730 431750 431770 431790 431810 431830 431850 431870 431890 33° 37' 36'' N
117° 44' 13'' W
33° 37' 36'' N
117° 44' 3'' W
33° 37' 31'' N
117° 44' 13'' W
33° 37' 31'' N N 117° 44' 3'' W
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 11N WGS84 0 50 100 200 300
Feet
0 15 30 60 90
Meters
Map Scale: 1:1,170 if printed on A landscape (11" x 8.5") sheet.

Soil Map may not be valid at this scale.

Page 893 of 1727 ends

MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map
measurements.

Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:

Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Orange County and Part of Riverside County, California
Survey Area Data: Version 17, Aug 30, 2023
Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(s) aerial images were photographed: Jan 17, 2023—Feb 8, 2023
The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident.

Hydrologic Soil Group—Orange County and Part of Riverside County, California Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/16/2024

Page 2 of 4 ends

Page 894 of 1727 ends

Hydrologic Soil Group
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 104 Alo variant clay, 15 to 30
percent slopes
D 1.1 27.4%
105 Alo variant clay, 30 to 50
percent slopes
D 2.9 72.6%
173 Myford sandy loam, 2 to
9 percent slopes
C 0.0 0.0%
Totals for Area of Interest 4.1 100.0%
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms.

The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows:

Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission.

Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture.

These soils have a moderate rate of water transmission.

Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission.

Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission.

If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes.

Hydrologic Soil Group—Orange County and Part of Riverside County, California Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
9/16/2024

Page 3 of 4 ends

Page 895 of 1727 ends

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III. APPENDICES

Page 897 of 1727 ends

APPENDIX A

EXISTING CONDITION RATIONAL METHOD AND

HYDROLOGY MAP

Page 898 of 1727 ends

25-YEAR

Page 899 of 1727 ends

____________________________________________________________________________ ****************************************************************************

Wilson Mikami, Inc
9 CORPORATE PARK, SUITE 100
IRVINE, CA 92606
(949) 679-0090
************************** DESCRIPTION OF STUDY ************************** * KHOSHBIN MILL CREEK PROPERTY *
* EXISTING CONDITION 25-YEAR HYDROLOGY *
* BY KAM 091524 *
************************************************************************** FILE NAME: EX_MC2.DAT
TIME/DATE OF STUDY: 12:57 09/16/2024
============================================================================ USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION:
============================================================================ --*TIME-OF-CONCENTRATION MODEL*--
USER SPECIFIED STORM EVENT(YEAR) = 25.00
SPECIFIED MINIMUM PIPE SIZE(INCH) = 18.00
SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE = 0.95 *DATA BANK RAINFALL USED*
*ANTECEDENT MOISTURE CONDITION (AMC) II ASSUMED FOR RATIONAL METHOD* *USER-DEFINED STREET-SECTIONS FOR COUPLED PIPEFLOW AND STREETFLOW MODEL* HALF- CROWN TO STREET-CROSSFALL: CURB GUTTER-GEOMETRIES: MANNING

WIDTH CROSSFALL IN- / OUT-/PARK- HEIGHT WIDTH LIP HIKE FACTOR NO. (FT) (FT) SIDE / SIDE/ WAY (FT) (FT) (FT) (FT) (n)
=== ===== ========= ================= ====== ===== ====== ===== ======= 1 30.0 20.0 0.018/0.018/0.020 0.67 2.00 0.0313 0.167 0.0150 GLOBAL STREET FLOW-DEPTH CONSTRAINTS:

1. Relative Flow-Depth = 0.00 FEET
as (Maximum Allowable Street Flow Depth) - (Top-of-Curb)

2. (Depth)*(Velocity) Constraint = 6.0 (FT*FT/S)
*SIZE PIPE WITH A FLOW CAPACITY GREATER THAN
OR EQUAL TO THE UPSTREAM TRIBUTARY PIPE.*
*USER-SPECIFIED MINIMUM TOPOGRAPHIC SLOPE ADJUSTMENT NOT SELECTED **************************************************************************** FLOW PROCESS FROM NODE 10.00 TO NODE 11.00 IS CODE = 21 ---------------------------------------------------------------------------- >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<<
>>USE TIME-OF-CONCENTRATION NOMOGRAPH FOR INITIAL SUBAREA<< ============================================================================ INITIAL SUBAREA FLOW-LENGTH(FEET) = 203.00
ELEVATION DATA: UPSTREAM(FEET) = 316.50 DOWNSTREAM(FEET) = 304.00 Tc = K*[(LENGTH** 3.00)/(ELEVATION CHANGE)]**0.20
SUBAREA ANALYSIS USED MINIMUM Tc(MIN.) = 5.000
* 25 YEAR RAINFALL INTENSITY(INCH/HR) = 4.824
SUBAREA Tc AND LOSS RATE DATA(AMC II):

DEVELOPMENT TYPE/ SCS SOIL AREA Fp Ap SCS Tc
LAND USE GROUP (ACRES) (INCH/HR) (DECIMAL) CN (MIN.)

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Laguna Hills City CouncilFebruary 10, 2026

Laguna Hills City Council
February 10, 2026