Appendix A - Engineering.pdf

Ten Year Operations and Maintenance Plan for the Glendale Narrows Reach of the Los Angeles River

Programmatic Environmental Assessment

Appendix A

Engineering Appendix

DEPARTMENT OF THE ARMY

U.S. ARMY CORPS OF ENGINEERS

LOS ANGELES DISTRICT

915 WILSHIRE BOULEVARD, SUITE 930

LOS ANGELES, CALIFORNIA 90017-3489

CESPL-EDH-H (1110-2-1403b2) August 25, 2022

MEMORANDUM FOR RECORD

SUBJECT: Median Removal and Channel Capacity of Los Angeles River Reaches 2 through 6

1. References:

a. U.S. Army Corps of Engineers. HEC-RAS River Analysis System, Version 6.0 Hydrologic Engineering Center. March 2022.

b. U.S. Army Corps of Engineers, Los Angeles District, Floodplain Analysis Los

Angeles River: Barham Boulevard to First Street Flood Plain Management Services (FPMS) Special Study. October 2016.

c. U.S. Army Corps of Engineers. MEMORANDUM FOR RECORD: Updates to the

Los Angeles River Floodplain Analysis. October 2020.

d. U.S. Army Corps of Engineers, Los Angeles District, Survey & Mapping Section.

Digital Terrain Model. 2021.

e. U.S. Army Corps of Engineers, Los Angeles District, Los Angeles County

Drainage Area Final Feasibility Report. December 1991.

f. U.S. Army Corps of Engineers, Los Angeles District, Los Angeles County Drainage Area Final Feasibility Report, Appendix A Part I & II Hydrology. December 1991, updated 1992.

g. U.S. Army Corps of Engineers, Los Angeles District, MEMO for Chief, Operations

Branch, ATTN: Lillian Doherty SUBJECT: Los Angeles River Capacity Analysis to Report River Capacity as a Result of Removing Emergency Flood Barriers. 06 May 2019.

2. Purpose

This memorandum for record (MFR) summarizes the HESCO barrier removal and channel capacity analysis for the Los Angeles River (LAR) ARBOR Reaches 2 through

6 completed by the U.S. Army Corps of Engineers (USACE), Los Angeles District

(SPL). These LAR Reaches run through the Glendale Narrows area, as shown on

CESPL-EDH-H (1110-2-1403b2)

Plate 1. These reaches have a soft channel bed and vegetation has occupied part of the channel within these reaches. Channel capacity of these reaches is below the design capacity (Ref g). This analysis includes updating an existing hydraulic model with more recent topographic survey and site conditions. Existing channel capacities (and updated return frequencies) were then determined from the updated model. After determining the current condition capacity, a phased 50% sediment removal plan was modeled to help guide future maintenance operation. A bank full capacity analysis was then completed to use as a baseline for targeted future capacity and compared to the 50% sediment removal condition. A recommendation is being made for future work to include running a sediment transport analysis in HEC-RAS to further analyze long term sediment behavior and better prioritize sediment removal activities.

3. Field Visit

A field visit was conducted on 25 June 2020 along ARBOR Reaches 1-6 of the LAR.

Current vegetation and sediment conditions were documented for all 6 reaches and the areas identified to prioritize 50% bed removal were: 1) the majority of Reach 4, specifically upstream and downstream of Colorado Blvd., and 2) Reach 6B in which maintenance has been limited to Arundo removal. Sediment accumulation and vegetation has grown up to 15 to 20 feet in height in Reaches 4 and 6. Photographs from the field visit are provided in Table 4.

4. Channel Capacity Analysis Without HESCO Barriers (Scenario 1 – Base Case, Current Condition)

As determined from the site visit, the segment where the HESCO barriers were removed by the City of Los Angeles and Caltrans is upstream of Colorado Blvd. to upstream of Los Feliz Blvd. For this area a new channel capacity analysis was required to determine the maximum channel capacity of each reach based on a channel without

HESCOs with pre-sediment and vegetation removal conditions.

An existing USACE HEC-RAS model (Ref. a) that was used in this analysis is a part of the Los Angeles River FPMS Floodplain Study model (Ref. b) that was updated in 2020 with more recent data for bridges and to address comments received from Federal

Emergency Management Agency (FEMA) (Ref. c). The model is a one-dimensional

(1D)/two-dimensional (2D) hydraulic model that uses 1D hydraulic computations in the channel and 2D floodplain computations in the overbank area. The model represents the existing condition sediment and vegetation in the channel reaches and encompasses the LAR from Barham Boulevard to First Street. The reach has three major confluences; Burbank Western Channel, Verdugo Wash, and the Arroyo Seco. In this analysis, the focus of the study was the LAR main channel, hence the overbank areas were not hydraulically evaluated. To analyze channel capacity of the LAR

Reaches 2 through 6, the 2D overbank flow areas were removed from the model to limit flow computations to the river channel.

For this analysis, the current condition base model was further updated using the latest

Los Angeles River channel survey data. The analysis used digital terrain model (DEM) survey data, provided by the Survey & Mapping Section completed in 2021 (Ref. d). The

DEM corresponds to North American Vertical Datum of 1988 and horizontal projection

California State Plane Zone V, North American Datum of 1983.

For Reach 3 concrete sections, the model cross section channel configuration and invert elevation were based on as-constructed design drawings of the ARBOR reach.

Cross section cut lines were extended at some locations or were moved to properly model features of interest (i.e. bridges, storm drainage structures and bike paths).

Roughness coefficients were also updated based on the field visit and Google imagery.

Table 4 includes Manning’s n-value adjustments that were made to the updated model at select locations using field visit observations.

The hydrology data from the 1992 Los Angeles County Drainage Area Final Feasibility

Report (Refs. e and f) was used to perform the hydraulic analysis. Model simulations were conducted to determine the peak flow rate for each reach considering the given freeboard. Design freeboard values for each reach were per the 1999 Operations &

Maintenance (O&M) Manual. In order to determine the current channel capacities with the allowance for freeboard, varying flow multipliers were necessary for each reach.

See Table 3, Scenario 1 for corresponding HEC-RAS plans.

Table 1 shows a comparison of the design channel capacity and the current channel capacity without the HESCOs in place. The upstream (U/S) and downstream (D/S) station numbers in Table 1 are O&M station numbers. Flood return frequency associated with each reach are also provided based on the 1992 hydrology update. In any specific reach, the reported capacity takes minimum freeboard into account

(ranging from 2-2.5 feet, see Table 1). Due to differences in the bank elevations along both sides of the river in some of the reaches, the reported discharge associated with the lower bank elevation is considered the channel capacity for that specific reach.

5. Estimated 50% Cut Elevation and Sediment Volume

The 50% cut line for sediment removal could be determined using two methods; by setting the cut line at 50% of the height of sediment buildup, or by setting that line to remove at least 50% of deposited sediment volume (see Figure 1). After discussions between the Los Angeles District Engineering staff and Operations staff, it was decided that the cut line corresponding to a 50% cut in volume would be used.

Figure 1 – Two methods to determine 50% cut line for sediment removal

An estimation of the current sediment volume in the river channel was determined based on the design channel invert elevation and the existing condition channel invert elevation. The design channel invert elevation was based on as-constructed design drawings. The existing condition channel invert elevation was based on the channel survey completed in 2021. Both channel invert datasets were imported into ArcGIS. The differences between these two datasets indicate sediment deposition and channel erosion. This analysis focused on sediment deposition. Channel reaches 2, 4, 5, and 6 were divided into small segments approximately 200-ft long, as shown in Plates 2 through 6. Reach 3 is not included because it is concrete bottom and recently underwent maintenance for sediment removal. The 50% cut bottom elevation at each cross section was set at a level such that at least 50% of the sediment volume in each segment will be removed. A few examples comparing the 50% cut elevation cross section with the existing condition cross section in HEC-RAS are shown in Figure 2 -

Figure 4. Calculating sediment removal for every segment ensures that sediment will be removed at all locations. If sediment removal is calculated for an entire river reach, it will very likely lead to no sediment removal at some locations and more sediment removal at other locations. This small segment approach is also better aligned with actual channel maintenance operations because channel maintenance work is usually contracted out for a small segment of the channel. The 50% cut sediment volumes are provided in Table 2. The elevation and sediment volume data are to guide future removal activities.

It should be noted that sediment conditions in the river channel are dynamic and constantly changing. The 50% cut sediment volume estimated in this analysis is a snapshot of the sediment condition based on the channel survey completed in 2021.

6. Channel Capacity Analysis with 50% Sediment Removal (Scenario 2)

A new scenario was created in the hydraulic model with the updated 50% cut elevations. Roughness values were updated to reflect a 50% bed removal condition

(Table 3, Scenario 2). The hydraulic analysis simulated different phased removal plans that prioritize reaches based on capacity and/or engineering judgement (downstream to upstream), and logistical constraints (access). The recommended reach priority list

(from high priority to low priority) is: 4C, 4B, 4A, 6C, 6B, 6A, 5C, 5A, 4D, 5B, and 2A.

This priority list generally targets the lower capacity reaches first.

Figure 2 – Comparison of existing geometry (black) with 50% sediment removal condition (magenta) at RAS station 436+84.1 (O&M Station 298+69, Reach 4A)

Figure 3 – Comparison of existing geometry (black) with 50% sediment removal condition (magenta) at RAS station 354+22.7 (O&M Station 216+07, Reach 5A)

Figure 4 – Comparison of existing geometry (black) with 50% sediment removal condition (magenta) at RAS station 199+94.4 (O&M Station 1347+20, Reach 6A)

7. Channel Capacity Analysis at Bank Full Elevation (Scenario 3)

Channel capacity was determined at bank full level, using the barriers as freeboard.

This base case channel capacity at bank full level was determined from model runs

(Table 3, Scenario 3) using the 2021 survey data cross section (Ref. d). Barriers were considered as freeboard on both sides of the riverbank. A multiplier was iteratively applied to the 25-year flow hydrograph to determine the highest discharge that equals but does not exceed the lowest bank station elevation for each reach. Example cross sections with bank-full flows are shown in Figure 5 - Figure 7.

Figure 5 - Bank-full discharge computation at RAS Station 450+78.4 (Reach 4A, multiplier 0.876, Q = 41,610 cfs)

Figure 6 - Bank-full discharge computation at RAS Station 412+25.50 (Reach 4B, multiplier 1.04, Q = 49,400 cfs)

Figure 7 - Bank-full discharge computation at RAS Station 394+92.55 (Reach 4C, multiplier 1.01, Q = 47,975 cfs)

An iterative procedure was proposed to determine the cut line elevation at soft-bottom reach cross sections that will provide the same channel capacity as the ‘with barriers’

(bank full capacity) scenario. However, after analyzing the 50% sediment removal case, it was found that this scenario equals or exceeds the bank full capacity with the barriers and was therefore deemed a sufficient sediment removal scenario for this investigation.

8. Vegetation Cleared Scenario

A hydraulic analysis was also conducted to simulate the capacity from clearing 50% of existing vegetation in channel. The analysis was based off 2016 channel geometry and adjusting n-values to simulate reduced vegetation growth in channel. After initial results and discussions with Operations division, it was decided that the 50% sediment removal condition is preferable.

9. Results and Conclusions

Current channel capacities were determined and compared to design channel capacities for with and without HESCO barriers. As shown on Table 1 the existing channel capacity is less than the design channel capacity for reaches 4-6. The reduced capacities are mainly due to the vegetation growth and accumulation of sediment along the river. To increase channel capacity, maintenance activities including vegetation management and sediment removal have been recommended. Table 2 provides the

50% cut elevation and estimated removal volumes within each reach. The table also provides a prioritization phased removal plan sequence.

10. Recommendations

This study can be further improved by preparing a sediment transport model in HEC-

RAS. It is recommended that the 50% cut line be compared with the results of a RAS sediment transport model with a historical/long term sediment transport hydrograph, which would ensure the 50% cut line is below the stable streambed/riverbed line, and confirm that dredging is needed within the area of interest. Once the 50% cut line is confirmed with the stable streambed, the HEC-RAS model can be run with a sediment transport component with a targeted dredge line (50% cut line). HEC-RAS will compute scour and deposition along the riverbed and compute a water surface profile. A scope of work has been prepared for this work and will be provided to SPL Operations and

Maintenance with the transmission of this memo.

11. Point of contact

For questions or comments on this analysis please contact Tim Brown at 213-452-3142 or timothy.brown@usace.army.mil.

TIM FAIRBANK, P.E.

Acting Chief, Hydrology & Hydraulics Branch Engineering Division mailto:timothy.brown@usace.army.mil

FAIRBANK

CESPL-EDH

THOMPSON

CESPL-EDH-H

KEMP WEITZMAN

CESPL-EDH-G

BROWN

CESPL-EDH-H

GURON

CESPL-EDH-G

SUBJECT: Median Removal and Channel Capacity of Los Angeles River Reaches 2 through 6

Plate 1. LAR Reaches Overview Map

Plate 2. Segments for Estimating Sediment Volume

Plate 3. Segments for Estimating Sediment Volume (continued)

Plate 4. Segments for Estimating Sediment Volume (continued)

Plate 5. Segments for Estimating Sediment Volume (continued)

Plate 6. Segments for Estimating Sediment Volume (continued)

Table 1. LA River Channel Capacity Analysis

Reach O&M U/S Station

O&M D/S Station

Approx.

Length

Design Channel Capacity

Current Channel Capacity

Final Channel Capacity - 50% Cut

Freeboard Assumed

Bank Full Capacity1,2

(feet) (year) (cfs) (year) (cfs) (year) (cfs) (feet) (yr) (cfs)

2A 406+00 366+86 3,900 7 40,000 8 41,800 13 48,300 2 - -

3 366+86 314+00 5,300 7 40,000 5 34,960 18 52,200 2.5 - -

4A 314+00 293+00 2,100 51 78,000 4 31,540 7 43,200 2.5 6 41,610

4B 293+00 274+00 1,900 51 78,000 5 37,525 14 52,400 2.5 11 49,400

4C 274+00 242+00 3,200 51 78,000 4 36,100 14 52,700 2.5 10 47,980

4D 242+00 221+23 2,100 51 78,000 7 43,795 22 61,900 2.5 17 56,720

5A 221+23 188+88 3,200 51 78,000 5 41,183 15 54,500 2.5 15 53,490

5B 188+88 146+28 4,300 51 78,000 11 49,637 25 66,000 2 21 61,280

5C 146+28 1417+39 1,200 51 78,000 5 40,185 13 52,000 2 - -

6A 1417+39 1366+00 5,100 57 83,700 5 42,989 22 65,600 2 - -

6B 1366+00 1326+00 4,000 57 83,700 5 37,763 19 61,300 2 - -

6C 1326+00 1289+50 3,700 57 83,700 5 38,760 19 61,800 2 - -

Notes:

1. Bank full capacity assumes HESCO barriers provide required freeboard.

2. Bank full capacity not analyzed for reaches that did not have HESCO barriers.

Table 2. Sediment Cut Volumes

Segment No.

RAS U/S

XS

RAS D/S

XS

O&M Station Reach 100% Cut

Sediment Volume

(cu. yard)1

50% Cut Sediment Volume

(cu. Yard)1

1 54396.45 54240.75 40425.00 2A 14 8

54240.75 54042.65 40227.00 2A 112 58

3 54042.65 53844.55 40029.00 2A 504 254

4 53844.55 53646.63 39831.00 2A 676 339

5 53646.63 53470.85 39655.00 2A 384 194

6 53470.85 53277.07 39462.00 2A 1008 504

7 53277.07 53145.35 39330.00 2A 1006 514

8 53145.35 53013.66 39198.00 2A 761 384

9 53013.66 52900.65 39085.00 2A 631 324

10 52900.65 52726.86 38911.00 2A 1041 533

11 52726.86 52522.11 38707.00 2A 787 404

12 52522.11 52351.77 38536.00 2A 359 185

13 52351.77 52152.34 38337.00 2A 1173 595

14 52152.34 51686.96 37872.00 2A 1228 625

15 51686.96 51502.94 37688.00 2A 89 46

16 51502.94 51004.84 37189.00 2A 668 339

17 51004.84 50493.38 36678.00 2A 764 392

18 50493.38 50243.2 36428.00 2A 747 400

19 50243.2 49993.1 36178.00 3 NA NA

20 49993.1 49742.9 35928.00 3 NA NA

21 49742.9 49492.82 35677.00 3 NA NA

22 49492.82 49137.41 35322.00 3A NA NA

23 49137.41 48977.87 35162.00 3A NA NA

24 48977.87 48798.47 34983.00 3A NA NA

Notes:

1. NA - volume of sediment not computed for concrete bottom sections.

Table 2. Sediment Cut Volumes (continued)

No.

RAS U/S

XS

RAS D/S

XS

O&M Station Reach 100% Cut

Sediment Volume

(cu. yard) 1

50% Cut Sediment Volume

(cu. Yard) 1

25 48798.47 48603.79 34788.00 3 NA NA

26 48603.79 48414.3 34599.00 3 NA NA

27 48414.3 48183.92 34369.00 3 NA NA

28 48183.92 47966.24 34151.00 3 NA NA

29 47966.24 47881.1 34066.00 3 NA NA

30 47881.1 47784.81 33969.00 3 NA NA

31 47784.81 47568.16 33753.00 3 NA NA

32 47568.16 47488.16 33673.00 3 NA NA

33 47488.16 47407.21 33592.00 3 NA NA

34 47407.21 47274.55 33459.00 3 NA NA

35 47274.55 47142.05 33327.00 3 NA NA

36 47142.05 47009.45 33194.00 3 NA NA

37 47009.45 46876.95 33062.00 3 NA NA

38 46876.95 46710.1 32895.00 3 NA NA

39 46710.1 46376.4 32561.00 3 NA NA

40 46376.4 46209.5 32394.00 3 NA NA

41 46209.5 46042.7 32227.00 3 NA NA

42 46042.7 45875.89 32061.00 3 NA NA

43 45875.89 45752.2 31937.00 3 NA NA

44 45752.2 45628.5 31813.00 3 NA NA

45 45628.5 45504.8 31689.00 3 NA NA

46 45504.8 45381.2 31566.00 3 NA NA

47 45381.2 45257.53 31442.00 3 NA NA

48 45257.53 45078.4 31263.00 4A 752 378

49 45078.4 44889.4 31074.00 4A 654 333

50 44889.4 44720.3 30905.00 4A 734 375

No.

RAS U/S

XS

RAS D/S

XS

O&M Station Reach 100% Cut

Sediment Volume

(cu. yard) 1

50% Cut Sediment Volume

(cu. Yard) 1

51 44720.3 44541.2 30726.00 4A 829 422

52 44541.2 44362.2 30547.00 4A 562 283

53 44362.2 44183.1 30368.00 4A 779 395

54 44183.1 44004.1 30189.00 4A 919 468

55 44004.1 43825.05 30010.00 4A 988 499

56 43825.05 43684.1 29869.00 4A 947 483

57 43684.1 43543.2 29728.00 4A 612 308

58 43543.2 43402.3 29587.00 4A 624 316

59 43402.3 43261.49 29446.00 4A 654 335

60 43261.49 43098.56 29283.00 4A 440 225

61 43098.56 42939.4 29124.00 4B 712 357

62 42939.4 42780.25 28965.00 4B 667 334

63 42780.25 42621.15 28806.00 4B 751 379

64 42621.15 42462 28647.00 4B 540 279

65 42462 42302.85 28487.00 4B 325 169

66 42302.85 42143.75 28328.00 4B 425 217

67 42143.75 41984.65 28169.00 4B 487 247

68 41984.65 41825.47 28010.00 4B 693 348

69 41825.47 41625.5 27810.00 4B 816 417

70 41625.5 41425.5 27610.00 4B 890 452

71 41425.5 41225.5 27410.00 4B 782 391

72 41225.5 41025.5 27427.38 4C 614 313

73 41025.5 40825.5 27010.00 4C 852 433

74 40825.5 40625.5 26810.00 4C 835 429

75 40625.5 40425.5 26610.00 4C 642 326

No.

RAS U/S

XS

RAS D/S

XS

O&M Station Reach 100% Cut

Sediment Volume

(cu. yard) 1

50% Cut Sediment Volume

(cu. Yard) 1

76 40425.5 40225.5 26410.00 4C 807 413

77 40225.5 40025.5 26210.00 4C 945 479

78 40025.5 39825.85 26010.00 4C 890 451

79 39825.85 39659.15 25844.00 4C 769 386

80 39659.15 39492.55 25677.00 4C 622 314

81 39492.55 39325.85 25510.00 4C 389 194

82 39325.85 39159.15 25344.00 4C 446 225

83 39159.15 38992.5 25177.00 4C 586 294

84 38992.5 38825.8 25010.00 4C 444 226

85 38825.8 38658 24843.00 4C 322 165

86 38658 38490.5 24675.00 4C 505 259

87 38490.5 38322.75 24507.00 4C 374 192

88 38322.75 38155 24340.00 4C 406 205

89 38155 37987.4 24172.00 4D 331 167

90 37987.4 37745.2 23930.00 4D 447 231

91 37745.2 37561.05 23746.00 4D 407 204

92 37561.05 37376.95 23562.00 4D 514 263

93 37376.95 37192.75 23377.00 4D 621 314

94 37192.75 37008.65 4D 599 302

95 37008.65 36824.52 23009.00 4D 432 219

96 36824.52 36695.65 22880.00 4D 363 183

97 36695.65 36566.75 22751.00 4D 390 196

98 36566.75 36437.85 22622.00 4D 82 42

99 36437.85 36308.91 4D 175 90

100 36308.91 36121.15 4D NA NA

101 36121.15 35877.25 22062.00 4D NA NA

No.

RAS U/S

XS

RAS D/S

XS

O&M Station Reach 100% Cut

Sediment Volume

(cu. yard) 1

50% Cut Sediment Volume

(cu. Yard) 1

102 35877.25 35622.66 21807.00 5A NA NA

103 35622.66 35422.66 21607.00 5A 1383 692

104 35422.66 35236.05 21421.00 5A 1338 672

105 35236.05 35022.66 21207.00 5A 1049 532

106 35022.66 34862.85 21047.00 5A 839 424

107 34862.85 34676.25 20861.00 5A 1250 627

108 34676.25 34489.62 20674.00 5A 859 433

109 34489.62 34293 20478.00 5A 1239 634

110 34293 34096.5 20281.00 5A 1550 794

111 34096.5 33850 20035.00 5A 1904 969

112 33850 33621.75 19806.00 5A 823 415

113 33621.75 33322 19507.00 5A 1287 658

114 33322 33172.5 19357.00 5A 533 271

115 33172.5 33023.1 19208.00 5A 593 298

116 33023.1 32873.69 19058.00 5A 642 325

117 32873.69 32703.2 18888.00 5B 847 431

118 32703.2 32509.35 18694.00 5B 1015 NA

119 32509.35 32311.95 18497.00 5B 923 NA

120 32311.95 32117.8 18302.00 5B 491 NA

121 32117.8 31895.4 18080.00 5B 360 182

122 31895.4 31723.37 17908.00 5B 609 311

123 31723.37 31490.84 17675.00 5B 706 361

124 31490.84 31200 17385.00 5B 1699 859

125 31200 30891.9 17077.00 5B 2045 1029

126 30891.9 30634.6 16819.00 5B 857 429

127 30634.6 30362.63 16547.00 5B 834 422

No.

RAS U/S

XS

RAS D/S

XS

O&M Station Reach 100% Cut

Sediment Volume

(cu. yard) 1

50% Cut Sediment Volume

(cu. Yard) 1

128 30362.63 30096.27 16281.00 5B 787 404

129 30096.27 29820.79 16005.00 5B 940 472

130 29820.79 29334.8 15519.00 5B 1736 871

131 29334.8 29152.35 15337.00 5B 764 391

132 29152.35 28970 15155.00 5B 678 347

133 28970 28787.55 14972.00 5B 534 270

134 28787.55 28605.13 14790.00 5B 487 249

135 28605.13 28443.12 14628.00 5C NA NA

136 28443.12 28312.27 14497.00 5C NA NA

137 28312.27 28137.15 14322.00 5C 2624 1319

138 28137.15 27961.95 14147.00 5C 3089 1559

139 27961.95 27786.75 13971.00 5C 3094 1557

140 27786.75 27478.29 142204.00 5C 5009 2540

141 27478.29 27294.44 142020.00 5C 3547 1784

142 27294.44 27028.42 141754.00 5C 4395 2221

143 27028.42 26865.25 141591.00 6A 2552 1276

144 26865.25 26702 141428.00 6A 2742 1380

145 26702 26538.97 141265.00 6A 1672 838

146 26538.97 26272.78 140998.00 6A 2673 1348

147 26272.78 25994.42 140720.00 6A 3302 1655

148 25994.42 25784.54 140510.00 6A 4219 2118

149 25784.54 25594.42 140320.00 6A 3707 1860

150 25594.42 25383.83 140109.00 6A 4501 2269

151 25383.83 25194.42 139920.00 6A 3679 1841

152 25194.42 24994.42 139720.00 6A 3539 1783

153 24994.42 24794.42 139520.00 6A 3063 1532

No.

RAS U/S

XS

RAS D/S

XS

O&M Station Reach 100% Cut

Sediment Volume

(cu. yard) 1

50% Cut Sediment Volume

(cu. Yard) 1

154 24794.42 24594.42 139320.00 6A 3582 1793

155 24594.42 24394.42 139120.00 6A 2891 1457

156 24394.42 24194.42 138920.00 6A 2155 1089

157 24194.42 23994.42 138720.00 6A 2077 1053

158 23994.42 23794.42 138520.00 6A 2282 1145

159 23794.42 23566.45 138292.00 6A 2142 1083

160 23566.45 23394.42 138120.00 6A 1093 547

161 23394.42 23194.42 137920.00 6A 1254 635

162 23194.42 22994.42 137720.00 6A 1327 668

163 22994.42 22794.42 137520.00 6A 1555 789

164 22794.42 22594.42 137320.00 6A 2528 1276

165 22594.42 22394.42 137120.00 6A 3442 1728

166 22394.42 22194.42 136920.00 6A 4543 2276

167 22194.42 21991.79 136717.00 6A 4057 2038

168 21991.79 21794.42 136520.00 6B 3503 1759

169 21794.42 21594.42 136320.00 6B 3133 1582

170 21594.42 21394.42 136120.00 6B 2747 1389

171 21394.42 21245.59 135971.00 6B 2323 1169

172 21245.59 20994.42 135720.00 6B 4042 2036

173 20994.42 20794.42 135520.00 6B 3285 1646

174 20794.42 20594.42 135320.00 6B 3745 1876

175 20594.42 20291.36 135017.00 6B 5527 2786

176 20291.36 19994.42 134720.00 6B 7576 3803

177 19994.42 19794.42 134520.00 6B 4933 2475

178 19794.42 19589.27 134315.00 6B 3621 1816

179 19589.27 19394.42 134120.00 6B 4201 2106

No.

RAS U/S

XS

RAS D/S

XS

O&M Station Reach 100% Cut

Sediment Volume

(cu. yard) 1

50% Cut Sediment Volume

(cu. Yard) 1

180 19394.42 19181.42 133907.00 6B 5211 2612

181 19181.42 18994.42 133720.00 6B 4344 2175

182 18994.42 18794.42 133520.00 6B 5160 2585

183 18794.42 18594.42 133320.00 6B 5679 2848

184 18594.42 18439.79 133165.00 6B 4053 2029

185 18439.79 18194.42 132920.00 6B 5790 2907

186 18194.42 17994.42 132720.00 6B 4568 2287

187 17994.42 17695.15 132421.00 6C 9082 4546

188 17695.15 17594.42 132320.00 6C 3239 1627

189 17594.42 17394.42 132120.00 6C 4686 2348

190 17394.42 17261.45 131987.00 6C 2207 1112

191 17261.45 16994.42 131720.00 6C 5135 2586

192 16994.42 16794.42 131520.00 6C 5417 2721

193 16794.42 16594.42 131320.00 6C 5503 2755

194 16594.42 16412.01 131138.00 6C 3873 1949

195 16412.01 16174.04 130900.00 6C 5122 2566

196 16174.04 15994.42 130720.00 6C 4142 2080

197 15994.42 15794.42 130520.00 6C 4856 2445

198 15794.42 15594.42 130320.00 6C 4052 2028

199 15594.42 15394.42 130120.00 6C 3057 1530

200 15394.42 15075.87 129801.00 6C 3133 1567

201 15075.87 added line 6C 1780 916

202 added line 14476.06 129202.00 6C NA NA

203 14476.06 14241.06 128967.00 6C NA NA

Table 3. Project Scenarios and Corresponding RAS Plan

Scenario Description Reach RAS Plan

Base Case - Current capacity without HESCO Barriers in place

2A 1D_base_2A_2020Update (p67)

3 1D_base_3A_2020Update (p68)

3 1D_base_3B_2020Update (p69)

4A 1D_base_4A_2020Update (p70)

4C 1D_base_4C_2020Update (p71)

4D 1D_base_4D_2020Update (p72)

5A 1D_base_5A_2020Update (p73)

5B 1D_base_5B_2020Update (p74)

5C 1D_base_5C_2020Update (p75)

6A 1D_base_6A_2020Update (p76)

6B 1D_base_6B_2020Update (p77)

6C 1D_base_6C_2020Update (p78)

4B 1D_base_4B_2020Update (p79)

Final Capacity - with 50% sediment volume removed All Reaches

1D_cut50_all_reaches_2021Update (p29)

Bank Full Capacity - Assuming HESCO Barriers provide freeboard

4A, 4B, 4C, 4D, 5A, 5B 1D_base_4A_bankfull (p30)

Table 4. Photographs from 2020 Field Visit and Corresponding Manning's n Values

Location n-value Photo

Reach 2A .06

Reach 2A, Upstream of Golden State Fwy

.05

Table 4. Photographs from 2020 Field Visit and Corresponding Manning's n Values (continued)

Reach 2A, Downstream of

Golden State Fwy

Reach 3A .014

Reach 4A (Approx. RAS River

Station 45257.53)

.014

Station 45078.40)

.07

Station 44541.20)

Reach 4A, Upstream of Colorado St FWY

Ext.

Reach 4B

Station 42939.4)

.04

Reach 4B

Station

42302.85)

Reach 4C

Station 40425.5)

(Approx. RAS River Station

39825.85)

River Station

38322.75)

Reach 5A

River Station

35422.66)

Reach 5C

River Station

27786.75)

.06

Reach 5C, Upstream of

Glendale Fwy

Reach 6A, Downstream of Glendale Fwy

Reach 6B .1

Reach 6C

River Station

17594.42)

.12

Reach 6C

River Station

15794.42)

CESPL-EDH-G 26 September 2018

MEMORANDUM FOR Operations Division, Attn: Kelly Howard

SUBJECT: Justification for Vegetation and Sediment Removal at Bridge Crossings in Los Angeles River

ARBOR Reach

1. References:

a. U.S. Army Corps of Engineers, Los Angeles District, Memorandum for Record, Hydrology

Section Justification for native vegetation removal at the Riverside Drive crossing of the LA

River dated 23 December 2015.

b. U.S. Army Corps of Engineers, Hydrologic Engineering Center, HEC-RAS Hydraulic

Reference Manual. February 2016.

c. U.S. Army Corps of Engineers, Los Angeles District, Hydrology & Hydraulics Policy

Memorandum No. 4, August 2004.

Background

1. This memorandum documents a recommended vegetation removal plan for nine bridge crossings along Los Angeles River ARBOR Reach. Dense vegetation in the Los Angeles River ARBOR Reach reduces the capacity of the channel to convey its design flows, particularly at bridge crossings where the capacity is further constrained. In the current condition, the dense vegetation and bridge piers are susceptible to collecting debris and/or creating a blockage which increases the potential severity and likelihood of a potential breakout. In order to help reduce the risk of flooding the areas adjacent to the

Los Angeles River bridge crossings the removal of native and non-native vegetation in the immediate vicinity of the bridges is necessary to restore passage of flows through the bridge area. The 2015

Memorandum advised for the removal of vegetation at Riverside Drive Bridge to increase the capacity in the Los Angeles River by 15,000 cfs locally at the bridge. Before and after vegetation removal photos are shown in Figures 1 through 4 of Enclosure 1.

Purpose

2. Operations Division requested Hydrology and Hydraulics Branch perform a similar analysis, as was performed at Riverside Bridge (USACE, 2015), for the remaining nine bridges between Riverside Drive and the Arroyo Seco confluence. They also asked for recommendations for the amount of vegetation and sedimentation removal at each bridge (Plate 1).

Vegetation Field Assessment

3. Adam Bier and Lauren Coe (EDH-G) inspected the bridge study areas on 23 May 2018. Enclosure 1 shows representative photos of each bridge crossing. The following sections provide an engineering assessment and documentation of field notes from the site visit for each bridge location starting at the upstream end:

Golden State Freeway (I-5) Bridge at O&M Sta. 378+00 – Channel is trapezoidal with natural bottom and concrete side slopes at this location and transitions to a concrete bottom approximately

500 feet downstream of the bridge. No dense brush vegetation was observed, however established trees and sedimentation at a depth of approximately 2 feet above the invert were noted in the center of the channel. (Figures 5 and 6, Enclosure 1).

State Route 134 Bridge at O&M Sta. 339+00 – Channel is rectangular and concrete lined in this location. Transition from natural invert occurs approximately 3,000 feet upstream of the bridge and transitions back to natural 2,300 feet downstream of the bridge. Transition to rectangular channel occurs 200 feet upstream of the bridge and transition to a trapezoidal channel occurs 900 feet downstream of the bridge. Some very minimal sedimentation was noted along the channel toe, but not to an extent to constrict capacity.

Colorado Boulevard Bridge at O&M Sta. 294+00 – Channel is trapezoidal with natural bottom at this location. Dense vegetation and sediment was noted for several hundred feet upstream and downstream of the bridge. Sediment was observed to be approximately two to four feet deep above the invert. (Figure 7, Enclosure 1).

Los Feliz Boulevard Bridge at O&M Sta. 221+00 – Channel is rectangular with concrete bed in this location. Transition from natural invert occurs approximately 400 feet upstream of the bridge and transitions back to natural 280 feet downstream of the bridge. The channel transitions from and to a trapezoidal channel approximately 150 feet upstream and downstream of the bridge centerline.

Minimal vegetation was noted upstream of the bridge and no dense vegetation was observed within approximately 600 feet downstream of the bridge (Figures 8 and 9, Enclosure 1).

Sunnynook Drive Pedestrian Bridge at O&M Sta. 199+00 - Channel has a natural bottom in this location. The bridge has four bridge piers and each is approximately 3 feet wide. Dense vegetation and trees were noted in this reach with trees extending above channel banks. Sediment depth was observed to be approximately two to four feet deep above the invert. (Figures 10 and 11, Enclosure

1).

Glendale Boulevard/Hyperion Avenue Bridge at O&M Sta. 188+00 – Channel has a concrete bed downstream of the bridge and natural bed upstream of the bridge. Transition from natural invert occurs approximately 150 feet upstream of the bridge and transitions back to natural 500 feet downstream of the bridge centerline. Dense vegetation and sediment was noted upstream of the bridge, however no vegetation was noted within approximately 400 feet downstream of the bridge.

Sediment depth was observed to be approximately two to four feet deep above the invert. (Figures

12, 13 and 14, Enclosure 1).

Fletcher Drive Bridge at O&M Sta. 146+00 – Channel has a concrete invert in this location that extends 175 feet both upstream and downstream of the bridge before transitioning back to natural invert. Approximately 5 feet of sediment above toe of slope and dense established vegetation was noted both upstream and downstream of the bridge (Figures 15 and 16, Enclosure 1).

State Route 2 Freeway Bridge at O&M Sta. 1417+00- Channel has a natural bottom in this location.

Approximately 5 to 8 feet of sediment above toe of slope upstream and downstream of bridge

(Figures 17 and 18, Enclosure 1). Moderate vegetation is established in the areas of heavy sedimentation.

Interstate 5 Near Arroyo Seco at O&M Sta. 1290+00 – Channel has a concrete invert in this location. The transition from a trapezoidal natural bed channel to a rectangular concrete bed channel occurs 500 feet upstream of the bridge. The channel has a concrete invert for the remainder of the ARBOR reach and no vegetation or sedimentation was observed in the immediate areas upstream or downstream of the bridge.

Hydraulics Analysis

4. A 2016 HEC-RAS 1D/2D unsteady model was used to determine the effects of vegetation and sediment removal down to as-built conditions at each of the bridges listed above. The hydraulic modeling was completed using 25-year hydrographs for Los Angeles River. The 2016 hydraulic model baseline condition was based on the condition of the channel prior to all vegetation removal, including that which was completed in 2017 at Riverside Drive. For the removal condition at Riverside Drive, the n-values and channel geometry were adjusted upstream and downstream of Riverside Bridge to reflect the vegetation removal that was completed in 2017 and the proposed sediment removal.

5. Vegetation and sediment removal upstream and downstream of each bridge was simulated by reducing the cross-section n-value from existing conditions and revising the invert geometry in HEC-RAS to match as-built conditions. Sensitivity analysis was performed to determine the extent of vegetation and sediment removal at bridge that provided the desired impact of lowering the water surface and/or increasing the flow at the bridge. An n-value of 0.035 was selected as a representative channel following the removal of vegetation and sediment to as-built conditions. This assumption accounts for some vegetation regrowth as a conservative assumption. The HEC-RAS Hydraulic Reference Manual recommends an n-value of 0.035 for mostly clean natural channels with some weeds and stones (HEC 2016). Based on Los Angeles

District Hydrology & Hydraulics Policy Memorandum No. 4, 2 feet of floating debris was added to each side of all piers that measure 6 feet or less in width (transverse direction). For piers with sloping noses, the debris depth was set to 6 feet below the water surface elevation. Floating debris was not added to piers greater than 6 feet in width. Sediment volumes were estimated using the end area method and comparing cross-sectional flow area between the pre and post removal condition. The removal plan is presented in

Table 1.

Table 1. Proposed Sediment and Vegetation Removal Plan for Los Angeles River ARBOR Reach Bridges.

Bridge Crossing Removal Plan 1 Note

Riverside Drive2 300 ft U/S and 200 ft D/S Sediment volume estimated from RAS terrain

Interstate Fwy 5 (U/S end) 250 ft U/S and

200 ft D/S

Sediment approximately 2 ft high, volume estimated from site visit observations

State Route 134 Fwy None recommended Concrete bed, no need for vegetation or sediment removal

Colorado Blvd 500 ft U/S and 500 ft D/S Sediment volume estimated from RAS terrain

Los Feliz Blvd None recommended Concrete bed, no need for vegetation or sediment removal

Sunnynook Drive 400 ft U/S and 300 ft D/S Sediment volume estimated from RAS terrain

Glendale- Hyperion Ave 500 ft U/S

U/S Sediment volume estimated from RAS terrain

Concrete bed D/S, no need for vegetation or sediment removal

Fletcher Dr 400’ U/S of Fletcher to

1,000’ D/S State Route 2

Sediment volume estimated from RAS terrain

State Route 2 Fwy Sediment volume estimated from RAS terrain

Interstate Fwy 5 NR Arroyo Seco None recommended Concrete bed, no need for vegetation or sediment removal

Notes: 1 Removal lengths measured from bridge centerline 2 Riverside Dr. Vegetation Removal was previously completed in 2017. Sediment removal proposed has yet to be completed

Table 2 shows the flow rate, water surface elevations, and associated return period for both the pre- and post-removal condition at each bridge. The estimated sediment volume to be removed is also presented.

Bridges at which the channel invert is concrete did not have a recommended vegetation or sediment removal plan because vegetation and sediment was minimal; however, flowrates and water surface elevations were still reported at these locations to demonstrate any impacts of removal at nearby bridge locations.

Table 2. Pre-Removal and Proposed Sediment and Vegetation Removal condition flow rates and water surface elevations (HEC-RAS).

Bridge Crossing Pre- Removal Q

(cfs)

Pre- Removal

WSE (ft)

Pre- Removal Q

Return Period

(yr)

Estimated

Sediment

Removal

(cu. yds)

Removal

Plan, Q (cfs)

Removal Plan Q

Return Period

(yr)

Removal Plan, WSE (ft)

Riverside Drive 44,560 471* 10* 6,000 53,600 19 468.8

Interstate Fwy 5 (U/S end) 52,770 461.0 18 2,000 53,600 18 461.0

State Route 134 Fwy2 52,450 442.1 18 N/A 53,400 18 441.8

Colorado Blvd 56,900 432.8* 17* 7,500 63,400 23 430.9

Los Feliz Blvd 58,370 396.1 19 N/A 61,660 21 396

Sunnynook Drive 58,360 387.8 19

6,000

61,600 21 383.5

Glendale- Hyperion Ave 58,350 380.0 19 61,600 21 380.3

Fletcher Dr 58,310 365.2 17

45,000

62,420 20 362.0

State Route 2 Fwy 58,320 361.8 19 62,400 22 360.3

Interstate Fwy 5 NR Arroyo

Seco 58,160 308.5 17 N/A 60,800 18 308.7

TOTAL Sediment Removal 66,500 CY

* The channel bank elevation at Riverside Drive is 469.6 feet. Therefore in the pre-removal condition, water escapes the channel below the 10-year frequency. The channel bank elevation at Colorado Blvd is 431.6 feet. Therefore in the existing condition, water escapes the channel below the 17-year frequency.

6. The results in Table 2 are a product of implementing all of the recommendations presented in

Table 1. By clearing vegetation and sediment at the bridges, channel capacity increased, resulting in more flow passing downstream It should be noted that there still remains potential for vegetation, transported from upstream of the clearing section, to be caught along bridge piers. Conveyance capacity at the bridge increased with a decrease in water surface elevation with a few exceptions. The water surface elevation remained the same at the

Interstate 5 Bridge (Sta. 378+00). Water surface elevations increased at the Glendale Blvd and Interstate 5 Bridge near Arroyo Seco (Sta. 1290+00). This increase in water surface elevation is due to increased flow in the channel at these locations due to the removal of sediment and vegetation at reaches upstream.

Recommendations

7. Table 3 outlines the recommended prioritization of vegetation and sediment removal locations based on increased capacity and an associated improvement of the return period flow the channel is capable of conveying at the bridge. As stated previously, the results of the removal plan assumes removal at all bridges is implemented.

Table 3. Recommended Vegetation and Sediment Removal Prioritization

High Priority

Colorado Blvd

Fletcher Drive

State Route 2 Freeway

Riverside Drive

Moderate Priority

Sunnynook Drive

Glendale- Hyperion Avenue

Interstate Freeway 5 (U/S end)

Low Priority (No recommended removal)

State Route 134 Freeway

Los Feliz Blvd

Interstate Freeway 5 NR Arroyo Seco

8. The recommendations from previous memoranda still apply, i.e. removal of all the vegetation that causes significant flow resistance. All trees too large to bend over with the flow must be removed. All other vegetation that is flexible or is prone to washing out altogether may remain.

The following are additional guidance:

Any woody perennial growth with a stem diameter greater than 1-inch should be cleared and grubbed. Only flexible vegetation is to be allowed in the river. Height of vegetation is not of vital concern, however, the main governing criteria is its density and ability to bend with flow.

All non-native plants, regardless of stem diameter, should be cleared and grubbed.

Fletcher Dr

Sunnynook Dr

Interstate 5

Interstate 5

Colorado Blvd

Glendale Fwy 2

Los Feliz Blvd

Ventura Fwy 134

Hyperion Ave / Glendale Blvd

U.S. ARMY CORPS OF ENGINEERS

LOS ANGELES DISTRICT

LAR VEGETATION

REMOVAL 2018

BRIDGE LOCATIONS

0 0.5 10.25 Miles

³ Legend !. Bridges

PLATE 1

Sources:

Imagery Background:

ESRI ArcGIS Online Basemap Sources Copyright:© 2012 Esri, DeLorme, NAVTEQ, TomTom Coordinate System:

State Plane California VI (FIPS 406, Feet) Datum: NAD 1983

1 inch = 1 miles

DATA TRANSMITTAL REPORT

Los Angeles River Reach 5C Sediment Sampling and Analysis

Los Angeles, California

Prepared for:

Unites States Army Corps of Engineers

915 Wilshire Blvd, 11th Floor

Los Angeles, California 90017

Prepared by:

Amec Foster Wheeler Environment & Infrastructure, Inc.

121 Innovation Drive, Suite 200

Irvine, California 92617-3094

(949) 642-0245

June 22, 2017

Project No. IR17166540

P:\166540\Docs\Data Transmittal Report\LA River Final Report_06-22-17.docx i

TABLE OF CONTENTS

Page

1.0 INTRODUCTION

2.0 BACKGROUND

3.0 PURPOSE

3.1 SCOPE OF WORK

3.2 SUMMARY OF INVESTIGATION APPROACH

4.0 PREFIELD ACTIVITIES

5.0 FIELD ACTIVITIES

5.1 FIELD SAMPLING

5.2 SEDIMENT SAMPLING, COLLECTION LOCATIONS, AND DEVIATIONS

5.2.1 Composite Sediment Sampling for Chemical Analyses and Collection Locations

5.2.2 Targeted Sediment Sample for Chemical Analyses

5.2.3 Discrete Sediment Samples for Geotechnical Testing

5.2.4 Field Sampling Deviation

5.3 DOCUMENTATION AND LITHOLOGIC LOGGING

6.0 LABORATORY TESTING

6.1 SAMPLES FOR CHEMICAL ANALYSES

6.2 CHEMICAL TESTING AND DEVIATIONS

6.2.1 Chemical Testing

6.2.2 Analytical Program Deviations

6.3 GEOTECHNICAL TESTING AND DEVIATIONS

6.3.1 Geotechnical Testing

6.3.2 Geotechnical Testing Deviations

7.0 RESULTS AND DATA EVALUATION

7.1 SUMMARY OF CHEMICAL ANALYTICAL RESULTS

7.2 DATA QUALITY REVIEW OF CHEMICAL DATA

7.3 CHEMICAL DATA EVALUATION

7.3.1 Regional Screening Levels

7.3.2 Waste Characterization Criteria

7.4 GEOTECHNICAL RESULTS

8.0 DISCUSSION OF DISPOSAL OPTIONS

9.0 SUMMARY AND CONCLUSIONS

10.0 REFERENCES

TABLE OF CONTENTS

(Continued)

Amec Foster Wheeler Environment & Infrastructure, Inc.

P:\166540\Docs\Data Transmittal Report\LA River Final Report_06-22-17.docx ii

TABLES

Table 1 Sample Locations and Depths for Composite and Targeted Sediment Samples Table 2 Sediment Sample Chemical Composites Table 3 Analytical Results for TRPH, PCBs, VOCs, Organochlorine Pesticides, and

PAHs in Sediment Samples Table 4 Analytical Results for pH and Metals in Sediment Samples Table 5 Analytical Results for Soluble Lead in Sediment Samples

FIGURES

Figure 1 Site Location Map Figure 2 Sediment Sample Locations

APPENDIXES

Appendix A USACE’s Scope of Work Appendix B Sampling and Analysis Plan Appendix C Photo Log Appendix D Trench Logs Appendix E Analytical Chemical Testing Laboratory Report and Chain-of-Custody

Documentation Appendix F Geotechnical Testing Laboratory Reports Appendix G Summary Data Quality Review Appendix H Disposal Option Forms and ROM Cost Estimate

P:\166540\Docs\Data Transmittal Report\LA River Final Report_06-22-17.docx 1

DATA TRANSMITTAL REPORT

Los Angeles River Reach 5C Sediment Sampling and Analysis

Los Angeles, California

1.0 INTRODUCTION

Amec Foster Wheeler Environment & Infrastructure, Inc. (Amec Foster Wheeler), has prepared this Data Transmittal Report (Report) on behalf of the United States Army Corps of

Engineers, Los Angeles District (USACE) to present the findings of the sediment sampling, chemical testing, and geotechnical testing of sediments at the Los Angeles River Reach 5C, between Fletcher Drive and the Glendale Freeway (California State Route 2), located in Los

Angeles, California (the Site or Reach 5C; Figure 1). This Report was prepared in general accordance with the USACE’s Scope of Work dated February 14, 2017 (SOW; Appendix A) and the April 4, 2017 Sampling and Analysis Plan prepared by Amec Foster Wheeler (SAP;

Appendix B).

2.0 BACKGROUND

As part of the emergency flood risk management associated with the forecasted 2016 El Nino winter storm season (Regional General Permit No. 63, Regulatory Memorandum For Record

Dates 07JAN2016), a Categorical Exclusion plan dated February 2016 was prepared by the

USACE. This Categorical Exclusion plan proposes to remove exotic-invasive vegetation from the Site. Sediment deposition within Reach 5C has resulted in a sediment bar that contains a high percentage of cobble-sized clasts, extends across approximately 215 feet of the channel, and covers an area of approximately 4.0 acres. The bar limits flow conveyance and confines the current thalweg to widths ranging from approximately 12 to 30 feet near the south side of the river embankment (USACE, 2016).

The USACE proposes to remove and transport off-site for disposal/reuse approximately

50,000 cubic yards (CY) of sediment accumulated in the sediment bar of Reach 5C. Based on our review of the approximate elevations and the design elevation provided by the USACE for this project, the sediments to be removed range in thickness from approximately 2 to 8 feet.

The area within which sediments are to be characterized was identified as approximately

174,500 square feet, or approximately 4 acres. The USACE has not identified the location for disposal/reuse of the sediments. The chemical and geotechnical properties of the sediments were evaluated to assess their suitability for potential disposal/reuse at offsite locations.

P:\166540\Docs\Data Transmittal Report\LA River Final Report_06-22-17.docx 2

This project was authorized as follows: “IAW Memorandum for the Record dated 28 Jan 2016, Recommended Repair of Levee Toe Erosion Damage and Other O&M Work, Los Angeles

River, paragraph 7- Los Angeles River sediment needs to be removed and disposed of properly based on sediment contamination.”

3.0 PURPOSE

The purpose of this project was to obtain data for use in identifying and evaluating potential disposal/reuse options for the sediment.

3.1 SCOPE OF WORK

The SOW for investigation of the site closely followed the SOW issued to Amec Foster

Wheeler by the USACE and included the following:

prepared a SAP;

performed a bird nesting survey prior to sampling each day (completed by a biologist with the USACE);

collected sediment samples at various depths from 25 locations at the Site using a backhoe;

performed chemical analyses on composite, targeted, and discrete sediment samples;

performed geotechnical testing of discrete sediment samples;

prepared lithologic logs of all trenches;

evaluated the results of the chemical and geotechnical testing to identify potential disposal/reuse options for the sediment proposed for removal from Reach 5C;

maintained quality assurance and quality control; and prepared this report.

3.2 SUMMARY OF INVESTIGATION APPROACH

Based on the Site area (approximately 174,500 square feet) and estimated volume

(50,000 CY) of sediments to be removed, the sampling program included the collection of

50 sediment samples from 25 locations (Amec Foster Wheeler, 2017). The sampling program was based on a sampling grid of approximately 85 by 85 feet. The actual sampling locations were selected in the field based on logistical conditions and access available during field work.

In addition, one targeted sample was collected from sediments that exhibited slight

P:\166540\Docs\Data Transmittal Report\LA River Final Report_06-22-17.docx 3 discoloration and an elevated photoionization detector (PID) measurement relative to other sediment samples collected from the Site.

Sediment samples for chemical analysis, except for the targeted sample, were composited by the analytical laboratory for analyses in accordance with the SAP. The targeted sediment sample was analyzed for the same constituents as the composite samples. Three discrete sediment samples were collected for geotechnical testing in accordance with the SAP.

Results for total lead in the composite samples indicated concentrations of total lead that exceeded10 times the soluble threshold limit concentration (STLC) and/or 20 times the toxicity characteristic leaching procedure (TCLP) for lead. Consequently, soluble lead analyses were performed on composite samples and total and soluble lead analyses were performed on discrete sediment samples selected based on the total lead concentrations of their corresponding composite samples. Soluble lead results for several of these discrete sediment samples exceeded the STLC for lead. To provide a more representative data set for soluble lead, with USACE’s approval, the remaining discrete sediment samples collected during this investigation were analyzed for STLC for lead.

To evaluate the sediment proposed for removal from the Site, Amec Foster Wheeler completed the following.

Chemical results were compared to their respective United States Environmental Protection Agency (EPA) Region 9 Regional Screening Levels (RSLs) for Chemical Contaminants at Superfund Sites (EPA, 2016), California Department of Toxic Substances Control (DTSC)-modified screening levels (DTSC-SLs) for residential and commercial/industrial soils (DTSC, 2016), and/or waste characterization criteria (STLC, TCLP and total threshold limit concentration [TTLC]). Arsenic concentrations in sediment were compared to the DTSC Los Angeles County upper bound limits (DTSC, 2008), rather than the RSLs or DTSC-SLs. Consistent with DTSC screening level policy (DTSC, 2016), lead concentrations in sediment were compared to the DTSC LeadSpread 8 screening levels for residential and commercial/industrial land use (DTSC, 2011), rather than the RSLs.

Performed a statistical analysis of the soluble (STLC) lead data, in general accordance with Chapter 9 of the EPA publication SW-846, Test Methods for Evaluating Solid Waste, Physical/Chemical Methods (SW-846). Using these methods the 95 percent (%) upper confidence limit (UCL) of the mean for soluble (STLC) lead in discrete sediment samples collected at the Site was calculated.

4.0 PREFIELD ACTIVITIES

Prefield activities performed by Amec Foster Wheeler included: (1) preparing a SAP specific to this project; (2) subcontracting with a backhoe operator and laboratories capable of performing

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