FEIS - Tahoe Regional Planning Agency

RESPONSE TO COMMENTS ON THE DEIS
B o u l d e r B a y C o m m u n i t y E n h a n c e m e n t P r o g r a m P r o j e c t E I S
o Stormwater runoff from the project area occurs in 6-7 days under E20 conditions
and 2-6 days for C20 conditions and does not occur for C100 conditions.
o Total sediment, fine sediment and nutrient loads are presented in Tables 2 and 3
of Appendix AB for a variety of wet and dry water year conditions. Field
monitoring of runoff from disturb soils indicates FSP load is 50 percent of TSS
loads from granitic soils and JBR data (DEIS Appendix P) reported levels as high
as 90%. For modeling and reporting purposes for the supplemental analysis, FSP
of less than 20 microns are reported as 60 to 90 percent of the TSS load. The
FSP load of less than 20 microns includes FSP loads of less than 16 microns. For
E20, C20 and C100, a dry year is forecasted to contribute 4,374 lbs, 1,714 lbs
and 134 lbs of FSP, respectively.
o The C100 SWMP will reduce total sediment loading by 97 to 100 percent as
compared to E20 SWMP.
• Wet Water Years/Worst-Case Scenarios (1994-1995 and 2005-2006) –
o E20 conditions result in possible discharge of approximately 17,000 to 32,000 lbs
of total sediment (note that the DEIS reports approximately 34,000 lbs based on
grab sample extrapolations) and 14,000 to 29,000 lbs of FSP leaving the project
area.
o Implementation of C20 reduces the landing compared to E20 by roughly 23 to 43
percent to ranges of 13,000 to 19,000 lbs of total sediment and 8,000 to 18,000
lbs of FSP.
o Implementation of C100 reduces loading compared to E20 by roughly 88 to 92
percent to ranges of 1,400 to 3,900 lbs total sediment and 800 to 3,500 lbs of
FSP.
o Stormwater runoff from the project area occurs on 34 to 42 days under E20
conditions, 16 to 27 days for C20 conditions and 3 to 5 days for C100 conditions.
o Stormwater runoff from the project area occurs under C100 conditions only for a
substantial rain-on-snow event of 5.37 inches (New Year’s Eve 2005) and after
sequential 2 inch rain-on snow events (January 2005).
o Data shows that in wetter years, which represent worst-case scenarios, total
sediment output from C100 SWMP is over an order of magnitude (10X) less than
those produced by E20.
Please see Appendix AB for supplemental analysis for additional quantification of surface water
quality benefits, notably predicted load reductions for total sediment, fine sediment and nutrients.
The analyses for Impacts HYDRO-1 and HYDRO-3 are presented in the format determined and
reviewed by TRPA Staff. The supplemental water quality analysis does not change the analysis
for HYDRO-1 and HYDRO-3 but provides additional quantified results that support the
conclusions that potential impacts discussed in HYDRO-1 and HYDRO-3 are reduced to a level
of less than significant.
SEPTEMBER 8 , 2010 HAUGE BRUECK ASSOCIATES PAGE 8- 15