HomeMy WebLinkAbout035-370-002 TRLC__CompWaterBalance_03052025
Central Valley Regional Water Quality Control Board
27 March 2025 WDID: 5A04NC00078
Donovan Dwyer
Trinity River Lumber Company
1375 Main Street
Weaverville, CA 96093
REVIEW OF COMPLETE WATER BALANCE, TRINITY RIVER LUMBER COMPANY
LOG YARD, 3000 SOUTH 7TH AVENUE, OROVILLE, BUTTE COUNTY
Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff
(Staff) have reviewed the 28 January 2025 Response to RWQCB Comments
Memorandum Request for Complete Water Balance submitted by your consultant
VESTRA Resources, Inc. (VESTRA). The water balance was submitted at the request
of Staff in a letter dated 3 December 2024. Below is a summary of the relevant site
conditions and parameters used in the water balance calculations.
WATER BALANCE CALCULATIONS
Per the December 2024 letter, the following considerations were to be included in the
water balance: a minimum of two feet of freeboard, historical local evapotranspiration,
pan evaporation, lake evaporation data (monthly average values), local precipitation
data with the 100-year return period, and projected long-term percolation rates
(including consideration of percolation from unlined ponds and the effects of solids
plugging on all ponds).
Average Annual Precipitation Water Balance
The average annual water balance incorporates average monthly precipitation from the
Oroville Municipal Airport. VESTRA assumed an initial seepage rate of 7.5 inches per
hour which is based on the vertical hydraulic conductivity of the exposed and underlying
geology. Additionally, VESTRA assumes that the seepage rates will decrease between
25 to 50 percent, therefore, it will be necessary to modify operational procedures or
upgrade the existing pond in 5 to 10 years to increase capacity. The average annual
water balance predicts that approximately 69,900 cubic feet of storage capacity is
required for pond design.
Trinity River Lumber Company - 2 - 27 March 2025
100-Year Annual Precipitation Water Balance
For the 100-year water balance, VESTRA multiplied the average monthly precipitation
by a common factor of 2.2 to obtain the 100-year annual precipitation so that was equal
to the 100-year annual precipitation as reported for the Oroville Bridge Station in DWR
Bulletin 195. The 100-Year annual water balance assumes an infiltration rate of 0.2
inches per hour which is characteristic of a loam soil. VESTRA concludes that based on
increased precipitation and lower infiltration rate, the surface area of the existing pond
would need to be increased from 0.3 to 0.4 acres and the depth would need to be
increased from 6.4 to 9.9 feet to accommodate the increased volume of water and
freeboard associated with the 100-year annual precipitation. That is, the 100-year
annual water balance predicts that approximately 151,700 cubic feet of storage capacity
is required for pond design.
RECOMMENDATIONS
The current plan is for the Facility to continue using the existing recycle pond until the
accumulation of fine-grained material results in surface discharge from the pond. At that
point, VESTRA proposes one or more of the following options to manage the excess
water:
1. Recycle accumulated water in the pond to irrigate the log deck. Per VESTRA, the
Facility is designed for this contingency.
2. Mechanically remove fine material from the recycled pond to increase infiltration.
3. Increase the size of the recycled pond to address decreasing seepage rates.
STAFF COMMENTS
Staff generally concur with the key assumptions used for calculating both water
balances (average annual precipitation and 100-year annual precipitation) and most of
the proposed options to manage the excess water. However, staff does not agree with
mechanically removing fine material from the recycled pond to increase infiltration of
process water into the subsurface. Central Valley Water Board anticipates the Facility
will have to modify the pond design to be able to accommodate the increase volume of
water and freeboard associated with increased precipitation and lower infiltration rate.
The modified pond design would likely include lining the pond to reduce water quality
impacts to the subsurface. Nonetheless, the water balances provided by VESTRA are
sufficient to move forward with preparing the new WDR.
Trinity River Lumber Company - 3 - 27 March 2025
If you have any questions, please contact me at (530) 224-4854,
Melissa.Buciak@waterboards.ca.gov, or by mail at the footer address below.
Melissa Buciak, P.G.
Engineering Geologist
Waste Discharge Requirements Unit
David Durette, P.E.
Senior Water Resource Control Engineer
Waste Discharge Requirements Unit
MAB: cc
cc electronically: Nikolay Ostroviskiy, Butte County Environmental Health Division, Oroville
John Andrews, VESTRA Resources, Inc., Redding