This document summarizes a water use study for a sand and gravel processing plant. It finds that: 1) The plant uses about 40 million gallons of water per week, mostly for washing sand and gravel. Current water sources can supply 7 million gallons per week. 2) Water recycling from clarification and dewatering processes can meet most water demands. Additional wells or city connections may provide 200 gallons per minute of backup supply. 3) Simulations found the main water storage tank would not refill without at least 670 gallons per minute of continuous makeup water if no recycling occurred. With 50% gravel and 60% sand pile recycling, the tank refilled with 430 gallons per minute of makeup water

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PROJECT MEMORANDUM NO. 91-1313/06
PLANT WATER USE
PROJECT NO. 90-1313 LONE STAR NORTHWEST
PIONEER AGGREGATES SAND AND GRAVEL PLANT SEATTLE, WASHINGTON
DATE: MARCH 16, 1992
REV I: MARCH 30, 1992
INTRODUCTION
The project uses about 40,000,000 gallons of water per week, of which approximately 90
percent is used to wash sand gravel. Available water sources currently are estimated at 709
gpm or maximum of 7,000,000 gallons per week. In order to meet plant water demands, water
must be recycled and conserved to the maximum extent possible. As part of the project
design, HGI has reviewed the water supply requirements of the project and investigated the
adequacy of the water supply.
1. WATER SUPPLY SYSTEM
Most of the project water supply requirements will be met by recycling. Water that
can be recovered from the sand and gravel wash process will be pumped to a clarifier
where solids will be removed. Overflow, or clarified water, will be discharged to a
1,000,000 gallon storage reservoir and. the solids, or underflow, will be pumped to belt
presses to be further dewatered.
I Water that is consumed by plant operations will be replaced by a 600 gpm well owned
by LSNW and by a 109 gpm potable water supply from the City of Dupont.
A block flow diagram (drawing 1313-SK-PFD-00I, rev 0) is attached and shows
instantaneous plant water flows. A more detailed discussion of these flows follows.
2. SAND AND GRAVEL PROCESS WATER REQUIREMENTS
Wa ter is used to wash and process sand and gravel at the following three locations.
2.1 Gravel Wash Plant: Based on the Faris flow sheets, 9600 gpm will be required
at the gravel wash plant. About 2300 gpm will come from the sand plant
overflow to pre-wet material and the balance will come from the 1,000,000
gallon storage reservoir to wash material on the screens. About 300 gpm will be
conveyed to the stockpiles and 9300 gpm will be pumped to the sand plant with
minus #8 sand.
2.2 Sand Plant: Sand will be split into three products by four rising current sand
classifying tanks and then dewatered by three spiral classifiers. The classifying
tanks will require 2000 gpm (500 gpm each tank) from the reservoir to supply
the rising current. Overflow from the tanks will be pumped to the clarifier at
10,100 gpm. The remaining flow of 1200 gpm will go with the sand products to
the spiral classifiers. The spiral classifiers will require about 500 gprn of clean
water from the reservoir for drain board flushing. From the spiral classifiers,
1100 gpm will be pumped to the clarifier and 600 gpm will go to the sand
stockpiles.
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2.3 Load Out Tower: Course material aggregates (#4 to 1.5 inches) will be rinsed at
the loadout tower before leaving the site. Rinse water requirements will be
2400 gprn at 2400 tph. About 200 gpm will leave with the product and the rest
will be returned either to the clarifier or to a loader sump to be recirculated.
Make-up water will come from the reservoir.
The current plan is to recirculate the rinse water until an undesirable amount
of fines accumulate, at which time the water will be pumped to the clarifier.
Rinse water may need to be recirculated for up to 60 hours if the clarifier
operates only when the processing plant operates. This mode of operation may
need to be adjusted if rinse water becomes to dirty to be recirculated.
3. OTHER WATER USES
Water will be required at several other locations in the plant. Estimated instantaneous
water use at these locations is listed below:
Location Demand GPM
1. Office and shops 25
2. Asphalt and concrete plant 160
3. Clean-up, dust suppression, evaporation 175
4. Irrigation 25
4. WATER LOSSES
Table 1 lists the estimated system water losses. The information in the table was
obtained from Faris flow sheets, a Faris letter dated January 24, 1991, LSNW
calculations dated November 22, 1991 and HGI estimates. These .estimates are
preliminary and will be further defined as equipment is selected and the project scope
is finalized.
TABLE 1: PLANT WATER LOSSES

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5. WATER SUPPLY ANALYSIS
To determine the adequacy of the water supply system, HGI simulated hourly water
use and supply for a typical week of plant operation. The following cases of water
use and water recycling were simulated. Each case was simulated for water make-up
capacities that ranged from 500 gpm to 1000 gpm.
Case 1: No water recovery from the gravel and sand piles.
Case 2: 50 percent water recovery from the gravel piles and 60 percent recovery
from the sand piles.
6. au ALIFICA TIONS AND ASSUMPTIONS
6.1 Water losses were based on Table I values.
6.2 The stockpile recovery percentages are based on Faris Associates' past
experiences.
6.3 Water loss in the sludge assumes 60 percent solids from the belt press.
6.4 Make-up water supply is available on a continuous basis.
7. SUMMARY AND CONCLUSIONS
The results of the water supply analysis are shown in detail on the attached tables and
graphs.
Case 1: At a continuous water make-up flow of 709 gpm, the reservoir never refills
during the 5 days the plant operates and the minimum reservoir tank
volume is 300,000 gallons. A minimum continuous make-up flow of 670
gpm is required to keep at least 100,000 gallons in the reservoir.
Case 2: At a continuous water make-up flow of 709 gpm, the reservoir refills at the
end of each day and the minimum reservoir tank volume is 700,000 gallons.
A minimum continuous make-up flow of 430 gpm is required to keep at
least 100,000 gallons in the reservoir.
The analysis indicates that the make-up water capacity of 709 gpm should be adequate
if the water loss assumptions used are correct. In any case, an additional make-up
water source of 200 gpm from either a shallow well or from the City of Dupont should
be enough to cover any contingency.
Report Prepared By:
HARRIS GROUP INC.
CRO/gbm
(S~
Project Manager
91-13131313pm06
j cc: Ron Summers, LSNW
JCL, File 1313.507
91-I313/1313PM06, Rev I - 3- 30 Mar 1992
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