\I

- '::::'./->0;;' )'.~ r;._". ?-__~~~~ __

PROJECT MEMORANDUM NO. 91-1313/06PLANT WATER USE

PROJECT NO. 90-1313PIONEER AGGREGATES SAND AND GRAVEL PLANT

LONE STAR NORTHWESTSEATTLE, WASHINGTON

DATE: MARCH 16, 1992REV I: MARCH 30, 1992

INTRODUCTION

The project uses about 40,000,000 gallons of water per week, of which approximately 90percent is used to wash sand gravel. Available water sources currently are estimated at 709gpm or maximum of 7,000,000 gallons per week. In order to meet plant water demands, watermust be recycled and conserved to the maximum extent possible. As part of the projectdesign, HGI has reviewed the water supply requirements of the project and investigated theadequacy of the water supply.

1. WATER SUPPLY SYSTEM

Most of the project water supply requirements will be met by recycling. Water thatcan be recovered from the sand and gravel wash process will be pumped to a clarifierwhere solids will be removed. Overflow, or clarified water, will be discharged to a1,000,000 gallon storage reservoir and. the solids, or underflow, will be pumped to beltpresses to be further dewatered.

Water that is consumed by plant operations will be replaced by a 600 gpm well ownedby 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 showsinstantaneous plant water flows. A more detailed discussion of these flows follows.

2. SAND AND GRAVEL PROCESS WATER REQUIREMENTS

Water 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 requiredat the gravel wash plant. About 2300 gpm will come from the sand plantoverflow to pre-wet material and the balance will come from the 1,000,000gallon storage reservoir to wash material on the screens. About 300 gpm will beconveyed to the stockpiles and 9300 gpm will be pumped to the sand plant withminus #8 sand.

2.2 Sand Plant: Sand will be split into three products by four rising current sandclassifying tanks and then dewatered by three spiral classifiers. The classifyingtanks will require 2000 gpm (500 gpm each tank) from the reservoir to supplythe rising current. Overflow from the tanks will be pumped to the clarifier at10,100 gpm. The remaining flow of 1200 gpm will go with the sand products tothe spiral classifiers. The spiral classifiers will require about 500 gprn of cleanwater 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 sandstockpiles.

~-----------------------II

,~< '------------------------~

2.3 Load Out Tower: Course material aggregates (#4 to 1.5 inches) will be rinsed atthe loadout tower before leaving the site. Rinse water requirements will be2400 gprn at 2400 tph. About 200 gpm will leave with the product and the restwill 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 amountof 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 clarifieroperates only when the processing plant operates. This mode of operation mayneed 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 instantaneouswater use at these locations is listed below:

Location Demand GPM

Office and shopsAsphalt and concrete plantClean-up, dust suppression, evaporationIrrigation

2516017525

1.2.3.4.

4. WATER LOSSES

Table 1 lists the estimated system water losses. The information in the table wasobtained from Faris flow sheets, a Faris letter dated January 24, 1991, LSNWcalculations dated November 22, 1991 and HGI estimates. These .estimates arepreliminary and will be further defined as equipment is selected and the project scopeis finalized.

TABLE 1: PLANT WATER LOSSES

~'----------------------- :,~-------------------------,

5. WATER SUPPLY ANALYSIS

To determine the adequacy of the water supply system, HGI simulated hourly wateruse and supply for a typical week of plant operation. The following cases of wateruse and water recycling were simulated. Each case was simulated for water make-upcapacities 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 recoveryfrom the sand piles.

6. auALIFICA TIONS AND ASSUMPTIONS

6.1 Water losses were based on Table I values.

6.2 The stockpile recovery percentages are based on Faris Associates' pastexperiences.

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 andgraphs.

Case 1: At a continuous water make-up flow of 709 gpm, the reservoir never refillsduring the 5 days the plant operates and the minimum reservoir tankvolume is 300,000 gallons. A minimum continuous make-up flow of 670gpm 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 theend 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 atleast 100,000 gallons in the reservoir.

The analysis indicates that the make-up water capacity of 709 gpm should be adequateif the water loss assumptions used are correct. In any case, an additional make-upwater source of 200 gpm from either a shallow well or from the City of Dupont shouldbe enough to cover any contingency.

Report Prepared By:

HARRIS GROUP INC.(S~Project Manager

CRO/gbm91-1313\1313pm06

j cc: Ron Summers, LSNWJCL, File 1313.507

91-I313/1313PM06, Rev I - 3 - 30 Mar 199211I-- -- --- ---------- ---- --- ~- .~--