E. LIVINGSTON ASSOCIATES CONSULTING GROUNDWATER GEOLOGISTS ' The work to date in the Selktrk College area consists of

Transcription

1 E#JIVRTON, P. Eng. E. LIVINGSTON ASSOCIATES CONSULTING GROUNDWATER GEOLOGISTS ' 1401 WEST BROADWAY, VANCOUVER, B.C. V6H 1H6 TELEPHONE: December 9, 1977 Mr. B.E. Marr,Deputy Minister of the Environment:, Department of Environment, Parliament Buildings, Victoria, B.C. V8V 1x5 Dear Sir, This is in reply to your letter of December 6th (file ) concerning Lower Columbia Water Supply, Selkirk College Aquifer. This letter contains a proposal to better define the capacity of the aquifer to supply a very large amount of water. Backeround Information the following : The work to date in the Selktrk College area consists of 1. In 1965 an unsuccessful 8" hole was drilled by Pacific Water Ilells in the northwest part of the College property (see attached map). The log is as follows: ft. 80 ft, 84 ft. 93 ft. 120 ft. 128 ft. 156 ft. 165 ft. 175 ft. boulders, sand and clay ) clay and sand;'very tight ) till? boulders ) clay and sand, very tight clay and sand, looser sand with clay fine to coarse sand, dirty fine sand and silt very fine sand, silt and clay \ cont'd... 2

2 Mr. B.E. Marr, Deputy.lLjater of the Environment Page 2 2. Also in 1965 a successful 8" well was constructed to supply water to the College. The log is as follows: 0-7 ft. boulders and clay (till) 7-24 ft. sandy clay ft. clay, pea gravel and sand ft. sand, fine to coarse ft. boulders ft. sand fine to coarse, some gravel Static level is 52 ft. The well was completed with 20' of screen with.080" slot from 94 to 104 ft, and.060" slot from 104 to 114 ft. This well was pump tested at 360 USgpm for 24 hours with about 1-1/2 ft. drawdown. 3. In 1974 a 12" production well was constructed,about 600 ft. south and east of the first production wel1,by A.C. Drillers Ltd. of Keremeos. The log is as follows: ft. till with numerous very large boulders ft. compact coarse sand and gravel ft. coarse to very coarse pebbly cobbly gravel ft. coal-se compact gravel with thin till-likcl interbeds. at 172 ft. very hard; may be bedrock. Static lcvel is 40 ft. The well was completed with 20 ft. of 10" pipe-size stainless steel Johnson screen with.25" slots set with the top at 124 ft. This well was pump tested for 525 minutes at a rate which fluctuated between 1571 and 1599 USgpm. The drawdown at the end of the test, when the rate was 1574 gpm, was 1.11 it. The pumping rate was limited by the maximum power output of the engine. The water quality is good; an analysis carried out in 1974 by Cantest Ltd. is as follows: IICHEMICAL ANALYSIS OF WATER SAMPLES Test ph (electrometric) 7.65 Color (Pt-Co scale) 0.5 Turbidity (Si02 scale) ppm Suspended Matter 0. Fixed 0.3 * Volatile 0.1,cont'd... 3

3 . Mr. B.E, Marr Deputy Minister of the Environment Page 3 CHEMICAL ANALYSIS OF WATER SAMPLES (continued) - Test Hardness (Calculated) Dissolved Anions Alkalinity Bicarbonates Carbonates Hydroxyl lon ' Chlorides Sulfates Phosphates Nitrates Fluoride Dissolved Cations Silica Iron Aluminum Calcium Magnesium Sodium Pot ass ium Manganese Copper Lead Zinc Total Iron Total Dissolved Solids Fixed Volatile L = less than HCO3 co3 OH c1 SO4 PO4 N F Si02 Fe A1 Ca Mg Na K Mn cu Pb Zn Fe L L 92. NIL NIL O We summarized the resilts of this work in a letter dated November 12, 1974 to Associated Engineering Services Ltd. as follows: 11 From these three holes it is obvious that the geology is quite complex. The arc shaped peninsula on which the college is located is probably a terminal moraine deposited by ice which advanced into the Columbia Valley from the Kootenay 'River Valley, The till which was found at surface in all three holes is extremely bouldery. Erosion has exposed a number of huge erratic boulders in the till along the slope facing the river. The sediments under the till are probably ice contact deposits which include, in the case of the successful wells, some clean, advance outwash gravel. The fine grained nature of the sediments under the till in the unsuccessful hole indicates that lake conditions existed in the Columbia Valley when ice advanced down the Kootenay Valley. Geol-ogic mapping downstream shows that lake conditions prevailed downstream at least as far as Waneta. cont'd... 4

4 .Mr. B.E, Marr Deputy Minister of the Environment Page 4 The aquifer at the new well is very good. It is not possible from the pump test, because there was no observation well and because the pumping rate was relatively low for the aquifer, to determine the aquifer characteristics. We know from the specific capacity that the transmissivity is extremely high, certainly over one million gallons per day per ft. width, The capacity of the well is unknown but we estimate it to be at least 4500 USgpm. At this very high rate the velocity through the screen would be higher than is usually recommended but with good quality water this would not likely cause problems. Excessive velocity may c-ause deposition of carbonates on the screen but this can be removed by acid treatment. Another pump test should be carried out before installing a pump with capacity greater than 3000 USgpm. Discussion is known, we are concerned with: Ordinarily in a's tuation of this type, where water qual ty 1. The extent of the aquifer, its configuration and the nature of its boundaries. 2. The aquifer characteristics - coefficients of transmissivity and storage. 3. Recharge - from where and how much. In this case we believe that the aquifer is an irregular mass of gravel, part of ice contact deposits. We know from one drill hole that it extends only a short distance westwards; its extent. in other directions is unknown. We have data from pump t:ests of the two Selkirk College wells. The specific capacity of the older 8" well is 240 USgpm/Et. drawdown; the specific capacity of the 12" well is about 1500 USgpm/ft. drawdown. In both cases, because of very small drawdown and absence of observation wells, it was not possible to determine the aquifer characteristics. However, assuming that the well loss is negligible, the minimum transmissivities are 3 x lo5 and more than 2 x lo6 USgal/day/ft. width respectively. As far as recharge is concerned, we were unable to detect any recharge problem when pumping the 12" well at more than 1500 USgpm. cont'd,.. 5

5 ..' Mr. B.E. Marr Deputy Minister of the Environment. 'a Page 5 In this special case, where the transmissivity is certainly extremely high, the extent of the aquifer is not the limiting factor, because the distance between very high capacity wells can be small, probably in the order of 100 ft. For the same reasons it is not necessary to accurately determine the aquifer characteristics at this time, We can estimate the coefficient of storage and we know that the transmissivity is extremely high in the vicinity of the 12" well. In this case where the aquifer is not extensive and where it must obtain most of its recb.arge from the Columbia River, the main constriction on the ability of the aquifer to supply a high capacity well field is recharge. Experience in other areas has shown that recharge to gravel aquifers from rivers is occasionally restricted by fine grained sediment in the river bed. It is essential to determine, if possible, whether recharge at high rates is restricted. In your letter in the third paragraph you state that you wish us to submit a proposal for firmly establishing 'I.. the overall aquifer characteristics and for making recommendations as to the method and estimated cost of developing the aquifer to its full potentia:l as a source of water... 'I. We wish to discuss this idea further. In certain situations where an aquifer is extensive, where it is fairly uniform in character and thickness, and where something is known about recharge, then "full potential" can often be estimated. In the special case of the Selkirk College aquifer it may not be possible to do this at a reasonable cost, For example, if the full potential is 50,000 gpm with recharge being the main constraint, it would require pumping at extremely high rates from several wells to indicate the full potential. In this case we suggest that it is preferable to decide on an arbitrary limit and design a program to indicate whether the aquifer can meet that demand or whether it can supply more than that limit. Therefore we suggest that a limit of 7000 igpm is realistic. Our proposal is based on this limit. If it is too low or too high we expect to be informed. cont'd... 6

6 , 'Mr, B,E. Marr Deputy Minister of the Environment Page 6 To determine the recharge capability when water is being withdrawn from the aquifer at a high rate, an additional high capacity well is required. Pumping a new well at a high rate, while the existing 12" College Well is being pumped at a maximum rate, should induce recharge at a high enough. rate so that any serious barriers to recharge can be detected. A single observation well in the vicinity of the wells is also required, permit more accurate determination of the aquifer characteristics. This will also Pumping of a new 16" well at about 2800 USgpm and the existing well at about 1600 USgpm for a total of 4400 gpm, should detect any recharge problem which might occur at a rate as high as 7000 gpm, when the river level is fairly low, say before mid-may. Naturally this is best done at a time Test pumps are available from B.C. contractors to pump at the rates mentioned above. By making a few alterations to existing test pumps it may be possible to increase the total capacity to almost 5000 USgpm. / An incidental benefit from the program outlined above is the construction of a high capacity production well which could be put into immediate use or could be left for use at any time in the future. The screen proposed here is stainless steel; a cheaper galvanized iron "irrigator" screen could be used if the well is used only.. or testing for saving of perhaps $2000. Proposal We propose the following program: , 4. Construct a 16" diameter screened well within 150 ft, of the 12" Selkirlc College well. Construct a screened 6" observation well 'between the new well and the 12" College well. Pump the 16" well at the highest possible rate using a test pump available in B.C. Simultaneously pump the 12" College well at the highest possible rate using the installed pump or a test pump, whichever can pump the greater amount of water. cont'd... 7

7 " MI'. B.E. Marr * Deputy Minister of the Environment Page 7 5. Analyse the pump test results and p:cepare a report with. recommendations and cost estimates for facilities required to produce the required 7000 igpm.,- We assume from your letter that, subject to acceptance of this proposal, we are to act as prime contractors. but are prepared to do so if necessary. If so, we would prefer to carry out the work through our limited company Pacific Hydrology Consultants Ltd. We estimate the cost of this proposal as follows: - We have seldom done this a, bo Cost to move equipment except test pump to and from Castlegar Cost of 16" drive shoe Cost to drill and case 16" to 145 $45/ft Cost of 6" drive shoe Cost to drill and case 6" to 130 Et. e $16/ft Cost of 4 ft. of 6" well $70/ft Cost of 20 ft. of 12" pipe size well $200/ft Cost of 40 hrs. of hourly work to install screens, develop wells, $50/hr Cost to move test: pumps to and from Castlegar Cost to install and remove test pumps; 20 hrs of hourly $45/hr Cost (lump sum) to supply and lay 600 ft. of discharge $.50 Cost to carry out 30 hour pump $50/hr Estimate total contractors charges In addition we estimate the cost of: Engineering, preparation of contract documents, supervision of work, sieve analyses, analysis of pump tests, and preparation of report including expenses in the field. Estimated at $45 per hour and $13 each for sieve analyses TOTAL ESTIMATE $ $ 19,630 3,700 $ 23,330 cont'd I -I-

8 Y Mr. Deputy hlilister of the Environment Page 8 We understand from the Association of Professional Engineers of B.C. "Outline of Services and Scale of Minimum Fees to be charged for General Engineering Projects" of 1975 that "the cost of all disbursements shall be increased not less than 5% to cover office services, and cost of handling... '' We have allowed for this in our estimated engineering fee. We estimate that the project, including the final report, could be completed within 6 weeks unless the weather is extremely bad, Yours truly, E.LIVINGSTON ASSOCIATES EL: jb encl. E. Livings t on, P, png

9 \