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Home My WebLink AboutCREEKVIEW ESTATES Aquifer Test S-11680Creekview Estates 511680 Aquifer Test Municipality Df Anchorage P.O. Box 196650 · 4700 Elmore Road Anchorage, Alaska 99519-6650 · (907) 343-7904 · Fax (907) 343-7997 http;//www.munLorg/Onsite Development Services Department On-Site Water & Wastewater Program Department June 26, 2009 Garness Engineering Group, Ltd. 3701 E. Tudor Road, Suite 101 Anchorage, AK 99507 Attention: Jeff Garness, P.E. Ref: Creekview Estates Subdivision Aquifer Test Report Approval Mr. Garness, Thank you for the submittal requesting review and approval of the Aquifer Test Report for Creekview Estates Subdivision (Creekview). The methods employed to test and analyze the Creekview aquifer appear to be in conformance with the MOA code and standard industry practice. The tests show that the aquifer is adequate to supply the domestic drinking water requirements for the eleven proposed Creekview homes, and Report for Creekview Estates Subdivision is approved. Please note the requirements shown below pertaining to the test wells. Each individual test well shall remain sealed and not in service until an approved septic system has been installed to accept any wastewater generated from the use of that individual well. 2. The current permits for the individual test wells can not be approved and closed out until inspection reports, well pump logs and water quality sampling results have been submitted to the department for review and approval. Sincerely,/ GARNESS ENGINEERING GROUP, Ltd. CONSULTANTS & GENERAL CONTRACTORS AQUIFER TEST REPORT FOR THE PROPOSED CREEKVIEW ESTATES SUBDIVISION (Rexview Terrace S/D - Tract B) June 16, 2009 DEVELOPED FOR: Mr. Jeff Regnart 15131 Oxford Bluff Circle Anchorage, Alaska 99515 Phone: 240-8978 DEVELOPED BY: Jeffrey A. Garness, P.E., M.S. Gamess Engineering Group, Ltd. 3701 E. Tudor Road, Suite 101 Anchorage, Alaska 99507-1259 Phone: 907-337-6179 Fax: 907-338-3246 Website: www.gamessengineering .com GARNESS ENGINEERING GROUP, Ltd. '~ '1 II '11 ' ' I I IrlCONSULTANTS&GENERALCONTRACTORS GARNESS ENGINEERING GROUP, Ltd. AQUIFER TEST REPORT FOR THE PROPOSED CREEKVIEW ESTATES SUBDIVISION TAB INDEX TAB 1 - Aquifer Test Engineering Report TAB 2 - Subdivision and Well Location Maps TAB 3 - Well Logs & Raw Pump Test Data TAB 4 - Well #3 - 24 Hour Test Results TAB 5 - Well #2 - 24 Hour Test Results TAB 6 - 20 Year Drawdown Predictions 3701 East Tudor Road, Suite 101 * Anchorage, Alaska 99507 Ph: (907) 337-6179 * Fax: (907) 338-3246 * Website: garnessengineering.com GARNESS ENGINEERING GROUP, Ltd. I III ', "1 .... III II/CONSULTANTS&GENERALCONTRACTORS AQUIFER TEST REPORT FOR THE PROPOSED CREEKVlEW ESTATES SUBDIVISION Tab 1 · Aquifer Test Engineering Report 3701 East Tudor Road, Suite 101 * Anchorage, Alaska 99507 Ph: (907) 337-6179 * Fax: (907) 338-3246 * Website: garnessengineedng.com GARNESS ENGINEERING GROUP, Ltd. CONSULTANTS & GENERAL CONTRACTORS June 16, 2009 Municipality of Anchorage Department of Development Services On-site Drinking Water and Wastewater Department 4700 Elmore Road Anchorage, AK 99507 Phone: (907) 343-7904 Subject: Creekview Estates Aquifer Test Garness Engineering Group, Ltd. (GEG) was hired by Mr. Jeff Regnart to evaluate results of aquifer pumping tests for Creekview Estates, a proposed subdivision also know as Tract B of Rexview Terrace Subdivision (Plat 70-162), located within the SW 1/4 of Section 35, Township 12 North, Range 3 West, Seward Meridian, Alaska, in the Anchorage Recording District. The subject parcel is approximately 26.6 acres in size and will create eleven lots for single family homes. Each lot will have its own private well and septic system. Please see Tab 2 for the plat showing the proposed subdivision layout. The aquifer test is one criterion of many for subdivision development. The purpose of an aquifer test is to verify and demonstrate that there is sufficient water in the aquifer to support the entire subdivision without affecting surrounding wells in the area. WELL CONSTRUCTION DETAILS AND INFORMATIONAL OVERVIEW Three exploratory well permits were issued by Dan Roth on April 21, 2009 for testing purposes. Two new wells were drilled during the week of April 20, 2009 by Alpine Drilling & Enterprises. Well #1 is located on proposed lot 4. Well #2 is located on proposed lot 5. Wells #1 & #2 were drilled using an air rotary driller and constructed of 6-inch diameter steel casings. The wells were grouted with two bags of bentonite granules each and disinfected with chlorine tablets upon completion. The wells ara capped with sanitary seals. Two new driller's logs for each well are included with this report for your review. Well #3 is an existing well that was reportedly drilled in the 1960s and it is located on proposed lot 6. No well leg was found for Well #3. Mr. Brian Wille of Aarow Pump & Well Service LLC inspected Well #3 with a video camera to a depth of 80.5'. The casing was constructed using 6" steel pipe. No perforations were noted above 43' below the top of the casing (TOC). Perforations are present below 43' from TOC. Well #1 is located 136.1' from Well #2; Well #2 is 200' from Well#3; Well # '1 is 330.2' from Well #3. Please see Tab 1 for a recent survey showing the locations of all three wells. Well #1 was drilled on April 23, 2009. The well was drilled to a total depth of 66' bgs (below ground surface) with a static water level of 28' from top of casing and has an 18" stickup. The subsurface soil strata consisted of organics and silt to 3' bgs, gravelly silt from 3' to 8' bgs, cobbly gravel from 8' to 33' bgs, water sand and gravel from 33' to 37' bgs, gravelly silt from 37' to 43' bgs, water sand and gravel from 43' to 45' bgs, cobbly gravelly silt from 45' to 63' bgs, and finally water sand and gravel from 63' to 66' bgs. The 6" steel casing was installed with an open-end intake. According to the driller's well log, lhe pumping rate measured after drilling was 5 gallons per minute (gpm) after 2 hours with a complete drawdown of 66'. The recovery rate was also measured at 5 gpm. Due to the absence of a screen, and 3701 East Tudor Road, Suite 101 * Anchorage, Alaska 99507-1259 Phone: (907) 337-6179 * Fax: (907) 338-3246 * Website: www.gamessengineering.c0m Page 2 of 5 the partial penetration into the aquifer, this well was considered a piezometer when used as an observation well. Well #2 was drilled on April 24, 2009. The well was drilled to a total depth of 87' bgs with a static water level of 21' from top of casing and has an 18" stickup. The subsurface soil strata consisted of organics and silt to 3' bgs, cobbly gravelly silt from 3' to 20' bgs, silty water sand and gravel from 20' to 23' bgs, gravelly silt from 23' to 32' bgs, silty water sand and gravel from 32' to 37' bgs, cobbly gravelly silt from 37' to 45' bgs, water sand and gravel (3 gpm) from 45' to 47' bgs, gravelly silt from 47' to 84' bgs, and finally water sand and gravel from 84' to 87' bgs. The 6" steel casing was installed with an open-end intake. According to the driller's well Icg, the pumping rate measured after drilling was 6 gpm after 2 hours with a complete drawdown of 87'. The recovery rate measured after drilling was 6 gpm. Due to the absence of a screen, and the partial penetration into the aquifer, this well should be considered a piezometer when used as an observation well, but when used as a pumped well, it was considered a vertical screened well with partial penetration of the aquifer so that the calculations would work properly. The 'screen", which is actually the open end of the casing pipe, was conservatively entered hto the equation as 1 linear foot in length. A well drilleCs Icg for the existing Well #3 was not found. As stated earlier, Aarow Pump and Well Service LLC inspected and provided documentation on the well. The well is 80.5' deep and has a static water level at 5' 8" below the top of the 6" steel casing. The casing is perforated below 43' from top of casing. The perforations are considered when used in calculations for the 24 hour pumping test performed on this well. Due to the age of the well, we suspect some silting and/or rusting have occurred and the rate at which water can be pumped from the well may have declined over the years. The 24 hour test on this well resulted in no change in the static water level in the other two wells used for observation. Well logs for new Wells #1 and #2, and a statement from Mr. Brian Wille detailing the inspection of the existing Well #3 are included at. Raw data from Aarow's pumping tests are also included at Tab 3. along with simple line graphs created from the drawdown data from the 24 hour pumping tests. AQUIFER TESTS Three separate 4 hour aquifer tests were performed on all three wells during the week of May 11, 2009. Water level sensors were used to measure the level in each of the wells during testing. No observation wells were used when performing the 4 hour test on Well #3. Observation wells were used when performing the 4 hour tests on Wells #1 and ¢2; however, no changes in the static water levels in the observation wells were observed. A 24 hour test (Aquifer Test #1) was then performed on May 19. 2009, using Well #1 as the production well and Wells #2 and #3 as the observation wells. No changes in the static water levels in the observation wells were observed. The pumping rate was lowered from 4 gpm to 3 gpm after 150 minutes due too excessive drawdown. Our single-well pumping calculations and solution are included at Tab 4, but this well did not provide enough data for us to adequately evaluate the aquifer characteristics. A 24 hour test (Aquifer Test #2) was then performed on May 21, 2009 on production Well #2 while monitoring water levels in observations wells #1 and #3. Observation well #3 showed a measurable drawdown, but Well #1 had a drawdown that was barely perceptible. Well #2 is the central well and provided the best matching curve when the Papadopulos-Cooper solution was applied. (See Tab 5.) Test Evaluation Procedure GEG evaluated the aquifer test results to determine the transmissivity of the aquifer(s), storativity and the long-term production capacity of the well(s) and the likely or predicted impact on surrounding wells. We used AQTESOLV software for analyzing the pumping test data. We also used the following equations taken from "Groundwater and Wells" Edition 2, by Driscoll (1986), so that the findings can be cross- checked using methods that are acceptable per Municipality of Anchorage aquifer test procedures. 3701 East Tudor Road, Sui~ 101 * Anchorage, Alaska 99507-1259 Phone: (907) 337-6179 * Fax: (907) 338-3246 * Website: www. garnessengineering,com Page 3 of 5 Transmissivity Transmissivity is the rate that water flows through a vertical strip of the aquifer 1 foot wide while extending through the full-saturated thickness and at less than a hydraulic gradient of 1. Transmissivity can range from less than 1,000 to over 1 million gpd/ft. If an aquifer has less than 1,000 gpd/ft, it can supply enough water for a domestic well only, which is conservative since a 4 bedroom home will typically require 600 gpd (150 gallons per bedroom per day). The calculation used for determining transmissivity is: T = 264 x Q, where Q = pumping rate (gpm) and z~s = change in draw down between any two 2,s times on the log scale whose ratio is 10 (one log cycle). The most accurate As values can typically be derived from data recorded towards the end of the 24 pumping test once the drawdown has had a chance to stabilize. Another method for estimating transmissivity is derived from the specific capacity of the pumped well at the end of the 24-hour test. The commonly used calculation is: T = 2000 x SC, where T= Transmissivity (gpd/ft), and SC = Specific Capacity (gpm/f[ of drawdown). Storativity Storativity indicates how much water can be removed by pumping. When transmissivity and storativity are calculated, we are able to indicate how multiple wells will affect each other and we are able to determine well intake efficiency. Storativity values are calculated from observation well data. The calculation used for determining storativity is: S = 0.3 Tt~, where T = Coefficient of Transmissivity (gpd/ft) ro2 to = Intercept of the straight line at zero drawdown, in days ro = distance, in feet, from the pumped well to the observation well where drawdown measurements were made. Specific Capacity Specific capacity of a well is its yield per unit of drawdown, usually expressed as gallons of water per minute per foot (gpm/fi) of drawdown after a given time has elapsed, usually 24 bourn. Dividing the yield of the well by the drawdown, when each is measured at the same time, gives the specific capacity. AQUIFER TEST #1 Aarow Well and Pump Services installed a pump in test Well #1 on May 19, 2009. Water level indicators were installed on the well casings of all three wells to take water level readings during the pumping test. The initial static water level in Well #1 was 21.91' and this level dropped to 57.3' after 150 minutes at a pumping rate of 4 gpm. The pump was throttled back to 3 gpm and the test continued. After 1260 minutes (21 hours), the drawdown reached its lowest reading of 53.3' and stabilized until the test was completgd after 1440 minutes. The pump was shut off and the recovery level after 60 minutes was 22.6'. There was no change to the static water level in either of the two observation wells. Storativity is normally calculated by using well drawdown data from nearby observation wells. In this case, the drawdown in either observation well was unchanged and the storativity calculation could only be estimated using data from the single pumped well. Aquifer Test #1 Results Please see Tab 4 for all test data. Transmissivity (T) was calculated at 171 gal/day/ff and storativity (S) was 0.0013 using the Papadopulos-Cooper solution method. Application of the Theis solution method resulted in a T value of 133.3 gal/day/ff and an S value of 0.01454. 3701 East Tudor Road, Suite 101 * Anchorage, Alaska 99507-1259 Phone: (907) 337-6179 * Fax: (907) 338-3246 * Website: www. garnessengineedng.c0rn Page 4 of 5 AQUIFER TEST #2 Aarow Well and Pump Services installed a pump in test Well #2 on May 21, 2009. Water level sensors were installed on the well casings of all throe wells to take water level readings during the pumping test. The initial static water level in Well #2 was 16.85' and this level dropped to 75.89' after 1440 minutes at a continuous pumping rate of 10 gpm (See Graph 2). The pump was shut off and the recovery level after 60 minutes was 31.43'. There were changes to the static water level in the two observation wells. Since Well ¢¢2 is the central test well, and the pumping rate was consistent throughout the 24 hour test period, and the observation wells both showed measurable drawdown level changes, we consider this test to be the most representative of the aquifer in the study area. The drowdown measured in observation Well #3 was more pronounced than the one measured in observation Well #1, which is up gradient from Well #2. Test #2 Aquifer Results Please see Tab 5 for all test data used for calculations and graphs of the pumping test results. DATA INTERPRETATION According to the two well logs, the aquifer is marginally confined, consisting of layered cobbly gravelly silt, gravelly, and water sand and gravel. Production Well ¢F2 was pumped at a rate of 10 gallons per minute. Based on data from both aquifer tests, transmissivity values of the aquifer ranged from 133 to 274 gpd/ft. The transmissivity values of the aquifer indicate that the rate of water flowing through the aquifer will supply enough water for a typical domestic well (assuming 4 bedroom homes and a daily demand of 600 gallons) without interfering with neighboring wells. Storativity values ranged from 0.0013 to 0.0007 (no units). According to "Groundwater and Wells" Edition 2, page 210, these storativity values are consistent for a confined aquifer, which typically range from 0.0001 to 0.01, although the flattening of the drawdown curve towards the end of the pumping test indicates the likelihood of a 'leaky' aquifer. LONG TERM YIELD Once the general aquifer characteristics were known, predictive data was gathered by varying the pumping rate and/or the time of constant pumping out to twenty years. Data from production Well #2 was used to calculate long-term yield and the influence pumping would have on neighboring wells at a given radial distance from the main pumping well. Graphic result~ are located at Tab 6. If Well #2 was pumped continuously at a rate of 5 gpm for twenty years, a total drawdown of 44' would be expected. We then tested the assumption that the throe exploratory wells could equally pump 2.5 gpm each for 20 years, which exceeds the daily demand for all 11 homes in the proposed subdivision (11 homes x 4 bedrooms x 150 gpd equals 6600 gallons per day of required production). The total production required was then divided by the number of minutes per day (6600 divided by 1440 equals 4.6 gpm of groundwater production required daily). The resulting graph shows that the total drawdown after 20 years of constant pumping would range between about 36' to 39' below the respective static water levels in each well. RADIUS OF INFLUENCE ON SURROUNDING WELLS We evaluated the idea of using one community well to serve all 11 homes without affecting surrounding wells in the area. As a well is pumped, drawdown will occur, causing an outward radial increase at the top of the cone of depression of the aquifer and possible interference of the ability of nearby wells to produce adequate water. As noted above, 11 homes will require a combined average daily flow of 4.6 gpm. Predictive testing was then concentrated on Well #2 to determine the effects of long-term pumping on neighboring wells. Three graphs were generated showing the distance-drawdown effects at pumping rates of 7.5 gpm, 5.0 gpm and 2.5 gpm. The distance-displacement graph in the worst care scenario (7.5 gpm) indicates that wells 800' from Well #2 would have no change in their drawdown levels resulting from this maximum pumping rate. Wells within 100' of Well #2 would experience a drawdown of approximately 7', which is still well within the ability of neighboring wells to draw additional water from this common aquifer. If this theoretical community well was placed in the middle of the proposed subdivision, existing wells at or greater than 800 feet away would experience minimal or no impact. 3701 East Tudor Road, Suite 101 * Anchorage, Alaska 99507-1259 Phone: (907) 337-6179 * Fax: (907) 338-3246 * Website: www.garnessengineering.com Page 5 of 5 CONCLUSIONS Aquifer Test #2 indicates a negligible effect on the observation wells while pumping the central well at 10 gallons per minute for a 24-hour duration. During the test, observation Well #1 was not effected until approximately 1080 minutes of pumping at 10 gpm had occurred, and observation Well #3 was not effected until showed 480 minutes into the test period. Surrounding well logs were evaluated to define where bedrock provides a lower limit of the aquifer since none of our exploratory wells were drilled deep enough to determine this factor. Bedrock was encountered at 89' bgs at Lot 3 of Sherwood Heights to the south of the study area, and at 147' at Lot 9 of Fairmount subdivision immediately to the west of the study area. Wells in Sea Turn subdivision tothe east, while not yielding bedrock depths, showed domestic private wells with initial production rates measured in the 8 to 15 gpm range. Lot 2 of Gudveina Estates which lies up gradient and to the east of the study area has an artesian well 141' deep with a measured initial production rate of 10 gpm. In short, this area appears to have a relatively abundant supply of groundwater. Furthermore, it is possible that a dedicated community well could be located in the central region of the subdivision, adequa~ly screened and drilled deeper into the confined aquifer in order to achieve full penetration. According to the cumulative aquifer test data in this study, it is our conclusion that the addition of 11 individual domestic drinking water wells will not have a significant impact on neighboring wells and there is sufficient water in the aquifer to service the wells for single-family homes in the proposed subdivision. If you have any questions or concerns, please contact me at 337-6179. ~Sincerely'~ Jeffrey . Garness, P.E., M.S. President Our firm is American Indian owned, is certified as a Disadvantaged Business Enterprise, and is Small Business Administration 8(a) certified for Federal projects. We can serve as your engineer and general contractor. 3701 East Tudor Road, Suite 101 * Anchorage, Alaska 99507-1259 Phone: (907) 337-6179 * Fax: (907) 338-3246 * Website: www.gamessengineering.com GARNESS ENGINEERING GROUP, Ltd. CONSULTANTS & GENERAL CONTRACTORS AQUIFER TEST REPORT FOR THE PROPOSED CREEKVIEW ESTATES SUBDIVISION Tab 2 Proposed Subdivision Map Test Well Location Map Test Well Elevation Data 3701 East Tudor Road, Suite 101 * Anchorage, Alaska 99507 Ph: (907) 337-6179 * Fax: (907) 338-3246 * Website: garnessengineering,com \ , , '-,,'"",~,x/ %:.5 ~ '- -' ~ ",~. i .- , ~_~ ,, Xl~ ',5 '...~' .>, <~ Id '.~ '"Lb': 0 '. ', ~,',~',,? ~x~'- ~ ~ / .,.....Z ,O~'L~L ~.. 0 ~Z Z ~uus3 3~)/ ,OL (!AI),~'gg6 (~l),g~7'gg6 (~1),!.g'066 C~I ~ A T~TFT AA CTT A k.T~TFTr'T/'NI~