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Home My WebLink AboutEKLUTNA HIGHLAND ESTATES S12730Onsite File EkI tna Highlands Estates #512730 EKLUTNA HIGHLANDS SEPTIC ANALYSIS & WATER AVAILABILITY REPORT Prepared For: EKLUTNA INC 16515 Centerfield Drive, Suite 201 Eagle River, AK 99577 Prepared By: REV JANUARY 2024 Prepared By: Grant Mathews, P.E. 1 Project Location Eklutna Highlands Subdivision consists of 105 acres multi-zoned tracts into seven 1+ acre lots and three tracts. Block 1 of the parcel is located east of Eklund Ave and Eagle River Drive and Block 2 is south of Prudhoe Bay Ave and northeast of Eagle River Road in Eagle River, Alaska. The three remnant tracts include two 16+ acre tracts north of Ekclund Ave and east of Eagle River Road, and one 55-acre tract south of Eagle River Road. The site is accessed via Glenn Highway, E Eagle River Loop, to Eagle River Road. The area north of the subject property consist of large-lot residential development. To the south, the project is bounded by the Eagle River greenbelt. The three large tracts will be sub-divided in the future and were not included in this analysis. Existing Conditions & Land Cover The site is currently undeveloped and well vegetated with mature trees and brush. Topographically, the site drains in a south or southwesterly direction. Most of the proposed lots have gradual slopes in the 10 – 15% range. Lots 3-5, Block 2 have steeper slopes ranging from 25 – 50% with an average slope of about 30%. The project resides within the Eagle River watershed and contains two unnamed streams as previously identified by Watershed Management (WMS). A screenshot of the WMS drainage mapper illustrates the general watershed configuration. Proposed Development Plan The proposed development intends to subdivide and create two blocks consisting of seven total residential lots and three tracts for future development. Each lot will be served by individual wells and onsite septic systems as no public water or sewer infrastructure exists within the area. The nine lots range in size from 1.0 to 2.7 acres. The subdivision is configured such that the nine lots are located along existing roads with access to List Cir, Prudhoe Bay Ave, and Eklund Ave as well as Eagle River Road frontage. Existing grades are generally less than 20% across the site, and the 40,000 sf minimum lot size is sufficient to support on site systems. Testing Process Triad Engineering, LLC performed septic testing onsite on June 26th, 2023. Weather conditions were generally cloudy and damp with temperatures in the mid-50’s in the morning to mid-60’s in the afternoon. Dirtworks mobilized a 200 series excavator to the site and provided an operator for the geotechnical exploration. WMS Drainage Maps (7.23.23) N Area analyzed 2 Test holes were staked and flagged by S4 Group in advance of testing. Access for the excavator was such that minimal clearing was required for testing. Each test hole was advanced to a depth of roughly 10 feet below ground surface (BGS). Upon completion of each test hole, a 4” diameter perforated pipe was placed within the excavation and backfilled with the stockpiled soils. A bench was excavated adjacent to each test hole at an appropriate elevation so that percolation testing could be completed. A roughly six-inch-deep hole was hand dug into undisturbed soils using a shovel and approximately two inches of pea gravel was placed at the bottom of the hole. A four-inch diameter perforated PVC pipe was placed vertically into the test hole and the annulus backfilled with pea gravel. Water was then carefully poured into the pipe to a level approximately six inches above the bottom of the hole. Measurements were then taken at 10 or 30-minute intervals using a standard tape measure. The process was repeated for each test hole as necessary to meet Title 15 requirements. The initial 30-minute reading in all test holes exceeded ½” drop, so pre-soaking was not required. The investigation proceeded from west to east, with Lot 2, Block 1 being completed first proceeding east to Block 2. The investigation finished with Lot 1, Block 1. Soils Soils encountered during the investigation were visually classified in general accordance with the Unified Soil Classification System (USCS). The subsurface profile encountered was largely consistent. It consisted of approximately 12 inches of surficial organics followed by dense, sandy gravel with silt to 10’. A few bores had trace organics and silt extending 5’. Bedrock Bedrock was not encountered during the investigation and is not anticipated to negatively impact future development of the lots. Percolation Test Results Below is a summary of the percolation test results by lot and the subsequent reserve area required. See the attached site plan for test hole locations on each lot. Table 1 - Septic Testing Results Summary Test Hole # Lot Block Perc Rate (min/in) Depth of TH (BGS) Groundwater (Initial) Groundwater Monitoring Reserve Area (ft2) TH-1 Lot 2 1 <1 12’ NGWE NGWE 10,000 TH-2 Lot 3 1 <1 10’ NGWE NGWE 10,000 TH-3 Lot 4 1 <1 10’ NGWE NGWE 10,000 TH-4 Lot 1 2 <1 10’ NGWE NGWE 10,000 TH-5 Lot 2 2 <1 12’ NGWE NGWE 10,000 TH-6 Lot 3 2 <1 10’ NGWE 4’ BGS 10,000 TH-7 Lot 4 2 11 10’ NGWE 4’ BGS 12,000 3 TH-8 Lot 5 2 8 10’ NGWE NGWE 12,000 TH-9 Lot 1 1 <1 10’ NGWE NGWE 10,000 Nitrate Levels Below is a map of the available nitrate data for the surrounding neighborhoods. The property to the south is currently undeveloped. Land to the north is developed and presently shoes nitrate values below 2 mg/l. The United States Environmental Protection Agency (EPA) sets the maximum contaminant level for nitrate at 10 milligrams per liter. Nitrate Values App (7/22/23) Groundwater During the initial investigation, groundwater was not encountered. Additionally, only Lot 3, Block 1 had subsurface flows, which were encountered as weeps in the sidewall of the excavation at approximately 5 feet. The subsurface flows were not substantial and did not affect the perc testing. It is unlikely that the water table would negatively impact future septic systems due to the lack of silt content witnessed for the full depth of the test holes. Seasonal changes to the water table elevation are expected to occur due to rainfall and snow melt runoff. Seasonal high groundwater monitoring was conducted in October of 2023. Test holes 6 and 7 both had water at 4-ft BGS. No water was encountered in the remaining monitoring tubes. Note that neither of these test holes N PROJECT SITE 4 are being used for the lot feasibility analysis since the lot configuration was revised and the total number of lots was reduced from nine to seven. Water Availability The MOA’s COSA database was reviewed to assess water availability in the immediate vicinity of the proposed subdivision. The properties surrounding this parcel are largely undeveloped. However, the five closest properties with published data were found to have flow rates of 4-10 gpm. A summary of those rates are as follows: Parcel ID Legal Description Well Depth Static Water Production Nitrate Levels (mg/L) 050-531-30 Virginia Rude, Lot 1, Blk 1 380 ft 89 ft 6 gpm 0.00 067-301-02 List, Lot 3 330 ft 50 ft 4 gpm 0.00 067-301-04 List, Lot 1 122 ft 87 ft 8 gpm 1.81 050-511-39 North Slope, Lot 1B, Blk 1 Unknown 33 ft 5 gpm 1.30 050-511-29 North Slope, Lot 2, Blk 1 85 ft 77 ft 10 gpm 0.94 Based on the available data, well production is not a concern for the proposed lots and no negative impacts to the well flows of adjacent properties is anticipated with the development of this subdivision. Steep Slope Development A portion of the reserve area for Lots 2-3, Block 2 is in an area with natural slopes ranging from 25%-30%. If a septic system is installed in this area, it will need to comply with 15.65.210.B.4. Steep slope disposal fields. Except as modified by this subsection, steep slope disposal fields shall comply with this chapter. a. General. A deep trench or non-mounded wide trench disposal field may be instaslled on a slope greater than 25 percent , but less than 46 percent, if it complies with all of the following conditions. i. Vertical separation distances below the disposal field shall be measured from the bottom of the drainrock at the up-gradient side of the disposal field. This condition can be met. ii. Trenches shall not exceed 60 inches in width. This condition can be met. iii. Natural vegetation within 50 feet down-gradient of the disposal field shall remain undisturbed, or the exposed slope shall be stabilized with erosion control vegetation or an approved equal prior to final operational approval. This condition can be met. The large lot size allows for natural vegetation to be retained, or the disturbed areas can be revegetated. iv. The distribution pipe invert shall be a minimum of 36 inches below the top of the natural organic surface, measured on the downhill side of the trench. (See chapter 15 for exceptions) 5 This condition can be met. v. The disposal field shall be a minimum of 100 feet up-gradient from any slope exceeding 46 percent. (See chapter 15 for exceptions) This condition can be met. The slope on Lot 2, Block 2 does not exceed 46%. There are constructed cut banks downslope of Lot 3, Block 2 that exceed 46 percent. However, the large lot size would allow for the drain field to be placed 100-ft upgradient from the cut banks. An additional test hole may be required when the system is designed for Lot 2. Conclusion In summary, perc test results indicate that each of the proposed lots contain soils capable of supporting on-site septic systems. Well-draining soils were encountered for Lots 1-4, Block 1 and Lots 1-2, Block 2. Slightly slower perc rates were only encountered on Lot 3, Block 2, where the in-situ soils had a higher silt content. Groundwater was encountered on Lots 2-3, Block 2. Review of available well log information indicates that water is adequate in the area with existing wells averaging 6.6 gpm of production. Thank you for your time and consideration in this matter. If you require additional information, please call 907- 720-6128 or email me at grantmathews@triadak.com. Sincerely, Triad Engineering, LLC Grant Mathews, P.E. Attachments: Location Map Test Hole Logs E N G I N E E R I N G , L L C GR A N T W . M A T H E W S CE 1 3 5 4 4 4 R E GI S TEREDPROFES S I O N A L E N GINEER 1- 1 7 - 2 4 Depth (Feet) 1- 2- 3- 4- 5- 6- 7- 8- 9- 10- 11- 12- 13- 14- 19- 20- FT AND FT I (ENGINEER'S SEAL) Performed For: Legal Description: 15- 16- PERC HOLE DIAMETER Date Gross Time Slope Site Plan PERCOLATION RATE (minutes/inch) Net Time Depth to Water Net DropReading COMMENTS TEST RUN BETWEEN 17- 18- PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPAL GUIDELINES IN EFFECT ON THIS DATE. DATE: CERTIFY THAT THIS TEST WASPERFORMED BY: (907)343-7904 Soils Log - Percolation Test Township, Range, Section: WAS GROUND WATER ENCOUNTERED? IF YES, AT WHAT DEPTH? S L O P E Date: Depth to Water After Monitoring? Date Performed: Municipality of Anchorage Development Services Department On-Site Water and Wastewater Section 4700 Elmore St. P.O. Box 196650 Anchorage, AK 99519-6650 www.muni.org/onsite Eklutna, Inc 6.26.23 See attached site plan No Eklutna Highlands, Lot 2, Block 1 Added approx 2 gal of water in less than 1 min. All water absorbed in less than 1 min. Repeated two times. <1 6" 3 4 Triad Engineering, LLC Grant Mathews TH-1 BOH @ 12'Backfilled to 9' & setmonitoring tube See comments Gravel w/ silt & sand (GM)Gray, dense12" cobbles Organics/root matSilty sand (SM) NGWE 10.5.23 10.5.23 Depth (Feet) 1- 2- 3- 4- 5- 6- 7- 8- 9- 10- 11- 12- 13- 14- 19- 20- FT AND FT I (ENGINEER'S SEAL) Performed For: Legal Description: 15- 16- PERC HOLE DIAMETER Date Gross Time Slope Site Plan PERCOLATION RATE (minutes/inch) Net Time Depth to Water Net DropReading COMMENTS TEST RUN BETWEEN 17- 18- PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPAL GUIDELINES IN EFFECT ON THIS DATE. DATE: CERTIFY THAT THIS TEST WASPERFORMED BY: (907)343-7904 Soils Log - Percolation Test Township, Range, Section: WAS GROUND WATER ENCOUNTERED? IF YES, AT WHAT DEPTH? S L O P E Date: Depth to Water After Monitoring? Date Performed: Municipality of Anchorage Development Services Department On-Site Water and Wastewater Section 4700 Elmore St. P.O. Box 196650 Anchorage, AK 99519-6650 www.muni.org/onsite Eklutna, Inc 6.26.23 See attached site plan No <1 6" 3 4 Triad Engineering, LLC Grant Mathews See comments Organics/root mat BOH @ 10'Backfilled to 9' & setmonitoring tube Silty gravel w/ sand (GM)Gray, dense12" cobbles Added approx 1 gal of water in less than 1 min. All water absorbed in less than 1 min. Added approx 2 gal of water in less than 1 min. All water absorbed in less 5 min. Eklutna Highlands, Lot 3, Block 1 TH-2 NGWE 10.5.23 10.5.23 Depth (Feet) 1- 2- 3- 4- 5- 6- 7- 8- 9- 10- 11- 12- 13- 14- 19- 20- FT AND FT I (ENGINEER'S SEAL) Performed For: Legal Description: 15- 16- PERC HOLE DIAMETER Date Gross Time Slope Site Plan PERCOLATION RATE (minutes/inch) Net Time Depth to Water Net DropReading COMMENTS TEST RUN BETWEEN 17- 18- PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPAL GUIDELINES IN EFFECT ON THIS DATE. DATE: CERTIFY THAT THIS TEST WASPERFORMED BY: (907)343-7904 Soils Log - Percolation Test Township, Range, Section: WAS GROUND WATER ENCOUNTERED? IF YES, AT WHAT DEPTH? S L O P E Date: Depth to Water After Monitoring? Date Performed: Municipality of Anchorage Development Services Department On-Site Water and Wastewater Section 4700 Elmore St. P.O. Box 196650 Anchorage, AK 99519-6650 www.muni.org/onsite Eklutna, Inc 6.26.23 See attached site plan No <1 6" 3 4 Triad Engineering, LLC Grant Mathews See comments BOH @ 10'Backfilled to 9' & setmonitoring tube Silty gravel w/ sand (GM)Gray, dense12" cobbles Added approx 2 gal of water in less than 1 min. All water absorbed in less than 2 min. Added approx 2 gal of water in less than 1 min. All water absorbed in less 6 min. TH-3 Eklutna Highlands, Lot 4 Block 1 Organics/root matSilty sand (SM) NGWE 10.5.23 10.5.23 Depth (Feet) 1- 2- 3- 4- 5- 6- 7- 8- 9- 10- 11- 12- 13- 14- 19- 20- FT AND FT I (ENGINEER'S SEAL) Performed For: Legal Description: 15- 16- PERC HOLE DIAMETER Date Gross Time Slope Site Plan PERCOLATION RATE (minutes/inch) Net Time Depth to Water Net DropReading COMMENTS TEST RUN BETWEEN 17- 18- PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPAL GUIDELINES IN EFFECT ON THIS DATE. DATE: CERTIFY THAT THIS TEST WASPERFORMED BY: (907)343-7904 Soils Log - Percolation Test Township, Range, Section: WAS GROUND WATER ENCOUNTERED? IF YES, AT WHAT DEPTH? S L O P E Date: Depth to Water After Monitoring? Date Performed: Municipality of Anchorage Development Services Department On-Site Water and Wastewater Section 4700 Elmore St. P.O. Box 196650 Anchorage, AK 99519-6650 www.muni.org/onsite Eklutna, Inc 6.26.23 See attached site plan No <1 6" Triad Engineering, LLC Grant Mathews See comments TH-4 Silty gravel w/ sand (GM)Brown-gray, dense12" cobblesHigher silt content w/ depth Silt w/ gravelTan, very dense BOH @ 10'Backfilled to 9' & setmonitoring tube Sand w/ gravel (SM-GM) Weeps @ 5' Silty sand w/ gravel (GM) 2 3 Added approx 2 gal of water in less than 1 min. All water absorbed in less than 1 min. Repeated test two times. Eklutna Highlands, Lot 3, Block 2 4.5' BGS 10.5.23 10.5.23 Depth (Feet) 1- 2- 3- 4- 5- 6- 7- 8- 9- 10- 11- 12- 13- 14- 19- 20- FT AND FT I (ENGINEER'S SEAL) Performed For: Legal Description: 15- 16- PERC HOLE DIAMETER Date Gross Time Slope Site Plan PERCOLATION RATE (minutes/inch) Net Time Depth to Water Net DropReading COMMENTS TEST RUN BETWEEN 17- 18- PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPAL GUIDELINES IN EFFECT ON THIS DATE. DATE: CERTIFY THAT THIS TEST WASPERFORMED BY: (907)343-7904 Soils Log - Percolation Test Township, Range, Section: WAS GROUND WATER ENCOUNTERED? IF YES, AT WHAT DEPTH? S L O P E Date: Depth to Water After Monitoring? Date Performed: Municipality of Anchorage Development Services Department On-Site Water and Wastewater Section 4700 Elmore St. P.O. Box 196650 Anchorage, AK 99519-6650 www.muni.org/onsite Eklutna, Inc 6.26.23 See attached site plan No <1 6" Triad Engineering, LLC Grant Mathews See comments TH-5 Eklutna Highlands, Lot 1, Block 2 Wood chips, fill Organics/root mat Silt, bluish gray (ML) Silty gravel w/ sand (GM)Gray, dense8" cobblesHigher sand content w/ depth BOH @ 12' Added approx 1.5 gal of water in less than 1 min. All water absorbed in less than 1 min. Repeated test two times. 5 6 NGWE 10.5.23 10.5.23 Depth (Feet) 1- 2- 3- 4- 5- 6- 7- 8- 9- 10- 11- 12- 13- 14- 19- 20- FT AND FT I (ENGINEER'S SEAL) Performed For: Legal Description: 15- 16- PERC HOLE DIAMETER Date Gross Time Slope Site Plan PERCOLATION RATE (minutes/inch) Net Time Depth to Water Net DropReading COMMENTS TEST RUN BETWEEN 17- 18- PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPAL GUIDELINES IN EFFECT ON THIS DATE. DATE: CERTIFY THAT THIS TEST WASPERFORMED BY: (907)343-7904 Soils Log - Percolation Test Township, Range, Section: WAS GROUND WATER ENCOUNTERED? IF YES, AT WHAT DEPTH? S L O P E Date: Depth to Water After Monitoring? Date Performed: Municipality of Anchorage Development Services Department On-Site Water and Wastewater Section 4700 Elmore St. P.O. Box 196650 Anchorage, AK 99519-6650 www.muni.org/onsite Eklutna, Inc 6.26.23 See attached site plan No <1 6" 3 4 Triad Engineering, LLC Grant Mathews See comments BOH @ 10'Backfilled to 9' & setmonitoring tube Eklutna Highlands, Lot 2 Block 2 TH-6 Organics/root mat Gravel w/ silt & sand (GM)Gray, dense12" cobbles Trace organics @ 6' Silt (ML)Dense, tan Added approx 1 gal of water in less than 1 min. All water absorbed in less than 1 min. Repeated test two times. 4' BGS 10.5.23 10.5.23 Depth (Feet) 1- 2- 3- 4- 5- 6- 7- 8- 9- 10- 11- 12- 13- 14- 19- 20- FT AND FT I (ENGINEER'S SEAL) Performed For: Legal Description: 15- 16- PERC HOLE DIAMETER Date Gross Time Slope Site Plan PERCOLATION RATE (minutes/inch) Net Time Depth to Water Net DropReading COMMENTS TEST RUN BETWEEN 17- 18- PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPAL GUIDELINES IN EFFECT ON THIS DATE. DATE: CERTIFY THAT THIS TEST WASPERFORMED BY: (907)343-7904 Soils Log - Percolation Test Township, Range, Section: WAS GROUND WATER ENCOUNTERED? IF YES, AT WHAT DEPTH? S L O P E Date: Depth to Water After Monitoring? Date Performed: Municipality of Anchorage Development Services Department On-Site Water and Wastewater Section 4700 Elmore St. P.O. Box 196650 Anchorage, AK 99519-6650 www.muni.org/onsite Eklutna, Inc 6.26.23 See attached site plan No 6" Triad Engineering, LLC Grant Mathews BOH @ 10'Backfilled to 9' & setmonitoring tube Organics/root mat Silty gravel (GM)Gray, dense6" cobbles Silty gravel to silt (GM - ML)Grayish brown, dense12" cobbles 2 3 0:00 0:30 0:00 0:30 1:00 1:300:30 5.25" 2.125" 5.25" 2.50" 5.25" 2.50" 3.125" 2.75" 2.75" --- --- --- 0:30 1 2 3 6.26.23 11 TH-7 Eklutna Highlands, Lot 4 ,Block 2 4 BGS 10.5.23 10.5.23 Depth (Feet) 1- 2- 3- 4- 5- 6- 7- 8- 9- 10- 11- 12- 13- 14- 19- 20- FT AND FT I (ENGINEER'S SEAL) Performed For: Legal Description: 15- 16- PERC HOLE DIAMETER Date Gross Time Slope Site Plan PERCOLATION RATE (minutes/inch) Net Time Depth to Water Net DropReading COMMENTS TEST RUN BETWEEN 17- 18- PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPAL GUIDELINES IN EFFECT ON THIS DATE. DATE: CERTIFY THAT THIS TEST WASPERFORMED BY: (907)343-7904 Soils Log - Percolation Test Township, Range, Section: WAS GROUND WATER ENCOUNTERED? IF YES, AT WHAT DEPTH? S L O P E Date: Depth to Water After Monitoring? Date Performed: Municipality of Anchorage Development Services Department On-Site Water and Wastewater Section 4700 Elmore St. P.O. Box 196650 Anchorage, AK 99519-6650 www.muni.org/onsite Eklutna, Inc 6.26.23 See attached site plan No 6" Triad Engineering, LLC Grant Mathews BOH @ 10'Backfilled to 9' & setmonitoring tube Organics/root mat Silty gravel (GM)Gray, dense6" cobbles 2 3 0:00 0:30 0:00 0:30 1:00 1:300:30 --- --- --- 0:30 1 2 3 6.26.23 Silt w/ gravel (ML-GM)Tan, dense6" cobbles 5.00" 0.00" 5.00" 1.125" 5.00" 1.125" 5.00" 3.875" 3.875" 8 TH-8 Eklutna Highlands, Lot 5, Block 2 NGWE 10.5.23 10.5.23 Depth (Feet) 1- 2- 3- 4- 5- 6- 7- 8- 9- 10- 11- 12- 13- 14- 19- 20- FT AND FT I (ENGINEER'S SEAL) Performed For: Legal Description: 15- 16- PERC HOLE DIAMETER Date Gross Time Slope Site Plan PERCOLATION RATE (minutes/inch) Net Time Depth to Water Net DropReading COMMENTS TEST RUN BETWEEN 17- 18- PERFORMED IN ACCORDANCE WITH ALL STATE AND MUNICIPAL GUIDELINES IN EFFECT ON THIS DATE. DATE: CERTIFY THAT THIS TEST WASPERFORMED BY: (907)343-7904 Soils Log - Percolation Test Township, Range, Section: WAS GROUND WATER ENCOUNTERED? IF YES, AT WHAT DEPTH? S L O P E Date: Depth to Water After Monitoring? Date Performed: Municipality of Anchorage Development Services Department On-Site Water and Wastewater Section 4700 Elmore St. P.O. Box 196650 Anchorage, AK 99519-6650 www.muni.org/onsite Eklutna, Inc See attached site plan No <1 6" 3 4 Triad Engineering, LLC Grant Mathews See comments BOH @ 10'Backfilled to 9' & setmonitoring tube TH-9 Eklutna Highlands, Lot 1, Block 1 Organics/root mat Gravel w/ sand & silt (GM)Gray, dense24" cobbles Silty gravel (GM)Tan-gray, dense Added approx 2 gal of water in less than 1 min. All water absorbed in less than 1 min. Repeated test two times. 6.27.23 NGWE 10.5.23 10.5.23