2010-11-17_REVISION - C1981008 (3)

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03/18/2009 12:29 9702475104 DMG DURANGO OFFICE PAGE 09/21 USDA criteria for prime farmland state that the total topsoil plus subsoil depth must equal or exceed Y V1'1 V) `� M L—W) 401nches. These criteria were used to modify the soil suitability criteria table (Table 2.04.9 -2,) in the DRMS permit, ` g All soil samples during the March 5 sampling event wcrc within suitable ranges for selected analytcs /`/► and field pararueters. The upper two feet of subsoil was investigated, but there was no change observed to the total soil pit depth in. any soil pit, suggesting that the soil suitability criteria would be met in the three to four feet of observed subsoil at all or most sampling locations. Re4ampling for pH anal ELeetrical Conductivity Comments from the DRMS in a letter dated May 28, 2008 .revealed that the March 5 subsoil analyses utilized 1:1 extract for the soil pH and electrical conductivity (8,C), rather than the pennit- required paste method forthese analyses. Walsh discussed the situation with ARMS andNRCS personnel and determined that there is a proportional relationship between 1:1 extract and paste extract EC results. A published formula was applied to the 1:1 PC results, and revealed that up to four sample points may exceed the paste EC criteria of 4.0 (samples 21, 26, 32, and 33). Based on this, the eight sarnple points that had 1:1 EC higher than 1,2 were resatmplcd and analy7cd for paste 1~C (Table 2). WFC personnel roaanapled soil at the original sampling points using a 2" hand auger for a total depth of 24• ", A fraction of the extracted, sample was placed in a Zap -loc bag and shipped. to Servi -Tech Labs of Hastings, Nebraska. T.he sampling points were located with a survey -grade GPS 'to match the March 5, 2008 sampling points. The sampled areas had not yet had topsoil placed at the time of sampling. Of the eight samples obtained, two exceeded the topsoil permit criteria of 4. These were sample 21 with a paste EC of 4.34 and sample 32 with a paste 18C of 7.33. The sample 32 location is near a top, soil pile, which play have aff'ectod this location.. The samplers noted that as many as five attern.pts were rrtadc at sample 32 to get a complete hole due to refusal of the hand auger. This suggests that sample 32 may not be representative of the si,ibsoil in the area, Discussion The original Boil survey (Intermountain P- source Inventories, Inc., 1998) performed laboratory analyses on three soil profiles within the prime farmland unit south, of 13B Road. Of these three, four individual soil horizons from the approximately 24 -48 inch subsoi.l interval we ro analyzed. Paste EC ranged from 0.7 to 3.$, with an average of 1.9 - Percent CaCO3 ranged from 3 to 36 %, with an average of 17 %. No cobbles, stones, or boulders were observed in the horizons, and lab analysis of gravel ranged from 9.1 to 31.5 %, with an average gravel content of 20.7 %. This indicates that the replacement subsoil has higher average paste tC (3,1 %), lower CaCO3 (2%4%), and lower coarse fraction (11.7 %) than the original tested subsoil, Sample averages arc shown on tables 1 and 2. Walsh discussed the impact of 1✓C on crops with Mr. Dave Dearatyric of the MRCS, who itndicatcd that crops are more sensitive to cl.ovated EC iii topsoil than in subsoil. Elevated. PC .in subsoil can impact established crops but not establishing crops, and established crops are generally more tolerant of elevated EC than establishing crops. Mr. Dearstync stated that subsoil with a paste EC up to 6 would not be detrimental to grasses or alfalfa. As such, establishing a paste EC criterion o:P6 for subsoil in prime farmland for the permit may he appropriate. (� w-a &,c� co 1'1'4 -A rnvjmnmcntal Sciemins and E21s1 --g, LLC +i, Ie_ dalAaA w (Revised Nov 2008) Attachment 2.05,4(2)(d) -1 -4