Make your own free website on Tripod.com

Environmental Assessment

NM 70078

City of Las Cruces West Mesa Wellfield Complex

Environmental Assessment NM-036-96-031



A. Introduction



The City of Las Cruces proposes to install nine (9) well pads and 5.5 miles of access roads in the western portion of Doña Ana County, approximately 8 miles west of Las Cruces, New Mexico. The project would be located on Federal lands administered by the Bureau of Land Management (BLM), Las Cruces District office, Mimbres Resource Area.

The project ROW consists of a 25 foot wide right of way with a 25 foot temporary construction easement. The City of Las Cruces has set back the 25 foot wide rights of way (water and gas) and wellpad sites 65 feet from both sides of the section lines to provide future rights of way for 130 foot wide major arterials.

The proposed easement extends 29040 feet in length. The proposed easement consists of a 25 foot right of way and a 25 foot temporary construction easement. The area affected by the proposed temporary easement is 16.67 acres, all of which is under BLM jurisdiction. The total area affected by the proposed permanent ROW easement is 16.67 acres. The proposed plan also includes permanent easements for nine (9) well pads aggregating 11.002 acres, all of which are on BLM lands. Consequently, a total of 44.34 acres of BLM lands would be directly affected by the proposed project.

The proposed action is consistent with the Mimbres Resource Management Plan.



B. Proposed Action and Alternatives



1. Proposed Action



a. The City of Las Cruces has submitted an application to construct nine (9) well pads and 5.5 miles of access roads in western Doña Ana County, New Mexico. The purpose of this project is fundamentally socioeconomic in character and is intended to provide additional water to portions of Doña Ana County in anticipation of future population growth.



b. The proposed wellfield complex is situated entirely on BLM lands. This project is located in the west-central portion of Doña Ana County. The general project area is situated between 2 and 3 miles south of I-10 and 5 miles west of the Rio Grande on the West Mesa. The project consists of 5.5 miles of access roads and 9 well pads. Access roads require a permanent 25 foot easement. Well pads 47, 48, 49, 50, 51, 52, 53 and 64 are 1 acre each in extent. Well pad 63 is 3.002 acres in extent.

For ease of description, access roads have been divided into four (4) segments and legal description(s) are as follows. Beginning at the half-section point between Sections 29 and 30 in T23S,R1E, Segment 1, which is 25 feet wide, is centered on a line that extends 65 feet west of a line running 0.5 miles south along the western side of the Section 29/30 boundary and for 1.0 miles along the western side of the Section 31/32 boundary. In T24S,R1E, Segment 1 continues 0.5 miles south along the western margin of the Section 5/6 boundary, terminating at the half-section monument.

Segment 2, which is 25 feet wide, is centered on a line that extends 65 feet north of a line running 1.0 miles westward from the half-section monument between Sections 31/32 in T23S, R1E to the half-section monument between T23S,R1W Section 36 and R23S,R1E Section 31.

Segment 3, which is 25 feet wide, is centered on a line that extends 65 feet east of a line running 1.0 miles south from the half-section monument between T23S,R1W Section 36 and R23S,R1E Section to the half-section monument between T24S,R1E Section 6 and T24S,R1W Section 1.

Segment 4, which is 25 feet wide, is centered on a line that extends 65 feet north of a line running 1.0 miles east from the half-section monument between T24S,R1E Section 6 and T24S,R1W Section 1 to the half-section monument between Sections 6/5 in T24S,R1E. Segment 4 continues eastward for another 0.5 miles from the half-section monument between Sections 6/5 in T24S,R1E to the center of Section 5 in T24S,R1E.

Well pads are located as follows. Well pad 63 is located in the SE 1/4 of the SE 1/4 of T23S,R1E, Section 30. Well pad 47 is located in the SW 1/4 of the NE 1/4 of T23S,R1E, Section 31. Well pad 48 is located in the SW 1/4 of the NW 1/4 of T23S,R1E, Section 31. Well pad 49 is located in the SW 1/4 of the SW 1/4 of T23S,R1E, Section 31. Well pad 53 is located in the SW 1/4 of the NW 1/4 of T24S,R1E, Section 6. Well pad 50 is located in the SW 1/4 of the NE 1/4 of T24S,R1E, Section 6. Well pad 51 is located in the NE 1/4 of the SE 1/4 of T24S,R1E, Section 6. Well pad 52 is located in the SW 1/4 of the NE 1/4 of T24S,R1E, Section 5. Finally, well pad 64 is located in the SE 1/4 of the SE 1/4 of T23S,R1E, Section 31.



c. Permanent 25 foot wide easements adjacent to temporary 25 foot construction easements would be required for each of the four (4) segments described in B(1)(b) above. These permanent easements are required to allow for safe construction and access to well sites over the approximately 40 year time period that this wellfield system is expected to be in operation. In each of the four segments, the permanent easements would permit safe movement of construction equipment throughout the wellfield complex and would permit access to all well pads for maintenance activities once construction is completed.



1. Access roads would consist of a 4 inch gravel base with six inch subgrade preparation. Subgrade preparation consists of compaction to 95% Modified Proctor. Water turnouts would be constructed where road slopes might present the potential for water erosion. These roads are designed for all-weather use.



d. Permanent easements would be required for each of the nine (9) well pads described in B(1)(b) above. These permanent easements are required to allow for safe construction and maintenance of well sites over the approximate 40 year time period that this wellfield system is expected to be in operation. Permanent well pad easements would permit access to all well pads once construction is completed. The City's Plan of Development, filed in November 1995 with the BLM, provides a comprehensive review of wellpad construction methods. These may be summarized as follows:



1. Each of the eight 1 acre wellpads described in B(1)(b) above would contain two structures. The first structure would house electrical controls, valves, chlorination equipment and other appurtenances. This structure would consist of slump block on a 6 inch concrete slab. A removable metal structure attached to the slump block structure would house pumping equipment. This equipment would include a natural-gas powered engine and pump. The engine transmits power to a turbine pump through a gear head. Finally, each wellpad would require one (1) small discharge pond. This pond is required to hold water discharged during start-up, shut-down, and cleaning operations at the well. At each of these nine wellpads, the structures and discharge pond would require an area of approximately 150 X 150 feet and would be surrounded by a 6 foot high rock wall.



2. The single three (3.0) acre wellpad would contain a storage tank, well # 63, a booster pump, and a discharge pond. The storage tank would be 40 feet high with a capacity of 4.5 million gallons. A slump block structure would house electrical controls, valves, chlorination equipment and other appurtenances with a removable metal structure attached to the slump block structure to house pumping equipment. A natural gas-powered booster pump would be housed in a 12 X 24 foot slump block structure similar to that described in B(d)(1) above. Finally, this wellpad would require one (1) small discharge pond. This pond is required to hold water discharged during start-up, shut-down, and cleaning operations at the well. At this 3.0 acre site, the structures and discharge pond would require an area of approximately 498 X 250 feet and would be surrounded by a 6 foot high rock wall.



e. The access road ROW easements and well pads would be constructed across the surface of the wellfield complex. Inasmuch as this wellfield complex is an integral component of the Water Development Plan (1988, rev. 1995) for the City of Las Cruces, the access roads and well pads would be needed in perpetuity. Construction activities would consist of limited blading to clear vegetation, trenching necessary to install pipe for the water lines, the installation of water lines, and closure by backfilling the trench. Remediation measures would include reseeding of the 25 foot temporary construction easement according to procedures outlined in B(1)(f)(4) below. A complete plan of development has been filed by the City of Las Cruces with the Las Cruces District Office of the BLM (November 1995) and is available for public review. The proposed development plan would impact a total of 44.34 acres, all of which is under BLM administration.



f. Construction of access roads and installation of water lines connecting each of the nine wells would proceed in four phases including ROW preparation, excavation, and installation. These phases are sequenced to allow timely completion of the project and are discussed in more detail below.



1. The ROW preparation phase would require periodic limited grading may be needed to remove terrain obstacles at various points along the ROW. Machinery needed to complete this phase includes bulldozers and transport vehicles.



2. The second phase, excavation, would include excavation of a single long trench within the permanent project ROW. This trench would vary between 4 and 6 feet in depth to allow installation of the water pipeline at a depth of no less than 4 feet below the present ground surface of the ROW. The trench would not exceed a maximum of 4 feet in width across the base of the trench. Valves would be placed every 0.5 miles along the length of the permanent ROW to allow routine maintenance. The width across the top of the trench would conform to OSHA standards regarding set-backs. Excavated fill from the trench would be stockpiled within the temporary 25 ft project ROW for future use in backfilling operations (see below). Trench excavation would be accompanied by placement of pipe along the length of the proposed permanent project ROW. Machinery to be used in completing this phase of the project includes loaders, track excavators and trenching machines depending upon terrain limitations, trucks to transport pipe and other equipment to and from the project ROW, backhoes for minor trenching, and water trucks to control dust.



3. The third phase would entail laying pipe into the excavated trench and subsequent backfilling operations. The pipe to be used is ductile iron (Pressure Class 350) and varies between 10 and 36 inches in diameter with an estimated discharge ranging from 1000 (10") to 7000 (36") gallons per minute (gpm). Pipe segments are sealed with rubber gaskets to prevent leakage. Where needed, on-site natural material stockpiled as backfill would be used as pipe bedding material, thereby eliminating the need to bring in fill from other areas. The machinery needed during this phase is much the same as in phase 2 and includes transport trucks, water trucks, and bulldozers.



4. The fourth phase would include site remediation. The 25 foot temporary construction easement would be reseeded following completion of the project. Reseeding would be completed in June or July to coincide with the onset of the summer monsoon and to eliminate the need for supplemental watering of reseeded areas. The ROW would be mulched with straw prior to reseeding at an application rate of not less than 2.0 tons per acre and when wind velocity is less than 15 miles per hour. Mulch would be anchored at no less than 2 inches below the ground surface with no more than two passes using discs situated at nine (9) inch intervals. Areas to be seeded would be tilled with disc, harrow or chisel attachments to a depth of no less than 4 inches. Tilling would be oriented perpendicular to the ground slope. Seeded areas would also be fertilized at the time of reseeding operations. Fertilizers would include either slow-release nitrogen at an application rate of 50 pounds per acre or phosphorous (P205) at an application rate of 46 pounds per acre. Approved seed mixes and seed proportions may be found in State of New Mexico standards and include various grama grasses, desert Baileya, bluestem, cottontop, globemallow, and brush muhley. Given the low slope of the area, drill seeding would be employed throughout the project. Machinery operating during these remediation phases of the project would include water trucks, muching machines, tractors with drill and broadcast attachments, and transport trucks pulling hay trailers. Because the City of Las Cruces is requesting permanent easements consistent with the 40 year time period that this wellfield is expected to remain in operation, remediation of the permanent 25 foot easement is not planned as part of this project.



g. Construction of well pads would proceed in four phases including pad preparation, excavation, and installation. These phases are sequenced to allow timely completion of the project and are discussed in more detail below.



1. The well pad preparation phase contains a single activity. Limited grading may be needed to remove terrain obstacles at various points within the boundary of each well pad. Machinery needed to complete this phase includes bulldozers and transport vehicles.



2. Access roads would consist of a 4 inch gravel base with six inch subgrade preparation. Subgrade preparation consists of compaction to 95% Modified Proctor. Water turnouts would be constructed where road slopes might present the potential for water erosion. These roads are designed for all-weather use.



h. Maintenance activities in the wellfield complex would consist primarily of access road maintenance. The frequency of road maintenance activities cannot be anticipated in advance, but would probably vary depending on the weather. Again, maintenance activities would occur as needed over the 40 year planning period indicated elsewhere in this document.



1. Maintenance would generally consist of periodic limited grading of access road rights of way. Machinery needed to complete this phase includes bulldozers and transport vehicles.



2. Alternative One - No Action Alternative



The no action alternative would reject this application by the City of Las Cruces. This alternative is not warranted given the high rate of population growth now evident in Las Cruces, the long-term need for supplemental water supplies throughout the city, and the deleterious socio-economic impacts that would be associated with water shortages in the City of Las Cruces' service area.



C. Affected Environment



1. General Setting



The project area lies in the Mexican Highlands Division of the Basin and Range Province at elevations ranging between 4192 and 4196 feet. The project area is situated on bluffs overlooking the floodplain of the Rio Grande and typically consists of moderately- to severely-dissected alternating ridge-wash systems extending in an east-west direction perpendicular the main stem of the Rio Grande. To the north is Picacho Mountain, to the south is Black Mountain, and to the southwest are the West Potrillo Mountains. All of these mountain ranges reflect volcanic activity and uplifting from Paleozoic times until present. Near-surface deposits along the pipeline corridor appear to date from the early Pleistocene and consist of fine loamy sands and coppice dunes. The following environmental data was obtained from the Soil Survey of Doña Ana County, New Mexico (1980). The project area elevations increase slightly from north to south, varying between 4196 and 4209 feet. The mean annual temperature is 62 degrees F, while the average frost free period is 210 days. The average precipitation is 8 inches per year. The project area traverses three soil groups including the Pajarito-Oñite-Pintura, Pintura-Wink, and Berino-Doña Ana associations. Each of these associations is described in more detail below.

The northern portion of the project area contains Pajarito-Oñite-Pintura soils. These soils are deep, and occur on nearly level to undulating terrain. The soils are well drained to somewhat excessively drained and are formed in alluvium, alluvium modified by wind, and aeolian material. Pajarito-Oñite-Pintura soils generally occur on fans and consist of gravelly fine sandy loam typically found on slopes varying between 3 and 15 percent. The vegetation normally found on this association includes bush muhly, black grama, cane bluestem, creosotebush, tarbush, and winterfat. The association is classified as having medium surface runoff, the erosion hazard slight, and the blowing hazard is moderate. Overall permeability is classified as moderate and the shrink-swell potential is low. Soils of this association are normally used for grazing and as wildlife habitat.

The central portion of the project area contains soils of the Pintura-Wink association. These soils are found on nearly level to undulating terrain. The soils are well drained to somewhat excessively drained and are formed in alluvium, alluvium modified by wind, and aeolian material. The association is most often found on fans. The soils usually consist of a loamy fine sand situated on slopes varying between 1 and 5 percent. This association is characterized by coppice dunes, with Wink soils in interdune swales and Pintura soils on the tops of coppice dunes. The surface runoff of Pintura-Wink soils is very slow, the water erosion hazard slight, and the shrink-swell potential is low. At the same time, however, Pintura-Wink soils have a very high blowing hazard. Vegetation of the Pintura-Wink association generally includes black grama, mesa dropseed, threeawn, fourwing saltbush, and mesquite. Soils of this association are normally used for grazing and as wildlife habitat.

Finally, the southern portion of the project area is characterized by Berino-Doña Ana soils. These soils are deep and consist of gently undulating to undulating soils that are well drained. Berino-Doña Ana soils are formed in alluvium and alluvium modified by wind and occur on fans, piedmonts, and in valley/basin floors on slopes varying between 1 and 5 percent. Berino-Doña Ana soils usually consist of a fine sandy loam with moderate permeability. These soils are classified as having medium surface runoff with moderate water erosion hazard and a high soil blowing hazard. The shrink-swell potential of Berino-Doña Ana soils is low to moderate. The vegetation of Berino-Doña Ana soils includes black grama, mesa dropseed, sand dropseed, threeawn, and mesquite. The soils of this association are generally used for grazing and as wildlife habitat.



2. Affected Resources



a. Cultural Resources - An archaeological clearance survey of the proposed project corridor was conducted in 1996. One prehistoric archaeological site and 8 isolated occurrences were found within the ROW.



b. Livestock grazing - Allottees using the proposed project area for grazing purposes have been advised by the BLM of this proposed project.



c. Special Status Vegetation and Wildlife Species - No special status vegetation or wildlife species are known to exist in the project area.



d. Visual resources - The proposed water line ROW is located in a VRM Class 3 area. The City of Las Cruces proposes to paint all above-ground structures, specifically tanks and related buildings, Carlsbad Canyon color to minimize long-term visual impacts.



e. Soils and Vegetation - The project area traverses three soil groups including the Pajarito-Oñite-Pintura, Pintura-Wink, and Berino-Doña Ana associations as described above. These three soil associations occur nearly level to undulating terrain, with the middle portions of the project area characterized by coppice dunes. The soils are well drained to somewhat excessively drained and are formed in alluvium, alluvium modified by wind, and aeolian material. Blowing hazards range from moderate (Pajarito-Oñite-Pintura) to high (Pintura-Wink). The vegetation normally found on these associations includes bush muhly, black grama, cane bluestem, creosotebush, tarbush, mesquite, and winterfat. Soils of these associations are normally used for grazing and as wildlife habitat.



f. Lands - The proposed wellfield complex is located 3 to 4 miles east of an existing municipal sludge disposal facility. The general characteristics of this facility are described in more detail below.



1. The City of Las Cruces has in place a discharge plan for the existing sludge facility that has been approved by the State of New Mexico Environment Department (DP-245, Las Cruces Sludge Disposal, Plan Approved by NMED 6/15/1993). According to this plan, digested municipal sludge containing no more than 2.8 percent solids is applied by injection into the soil at a depth of 8-15 inches below the ground surface at a rate of 24,000 gallons per day (gpd). The site has berm systems providing buffer zones to prevent surface runoff across the sludge injection areas and to prevent internally generated runoff from leaving the injection area. The design rate for the facility is 61,200 gpd to take into account anticipated increases in sludge disposal through a 40 year planning horizon.



2. The City of Las Cruces sludge disposal facility is located in the SE 1/4 of Section 25, Township 23 South, Range 1 West. The proposed wellfield complex lies 3-4 miles east of the sludge facility in Sections 31 and 32 of Township 23 South, Range 1 East and Sections 5 and 6 of Township 24 South, Range 1 East.



3. The primary concern is that nitrogen in the sludge could be oxidized and percolate downward, thereby causing nitrate contamination of groundwater. This is not likely for the following reasons.



a. According to well log data (Molzen-Corbin & Associates, letter dated 8/19/1982), there is a geological fault line situated between the sludge disposal facility and the proposed wellfield. To the east of the fault line, in the wellfield vicinity, groundwater is situated at depths ranging between 300-400 feet below the ground surface and drains east toward the Rio Grande. To the west of the fault line, in the vicinity of the sludge disposal facility, groundwater lies at a depth of 325 feet below the ground surface and drains to the west (Molzen-Corbin & Associates, letters of 19 August 1982 and 20 August 1982). Consequently, groundwater levels beneath the sludge facility and the proposed wellfield are at different levels and, more importantly, the aquifers underlying these two localities are geologically and physically distinct. Accordingly, intermixing of groundwater in these two areas is unlikely.



b. Soils underlying the sludge disposal facility have a low coefficient of permeability. Under these conditions, downward percolation of nitrate-bearing water from the sludge disposal facility is extremely unlikely (Final EIS Consultation, 1982, II-10).



c. The sludge facility has a negative water balance of about 5 feet/year. Downward percolation of nitrogen-bearing water under this climatic regime is unlikely (Final EIS, 1982, Section 6.2.7.2). For projects having similar characteristics, i.e., a negative water balance of this magnitude, NMED has concluded that groundwater contamination is not a hazard.



d. Since 1982, the City of Las Cruces has maintained a monitoring well in the extreme southeast corner of the sludge disposal facility. Water quality evaluations, including nitrates, are conducted on an annual basis (Molzen-Corbin & Associates, letter dated 20 August 1982). Consequently, in the unlikely event that nitrates begin to migrate into the groundwater, the City of Las Cruces would have advance notice of such contamination.



e. In the unlikely event of contamination, the City of Las Cruces has already agreed to (1) move sludge disposal activities to another site and (2) conduct groundwater studies as needed to determine whether the level of contamination poses any threat to the region's groundwater (Molzen-Corbin & Associates, letter dated 20 August 1982).



g. Socioeconomic impacts - The proposed service area for the City of Las Cruces is currently undergoing rapid population expansion. Completion of the proposed wellfield complex would allow growth in the region and enhance the social and economic characteristics of the Las Cruces, NM region.



h. Safety - All construction would proceed in conformity with OSHA standards. There are no known safety issues of concern within the ROW of the proposed project.



D. Environmental Consequences



The following elements have been analyzed and would not be affected by the proposed wellfield complex. Areas of Critical Environmental Concern (ACEC), cultural resources, special status vegetation and wildlife species, prime and unique farmlands, floodplains, Native American concerns, air quality, drinking and groundwater quality, wetlands or riparian areas, wild and scenic rivers, wilderness values, and minority or low-income populations or communities. Solid or hazardous waste concerns have been raised by the BLM with respect to the proximity of the proposed wellfield complex to the City of Las Cruces municipal sludge disposal facility. This concern is addressed in detail in Part 2(f)(1-3) above.



1. Proposed Action



The proposed plan for this wellfield complex would be the most cost-effective for the City of Las Cruces. Segments 1 to 4 of the access roads that cross BLM lands permit the installation of water lines connecting each of the nine wells into an integrated water system. The amount of BLM land affected by these access roads is minimal and the road configuration would permit the City of Las Cruces to maintain the roads with minimal disturbance.



a. Cultural resources - An archaeological clearance survey of the proposed project corridor was conducted in the spring of 1996. One prehistoric archaeological site and 8 isolated occurrences were found within the ROW. Previous consultation with the BLM and State Historic Preservation Office determined that this site, LA 107951, was not eligible for nomination to the National Register of Historic Places under Criterion d of Section 106 of the NHPA and a no adverse effect determination was made for this project.



b. Special Status Vegetation and Wildlife Species - No special status vegetation or wildlife species are known to exist in the project area.



c. Visual resources - The proposed water line ROW is located in a VRM Class 3 area. Since the proposed water line corridor is entirely below ground, no long-term visual resource impacts are associated with this project. The City of Las Cruces proposes to paint all above-ground structures, specifically tanks and related buildings, Carlsbad Canyon color to minimize long-term visual impacts.



d. Soils and Vegetation - Soils and vegetation would be disturbed throughout the construction phase of the proposed project. A total of 44.34 acres, all of which is under BLM jurisdiction, would be affected. Trenches would be backfilled within two days after pipe was laid. The soil types on which the proposed access roads and well pads are situated pose only a slight water erosion hazard. Site remediation would include reseeding of the 25 foot temporary construction easement consistent with procedures outlined in B(1)(f)(4) above.



e. Livestock grazing - The proposed project would have no long-term effects on allottees using the proposed project area for grazing purposes.



f. Lands - For reasons discussed in Section 2(f)(1-3) , the proposed west mesa wellfield would not be adversely affected by the proximity of the City of Las Cruces sludge disposal facility.



g. Socioeconomic impacts - The proposed service area for this water line is currently undergoing rapid population expansion. Completion of the proposed wellfield complex would permit growth in the region and enhance the social and economic characteristics of the Las Cruces, NM region.



h. Safety - All construction activities would proceed in conformity with OSHA standards. No other safety issues are associated with this project.



3. Alternative Two - No Action



The no action alternative would reject the City of Las Cruces application and the wellfield complex would not be constructed. This alternative would result in no new impacts to soils, vegetation and wildlife, or visual resources. If this alternative is selected, the City of Las Cruces would have to develop alternative water sources that would be equally, if not more, expensive and would likely affect an equal amount of Federal land. Given population projections for the City showing high growth rates, this could inhibit continued growth of the Las Cruces metropolitan area. The selection of this alternative would, therefore have a negative effect upon development in the region.



E. Persons, Groups, and Agencies Consulted



1. Persons, Groups, and Agencies Consulted:



a. BLM Specialists:



Gilda Fitzpatrick - EA Coordinator

Scott Ludwig - Hazardous/Solid Waste

Pam Smith - Cultural Resources

Shirley Miller - Lands



b. City of Las Cruces:



Dr. Jorge Garcia, P.E.



2. List of Preparers:



This EA was prepared by Neal W. Ackerly, Ph.D., under the guidance and direction of the BLM.









___________________ ___________________

Neal W. Ackerly, Ph.D. Date