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The striking Strontia Springs Diversion Dam, wedged in a narrow, steep section of the South Platte Canyon 6V, miles above Waterton, backs up 7,700 acre feet of water in a reservoir 1.7 miles long. Surface area totals 98 acres. The graceful thin arch, double curvature dam rises to a structural height of 299 feet, with a spillway elevation of 6,002 feet. More than 100,000 cubic yards of concrete were placed, forming the dam in 50 blocks, as well as two intake towers, for Denver and Aurora. Each is capable of taking water from selected reservoir levels. The dam is 31 feet thick at the base, narrowing to 10 feet at the crest. Outlet capacity is 4,000 cubic ft.lsec. (ds); spillway capacity is 90,000 ds. Strontia Springs Dam was designed by Harza Engineering Co., Chicago and built by Morrison- Knudsen Co., Inc., Boise, Idaho. Because of environmental and physical constraints of the site, crawler drills and parts of a disassembled bulldozer were lifted in by helicopter; drillers and pneumatic crawlers were suspended by cables from the canyon top. "Powder monkeys" carried 50-pound sacks of explosives in backpacks up the steep rock walls. Left, construction on upstream face of dam shows curvature. Below, Commissioners James B. Kenney Jr., D. Dale Shaffer, John A. Yelenick; Congressman Tim Wirth and Mayor William H. McNichols Jr. Not in "iew; Commissioners Charles F. Brannan and Marguerite S. Pugsley. The arch dam was sited where igneous and metamorphic rocks form a nearly symmetrical (/VJI shape between steep canyon walls. Sixty bore holes were drilled in predesign and design stages to position the dam axis. A generator installed below the valve house furnishes power through a.9 megawatt turbine to operate the dam, with excess power for sale. A 3.4-mile tunnel and a 1,700' conduit connect Denver's intake tower at the dam with the headworks of the Foothills Treatment Plant. The west bore from the dam was driven through metamorphic rock with conventional drilling and blasting mining methods. From the eastern end, a tunnel-boring machine excavated 4,600 feet of sedimentary rock. Most of the 93,000 cubic yards of material removed from the west bore was hauled out of the canyon by a contractor for use in construction. less than ten percent was spread near Stevens Gu Ich, covered with topsoil and the area seeded. The 24,000 cubic yards removed from the east bore was blended into the land form of the plant site, covered with topsoil and seeded. The tunnel required 3.2 million pounds of steel and 59,000 cubic yards of concrete for structural support and lining. The 10Y2-foot diameter tunnel is pressure competent with a capacity of 750 mgd or 1,160 ds. The 15-foot diameter surge chamber is 300 feet deep. DMJM- Phillips, Reister Inc., Denver, designed the tunnel; Shank-Artukovich/]V of Goodyear, Arizona was the contractor.