by BRAD ROLLINS

SAN ANTONIO — Underscoring the severity of a years-long drought, San Marcos officials will impose Stage 4 water restrictions for the first time at noon on Sunday, Aug. 17.

On Tuesday, the Edwards Aquifer Authority announced that the 10-day average aquifer level was 629.7 feet above mean sea level as measured at the J17 index well in Bexar County, just below the 630-foot trigger for implementing Stage 4. The San Antonio pool of the aquifer is approaching a historic low of 612 feet, recorded on August 17, 1956.

Formations of the aquifer that feed the San Marcos springs are faring slightly better, in relative terms, with levels that exceed the one-year average but are less than the six-month average. On Tuesday, the aquifer level in the San Marcos pool stood at 116 feet above sea level with a 10-day average of 119 feet. The one-year average aquifer level in the San Marcos pool is 110 feet above sea level; the six-month average is 150 feet above sea level.

Unlike the first three stages of drought, the city of San Marcos’ drought response ordinance does not spell out specific water restrictions for Stage 4. Instead, the ordinance states, officials “may adopt and enforce any or all additional measures as needed to protect water supplies and the aquifer.”

For now, at least, the city will simply enforce Stage 3 water restrictions more rigorously, said Jan Klein, the city’s conservation coordinator.

“Instead of a new set of restrictions, we have decided to stay with the Stage 3 rules and increase our enforcement efforts,” Klein said.

Stage 3 rules prohibit washing driveways and other impervious cover; prohibit filling swimming pools; and limit the use of sprinklers to water lawns to once every other week according to a set schedule.

Officials will “actively patrol and log instances of drought restriction violations” and send notices to people who ignore the rules, Klein said. Offenses are punishable by fines of $125 to $1,000 per offense per day.

During Stage 4, the aquifer authority requires EAA permit holders — including the cities of San Marcos, Kyle and Buda — to reduce pumping by 40 percent. The required reductions have little direct, practical effect on San Marcos’ city-owned water utility, which each year uses an ever-smaller fraction of the groundwater it is permitted to pump.

Since the city began buying Canyon Lake surface water wholesale from the Guadalupe-Blanco River Authority in 2000, San Marcos water utility’s annual Edwards Aquifer pumping has been reduced by 92½ percent, from a high of 7,500 acre-feet in 1999 to 565 last year. An acre-foot is about 325,851½ gallons, the amount of it would take to cover one acre of surface area with liquid one foot deep.

This year, the San Marcos water utility is projected to use only 470 of the 5,433 acre-feet of Edwards Aquifer groundwater it is permitted to pump under the aquifer authority’s rules, Tom Taggart, the city’s public services division director told council members in December. Under the the most extreme groundwater shortages, EAA can lower the city’s allotment to a minimum of 2,940 acre-feet per year, Taggart said.

Combined with 380 acre-feet the city has committed not to pump as part of a regional habitat conservation plan and 1,000 acre-feet it subleases to Martin Marietta Materials Inc., the city expects to use no more than 1,850 acre-feet of water this year, less than two-thirds of its lowest possible legal allotment.

Stage 3 drought rules restrict use of sprinklers to once every other week on a designated weekday between 6 a.m. and 10 a.m. or 8 p.m. and midnight.

Soaker hose and drip irrigation are allowed one day per week on the designated weekday before 10 a.m. or after 8 p.m. Hand watering is allowed on any day before 10 a.m. or after 8 p.m.

San Marcos has been under water use restrictions almost continuously since April 2011 and under Stage 3 restrictions since April this year.