Water quality testing samples came back clean Thursday at Twain Harte Lake, and authorities announced the popular, private recreation reservoir will reopen for normal business on Friday.

The reservoir had been closed since Sunday, when a property owner’s sewer line backed up and overflowed about 30 gallons of wastewater into a drain near Twain Harte Lake, according to staff with Twain Harte Lake Association and Twain Harte Community Services District.

The popular spot was closed for Memorial Day. Twain Harte Lake Association has 805 dues-paying members.

“Our Water Test results are in and we are GOOD TO GO!!!” staff with Twain Harte Lake Association announced Thursday afternoon on www.thlake.org. “We will reopen tomorrow, Friday, June 1. Thank you so much for your patience and understanding, cheers to a GREAT SUMMER!!!”

Tom Trott, general manager for Twain Harte Community Services District, said test samples came back clean and the lake will be open Friday with normal operating hours. Earlier this week, Trott said he was expecting confirmed test results by noon Thursday.

Staff at the reservoir had the water tested Monday morning, Lauren Gerber, the general manager and lake director for Twain Harte Lake, said earlier this week. With the Memorial Day holiday it was going to take 48 hours or more to get test results.

The unidentified property owner’s sewer line blockage was primarily a result of root intrusion and attempting to flush wipes, which are common causes of blockages in the Twain Harte Lake area, Trott said.

Trott advised Twain Harte Community Services District customers to be aware that primary causes of private sewer lateral back-ups are a combination of roots, grease and non-soluble items flushed down toilets.

Non-soluble items include wipes and swiffers that are not flushable, Trott said.

Trott reminded Twain Harte Community Services District customers to refrain from flushing anything other than human waste and toilet paper, as well as putting grease down drains. Reducing garbage disposal waste by scraping plates into the trash and using enzyme cleaners to help break down roots are also good ideas, Trott said Tuesday.

“Many of our out-of-town customers experience back-ups because new roots have grown into their laterals over the few months since they last visited their home,” Trott said in a recent announcement. “As soon as the lateral experiences heavy use, toilet paper and other products catch on the roots and cause a clog.”

Twain Harte Lake was closed as a precautionary measure until the water was confirmed to be safe for human contact, according to Twain Harte Lake Association and Twain Harte Community Services District staff.

A separate sewage incident reported Sunday west of the Crystal Falls subdivision in the Sullivan Creek watershed was unrelated to the situation at Twain Harte Lake.

The Sheriff’s Office stated in a social media post Sunday that sewage had not reached Sullivan Creek. Sheriff’s staff said “As a precaution the public is advised to not swim, drink, fish or carry out any recreational activities near or in the water. Avoid the area of the Sullivan Creek drainage until further notice.”

Robert Bernstein, the new health officer for Tuolumne County, said earlier this week the incident occurred at Hidden Valley Trailer Park. He said he spent four hours, from 5 to 9 p.m. Sunday, communicating with county Environmental Health, the Office of Emergency Services, a physician at Adventist Health Sonora, and on-site responders that included law enforcement, fire and utility workers.

Bernstein said a reverse 911 notice was sent to the public advising people to refrain from drinking, swimming, fishing or doing any other recreational activities in the Sullivan Creek below the spill area.

A Tuolumne Utilities District field investigator went to the park Sunday evening and noted the spill had apparently stopped and the fire department had placed a dam to prevent further leakage into the creek, Bernstein said.

Bernstein said he went to visit the trailer park Monday morning for about two hours, examined and photographed the site of the sewage spill, and spoke with four residents who said that trailer park management had not responded to numerous calls about the sewage spill and the poor, broken condition of the system for controlling wastewater in the park.

It was not clear how much contamination occurred in terms of volume or bacterial level, Bernstein said. No gastrointestinal illnesses were reported by Adventist Health Sonora. Hidden Valley Trailer Park management could not be reached for comment.