Three-year-old Alejandro Monterroso is in hot pursuit of his 7-year-old sister Emily on a dusty side yard at Lorena Street Elementary School in Boyle Heights. They weave around big leafy bushes, kicking up dirt as they run. The pair often play here after Emily, a first-grader, is done with classes, as well as during the summer.

"We live in an apartment and it’s closed in at home so that’s why we are here," says their mother, Sandra Cardenas, who watches her children while sitting on a nearby ledge. "They love to run, they are kids."

What Cardenas did not know until this recent afternoon is that two soil samples taken from the yard where her children are playing had elevated lead levels. The state Department of Toxic Substances Control collected the samples a year ago, but it has not decided whether to remove the tainted soil.

Siblings Alejandro, 3, and Emily, 7, often play on this outside yard at Lorena Street Elementary School, where Emily attends a charter school. The Boyle Heights school is one of several that tested high for lead. Elizabeth Aguilera/KPCC

After being informed of the test results by a reporter, Cardenas thinks the choice should be clear.

"If they find a bad spot they should clean it up," she says.

Lorena Street is one of two elementary schools where regulators working on the cleanup around the former Exide battery recycling plant found high levels of lead in yards where kids play before or after school, according to state data. The other is Fishburn Avenue Elementary School in Maywood.

Altogether, Toxic Substances Control found elevated levels at five schools in samples collected one year ago. Neither the agency nor the Los Angeles Unified School District have notified the public about these findings.

Toxic Substances Control sent the information to L.A. Unified; KPCC obtained it through a public records request.

In addition to Lorena and Fishburn, which had levels ranging from 144 to 219 parts per million, Toxic Substances Control found a somewhat elevated level - 105 parts per million - in a tree well at Rowan Avenue Elementary School in East L.A.

Fishburn Avenue Elementary School school in Maywood is one of several LAUSD schools that tested high for lead. Elizabeth Aguilera/KPCC

Carlos Torres, the deputy director of the district's office of environmental health and safety, said the district may consider cleaning up the tree well at Rowan. He said the areas at the other schools are "not children's play areas," and the district will wait for the state agency's final determination.

The state removes soil from residential properties if lead levels are above 80 ppm, but regulators assess schools differently, says Sarah Cromie, the Toxic Substances Control senior scientist overseeing the Exide cleanup.

The agency determines whether cleanup is needed based on factors that include the age of the students, how much time they spend at school and access to certain soil areas , she says.

"You don’t have a kid who is going to be in that one spot that is at 90 [ppm] for every day for 8 hours a day eating dirt in that area," she says. "That’s how you have to think about it, the risk for the whole property."

The agency has notified L.A. Unified that it will conduct additional tests at Lorena, Fishburn and Rowan, according to the school district.

LAUSD environmental health and safety officials Robert Laughton (right) and Bill Piazza (left) explain how they changed the dirt around this tree at Eastman Avenue Elementary School when it was found to have elevated levels of lead. Elizabeth Aguilera/KPCC

Regulators discovered much higher lead levels - ranging from 220 to 688 ppm - in two tree wells on the playground at Eastman Avenue Elementary in East Los Angeles. L.A. Unified decided to remove the soil at Eastman last year on its own at a cost of roughly $10,000, says Robert Laughton, director L.A. Unified's office of environmental health and safety.

Two samples taken from the grass quad at Huntington Park High School had somewhat elevated levels as well - 100 to 110 ppm. Regulators determined that they would not need to remove the soil from Huntington.

"The major concern is with kids who are under 7 because their brains are still developing when they are young," says Cromie. "When you’re dealing with high school kids their nervous systems and brains are all developed so you could say they could handle more lead."

But Jill Johnston, a USC environmental health professor who is studying the Exide plant's health effects, worries that the state doesn't have a complete picture of the lead situation at Huntington Park High, since it only took five samples, and didn't take any from the school's athletic fields.

"If you find these high levels and it's on a baseball field or soccer fields you are going to have kids coming into contact with the dirt even if it's not seven days a week," she says. "They could get a lot of exposure during the time they are playing there."

Kids play on Lorena Street Elementary School's outside lawn after school. The Boyle Heights school is one of several that tested high for lead. Elizabeth Aguilera/KPCC

Lead is a neurotoxin and is particularly harmful for young children and pregnant women. It can cause learning deficits and damage the brain and kidneys as well as bring on other health issues.

Toxic Substances Control took soil samples from a total of 22 campuses in 2014 and 2015, all of them within the 1.7-mile radius around the former Exide plant where most of the residential properties that have been tested so far will require cleanup.

The agency has notified L.A. Unified that the 17 other campuses it tested are safe because they had lead levels lower than 80 ppm.

Critics say those conclusions may not be justified, because of the process Toxic Substances Control routinely uses to check schools and parks for contamination, known as composite sampling.

"To do a composite you take a pinch out of every bag [that contains a sample from a particular site] and put it in another bag, shake it up and send it to a lab," says L.A. Unified's Laughton. "If the composite doesn’t come above [80 ppm], there is no reason to go back and sample every piece you took."

If a composite test result shows elevated levels, then Toxic Substances Control will go back and test soil samples from each dig site separately, says the agency's Cromie. That's what happened at the five schools where regulators ultimately found high levels.

California Department of Toxic Substances Control senior scientist Sarah Cromie at an April 2016 soil removal operation at an East Los Angeles home, part of the Exide cleanup. Maya Sugarman/KPCC

The approach is "a screening tool, it allows us to look at a larger area and get information about that area quickly," she says.

But critics say composite sampling can miss lead hot spots.

"If some of the samples were very low and then you had something that was 200 [ppm] ... when you mix them all together you’d have a level of 60 or 70," says USC's Johnston.

"The use of composite sampling is a way in which you can game the system and dilute the lead you find," says Jane Williams, executive director of the California Coalition Against Toxics.

The method has been a point of contention for the Exide Community Advisory Group, which is made up of local officials, activists and residents, she says.

"This is one of the reasons the CAG is fundamentally distrustful of the agency," says Williams.

Exide was closed down by the state last year after operating on a temporary permit for three decades. Initially, the state required the company to test and clean up around 200 homes. Toxic Substances Control subsequently expanded the testing area and in February Gov. Brown signed a bill allocating an additional $176 million for the Exide cleanup. The state plans to seek reimbursement from Exide in the future.

An earlier version of this story misidentified Jill Johnston. KPCC regrets the error.