# GUIDANCE FOR SCHOOL SITE RISK ASSESSMENT PURSUANT TO HEALTH AND SAFETY CODE SECTION 901(f):

GUIDANCE FOR ASSESSING EXPOSURES AND HEALTH RISKS AT EXISTING AND PROPOSED SCHOOL SITES
FINAL REPORT

February 2004

Integrated Risk Assessment Section
Office of Environmental Health Hazard Assessment California Environmental Protection Agency

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## Guidance for Assessing Exposures and Health Risks

at Existing and Proposed School Sites Pursuant to Health and Safety Code §901(f):

FINAL REPORT

February 2004



## Integrated Risk Assessment Section
Office of Environmental Health Hazard Assessment California Environmental Protection Agency 1001 I Street, 12 th 

## Floor
P.O. Box 4010 Sacramento, California 95812-4010ii LIST OF CONTRIBUTORS

Primary Author Jim Carlisle, D.V.M., M.Sc.

Collaborators Deborah Oudiz, Ph.D.
Thomas Booze, Ph.D. Gerald Chernoff, Ph.D.

David Chan, D.Env. Susan Knadle, Ph.D., DABT

Web-site Posting

Laurie Monserratiii 

### Executive Summary This guidance document was prepared to comply w ith California Health and Safety Code Section 901(f), which requires the Office of Environmen tal Health Hazard Assessment (OEHHA) to develop and publish a guidance document for use by the Department of Toxic Substances Control and other state and local environm ental and public health agencies to assess exposures and health risks at existing and proposed school sites. It presents methodology for estimating exposure of school users to toxic chemicals found as contaminan ts at existing and proposed school sites, and the health risks from those exposures. It incor porates exposure factors unique to the school environment, and considers the activity patterns of children from birth through age 18, and of adult school employees. It discusses uncertainties a nd steps that can be ta ken to address these uncertainties.iv 

## Table Of Contents

Introduction and Purpose .................................................................................................... 1 Schools Conceptual Site Model........................................................................................... 2 Potentially Exposed Sub-popul ations at Schools ................................................................ 4 Exposure and Source Media at Schools ............................................................................. 5 Exposure Pa thways............................................................................................................. 6

Model Para meters ............................................................................................................. 11

Risk Assess ment............................................................................................................... 2 3 Sensitivity Analys is........................................................................................................... . 24 Uncertainty Analysi s.......................................................................................................... 2 6
REFERENC ES.................................................................................................................. 31 Appendix 1: Summary and Interpretati on of Results of RTI Study .................................A1-1 Appendix 2: Comment s and Respons es ....................... A2- Error! Bookmark not defined.2/5/2004 1 

### Introduction and Purpose Section 901(f) of the California Health and Safety Code states that: “On or before December 31, 2002, the Office (of Environmental Health Hazard Assessment, OEHHA) shall publish a guidance document, for use by the California Department of Toxic Substances Cont rol (DTSC) and other state and local environmental and public health agencies to asse ss exposures and health risks at existing and proposed school sites. The guidance document shall includ e, but not be limited to, all of the following: (A) Appropriate child-specific routes of exposure unique to the school enviro nment, in addition to those in existing exposure assessment models. (B) Appropriate available child-specific numerical health effects guidance va lues and plans for the development of additional child-specific numerical health effects guidance values. (C) The identification of uncertainties in the risk assessment guidance and t hose actions that should be taken to address those uncertainties.” Pursuant to HSC§901(f)(A) and (C), OEHHA is proposing these guidelines for multimedia, multipathway, risk assessment at existing and propos ed school sites. HSC§901(f)(B) is addressed in a separate document (OEHHA, 2002a).

Need for Guidance Children differ from adults anatomically, physiological ly, and behaviorally in ways that may affect their exposure or their response to exposure to environmental c ontaminants. For example, on a body weight basis, children require more oxygen, f ood, and water, and have a higher skin surface area than adults. Children’s ac tivity patterns are different. Child ren are in a period of continuous change as they move from infancy through puberty and into adulthood. Most previous guidance has focused on residential or occupational scenarios, and has treated childhood as a homogeneous life stage. Recognizing that children are undergoing rapid development, this guidance addresses the differences between children and adults, and betw een the school setting and other settings.
Scope of Guidance As required by HSC§901(f), this gu idance is intended to support as sessment of chemical exposures and health risks at existing and proposed school sites, to characterize uncertainty in assessing exposure and risk in the school se tting, and to suggest which areas are most in need of further research. It is intended to be sufficiently flexible to accommodate a variety of situations: It may be used to support the evaluation of the suitability of a site for futu re school construction or to support the assessment of toxicologi cal risk at an existing school site. These contrasting situations present different opportunities to measure c ontaminant concentrations in envi ronmental media. In the first scenario, soil, soil gas, air, and ground water may be available for sampling, but concentrations in indoor media will have to be estimated. In the second scenario, indoor media such as surface dust and air may be available for sampling. By sampling these media, additional sources of contaminants, such as chemicals in building ma terials and furnishings and chemicals used in school operations, can be included in the assessment. This guidance specifies toxicity criteria that should be used in assessing ri sk and hazard. It only addresses risk assessment for schools; it does not a ddress chemical exposures that students and staff may receive outside the school setting. It does not include project-specific guidance such as selection of chemicals of potenti al concern, site characterization, sampling and analyses strategies, and determination of appropriate exposure point concentrations. This guidance does not provide2/5/2004 2 risk management application or decision-maki ng criteria. For information regarding the application of this document to regulatory program s, contact DTSC or other agencies that may utilize this guidance as a part of their regulatory program. This gui dance assumes that the user is familiar with the principles of chemical risk assessment; it is not intended to provide basic instruction in risk assessment. 

### In-progress research is expected to result in information that may render this guidan ce out-dated. The guidance will be revised as new information becomes available.

Tiered Approach The model is designed to support a tier ed approach to assessment of ri sk. It can be used in screening (Tier 1) mode, with conservative default input va lues and all pathways included (except pathways 9, 10, and 12 when these are not appropr iate). It also accommodates a Tier 2 analysis using usersupplied site-specific input parameters and/or elimin ation of pathways that are not appropriate for a given site. In some cases, it may be appropriate to add in additional sources of chemicals in the environment. For example there may be off-site em issions that may impact on-site concentrations. 

### Representative measured contaminant co ncentrations in various environmental media may be used in lie u of modeled values. Case-specific approaches may be appropriate for these situations in lieu of, or in addition to default methods. Users should document and justify all departures from default conditions so that reviewers can duplicate the modeling conditions and verify the result. Use of this guida nce in Tier 1 or Tier 2 mode should be discussed with and approved by DTSC or other regulatory pr ograms for which the risk assessment is being conducted.

Mathematical models Mathematical models can be used to predict expo sures and risks to specified groups of people from chemicals in specified environmental media under defined conditions. This guidance lays out a modeling approach to predicting exposures and risk s to preschoolers, students, teachers and other school personnel, and their offspring, from chemi cals in the soil, shallow ground water, and air at the school site. A separate document, (OEHHA, 2003) presents a spreadsheet adaptation of this model. The use of this spreadsheet (SchoolScre en.xls) is optional, a nd the user retains the responsibility to ensure that the model parameters including toxicity para meters are current and correct. The model is applicable to most chem icals, the notable exce ption being lead. OEHHA recommends the use of the DTSC Lead Risk Assessment Spreadsheet (http://www.dtsc.ca.gov/ ScienceTechnology/ledspred.html) for assessment of exposure to lead at school sites.



### Schools Conceptual Site Model A conceptual site model includes the contaminat ed environmental media, the movement of the chemicals within and between environmental compartments (intermedia transfers), the concentration of the chemical(s) in various person al exposure media, exposure pathways and routes, exposed populations, and the amount of the chemi cal(s) taken into the bod y. These movements and concentrations may be described by a series of ma thematical relationships. This guidance proposes a series of such mathematical relatio nships, which are described below. As depicted in Figure 1, this model considers co ntaminated soil, ground water, and unspecified offsite sources as primary source media. Contaminat ed soil can be an exposur e medium (by ingestion or dermal contact) and can be a source for transfer into other media. Chemicals can vaporize from soil into indoor or outdoor air and can be entrained into the susp ended particle phase. As a default,2/5/2004 3 soil is treated as the source of outdoor suspended pa rticulate matter, but a measured concentration in on-site particulate matter may replace the calculat ed value. By this means, total particle-bound contaminants from off-site and on-site sources can be included. Vapors can be inhaled indoors or outdoors. Soil can be transported indoors, wher e it becomes a component of interior dust.

CONTAMINANT

SOURCES ENVIRONMENTAL MIGRATION EXPOSURE MEDIUM EXPOSURE MEDIUM ROUTE OF EXPOSURE FIGURE 1: SITE CONCEPTUAL MODEL FOR EXISTING OR PROPOSED SCHOOL SITES

ON-SITE

SOIL GROUND WATER

VAPORIZATION VAPORIZATION

PARTICLE EMISSION

INGESTION MATERNAL MILK INGESTION SURFACE SOIL PARTICLE EMISSIONUPWIND OFFSITE SOURCES

VAPORIZATION

OUTDOOR AIR* INHALATION School & preschool children Nursing infants School Staff School Staff

INDOOR AIR* Y Y Y INHALATION

DERMAL CONTACT

INGESTION INDOOR SURFACE DUST* DERMAL CONTACT TRACKED-IN & WIND-BLOWN

MATERNAL DOSE (sum of all pathways) POTENTIALLY EXPOSED POPULATIONS

INGESTION

* Available representative measur ed concentrations in these exposure media may be substituted for t he model-based estimates

.

Exposure to this dust can be by ingestion or dermal contact, or it can be re -suspended and inhaled. Ground water is treated as a source of drinking water (if pathway 12 is selected) and as a source of chemicals that may vaporize and contribute to soil vapors. However, a measured soil vapor concentration may be substituted for the value esti mated from soil and ground water concentrations. As depicted in Figure 2, hazard quotients and in cremental risks are estimated for each chemical; then the hazard quotients and incr emental risks associat ed with the individua l chemicals are added to arrive at the total hazard index and total risk. If the total hazard index does not exceed one, then it may be assumed that the non-cancer toxic effects are unlikely and further analysis of non-cancer effects is not necessary. If the total hazard index exceeds one, then it may be useful to separate chemicals by target organ and/or mode of ac tion and add the hazard quotients of only those chemicals that are likely to act in an additive mann er. This target organ/mode of action analysis should be documented.2/5/2004 4 FIGURE 2: RISK ESTIMATION FOR EXISTING OR PROPOSED SCHOOL SITES

INGESTION OF MOTHER’S MILK SOIL INGESTION

INHALATION OF VAPORS

INHALATION OF PARTICLES

DERMAL CONTACT WITH SOIL

WATER INGESTION DERMAL CONTACT WITH DUST INHALATION DOSE

DERMAL UPTAKE

AND INGESTION DOSE CANCER POTENCY (INHALATION)

CANCER POTENCY (INGESTION)

REFERENCE DOSE (INHALATION)

REFERENCE DOSE (INGESTION) SINGLECHEMICAL

CANCER

RISK

SINGLECHEMICALNONCANCER HAZARD QUOTIENT MULTIPLECHEMICAL

CANCER

RISK

MULTIPLECHEMICALNONCANCER HAZARD INDEX* DUST INGESTION

* Additivity considered as appropriate, depending on target organ and/or mode of action



### Potentially Exposed Sub-populations at Schools The model addresses the following school sub-popul ations. With the exception of pregnant or nursing women, genders are not separated.
1) Students from kindergarten through high school 2) Staff 3) Pregnant or nursing women 4) Pre-schoolers aged one through four 5) Nursing infants less than one year of age in day care at the school site whose mothers are students or staff. No sources of contaminants other than those associ ated with the school environment are considered in calcula ting the concentration in breast milk. Other groups that may use or visit the school facilities, such as pa rents and members of the general community are not explicitly consid ered. Since their visits would be less frequent than the students and staff, their long-term average exposure would be less than that of the groups listed above. Also, it would be possible to assess expos ure of nursing infants who did not spend time at the school site, but whose mothers were students or staff. However, these children would be exposed less than infants described above (group #5).2/5/2004 5 

### Exposure and Source Media at Schools

Potential Source Media at Schools

Soil Soil is often the primary environmental medium to be contaminated when toxic materials are spilled or dumped. Soil may be a source medium for contam ination of other media such as surface dust or airborne particulate matter or va pors. The model can estimate the c oncentrations of contaminants in soil gas based on the concentrations in soil matrix and/or ground water, or these concentrations may be measured directly. Soil may be directly contaminated by spills or leaks occurring on the site, or may be contaminated by wet or dry deposition from off-site sources. The m odel does not explicitly consider deposition; rather it is assumed that th is type of contamination will be included in the results of the on-site soil sampling.

Ground water Ground water may be a source of volatile contaminants in indoor and outdoor air. Off-site ground water plumes may need to be considered if they are likely to move on-site.

Off-site sources Atmospheric emission sources within 1⁄2 mile of the site that have the potential to contaminate onsite air may be important in estimating overall toxic exposures. Examples could include fixed facilities with known emissions and mobile sources such as highways, heavily traveled streets, or vehicle loading areas. Modeling should evaluate atmospheric c oncentrations during time frames that reflect conditions to which sc hool users will be exposed.
Potential Exposure Media at Schools

Soil Students and others at school site s may be exposed to soil on th e campus. Bare dirt may cover a portion of the campus area. Playgrounds and athletic fields may have patches of bare dirt. Even paved areas may contain a layer of soil. Soil ma y be ingested or may contaminate the skin.

Dust Interior surfaces including floors, desks, shelve s, and windowsills, may accumulate a layer of dust between cleanings. This dust may come from multiple sources, including tracked-in or blown-in outdoor soil. Dust may be ingested or may contaminate the skin.

Air Air may contain vapor-phase and/or particulate contaminants. The multiple sources of vapors and particles may include on-site and off-site s ources. The model estimates indoor and outdoor concentrations of pollutants in th e particulate or vapor phases based on concentrations in on-site soil and/or ground water. Representative measured concentrations of vapor -phase or particulate contaminants in outdoor air may be substituted for estimated values. At existing schools corresponding indoor measurements may also be used. Measurements should be made in an appropriate manner to reflect conditions th at school users will be exposed to.

Drinking Water Since ground water may be a sour ce of drinking water (RTI, 2003), the model includes an optional equation for assessing exposure vi a the drinking water pathway. This equation does not predict concentrations of contaminants in ground wa ter, but relies on measured values.

Air contamination by vapor- or partic le-phase pollutants originating off-site Depending on program requirements, modeled on-site concentrations of contaminants originating from off-site sources may be added to estimated concentrations of contaminants from on-site2/5/2004 6 sources. Modeling should evalua te atmospheric concentrations during time frames that reflect conditions to which school users will be exposed . If on-site concentrations are measured under representative meteorological condi tions (as opposed to modeled), c ontributions from these off-site contamination sources generally should not be a dded to the resulting measured concentrations, because the measured concentrations should include the off-site component.
Other potential exposure media In a recent survey, nearly 8 percent of schools reported that produce for human consumption was grown at the site (RTI, 2003). OEHHA considered including food grown in the site soil as an exposure pathway, however, a variety of simulati ons using an array of chemicals representing various chemical classes (incl uding volatile organic chemicals, lipophilic organic chemicals, and heavy metals) showed that the food pathway never cont ributed as much as 1 percent of the total risk or hazard, even assuming up to 5 percent of the diet being site-grown produce. Therefore, food is not included as an exposure medium in the schools exposure model.
Building materials and indoor products may be important sources of indoor exposure to toxic constituents at schools. It may be appropriat e to include these source s of chemical exposures in the overall assessment of overall hazards and risks at existing schools. Typically these assessments would be based on measured atmos pheric concentrations in classrooms and other indoor areas, and estimated risks, using the same exposure parameters, would be added to site-related risks. Hazards would be additive among chem icals sharing a common target organ and/or mode of action.
Background (non-site-related) Exposures
A small incremental dose of a toxi c constituent that would otherwis e be of no concern, may become a concern if the exposed person is already rece iving a background dose of the constituent and the combined exposures may exceed the toxic threshold. For this reason, risk managers may wish to take background exposures into account in their d ecision-making process. This is of primary importance for non-carcinogenic toxic effects, wh ich are generally thought to exhibit a toxic threshold. For carcinogens, which are generally tr eated as exhibiting no th reshold, the incremental risk posed by a given exposure to a carcinog en does not depend on the individual’s background exposure to that or any other carcinogen. 

### Exposure Pathways Exposure pathways can be direct or indirect. A direct exposure path way consists of a contaminated environmental medium and an exposure route by which the contaminated medium contacts and enters the body (e.g. ingestion of contaminated soil, pathway 1, below). An indirect exposure pathway consists of a contaminated environm ental medium, one or more transfers between environmental media and ultimately an exposur e medium, and an exposure route by which the exposure medium contacts and enters the body (e.g. tran sfer of chemicals from contaminated soil to indoor dust and ingestion of indoor dust, pathway 3, below).
Exposure Pathway Equations Figure 1 depicts the movements of contaminants into and between environmental and exposure media. These movements and the resulting exposures may be described by a series of mathematical relationships. This model includes up to 12 path ways by which school users could be exposed to chemicals at the school site. Each pathway can be represented by an equation which describes a concentration in the source medium, up to two transfer factors that relate the concentration in the source medium to a concentration in an intermediate or exposure medium, and a contact rate that2/5/2004 7 describes the daily intake of, or contact with, the exposure medium . When the exposure pathway is direct (i.e. the environmental medium and the expo sure medium are the same , such as ingestion of outdoor soil), then no transfer fact ors are required. The annual average daily dose associated with each of these pathways is estimated as follows:

1. Ingestion of outdoor soil: D = C S * I S * A I * F S * F O * EF/(BW * 365 (days/year)) , where:

D = Pathway-specific annual average daily dose of contaminant (mg/kg BW /day) C S = Concentration of contaminant in soil (mg/kg soil ) I S = daily soil/dust ingestion (kg soil /day) A I = route-specific absorption fact or for ingestion (unitless) F S = fraction of daily soil/dust ingestion and derm al contact that occurs at school (unitless) F O = fraction of daily soil/dust ingestion and derm al contact that occu rs outdoors (unitless) BW = age-specific body weight (kg) EF = exposure frequency (days/year)

2. Dermal contact with outdoor soil: D = C S * A D * F S * F O * D S * EF / 365 (days/year) , where:

D = Pathway-specific annual average daily dose of contaminant (mg/kg BW /day) C S = Concentration of contaminant in soil (mg/kg soil ) A D = route-specific absorp tion factor (unitless) F S = fraction of daily soil/dust ingestion and derm al contact that occurs at school (unitless) F O = fraction of daily soil/dust ingestion and derm al contact that occu rs outdoors (unitless) D S = Daily dermal contact with soil/dust (kg soil /kg BW /day) = ∑ (A BP * L BP ), where A BP = body-part-specific area (cm 2 /kg) L BP = body-part-specific skin loading (kg soil /cm 2 /day) EF = exposure frequency (days/year)

3. Migration of chemicals from outdoor soil to indoor dust; ingestion of indoor dust: D = C S * TF SD * I S * A I * F S * F I * EF/(BW * 365 (days/year)) , where:

D = Pathway-specific annual average daily dose of contaminant ( μ g/kg BW /day) C S = Concentration of contaminant in soil (mg/kg soil ) TF SD = Transfer factor from soil to indoor dust ((mg/kg dust )/(mg/kg soil )) I S = daily soil/dust ingestion (kg soil /day) A I = route-specific absorption fact or for ingestion (unitless) F S = fraction of daily soil/dust ingestion and derm al contact that occurs at school (unitless) F I = fraction of school soil/dust ingest ion that occurs indoors (unitless) BW = age-specific body weight (kg) EF = exposure frequency (days/year)2/5/2004 8 4. Migration of chemicals from outdoor soil to indoor dust; dermal contact with indoor dust: D = C S * TF SD * A D * F S * F I * D S * EF / 365 (days/year) , where

D = Pathway-specific annual average daily dose of contaminant (mg/kg BW /day) C S = Concentration of contaminant in soil (mg/kg soil ) TF SD = Transfer factor from soil to indoor dust ((mg/kg dust )/(mg/kg soil )) A D = route-specific absorp tion factor (unitless) F S = fraction of daily soil/dust ingestion and derm al contact that occurs at school (unitless) F I = fraction of daily soil/dust dermal c ontact that occurs indoors (unitless) D S = Daily dermal contact with soil/dust (kg soil /kg BW /day) = ∑ (A BP * L BP ), where A BP = body-part-specific area (cm 2 /kg BW ) L BP = body-part-specific skin loading (g/cm 2 ) EF = exposure frequency (days/year)

5. Suspension of soil particles in outdoor air; inhala tion of suspended particulate matter (PM10) in outdoor air: D = C S * TF PM/S * PM 10 * B O * T O * A In * EF / 365 (days/year) , where

D = Pathway-specific annual average daily dose of contaminant (mg/kg BW /day) C S = Concentration of contaminant in soil (mg/kg soil ) PM 10 = Respirable particle load for outdoor ai r due to resuspension of site soil (kg PM10 /L air ) B O = Body-weight-normalized brea thing rate outdoors (L/min/kg BW ) T O = Time outdoors at school daily (min/day) A In = route-specific absorp tion factor (unitless) EF = exposure frequency (days/year) TF PM/S = Ratio of the concentration of contaminant in outdoor PM 10 originating from site soils to the concentration of contaminant in soil ((mg/kg PM10 )/(mg/kg soil )) A representative measured value for concentration of a chemical in outdoor PM 10 may replace the value estimated from soil data; in that case the equation becomes: D = C PM10 * PM 10 * B O * T O * A In * EF / 365 (days/year) , where C PM10 = Measured concentration in PM 10 ( μ g/g)

6. Suspension of respirable indoor dust particles (PM10) in indoor air; inhalation of PM10 in indoor air: D = C S * TF S/D * TF PM/D * S F * B I * T I * A In * EF / 365 (days/year) , where

D = Pathway-specific annual average daily dose of contaminant (mg/kg BW /day) C S = Concentration of contaminant in soil (mg/kg soil ) S F = Respirable particle load for indoor air due to resuspension of dust particles (kg PM10 /L air ) B I = Weight-normalized br eathing rate indoors (L air /min/kg) T I = Time indoors at school daily (min/day) A In = route-specific absorp tion factor (unitless) TF PM/D = Ratio of the concentrati on of contaminant in indoor PM 10 to the concentration of contaminant in indoor surface dust ((mg/kg PM10 )/(mg/kg dust )) TF SD = Transfer factor from soil to indoor dust ((mg/kg dust )/(mg/kg soil )) EF = exposure frequency (days/year)2/5/2004 9 7a

. Vaporization of volatile chemicals from the so il; penetration of vapors into building interior; inhalation of vapors mixed with indoor air: D = C S * α * VC S * CF * B I * T I * A In * EF / 365 (days) /year , where:

D = Pathway-specific annual average daily dose of contaminant (mg/kg BW /day) C S = Concentration of contaminant in soil (mg/kg soil )

α = Ratio of chemical concentration in i ndoor air to that in soil vapor (unitless) 1
VC S = Volatilization factor from soil (g soil /L vapor ) CF = Conversion factor (0.001 kg/g) B I = Weight-normalized breathi ng rate indoors (L/min/kg) T I = Time indoors at school daily (min/day) A In = route-specific absorption fact or for inhalation (unitless) EF = exposure frequency (days/year) A measured soil vapor concentration may be used in place of the value estimated from soil matrix data. 1 In that case the equation becomes: D = C SV * α * B I * T I * A In
, where: C SV = concentration in soil vapor (mg/L) and 7a and 7b collapse into a single pathway 7.

7b

. Vaporization of volatile chemicals from shallo w ground water; penetration of vapors into building interior; inhalation of vapors mixed with indoor air: D = C GW * α * VC GW * CF * B I * T I * A In * EF / 365 (days/year) , where:

D = Pathway-specific annual average daily dose of contaminant (mg/kg BW /day) C GW = Concentration of contam inant in ground water (mg/L)

α = Ratio of chemical concentration in i ndoor air to that in soil vapor (unitless) 1
VC GW = Volatilization factor from ground water (ml water /L vapor ) CF = Conversion factor (0.001 L/ml) B I = Weight-normalized breathi ng rate indoors (L/min/kg) T I = Time indoors at school daily (min/day) A In = route-specific absorption fact or for inhalation (unitless) EF = exposure frequency (days/year) A measured soil vapor concentration may be used in place of the value estimated from ground water data. 1 In that case the equation become s: D = C SV * α * B I * T I * A In
, where: C SV = concentration in soil vapor (mg/L), and 7a and 7b collapse into a single pathway 7.

8. Inhalation of chemicals vaporized from outdoor soil: D = C S * 1/VF * CF * (B O * T O + B I * T I ) * A In * EF / 365 (days/year) , where:

D = Pathway-specific annual average daily dose of contaminant (mg/kg BW /day) C S = Concentration of contaminant in soil (mg/kg soil ) VF = Volatilization Factor (ra tio of concentration in air to concentration in soil)(L air /g soil ) CF = Conversion factor (0.001 kg/g) B O = Weight-normalized breathing rate outdoors (L/min/kg) T O = Time outdoors at school daily (min/day) B I = Weight-normalized breat hing rate indoors (L/min/kg) 2
T I = Time indoors at school daily (min/day) 2
A In = route-specific absorp tion factor (unitless) EF = exposure frequency (days/year)
1 The decision as to which one to use should be made in consultation with the lead agency for the project. 2 Assumes that HVAC system circulat es outdoor air to the indoor spaces.2/5/2004 10 9. Inhalation of contaminants in vapors that originate off-site ** : D = C A * (B I * T I + B O * T O ) * A In * EF / 365 (days/year) , where:

D = Pathway-specific annual average daily dose of contaminant (mg/kg BW /day) C AV = Concentration of contaminan t vapor in site air (mg/L) B I = Weight-normalized breathi ng rate indoors (L/min/kg) T I = Time indoors at school daily (min/day) B O = Weight-normalized breathi ng rate outdoors (L/min/kg) T O = Time outdoors at school daily (min/day) A In = route-specific absorption fact or for inhalation (unitless) EF = exposure frequency (days/year) This pathway accommodates modeled on-site concentra tions from off-site sources. It is independent of (and therefore added to) modeled on-site c oncentrations. However, representative on-site concentrations measured under conditions that would capture contaminants originating both off-site and on-site, should include the contribution from both sources and therefore would replace modeled concentrations based on on- and off-site sources

. 10. Inhalation of contaminants in suspended particles that originate off-site. D = C AP * (B I * T I + B O * T O ) * A In * EF / 365 (days/year) , where:

D = Pathway-specific annual average daily dose of contaminant (mg/kg BW /day) C AP = Concentration of particulate contaminant in site air (mg/L) B I = Weight-normalized breathi ng rate indoors (L/min/kg) T I = Time indoors at school daily (min/day) B O = Weight-normalized breathing rate outdoors (L/min/kg) T O = Time outdoors at school daily (min/day) A In = route-specific absorption fact or for inhalation (unitless) EF = exposure frequency (days/year) This pathway accommodates modeled on-site concentra tions from off-site sources. It is independent of (and therefore added to) modeled on-site c oncentrations. However, representative on-site concentrations measured under conditions that would capture contaminants originating both off-site and on-site, should include the contribution from both sources and therefore would replace modeled concentrations based on on- and off-site sources. This pathway may be inappropriate for some
programs.
11. Ingestion of contaminants in breast milk (only for infants up to one year old) D = C BM * I BM * A I * EF / 365 (days/year) , where:

D = Pathway-specific annual average daily dose of contaminant (mg/kg BW /day) C BM = Contaminant concentra tion in breast milk (mg/kg milk ), estimated as: B BM * BW M * maternal annual average daily dose (mg/kg/day) where: B BM = breast milk biotransfer factor ((mg/kg)/(mg/day)) BW M = Maternal body weight (kg) I BM = Age-specific, weight normalized daily breast milk ingestion (kg milk /kg BW /day) A I = route-specific absorption fact or for ingestion (unitless) EF = exposure frequency (days/year)2/5/2004 11 12. Ingestion of contaminated drinking water: D = C DW * I DW * F S * A I * EF / 365 (days/year) ; where:

D = Pathway-specific annual average daily dose of contaminant (mg/kg BW /day) C DW = User-supplied contaminant concentr ation in school drinking water (mg/L). I DW = Age-specific, weight normalized daily drinking water ingestion (ml/day/kg) F S = fraction of daily water ingesti on that occurs at school (unitless) A I = Ingestion absorption factor (unitless) EF = exposure frequency (days/year)

** Vapor inhalation pathways may be omitted for chemicals whose boiling point exceeds 600oK Each of these equations gives a pathway-specific annual average daily dose of the chemical in question. Doses via all pathways that involve the same exposure route (e.g. ingestion) are added together to determine the route-specific annual average daily dose. The latter is divided by the route-specific reference dos e (RfD) to arrive at the route-specif ic hazard quotient (HQ). Dermal exposures are usually combined with ingestion ex posures. The route-specific HQs are added to give the chemical-specific HQ. In a screeni ng analysis, the chemical-specific HQs for each chemical are added to give the Hazard Index. In a more detailed (tier 2) an alysis, target organs and mechanisms of toxic action may be considered in determining the appropriateness of adding the HQs for individual chemicals. To compute cancer risk, the route- specific annual average daily dose is converted to a route-specific lifetime average daily dose by multiplying by the fraction of a lifetime represented by each exposure scenario (ED/AT), i.e. 1/ 70 of a lifetime for each year of exposure. The route-specific lifetime average daily dose is multiplied by the ro ute-specific cancer potency factor to obtain the risk for that pathway. The route-specific risks for relevant pathways are added to give the chemicalspecific risk. Finally the chemical -specific risks for each chemical are added to give the total cancer risk. Annual risks may be added fo r a series of years to obtain th e total risk for that period.



### Model Parameters The pathway equations above require numerical valu es or parameters, which can be divided into “intermedia transfer factors” and “exposure fact ors,” which are described below and summarized in a table at the end of each section:

Intermedia Transfer Factors When the environmental medium and the expos ure medium are not the same, one or more intermedia transfer factors are involved. Transf er factors describe the relationship between the concentration of a chemical in one compartment a nd the concentration of the chemical in another compartment, or, in some cases, th e concentration of one medium in another, such as the amount of suspended particulate matter in the air. Some i ndirect pathways – such as vaporization of soil contaminants and movement of the vapors into indoor spaces – involve two or more intermedia transfer factors. Some transfer factors are chemi cal-specific; others are general. Many of the intermedia transfer factors in th is guidance have a default value of one. This begs the question, ”Why include them if the value is one?” The r easons for their inclusion are 1) including the parameter facilitates incorporating a site-specific value without altering the equation structure, and 2) further research may support a defau lt value other than one in the future.

Transfer factor from soil to indoor dust (TF SD ) TF SD is the ratio of the concentration of a chem ical in the dust on surf aces inside the school building(s) to its concentration in outdoor soil from the schoolyard. This is important because dust2/5/2004 12 on indoor surfaces may be a significant source of exposure to chemicals or iginating in soil and transported to the building’s interior through open doors and windows, hea ting, ventilation, and air conditioning (HVAC) systems, buildi ng infiltration, and on shoes, clot hing, and objects carried into the rooms. OEHHA recommends a default value of 2 for this parameter (see Appendix 1 for further explanation).

Transfer factor from soil to outdoor particulate matter (TF PM/S ) TF PM/S is the ratio of the concentrat ion of contaminant in outdoor PM 10, resulting from resuspension of on-site soil, to the concentr ation of contaminant in outdoor soil from the schoolyard. This is important because students and ot her school users may inhale suspe nded respirable particles in the outdoor air. OEHHA r ecommends a conservative default value of one (1). If samples of outdoor PM 10 are collected and analyzed, this transfer factor is not needed.

Transfer factor from indoor surface dust to indoor respirable particulate matter (TF PM/D ) TF PM/D is the ratio of the concentration of a chemical in indoor PM 10 to its concentration in indoor surface dust. This is important because students and other school users may inhale suspended respirable particles in the indoor air. OEHHA recommends a defa ult value of one, implying that indoor dust is resuspended in indoor air with no change in its chem ical contaminant concentration.
Soil vapor to Indoor air ( α ) Alpha is the unitless ratio of the c oncentration of a chemical in indoor air to its concentration in soil vapor. It is a dilution factor for vapors moving fro m relatively confined spaces in soil pores to the better-ventilated building interior. OEHHA reco mmends the use of the EPA adaptation of the Johnson and Ettinger (J&E) model to estimate a value for this parameter. OEHHA recommends a default air exchange rate of 4.7 per hour, based on the lower confidence limit on the weighted mean value from 94 portable and 26 traditional classr ooms (see Appendix 1 for further discussion). Default values may be used for the remaining para meters including a sandy soil type. Site-specific parameters may be used when justified.
Volatilization factor from soil (VC S ) VC S is the ratio of the concentration of a chemical in soil vapor to its concentration in the soil matrix. This ratio, in g soil /L vapor , depends on the physical and chemical properties of the chemical, and on the properties of the soil. OEHHA recomm ends the Johnson and Ettinger screening model (EPA, 2003) to estimate this value.
Volatilization factor from ground water (VC GW ) VC GW is the ratio of the concentration of a chemical in soil vapor to its concentration in shallow ground water. This ratio, in ml water /L vapor , depends on the physical and chemical properties of the chemical, and on the properties of the soil. OEHHA recommends the Johnson and Ettinger screening model (EPA, 2003) to estimate this value.
Volatilization factor (VF) VF is the ratio of the concentration of a chemical in soil to its concentr ation in outdoor breathing zone air. To calculate VF, OEHHA recommends the use of the equations in EPA’s Soil Screening Guidance (EPA, 1996) with chemical-specific paramete rs and one modification: to better represent the possible contaminated area on a school site, EP A’s default high-end value of Q/C of 68.8 for a 0.5-acre contaminated site is adjusted to 41.24, co rresponding to a 10-acre contaminated site.
Breast milk biotransfer factor (BBM) B BM (d/kg) of organic chemicals is estimated as 0.0000002 * K OW
. The value of 0.0000002 is an empirically determined constant (DTSC, 1994).

Other Constants2/5/2004 13 Respirable particle lo ad for outdoor air (PM 10 ) OEHHA recommends a default concentration of 1.8 E-12 kg PM /L (1.8 μ g PM /m 3 ) for site related PM 10 (particular matter less than 10 microns in diameter) in outdoor air. This value is based on the EPA Soil Screening Levels document (EPA, 1996).
Respirable particle load for indoor air (S F ) S F is the concentration in indoor ai r of particulate material less than 10 microns in diameter (PM 10 ) originating from on-site soil. OEHHA r ecommends a default value of 1.8E-12 kg PM /L (1.8 μ g PM /m 3 ). This assumes that indoor PM levels are the same as outdoor PM levels.

Table 1: Transfer Factors and Other Constants

Factor Units Value Discussed on Page

TF SD Unitless 2 17

TF PM/S Unitless 1 17

PM 10 kg PM 10 /L air 1.8 E-9 18

TF PM/D Unitless 1 17

S F kg PM 10 /L air 1.8 E-9 18

α Unitless Chemical-specific 17

VC S g soil /L vapor Chemical-specific 18

VC GW ml water /L vapor Chemical-specific 18
VF g soil /L air Chemical-specific 18

B BM d/kg Chemical-specific 18
Exposure Parameters Most existing risk assessment guidance is focused on multi-year residential or occupational exposure scenarios. Exposure parameters give n in existing guidance are generally long-term averages. This guidance is specifically aimed at school populations, including students, teachers and other staff, and users of on-site day care. Because children are rapidly changing anatomically, physiologically and behaviorally, we recommend a set of exposure parameters for each year until age 18. We believe that it is useful to evaluate the exposure of growing children on a year-by-year basis for several reasons: (1) Some chemicals may exhibit age-specific toxicity. OEHHA is currently evaluating this aspect, and plans to publish age-specific toxi city criteria in the near future. Age-specific toxicity criteria should be paired with corresponding age-specific exposure estimates, to the extent possible. (2) If the exposure parameters are given on a ye ar-by-year basis, model users can aggregate the years in a manner that best supports the risk ma nagement process. Conversely, if OEHHA were to recommend exposure parameters that were averag ed over a multi-year period, that averaging period might not match the existing or pr oposed school scenario. In that case it would be difficult to disaggregate the exposure parameters then re-a ggregate them to match the exposure scenario. The principal sources of exposure factor data for this guidance were the Technical Support Document for Exposure Assessment and Stochast ic Analysis (OEHHA, 2000), the Children’s Exposure Factors Handbook (EPA, 2002). When mo re than one value was available for an exposure parameter, preference was given to values that were reported in a way that conformed to the assessment methodology, such as age-specific or short age intervals, a nd values reported as a2/5/2004 14 function of body weight. This avoided or reduced the need to interpolate or extrapolate data and to convert data to appropriate units using uncertain conversion factors. When percentile estimates were available, preference was given to the ninetieth percentile to be consis tent with the reasonable maximum exposure (RME; EPA, 1989). Where data were considered equally appropriate for the analysis, preference was given to OEHHA values. C onsideration was given to entering the data as distributions rather than as point estimates, but distribut ions were not availabl e for several critical parameters. This approach will be considered in th e future if sufficient data become available. This guidance includes the following parameters. Recommended parameter values are summarized in Table 8, at the end of this section:

Soil Ingestion (I S ) I S is the estimated total daily in advertent soil and dust ingestion. Geophagia or soil pica is not addressed in this document. EPA (2002, Table 5-19) estimated total daily soil and dust ingestion by children 1-6 years of age as 100 mg/day mean, wi th 400 mg/day as an upper end, adding that 200 mg/day may be taken as a conservative estimate of the mean. EPA (1997) recommended a value of 50 mg/day for adults. OEHHA (2000, page 4-15) recommends default values of 200 mg/day for children 1 - 6, and 100 mg/day for everyone over the age of 6. The estimate d daily soil ingestion rates at school, shown in the la st column of Table 2, are base d on OEHHA recommendations. Soil ingestion is not normalized to body weight because a) it is not re lated to any physiologic process that would be a function of weight and b) it is not reported in that way in any of the references cited.

Table 2: Soil Ingestion
EPA estimates (mg/day) Age (years) Mean Conservative mean Upper end Recommended value (mg/day)

<1 0
1-6 100 200 400 200
>6 50 100

Fraction at school (F S ) F S is the estimated fraction of total daily soil and dust ingestion and dermal contact that occurs at school on school days. It is calculated as the to tal time at school (indoors plus outdoors) divided by 16 hours per day. This is based on the assumptions that soil and dust ingestion and dermal contact are proportional to time spent at a given locale, and th at soil and dust ingestion occur only during waking hours, which comprise 16 hours per day.

Body-part-specific skin loading rate (L BP ) EPA (2002, chapter 8) recommends the data of Ki ssel et al. (1996, 1998) and Holmes et al. (1996) as a basis for estimating body-part- and activity-specific so il skin loading (L BP , kg/cm 2 /day). Geometric mean body-part-specific load ings ranged from 0.02 to 0.09 mg/cm 2 for the day-care kids (see table below). Although this reference does not provide values for the head and trunk, these body parts are likely to be contaminat ed by soil at rates less than or similar to the legs. Therefore, OEHHA recommends a value of 0.02 mg/cm 2 for the head and trunk. A “fraction exposed” term is not used, since the studies were based on entire body parts irrespective of whether they were partially clothed or not.

OEHHA considers these data to be the best av ailable because they are based on real-world exposures to young children in day-ca re centers, (daycare kids #1a, 1b, 2, and 3) an exposure setting similar to that being assessed. The children rang ed in age from 1 to 6.5 years and included 17 boys2/5/2004 15 and 4 girls (groups 1a and 1b were the same children, measured in the morning and afternoon). They wore long pants (16) or shorts (5), long slee ves (7) or short sleeves ( 14). Most children wore low socks and shoes, but 5 were barefoot. E xposure times ranged from 3.5 to 8 hours, with no obvious correlation between time and dermal loadi ng. These data are limited by low numbers of children, high inter-individual variability, limited ag e range and the need to match their activities with those being assessed. The daycare data are preferred for young child ren because the setting was most similar to the school se tting. Data from other groups of children are available: The indoor kids (3 to 13 years of age) and tae-kwon-do participants (8 to 42 years) playing on a carpeted surface for 1.5 to 2 hours generally had lower dermal e xposures to soil than the daycare kids. Nine to 14-year-old kids playing in mud for 10 to 20 minutes had much higher dermal exposures (2 – 3 logs). Thirteen to 15-year-olds playing soccer on grass and bare earth for 40 minutes had a soil exposure that was generally si milar to the daycare kids.
Skin Surface area (A BP ) As stated above, EPA (2002) recommends using body- part- and activity-speci fic soil skin loading rates. In order to do this, skin surface area ne eds to be calculated on a body-part-specific basis. Data on fractional area of various body parts ar e found in Table 8-3 (EPA, 2002). Age-specific body surface area data are found in tables 8-1 and 8-2 (EPA, 2002). Table 8-4 (EPA, 2002) supplies surface-area to body weight ratios, but these are pooled for ages 2.1 to 19 years. Since it is apparent from analyzing the da ta in Tables 8-1, 8-2 and 11-1 (EPA, 2002) that surface-area-tobody-weight ratios change markedly with age, OEHHA recommends using the age-specific data in Tables 8-1, 8-2, and 8-3 to calcu late these ratios for children 2 years and older. A sample calculation (for a 1-year-old child) is shown below.

Body part Fraction of Body a Total skin Area b

cm 2 /kg Fractional Area

c m 2 /kg Skin Loading d

g/cm 2 Skin Loading e g/kg

Head 16.5% X 641 = 105.8 X 0.000020 f = 0.0021
Trunk 35.5% X 641 = 227.6 X 0.000020 f = 0.0044
Arms 13.0% X 641 = 83.3 X 0.000023 = 0.0019
Hands 5.7% X 641 = 36.4 X 0.000092 = 0.0034 Legs 23.1% X 641 = 148.1 X 0.000020 = 0.0029

Feet 6.3% X 641 = 40.2 X 0.000065 = 0.0026
Total 100% 641 0.0173

a EPA, 2002, Table 8-3 b Estimated from EPA, 2002, Tables 8-4. d EPA, 2002, Table 8-13 e Assumes that the school children will be clothed simila rly to those in the study (see EPA, 2002, Table 8-12). f There are no data for trunk and head. OEHHA suggests that the va lue for the legs, i.e. 0.02, be adopted for the head and tru nk.

Fraction outdoors (F O ) F O is the estimated fraction of the daily school-relate d dermal and ingested soil/dust exposure that is acquired outdoors. This is calcul ated as the time spent outdoors divided by the total time spent outdoors and indoors (see below). The implicit a ssumption is that indoor and outdoor exposure are proportional to time spent in those environments.2/5/2004 16 Fraction indoors (F I ) F I is the estimated fraction of the daily school-relate d dermal and ingested soil/dust exposure that is acquired indoors. It is calculated as 1- F O
. Body weight (BW) BW for children up to 3 years ol d is from EPA, 2002, Ta ble 11-1. The 50th percentile values for boys and girls within each year of age were averag ed to obtain a representative value. E.g. the body weight for one-year-olds is the average of male and female 50 th percentile values at 12, 18, and 24 months. Body weights for children older than 3 years are the means for boys and girls at the beginning and end of each age interval from Table 11-2 (EPA, 2002). E.g. the body weight estimate for four-year-olds is the average of male and female means (including clothing) at 4 and 5 years. Mid-range values for body weight are recommended because th is parameter appears only in the denominator of the soil ingestion and dermal contact equations, and since the numerators are thought to be conservative estimates of these para meters, it would be excessively conservative to use a low-end body weight. Estimated body weight s for various ages are in Tables 3 and 7.

Table 3: Age Related Body Weights
Age (years) Weight (kg) Age (years) Weight (kg) Age (years) Weight (kg)

6-7 23.75 13-14 53.20

0-1 7.04 7-8 26.50 14-15 57.05

1-2 11.08 8-9 29.80 15-16 60.35

2-3 13.29 9-10 33.90 16-17 62.90

3-4 16.35 10-11 38.70 17-18 64.15

4-5 18.55 11-12 43.20

5-6 21.15 12-13 47.85 Nursing

moms 63.2

Exposure time, outdoors (T O ) Estimates of daily outdoor exposure time (T O ), shown in Table 4, are from EPA (2002) Table 9-40. The data are based on national activity pattern surv ey data, and are weighted according to gender, age, race, employment status, re gion, season, etc, to represent the U.S. population (Klepeis et al., 2001). OEHHA recommends the 75 th percentile values (in bol d below) because when 75 th percentile values for time indoors at school and for time outdoors at sc hool are added, the combined time at school ranks at the 95 th to 99 th percentile for total time spent at school. Data for infants <1 are not available, so the values for 1-y ear-olds are recommended as a surrogate.

Table 4: Minutes Spent Out doors At School Per School Day

Age 50 th percentile 75 th percentile 95 th percentile

1-4 65 140 175

5-11 60 120 220

12-18 55 105 2252/5/2004 17 Exposure time, indoors (T I ) Estimates of daily outdoor exposure time (T I ), shown in Table ,5 are based on EPA (2002) Table 9- 39). OEHHA recommends 75 th percentile values (in bold below) because when 75 th percentile values for time indoors at school and for time out doors at school are added, the combined time at school ranks at the 95 th to 99 th percentile for total time spent at school (EPA, 2002, Table 9-34). Data for infants less than 1 year of age are no t available, so the values for 1-year-olds are recommended as a surrogate.

Table 5: Minutes Spent Indoor s At School Per School Day

Age 50 th percentile 75 th percentile 95 th percentile

1-4 269 500 595

5-11 403 445 565

12-18 420 450 565

Breathing rate, outdoors (B O ) B O is the estimated breathing rate for outdoor sch ool activities like walkin g and running, estimated from the data of Wiley, et al. in OEHHA, 2000, p. 3-27. This Guidance recommends using a value of 0.75 L/min-kg for all ages. This value assume s that 50 percent of outdoor time is spent in moderate activity like outdoor pla y, outdoor leisure, and golf with a ventilation rate of 0.6 L/min-kg and 50 percent in is spent in heavy activity like wa lking and active sports with a ventilation rate of 0.9 L/min-kg. Both sets of descriptors in the Wiley, et al. report (mode rate activity and heavy activity) were deemed consistent with outdoor activities at school.
Breathing rate, indoors (B I ) The estimated breathing rate for indoor school activ ities, were estimated from the data of Wiley, et al. (in OEHHA, 2000, p. 3-25 to 3-26). The lig ht activity category (0.3 L/min-kg) contained activity descriptions comp atible with indoor activi ties at school, such as eating, talking, reading, and homework. The moderate activity category ( 0.6 L/min-kg) also contained some activity descriptions compatible with indoor school ac tivities for younger children, e.g. indoor play. Therefore we recommend using an average of the ve ntilation rates for light and moderate activity, i.e. 0.45 L/min-kg, for children up through age 5. Fo r older children the light activity ventilation rate of 0.3 L/min-kg is recommended for indoor ac tivities, since their mo re vigorous activities typically take place outdoors.
Exposure frequency (EF) The estimated number of days students or other sc hool users attend school annually. Survey data show that the distri bution of days of school pe r year is bimodal, with 94 percent reporting a school year of 161 to 187 days and another 6 percent repo rting a school year of 228 to 238 days (RTI, 2003). Based on these results, the recommended de fault value for a 9-month school year is 180 days, the modal value for a standard 9-month sc hool year. For year-round schooling, a value of 233 days per year, the midpoint of the upper range is recommended.
Breast milk intake (I BM ) This Guidance recommends a daily breast milk inge stion of 130 g/kg/day for the first 12 months of life (OEHHA, 2000, Table 5.13, 90th percentile).2/5/2004 18 Daily Water Intake (I DW ) Daily water intake at school was estimated from EPA, 2000, Table 4-12 and EPA, 1989, Table 3- 30. Since OEHHA did not identify any data con cerning the proportion of da ily water intake that occurs at school, we recommend a value of 1⁄2 the 90 th percentile daily water intake, based on the proportion of waking hours spent at school on school days (E PA, 2000, Table 9-34). The recommended water intake rates at school in the last column below are 1⁄2 the 90 th percentile value from EPA, 2000. Table 6: Water Consumption
Age EPA Mean EPA Median EPA 90 th %ile EPA 95 th %ile Water intake at

<1 46 19 127 156 63.5

1-3 23 17 51 67 25.5

1-10 19 15 42 56 21

11-19 12 9 26 33 13 Pregnant women 18 16 35 40 17.5 Lactating women 21 21 35 37 17.5

Adults 21 19 34 17

Fraction absorbed, inhalation (A In ) The chemical-specific ratio of the total dose of a chemical absorbed through the respiratory tract to the total amount of the chemical i nhaled. In the absence of data to support an alte rnative value, a default value of one should be used.
Fraction absorbed, ingestion (A I ) The chemical-specific ratio of th e total dose of a chemical absorbed through the gastro-intestinal tract to the total amount of the chemical ingested. In the absence of data to support an alternative value, a default value of one should be used.2/5/2004 19 Fraction absorbed, dermal (A D ) The chemical-specific ratio of the total dose of a chemical absorbed through the skin to the total amount of the chemical that is adsorbed onto th e skin. Suggested values in Table 7 are from (DTSC, 1994) Table 2. page A-6): Table 7: Dermal Absorption Fractions for Compound Classes

Com p ound A bsor p tion Source

A rsenic 0.04 OEHHA

, 2000

Ber y llium 0.01 OEHHA

, 2000
Cadmium 0.001 OEHHA

, 2000
Hexavalent chromium 0.01 OEHHA

, 2000
Lead 0.01 OEHHA

, 2000

Mercur y 0.1 OEHHA

, 2000
Nickel 0.04 OEHHA

, 2000

Pol y chlorinated bi p hen y ls 0.14 OEHHA

, 2000

Pol y chlorinated dibenzo- p -dioxins and dibenzofurans 0.02 OEHHA

, 2000

Hexachloroc y clohexanes 0.1 OEHHA

, 2000

Pol y nuclear aromatic h y drocarbons

, 0.13 OEHHA

, 2000
DEHP 0.1 OEHHA

, 2000

4

, 4’ meth y lene dianiline 0.1 OEHHA

, 2000
Or g ano p hos p hates

, p entachloro p henol 0.25 DTSC

, 1994
Chlorinated insecticides 0.05 DTSC

, 1994
Other or g anic chemicals 0.1 DTSC

, 1994
Other metals and com p lexed c y anides 0.01 DTSC

, 1994

Free c y anide 0.1 DTSC

, 1994

Lifetime Exposure Fraction (ED/AT) The fraction of a lifetime represented by each exposure scenario. It enters into the calculation of cancer risk but not the calculation of the hazard index. Exposures n eed to be adjusted according to the lifetime exposure fraction because while cancer potency factors are based on lifetime exposure, this model estimates school-relate d exposure and risk for a series of one-year intervals beginning at birth. Since exposures differ from year to year , risks for each year are unique. For single-year scenarios, ED/AT is 1/70 or 0.014. For staff, the exposure duration is 40 years, a standard occupational exposure duration. Annual risks may be added to obtain the aggregate risk for any multi-year period. Risks are treated on an individual ri sk basis. An alternative would have been to consider population cancer burden. The latter is unaffected by indi vidual exposure duration, as long as the source and the number of exposed peopl e do not change. Treatin g children’s risk on an annual basis has a somewhat similar effect.2/5/2004 20 

# P P a a g

g e e L L e e f

f t

t B B l l a

a n

n k k2/5/200421Table 8: Summary of Recommended Exposure ParametersRecommended values for ageParameterAbbreviationSeepageUnits <1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12 12-13 13-14 14-15 15-16 16-17 17-18 Mothers StaffSoil IngestionaIS19 mg/day 0 200 200 200 200 200 100 100 100 100 100 100 100 100 100 100 100 100 100 100Fraction at schoolbFS19 unitless 0.67 0.67 0.67 0.67 0.59 0.59 0.59 0.590.59 0.59 0.59 0.580.58 0.58 0.58 0.580.58 0.58 0.58 0.58Fraction outdoorscFO21 unitless 0.22 0.22 0.22 0.22 0.22 0.21 0.21 0.210.21 0.21 0.21 0.210.19 0.19 0.19 0.190.19 0.19 0.19 0.11Body weightdBW 22 Kg 7.04 11.1 13.3 16.4 18.6 21.2 23.8 26.5 29.8 33.9 38.7 42.3 47.9 53.2 57.1 60.4 62.9 64.2 64.2 70Surface area, headeSA 20 Cm2/kg 117 106 63 55 54 50 47 45 42 38 33 29 25 28 26 23 21 20 20 20Loading rate, headfLBP19-20 g/cm2/day 2e-5 2e-5 2e-5 2e-5 2e-5 2e-52e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-52e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5Surface area, trunkeABP20 Cm2/kg 229 228 171 128 122 124 126 122 116 107 104 101 99 91 91 89 87 85 82 85Loading rate, trunkfLBP19-20 g/cm22e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-52e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5Surface area, armseABP20 Cm2/kg 88 83 53 58 54 50 47 45 42 39 39 39 39 34 34 35 35 47 45 47Loading rate, armsfLBP19-20 g/cm22e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-52e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5Surface area, handseABP20 Cm2/kg 34 36 24 24 22 19 17 17 17 17 16 16 15 14 15 15 15 14 13 14Loading rate, handsfLBP19-20 g/cm29e-5 9e-5 9e-5 9e-5 9e-5 9e-5 9e-5 9e-5 9e-5 9e-59e-5 9e-5 9e-5 9e-5 9e-5 9e-5 9e-5 9e-5 9e-5 9e-5Surface area, legseABP20 Cm2/kg 132 148 103 108 108 102 98 97 95 90 89 88 87 89 90 90 90 82 79 82Loading rate, legsfLBP19-20 g/cm22e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-52e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5 2e-5Surface area, feeteABP20 Cm2/kg 42 40 32 29 28 26 25 25 25 24 23 21 20 22 21 20 19 19 19 19Loading rate, feetfLBP19-20 g/cm27e-5 7e-5 7e-5 7e-5 7e-5 7e-5 7e-5 7e-5 7e-5 7e-57e-5 7e-5 7e-5 7e-5 7e-5 7e-5 7e-5 7e-5 7e-5 7e-5Breathing rate, outdoorsgBO23 L/min-kg 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.7Exposure time,outdoorshTO22 min/day 140 140 140 140 140 120 120 120 120 120 120 120 105 105 105 105 105 105 105 60Breathing rate, indoorsiBI23 L/min-kg 0.45 0.45 0.45 0.45 0.45 0.45 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3Exposure time, indoorsiTI23 min/day 500 500 500 500 500 445 445 445 445 445 445 445 450 450 450 450 450 450 450 480Exposure frequencynEF 23 days/yr 180 180 180 180 180 180 180 180 180 180 180 180 180 180 180 180 180 180 180Exp. freq. (year-round)oEF 23 days/yr 232 232 232 232 232 232 232 232 232 232 232 232 232 232 232 232 232 232 232 250Breast milk intakepIBM23 g/kg/day 130 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Water IntakeIDWml/kg/da 63.5 25.5 25.5 25.5 21 21 21 21 21 21 13 13 13 13 13 13 13 13 17.5 17.5Exposure durationqED 24 Years 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 40Averaging timerAT 24 Years 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 70 702/5/200422aThe estimated total daily inadvertent soil and dust ingestion, based on OEHHA 2000, page4-15. Geophagia or soil pica is not addressed in this document.bFraction of daily soil and dust ingestion and dermal loading that occurs at school,based on the number of hours at school daily divided by 16. OEHHA recommends default values of 0.67 for infants <1 and 0.563 (9 of 16 hours daily) for staff.cFraction of daily site-related dermal and ingested soil/dust load that is acquiredoutdoors. Calculatedas the time spent outdoors divided by the time spent outdoors plus the time spent indoors.dBody weight data for children up to 3 years old were taken from EPA, 2002: Table 11-1 (50th percentile; mean of boys and girls). For older children, values were taken from Table 11-2, the mean for boys and girls and the average of the beginning and endof the interval.eEPA, 2002, Table 8-13 (Assumes that the school children will be clothed similarly tothose in the study; see EPA, 2002, Table8-12).fEstimated from EPA, 2002, Tables8-1, 8-2 and 8-3 OEHHA suggests that the valuefor the legs, i.e. 0.02, be adopted for the head and trunkgBased on (OEHHA, 2000, p. 3-27).hBased on 75thpercentile values from EPA, 2002, Tables 9-39 and 9-40. Since data for adult staff are not available, OEHHA recommends a default value of 60 minutes dailyiOEHHA recommends a value of 0.45 L/min-kg for children up through age 5, and a value of 0.3 L/min-kg for older children and adults based on (OEHHA, 2000, p. 3-25 to 3.26).jBased on 75thpercentile values from EPA, 2002, Tables 9-39 and 9-40. Since data for adult staff are not available, OEHHA recommends a default value of 480 minutes daily.nThe recommended default value for a 9-month school year is180 days, the standard school-year length in California.oFor year-round schooling, a value of 223 days may be used.pBased on (OEHHA, 2000, Table 5.13, 90th percentile).qExposure Duration is the number of consecutive years of exposure represented by the exposure scenario under evaluation.SOEHHA recommends a default value of 70 years.2/5/2004 23 

### Risk Assessment

Chemicals of Concern
Chemicals of concern should be determined in consultation with the lead regulatory agency on the project. Suggested guidan ce includes DTSC, 1994, section 2.4.6.7.
Exposure Point Concentration Exposure point concentration shou ld be determined in consulta tion with the lead regulatory agency on the project. Suggested guid ance includes DTSC, 1992, Chapter 2.
Toxicity Criteria OEHHA cancer potency values and reference exposure levels, which are available at ( http://www.oehha.ca.gov/risk/ChemicalDB/index.asp ) should be preferentially used. Child-specific reference doses (chRD) should be used when availa ble. When OEHHA criter ia are not available, U.S. EPA criteria found in the Integrated Risk Information System (IRIS) database ( http://www.epa.gov/iriswebp/iris/index.html ) should be used when available. If criteria for a given chemical are not available either from OEHHA or in IRIS, criter ia from other published sources may be used, subject to appr oval by the reviewing agency.

Risk and Hazard Calculation Hazard quotients and incremental risks from all exposure routes are estimated and summed for each chemical. The hazard quotients and incrementa l risks for the individual chemicals are then added to calculate the total hazar d index and total risk. For sc reening assessment, the default assumption is that hazards posed by individual chemicals are additive. Some non-cancer toxic effects of individual chemicals are unlikely to be additive. In those cases, a statement to that effect, with documentation based on target orga n and/or mode of action, should be included.

Risk Characterization Following the methodology described herein will produce age-specific estimates of hazard and risk. At a minimum, the risk characterization should present risk and hazard for each year or group evaluated. In order to calculate the risk for a multi-year period, the risks for individual years must be added. Hazards are not usually consid ered to be additive fr om year to year (i.e. the chemical exerts its full effect of within one year). It may be useful to show contributions of individual chemicals and/or individual pathways to total risk and hazard. Dose (route a) /RfD (route a) = Hazard Quotient (route a) Dose (route b) /RfD (route n) = Hazard Quotient (route n) Hazard Quotient (chemical a) = ∑ Hazard Quotient (route a...n)

Hazard Index = ∑ Hazard Quotient (chemical a...n)* * For chemicals acting by a similar mode of action or affecting the same target organ Dose (route a) * CPF (route a) = Risk (route a) Dose (route b) * CPF (route n) = Risk (route n) Risk (chemical a) = ∑ Risk (route a...n)

Total Risk = ∑ Risk (chemical a...n)2/5/2004 24 

### Sensitivity Analysis The calculated risk or hazard may be relatively sensitive or insensitive to changes in various input parameters. Sensitivity analysis is important because it can help direct research or data gathering toward those parameters that will have the most effect on the outcome. For example it would not be highly produc tive to measure indoor PM 10 levels at a site where the primary contaminant of concern is trichloroethylene. Loca l sensitivity is the percent change in the total risk or hazard index corresponding to a small cha nge in the value of a sp ecific parameter divided by the percent change in that parameter. It is investigated by cha nging the input parameter values one at a time and measuring the effect on the risk or hazard. The local sensitivity is dependent on how the parameter is mathematically related to the result. However, it can change, depending on other inputs. For example, the model is very sensitive to changes in soil ingestion rate when soil contamination is the primary problem at a site, but relatively insensitive to changes in soil ingestion rate when ground water contamination is the primary problem at the site. The local sensitivity is also heavily infl uenced by the properties of the contaminant. For example, risk from volatile chemicals is sensitive to changes in breathing rate and hours spent indoors daily, while risk from non-vol atile chemicals is re latively insensitive to changes in these parameters. Because of this variation in sensitivity, we focused on the maximum sensitivity observed under the conditi ons of our simulations. For this analysis, representative conditions were selected. The only i nputs were 0.15 mg/kg of the chemical in soil and 0.1 μ g/L in shallow ground water. Th e following table shows the results of the analysis for 1-year-olds. The ratio of ch ange in output/change in input has been converted to percentages, i.e. a 1:1 ratio would be shown as 100%. Some parameters (e.g. those that appear in the denominator) change the output in the opp osite direction; these are shown as negative percentages. Four chemicals were selected to represent a range of physical and chemical characteristics. They include a volatile ch emical, a relatively non-vol atile lipophilic organic chemical, a metal and a metal that is carcinoge nic by inhalation but not by ingestion. Each chemical was evaluated based on its most sens itive endpoint: For the first three the most sensitive endpoint was carcinogenicity; for th e fourth, non-carcinogenic toxicity was limiting.

Table 9: Local Sensitivity
Local Sensitivity*

Parameter Vinyl chloride DDT Cadmium Chromium VI Maximum Parameter Uncertainty

Indoor dust/outdoor soil 0.10% 74.00% 77.34% 77.29% 77.34% High
Outdoor PM10/outdoor soil 0.00% 0.00% 0.00% 0.000% 0.000% High
Outdoor PM10 0.00% 0.00% 0.00% 0.000% 0.000% High

Indoor PM10 0.00% 0.00% 0.00% 0.000% 0.000% Moderate
Indoor vapor/Soil vapor ( α ) 93.90% 3.00% 0.00% 0.000% 93.900% High

Kow -0.028% 0.00% 0.00% 0.000% -0.028% Moderate
Fraction absorbed, resp 97.30% 4.10% 0.00% 0.000% 97.30% Moderate
Fraction absorbed, ingest 0.20% 94.90% 99.19% 99.40% 99.40% Moderate
Fraction absorbed, dermal 2.50% 1.20% 1.05% 0.73% 2.500% High
Soil vapor/soil matrix (VC S ) 91.10% 0.00% 0.00% 0.00% 91.10% High2/5/2004 25 Local Sensitivity*

Parameter Vinyl chloride DDT Cadmium Chromium VI Maximum Parameter Uncertainty

Soil vapor/groundwater (VC GW ) 2.90% 3.00% 0.00% 0.00% 3.00% High
Volatilization Factor (VF) -5.40% -1.00% 0.00% 0.00% -5.40% High
Soil Ingestion 0.20% 93.20% 98.50% 98.74% 98.74% High
Fraction at school 0.20% 94.40% 98.50% 98.74% 98.74% High

Surface area 0.00% 0.80% 0.81 % 0.567% 0.81 % Moderate

Fraction outdoors 0.00% 0.50% 0.54% 0.38% 0.54% Moderate
Body weight -0.20% -85.80% -89.54% -89.77% -89.77% Low
Breathing rate, outdoors 3.40% 1.60% 0.00% 0.00% 3.40% Moderate
Exposure time, outdoors 3.40% 1.50% 0.41% 0.29% 3.40% Moderate

Exposure time, indoors 93.90% 2.60% -0.39% -0.27% 93.90% Moderate
Breathing rate, indoors 93.90% 3.00% 0.00% 0.00% 93.90% Moderate
Exposure frequency 100.00% 100.00% 100.00% 100.00% 100.00% Moderate

Exposure duration 100.00% 100.00% 100.00% 0.000% 100.00% High
Averaging time -90.90% -90.90% -90.90% 0.00% 0.00% Low

Area fraction Head 0.00% 0. 30% 0.07% -0.044% 0.30% Low

area fraction Trunk 0.00% 0.10% 0.15% -0.076% 0.15% Low

area fraction Arms 0.00% 0.00% 0.06% -0.050% 0.062% Low

area fraction Hands 0.00% 0.10% 0.11% 0.052% 0.11% Low
Area fraction Legs 0.00% 0.10% 0.09% -0.019% 0.10% Low

area fraction Feet 0.00% 0.10% 0.08% 0.027% 0.10% Low
Loading Head 0.00% 0.30% 0.07% 0.069% 0.30% High
loading Trunk 0.00% 0.10% 0.15% 0.15% 0.15% High
loading Arms 0.00% 0.00% 0.06% 0.062% 0.062% High
loading Hands 0.00% 0.10% 0.11% 0.109% 0.11% High
Loading Legs 0.00% 0.10% 0.09% 0.094% 0.10% High

loading Feet 0.00% 0.10% 0.08% 0.084% 0.10% High
Reference Dose 0.00% 0.00% 0.00% 100.00% 100.00% High
Cancer potency 100.00% 100.00% 100.00% 0.00% 100.00% High * Change in risk or hazard divide d by change in the input parameter Parameters that are well characterized (i.e. posse ssing low uncertainty) are not large contributors to uncertainty in the outcome, regardless of the sensitivity of the outcome to the parameter. Therefore, if either the local sensitivity or th e range of uncertainty for any given parameter is small, changes in that parameter are unlikely to have appreciable impact on risk or hazard. In turn, research to reduce the uncertainty in that parameter will be a lower priority because the results will have less effect on th e outcome than those with greater local sensitivity or uncertainty.2/5/2004 26 For example for a parameter with a local sensitivity of less than 1 percent, a 10-fold error in the parameter value would change the hazard or risk by less than 10 percent. A change of less than 10 percent is not likely to change the result expressed to one significant figure. Risk assessors generally acknowledge that their re sults are good to only one significa nt figure at best. Therefore, the analysis of parameter uncertainty below is focused on those with 1 percent or greater local sensitivity and moderate to high uncertainty.



### Uncertainty Analysis
Model Uncertainty In time-dependent models, concentrations, flow ra tes, and dose rates change with time. Timeindependent models like the one described herein assume that conditions are at equilibrium and do not change over time. They do not account fo r source depletion. This could result in overestimating risk, particularly if mu lti-year exposures are considered. This model does not consider all possible transp ort mechanisms or all possible factors affecting environmental fate and transport of environm ental contaminants. For example, it does not consider transport of soil contaminants to groun d water, transfer from soil or air into edible plants, or redeposition of particulate matter. However, the authors believe it considers the principal determinants of chemical exposures at schools.
Exposure Pathway Uncertainty This model does not consider all possible expos ure pathways. For example, crops could be grown in site soil and contaminated ground water could be used to irrigate site-grown crops, thereby transferring contaminants to produce eate n by students and staff. Inhalation of volatile chemicals while showering is not included. The contribution of these pathways to the overall risk or hazard is minimal.
Parameter Uncertainty In addition to a unique exposure scenario, exposur e assessment for schools requires a unique set of exposure parameters. For example, buildi ng parameters, and age distribution and activity patterns of the school users differ from typical residential, recreationa l, and occupational settings. As discussed above, unde r the heading “Sensitivity Analys is,” parameters with a local sensitivity of 1 percent or greater and those that have a high level of uncertainty are the primary focus of this discussion.

Transfer factor from soil to indoor dust (TF SD ) Interior dust is an important exposure medium in school site exposure assessment because students typically spend much of their time at sc hool in classrooms and other indoor areas. The fraction of dust that comes from site soil is poor ly characterized, but sign ificant, inasmuch as other sources of interior dust are less affected by site selection. This parameter was considered a good candidate for further study because it has hi gh local sensitivity (77 percent) and there are no published values for this parameter in the sc hool setting. The recommended default dust/soil transfer factor (2) is based on relative concentr ations of several elements in outdoor soil and interior dust at California schools (RTI. 2003b, see Appendix 1).
Soil vapor to Indoor air ( α ) The ratio of chemical concentration in indoor air to that in soil vapor parameter (alpha) is a good candidate for further study because it has a high local sensitivity for some chemicals (up to 94 percent) and because there are limited data for ven tilation rates at schools. Site-specific factors such as operation of the HVAC system (positive or negative pressure, ventilation rates, etc.),2/5/2004 27 type of foundation, and use of doors and windows will substantially affect alpha. The recommended default ventilation rate for use in the Johnson and Ettinger model (4.7 changes/hr) is based on ventilation rate data from California schools (RTI, 2003a, see Appendix 1).
Volatilization factor from soil (VC S ) The ratio of the contaminant concentration in soil vapor to that in soil matrix depends on the physical and chemical properties of the chemical , as well as soil properties. This ratio, in μg/L vapor /(μg/g soil ) (or g soil /L vapor ), has a high local se nsitivity (up to 91 percent for volatile chemicals) and is relatively uncertain. Howeve r, the uncertainty can be partially offset by sampling soil vapors in addition to soil matrix. Since there is no reason to believe that VC S would be different in a school environment than in other environments, OEHHA recommends the Johnson and Ettinger model (EPA, 2000 (2)) to estimate this value.
Volatilization factor from ground water (VC GW ) The ratio of the contaminant concentration in so il vapor to that in shallow groundwater depends on the physical and chemical proper ties of the chemical, as well as soil properties. This ratio, in μg/L vapor /(μg/ml water ) (or ml water /L vapor ), has a moderate local sens itivity (up to 3 percent for volatile chemicals) and is relative ly uncertain. However, the uncer tainty can be partially offset by sampling soil vapors in addition to ground water. Since there is no reason to believe that this factor would be different in a school envi ronment than in other environments, OEHHA recommends the Johnson and Ettinger model (EPA, 2000 (2)) to estimate this value.
Volatilization factor (VF) The volatilization factor has a moderate local se nsitivity – up to 5.4 percent. It is based on a well-reviewed document. However, OEHHA reco mmends adjusting the contaminated area to 10 acres (compared to the default valu e of 0.5 acres) to more closely re flect the size of a school site. This reduces VF by approximately 40 percent, wh ich increases the atmospheric concentration by about 67 percent, since atmospheric c oncentration is a function of 1/VF.
Soil Ingestion (I S ) Soil and dust ingestion is a good candidate for furt her study because it has a high local sensitivity (up to 99 percent) and high parameter uncertainty. U.S. EPA has estimated soil/dust ingestion by children and adults, and these valu es are widely applied in the re sidential setting. There are no estimates specific to the school en vironment; however, some of th e data, collected in day care facilities, may be relevant to a school environment. Research in the area of soil and dust ingestion in schools could reduce unc ertainty in this parameter. Since the recommended value is equivalent to U.S EPA’s conservative estimate of central tendency, th e model is unlikely to underestimate soil ingestion for most children an d adults. However a few children at the upper end of the distribution may ingest more soil than the 200 mg/day default.
Fraction at School (FS) The fraction of the daily soil ingestion and dermal contact that occurs at school on school days is another parameter with a high local sensitivity (up to 99 percent). The recommended values are based on the estimated fraction of the waking hour s that are spent at school, and the assumption that these exposure pathways are proportional to time spent in an environment (i.e., that soil ingestion and dermal contact do no t occur preferentially at school or at home). The uncertainty is in both directions, but the maximum undere stimate is less than two-fold, since the recommended values range from 58 to 67 per cent and the true value could not exceed 100 percent.2/5/2004 28 Body Weight (BW) Body weight has a high local sensitivity (up to -90 percent) for chemicals whose exposure is primarily by soil ingestion. This is because so il ingestion is not normalized to body weight in this model. The negative sign indicates that ri sk decreases as body weight increases. However, body weight is not particularly uncertain.
Breathing Rate, Outdoors and Indoors (B O , B I ) Outdoor breathing rate has a moderate local sensi tivity (up to 3.4 percent fo r volatile chemicals). Indoor breathing rate has a high local sensitivity (up to 94 percent for volatile chemicals). The recommended breathing rates are based on studies involving 52 children ranging in age from 3 to 12 years and another 160 children and adults fr om age 6 to 77 (OEHHA, 2000, p. 3-8 to 3-13). Since activity-specific breathing rate s are not available for children in a school environment, we assigned average breathing rates for indoor and ou tdoor activities based on breathing rates for similar activities that were reported in those st udies. Detailed observati ons of pre-school and school children of various ages could help to reduce the uncertainty in these parameters. However, even with more data, variation between schools and between individuals is likely to be considerable, and inferences would still have to be made concerning which measured respiration rates correspond to the observed activities.
Exposure Time, Outdoors and Indoors (T O , T I ) The outdoor exposure time has a moderate local sensitivity (up to 3.4 percent for volatile chemicals). Indoor exposure time has a high lo cal sensitivity (up to 94 percent for volatile chemicals). Data from EPA, 2002, Table 9-40 (used to estimate time spent outdoors on school grounds) may overestimate actual time spent outdoor s on school grounds since they include time spent at playgrounds as well as at school grounds. The sum of the recommended 75th percentile exposure times indoors and outdoors is 555 to 620 minutes per day. Cali fornia law requires a minimum of 50,400 minutes of instructional time pe r year for grades 1-8. Based on a typical 180-day schedule, this translates to 280 minutes per day. Even allowing another 90 minutes for lunch, recesses, and/or between-class time brings the total to 370 minutes, considerably less than the recommended 75th percentile estimates. Part of the difference could be explained by other time spent at school such as part icipation in before- or after-sc hool activities. Surveys focused specifically on the school environment could he lp to narrow this range of uncertainty. Exposure Frequency (EF) Exposure frequency has a high local sensitivity (100 percent) because this va lue enters into every calculation of risk and hazard. While it is not part icularly uncertain, it is quite variable, ranging from the minimum days per year required by la w to a maximum for a student, staff member, or day-care child who attends the school year-r ound. Table 10 shows the reported number of planned school days for the curr ent school year for the 54 Californi a schools that interpreted the question correctly (RTI, 2003). The bimodal dist ribution suggests that a single value may not adequately represent the data.

Table 10: Frequency Distribution of Annual School Days

Number of Da y s Number of Schools Percent
Less than 180 da y s 9 16.7
180 da y s 34 63.0
181 to 187 8 14.8
188 to 227 0 0
228 to 238 3 5.62/5/2004 29 Lifetime Exposure Fraction (ED/AT) Lifetime exposure fraction is the fraction of a life time represented by each exposure scenario. It has a local sensitivity of 100 per cent for carcinogenicity but does not enter into the calculation of the hazard index. For single-ye ar scenarios, ED/AT is 1/70 or 0.014. Averaging time (in effect, the expected life span) has a relatively low uncerta inty and is a widely ap plied value. Exposures need to be adjusted according to the lifetime exposure fraction because while cancer potency factors are based on lifetime exposure, this mode l estimates school-related exposure and risk for a series of one-year intervals beginning at birt h. This involves inter polation and therefore introduces uncertainty. Since expos ures differ from year to year, risks for each year are unique. Because the risks are calculated on a year-by-year basis, annual risks may be added to obtain the aggregate risk for any multi-year period.
Reference Dose (RfD) Reference dose has a high local sensitivity (100 percent for non-carcinogenic effects). The uncertainty varies from minimal (when the Rf D is based on data from sensitive humans) to considerable (when multiple uncertainty factors are involved such as when the RfD is based on laboratory animals and/or inadequate studies). The need for reference doses reflecting the potentially greater sensitivity of children to t oxic effects of some chem icals is under evaluation by OEHHA.
Cancer Potency Cancer potency has a high local sensitivity ( 100 percent for carcinogenic effects). The uncertainty varies from moderate (when the poten cy is based on human cancer incidence data) to high (when extrapolated from high-dose rodent data). There is addi tional uncertainty in extrapolating carcinogenic potency determined in a full lifetime study to less-than-lifetime exposure scenarios. The typical approach is to assume linearity, i.e. half the exposure is equivalent to half the risk. However, there is evidence that less-than-l ifetime exposure of some carcinogens to children and infants may be mo re potent in inducing cancer than the same exposure later in life. Because exposures at sc hool sites are changing from year to year, and because they may be for shorter time periods than residential or occupational exposures, OEHHA deems it beneficial to assess risks on a year-by-year basis. Year-by-year exposure estimates have the potential to be used in conjunction with future age-specific potency estimates. Methodology to evaluate carcinogenic potency of early-in-life exposures is the subject of ongoing OEHHA and U.S. EPA projects. EPA’s draft policy for evaluating carcinogenic potency of early-in-life exposures has been revi ewed by the Science Advisory Board, and EPA is responding to the Board’s co mments and public comments

. Fraction Absorbed, Resp (AIn), Fraction Absorbed, Ingest (AI) The fraction absorbed by the respiratory and inge stion routes has a high lo cal sensitivity (up to 99 percent). The recommended default value of one implies that absorption is the same in the exposure situation as in the study (s) that are the basis for the t oxicity criteria, an assumption widely accepted in the risk assessment community. In reality, the rats may have been fed or dosed with the test chemical mixed into a vehicl e that enhances absorption compared to the form to which humans will be exposed. Conversely, the rats may have been exposed to a poorly absorbed form while humans are exposed to a readily absorbed form, though this seems less likely. Route-specific absorption is an impor tant issue for inter-route extrapolation. The uncertainty is in both directions but is not likely to exceed a two- or three-fold error, since most2/5/2004 30 compounds are readily absorbed the gastro-intes tinal or the respiratory mucosa. OEHHA has no current plans for research on these parameters.
Fraction Absorbed, Dermal (AD) Although the fraction absorbed by th e dermal route has a moderate local sensitivity (up to 2.5 percent), it is potentially an important pa rameter because data on chronic toxicity or carcinogenicity by the dermal route are genera lly not available and therefore inter-route extrapolation is the rule. Current estimates, based on models and experiments using laboratory animals and cadaver skin, are relatively uncertain for some chemicals. However, there is no reason to believe that dermal uptake would be di fferent in a school environment than in other exposure scenarios, and OEHHA has no current plans for dermal uptake research. The uncertainty is in both directions.2/5/2004 31 

### REFERENCES DTSC, 1994. Preliminary Endangerment Assessmen t Guidance Manual, State of California, Environmental Protection Agency, Depart ment of Toxic Substances Control. DTSC, 1992, Supplemental Guidance for Human Health Multimedia Risk Assessments of Hazardous Waste Sites and Perm itted Facilities (Second printi ng, 1999), State of California, Environmental Protection Agency, Depart ment of Toxic Substances Control. EPA, 1989; U.S. Environmental Protection Agency Risk Assessment Guidance for Superfund, Human Health Evaluation Manual EPA, 1996, Soil Screening Guidance User’s Guide, (EPA540/R-96/018) , OSWER, July, 1996 http://www.epa.gov/superfund/re sources/soil/index.htm U.S. Environmental Protection Agency (E PA), 2002; Child-Specific Exposure Factors Handbook, Interim Report, September, 2002, Nationa l Center for Environmental Assessment, Washington, DC; EPA-600- P-00-002B available at http://www.EPA.gov/NCEA U.S. Environmental Protection Agency (EPA), 1989; Exposure Factors Handbook, May, 1989 Update, National Center for Environmenta l Assessment, Washington, DC; EPA600/8-89/043 available at http://www.EPA.gov/NCEA EPA, 2003 Johnson and Ettinger (1991) Model for Vapor intrusion into Buildings (revised) http://www.epa.gov/superfund/programs/ risk/airmodel/johnson_ettinger.htm U.S. Environmental Protection Agency (E PA), 1997; Exposure Factors Handbook, National Center for Environmental Assessment, Wash ington, DC; EPA-600-P-00-002B available at http://www.EPA.gov/NCEA Kissel, J., K. Richter, and R. Fenske, (1996) , Field Measurements of Dermal Soil Loading attributable to Various Activiti es: Implications for Exposure A ssessment. Risk Anal. 15(1)116- 125. Kissel, J., J. Shirai, K. Richter, and R. Fenske , (1998), Investigation of Dermal Contact with Soil in Controlled Trials. J. of Soil Contamination 7(6) 737-752 Klepeis, NE, Nelson WC, Ott WR, Robinson JP, Tsang AM, Switzer P, Behar JV, Hern SC, Engelmann WH, The National Human Activity Pattern Survey (NHAPS): A Resource for Assessing Exposure to Environmental Polluta nts, Journal Of Exposure Analysis and Environmental Epidemiology, 11 (3): 231-252 May-Jun 2001. OEHHA, 2000; California Office of Environmental Health Hazar d Assessment; Air Toxics Hot Spots Program Risk Assessment Guidelines: Part IV - Technical Support Document for Exposure Assessment and Stochastic Analysis OEHHA, 2002 Office of Environmental Health Hazard Assessment, California Environmental Protection Agency OEHHA, 2003; “SCHOOLSCREEN.xls” Draft Sc hools Risk Screening Model, a Spreadsheet Adaptation of the Guidance for Assessment of Exposures and Health Risks at Existing and Proposed School Sites, Office of Environmen tal Health Hazard A ssessment, California Environmental Protection Agency, February 5, 2004 RTI 2003a, Portable Classrooms Study2/5/2004 32 RTI 2003b, Addendum To The California Portable Classrooms Study Soil Sampling And Metals Analyses University of California, Davis, 1994, Caltox TM , a Multimedia Total Exposure Model for Hazardous Waste Sites - Spreadsheet Users Guide version 1.5A1-1 

### Appendix 1: Summary and Interpretation of Results of RTI Study

OEHHA-recommended values for three exposure parameters in the schools risk assessment model are based on RTI (2003): 1) Composition of interior surface dust with respect to outdoor soil 2) Classroom ventilation rates 3) Days of instruction per year
Composition of interior surface dus t with respect to outdoor soil
RTI investigated the rela tionship of the concentration of nine elements, (As, Cd, Cr, Cu, Pb, Ni, Se, Vd, Zn) in soil at 67 school sites to the conc entration of those elements in classroom floor dust (RTI, 2003). The concentrations of three of the nine elements, chromium, nickel, and vanadium, were significantly correlated (r = 0.55–0.64, p<0.001) between these two media. The 95 percent upper confidence limits (UCL 95 ) on the median dust/soil concentration ratios for these three elements were 1.90, 2.54, and 1.53, respective ly (Table A-1). OEHHA, therefore, recommends a default value of 2 for the “tra nsfer factor from soil to indoor dust” (TF SD ), based on the mean of the three median UCL 95 s. Table A-1: Indoor Du st to Soil Ratios Correlation Significance Median Ratio 95% C.I.

Arsenic 0.19 0.10 1.88 1.62-2.05

Cadmium 0.06 0.58 2.95 2.51-4.00

Chromium 0.64 <0.001 1.71 1.48-1.90 Copper 0.03 0.81 2.95 2.39-3.48

Lead 0.17 0.13 3.07 2.27-3.81

Nickel 0.58 <0.001 2.18 1.81-2.54

Selenium 0.19 0.09 0.20 NA 1- 0.73

Vanadium 0.55 <0.001 1.37 1.26-1.53

Zinc 0.07 0.55 9.67 7.05-13.64

1 LCL on ratio not calculated due to values below the detection limit.
Other elements studied had lower correlations, but with the exception of selenium and zinc, still had similar median dust/soil ratios in the range of 1.88 to 3.07. The ratio for selenium is not reliable because of failure to detect selenium in some samples. The high dust/soil ratio for zinc is unclear, but could be the re sult of some (unknown) indoor source of zinc.

Classroom Ventilation Rates
RTI (2003a) reported average outdoor airflow in to the classrooms of 0.8737 c.f.m. per ft 2 of floor area (95% C.I. = 0.7894-0.9579)(Table A-2) . No data were collected on classroom volume. Assuming a ceiling height of 10 feet , this would yield an average classroom ventilation rate of 0.087 (95% C.I. = 0.079-0.096) c.f.m. per ft 3 (i.e. changes per minute). Multiplying by 60 min/hr yields a mean exchange rate of 5.2 changes per hour (95% C.I. =A1-2 4.7-5.7). OEHHA recommends a default air exchange rate of 4.7/hr, based on the 95 percent LCL on the mean.

Table A-2: Classroom Ventilation Rates
Parameter units mean 95% C.I. 5-95 percentile
Outdoor air flow/sq.ft. cfm/ft 2 0.8737 0.7894-0.9579 0.3179-1.3854
Days of Instruction per year
Table A-3 shows the reported number of planne d school days for the current school year for the 54 California schools that interpreted the question correctly (RTI, 2003b). The bimodal distribution suggests that a sing le value may not adequately re present the data. Therefore OEHHA recommends 180 days per year for traditional 3-season schools and 232 days per year for year-round schools.

Table A-3: Days of Instruction per year Number of Days Number of Schools Percent Cumulative Percent Less than 180 days 9 16.7 16.7 180 days 34 63.0 79.6

181 to 187 8 14.8 94.4

188 to 227 0 0 94.4

228 to 238 3 5.6 100.0A2-1 

### Appendix 2: Comments and Responses

UNIVERSITY OF CALIFORNIA PEER REVIEWER COMMENTS

William W Nazaroff Department of Civil and Environmental Engineering University of Calif ornia, Berkeley

OVERALL SUMMARY COMMENT
Overall, I found the document cl ear, generally well organized and easy to follow. The goals, methods, and limitations of the approach are we ll expressed. The document is also concise, which is a virtue. I have a concern about th e overall scope of the document. Some potentially important exposures are not bei ng considered and the justification for the omission is unclear. See below for detailed discussion.
Technically, the equations for a ssessing exposure and analyzing ri sk are generally appropriate for a screening-level assessment. Some improveme nt in how the parameters are presented and discussed would strengthen the report. I like that a sensitivity analysis was conducted and is presented. I think that the identifi cation of parameters that contri bute most to uncertainty should be expanded. A few concerns and several specifi c suggestions for improvement are described in greater detail in the following section of this review.

DETAILED COMMENTS
1. Comment - Scope of Guidance (page 8)
“Exposures to chemicals in building materials and furnishings and chemicals used in schools are beyond the scope of this guidance.” It is not clear that excluding su ch exposures is responsive to the legislation that mandated this document. I find nothing in Health and Safety Code Section 900-901 that justifies such exclusion. Even if this can be justified, some other exposures could be of considerable concern and are neither addre ssed in the document nor specifically excluded. In particular, exposure to emissions fr om diesel school buses and to he rbicides or pesticides used on the school grounds should be considered.
Response
Health and Safety Code Section 901(f) stat es that OEHHA is to develop guidance for assessing exposures and risks at existing and pr oposed schoolsites. The following text has been added to the Guidelines to clarify this issue (see page 6): “Building materials and indoor products may be important sources of ind oor exposure to toxic constituents at schools. It may be appropriate to include these s ources of chemical e xposures in the overall assessment of overall hazards and risks at exis ting schools. Typically these assessments would be based on measured atmospheric con centrations in classr ooms and other indoor areas, and estimated risks, using the same e xposure parameters, would be added to siterelated risks. Hazards would be additive among chemicals sharing a common target organA2-2 and/or mode of action.” See also added text on page 2: “ Representative measured contaminant concentrations in various environmental medi a may be used in lieu of modeled values.”

Comment

In the section “Schools Conceptual Site Model” it is st ated that “this model considers contaminated soil and shallow ground water as primary source media.” In fact, the exposure assessment equations include inhalation exposure to contaminants that originate offsite (such as at an upwind freeway or industrial facility ). The inclusion of these sources should be clarified in this section.
Response
The wording on page 8 has been revised to in clude the following sentence: “As depicted in Figure 1, this model considers contaminated so il, shallow ground water, and unspecified offsite sources as primary source media.”

Comment
Table 1 — Exposure Pathways (p. 11) Path ways 9 and 10 can lead to exposures by inhalation of indoor air as well as outdoor air. The equations incorporate this pathway. The column “exposure medium” should be modified to reflect this.
Response
Figure 1 is revised to reflect th is change: an arrow now indicat es that outdoor particulate and vapor-phase contaminants can move indoors.

Comment
3. The term “Fraction of school soil/dust inges tion that occurs indoors” (FI p. 12) appears in a few pathway equations, but is not explicitly defined in the later section on Exposure Parameters.
Response
The text on page 21 has been revised to incl ude the following defin ition: Fraction indoors (FI) is the estimated fraction of the daily school-related dermal and ingested soil/dust exposure that is acquired indoors. It is calculated as 1- FO.

Comment
Concentration of PM10 in outdoor air, PM10 (p . 12). In the pathw ay equations, this parameter needs to be more ca refully defined. It is the PM10 concentration on-site because of emissions from site soil. In fact, this will be a small fraction of the total PM10 concentration. Failure to clarify the distinct ion could cause important confusion. Also, below the equation for pathway 5, the CP M10 parameter should have its units specified.A2-3 Response

The definition of PM 10 has been revised as follows: PM 10 = Respirable particle load fo r outdoor air due to resuspension of site soil (gPM/Lair). The units “μg/g” have been added to the definition of CPM10 in equation 5.

Comment
5. Respirable particle load for indoor air, SF ( p. 12 and p. 15). The definition of this parameter should be more carefully delimited. It refers to the indoor air concentration of crustal materials that originated on the site.
Response
The equation has been revised to treat indoor su spended particles as a function of indoor dust, which is, in turn, a function of outdoor soil. The default transfer factors are one (1) and two (2), respectively (See pathway 8 page 15).

Comment
6. Pathway 8 should include inhalati on of indoor air (p. 13). If a ch emical is vaporized from soil into outdoor air, then that chemi cal can enter indoor air with ventil ation and be inhaled there. This is a distinct pathway from direct intrusion of the vapor into the building from the soil (as addressed by the Johnson & Ettinger model). This pathway, ther efore, should have a term (BI*TI + BO*TO) in place of (BO*TO).
Response
The term (BI*TI + BO*TO) has been added to pathway 8 (See page 15).

Comment
7. Clarify that penultimate paragraph on p. 14 refers to the case of noncarcinogens only.
Response
We presume that the comment refers to the following paragraph:

Each of these equations gives a pathway-specific annual average daily dose of the chemical in question. The pathway-specific annu al average daily dose is divided by the route-specific reference dose (RfD) to arrive at the pathw ay-specific hazard quotient (HQ) . The pathway-specific HQs are added to give the chemical-specific HQ. In a screening analysis, the chemical-specific HQs for each chemical are added to give the Hazard Index. In a more detailed (tier 2) analysis, target organs and mechanisms of toxic action may be considered in determining the appropriateness of adding the HQs for individual chemicals.
The paragraph refers to non-carcinogenic e ffects of both carcinogeni c and non-carcinogenic chemicals. Carcinogenicity is handled separately.

Comment
8. Provide a logical ordering of Intermedia Tran sfer Coefficients and Exposure Parameters (p. 15-21). It would be easier to follow the developments if the presentation and discussion of the parameters had a transpar ent logical structure. For exam ple, a table could be providedA2-4 that listed all of the paramete rs in alphabetical order (according to the symbols), defined them in words (1 line), and listed the page num ber on which the parameter value is discussed.
Response

A column has been added to tables 1 and 2 to indicate where each parameter is discussed.

Comment

9. Clarification of transfer factor from soil to outdoor particulate matter, TFPM/S (p. 15). The text should make clear that this is the transfer factor that relates the contaminant concentration in soil to the contaminant concen tration in the outdoor PM that results from suspension of site soils. Because of windborne transport, the total PM10 level on site would often be much larger than that resulting from releases on site.
Response

The TF PM/S has been re-defined as the ratio of th e concentration of contaminant in outdoor PM 10 originating from site soils to the concen tration of contaminant in soil (see page 13).

Comment
10. Default parameters for Johnson and Ettinger m odel (p. 15): I believe that the default conditions for the J&E model are appropriate for residential construction but may not be for schools. Details like the height of the building, the land area it covers, and the ventilation rate may be different between schools and residences. This issue requi res some attention, at least at the level of further discussion in the document.
Response
The air exchange rate has been increa sed to 4.7 changes per hour (6.13e+5 cm 3 /sec) based on (RTI, 2003)

Comment
11. Fraction at school, FS (p. 17): Clarify that this parameter represents the fraction of a school day (as opposed to an average day) th at an exposed individual spends at school.
Response
Revisions on pages 13 and 20 indicate that FS represents the fraction of a school day.

Comment
12. Update NHAPS data and reference? (p. 19): Assuming that the appropriate information is contained there, the reference to Tsang and Klepeis (not “Klepis”) should be updated to the following archival report: Klepeis NE, Ne lson WC, Ott WR, Robinson JP, Tsang AM, Switzer P, Behar JV, Hern SC, Engelma nn WH, The National Hu man Activity Pattern Survey (NHAPS): a resource for assessing expos ure to environmental pollutants, JOURNAL OF EXPOSURE ANALYSIS AND ENVIR ONMENTAL EPIDEMIOLOGY, 11 (3): 231- 252 MAY-JUN 2001

. ResponseA2-5 The reference has been changed.

Comment
13. Table 3 typgraphical error: Change “Cm” to “cm2” in 6 places in the second column.
Response

The error has been corrected.

Comment
14. Strengthen Uncertainty Analysis: The sensit ivity and uncertainty an alysis is a welcome part of this report. Table 4 presents an impor tant, but only partial picture of the degree to which different parameters affect the outcome , by indicating the change in intake per unit change in each parameter. The other important f actor, recognized in the text, is how variable and how uncertain the parameters are themselv es. Certain parameters vary only over narrow ranges, e.g. a factor or two or less. Other parameters can vary over orders of magnitude. The parameters that are narrowly variable and we ll characterized (so possessing low uncertainty) are not large contributors to un certainty in the outcome, regardless of the sensitivity of the outcome to the parameter. I would like to s ee Table 4 complemented by another table that provides some indication of th e variability of each parame ter, and the likely degree of uncertainty in its determination. The combinati on of all of these would provide an overall sense of which of the parameters is most im portant in the overall unc ertainty of the risk
assessment.
Response
An ‘uncertainty” column has been added and the discussion revised (see page 28).

Comment
15. Improve reference list: Wherever possible, web links should be provided to government reports.
Response
Web links have been provided where appropriate.A2-6 Michael T. Kleinman Department of Community and Environmental Medicine University of California, Irvine
General Comments:
This guidance is intended to:

• Support assessment of chemical exposures a nd health risks at existing and proposed school sites,

• Characterize uncertainty in assessing exposure and risk in the school setting,

• Suggest which areas are most in need of further research.
To this end, the guidance addresses the differe nces between children and adults, and between the school setting and other settings. Recognitio n is given to the concept that children differ from adults anatomically, physiologically, and beha viorally in ways that affect their exposure to environmental contaminants. A modeling appr oach is used to predict exposures and risks to preschoolers, students, teachers and other school personnel, and their offspring, from chemicals in the soil, shallow ground water, and air at the school site. A spreadsheet is provided which facilitates the ap plication of the model to esti mating exposures. Overall the guidance provides and integrated exposure asse ssment approach, and achieves many of the objectives for the guidance. There are, howev er, some areas in which the guidance could have been improved. Some exampl es of these are provided below.

Comment
Other sources – the document states “in some cases, it may be appropriate to add in additional sources of chemicals in the envir onment. For example there may be off-site emissions that may impact on-site concentrations”. It is not clear what those sources might be and some concrete examples would be helpful.
Response
The following language has been added to the Guid elines to clarify this issue (see page 11):

“ Atmospheric emission sources within 1⁄2 mile of the site which have the poten tial to contaminate onsite air may be important in estimating overall toxic exposures. Examples could include fixed facilities with known emissions and mobile sources su ch as highways, heavily traveled streets, or vehicle loading areas .”

Comment
1. In addition, it is stated that “Exposures to chemical s in building materials and furnishings and chemicals used in schools are beyond the scope of this guidance” No justification is given as to why these on-site sources would not be considered while some unspecified off-site sources would be includ ed. An example that comes to mind would be radon from building materials, formaldehyde from floor coverings etc. The guidance should provide a generalized approach as to how these factors could be included in a total exposure assessment.A2-7 Response
The following text has been added to the Guide lines to clarify this issue (see page 12): “Building materials and indoor products may be important sources of indoor exposure to toxic constituents at schools. It may be a ppropriate to include these sources of chemical exposures in the overall assessment of overall hazards and risks at existing schools. Typically these assessments would be based on measured atmospheric concentrations in classrooms and other indoor areas, and estimated risks, using the same exposure parameters, would be added to site-related risks. Hazards would be additive among chemicals sharing a common target organ and/or mode of action.”

Comment
2. Target Organs – The document states “H azard quotients and incremental risks are estimated for each chemical; then the hazard quotients and incremental risks associated with the individual chemicals ar e added to arrive at the tota l hazard index and total risk. If the total hazard index does not exceed one, then it may be assumed that the non-cancer toxic effects are unlikely and fu rther analysis of non-cancer e ffects is not necessary. If the total hazard index exceeds one, it may be us eful to separate chemicals by target organ and/or mode of action and add the hazard quotie nts of only those chemicals that are likely to act in an additive manner. This target organ/mode of action analysis should be documented.”. Having said that it would have been useful for the document to specify precisely how such a target organ approach might be addressed, at least in general terms. Thus it would be very useful if the worksheet of potential contamin ants could be indexed with respect to target organs to facilitate the computation of target organ specific hazard indices as suggested in USEPA OAQPS 2001.
Response
We agree that it would be useful if the worksheet of potential contaminants were indexed with respect to target organs to facilitate the computation of target organ specific hazard indices; this is something we will address as resources permit.

Comment
3. The approach taken to distinguish between characteristics of children in different age groups is reasonabl e and appropriate.
Response
No response

Comment
4. The factor that lowers enthusiasm for this guidance the most is that it treats school exposure for the most part in a vacuum, i. e. personal exposure of individuals also includes exposures incurred away from school and from other sources. The risks from the school exposures, if any, ar e only a part of the overall risk. While it may be beyond the scope of this specific document to estimate these risks, it should be clearly expostulated within the document that childr en in different part s of California have different background exposures. It would seem to be important that these be considered at least in part before determining that expos ures to be incurred in a school setting areA2-8 acceptable. Some suggestions should be in cluded as to how these background risks can be estimated – at least on some average le vel. There are some modeling approaches (ASPEN) and emissions inventories (Toxic Rele ase Inventory) that could be used to establish and update potential community background levels for specific chemicals found on the school site so that the school exposure does not represen t the “straw that breaks the camel’s back”.
Response
A given incremental dose of a toxic constituent that would otherwise be of no concern, may be a concern if the receptor is already rece iving a background dose of the constituent near the toxic threshold. For th is reason, risk managers may wish to take background exposures into account in their decision-making process. This is suggested in new language added to the Guidelines (see page 12). The “camel’s back” phenomenon would impact only those sites where risk management decisions are driven by non-carcinogenic effects. Since carcinogens are treated as exhibiting no threshold, bac kground exposure levels would not affect the incremental risk posed by the contamination at the school site.

Comment

5. The document states “Concentration of site-r elated particulate ma terial less than 10 microns in diameter in outdoor air (PM 10 ) . OEHHA recommends a default value of 1.8 E-9 g PM/L (1.8 μ g/m 3 ). This value is based on the EPA Soil Screening Levels document (EPA, 1996)”. This value seems to be very low when contrasted with measurements of resuspended dust in Calif ornia made by the Air Quality Management District. On an annual basis resuspende d surface material co ntributes about 20-30 percent of PM10. Given the average PM10 concen tration in California is higher than that in most communities in the US, a more realis tic default value would be on the order of 5 to 10 μg/m 3 . The authors should consider increasi ng this default value and re-estimating the sensitivity to this parameter.
Response
The proposed value is for respirab le particulate matter resuspended from the site . If the suggested value of 5 to 10 μg/m 3 represents total resuspended surface material, then the proposed value of 1.8 μ g/m 3 would represent 18 to 36 percent of the total, which we believe is a conservative estimate of the fraction of to tal resuspended surface material that would be from the site.

Comment
The use of the spreadsheet was mentioned but it would be extremely helpful to provide the documentation and instructions as a a ppendix to the guidance document.
Response

A new sheet “User’s Guide” has been added to th e spreadsheet, in order to clarify how the spreadsheet should be used. We have avoide d making the spreadsheet part of the Guidance in order to avoid the implica tion that the spreadsheet must be used in order to comply with the guidance.A2-9 Comment
I attempted to use the spread sheet, and inserted Soil Clea nup Levels for several toxic compounds. I estimated that at a benzene le vel of 60 μg/kg soil the exposure produced a cancer risk of 2.5 x 10 -5 . Other toxic compounds produced hi gher values. I presume that I did the calculations incorrectly but it would be useful to chec k the spreadsheet’s output with values taken form some se t of soil cleanup guidelines.
Response
The spreadsheet gives a single-highest-year ri sk estimate of 1.6e-8 for 1-2 year-olds at a benzene level of 60 μg/kg soil . There is reason to expect th at the estimated risk at a soil concentration corresponding to a So il Cleanup Levels would not be 10 -6 if the Soil Cleanup Level is based on a scenario other than the sc hool scenario. The legislature mandated that we develop methodology for estimating risk at schools based on the assumption that risk at schools would be different from risk associat ed with residential, commercial, and other scenarios.

COMMENTS RECEIVED DURING THE PUBLIC COMMENT PERIOD December 20, 2002 – January 30, 2003 AND PUBLIC WORKSHOP, January 24, 2003

Dr. Mark C. Rigby, Tetra Tech

Comment
“The purpose of this [PEA] scr eening evaluation is to provid e the risk manager with an estimate of the potential chronic health h azard from contamination at the site. The anticipated use of this screening evaluation is to assist the risk mana ger in deciding whether further site characterization, risk assessment, or remediation is necessary." The objective of the PEA at a proposed school site is to provide a timely and h ealth-protective screening level evaluation, as stated in the quot e above from the PEA manual.
Response
The draft guidance document was prepared to comply with California Health and Safety Code Section 901(f), which re quires OEHHA to develop a nd publish a guidance document for use by the Department of Toxic Substances Control (DTSC) and other state and local environmental and public health agencies to a ssess exposures and health risks at existing and proposed school sites. Although DTSC may ch oose to use the Guidance within the PEA framework, there is no such requirement in the law. Other agencies may use the Guidance in other contexts such as CEQA. The law mandates the use of “appropriate child-specific routes of exposure unique to the school envi ronment, in addition to those in existing exposure assessment models” and the “identifica tion of uncertainties in the risk assessment guidance and those actions that should be taken to address thos e uncertainties.”A2-10 Comment
The exposure equations are not in the standard form given in U.S EPA's RAGS and use a different terminology.
Response
While some minor aspects may differ, the genera l form of the equations is consistent with U.S EPA's RAGS, i.e. the concentration in a co ntact medium times a contact rate with that medium times an absorption rate to give a daily dose, which, when multiplied by an exposure frequency (expressed as a fraction of a year) gives an annual average daily dose. The annual average daily dose, multiplied by exposure duration divided by averaging time gives a lifetime average daily dose.

Comment
The dermal exposure equation provided in the dr aft guidance is more complicated than that given in RAGS.
Response
The draft guidance follows the methodology f ound in the EPA Children’s Exposure Factors Handbook, which more accurately describes the way soil adheres to skin in a “real-world” situation.

Comment
Several exposure parameters not in RAGS are used, for which the default factor is assumed to be 1. Eliminating these exposure factors would simplify and expe dite the use of the guidance and would not change the outcome from the default scenario. The exposure parameters that with a default of 1 are: AI AD TFSD TFPM/S TFI/O Ain. The indoor dust pathway, as provided in the default form give n in the draft guidance, does not differ from the outdoor dust/soil exposure pathwa y. As such, it is redundant.
Response
A guiding principle in developi ng this guidance was that im plicit assumptions should be made explicit. Besides making the methodology mo re transparent, this allows for replacing the value of one (1) with a chemical-specific va lue other than one, when new data support an alternative value. The legislative mandate requires identification of uncertainties in the risk assessment guidance and those actio ns that should be taken to address those uncertainties. These transfer factors are uncer tain and therefore must be in cluded in order to capture the uncertainty. A discussion of the fact ors mentioned in the comment follows:
TFSD, TFPM/S, and TFI/O are tr ansfer factors, not exposure parameters. Since RAGS does not deal with intermedia transport, these parame ters would not be expected to be in RAGS.
TFSD - OEHHA currently recommends a default value of 2 for TFSD, based on the results of recent research.A2-11 AD - Absorption by the dermal route is found in RAGS and chemical-class-specific values are proposed.
AIn and AI - Absorption by the inhalation and inge stion routes have implicit values of unity in RAGS. This guidance make s the value of unity explicit.

Comment
Exposure parameters are given for 1 year inte rvals for children. This requires that the consultant derive appropriate exposure parame ters for each site de novo, demonstrate that they are appropriate, and that DTSC approve them. This may lengthen the PEA process for each site. To expedite the process, default exposure parameters could be provided for the most frequent types of school s, e.g. pre-schools, Kindergarte ns, Elementary schools, Middle schools w/elementary schools, Middle school s, High schools w/middle schools, and High Schools. Providing the yearly exposure parameters in an Appendix would allow consultants to derive specific exposure parameters for those cases that did not fit into the defaults given above.
Response
Default exposure parameters are provided for each year from birth through age seventeen and for adults. The burden of gathering this information is not placed on the user. Default parameters for multi-year periods were considered and rejected because this method would base the hazard index on an average e xposure for a multi-year time period and would not capture the single highest year. Furthe rmore, the use of individual years gives the assessor and the reviewing agency more fl exibility. While indi vidual years can be aggregated into groups to match a proposed e xposure scenario, multi-year bins can not be easily disaggregated. Disaggregation would be necessary if the a ssessment period did not match the exposure scenario. For example some districts have elementary schools covering grades K-6, while others have primary sc hools from K-3 and middle schools from 4-6 on different sites.

Comment
The draft guidance provides a si mplified equation for determini ng outdoor air concentrations of volatiles that have migrated from subs urface soil or shallow groundwater sources. The consultant need only supply the chemical concentration in soil/groundwater and the chemical-physical properties. For indoor air, however, the draft guida nce states that the Johnson and Ettinger model from USEPA should be used, but no defaults are supplied. The PEA process would be greatly expedited if de fault building and soil properties, as well as contaminant depths, were supplied. If this were done, a simplified model could be derived (akin to the VF emissions model) that only re quires the input of chem ical concentration in soil/groundwater and chemical-physical properties.
Response
OEHHA is proposing a default air excha nge rate of 4.7 changes per hour (613,426 cm 3 /sec in the EPA indoor air model with the default bu ilding volume – any cha nges in building volume would have to be accompanied by corresponding ch anges in flow rate to maintain the same exchange rate), based on recent studies of California classrooms (RTI, 2003).(see GuidanceA2-12 page 17). Default parameter values will be co nsidered for other parameters. DTSC’s indoor air working group is devel oping recommended default valu es for some parameters.

Comment
To expedite the PEA process as much as possible, default simplified risk assessment equations could be provided. Such equations were provided in the original PEA manual (DTSC 1999) and only require the input of chemical concentrati ons and toxicity values (in addition to any modeling necessary to calculate concentrations).
Response
Default risk assessment equations are provide d. They are not simplified, but they only require the input of chemical c oncentrations in selected media and toxicity values (which are provided for some chemicals). These risk assess ment equations have been incorporated into a spreadsheet, which can be reca lculated virtually instantaneou sly by most computers. While it would be possible to further simplify the e quations by collapsing all exposure parameters into a single pathway exposure factor as the PE A does, this would sacrifice transparency and the ability to substitute case-specific paramete rs in a tier 2 assessmen t when appropriate.

Comment
The draft guidance includes the assessment of risks from the migration of offsite dusts and vapors to the school site. This is more appr opriately addressed in an EIA/EIS. Risk assessments normally evaluate the risks from contaminants that originate at the site.
Response
This guidance may be used in a variety of cont exts including environmental impact analysis. For some purposes, some pathways in the mode l may not be appropriate. Pathways may be eliminated with the approva l of the reviewing agency.

Comment If local background is evaluated in the risk assessment, it is to subtract the risks from local background from the site-specific risks
Response The guidance addresses methodology for estimati on of dose and risk from environmental contamination at a proposed or existing school site. Contaminant source allocation, and management of contamination are in the domai n of risk management, and are outside the scope of this guidance.

Comment Draft USEPA guidance is cited as the source of some of the information. However, by its very nature, draft guidance is rather labile.
Response The guidance referred to is now interim final.A2-13 Bill Piazza, Los Angeles Unif ied School District (LAUSD)

Comment
In general, the District ag rees with the refined methodol ogy recommended in the draft assessment protocol which allows considera tion of "reasonable" e xposures anticipated to occur at school sites. Nevertheless, th e methodology is unnecessarily specific in its attempt to quantify risk. The District contends that until toxicity factors are developed for school aged children, the quantification of risk for each grade level will not reveal a significant difference over the risk value predicted with average exposure factors for a given occupancy. Response
For some chemicals, the estimated dosage in the first year of life is as much as 2.7 times the average for birth through age seventeen. OEHHA considers a 2.7-fold difference worth considering. And once the algorithms are in corporated into a spreadsheet, the extra calculations are little, if any, extra effort.
Comment
In addition, the methodology is not consiste nt with existing assessment methodologies utilized for the Safe Drinking Water and Toxi c Enforcement Act (Proposition 65), Air Toxic "Hot Spots" Information and Assessment Act (AB 2588) and related California Air Resources Board (ARB) assessment activities pr epared under the auspices of the Toxic Air Contaminant Identification and Control Ac t (AB 1807). The District's concern is exemplified with the pending adoption of ARB's Regulation Or der to limit school bus idling and idling at schools. The purpose of the air toxic control measure is to "reduce public exposure, especially school aged children's exposure" to pollutants by "limiting unnecessary idling" of specified vehicular sources "at and around schools and wh ile riding school buses and other types of school transportation." Pleas e note that the ARB utilized the assessment methodology outlined in OEHHA's Air Toxic Hot Spot Program Risk Assessment Guidelines, Part IV, Technical Support Docu ment for Exposure Assessment and Stochastic Analysis to establish a set of defined contro l measures. The specific exposure assumptions are presented in ARB's Staff Report: Initial Statement of Reasons (ISOR), Appendix C: Idling Diesel School Bus Health Risk Assessm ent Methodology. The District believes that due to the regulatory nature of the assessmen t, which identifies operational controls for school bus owner/operators to actually reduce sc hool-based exposures, jus tifies its use as an appropriate methodology. Neverthele ss, the District is aware th at one may argue that the various State agencies and th eir associated regulatory programs require different methodologies to assess risk. As such, assumpti ons such as exposure frequency and duration may differ producing varying risk values for a given exposed population. However, the District believes that a school is a school re gardless of the specific regulatory program. To argue that one agency should assess school e xposures with one set of assumptions while another consider different expos ure variates for the same o ccupancy, promotes a lack of consistency between the various State boards and departments and does little to encourage the harmonization in the practice of risk a ssessment within Cal/EPA. As a result, the assessment of a school-based occupancy must be consistent with all pr ograms which quantify risk for this sens itive subpopulation.A2-14 Response

This Guidance also utilizes some of th e assessment methodology and parameter values outlined in OEHHA's Air Toxic Hot Spot Progr am Risk Assessment Guidelines, Part IV, Technical Support Document for Exposure Asse ssment and Stochastic Analysis. To the extent that there are differences, these refl ect the different mandate for this program.
Comment

1. Units of measure are not consistent with industry standard. This may present an unnecessary source of error upon uni t conversion and present some difficulty in reviewing empirical data and related wor kbook calculations. For example:

• Soil concentration (e.g., ug/g to mg/kg)

• Particulate airborne concentr ations (e.g., ug/l to ug/m3)

• Volatile airborne concentr ations (e.g., ug/l to ug/m3))

• Cancer Potency Factors (e.g., ug/kg/day to mg/kg/day) Response

• Soil concentration units have been changed to mg/kg

• Particulate and volatile ai rborne concentrations have been changed to mg/l

• Cancer Potency Factors units have been changed to (mg/kg/day)-1
Comment

2. Calculation of the ha zard index does not cons ider toxicological endp oints. This is not consistent with ex isting guidance (OEHHA, 2000). The inclus ion of this refinement is most relevant as many removal actio ns currently undert aken by the District are based upon screening values. As su ch, unity may be exceeded necess itating an unwarranted response action. The ability to readily identify and quan tify the hazard index sh ould be included in the proposed methodology. The following excerpt from U. S. EPA's Risk Assessment Guidance for Superfund Volume I - Human Health Evaluati on Manual (RAGS) underscores the viability of the District's concern regardi ng dose additivity. Anothe r limitation with the hazard index approach is that the assumption of dose additivity is mo st properly applied to compounds that induce the same effect by the same mechanis m of action. Consequently, application of the hazard inde x equation to a number of com pounds that are no t expected to induce the same type of effect s or that do not act by the sa me mechanism could overestimate the potential for effects, although such an approach is appropri ate at a screening level. This possibility is generally not of concern if only one or two su bstances are re sponsible for driving the HI above un ity. If the HI is greater than un ity as a consequence of summing several hazard quo tients of similar value, it woul d be appropriate to segregate the compounds by effect and by mechanism of action a nd to derive separate hazard indices for each group.
Response

Calculation of the hazard index does consider toxicological endpoints. See pages 8 and 25.

Comment
3. Several exposure variates differ from ex isting guidance (OEHHA, 2000). Many are taken from a draft guidance document (U.S. EPA, 200 0). If these values are more appropriate, then OEHHA should revise current guida nce for consistency. For example:A2-15 • Skin surface area (U-S- EPA, 2000)

• Breathing Rates (not consistent with OEHHA recommended values)

• Body Weights (U.S. EPA, 2000) Response
The Child-Specific Exposure Factors Ha ndbook is now a citable Interim Report
The skin surface area data were generated in a setting similar to a school environment (day care) and are therefore relevant for school exposure estimation.
The OEHHA-recommended breathing rates (Tab le 3.22, in Technical Support Document for Exposure Assessment and Stochastic Analysis , OEHHA, September 2000) are for assessment of long-term average exposures. They are not activity-spe cific as required.
The recommended body weights have been revise d to agree with Tables 10.1 (staff) and 10.3 in (Technical Support Document for Exposur e Assessment and Stochastic Analysis, OEHHA, September 2000).

Comment
4. Exposure times should be reviewed and re vised, as appropriate, following input from school district personnel. Stakeholder input, rather that U.S. EPA's draft documentation, should be utilized to devel op viable exposure times. For example, OEHHA assumes most kindergarten students spend ove r nine hours per day at school . To the contrary, most kindergarten students spend no more than 4 hours per day at school.
Response
The guidance has been revised to reflect recen t survey data (RTI, 2003) with respect to exposure frequency. Children 0-6 may be in day care for a full school or work day.

Comment
5. Uncertainty with the use of the Johnson a nd Ettinger Model should be discussed. OEHHA should address concerns raised regarding the m odel's accuracy before recommending its use.
Response
Uncertainty associated with the use of the J ohnson and Ettinger Model is discussed in the Uncerainty section.

Comment
If utilized, the model must be programmed to a ccount for vapor intrusion into institutional (e.g., Department of Education approved) buildings and not a single-family residence. For example, a default air exchange rate of 0.45 per hour is inappropriate for institutional buildings with markedly higher ventilation ra tes which range from 4 to 7 air changes per hour (e.g., 50 CFM per person).
Response
The guidance has been re vised to reflect recent survey data (RTI, 2 003) with respect to default air exchange rates.A2-16 Comment
6. The school's conceptual site model must be further defined. School-based exposures must be plausible and likely to occur for a given occupancy. A discussion similar to U.S. EPA guidance must be included to further define "r easonable" exposure pathways. The District's recommendation is exemplified by the following excerpt from RAGS. There are two steps required to determine whether risks or hazard indices for two or more pathways should be combined for a single exposed individual or grou p of individuals. The first is to identify reasonable exposure pathway combinations. The second is to examine whether it is likely that the same individuals would consisten tly face the "reasonable maximum exposure" (RME) by more than one pathway. Identify expo sure pathways that have the potential to expose the same individual or subpopulation at the key exposure areas evaluated in the exposure assessment, making sure to consider areas of highest exposure for each pathway for both current and future land uses (e.g., n earest downgradient well, nearest downwind receptor). For each pathway, the risk estimates and hazard indices have been developed for a particular exposure area and time period; they do not necessarily apply to other locations or time periods. Hence, if two pathways do not affect the same indi vidual or subpopulation, neither pathway's individual risk estimate or hazard index affects the other, and risks should not be combined. Once reasonable exposure pathwa y combinations have been identified, it is necessary to examine whether it is likely that the same individuals would consistently face the RME as estimated by the methods descri bed in Chapter 6. Remember that the RME estimate for each exposure pathway includes many conservative and upper-bound parameter values and assumptions (e.g., upper 95th c onfidence limit on amount of water ingested, upper-bound duration of occupancy of a single residence). Also, some of the exposure parameters are not predictable in eith er space or time (e.g., maximum downwind concentration may shift compass direction, maximum ground-water plume concentration may move past a well). For real world situati ons in which contaminant concentrations vary over time and space, the same individual may or may not experience the RME for more than one pathway over the same period of time. One individual might face the RME through one pathway, and a different individual face the RME through a different pathway. Only if you can explain why the key RME assumptions for more than one pathway apply to the same individual or subpopulation shoul d the RME risks for more than one pathway be combined.
Response
All pathways included in the guidance may aff ect the same child with two exceptions: The breast milk pathway does not aff ect children above one year of age, and the soil ingestion pathway does not affect children less than one year of age. Thus, these pathways are not additive. A column has been added to Table 2 indicating for each exposure parameter whether it is mid-range or upper end, and some discussion of upper end versus mid-range has been added to the uncertainty section on page 30.

Comment
Some discussion on acceptable level of risk should be in troduced. OEHHA administers Proposition 65 which supports the State's "level posing no significant risk" of one in one hundred thousand (I.0E-05), not the value of one in one million (I 0E-06) as used in Environmental Assessment screening guidance and adopted as the Department of Toxic Substances Control's acceptable level of risk. As noted above, removal actions currently undertaken by the District are based upon these screening evalua tions. The Distri ct contendsA2-17 that the "no significant risk levels" establishe d by the State are releva nt and appropriate and should be considered when refined assessm ent activities are conducted.
Response
Acceptable or target risk levels are in the risk management domain. The guidelines cover risk assessment and exclude risk management.

Comment

Please note that the District co nsiders all relevant a nd appropriate exposures to assess risk for its existing school occupancies. As such, th e District has developed a guidance document and associated Excel spreadsh eet to quantify school-based risk. The methodology is based upon the above referenced technical suppor t document (OEHHA, 2000) with exposure parameters assigned by occupancy (e.g., kinde rgarten through the 6 grade). The District believes it is consistent with OEHHA's existing assessment methodology. The program's format allows for quick data entry and is robus t in its computational ab ility to quantify risk for a suite of identified compounds. The guida nce document is included for your review and consideration. Staff is currently finalizing th e Excel spreadsheet for distribution and will forward an electronic copy for your re view the week of February 3rd.
Response

OEHHA has received and revi ewed LAUSD’s guidelines.

Lee Shull and Mark Bowland, M ontgomery Watson Harza (MWH)

General Comment
As a follow up to recent discussions, this letter presents MWH's review comments on OEHHA's draft (File date 10/3/02, header da te August 20, 2002) Schools Risk Screen Model (Model). The Model we re viewed was provided by OEHHA to Mr. Ernest Silva of the Coalition for Adequate School Housing (CASH). Our review has been performed on behalf of CASH. Both CASH and MWH greatly apprec iate the opportunity to review the Model and provide these comments, and look forwar d to assisting OEHHA however we can as the agency continues its development of the schools program. Whereas this letter provides substantively technical comments , we will provide ou r comments on the Model as it relates to policy and implementation issues in a separate letter.
For practical purposes, we have organized our comments on the Model and the associated guidance document into four basic areas: (1) identifi cation of potentially fatal flaws/errors/omissions in the Model, (2) critical flaws/er rors/omissions in the Model, (3) suggested user inte rface improvements, and (4) general/editorial comments.

Comment
1. Input-output sheet. Results in clude a "0-18 + staff' endpoint . This endpoint assumes that a child spends the entirety of his/her education (preschool th rough high school) at a single campus, and then post college teaches an entire career at th e same campus. ThisA2-18 essentially assumes 43-year exposure duration (ED), which is greater than the current residential default assumption. We believe this endpoint is an unreasonable point of departure for decision making . We encourage OEHHA to deve lop a more reasonable ED value for inclusion in the model.
Response
Which years are aggregated is a case-specific, user /reviewer decision. We have removed the cells labeled "0-18 + staff” to avoid the implication th at any particular exposure duration is "approved" by OEHHA.
Comment
2. Groundwater and soil vapor input cell. If a value of "0" is pl aced in both the groundwater and soil vapor concentration input cells, calcul ation errors (#value! ) Prevent production of useful risk or hazard values.
Response

This error has been corrected.

Comment

3. J&E model database. If a chemical that is not part of the J&E model database is selected, calculation erro rs occur due to J&E malfunction. Document ation instructs the user to add the chemical to the database, but gives no procedure for performing this func tion (the sheet is password protected).
Additionally, no guidance is given to direct the user when it is essential to add a volatile chemical to the database, or what data must be entered into all the relevant "vlookups" sheets for all three J&E model components (i.e ., soil, soil gas, groundwater). Additional text should be added to the model documentation and model spreadsheets outlining the procedures necessary for adding these featur es. Also, we suggest a single "vlookups" sheet for all three model component s to reduce the potential for user entry error.
Response The duplicate "vlookup" and "chemprops" sheets have been eliminated, so that the relevant information needs to be added in only one place. Gu idance has been adde d as to when and how to add chemicals to the database.
Comment

4. Route-to-route extrapolation . In cases where route-to-route extrapolation is rejected in Input-Output (cells B 13 an d/or B 18 given valu es of "0"), all ex posure sheets do not reference the user suppli ed RfD or CSF values fo r soil dire ct contact. Response

This error has been corrected.
Comment
5. Input-Output Sheet. If a user allows the m odel to perform route-to-r oute extrapolation of oral and dermal toxicity crit eria from inhalation toxicity cr iteria, the model may use anA2-19 inappropriate toxicity metric for the oral and dermal pathwa ys. For example, the inhalation cancer slope factor for 1,4- dichlorobenzene is 4 x 10 -2 . The oral cancer slope factor is 5.4 x 10 -3 , or 7 times lower. Similarly, the inhalation cancer slope factor for 1,3-butadien e is 0.6, whereas the oral cancer slope factor is 3.4, or si x times higher. An additi onal issue with this procedure is the implication that use of inhalati on toxicity factors as surrogates for oral and dermal exposures is a ppropriate. For numerous inorganic chemicals (n ickel, chromium 6+, cadmium) this implication has potentially enor mous ramifications, as these inorganics are not currently considered carcinogens by the or al routes. We sugge st adding a toxicity criteria table containing both oral/dermal and in halation toxicity criteria , or defaulting to a user input toxicity criteria fo r each route and for each chem ical for the oral and dermal pathways. Response The intent is not to automatically default to inter-rout e extrapolation. In order to make this intent clearer, the spreadshee t now uses an exclusive user -supplied CPF and RfD as an alternative when these parameters are not in th e database. The reviewer should ensure that the assessor documents any us er-supplied CPFs or RfDs.
Comment
6. Input-Output Sheet. Results for cancer risk for scenario 0-4 sums 0-5 results, 5-10 scenarios sums 0-6 resu lts, not 5-10 results. Response The error for 5-10 year olds has been correcte d. The sum for ages 0- 4 should include 4-5, since these are four-year-olds

. Comment
7. Volatilization assumption It is doubtful that DDT (and similar semi-volatile compounds) would actually volatilize in appreciabl e concentrations. It is our opin ion that semi-volatiles such as DDT should not be modeled to indoor air.
Response
We agree that DDT and similar semi-volatil e compounds will not volatilize in appreciable concentrations, because of the low volatility of these compounds. For example, the indoor air pathway contributes 0.04 percent of total risk for DDT.

Comment

8. Fate. Cell C22 contains a reference error that pr events a breast milk pathway calculation.
Response

This error has been corrected.

Comment
9. Input-Output sheet + Fate. Units for chemical concentration in PM10 are different between these sheets (ug/L versus ug/g).A2-20 Response

This error has been corrected.

Comment

10. Fate. Toggles don't function wh en a chemical is not in the database (e .g., metals) because an error message is created. Logic equations rather than simple arithmetic equations would prevent this from occurring. Also, see comment #3.
Response
I was unable to replicate the problem

Comment

11. Fraction at school is used to partition daily soil ingestion. Guidance documents indicate that this fraction should also be incorporated into dermal dose calculations as indicated by the equation on page 4 of the guidanc e document. We agree with this conclusion. However, this fraction appears only to be included in the age 3- 4 exposure spreadsheet and in none of the other dermal dose calculations.
Response

This error has been corrected.

Comment
12. Dermal exposure assessment. The approach for dermal expos ure assessment represents a departure from current OEHHA, DTSC, and USEPA dermal assessment protocols. Additional discussion highlighting the need/u tility of this new protocol should be incl uded in the guidance document.
Response
The selected approach is recommended by EPA, and is based on data relevant to the school scenario. The Guidance discusses the salient arguments for selection of this approach.

Comment

13. Fate. Cell H7. The on-site soil-to-i ndoor dust Transfer Coefficient (dermal) does not appear to be used in the calculation.
Response

This error has been corrected.

Comment
14. Indoor air modeling. Default indoor air modeling is based on Johnson and Ettinger model parameters for residential homes, which clearl y do not apply to schools. The model and model documentation do not provide adequate guidance on what model parameters may be modified or how such modifications may be incorporated. We suggest, for sc reening, applying conservative but non-residential parameters.A2-21 Response
OEHHA proposes a default air exchange rate of 4.9 per hour, the lower confidence limit on the weighted mean value from 94 portable and 26 traditional classrooms (RTI, 2003). This and other parameters may be changed from defa ult values when justified and documented.

Comment
15. Age-specific exposure sheets. Soil Ingestion. P. 11. Of the OEHHA school model guidance document cites OEHHA (2000) guidance for soil ingestion. OEHHA (2000) recommends 200 mg/day soil ingestio n for children age 1- 6 and 100 mg/day for "everyone else." This approach is inconsistent with the available da ta, which indicate adults, and especially adults in non-soil intensive exposure work e nvironments, do not consume 100 mg/day. This approach is also inconsistent with other Cal/E PA guidance for worker soil and dust exposures, and is also inconsistent with USEPA's recommended 50 mg/day for adults.
Response
The soil ingestion rate in question (100 mg/day) is partioned such that only 58 percent of that amount (58 mg/day) is assumed to occur at school. Since most estimates of occupational exposure consider only the fraction of total exposure that occurs in the occupational setting, the assumptions are not far apart (50 mg/day versus 58 mg/day).
Comment
16. Potential users of the spreadsheet. It is critical that OEHHA st ate that the spreadsheet and guidance document are `expert tools' and not intended to be layperson tools.
Response
The follosing sentence has been added on page 8: “ This guidance assumes that the user is familiar with the principles of chemical risk assessment; it is not intended to provide basic instruction in risk assessment.”
Comment
17. Dust exposure. The utility of differentiati ng indoor dust from outdoor dust in the model is uncertain. Most schools will go through the a ssessment process prior to construction and performing any measurement of ch emical concentrations in indoor dust. Separating soil ingestion, dermal and inhalation pathways in this fashion may lead to more confusion than clarity.
Response

Recent field studies have demonstrated a concentr ating effect for several elements in indoor dust compared to school-yard soil (RTI , 2003). OEHHA is now recomme nding a default value of 2 for the soil/dust transfer factor (see page 17).
Comment
18. Toxicologic endpoints. No discussion or delineation in the model/model documentation is presented that addresses assessment of specifi c toxicologic endpoints (also referred to as target organ toxicity). This is an important subject and should be explicitly addressed in the guidance, and where possibl e, in the model itself.A2-22 Response
The additivity of hazard quotients for different ch emicals based on their target organ and/or mode of action is discussed on page 9: “If the tota l hazard index does not exceed one, then it may be assumed that the non-cancer toxic effects are unlikely and further analysis of non-cancer effects is not necessary. If the total hazard index exceeds one, it may be useful to separate chemicals by target organ and/or mode of action and add the hazard quotients of only those chemicals that are likely to act in an additive manner. This target organ/mode of action analysis should be documented.” Similar language is in the sheet “user’s guide.” Chemical-specific information on additivity is available elsewhere.
Comment
19. Stakeholder involvement in Model development. No indication is prov ided in the guidance documents that stakeholders have been included in the development of key exposure parameters such as exposure time and exposure frequency. This lack of involvement increases uncertainty as to whether the values used in the model for these parameters are repr esentative of California school conditions. CASH is in a unique position to provide data specific to public schools for these parameters.
Response
The opportunity for stakeholder involvement was open through May 2003. All recommendations for parameter values that were suppor ted by documentation were considered.

Comment

20. Annual risk estimations. The assessment of theoretical upper-bound cancer risk and noncancer hazard indices on a year-by- year basis is a new risk assessment approach. Hopefully, OEHHA has carefully consider ed the propriety of this approach. We assume th at this approach is used in consideration of the ne w age-specific toxicity criteria (OEHHA, 2002 draft, p.11) under development by OEHHA. Until these criteria are developed, we are uncertain of this approach.
Response
The language in HSC Sect ion 901 suggests that th e legislators were co ncerned that typical risk assessment paradigms (which use longer-term average expos ure rates) fail to consider the specific exposures and sens itivities of children. OEHHA took this as a mandate to look specifically at the exposure pa rameters of young children. To do this effectively required using age-specific exposure parame ters. As noted in the comme nt, this approach is also anticipates development of age-spec ific toxicity criteria by OEHHA.
Comment
21 Consistency with other OEHHA guidance. The model incorporates assumptions that vary from other currently available OEHHA risk assessment guidance (OEHHA, 2000) without defining the need for the va riation. Variations from published agency guidance s hould be discussed including rationale as to why OEHHA believes the approach/assumptions in the model is more applicable to the schools risk assessments.
Response
Though it is not further described in the comment letter, we assume that “(OE HHA, 2000)”A2-23 refers to the “Technical Support Document for Exposure Assessment and Stochastic Analysis” (TSD). The TSD was created for a different purpose than the Schools Guidance. and the differences in mission and mandate require so me differences between the two. For example, the Schools Guidance must include “Appropriate child -specific routes of e xposure unique to the school environment in addition to those in existing exposure assessment models.” This requires a different approach, focusing on the rapidly chan ging exposure patterns of young children and the unique features of the school e nvironment as they affect exposur es. Because children are rapidly changing anatomically, physiologically and be haviorally, we recommend a set of exposure parameters for each year until age 18. In cont rast, the TSD presents methodology for estimating long-term average exposures in a 24-hour-per-day exposure set ting. Nonetheless, internal consistency to the extent possible was a consid eration in developing this guidance. Exposure parameters are discussed below in th e context of inte rnal consistency. The proposed value for Soil Ingestion , 200 mg/day is the value recommended in the TSD, and ie equivalent to EPA’s “cons ervative estimate of the mean.

Fraction at school : There is no equivalent parameter in the TSD.
Body-part-specific skin loading rate and body-part-specific skin surface area differ from the methods and parameters recommended in the TSD. These methods and parameters are from EPA (2002) guidance which antedates the TS D. OEHHA considers these data to be the best available for the Guidance because they are based on real-world exposures to young children in day-care centers, an exposure setting sim ilar to the School sett ing addressed in the Guidance

Fraction outdoors and Fraction indoors also have no equivalent parameter in the TSD. However, these parameter values are based on time-activity studies reported in the TSD.
Body weight data for children 1 to 18 years are from OEHHA, 2000, Table 10.3. For pregnant or nursing women, and for staff the data are from OEHHA, 2000, Table 10.1. The value for children up to 1 year old is from EP A, 2002, because there is no equivalent value in the TSD (OEHHA, 2000).
Exposure time, outdoors and Exposure time, indoors: Although OEHHA (2000) considered activity-related breathing rates and time spent at those activities, the focus was to develop an amalgamated breathing rate over time. The Guidance differs in that it considers indoor and outdoor breathing rates separatel y, since these environments may have different contaminant loadings. Again, OEHHA believes that this a pproach is consistent with the legislative mandate.
Breathing rate, outdoors and Breathing rate, indoors were estimated from the data of Wiley, et al in OEHHA, 2000, pp. 3-25 to 3-27. These ventilation rates are based on the activity descriptors in the Wiley, et al. report, that were deemed consistent with outdoor and indoor activities at sc hool, respectively
Exposure frequency , the estimated number of days st udents or other school users attend school annually is based on California DHS and ARB survey data. There is no equivalent parameter in the TSD.

The recommended Breast milk intake of 130 g/kg/day for the first 12 months of life is based on (OEHHA, 2000, Table 5.13, 90th percentile).A2-24 Lifetime Exposure Fraction (ED/AT) The TSD recommends an exposure duration of 70 years (ED/AT = 1). This is not rele vant for a schools exposure scenario.
Fraction absorbed, inhalation and Fraction absorbed, ingestion are not found in the TSD. The Guidance does not at present suggest values other than unity. Indeed, some commentors have suggested that a factor with a value of one is pointless, and should be omitted. HSC Section 901 requires considerati on of uncertainty in the mode l. To omit these absorption fractions would be to igno re a source of uncertainty.
Fraction absorbed, dermal : In order to maximize consis tency with the TSD, OEHHA now recommends the following dermal absorption fractions:
Compound Absorption fraction Source

Arsenic 0.04 OEHHA, 2000
Beryllium 0.01 OEHHA, 2000
Cadmium 0.001 OEHHA, 2000
Hexavalent chromium 0.01 OEHHA, 2000
Lead 0.01 OEHHA, 2000
Mercury 0.1 OEHHA, 2000
Nickel 0.04 OEHHA, 2000
Polychlorinated biphenyls 0.14 OEHHA, 2000
Polychlorinated dibenzo-p-dioxins and dibenzofurans 0.02 OEHHA, 2000

Hexachlorocyclohexanes 0.1 OEHHA, 2000
Polynuclear aromatic hydroc arbons, 0.13 OEHHA, 2000
DEHP 0.1 OEHHA, 2000
4,4’ methylene dianiline 0.1 OEHHA, 2000
Organophosphates, pentachlor ophenol 0.25 DTSC, 1994
Chlorinated insecticides 0.05 DTSC, 1994
Other organic chemicals 0.1 DTSC, 1994
Other metals and complex ed cyanides 0.01 DTSC, 1994
Free cyanide 0.1 DTSC, 1994A2-25 Comment
22. Acceptable risk. No indicators in the guidance or in the model are provided as to what metrics OEHHA is applying for judgin g what is an "a cceptable risk."
Response
Acceptable or target risk levels are in the risk management domain. The guidelines cover risk assessment and not risk management.
Comment
23. Model parameters. All model parameters that can be ch anged should be clearly and plainly listed on the input-outpu t sheet. This would in clude all pathway toggles, dermal, oral, and inhalation absorption parameters, chemical properties, exposure frequency, etc.
Response
Use of the model in screening mode with all defaults involv es entering data only in the shaded cells in “Input-output” column B. Changing values outside that ra nge will move the user into tier 2 and will require justific ation of all proposed changes from the default condition.
Comment
24. Input-Output Sheet. For hazard results, no indication is prov ided as to which hazard estimate to use. We suggest a "=max (range)" fo rmula be inserted for each scenario.
Response
This suggestion has b een adopted. See Inpu t-output cell H25.

Comment

25. E quations. We suggest locking cells containing e quations that should not be modified.
Response
Sheets other than “Input-output ” will be locked when the spreadsheet is released, to prevent inadvertent changes to formulas and parameter values. Howe ver, reviewers should still verify the calculati ons against their own (unmodified) copy of the workbook.

Comment
26. Chemical properties. We suggest adding chemical property input cells on Input Output sheets that are activated only wh en a chemical is not in the database.
Response
Chemical properties can be ente red in the “Vlookup” sheet.

Comment
27. Input-Output Sheet. Currently no dermal absorption fracti ons are defined in the "database", but are presented in the guidance document. We su ggest adding a table of values from the guidance into the model. See comment #21 above.A2-26 Response

This has been done.

Comment
28. Fate sheet. Q/C value based on 10-acre site for LA. Meteorologica l conditions are different for Northern and Sout hern California. We suggest a table containi ng a range of Q/C values, with a toggle to allow the user to define what region of California in which the site is located.
Response
Regional Q/Cm ratios would make a minor change in a minor pathway. It is not clear that the added complexity brings commensurate benefit.
Comment
29. Age-specific exposure sheets. Dividing soil ingestion rate by body weight to create a soil ingestion per kilogram body weight rate implies that soil ingestio n is directly correlated with body weight, which is not consistent with the exposure equations listed in the guidance document. These two parameters are not directly correlated.
Response
Cell H18 is now changed to g/ day, then divided by body weight in the “contact rate” cell, in order to avoid the appearan ce that soil ingestion an d body weight ar e treated as correlated.

Comment

30. J&E Model parameters. We suggest including pertinent Johnson & Ettinger model parameters in the Input-Output sheet.
Response

This will be considered for future spreadsheet enhancements

. Comment

31. Grammatical errors. Numerous spelling and grammatica l errors exist throughout the model spreadsheets, and associated documentation.
Response
We will correct these as we identify them.
Comment

32. Fate. Breast milk BCF reference should be Un iversity of Calif ornia (1994), not DTSC (1994).
Response

This has been corrected.A2-27 Comment

33. Fate + individual age rang e calculation spreadsheets. We suggest adding additional clarification for each pathway delineated by a number. When printed, there is no indication which pathway is soil ingesti on or dermal contact (1 vs. 2 vs. 3).
Response
Widening column 1 to accommoda te the pathway name would make the sheet will be too wide to display on a single screen and woul d duplicate information in column B (exposure medium) and column E (exposure route).
Comment

34. Units. Input output sheet does no t specify units for user defined CSF or RfD.
Response

This has been corrected.
Comment

35. Fate sheet. Units of M8 & M9 should be μg/L.
Response

This has been corrected.
Comment

36. Age-specific intake spreadsheets. The water intake paramete r is not used in any calculations.
Response

This has been eliminated
Comment

37. Gui dance document, p.10. Outdoo r air PM10 levels. The document states OEHHA recommends 1.8E-9, but the spreadsheet uses 5.0E-8.
Response

This has been corrected.

REFERENCES (Cited in the reponses)
1. RTI, 2003, Final Report, OEHHA Soil Sampling Augmentation, RTI International Project #RTI/08381-01F, April 2003
2. OEHHA, 2000 Technical Support Document for Exposure Assessment and Stochastic Analysis, Air Toxics Hot Spots Program Risk Assessment Guidelines Part IV, September, 2000A2-28 COMMENTS RECEIVED DURING THE PUBLIC COMMENT PERIOD November 7, 2003 - December 8, 2003

Deborah Oudiz, Department of Toxi c Substances Control (DTSC)

Comment

1. The title is too restrictive. Please drop “existing and propos ed” from the title. Response
The title of the document comes directly from the enabling legislat ion. OEHHA staff feel that removing the word “Propose d” from the title actually re stricts the sites where this guidance should be used, while in clusion of the word covers those site s intended by the legislation. Therefore, OEHHA deems it appropriate that the title of the document be a direct reflection of the langua ge in the statue: “...the office shall publish a guidance document, for use by the Department of Toxic Substances Control and other state and local environmental and public health agencies, to as sess exposures and health risks at existing and proposed schoolsites.”

Melanie Marty, Office of Environment al Health Hazard Assessments (OEHHA)

Comment
1. Please add text discussing the possibility of future ag e-specific cancer potency. Response Text discussing the possi bility of future age-specific canc er potency has been added (see page33).

Comment

2. Please add text discus sing about population risk
Response Two sentences discussing population risk have been added (see page 24).

Comment
3. Please change the exposure duration for staff to 40 years to be consistent with other OEHHA guidance. Response The exposure duration for staff has been ch anged to 40 years (s ee pages 24 and 25).A2-29 Bill Piazza, Los Angeles Unified School District

Comment The timeline specifted for public comment is in adequate. The District is cognizant of OEHHA's reliance on the requirements set forth in Health and Safety Code Section 57003 for receiving public comment. However, not hing in the statute precludes OBHHA from extending the timeline to ensu re that the proposed guide lines are "based upon sound scientific methods, knowledge and practice." In fact, the st atute does not limit the public comment period to 30 days but specifically states that following the public workshop the proposed guidance shall be circulat ed "for a period of at least 30 days." The District believes its request to extend the public comment period is appropriate and underscored by the extent of time OEHHA has taken to amend and respond to initial comments on the original draft guidance. The District did not receive a copy of the revised guidance nor its response to comments until November 7, 2003. This is more than 280 days from our initial comment submittal of January 31, 2003. Notwithstanding, the Di strict is aware that time is required to review and respond to both peer and pubic comments, as well as revise the draft guidance, as appropriate. In fact, OEHHA co mmissioned additional classroo m studies, one of which was designed to determine the contaminant compositi on of interior surface dust (i.e., dust mat and classroom floor dust) to outdoor soil concentrations. Although th e District is supportive of this effort, this data is new information which was not previously available for public scrutiny.. Clearly, additional time is required to address the adequacy of this study and exposure potential of indoor cont aminants to a given school occupy.
Response Three substantive changes were introduced in the current draft of the Guidance: Minor changes to the default school calendar, inclus ion of an outdoor/indoor transfer factor, and revised default outdoor/indoor ai r exchange, all based on the RT I, 2003 report. The relevant section of the RTI report (Attachment 1) is 2 pa ges long. Thirty days appears to be adequate time to review and comment on the report and the interpretation thereof.

Comment This is most relevant as OEHHA relies upon the study's findings to recommend a default soil to indoor dust transfer factor of two (2). This assumption is significant and may drive the risk estimate for a given occupancy. The District be lieves this default assumption is problematic. One major flaw is that OEHHA assumes "day care centers" are repres entative of student exposures in the first through the twelfth grad e. To the contrary, the study relied upon by OEHHA collected indoor dust from floor surfaces. It is unlikely that students at these grade levels will sit, play, and crawl on the floors for the preponderance of their tenure at school. This is relevant as it is reported in the Repor t to the California Legi slature, Environmental Health Conditions in California's Portable Cl assrooms (ARB, DHS, June 2003) that floor dust contaminants are "especially a concern for young childre n who spend time on the floor and can be exposed to the dust contaminants by hand-to-mouth contact and skin contact." The District agrees that special c onsideration be given to this sensitive occupancy, however, we believe most older students generally walk into their classrooms and sit at desks or a similar work surface, thereby eliminating a direct expos ure pathway to surface floor dust. Please note, the OEHHA commissioned study did not identify dus t loadings or contaminant concentrations at task level (e.g., desk and rela ted working surfaces) where direct contact is likely to occur. Nor did the study provide any information to a ssess the reentrainment potential of floor dustA2-30 which may contribute to task level loadings and exposures through the inhalation pathway, District staff is cognizant of the U.S. Envir onmental Protection Agency's (U.S. EPA) guidance to assess the reentrainment potential of road surface dust from the movement of vehicular sources along a roadway segment. We are unawa re of similar guidance associated with the inhalation of resuspended floor dust from a student walking across a classroom floor.
Response OEHHA made no assumption that "day care cente rs" are representative of student exposures in the first through the twelfth grade. On the contrary, exposure parameters change year by year, with the exposure parameters for high school students closely resembling those for adults. OEHHA acknowledges that the concentration of contaminants in dust vacuumed from the floor may be different from that in dust on table-tops and window sills ond other surfaces, and that more data on these potential exposure me dia would be desireable. Nonetheless, the multiple sources of interior dust are essent ially the same (though possibly in different proportions) whether the dust is suspended in the air as particulate matter, or collected from table-tops, window sills, or floors. If a site is to be assessed prior to construction of a school, some assumption must be made about the con centration of contaminants in indoor dust on various surfaces. The comment does not incl ude a suggested altern ative value. OEHHA believes that the existing data on the concentration of contaminants in floor dust relative to the concentration in outdoor soil provide the best currently available estimate of concentration of contaminants in all interior dust relative to the c oncentration in outdoor soil.

Comment To evaluate the adequacy of the dose algorithms utilized in the draft gui dance, District staff prepared a comparative analysis of values pred icted utilizing identifie d equations consistent with U.S. EPA's Risk Assessment Guidance for Superfund (RAGS). According to OEHHA's response to concerns raised regarding th e discrepancy between the proposed exposure equations and the "standard form given in th e U.S. EPA RAGS" guidance, it was reported that although "some minor aspects may differ, the general form of the equations is consistent with U.S. EPA RAGS." To that end, the valu es predicted by either approach should be consistent. With all exposure variates being eq ual, the District was una ble to predict similar values for several exposure pathways. In fact, the District's annual average daily dose values were as much as two to three orders of magnit ude more 'conservative (i.e., health protective) than those identified with the OEHHA predictive model. Due to the limited time to address this discrepancy, the District requests clarification and validation of the proposed exposure equations relative to the established format identified in regulatory guidance.
Response The general form of the equations is consiste nt with U.S. EPA RAGS. This does not mean that the input values or the act ual output results are the same as in RAGS. Indeed, if they were, there would be no reason to have schools risk assessment guidance. The equations and inputs referred to in the comment are from EPA’s Children’s Exposure Factors Handbook. “Validation” in this context usually refers to fi eld testing of theoretica l equations to describe nature. In this case, the algorithms are base d on field measurements. EPA apparently felt that they were sufficiently “va lid” to adopt in their guidance.A2-31 Comment In addition to the lack of reproducibility of several dose values, OEHHA's report of only "minor" changes to other exposure pathway e quations (e.g., inhalation of contaminants in vapors that originate off site) may arbitrarily bias the predicted annual average daily dose. For example, by scaling the breathing rate fo r the time spent in school (e.g., 540 minutes per day), the modeled concentration must coincide with the identified school-based exposure. This is not standard practice and would requ ire post-processing of the model output to generate the appropriate value. Existing guida nce would simply util ize the model scalar option to predict the annual average exposures for a given time period (i.e., ending hours 8 through 16) averaged over the number of hours sp ecified in the meteorol ogical data set (i,e., 8760 hours). As such, the dose algorithm would simp ly require a daily breathing rate value. In anticipation of OEHHA's concern that th ere are differences in indoor versus outdoor breathing rates that would preclude the use of a da ily breathing rate, the District believes that reasonable assumptions can be made to appr oximate an enhanced rate which accounts for variable light, moderate and heavy activity le vels representative of a public school setting. This approach is discussed in OEHHA's disc ussion characterizing the proposed ventilation rates for the proposed guidance. In additi on, OEHHA's Technical Support Document for Exposure Assessment and Stochastic Analysis provides a detailed discussion on ventilation rates and related distribution prof iles to assist in developing high end estimates that reflect daily activity patterns associated with student and staff exposures. Notwithstanding, the proposed guidelines should either be revised to reflect the form and format of the exposure pathway equations that reflect existing regulatory guidance and pr actice or direct the user to make the appropriate adjustments to the dispersion model output.
Response Changes have been made to the Guidance to direct the user to make the appropriate adjustments to the dispersion m odel output (see pages 10 and 11).

Comment
Please note, there are additional issues which re quire further consideration. However, due to the time allotted for public comment, the District is limited to its curre nt discourse. However, the District trusts that its c oncerns will be addressed to al low for continued discussion and comment on the proposed guidelines. In its curren t form, the District ha s reservations about the adequacy of the proposed guidance. I can be reached at (213) 241-3926 should you have any questions or need additional information.
Response No response