PUBLIC HEALTH ASSESSMENT
NAVAL SUPPORT ACTIVITY, MECHANICSBURG
(Aliases: NAVY SHIPS PARTS CONTROL CENTER AND NAVAL INVENTORY CONTROL POINT)
MECHANICSBURG, CUMBERLAND COUNTY, PENNSYLVANIA
the area of a playground that has contaminated dirt, a contaminated spring used for drinking water, the location where fruits or vegetables are grown in contaminated soil, or the backyard area where someone might breathe contaminated air.
APPENDIX B: ATSDR'S ASSESSMENT METHODOLOGY AND COMPARISON VALUES
Human Exposure Pathway Evaluation and the Use of ATSDR Comparison Values
The Agency for Toxic Substances and Disease Registry (ATSDR) assesses a site by evaluating the level of exposure in potential or completed exposure pathways. An exposure pathway is the way chemicals may enter a person's body to cause a health effect. It includes all the steps between the release of a chemical and the population exposed, including: (1) a chemical release source, (2) chemical movement, (3) a place where people can come into contact with the chemical, (4) a route of human exposure, and (5) a population that could be exposed. In this assessment, ATSDR evaluates chemicals in environmental media that people residing near a site may consume, inhale, or contact.
Health assessors use comparison values (CVs) as screening tools to evaluate environmental data that is relevant to the exposure pathways. CVs represent media-specific contaminant concentrations that are used to select contaminants for further evaluation to determine the possibility of adverse health effects. CVs used in this document include ATSDR's environmental media evaluation guide (EMEG) and cancer risk evaluation guide (CREG). CVs are derived from available health guidelines, such as ATSDR's minimal risk levels and EPA's cancer slope factor.
Category of CVs used in this public health assessment are described below and the specific CVs are listed in Table B-1.
Cancer Slope Factor (CSF)
Usually derived from dose-response models and expressed in mg/kg/day, CSFs describe the inherent potency of carcinogens and estimate an upper limit on the likelihood that lifetime exposure to a particular chemical could lead to excess cancer deaths.Cancer Risk Evaluation Guide (CREG)
Estimated contaminant concentrations that would be expected to cause no more than one excess cancer in a million (10-6) persons exposed over a 70-year life span. ATSDR's CREGs are calculated from EPA's cancer potency factors.EPA Region III Risk-Based Concentration
EPA combines reference doses and carcinogenic potency slopes with "standard" exposure scenarios to calculate risk-based concentrations, which are chemical concentrations corresponding to fixed levels of risk (i.e., a hazard quotient of 1, or lifetime cancer risk of 10-6, whichever occurs at a lower concentration) in water, air, fish tissue, and soil.Lowest Observed Adverse Effect Level (LOAEL)
The lowest dose of a chemical that produced an adverse-effect when it was administered to animals in a toxicity study.Maximum Contaminant Level (MCL)
The MCL is the drinking water stand established by EPA. It is the maximum permissible level of a contaminant in water that is delivered to a free-flowing outlet. MCLs are considered protective of human health over a lifetime (70 years) for individuals consuming 2 liters of water per day.Minimal Risk Levels (MRL)
MRLs are estimates of daily human exposure to a chemical (i.e., doses expressed in mg/kg/day) that are unlikely to be associated with any appreciable risk of deleterious noncancer effects over a specified duration of exposure. MRLs are calculated using data from human and animal studies and are reported for acute (< 14 days), intermediate (15-364 days), and chronic (> 365 days) exposures. MRLs are published in ATSDR Toxicological Profiles for specific chemicals.
The derivation of a CV uses conservative exposure assumptions, resulting in values that are much lower than exposure concentrations observed to cause adverse health effects; thus, insuring the CVs are protective of public health in essentially all exposure situations. That is, if the concentrations in the exposure medium are less than the CV, the exposures are not of health concern and no further analysis of the pathway is required. However, while concentrations below the CV are not expected to lead to any observable health effect, it should not be inferred that a concentration greater than the CV will necessarily lead to adverse effects. Depending on site-specific environmental exposure factors (for example, duration of exposure) and activities of people that result in exposure (time spent in area of contamination), exposure to levels above the CV may or may not lead to a health effect. Therefore, ATSDR's CVs are not used to predict the occurrence of adverse health effects.
The CVs used in this evaluation are defined as follows: The CREG is a concentration at which excess cancer risk is not likely to exceed one case of cancer in a million persons exposed over a lifetime. The CREG is a very conservative CV that is used to estimate cancer risk. Exposure to a concentration equal to or less than the CREG is defined as an insignificant risk and is an acceptable level of exposure over a lifetime. The risk from exposure is not considered as a significant risk unless the exposure concentration is approximately 10 times the CREG and exposure occurs over several years. The EMEG is a concentration at which daily exposure for a lifetime is unlikely to result in adverse noncancerous effects.
Elements of a Completed Exposure Pathway
In evaluating public health hazards, ATSDR first tries to determine exposure in the past, present, and future. ATSDR does this by carefully evaluating the elements of an exposure pathway that might lead to human exposure. These elements include: (1) a source of site-related contamination, such as drums or waste pits; (2) an environmental medium in which the contaminants might be present or from which they might migrate, such as groundwater or soil; (3) points of human exposure, such as drinking water wells or gardens; (4) routes of exposure, such as breathing, eating, drinking, or touching a substance containing the contaminant; and (5) a receptor population. (Figure 3 explains the exposure pathway evaluation in more detail.) ATSDR then identifies an exposure pathway as completed or potential, or eliminates that pathway from further evaluation. A completed exposure pathway exists in the past, present, or future if all elements of human exposure link the contaminant source to a receptor population. A potential pathway is one that ATSDR cannot rule out, even though we cannot find one of the necessary elements.
If a completed or potential exposure pathway exists, ATSDR then considers whether any chemicals were present, are present, or are expected to become present.
Selecting Chemicals for Further Evaluation
Identifying chemicals for further evaluation is a process that requires ATSDR to examine contaminant concentrations at the site, the quality of environmental sampling data, and the potential for human exposure. A thorough review of each of these issues is required to accurately select chemicals in the site-specific human exposure pathway. The following text describes the selection process.
In the first step of the chemical selection process, the maximum contaminant concentrations are compared directly to health-based CVs. ATSDR considers site-specific exposure factors to ensure selection of appropriate health CVs. If the maximum concentration reported for a chemical is less than the health CV, ATSDR concludes that exposure to that chemical is not of public health concern; therefore, no further data review is required for that chemical. However, if the maximum concentration is greater than the health CV, the chemical is selected for additional data review. In addition, any chemicals detected that do not have relevant health CVs are also selected for additional data review.
CVs have not been developed for some contaminants, and, based on new scientific information other CVs may be determined to be inappropriate for the specific type of exposure. In those cases, the contaminants are included for further review if current scientific information indicates exposure to those contaminants may be of public health concern.
The next step of the process requires a more in-depth review of data for each of the contaminants selected. Factors used in the selection of the chemicals includes the number of samples with detections above the minimum detection limit, the number of samples with detections above an acute or chronic health CV, and the potential for exposure at the monitoring location.
Table B-1. Comparison Values by Chemical and Environmental Medium
| Contaminant | Groundwater/ Surface Water Comparison Values |
Soil/Sediment Comparison Values |
||
| Value (ppb) | Source | Value (ppm) | Source | |
| Volatile Organic Compounds | ||||
| Benzene | 0.6 5 |
CREG MCL |
10 | CREG |
| Chlorobenzene | 100 4,000 |
MCL child I-EMEG |
20,000 | child C-EMEG |
| Chloroform | 6 80 |
CREG MCL |
500 | child C-EMEG |
| 1,2-Dichloroethene, total |
100 4,000 |
MCL child I-EMEG |
10,000 | child I-EMEG |
| Methylene chloride | 5 600 |
CREG child RMEG |
3,000 | child C-EMEG |
| Tetrachloroethylene | 5 | MCL | 500 | child C-EMEG |
| Trichloroethylene | 5 | MCL | 0.087 | RBC, residential |
| Vinyl chloride | 2 | MCL | 0.1 | CREG |
| Semi-volatile Organic Compounds | ||||
| Benzo(a)pyrene | 0.005 0.2 |
CREG MCL |
0.087 | RBC, residential |
| 1,4-Dichlorobenzene | 75 4,000 |
MCL child I-EMEG |
0.1 | CREG |
| bis(2-Ethylhexyl)phthalate | 3 6 |
CREG MCL |
0.32 | RBC, residential |
| Pesticides/Polychlorinated Biphenyls | ||||
| Aroclor 1260 | 0.2 | child C-EMEG for Aroclor 1254 | 0.2 | child C-EMEG for Aroclor 1254 |
| Metals (total) | ||||
| Antimony | 4 6 |
RMEG MCL |
20 | child RMEG |
| Arsenic | 0.02 50 |
CREG MCL |
0.5 | CREG |
| Barium | 700 2,000 |
child RMEG MCL |
50 | child C-EMEG |
| Beryllium | 4 10 |
MCL child C-EMEG |
4,000 | child RMEG |
| Cadmium | 2 5 |
child C-EMEG MCL |
10 | child C-EMEG |
| Chromium | 30 | child RMEG (chromium VI) |
200 | child RMEG(VI) |
| Lead | 15 | EPA action level | 400 | EPA SSL |
| Mercury | no value | 3,000 | child RMEG | |
| Manganese | 500 | child RMEG | 1,000 | child RMEG |
| Nickel | 200 | child RMEG | 5.5 | RBC, residential |
| Thallium | 2 | MCL | 200 | child I-EMEG |
| Vanadium | 30 | child I-EMEG | 30 | child I-EMEG |
| Abbreviations | |
| C-EMEG - chronic environmental Media Evaluation Guide CREG - Cancer risk Evaluation Guide I-EMEG - intermediate environmental media evaluation guide MCL - EPA's maximum contaminant level |
ppb - parts per billion ppm - parts per million RBC - EPA Region III risk-based concentration RMEG - reference dose media evaluation guide |
APPENDIX C: ATSDR'S EXPOSURE EVALUATION PROCESS
Estimates of Human Exposure Doses and Determination of Health Effects
After identifying contaminants in site media above comparison values, ATSDR further evaluates exposures to these contaminants considering information about exposures combined with scientific information from the toxicological and epidemiological literature. If necessary, ATSDR estimates exposure doses, which are estimates of how much contaminant a person is exposed to on a daily basis. Variables considered when estimating exposure doses include the contaminant concentration, the exposure amount (how much), the exposure frequency (how often), and the exposure duration (how long).
The estimated exposure doses can be used to evaluate potential noncancer and cancer effects associated with contaminants detected in site media. When evaluating noncancer effects, ATSDR compares the estimated exposure dose to standard toxicity values, including ATSDR's minimal risk levels (MRLs) and the U.S. Environmental Protection Agency's reference doses (RfDs), to evaluate whether adverse effects may occur. The chronic MRLs and RfDs are estimates of daily human exposure to a substance that is likely to be without appreciable risk of adverse noncancer effects over a specified duration. The chronic MRLs and RfDs are conservative values, based on the levels of exposure reported in the literature that represent no-observed-adverse-effects levels (NOAEL) or lowest-observed-adverse-effects-levels (LOAEL) for the most sensitive outcome for a given route of exposure (e.g., dermal contact, ingestion). Uncertainty (safety) factors are applied to NOAELs or LOAELs to account for variation in the human population and uncertainty involved in extrapolating human health effects from animal studies. ATSDR also reviews the toxicological literature and epidemiology studies to evaluate the weight of evidence for adverse effects.
When evaluating the potential for cancer to occur, ATSDR uses cancer slope factors (CSF) that define the relationship between exposure doses and the likelihood of an increased risk of developing cancer over a lifetime. The CSFs are developed using data from animal or human studies and often require extrapolation from high exposure doses administered in animal studies to lower exposure levels typical of human exposure to environmental contaminants. The CSF represents the upper-bound estimate of the probability of developing cancer at a defined level of exposure; therefore, they tend to be very conservative (i.e., overestimate the actual risk) in order to account for a number of uncertainties in the data used in extrapolation. ATSDR also considers the cancer effect levels (CELs) reported in the literature. The CEL is the lowest dose of a chemical in a study, or group of studies, that was found to produce increased incidences of cancer (or tumors).
Exposure from Inadvertent Ingestion of Surface Soil at Site 14: Water Towers 16-A, O-C2, and 504-A
Elevated levels of arsenic and lead were detected in surface soil in the past at Site 14. ATSDR identified dermal contact and incidental ingestion of contaminated soil for further evaluation. Determining whether health effects might develop from exposure to environmental contaminants requires evaluating the concentrations of the contaminants to which people may have been exposed and how often and how long exposure to those contaminants occurred. Health effects are also related to individual characteristics such as age, gender, and nutritional status that influence how a chemical might be absorbed, metabolized, and eliminated by the body. Together, these factors help influence the individual's physiological response to chemical contaminant exposure and potential noncancer (noncarcinogenic) or cancer (carcinogenic) outcomes.
Arsenic
Noncancer Effects
The estimated concentrations of arsenic in Site 14 soils (up to 101 J ppm) were below ATSDR's adult EMEG of 200 ppm, but exceeded the child EMEG of 20 ppm. These screening values have uncertainty, or "safety", factors built in. Both EMEG values, however, are based on the assumption of chronic, daily exposure, and, because the soil samples came from around the water towers rather than from highly frequented, popular play areas, the derived exposure doses will likely overestimate actual exposures, perhaps significantly. Furthermore, the EMEG is based on a drinking water study. The drinking water study assumed 100% bioavailability of arsenic in water; however, bioavailability of arsenic in soil is much lower (estimated at 3% to 50%). Only a portion of arsenic in soils, therefore, is expected to be readily absorbed into the human body. In addition, the frequency of exposure to these particular soils will be much less than the daily exposure to drinking water. The population in the drinking water study may have also been more sensitive to arsenic's toxicity because of its poor nutritional status (ATSDR 1998).
ATSDR also reviewed available toxicological literature on arsenic. Most available information on this metal comes from laboratory animal studies and epidemiologic studies in humans drinking contaminated water, which limits the studies' usefulness in assessing health effects for individuals exposed to contaminated NSA soil. Actual doses at the water towers might have been lower, and absorption of arsenic from soil would be lower than that from drinking water. (The ATSDR oral MRL is based on drinking water studies.) Several epidemiologic studies of moderate-sized populations (20 to 200 people) exposed to arsenic through drinking water have detected no dermal or other effects at average chronic doses of 0.0004 to 0.01 mg/kg/day (ATSDR 1998). Using the default assumption that a 10 kilogram (kg) (or 22 pound) child ingests 200 milligrams (mg) of Site 14 soil per day, the corresponding dose of soil-derived arsenic would be much less than doses that result in adverse health effects as reported in the literature. Therefore, ATSDR does not expect that the levels of arsenic detected in soil at the water towers would result in any noncancer adverse health effects.
Cancer Effects
The concentrations of arsenic in Site 14 soil (estimated up to 101 J ppm) exceeded ATSDR's conservative CREG of 0.5 ppm, but the levels are not sufficient to pose a carcinogenic hazard under site-specific conditions of exposure. The Department of Health and Human Services, the International Agency for Research on Cancer, the National Toxicology Program, and EPA have all independently determined that arsenic is carcinogenic to humans. When exposure occurs by the oral route, the main carcinogenic effect appears to be an increased risk of skin cancer. This conclusion is based on a number of studies of populations exposed to elevated levels of arsenic in drinking water (ATSDR 1998). However, there are no studies that specifically address the carcinogenic potential of arsenic in contaminated soil. It should be noted that only about 300 cases of arsenical skin cancer have been reported in the United States, and virtually all of them were related to occupational exposures. Because arsenic may not be as bioavailable in soil as in water, and because the human body has the ability to detoxify low doses of the metal, it is unlikely that the level of arsenic detected in NSA soils would increase the risk of cancer (ATSDR 1998).
Lead
Small children might be particularly sensitive to the effects of long-term exposure to lead. Health officials assess lead exposure by determining blood lead levels. Correlations between blood lead levels and adverse effects are fairly well understood and are studied to evaluate the potential for lead exposure to cause adverse health effects (e.g., nervous system effects, slowed child growth, and developmental brain damage). The relationship between environmental concentrations of lead and blood lead levels can be estimated by multiplying the detected concentration by a media-specific slope factor of 0.0068 for soil (ATSDR 1999a). Because blood lead levels begin to taper off at higher soil concentrations (the relationship is not linear at high concentrations), this formula is useful when evaluating exposures occurring to relatively low levels. The formula considers the extent to which lead from various routes of exposure (ingestion, inhalation) may cause blood lead levels to rise.
ATSDR estimated the possible contribution of lead in soil using the above equation and the maximum concentration of lead (5,030 ppm) present at Site 14. For comparison, ATSDR uses the Centers for Disease Control and Prevention (CDC) recommended guideline for lead. CDC recommends follow-up and/or treatment for children with blood lead levels equal to or greater than 10 micrograms per deciliter (µg/dL). Scientific studies have shown blood lead levels above 10 µg/dL may be associated with neurological or behavioral problems (ATSDR 1999a).
Our estimates suggest that the blood lead level would have risen to 34 µg/dL for a child who incidentally ingested the most highly lead-contaminated soil at Site 14. This level is three times greater than the CDC's screening level of 10 µg/dL. This estimate is based on the maximum detected concentration, however, it likely over estimates actual past exposures of a child to lead in soil. Our estimate was derived from the maximum soil concentration and assumed that a child would be in the area and would always contact the area of greatest contamination. In all likelihood, the greatest part of a child's visit to the area would not be spent on soil containing the highest detected concentrations of lead. First, the area was covered with grass. Second, a majority of the samples contained lead levels below 400 ppm. ATSDR therefore further analyzed exposure to lead using the geometric mean of 290 ppm. (The geometric mean is used when the data show a wide range of concentrations.) The blood lead level using the geometric mean is 2 µg/dL, a level well within the CDC screening level of 10 µg/dL.
Exposure to PCBs from Consumption of Fish from Trindle Spring Run
PCBs were the contaminants detected at the highest concentrations and posing the greatest potential health hazard to individuals eating fish caught in Trindle Spring Run. Although concentrations in Trindle Spring Run rainbow trout (0.6 to 1.2 ppm) and slimy sculpin (0.2 to 1.2 ppm) were below FDA's tolerance levels of 2 ppm, the levels exceeded levels found in fish taken from a control stream (0.2 ppm). The highest PCB levels reported for rainbow trout were measured in the composite sample of fish from the upstream portion, suggesting that other sources of PCBs may be found upstream of the storm water drainage ditch's (SWDD's) confluence with the creek. For slimy sculpins, the highest concentrations were noted in fish samples collected from the downstream extent of the creek. Over months or years eating contaminated fish, PCBs can accumulate to levels that would affect your health. Therefore, people who eat fish regularly can be particularly susceptible to PCBs that build up over time. Today, a limited fish consumption advisory issued by the Pennsylvania Department of Environmental Protection (PADEP) urges people to limit consumption of rainbow trout caught from Trindle Spring Run to one meal a month. Nonetheless, ATSDR evaluated the fish sampling data to assess potential public health hazards.
Noncancer Effects
Some of the ways in which PCBs cause noncancer effects in adults include changes in the blood, liver, and immune functions. Children appear to be even more sensitive to the effects of PCBs than adults. Developmental problems have been reported in children whose mothers were exposed to PCBs even before becoming pregnant. PCBs can also pass through a mother's milk to her baby. Babies exposed to PCBs while in the uterus can have lower birth weights and delayed physical development.
ATSDR estimated exposure doses using the maximum detected concentration of PCBs in rainbow trout collected downstream of the SWDD and different consumption rates. (Even though slightly higher levels were reported for slimy sculpins than were reported for rainbow trout, ATSDR used the rainbow trout data in exposure estimates because rainbow trout is the more widely sought after and consumed species at Trindle Spring Run.) A person who eats one meal per month might incur an exposure dose that is slightly higher but within the same order of magnitude as the MRL for PCBs (Aroclor 1254) of 0.00002 mg/kg/day. For more frequent consumption of Trindle Spring Run (two or more meals per month), estimated exposure doses exceed the MRL by more than one order of magnitude.
Table C-1. Estimated Exposure Doses from Consumption of Trindle Spring Run Fish
| Number of Trindle Spring Fish Meals per Month | Estimated Dose of PCBs (mg/kg/day) |
MRL (mg/kg/day) |
| 1 8 -ounce | 0.00009 | 0.00002 |
| 2 8-ounce | 0.00018 | 0.00002 |
| 4 8-ounce | 0.00045 | 0.00002 |
| 7 8-ounce | 0.00076 | 0.00002 |
Even though one fish meal per month slightly exceeds the MRL, no harmful effects are expected at this level. The estimated exposure dose for consuming fish is in fact about one order of magnitude lower than the most conservative NOAEL found in other chronic oral animal studies (ATSDR 1999b). Therefore, ATSDR does not expect any adverse non-cancer effects for people who continue observing the PADEP fish consumption advisory warning for Trindle Spring Run.
Cancer Effects
A number of animal studies have examined the possibility of PCBs causing cancer, but epidemiological studies in humans do not provide enough information to determine if PCBs are carcinogenic. Several reviews of epidemiological studies (primarily, worker exposures to PCBs) have been inconclusive or have not shown an association between PCBs and cancer (ATSDR 1999b). Compared to the cancer effect level found in animal studies, ATSDR's estimated human exposure dose (based on one fish meal per month) of 3.9 x 10-5 mg/kg/day for adults is approximately five orders of magnitude lower than the administered doses that induced cancer effects in rats. Rats that ingested certain PCB mixtures over their lifetimes developed liver cancer. Based on these animal studies, EPA classifies PCBs as a Category B2 carcinogen, indicating that it is a probable human carcinogen. The EPA's National Center for Environmental Assessment recommended that a cancer slope factor of 2.0 (mg/kg/day)-1 be used for PCBs in biota. Therefore, the cancer risk from eating rainbow trout from Trindle Spring Run under the assumed exposure scenario would be 8 x 10-6 .This risk level is lower than the range typically acceptable for the general population.
Again, it should be emphasized that the risk level calculation is extremely conservative and likely overestimates exposures. Moreover, given the inconclusive link between oral PCB exposure and human cancer, it is highly unlikely that the consumption of Trindle Spring Run fish is going to result in adverse cancer effects for the local fishing population. Still, as a prudent public health measure, ATSDR recommends that people continue to observe the limited fish consumption advisory for Trindle Spring Run.
References
Agency for Toxic Substances and Disease Registry (ATSDR). 1996. Toxicological Profile for Arsenic (Update). August 1998.
Agency for Toxic Substances and Disease Registry. 1999a. Toxicological Profile for Lead (Update). Agency for Toxic Substances and Disease Registry, U.S. Department of Health and Human Services. Research Triangle Institute. July 1999.
Agency for Toxic Substance and Disease Registry. 1999b. Toxicological Profile for Polychlorinated Biphenyls (PCBs) (Draft). Agency for Toxic Substances and Disease Registry, U.S. Department of Health and Human Services. Research Triangle Institute. April 1999.
APPENDIX D: RESPONSE TO PUBLIC COMMENT
The Agency for Toxic Substances and Disease Registry (ATSDR) released the Naval Air Station, Mechanicsburg (NSA) Public Health Assessment (PHA) on February 28, 2002, for public review and comment. That public comment period ended April 15, 2002. During that period, ATSDR received the following comments/questions from two restoration advisory members (RAB) and two agency representatives.
For comments that questioned the validity of statements made in the PHA, ATSDR verified or corrected the statements. ATSDR has not addressed requests for information to be included in the PHA, unless the party who filed the request provided the supporting documentation. The list of comments does not include editorial comments concerning such things as word spelling or sentence syntax.
Response: The Navy will continue to monitor on-site groundwater wells on a periodic basis, including new wells that are being added to better characterize groundwater contamination beneath Sites 3 and 9. Off-site monitoring wells are currently in place to determine the outer limits of NSA-related contaminant migration in the groundwater. Using this system, the Navy will monitor groundwater movement from the NSA and off-site groundwater quality to identify and diminish the threat of potential health hazards to off-site communities. Even though contaminants exist in the groundwater beneath the NSA, it is very important to note that there is no public exposure to the groundwater contaminants. Groundwater underlying NSA has never been used as a source of drinking water, nor will it be used for potable water in the future. NSA and the surrounding community receive drinking water from municipal water sources that safely meet federal and state drinking water standards.
As a reminder, ATSDR scientists generally do not collect environmental sampling data. Instead, they review information provided by the Navy or from other groups, such as the U.S. Environmental Protection Agency (EPA), other government agencies, businesses, and the public.
Response: Contamination from NSA has not affected the drinking water delivered to residential taps. Most area residents receive their drinking water from either the PAWC or United Water Pennsylvania. EPA's Safe Drinking Water Act requires municipal water suppliers to test their water regularly for the presence of contaminants, including trichloroethylene (TCE). Each of the Mechanicsburg public water suppliers tests for TCE in their system or production wells either on a quarterly or annual basis. In recent sampling of the public water supplies, no TCE was detected at concentrations above ATSDR's comparison values (CVs) or EPA's maximum contaminant levels (MCLs). Should a contaminant be detected above its MCL, the supplier is required to switch to an alternative drinking water source or to purify the contaminated water.
Some Mechanicsburg residents receive their drinking water from private wells. The Navy identified two off-base wells as possibly being impacted by NSA contamination based on groundwater flow from NSA and the well's proximity to the site. These private wells are located about 3,000 feet west of the property and are reportedly used for drinking water. Results of the well water sampling indicate that contaminants were either not detected or were detected at levels below ATSDR's CVs and EPA's MCLs, levels that are not considered harmful. (CVs and MCLs are developed from scientific literature available on exposure and health effects. These values reflect an estimated contaminant concentration that is not expected to cause harmful health effects.) To date, the regulators and Navy are not aware of any other downgradient wells from the site that have been or are expected to be impacted by NSA contaminants.
Response: PCBs are not present in municipal drinking water supplies at unacceptable levels. As stated in the PHA, and reiterated above, local municipal water suppliers must conduct scheduled testing of the finished water quality to ensure it meets EPA drinking water standards. These tests include testing the drinking water for PCBs. Tests to date have not detected PCBs in drinking water at levels above the EPA's MCL of 0.5 ppb. Even though PCBs have been detected in soil, PCBs bind strongly to soil, thus limiting their movement down through the deeper soil layers to the underlying groundwater. This is particularly true for Aroclors of PCBs with higher chlorine content, such as Aroclor 1260 that was detected in NSA soil.
Response: ATSDR discusses PCBs at Site 9 in the Evaluation of Surface Water and Sediment Pathway section of this PHA. As noted in that section, PCBs have been detected at levels greater than 100 parts per million (ppm) in Segment 1 of Site 9, the storm water ditch. NSA has implemented several measures to prevent downstream migration of sediment, including construction of a gabion dam and removal of contaminated sediment. Post cleanup tests confirmed that the PCB levels in sediment were lower (0.08 ppm) and below EPA's risk-based concentration of 0.32 ppm.
Response: The data reviewed by ATSDR do not indicate that contaminants have accumulated in Trindle Spring Run at levels that would be harmful to its recreational users. Sediment samples collected from the Trindle Spring Run downstream of its confluence with NSA storm water drainage ditch (SWDD) had PCB concentrations ranging from 0.07 ppm to 0.104 ppm. These concentrations are many times lower than ATSDR's CVs for soil of 10 ppm for an adult and 1 ppm for a child, and below levels of known health effects. In addition, only low levels of PCBs were detected in surface water and sediment samples collected from both upstream and downstream of Trundle Spring Run's confluence with the SWDD. Furthermore, descriptions provided to ATSDR suggest that these surface water bodies are not desirable for swimming or wading. Contact with or incidental ingestion of surface water or sediment containing the detected levels of PCBs is therefore not expected to harm people who might occasionally use Trindle Spring Run for limited recreational activity. Since only low concentrations were detected in Trindle Spring Run, surface water or sediment entering the Condoquinet River is not expected to be affected by harmful levels of NSA-related contaminants.
Response: Dioxins were detected in soil at Site 3, but generally at low levels. Only 1 of the 32 samples collected from this site had a toxic equivalent (TEQ) dioxin soil concentration above ATSDR's acceptable screening value for dioxin TEQs of 1 ppb. (Dioxin results were calculated in terms of TEQs to convert the concentration of individual dioxin congeners to an equivalent concentration of 2,3,7,8-tetrachlorinated dibenzo-p-dioxins, the most toxic of the dioxin congeners.) The only sample exceeding ATSDR's screening value had a TEQ of 3.4 ppb. This sample was collected 4 feet below grade from the subsurface soil beneath the 5,000 Cubic Yard Pile, where the general public is unlikely to have access. Based on this information, ATSDR finds no evidence to suggest that dioxins at Site 3 pose a threat to public health. ATSDR added this information to the PHA.
Response: Thank you. ATSDR has added the information to the Demographic Section of the PHA.
Response: Thank you. ATSDR has added the information to appropriate sections of the PHA.
Response: ATSDR's primary goal in its PHA is to put possible exposures to environmental contaminants into meaningful perspective for the public. ATSDR scientists reviewed environmental data to see how much contamination occurred at and near NSA and how people might come into contact with it. Exposures are only possible if people come in contact with contaminated media (e.g., drinking, touching, inhaling). For cases where exposure was or is possible, ATSDR tried to explain the likelihood that exposure to the detected level of a particular chemical may or may not cause harm. As for the NSA area, ATSDR did not find reason to suspect that people working at or living around NSA have been or could be exposed to harmful levels of contaminants.
Response: In its PHA, ATSDR uses "never" only in relation to the use of the groundwater beneath NSA as a source of drinking water. ATSDR's review of site information and discussions with site personnel found that the groundwater has not ever been used for drinking water. ATSDR believes its use of "never" in this context is both unambiguous and accurate.
Response: ATSDR's evaluation of available fish sampling data from Trundle Spring Run supports the PADEP current limited advisory. The advisory for Trundle Spring Run recommends for people to limit their consumption of rainbow trout from the run to one fish meal per month and encourages sensitive individuals, such as children, women of child-bearing age, and pregnant women, to follow more stringent limitations. Along with the advisory, the PADEP provides instructions to further reduce exposure to PCBs when preparing and cooking trout. ATSDR's very conservative evaluation found that people could safely eat on average one Trundle Spring Run trout meal each month without encountering a greater likelihood of developing health effects. No evidence to date supports expanding this advisory to other species of fish or strengthening the current restrictions. If, however, new sampling data become available suggesting that the PCB levels are increasing in Trundle Spring Run fish, ATSDR will reevaluate the need for additional action protective of public health, such as recommending stronger restrictions in the advisory.
If you have questions about the clarity or the physical posting of the signs you should contact the PADEP (717) 787-9657.
Response: Stock piles of mineral ores have been maintained by the Defense National Stockpile since the 1950s within the 14-acre Site 8 in the southwest portion of NSA. Chromite and manganese ores were stored in the north and west portion of Site 8; kyanite and aluminum oxide were stored in the southeast portion of Site 8. Site 8 once contained up to 39 piles of ore. Today, this area consists of only four grass-covered piles and one additional pile staged on concrete. This information has been added to sections of the text and to Table 2 as needed.
